Separator for secondary battery and secondary battery comprising the same

Abstract

A separator for secondary batteries according to the present application includes a base material and a coating layer stacked on a surface of the base material and containing inorganic particles. A degree of orientation of the base material calculated from a puncture strength of the separator and a weight per unit area of the base material can fall within a prescribed range. A secondary battery according to the present application includes an electrode assembly including a positive electrode, a negative electrode, and the separator for secondary batteries. Heat stability of the separator and the secondary battery can be improved.

Description

Technical Field

[0001] This invention relates to a separator for secondary batteries and a secondary battery including the separator. More specifically, it relates to a separator for secondary batteries comprising a substrate and a coating, and a secondary battery including the separator. Background Technology

[0002] Rechargeable batteries are batteries that can be recharged and discharged repeatedly. With the development of the information communication and display industries, rechargeable batteries are widely used in portable electronic communication devices such as portable cameras, mobile phones, and laptops. In recent years, battery packs that include rechargeable batteries have been developed for use as power sources in environmentally friendly vehicles such as electric vehicles.

[0003] A secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator (separation membrane). Damage, defects, external impacts, overcharging, etc., of a secondary battery may lead to thermal runaway. For example, an internal short circuit can cause excessive current, which may result in an increase in internal temperature. The increased internal temperature may cause the decomposition of the active materials or electrolyte contained in the positive and negative electrodes, and the chain reaction of high-temperature gases generated during the decomposition process may lead to thermal runaway. Summary of the Invention

[0004] (a) Technical problems to be solved One technical problem of the present invention is to provide a separator for secondary batteries with improved stability.

[0005] One technical problem of the present invention is to provide a secondary battery with improved stability.

[0006] One technical problem of the present invention is to provide a secondary battery module with improved stability.

[0007] (II) Technical Solution A separator for a secondary battery according to an embodiment of the present invention comprises: a substrate; and a coating, the coating being laminated on the surface of the substrate, and the coating comprising inorganic particles. The substrate orientation degree of the separator, as defined by Formula 1 below, is 90 gf / g·m. 2 above.

[0008] [Formula 1] Substrate orientation degree = S / W In Formula 1, S is the puncture strength of the diaphragm, and W is the weight per unit area of ​​the substrate.

[0009] According to an exemplary embodiment, the substrate orientation degree can be 90 gf / g·m. 2 Up to 120 gf / g·m 2 .

[0010] According to an exemplary embodiment, the content of inorganic particles in the total weight of the coating can be 40% by weight or more.

[0011] According to an exemplary embodiment, the inorganic particles may comprise one or more of aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, calcium oxide, barium sulfate, boehmite, titanium dioxide, silicon dioxide, and clay.

[0012] According to an exemplary embodiment, the weight per unit area of ​​the substrate can be 4.0 g / m². 2 Up to 5.0g / m 2 .

[0013] According to an exemplary embodiment, the machine direction (MD) thermal shrinkage rate of the diaphragm, measured after being stored at 130°C for 1 hour, can be less than 3.0%.

[0014] According to an exemplary embodiment, the transverse (TD) thermal shrinkage rate of the diaphragm measured after being stored at 130°C for 1 hour can be less than 2.0%.

[0015] According to an exemplary embodiment, one or more of the machine direction (MD) stretch ratio and transverse (TD) stretch ratio of the substrate can be 3 to 8 times.

[0016] According to an exemplary embodiment, the thickness of the substrate can be from 1 μm to 15 μm.

[0017] According to an exemplary embodiment, the coating may further comprise polyethylene organic particles.

[0018] According to an exemplary embodiment, the coating may further comprise an adhesive, which may comprise one or more of polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene oxide, ethylene-vinyl acetate copolymer, and copolymers thereof.

[0019] A secondary battery according to an embodiment of the present invention includes an electrode assembly comprising: a positive electrode; a negative electrode; and a separator for a secondary battery according to the above embodiment, the separator being disposed between the positive electrode and the negative electrode.

[0020] According to an exemplary implementation, after the self-heating time point of the electrode assembly at 0.02°C / min or higher, the temperature at which the self-temperature change of the electrode assembly reaches 1°C / second can be above 175°C.

[0021] The secondary battery module according to an embodiment of the present invention includes a structure in which multiple secondary batteries according to the above embodiment are stacked on top of each other.

[0022] According to an exemplary implementation, the plurality of secondary batteries may include any first secondary battery and any second secondary battery not in contact with the first secondary battery, and the ignition transfer time from the ignition of the first secondary battery to the ignition of the second secondary battery may be more than 70 seconds.

[0023] (III) Beneficial Effects The substrate orientation of the separator for a secondary battery according to one embodiment of the present invention can be included within a specified range. Therefore, the self-heating temperature of the secondary battery including the separator can be increased, and the transfer of ignition can be suppressed. Thus, the thermal stability of both the separator and the secondary battery can be improved. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view showing a separator for a secondary battery according to an exemplary embodiment.

[0025] Figure 2 and Figure 3 These are a plan view and a cross-sectional view of a secondary battery according to an exemplary embodiment.

[0026] Figure 4 This is a schematic cross-sectional view showing a secondary battery module according to an exemplary embodiment. Detailed Implementation

[0027] Embodiments of the present invention provide a separator for a secondary battery (hereinafter, simply referred to as "separator") comprising a substrate and a coating. Furthermore, a secondary battery comprising a separator and a secondary battery module comprising the secondary battery are provided.

[0028] The exemplary embodiments will be described in more detail with reference to the accompanying drawings. However, the drawings and embodiments in this specification serve to further understand the technical concept of the invention, and therefore the invention should not be construed as being limited to the contents described in these drawings and embodiments.

[0029] The terms "first," "second," "upper," "upper layer," "lower," and "lower layer" used in this invention do not specify absolute positions, but are used in a relative sense. For example, these terms are used relatively to specify other regions relative to a specific reference plane.

[0030] Figure 1 This is a schematic cross-sectional view showing a separator for a secondary battery according to an exemplary embodiment. Figure 1The machine direction (MD) shown indicates the direction in which the membrane process is carried out, and can be the length direction of the membrane. For example, the machine direction (MD) can be the direction in which the substrate exits the manufacturing equipment during the substrate manufacturing process. The transverse direction (TD) is the direction perpendicular to the machine direction (MD), and can be the width direction of the membrane.

[0031] Reference Figure 1 The separator 140 for secondary batteries may include a substrate 142 and a coating 145 laminated on one side of the substrate 142.

[0032] The substrate 142 may comprise a polyolefin-based polymer. For example, the substrate 142 may comprise a membrane made of a polyolefin-based polymer (e.g., a porous polyolefin-based membrane). Therefore, the stretching direction can be controlled while blocking the short circuit between the positive and negative electrodes through the diaphragm 140.

[0033] For example, the polyolefin-based polymer may include polyethylene, polypropylene, polybutylene, polyisobutylene, polypentene, poly-4-methyl-1-pentene, polyhexene, polyheptene, polyoctene, polydecene, copolymers containing one or more of these, mixtures thereof, etc.

[0034] Examples of polyethylene include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE). In one embodiment, high-density polyethylene with high crystallinity and a high resin melting point can be used. Therefore, thermal stability can be improved while ensuring the mechanical stability of the substrate.

[0035] In one embodiment, the substrate 142 may be substantially composed of high-density polyethylene.

[0036] The copolymer may contain the aforementioned polyolefin as part of the polymer. Examples of the copolymer include ethylene propylene rubber, ethylene-octene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, etc.

[0037] In some embodiments, the substrate 142 may further comprise resins such as polyether, polyacetal, polyamide, polycarbonate, polyimide, polyamide-imide, and polyether-imide.

[0038] For example, the raw material resin of the aforementioned polyolefin-based resin can be melted and mixed, then cooled and cut to prepare resin granules. For example, the resin granules can be extruded using a T-die extruder at a temperature above 200°C to form a preliminary sheet. The preliminary sheet can be cooled to produce an unstretched sheet.

[0039] The unstretched sheet can be stretched to form substrate 142. The stretching method may include uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, extrusion stretching, multi-stage stretching, and multiple stretching. Simultaneous biaxial stretching can refer to a stretching method that simultaneously performs MD stretching and TD stretching, and the stretching ratios in each direction can be different.

[0040] In one embodiment, the substrate 142 can be formed by simultaneous biaxial stretching in terms of the strength of the substrate 142, the uniformity of film properties, ensuring isotropy, and the control of the orientation degree described below.

[0041] According to an exemplary embodiment, the MD stretch ratio of the substrate can be 3 to 8 times. According to an exemplary embodiment, the TD stretch ratio of the substrate can be 3 to 8 times. According to an exemplary embodiment, one or more of the MD stretch ratio and TD stretch ratio of the substrate can be 3 to 8 times. For example, when one or more of the MD stretch ratio and TD stretch ratio of the substrate is less than 3 times, the film alignment of the substrate 142 is low, and therefore the substrate orientation described below may not be included within the specified range. For example, when one or more of the MD stretch ratio and TD stretch ratio of the substrate is greater than 8 times, the heat shrinkage characteristics may be excessively increased.

[0042] The MD stretch ratio and TD stretch ratio can represent the stretch ratio based on the unstretched sheet. The MD (or TD) stretch ratio can refer to the stretch ratio applied along the MD (or TD) direction of the sheet, and can be defined as (length of the sheet after stretching along the MD (or TD) direction) / (length of the sheet before stretching along the MD (or TD) direction). For example, when the MD stretch ratio of the substrate 142 is 5 times, it can mean that its length is increased to 5 times compared to the length of the unstretched sheet in the MD direction.

[0043] In some embodiments, the MD stretch ratio of the substrate can be 4 to 8 times, 5 to 8 times, or 5.5 to 7.5 times. In some embodiments, the TD stretch ratio of the substrate can be 4 to 8 times, 5 to 8 times, or 5.5 to 7.5 times.

[0044] When the MD stretch ratio and TD stretch ratio of the substrate are adjusted to the above range, the following substrate orientation value can be controlled within the specified range.

[0045] According to an exemplary embodiment, the substrate orientation degree of the diaphragm 140 according to the following formula 1 can be 90 gf / g·m. 2 above.

[0046] [Formula 1] Substrate orientation degree = S / W In Equation 1, S is the puncture strength of the diaphragm 140, and W is the weight per unit area of ​​the substrate 142.

[0047] The puncture strength can be measured using known methods, for example, after fixing the diaphragm 140 with a fixing device, a universal testing machine is used to increase the force at a constant speed until the diaphragm 140 is penetrated. The maximum load applied just before the diaphragm is penetrated can be expressed as the puncture strength of the diaphragm 140.

[0048] According to an exemplary embodiment, the substrate orientation degree can be 120 gf / g·m. 2 The following is 118 gf / g·m 2 The following is 116 gf / g·m 2 The following is true: 114 gf / g·m 2 The following, 112 gf / g·m 2 The following, 110 gf / g·m 2 The following, 108 gf / g·m 2 Below, 107 gf / g·m 2 Below, 106 gf / g·m 2 Below or 105 gf / g·m 2 the following.

[0049] In some embodiments, the substrate orientation degree can be 90.5 gf / g·m. 2 Above, 90.8 gf / g·m 2 Above or 91 gf / g·m 2 above.

[0050] For example, the substrate orientation degree can be 90 gf / g·m 2 Up to 120 gf / g·m 2 90gf / g·m 2 Up to 116 gf / g·m 2 90gf / g·m 2 Up to 112 gf / g·m 2 90gf / g·m 2 Up to 110 gf / g·m 2 90gf / g·m 2 Up to 108 gf / g·m 2 90gf / g·m 2 Up to 106 gf / g·m2 Or 90gf / g·m 2 Up to 105 gf / g·m 2 .

[0051] Within the aforementioned range, the thermal stability of the secondary battery can be further improved by the separator 140. For example, when the substrate orientation is less than the aforementioned range, the ignition temperature due to the increase in internal temperature of the secondary battery may be lower, and the ignition transfer time may be shortened. For example, when the substrate orientation exceeds the aforementioned range, mechanical stability may not be guaranteed, which may lead to an increase in the internal short-circuit rate of the secondary battery.

[0052] According to an exemplary embodiment, the weight per unit area of ​​the substrate 142 can be 4.0 g / m². 2 Up to 5.0g / m 2 In some embodiments, the weight per unit area of ​​substrate 142 can be 4.1 g / m². 2 Up to 4.9g / m 2 4.2g / m 2 Up to 4.8g / m 2 4.25g / m 2 Up to 4.75g / m 2 Or 4.3g / m 2 Up to 4.7g / m 2 .

[0053] Within the aforementioned range, the orientation degree of the substrate can fall within the specified range, thereby further improving the thermal stability of the secondary battery.

[0054] According to an exemplary embodiment, the thickness of the substrate 142 can be from 1 μm to 15 μm. In some embodiments, the thickness of the substrate 142 can be from 2 μm to 14 μm, 3 μm to 13 μm, 4 μm to 12 μm, or 5 μm to 11 μm. Within the above ranges, substrate breakage can be suppressed, and the content of substantial active material in the secondary battery can be increased, thereby improving the energy density.

[0055] The coating 145 can be laminated on one side of the substrate 142. According to an exemplary embodiment, the coating 145 can be formed on either the top or bottom surface of the substrate 142. According to an exemplary embodiment, the coating 145 can be formed on both sides of the substrate 142. When using a single-sided coated separator, capacity reduction of the secondary battery can be prevented; when using a double-sided coated separator, the thermal stability of the secondary battery can be further improved.

[0056] According to an exemplary embodiment, coating 145 may comprise inorganic particles. The inorganic particles may represent ceramic particles.

[0057] For example, the inorganic particles may include spinel, cordierite, mullite, kaolinite, silica, talc, forsterite, corundum, alumina, zircon, silicon carbide, boehmite, zirconium oxide, clay, aluminum hydroxide, magnesium hydroxide, alumina, magnesium oxide, calcium oxide, barium sulfate, titanium dioxide, etc. These can be used alone or in combination of two or more.

[0058] According to an exemplary embodiment, the inorganic particles may comprise one or more of aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, calcium oxide, barium sulfate, boehmite, titanium dioxide, silicon dioxide, and clay. In one embodiment, the inorganic particles may comprise boehmite. Therefore, the self-heating temperature of the secondary battery can be increased, thereby suppressing fire.

[0059] According to an exemplary embodiment, the content of inorganic particles in the total weight of coating 145 can be 40% by weight or more, 40.5% by weight or more, 41% by weight or more, or 41.5% by weight or more. According to an exemplary embodiment, the content of inorganic particles in the total weight of coating 145 can be 60% by weight or less, 50% by weight or less, 47% by weight or less, 46% by weight or less, or 45% by weight or less.

[0060] For example, the content of the inorganic particles in the total weight of the coating 145 can be 40% to 60% by weight, 40.5% to 50% by weight, 41% to 47% by weight, or 41.5% to 45% by weight. Within the above range, the difference in thermal shrinkage between the coating and the substrate 142 can be reduced, and the ignition of the secondary battery can be further suppressed.

[0061] The content of the inorganic particles can be expressed as a value obtained by thermogravimetric analysis (TGA) of the diaphragm 140. For example, the content of the inorganic particles can be expressed as a value obtained by heating the diaphragm from room temperature to 900°C using a thermogravimetric analyzer.

[0062] According to an exemplary embodiment, coating 145 may contain organic particles.

[0063] In some embodiments, the organic particles may comprise polyethylene-based particles. For example, the polyethylene-based particles may comprise polyolefin-based homopolymers, copolymers formed by the reaction of polyolefin-based monomers and comonomers, etc.

[0064] According to an exemplary embodiment, the content of the organic particles in the total weight of the coating 145 can be 40% to 60% by weight, 42% to 55% by weight, 44% to 53% by weight, or 45% to 50% by weight.

[0065] According to an exemplary embodiment, coating 145 may further comprise an adhesive. For example, the inorganic particles may be mixed with an adhesive and a solvent (e.g., water) to prepare a coating slurry. The coating slurry may be applied to one side of substrate 142 and then dried to form coating 145.

[0066] The adhesive can improve the stability of coating 145. Non-limiting examples of the adhesive include: polymethyl methacrylate, polyethyl acrylate, polybutyl acrylate, polybutylmethacrylate, and other poly(meth)acrylate alkyl esters; polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinyl acetate, ethylene vinyl acetate copolymer, cellulose acetate, polyacrylonitrile, polyvinyl alcohol, polyvinyl pyrrolidone, polyimide, carboxymethyl cellulose (CMC), polyethylene oxide, and polypropylene oxide. These can be used alone or in combination of two or more.

[0067] According to an exemplary embodiment, the adhesive may comprise one or more of polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene oxide, ethylene-vinyl acetate copolymer, and copolymers thereof. Therefore, the stability of the adhesive at high temperatures can be improved, thereby increasing the ignition delay time through coating 145.

[0068] The adhesive may be included as a remainder of the total weight of coating 145. For example, the adhesive may be included as a remainder other than the content of the inorganic particles and the organic particles.

[0069] In some embodiments, the average particle size (D) of the inorganic particles 50 The particle size can be from 0.1 μm to 5 μm, 0.4 μm to 3 μm, or 0.5 μm to 1.5 μm. Within the above range, a porous structure of coating 145 can be formed by inorganic particles, and coating 145 can be prevented from peeling off at high temperatures.

[0070] The "average particle size (D)" 50 ")" can refer to the median particle size corresponding to 50% of the cumulative distribution (a distribution based on quantity) in which the corresponding particles are arranged in order of size.

[0071] In an exemplary embodiment, the total thickness of the diaphragm 140 can be from 5 μm to 30 μm. In some embodiments, the total thickness of the diaphragm 140 can be from 10 μm to 20 μm.

[0072] According to an exemplary embodiment, the thickness of coating 145 can be from 1 μm to 10 μm. In some embodiments, the thickness of coating 145 can be from 1 μm to 8 μm or from 2 μm to 6 μm.

[0073] According to an exemplary embodiment, the MD heat shrinkage rate of the diaphragm 140 can be less than 3.0%, less than 2.8%, less than 2.6%, less than 2.5%, less than 2.4%, less than 2.3%, less than 2.2%, less than 2.1%, less than 2.0%, or less than 2.0%.

[0074] There is no lower limit to the MD heat shrinkage rate of the diaphragm 140, but for example, the MD heat shrinkage rate of the diaphragm 140 may be 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, or 0.5% or more.

[0075] For example, the MD heat shrinkage rate of the diaphragm 140 can be greater than 0.1% and less than 3.0%, 0.2% to 2.8%, 0.3% to 2.5%, 0.4% to 2.2%, 0.5% to 2.0%, or greater than 0.5% and less than 2.0%.

[0076] According to an exemplary embodiment, the TD heat shrinkage rate of the diaphragm 140 can be less than 2.0%, less than 1.8%, less than 1.6%, less than 1.5%, less than 1.4%, less than 1.3%, less than 1.2%, less than 1.1%, or less than 1.0%.

[0077] There is no lower limit to the TD heat shrinkage rate of the diaphragm 140, but for example, the TD heat shrinkage rate of the diaphragm 140 may be 0.01% or more, 0.05% or more, 0.1% or more, 0.2% or more, or 0.25% or more.

[0078] For example, the TD heat shrinkage rate of the diaphragm 140 can be greater than 0.01% and less than 2.0%, 0.05% to 1.8%, 0.1% to 1.5%, 0.1% to 1.3%, 0.2% to 1.1%, or 0.25% to less than 1.0%.

[0079] Within the aforementioned range, the self-heating temperature of the diaphragm 140 can be increased, thereby achieving the characteristic of preventing thermal shrinkage. Furthermore, deformation of the diaphragm caused by differences in thermal shrinkage can be suppressed, thus ensuring thermal stability.

[0080] According to an exemplary embodiment, the ratio of the MD heat shrinkage rate to the TD heat shrinkage rate of the diaphragm 140 can be 0.5 to 2.5, 0.75 to 2.25, 0.9 to 2.1, or 1.0 to 2.0. Within the above ranges, deformation and separation of the substrate 142 and the coating 145 due to heat can be suppressed.

[0081] The term "heat shrinkage rate" as used in this invention refers to the ratio of the reduced length after storage in a chamber at 130°C for 1 hour to the initial length. For example, the MD (or TD) heat shrinkage rate can represent the ratio of the reduced length of the diaphragm 140 in the MD (or TD) direction after storage in a chamber at 130°C for 1 hour to the initial length in the MD (or TD) direction.

[0082] Figure 2 and Figure 3 These are schematic plan views and schematic cross-sectional views illustrating a secondary battery according to an exemplary embodiment. For example, Figure 3 It is along Figure 2 A cross-sectional view taken along the thickness direction of the I-I' line.

[0083] Figure 2 and Figure 3 The secondary battery shown is schematic for ease of explanation, and the structure of the secondary battery of the present invention is not limited to that shown. Figure 2 and Figure 3 The structure shown.

[0084] Reference Figure 2 and Figure 3 The secondary battery includes the aforementioned positive electrode 100 and negative electrode 130, and also includes the aforementioned separator 140 according to an embodiment of the present invention, the separator 140 being disposed between the positive electrode 100 and the negative electrode 130. Figure 3 In the illustration, the diaphragm 140 is shown as a single layer, but if referring to... Figure 1 As shown in the description, the diaphragm 140 includes a substrate 142 and a coating 145, and may have a single-sided coating structure or a double-sided coating structure.

[0085] The positive electrode 100 may include a positive electrode active material layer 110, which is formed by coating the positive electrode active material onto the positive electrode current collector 105. The positive electrode active material may contain compounds that allow lithium ions to be reversibly inserted and extracted. In this case, the secondary battery can be provided as a lithium secondary battery.

[0086] The positive current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive current collector 105 may also include aluminum or stainless steel that has been surface-treated with carbon, nickel, titanium, or silver.

[0087] According to an exemplary embodiment, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0088] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1.

[0089] [Chemical Formula 1] Li x Ni a M b O 2+z In chemical formula 1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0090] The chemical structure represented by Formula 1 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 1 is provided to represent the bonding relationships of the main active elements and should be understood as including the introduction and substitution of additional elements.

[0091] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure and form bonds; this should be understood to also include the chemical structures represented by Formula 1.

[0092] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0093] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0094] [Chemical Formula 1-1] Li x Ni a M1 b1 M2 b2 O 2+z In chemical formula 1-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 1-1, the following conditions may be met: 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, -0.5≤z≤0.1.

[0095] The positive electrode active material may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more combinations of the elements described above can be used as coating elements or doping elements.

[0096] The coating element or doping element may exist on the surface of the lithium-nickel metal oxide particles, or may penetrate through the surface of the lithium-nickel metal oxide particles and be contained in the bonding structure represented by chemical formula 1 or chemical formula 1-1.

[0097] The positive electrode active material may contain nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0098] Ni can be provided as a transition metal related to the power and capacity of a lithium secondary battery. Thus, as described above, by using a high-Ni composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0099] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or the secondary battery may be relatively reduced, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, and life stability and capacity retention characteristics can be improved by Mn.

[0100] In the NCM-based lithium oxide, the content of Ni (for example, the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni can 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.

[0101] In some embodiments, the positive electrode active material may further 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 (for example, LiFePO4).

[0102] In some embodiments, the positive electrode active material may include, for example, a Mn-rich-based active material having a chemical structure or crystal structure represented by Chemical Formula 2, a Li rich layered oxide (LLO) / Over Lithiated Oxide (OLO)-based active material, or a Co-less-based active material.

[0103] [Chemical Formula 2] p[Li2MnO3]·(1-p)[Li q JO2] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0104] For example, the positive electrode active material can be mixed in a solvent to prepare a positive electrode slurry. After the positive electrode slurry is coated on the positive electrode current collector 105, it can be dried and calendered to prepare the positive electrode active material layer 110.

[0105] The positive electrode active material layer 110 may further include a binder, and optionally may further include a conductive material, a thickener, etc.

[0106] The positive electrode binder may include organic binders such as polyvinylidene fluoride (PVDF), PVDF-co-HFP, polyacrylonitrile, and polymethyl methacrylate; and water-based binders such as styrene-butadiene rubber (SBR). Furthermore, for example, the binder used for the positive electrode may also be used with a thickener such as carboxymethyl cellulose (CMC). In one embodiment, a PVDF-based binder may be used as the positive electrode binder.

[0107] For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; and metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0108] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120.

[0109] The negative current collector 125 may include the metal or alloy mentioned in the positive current collector. In some embodiments, the negative current collector 125 may include copper or a copper alloy.

[0110] The negative electrode active material layer 120 can be formed on the upper and / or lower surface of the negative electrode current collector 125. The negative electrode active material layer 120 can be formed on the upper and lower surfaces of the negative electrode current collector 125, respectively.

[0111] The negative electrode active material layer 120 may include a negative electrode active material and a negative electrode binder.

[0112] The negative electrode active material can be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon (Si)-based compounds or tin, etc.

[0113] Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0114] Examples of crystalline carbon include natural graphite, artificial graphite, graphitized coke, graphitized mesophase carbon microspheres (MCMB), graphitized mesophase pitch-based carbon fibers (MPCF), and other graphite-based carbons.

[0115] As the elements contained in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. can be cited.

[0116] The silicon-based compound may include, for example, silicon (Si), silicon oxide (e.g., SiOx, 0 < x < 2), or a silicon-carbon composite compound containing silicon carbide (SiC).

[0117] For example, the negative electrode active material, the binder, the conductive material, the thickener, etc. can be mixed and stirred together in a solvent to prepare a negative electrode paste. After the negative electrode paste is coated on at least one surface of the negative electrode current collector 125, it can be dried and calendered to manufacture the negative electrode 130.

[0118] The binder and the conductive material can use substances that are substantially the same or similar to those used in the positive electrode active material layer 110. In some embodiments, for example, for the compatibility with the carbon-based active material, the negative electrode binder may include a water-based binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0119] According to an exemplary embodiment, the electrode assembly 150 may be defined by a positive electrode 100, a negative electrode 130, and a separator 140. The electrode assembly 150 may be of a winding type, a stacking type, a z-folding type, or a stack-folding type.

[0120] The electrode assembly 150 may be accommodated in a housing 160 together with an electrolytic solution, thereby defining a secondary battery. According to an exemplary embodiment, the electrolytic solution may use a non-aqueous electrolytic solution.

[0121] The non-aqueous electrolytic solution may contain a lithium salt as an electrolyte and an organic solvent. The lithium salt may be represented, for example, by Li + X - As the anion (X - ) of the lithium salt, 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 - (CF3CF2SO2)2N - wait.

[0122] The organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, 1,2-dimethoxyethane, 1,2-diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These may be used alone or in combination of two or more.

[0123] like Figure 2 and Figure 3 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to one end of the housing 160. The tabs can be fused to said one end of the housing 160 and connected to electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0124] Figure 2 The diagram shows the positive electrode lead 107 and the negative electrode lead 127 protruding from the upper side of the housing 160 in a planar direction, but the position of the electrode leads is not limited thereto. For example, the electrode leads may protrude from at least one of the two sides of the housing 160, or from the lower side of the housing 160. Alternatively, the positive electrode lead 107 and the negative electrode lead 127 may be formed to protrude from different sides of the housing 160, respectively.

[0125] The secondary battery can be made in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0126] The aforementioned secondary battery may include a separator 140 according to an embodiment of the present invention. For example, by employing a separator 140 having a single-sided coating structure, the number of layers of the positive electrode 100 and the negative electrode 130 can be relatively increased.

[0127] like Figure 3 As shown, an electrode assembly 150 can be defined, including a positive electrode 100, a negative electrode 130, and a separator 140. The separator 140 can be disposed between the positive electrode 100 and the negative electrode 130. For example, a secondary battery may include multiple electrode assemblies.

[0128] Therefore, the level of temperature change of the electrode assembly 150 can be reduced. For example, when a short circuit inside the electrode assembly 150 causes an increase in internal temperature, the temperature of the electrode assembly 150 may increase. For example, a lower level of temperature change can be considered when the rate of increase of the self-temperature is reduced or when the temperature at a specific point is higher than the rate of change of the self-temperature.

[0129] According to an exemplary implementation, after the self-heating time point of the electrode assembly 150 at 0.02°C / min or higher, the temperature at which the self-temperature change of the electrode assembly 150 reaches 1°C / second can be 175°C or higher.

[0130] In some implementations, the temperature at which the self-temperature change reaches 1°C / second can be above 175°C, 175.3°C, 175.5°C, 176°C, 176.5°C, 177°C, 177.5°C, or 178°C. Within the above range, thermal runaway of the secondary battery can be suppressed.

[0131] For example, due to external impacts, the active material and electrolyte inside the electrode assembly 150 may decompose, potentially leading to self-heating. The decomposition of the active material and electrolyte may cause the temperature inside the electrode assembly 150 to rise, which could further promote the aforementioned decomposition and accelerate the temperature change of the electrode assembly 150. As the temperature change of the electrode assembly 150 accelerates, its own temperature change may rise to over 1°C / second. Due to the delay in heat transfer and the suppression of internal heating within the electrode assembly 150, the temperature at which the self-temperature change of the electrode assembly 150 reaches 1°C / second can be quite high.

[0132] The temperature at which the temperature change of the electrode assembly reaches 1°C / second can vary depending on the type of active material, the size of the positive and negative electrodes, the size of the separator, etc. For example, the above temperature can represent the temperature of an electrode assembly including a separator with a size of 50mm × 50mm.

[0133] Figure 4 This is a schematic cross-sectional view showing a secondary battery module according to an exemplary embodiment.

[0134] Reference Figure 4 The secondary battery module may include multiple secondary batteries 200. The secondary battery module may include a cooling plate 220, which is disposed on the lower side in a direction parallel to the direction in which the multiple secondary batteries 200 are stacked. The multiple secondary batteries 200 may be housed within a cover 230.

[0135] According to an exemplary embodiment, the cover 230 may include: a lower cover adjacent to the cooling plate 220; an upper cover disposed on the opposite side of the cooling plate 220; and a side cover between the lower cover and the upper cover.

[0136] For example, the side cover may include a front cover and a back cover. For example, the cover may cover the six outer sides of multiple stacked secondary batteries 200. For example, the lower cover, upper cover, and side cover may be integrally formed.

[0137] According to an exemplary embodiment, multiple secondary batteries 200 may be stacked on top of each other and in direct contact. According to an exemplary embodiment, the multiple secondary batteries 200 may be stacked on top of each other, with one side of all the multiple secondary batteries 200 in contact with the cooling plate 220.

[0138] According to an exemplary embodiment, the secondary battery module may include a surface pressure pad 240 disposed on an upper side in a direction parallel to the direction in which the plurality of secondary batteries 200 are stacked. For example, the surface pressure pad 240 may be formed of an insulating material with elastic reaction force. For example, the surface pressure pad 240 may provide stability to the stacked structure of the secondary batteries. For example, thermally conductive components may be filled in the gaps formed between the surface pressure pad 240 and the plurality of secondary batteries 200.

[0139] According to an exemplary embodiment, the surface pressure pad 240 may also be omitted. For example, multiple secondary batteries 200 may be in direct contact with the cover 230 on the upper side.

[0140] According to the exemplary implementation, the fire transfer of the secondary battery 200 can be suppressed.

[0141] According to an exemplary embodiment, more than one secondary battery may be included between the first secondary battery 200a and the second secondary battery 200b. For example, the first secondary battery 200a and the second secondary battery 200b may represent two secondary batteries that are not in contact with each other and are spaced at any distance.

[0142] In some implementations, two secondary batteries may be included between the first secondary battery 200a and the second secondary battery 200b.

[0143] According to an exemplary embodiment, the ignition transfer time from the ignition of the first secondary battery 200a to the ignition of the second secondary battery 200b can be 70 seconds or more. In some embodiments, the ignition transfer time can be 70 seconds or more, 71 seconds or more, 72 seconds or more, 73 seconds or more, 74 seconds or more, or 75 seconds or more.

[0144] The ignition transfer time can vary depending on the size of the secondary battery, its stacked structure, the type of cooling plate, and the type of active material. For example, the ignition transfer time can refer to the ignition transfer time between secondary batteries including a separator with a size of 50mm × 50mm.

[0145] The term "ignition" can refer to the point in time when the fire initially began to burn. For example, it can be considered as the point in time when the fire is observed from the appearance of the electrode assembly 150.

[0146] For example, the fire transfer time can represent the time between the first secondary battery 200a and the second secondary battery 200b, including the state of two secondary batteries.

[0147] The following specific experimental examples are provided to aid in understanding the present invention. However, these examples are only for illustrating the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept, which is obvious to those skilled in the art. Such variations and modifications are naturally within the scope of the claims.

[0148] Examples and Comparative Examples (1) Manufacturing of the diaphragm Manufacture a diaphragm having the inorganic content, puncture strength and substrate weight per unit area as shown in Table 1.

[0149] Specifically, granules made from high-density polyethylene (HDPE) resin are mixed with oil at a volume ratio of 3:7 to obtain a mixture. Using a T-die extruder, the mixture is extruded into a sheet at 200°C, and then cured by cooling rollers to obtain an unstretched sheet. The unstretched sheet is then subjected to TD stretching and MD stretching (at a ratio of 5 times or more) at 120°C, and then heat-set at 130°C to obtain a substrate.

[0150] Boehmite and polymethyl methacrylate binder are added to water and mixed to prepare a slurry. The slurry is then coated onto the substrate and dried to form a coating. By varying the coating thickness, the ratio of inorganic particles to binder in the coating, etc., the diaphragms shown in Table 1 below are obtained.

[0151] (2) Analysis of the characteristics of the diaphragm Analysis of substrate orientation The substrate orientation is measured according to Equation 1 below. The puncture strength in Equation 1 is measured using a Universal Testing Machine (UTM) (Instron 3345). Specifically, after the diaphragm is fixed with a fixing device, a puncture needle is positioned so that it is in perpendicular contact with the diaphragm. The force is increased at a constant rate until the puncture needle penetrates the diaphragm, and the maximum load applied just before the diaphragm is penetrated is defined as the puncture strength.

[0152] [Formula 1] Substrate orientation degree = S / W In Formula 1, S is the puncture strength of the diaphragm, and W is the weight per unit area of ​​the substrate.

[0153] Analysis of inorganic content The inorganic content of the diaphragm was analyzed using thermogravimetric analysis (TGA). Specifically, measurements were performed using a TGA 5500 thermogravimetric analyzer, with the temperature increased from room temperature to 900°C at a rate of 10°C / min under a nitrogen atmosphere. Measurements were performed in air at temperatures above 700°C.

[0154] Analysis of thermal shrinkage rate A diaphragm measuring 50mm × 50mm, marked with its length direction (MD) and width direction (TD), was placed in an oven (hot air furnace) at a stable temperature of 130°C for 1 hour. The change in length of the diaphragm after placement was measured, and the heat shrinkage rate was calculated according to Equation 2 below.

[0155] [Equation 2] MD heat shrinkage rate (%) = {(initial length - length after storage) / initial length} × 100 TD heat shrinkage rate (%) = {(initial width - width after storage) / initial width} × 100 [Table 1] Experimental Example Manufacturing of secondary batteries 94% by weight of lithium-nickel-cobalt-manganese oxide (LiNi) was used as the positive electrode active material. 0.88 Co 0.06 Mn 0.06 2.5% by weight of polyvinylidene fluoride (PVDF) as a binder and 3.5% by weight of Super-P as a conductive material were added to N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum substrate with a thickness of 12 μm and then dried and calendered to obtain a positive electrode.

[0156] A negative electrode slurry was prepared by adding 95% by weight of graphite-based active material (artificial graphite:natural graphite weight ratio of 70:25) as the negative electrode active material and 5% by weight of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders to water. The negative electrode slurry was then uniformly coated onto a copper substrate with a thickness of 8 μm and dried and calendered to obtain the negative electrode.

[0157] The positive and negative electrodes are notched to predetermined sizes and then stacked in such a manner that the diaphragm of the embodiment and the comparative example is placed between the positive and negative electrodes to obtain an electrode assembly.

[0158] The electrode assembly is placed in a soft package, and the three sides except for the electrolyte injection surface are sealed. At this time, the portion with the tabs is included in the sealed portion. Electrolyte is injected through the electrolyte injection surface, and the electrolyte injection surface is sealed. Then, it is immersed for more than 12 hours to obtain a 2000mAh lithium secondary battery.

[0159] The electrolyte used was a 1M LiPF6 solution with a mixed solvent of EC / EMC / DMC (25 / 45 / 30; volume ratio).

[0160] (1) Evaluation of Accelerated Rate Calorimetry (ARC) A temperature sensor was attached to the fabricated secondary battery and placed in a chamber. The temperature was raised to 50°C, and then increased at a rate of 5°C / min. The temperature rise rate of the secondary battery was monitored every 30 minutes. Heating of the chamber was stopped when the temperature rise rate of the secondary battery reached 0.02°C / min or higher, and the temperature at which the temperature change of the secondary battery itself reached 1°C / second was measured.

[0161] When the measured temperature is above 175℃, the evaluation is "○"; when the measured temperature is below 175℃, the evaluation is "×".

[0162] (2) Evaluation of fire delay time Multiple secondary batteries are stacked on a heating pad on a lower jig, and then the upper jig is stacked on top. After the temperature of the heating pad is raised, the time from the initial ignition time of the first secondary battery that is set to contact the heating pad to the time when the ignition transfers to the heating pad for the fourth secondary battery is measured.

[0163] When the fire ignition delay time is more than 70 seconds, the rating is "○"; when the fire ignition delay time is less than 70 seconds, the rating is "×".

[0164] The evaluation results are shown in Table 2 below.

[0165] [Table 2] Referring to Table 2, in the secondary batteries using the diaphragm according to the embodiments, the overall performance exhibits a higher self-heating temperature or a longer ignition delay time as evaluated by ARC.

[0166] In secondary batteries using a separator from a comparative example with a lower substrate orientation, a lower self-heating temperature was observed according to ARC evaluation, and the ignition delay time was shortened.

[0167] In Example 5, which has a relatively low substrate orientation and relatively low puncture strength and / or inorganic content, a relatively low self-heating temperature and a relatively short ignition delay time were observed.

[0168] In Example 6, where the substrate orientation is relatively high, a relatively low self-heating temperature is observed.

Claims

1. A separator for a secondary battery, comprising: Substrate; as well as A coating, said coating being laminated on the surface of the substrate, and said coating comprising inorganic particles. Wherein, the substrate orientation degree defined by the following formula 1 is 90 gf / g·m 2 above, [Formula 1] Substrate orientation degree = S / W In Formula 1, S is the puncture strength of the diaphragm, and W is the weight per unit area of ​​the substrate.

2. The separator for secondary batteries according to claim 1, wherein, The substrate orientation degree is 90 gf / g·m 2 Up to 120 gf / g·m 2 .

3. The separator for secondary batteries according to claim 1, wherein, The inorganic particles comprise 40% by weight or more of the total weight of the coating.

4. The separator for secondary batteries according to claim 1, wherein, The inorganic particles comprise one or more of the following: aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, calcium oxide, barium sulfate, boehmite, titanium dioxide, silicon dioxide, and clay.

5. The separator for secondary batteries according to claim 1, wherein, The substrate has a unit area weight of 4.0 g / m². 2 Up to 5.0g / m 2 .

6. The separator for secondary batteries according to claim 1, wherein, The machine-direction thermal shrinkage rate of the diaphragm, measured after storage at 130°C for 1 hour, is less than 3.0%.

7. The separator for secondary batteries according to claim 1, wherein, The transverse thermal shrinkage rate of the diaphragm measured after being stored at 130°C for 1 hour was less than 2.0%.

8. The separator for secondary batteries according to claim 1, wherein, The substrate has a machine direction stretch ratio and a transverse stretch ratio of 3 to 8 times.

9. The separator for a secondary battery according to claim 1, wherein, The thickness of the substrate is 1 μm to 15 μm.

10. The separator for a secondary battery according to claim 1, wherein, The coating further comprises polyethylene organic particles.

11. The separator for a secondary battery according to claim 1, wherein, The coating further comprises an adhesive comprising one or more of polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene oxide, ethylene-vinyl acetate copolymer, and copolymers thereof.

12. A secondary battery comprising an electrode assembly, in, The electrode assembly includes: a positive electrode; a negative electrode; and a separator for a secondary battery as described in claim 1, the separator being disposed between the positive electrode and the negative electrode.

13. The secondary battery according to claim 12, wherein, After the self-heating time point of the electrode assembly exceeding 0.02℃ / min, the temperature of the electrode assembly when its own temperature change reaches 1℃ / second is above 175℃.

14. A secondary battery module comprising a structure in which multiple secondary batteries as described in claim 12 are stacked on top of each other.

15. The secondary battery module according to claim 14, wherein, The plurality of secondary batteries includes any first secondary battery and any second secondary battery that is not in contact with the first secondary battery. The ignition transfer time from the ignition of the first secondary battery to the ignition of the second secondary battery is more than 70 seconds.

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