Electrode assembly and electrochemical device including same

Abstract

The present invention relates to: a novel structure of an electrode assembly applicable to a process for manufacturing the electrode assembly by sequentially stacking a positive electrode, a separator, and a negative electrode through lamination and stacking techniques; and a method for manufacturing same. The electrode assembly includes at least one electrode laminate including a first separator, a first electrode, a second separator, and a second electrode sequentially laminated in the thickness direction, wherein the first separator includes a first separator substrate manufactured by a wet method, the second separator includes a second separator substrate manufactured by a dry method, and the first separator substrate has a thickness of 10 μm or less and a porosity of 45 vol% or more. Using an electrode assembly according to an aspect of the present invention has the advantage that an electrochemical device can have a significantly reduced short circuit failure rate while having excellent output characteristics.

Description

Electrode assembly and electrochemical device including the same

[0001] The present invention relates to an electrode assembly for an electrochemical device and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Application No. 2024-0145139 filed with the Korean Intellectual Property Office on October 22, 2024, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] Lithium-ion batteries are widely used as power sources for portable electronic devices such as laptops, mobile phones, digital cameras, and camcorders. Furthermore, due to their high energy density, these batteries are recently being applied in various fields, including automobiles.

[0004] Lithium secondary batteries are manufactured through a process in which an electrode assembly, comprising a positive electrode, a separator, and a negative electrode as a single unit, is inserted into a battery case, and then an electrolyte is injected and sealed. Polyolefin-based porous substrates are typically used as separators for lithium secondary batteries, and, if necessary, porous coating layers are provided on the porous substrate to mitigate the thermal shrinkage phenomenon characteristic of polymer substrates.

[0005] Meanwhile, manufacturing methods for porous substrates are broadly classified into wet processes and dry processes. A wet process refers to a process in which a polymer material is mixed with a plasticizer, extruded to form a sheet, and then the plasticizer is removed from the sheet to form pores. In a wet process, the pore size is determined by the type of plasticizer and the compatibility between the plasticizer and the polymer material, so there is an advantage of uniform pore size; however, the process is not easy to operate depending on changes in the polymer material, and there is a problem that the solvent used to extract the plasticizer is harmful to the human body and the environment.

[0006] The dry process is a process in which a precursor polymer film is manufactured through extrusion, fiber orientation is controlled through heat treatment, and pores are formed by tearing the fibers of the polymer film through stretching. Unlike the wet process, the dry process does not use an extraction solvent for plasticizer extraction, so it has the advantage of being more environmentally friendly compared to the wet process.

[0007] Meanwhile, it is important for lithium secondary batteries used in Hybrid Electric Vehicles (HEVs) to have high output performance in order to perform engine power assistance functions in low-efficiency ranges. Due to the characteristics of materials and processes, separators using porous substrates manufactured by a dry process compared to a wet process have the advantage of providing a more favorable effect on the output performance of the battery. Therefore, the application of dry separators may be preferred in batteries where output characteristics are important.

[0008] However, due to the inherent splitting phenomenon of dry separators, there is a problem that when batteries are manufactured using this method, the short-circuit failure rate within the monocell is high due to the rupture of the separator. Furthermore, when manufacturing stack cells through the Lamination & Stacking (L&S) process, in which monocells with stacked anodes, separators, cathodes, and separators are sequentially stacked, the dry separator located at the bottom of the monocell may come into contact and friction with mechanical parts such as conveyor belts, which can cause problems that further degrade the insulation characteristics of the stack cell.

[0009] Therefore, the problem that the present invention aims to solve is,

[0010] The present invention aims to provide an electrochemical device that solves the aforementioned problems and has excellent output characteristics while significantly improving the short-circuit failure rate caused by separator rupture. Specifically, according to one aspect of the present invention, the invention aims to provide a lithium secondary battery that has excellent output characteristics, excellent capacity retention rate, and significantly reduced short-circuit failure rate.

[0011] More specifically, the present invention aims to provide an electrode assembly with a novel structure and a method for manufacturing the same, which reduces damage to the separator caused by friction at the contact point between the bottom of the monocell and the conveyor belt when assembling a stack cell using the L&S process, thereby enhancing the stability of the electrochemical device manufactured accordingly.

[0012] In order to solve the above problem,

[0013] According to one aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0014] The electrode assembly according to the first embodiment is,

[0015] One or more electrode stacks comprising a first separator, a first electrode, a second separator, and a second electrode sequentially stacked in the thickness direction, and

[0016] The first separator above comprises a first separator substrate manufactured by a wet method, and

[0017] The above second separator comprises a second separator substrate manufactured by a dry method, and

[0018] The above-mentioned first separator substrate has a thickness of 10 μm or less and a porosity of 45 volume% or more.

[0019] According to the second embodiment, in the first embodiment,

[0020] The thickness of the second separator substrate may be equal to or thicker than the thickness of the first separator substrate.

[0021] According to the third embodiment, in the first embodiment or the second embodiment,

[0022] The thickness of the second separator substrate is equal to or thicker than the thickness of the first separator substrate, and

[0023] The thickness deviation according to Formula 1 below may be 40% or less.

[0024] [Equation 1]

[0025] Thickness deviation (△d) = [(T2-T1) / T1] X 100 (%)

[0026] In the above Equation 1,

[0027] T1 is the thickness of the first separator substrate, and

[0028] T2 is the thickness of the second separator substrate.

[0029] According to the fourth embodiment, in any one of the first to third embodiments,

[0030] The porosity of the second separator substrate may be 40 volume% to 70 volume%.

[0031] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0032] The difference in electrical resistance (△ER) between the first separator substrate and the second separator substrate may be 30% or less.

[0033] According to the 6th embodiment, in any one of the 1st to 5th embodiments,

[0034] The average pore size of the first separator substrate may be 40 nm or more.

[0035] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0036] The average pore size of the second separator substrate may be 40 nm or less.

[0037] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0038] The first separation membrane and the second separation membrane may each independently include a porous coating layer comprising inorganic particles and a binder resin on one or both sides of the separation membrane substrate.

[0039] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0040] The interface between the first separator and the first electrode,

[0041] The interface between the first electrode and the second separator, and

[0042] At least one interface between the second separator and the second electrode may include one or more adhesive binders.

[0043] According to the 10th embodiment, in the 9th embodiment,

[0044] A concentration gradient may be formed from the surface of an adjacent electrode to the surface of an adjacent separator so that the concentration of the adhesive binder included in the above-mentioned at least one interface becomes lower as it approaches the adjacent separator.

[0045] According to the 11th embodiment, in the 9th embodiment,

[0046] The above adhesive binder may include a fluorine-based binder.

[0047] According to the 12th embodiment, in any one of the 1st to 11th embodiments,

[0048] The above-mentioned first separator substrate is manufactured by biaxial stretching, and

[0049] The above second separator substrate may be manufactured by uniaxial stretching.

[0050] According to the 13th embodiment, in any one of the 1st to 12th embodiments,

[0051] The above electrode assembly may be a stacked electrode assembly.

[0052]

[0053] According to another aspect of the present invention, electrochemical elements of the following embodiments may be provided.

[0054] The electrochemical device according to the 14th embodiment is,

[0055] An electrode assembly according to any one of the first to thirteenth embodiments and an electrolyte may be included.

[0056] According to the 15th embodiment, in the 14th embodiment,

[0057] The above electrochemical device can exhibit a capacity retention rate of 90% or more according to Equation 2 below.

[0058] [Equation 2]

[0059] Capacity retention rate (%) = (C m+200 / C m ) X 100 (%)

[0060] In the above Equation 2,

[0061] Cm represents the discharge capacity measured during m charge-discharge cycles, and

[0062] Cm+200 represents the discharge capacity measured during m+200 charge-discharge cycles, and

[0063] m represents an integer greater than or equal to 1.

[0064] An electrode assembly according to one embodiment of the present invention can improve output performance by applying a dry separator as a separator between electrodes, and can exhibit the effect of significantly improving the short circuit failure rate between monocells by applying a wet separator as a separator between the bottom part of the electrode assembly and the monocell.

[0065] In addition, the electrode assembly according to one embodiment of the present invention may have the advantage of improving the capacity retention rate by lowering the resistance of the electrochemical device using the same by selecting and using a thin and low-resistance dry separator and a wet separator, but the effects of the present invention are not limited thereto.

[0066] FIG. 1 shows a schematic diagram of an electrode assembly (1) comprising one or more electrode stacks (10) according to one embodiment of the present invention.

[0067] FIG. 2 shows a schematic diagram of a first separator (101) according to one embodiment of the present invention.

[0068] FIG. 3 shows a schematic diagram of a second separator (103) according to one embodiment of the present invention.

[0069] FIG. 4 shows a schematic diagram of an electrode assembly (1) comprising an adhesive binder (107) at at least one location among the interfaces between the separator and the electrode according to one embodiment of the present invention.

[0070] The present invention will be described in detail below.

[0071] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0072] In this specification, the description of the term "A and / or B" means "A or B, or both."

[0073] In this specification, words indicating directions such as up and down are for convenience only and are not intended to limit the invention.

[0074] The present invention relates to an electrode assembly for an electrochemical device and a method for manufacturing the same. In the present invention, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept that includes primary batteries and secondary batteries. The secondary battery is capable of charging and discharging and is a concept that encompasses lithium-ion batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc.

[0075]

[0076] [Electrode Assembly]

[0077] An electrode assembly according to one aspect of the present invention comprises one or more electrode stacks including a first separator, a first electrode, a second separator, and a second electrode, which are sequentially stacked in the thickness direction.

[0078] An electrode assembly according to one aspect of the present invention may also be named a stacked electrode assembly.

[0079] In this specification, the term 'thickness direction' refers to the direction in which the cathode, separator, and anode are stacked within the electrode assembly.

[0080] FIG. 1 illustrates a schematic diagram of an electrode assembly (1) according to one embodiment of the present invention. Referring to FIG. 1, the direction in which n electrode stacks (10) are stacked within the electrode assembly (1) is referred to as the thickness direction of the electrode assembly.

[0081] According to one aspect of the present invention, the electrode assembly (1) comprises one or more electrode stacks (10) including a first separator (101), a first electrode (102), a second separator (103), and a second electrode (104) that are sequentially stacked in the thickness direction. The first electrode and the second electrode have different polarities; for example, if the first electrode is a positive electrode, the second electrode is a negative electrode, and if the first electrode is a negative electrode, the second electrode is a positive electrode. In this specification, an electrode stack in which different polarities are stacked with a separator in between as described above may also be referred to as a mono cell.

[0082] According to one embodiment of the present invention, the electrode assembly (1) may further include a third separator (not shown) at the top of the electrode stack (10). In this case, when two or more electrode stacks are stacked, the third separator may be further included only at the top of the electrode stack located at the top, but the present invention is not limited thereto.

[0083] In this specification, a laminate in which only one electrode is interposed between the separators, unlike the electrode laminate (10), may be referred to as a half cell.

[0084] According to another embodiment of the present invention, the electrode assembly (1) may further include a half cell comprising a third separator, a third electrode, and a fourth separator at the top of the electrode stack (10). In this case, the third electrode has a polarity different from that of the second electrode, for example, when the second electrode is a negative electrode, the third electrode is a positive electrode, and when the second electrode is a positive electrode, the third electrode is a negative electrode.

[0085] In one embodiment of the present invention, the first electrode, the second electrode, and the third electrode may each be an anode or a cathode as described above. Since the specific configurations of the anode and cathode can be conventional, a description thereof will be omitted.

[0086] In this specification, a structure formed by stacking at least one monocell as described above, or a structure in which at least one monocell and one halfcell are sequentially stacked, may also be referred to as a stacked cell. The number of monocells stacked in the stacked cell may vary depending on the specifications of the electrochemical device used, and for example, may include n monocells, wherein n may be an integer greater than or equal to 1. For example, depending on the specifications of the electrochemical device, n may be 1 to 200, 5 to 150, 10 to 100, 15 to 90, 20 to 80, 25 to 70, or 25 to 50, and is not particularly limited thereto.

[0087] An electrode assembly according to one aspect of the present invention comprises a separator substrate manufactured by a dry method as a second separator between a first electrode and a second electrode. Accordingly, the second separator may also be referred to as a "dry separator" in this specification. This enables the realization of high-output performance of an electrochemical device to which the electrode assembly is applied, but the mechanism of the present invention is not limited thereto.

[0088] An electrode assembly according to one aspect of the present invention comprises a separator substrate manufactured by a wet method as a first separator provided at the bottom of an electrode stack, that is, at the bottom of a first electrode. Accordingly, the first separator may also be referred to as a "wet separator" in this specification. This prevents or minimizes damage to the separator when the electrode stack comes into contact with a mechanical part such as a conveyor belt. Additionally, it prevents or minimizes damage to the separator caused by friction between electrode stacks when a plurality of electrode stacks are stacked within the electrode assembly. This allows for the improvement of the insulation yield and stability of an electrochemical device to which the electrode assembly is applied, but the mechanism of the present invention is not limited thereto.

[0089] In one embodiment of the present invention, the electrode assembly utilizes a separator provided between two electrodes and a separator provided at the bottom of the electrode assembly, each having a different manufacturing method, so there may be differences in the basic physical properties between the separators. For example, since the separator substrate manufactured by the dry method and the wet separator differ in the degree of crystallization of the polymer fibers and pore characteristics, a difference may appear in terms of the resistance of the separator substrate itself.

[0090] According to one embodiment of the present invention, it may be preferable that the electrical resistance difference between the dry separator substrate (second separator substrate) and the wet separator substrate (first separator substrate) be 30% or less. For example, the electrical resistance difference between the two separator substrates may be 25% or less, 20% or less, 15% or less, or 10% or less. Specifically, the electrical resistance difference between the two separator substrates may be 0% to 30%, 5% to 30%, 5% to 20%, or 5% to 10%, but the present invention is not limited thereto. By implementing the electrical resistance difference between the first separator substrate and the second separator substrate within the range described above, there is an advantage in that the resistance balance between the separators can be adjusted during the charging and discharging of the electrochemical device to which the electrode assembly is applied, thereby further improving the output characteristics of the electrochemical device, but the present invention is not limited thereto.

[0091] In this specification, the electrical resistance deviation between the first separator substrate and the second separator substrate represents a value calculated as a percentage (%) of the difference between them after measuring the electrical resistance of each separator substrate by the following method. First, the electrical resistance of the separator substrate can be measured by the EIS method after injecting the separator substrate to be measured and the electrolyte into a CR2016 battery case and sealing it. At this time, the separator substrate is punched to a size of 19Φ and placed in a CR2016 battery case, and an electrolyte composed of 1M LiPF6, ethyl carbonate (EC), ethyl methyl carbonate (EMC) (3 / 7 v / v), and 2 wt% vinylene carbonate (VC) is injected and the cap is closed to prepare a resistance measurement sample. The EIS measurement can be performed using known instruments and measurement methods. For example, the EIS measurement can be performed using the Solartron analytical EIS instrument of Solartron and the resistance value can be measured under conditions of a frequency of 100,000 to 10,000 Hz.

[0092] Hereinafter, the first separator and the second separator used in the electrode assembly according to one aspect of the present invention will be described in detail.

[0093]

[0094] First membrane (wet membrane)

[0095] According to one embodiment of the present invention, in order to strengthen the mechanical properties of a separator provided at the bottom of an electrode stack and thereby reduce the rate of short circuits between electrode stacks, a wet separator is included as a separator (first separator) at the bottom of an electrode stack.

[0096] As described above, the first separator may also be referred to as a wet separator in that it includes a separator substrate manufactured by a wet method. Additionally, the separator substrate included in the first separator may be referred to as the first separator substrate.

[0097] In this specification, the first separation membrane substrate refers to a polymer substrate manufactured by including a series of processes including mixing a raw material such as a polymer resin with a diluent, followed by extrusion, molding, stretching, extraction, and heat setting.

[0098] According to one embodiment of the present invention, the first separation membrane substrate comprises a plurality of pores generated as a diluent is extracted from an extruded polymer film. At this time, the diluent is uniformly distributed within the polymer film formed by uniformly mixing the polymer resin constituting the separation membrane substrate and the diluent. Therefore, when the diluent is extracted using an extraction solvent, a plurality of pores having a relatively uniform size are formed within the polymer film, so the first separation membrane substrate can be characterized by having a uniform pore size. Furthermore, the separation membrane substrate manufactured by the wet method has the advantage of excellent mechanical strength as it has the characteristic of irregularly dispersing pores having a uniform size. Accordingly, the first separation membrane substrate manufactured by the wet method has the advantage of being easy to achieve a thin thickness compared to the second separation membrane substrate manufactured by the dry method described later.

[0099] Accordingly, according to one aspect of the present invention, the first separator substrate is preferably provided with a thickness of 10 μm or less to lower the resistance of the first separator itself and to balance the resistance with the second separator.

[0100] Furthermore, according to one aspect of the present invention, the first separator substrate, which is thinly implemented, is preferably configured to have a porosity of 45 volume% or more in order to lower the resistance value and achieve high porosity.

[0101] According to one aspect of the present invention, the first separator substrate has a thickness of 10 μm or less and a porosity of 45 volume% or more.

[0102] In one embodiment of the present invention, the thickness of the first separator substrate may be 5 μm to 10 μm, 6 μm to 10 μm, 7 μm to 10 μm, 8 μm to 10 μm, 8.5 μm to 9.5 μm, or 8 μm to 9 μm. While having the thickness of the first separator substrate within the above-described range may be advantageous for achieving low resistance of the first separator substrate and the first separator, the present invention is not limited thereto.

[0103] In this specification, the thickness of the first separator substrate can be measured according to a known method for measuring the thickness of each component of the separator. For example, a known thickness measuring instrument capable of measuring the thickness of the thin film can be used, and specifically, a thickness measuring instrument from Mitutoyo can be used, but the present invention is not limited thereto.

[0104] In one embodiment of the present invention, the porosity of the first separator substrate may be, for example, 45 volume% to 70 volume%, 45 volume% to 60 volume%, 45 volume% to 55 volume%, 45 volume% to 50 volume%, 45 volume% to 47 volume%, or 45 volume% to 46 volume%. When the porosity of the first separator substrate is within the ranges described above, advantageous effects may be exhibited in terms of ion permeability and resistance of the first separator, but the present invention is not limited thereto.

[0105] In this specification, the porosity of the first membrane substrate may be measured according to a known method for measuring the porosity of a membrane substrate. For example, the porosity of the membrane substrate may be measured by applying pressure continuously within a pressure range of 0.5 to 60,000 psi according to ASTM D4284-92 standards, measuring the diameter of the pores filled with mercury at a constant pressure, and measuring the volume of mercury filled in the entire pore. The porosity value may be derived from a value automatically measured and calculated by a measuring device. For example, the Autopore IV 9500 from Micrometrics may be used as the measuring device, and the measurable pore size range of said device is 0.003 μm to 360 μm, but the present invention is not limited thereto.

[0106] According to one embodiment of the present invention, the first separator substrate comprises a plurality of pores, and as long as the porosity range is satisfied, the specific pore characteristics are not significantly limited. However, in order to reduce the electrical resistance difference between the first separator substrate and the second separator substrate, and to avoid significantly increasing the resistance of the first separator even if a porous coating layer is included on the first separator substrate as described below, it may be desirable to limit the size of the pores within the first separator substrate to a predetermined range. For example, it may be desirable for the average size of the pores within the first separator substrate to be 30 nm or more and 80 nm or less. Specifically, the average size of the pores within the first separator substrate may be 30 nm to 80 nm, 30 nm to 70 nm, 40 nm to 60 nm, 40 nm to 50 nm, 45 nm to 50 nm, or 45 nm to 46 nm, but the present invention is not limited thereto.

[0107] In this specification, the average pore size within the first membrane substrate can be measured in the following manner. First, a sample is prepared by stamping out a (width x height) 5 cm or (MD x TD) 5 cm sample. For the prepared sample, a dry-up curve is obtained using a known pore measuring instrument, for example, a Perm-porometer (CFP-1500A) from Porous Materials Inc. (PMI), and a wet-up curve is obtained using a wet-up method. For the wet-up method, the membrane substrate is filled with a Galwick solution (PMI) and then a pressure in the range of 50 to 350 psi is applied. Using the obtained dry and wet curves, the average pore size is measured by a known formula that converts the pore diameter from the pressure at the point where the wet curve intersects the curve representing half the slope of the dry curve.

[0108] A wet method for manufacturing a first separation membrane substrate according to one embodiment of the present invention may include the following steps.

[0109] S1-1) A step of obtaining a polymer sheet by extruding, cooling, and molding a polymer resin raw material,

[0110] S1-2) Step of stretching the obtained polymer sheet in MD and TD,

[0111] S1-3) A step of removing a diluent from a stretched polymer sheet, and

[0112] S1-4) A step of obtaining a separation membrane substrate by heat-fixing a polymer sheet from which the diluent has been removed.

[0113] According to one embodiment of the present invention, the first separator substrate is formed by using a polymer resin as a raw material and processing the polymer resin into a polymer sheet through a series of high-temperature extrusion, cooling, and stretching processes. At this time, the polymer sheet has the characteristic that the pore characteristics formed on the surface change depending on the temperature and / or pressure applied during the manufacturing process. In order to manufacture a porous polymer substrate without damaging the polymer sheet during this series of processes, a polyolefin resin may typically be used as the polymer resin.

[0114] In one embodiment of the present invention, the polyolefin resin may include polyethylene resin, but any polyolefin-based resin other than polyethylene resin may be used without limitation.

[0115] In one embodiment of the present invention, the polyolefin resin may include, for example, a weight-average molecular weight (Mw) of 500,000 g / mol to 5,000,000 g / mol. Specifically, the weight-average molecular weight of the polyolefin resin may be 500,000 g / mol to 2,000,000 g / mol, 500,000 g / mol to 1,000,000 g / mol, 500,000 g / mol to 800,000 g / mol, 500,000 g / mol to 700,000 g / mol, or 550,000 g / mol to 650,000 g / mol. More specifically, the weight-average molecular weight of the polyolefin resin may be 600,000 g / mol, for example, but the present invention is not limited thereto.

[0116] At this time, the weight-average molecular weight of the polymer may be a value measured by a conventional measurement method, for example, a value measured using a gel permeation chromatograph (GPC). At this time, the GPC measurement conditions may be measured by referring to the following conditions, but the present invention is not limited thereto.

[0117] - Column: PL Olexis (Polymer Laboratories)

[0118] - Solvent: TCB (Trichlorobenzene)

[0119] - Flow rate: 1.0 ml / min

[0120] - Sample concentration: 1.0 mg / ml

[0121] - Injection volume: 200 µl

[0122] - Column temperature: 160℃

[0123] - Detector: Agilent High Temperature RI detector

[0124] - Standard: Polystyrene (corrected by a cubic function)

[0125] In one embodiment of the present invention, the polyolefin resin for manufacturing the first separator substrate may include, for example, high-density polyethylene VH035 of Daehan Chemical Co., Ltd., but the present invention is not limited thereto.

[0126] The above step (S1-1) is a step of obtaining an extruder by extruding a raw material containing the polymer resin described above, and obtaining a polymer sheet by cooling and molding the high-temperature extruder.

[0127] In one embodiment of the present invention, the extrusion may be performed by a conventional process for extruding polymers in the field of manufacturing separation membranes. For example, a uniaxial compressor or a twin-screw compressor may be used as the extruder for the extrusion, but is not limited thereto.

[0128] In one embodiment of the present invention, the extrusion may be performed by introducing a polymer resin and a diluent into an extruder and melt-extruding at a temperature of, for example, 170°C to 250°C, for example, 200°C.

[0129] In one embodiment of the present invention, the diluent may be used with a conventional diluent generally used in the manufacturing process of a separation membrane for diluting raw materials. The diluent refers to a substance that can form pores by undergoing phase separation and removal upon cooling after being mixed with a polyolefin resin to form an extruded product. The diluent is not particularly limited as long as it satisfies this function. Non-limiting examples of such diluents include, but are not limited to, aliphatic hydrocarbon solvents such as paraffin oil; vegetable oils such as soybean oil; or plasticizers such as dialkyl phthalates. Among these, liquid paraffin oil having excellent compatibility with polyolefin resins, such as paraffin oil having a kinematic viscosity of 20 to 200 cSt at 40°C, may be suitably used. The diluent may be used alone or in the form of a mixture of two or more types.

[0130] In one embodiment of the present invention, the diluent may include, for example, LP350F of Kukdong Oil & Chemical Co., Ltd., but the present invention is not limited thereto.

[0131] In one embodiment of the present invention, the extruded molten material can be drawn out through a die, and the thickness of the first separator substrate manufactured can be controlled by controlling the amount discharged at this time.

[0132] Next, after obtaining the extruder, the extruder can be cooled to obtain a polymer pre-sheet.

[0133] According to one embodiment of the present invention, the extruded product obtained above can be formed into a sheet shape using a cooling casting device at a temperature of 20°C to 60°C. For example, the extruded product discharged from the extrusion section can be formed into a polymer sheet shape while cooling the extruded product by passing it between a pair of cooling casting rolls at a travel speed of 7 m / min at a temperature of 40°C.

[0134] The above step (S1-2) is a step of biaxially stretching the obtained polymer sheet in the machine direction (MD) and the transverse direction (TD) perpendicular thereto, respectively.

[0135] In one embodiment of the present invention, the step (S1-2) may include a process of sequentially stretching the polymer sheet in the machine direction and the transverse direction, for example, by using a tenter-type stretcher to stretch it 4 to 10 times in the machine direction and 4 to 10 times in the transverse direction.

[0136] In one embodiment of the present invention, the pore size formed in the polymer sheet may be modified according to the MD and TD stretching ratios and / or temperature. Accordingly, to control the porosity and / or average pore size of the first separation membrane substrate obtained, the MD and TD stretching ratios and / or temperature may be performed as follows.

[0137] A method for manufacturing a first separator substrate according to one aspect of the present invention may, in particular, perform at least one of the MD stretching and TD stretching processes at a temperature of 130°C or higher. For example, at least one of the MD stretching and TD stretching processes may be performed at a temperature of 130°C or higher and 145°C or lower.

[0138] In one embodiment of the present invention, the stretching step may be performed by sequentially performing MD stretching and TD stretching, and then performing TD stretching after MD stretching.

[0139] At this time, according to one embodiment of the present invention, the subsequent TD stretching step may be performed at a temperature of 130°C or higher and 145°C or lower, but the present invention is not limited thereto.

[0140] According to one embodiment of the present invention, the stretching step may include stretching in the MD direction and then stretching in the TD direction, and may include performing the MD stretching at a temperature of 110°C or higher and 125°C or lower and performing the TD stretching at a temperature of 130°C or higher and 140°C or lower, but the present invention is not limited thereto.

[0141] In one embodiment of the present invention, the MD stretching may be performed at a temperature of 125°C or lower, for example, 110°C to 125°C, 110°C to 120°C, 110°C to 115°C, or 110°C to 112°C, taking into account the melting temperature of the polymer resin. If the MD stretching temperature becomes too high, a problem may arise in which sufficient porosity of the separator substrate obtained adjacent to the melting point of the polymer resin is not secured.

[0142] In one embodiment of the present invention, the MD stretching may be performed at a stretching ratio of 4 to 10 times, 6 to 9 times, 6 to 8 times, 6 to 7 times, specifically 6.0 to 6.5 times, 6.0 to 6.3 times, or 6.0 to 6.1 times, but the present invention is not limited thereto.

[0143] In one embodiment of the present invention, the MD stretching may be performed at a temperature of 110°C to 115°C at a stretching ratio of 6.0 to 6.5 times, but the present invention is not limited thereto.

[0144] In one embodiment of the present invention, the TD stretching may be performed sequentially after the MD stretching. At this time, as the degree of crystallization of the polymer sheet increases through the MD stretching, it may be preferable to perform the TD stretching at a temperature a predetermined range higher than that of the MD stretching. For example, the TD stretching may be performed at a temperature 5°C or higher, 10°C or higher, 15°C or higher, 20°C or higher, or 5°C to 20°C, 10°C to 20°C, 15°C to 20°C, 19°C to 25°C, or 19°C to 21°C higher than the MD stretching temperature. For example, the TD stretching may be performed at a temperature of, for example, 130°C to 135°C or 130°C to 133°C, but the present invention is not limited thereto.

[0145] In one embodiment of the present invention, the TD stretching may be performed at a stretching ratio of 6 to 10 times, 7 to 10 times, 8 to 10 times, 8 to 9 times, 8 to 8.5 times, for example, 8.0 to 8.1 times, but the present invention is not limited thereto.

[0146] In one embodiment of the present invention, the TD stretching may be performed at a temperature of 130°C to 135°C at a stretching ratio of 8.0 to 8.5 times, but the present invention is not limited thereto.

[0147] The above step (S1-3) is a step of removing a diluent from the polymer sheet stretched as above to form a large number of pores.

[0148] In one embodiment of the present invention, a process of extracting and removing the diluent using a suitable solvent may be performed to remove the diluent. The solvent available for removing the diluent is not particularly limited, and any solvent capable of extracting the diluent used in the extrusion step may be used. For example, methyl ethyl ketone, methylene chloride, hexane, etc., which have high extraction efficiency and rapid drying, may be used, and preferably, methylene chloride may be used. The extraction method may use any general solvent extraction method, such as an immersion method, a solvent spray method, or an ultrasonic method, either individually or in combination.

[0149] In one embodiment of the present invention, it may be preferable that the amount of diluent remaining in the polymer sheet formed after extraction of the diluent be 1% by weight or less based on the total weight of the polymer sheet. If the amount of remaining diluent exceeds 1% by weight, there may be a problem of reduced physical properties and decreased permeability of the membrane, but the present invention is not limited thereto.

[0150] The above step (S1-4) can be performed according to a conventional method as a step to remove residual stress and reduce thermal shrinkage characteristics by applying heat to a polymer sheet with pores formed by removing the diluent above.

[0151] In one embodiment of the present invention, the heat setting temperature may be performed at a temperature within 5°C of the TD stretching temperature. For example, performing the heat setting temperature at a temperature within 1°C to 2°C of the TD stretching temperature may have a desirable effect in securing porosity, but the present invention is not limited thereto.

[0152] In one embodiment of the present invention, the heat fixation may be performed at a temperature of, for example, 125°C to 140°C, 130°C to 135°C, or 131°C to 132°C, but the present invention is not limited thereto.

[0153] Accordingly, according to one embodiment of the present invention, the first separator substrate obtained above may consist only of pores, which are empty spaces between polymer fibers. Thus, according to one embodiment of the present invention, a separator substrate having a thickness of 10 μm or less and a porosity of 45 volume% or more may be obtained, but the method of manufacturing the first separator substrate is not limited to the method described above.

[0154] In one embodiment of the present invention, the first separator may be composed solely of the first separator substrate.

[0155] In another embodiment of the present invention, the first separator may comprise the first separator substrate and a porous coating layer provided on one or both sides of the first separator substrate. The porous coating layer represents a coating layer comprising inorganic particles and a binder resin for improving the heat resistance of the separator.

[0156] FIG. 2 illustrates a schematic diagram of the structure of a first separator (101) according to one embodiment of the present invention. Referring to FIG. 2, the first separator (101) may have a structure in which porous coating layers (1011, 1012) are provided on each side of the first separator substrate (1010), but the structure of the present invention is not limited thereto.

[0157] In one embodiment of the present invention, the porous coating layer comprises a binder resin capable of imparting a binding force between inorganic particles capable of improving the heat resistance of the separator or imparting an adhesion force with an adjacent electrode, and the method of formation and the composition thereof are not particularly limited.

[0158] For example, the above-mentioned inorganic particles may be used without particular limitation as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). Non-limiting examples of such inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 Examples include O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, and TiO2, and one or more of these may be included.

[0159] In one embodiment of the present invention, the average particle size (D) of the inorganic particles 50 ) may be, for example, 100 nm or more. Specifically, the average particle size (D) of the inorganic particles. 50 The average particle size of the inorganic particles may be 100 nm to 1 μm, or 100 nm to 500 nm. When the average particle size of the inorganic particles is within the range described above, it may exhibit an advantageous effect in terms of suppressing the increase in resistance of the separation membrane, but the present invention is not limited thereto.

[0160] The particle size of the above-mentioned inorganic particles can be measured by known particle size measurement methods, for example, using a Particle Size Analyzer (PSA) from Melbourne. In addition, the above-mentioned average particle size (D 50) refers to the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size, and may be measured through a known laser diffraction method. In this case, the laser diffraction particle size measuring device may use, for example, the Microtrac S3500 from Microtrac Corporation.

[0161] In one embodiment of the present invention, the binder resin may be used without particular limitation as long as it is capable of exhibiting the characteristics described above. For example, the binder resin may be a fluorinated resin, a non-fluorinated resin, or a mixture thereof, but is not limited thereto.

[0162] The above-mentioned fluorine-based resin is not particularly limited as long as it contains at least one fluorine (F) atom within the binder structure. For example, the above-mentioned fluorine-based binder may include, for example, a PVDF-based binder.

[0163] In one embodiment of the present invention, the PVDF-based binder may comprise one or more of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of vinylidene fluoride with a monomer capable of copolymerizing with vinylidene fluoride, and a mixture thereof. The monomer capable of copolymerizing with vinylidene fluoride may be, for example, a fluorinated monomer and / or a chlorinated monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkylvinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethylvinyl) ether (PEVE), and perfluoro(propylvinyl) ether (PPVE); and perfluoro(1,3-dioxol). and perfluoro(2,2-dimethyl-1,3-dioxol) (PDD), etc., and one or more of these may be included.

[0164] In one embodiment of the present invention, the PVDF-based binder may include, for example, one or more selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-chlorofluoroethylene (PVDF-CTFE), polyvinylidene fluoride-tetrafluoroethylene (PVdF-TFE), and polyvinylidene fluoride-trifluoroethylene (PVdF-TrFE).

[0165] In one embodiment of the present invention, the binder resin may include, for example, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as a fluorine-based binder. In this case, the substitution content of HFP in the PVDF-HFP may include, for example, 3 mol% to 20 mol%, specifically 5 mol% to 15 mol% based on the total molar amount of PVDF-HFP, but the present invention is not limited thereto.

[0166] In this specification, when a copolymer of two or more monomers is included as the PVDF-based binder, for example, when PVDF-HFP is included, the substitution content of monomers other than vinylidene fluoride within the copolymer can be measured through conventional analytical methods. For example, it can be measured using a known method of analyzing substituent content using C-NMR, but the present invention is not limited thereto.

[0167] The above non-fluorine binder is a general term for binders that do not correspond to fluorine binders and exhibit adhesive strength, and may include, for example, acrylic binders.

[0168] The above acrylic binder may include, for example, polyacrylic acid (PA), polyacrylonitrile (PAN), polyacrylamide (PAA), or (meth)acrylic polymers or a mixture of two or more of these, but the present invention is not limited thereto. The above (meth)acrylic polymer refers to a polymer comprising (meth)acrylic acid esters as monomers. These monomers may include, for example, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, or a mixture of two or more of these, but the present invention is not limited thereto.

[0169] In one embodiment of the present invention, the method of forming the porous coating layer is not particularly limited as long as it comprises the inorganic particles and the binder resin, and may be formed, for example, by a humidification separation method. For example, it may be formed by applying a composition for forming a porous coating layer comprising the inorganic particles and the binder resin to at least one surface of the separator and then drying it under humidification conditions. According to the humidification separation method, the binder resin in the composition rises to the surface of the porous coating layer along with the solvent in the composition for forming the porous coating layer, which has the advantage of increasing adhesion to the electrode, but the present invention is not limited thereto.

[0170] In one embodiment of the present invention, the weight ratio of inorganic particles and binder resin in the porous coating layer may be, for example, 85:15 to 50:50, 80:20 to 55:45, or 80:20 to 60:40, but the present invention is not limited thereto.

[0171]

[0172] Second separator (dry separator)

[0173] According to one embodiment of the present invention, the separator between the first electrode and the second electrode within the electrode laminate comprises a dry separator to increase the insulation performance of the electrode assembly and improve the output characteristics of the electrochemical device.

[0174] As described above, the second separator may also be referred to as a dry separator in that it includes a separator substrate manufactured by a dry method. Additionally, the separator substrate included in the second separator may be referred to as the second separator substrate.

[0175] In this specification, the second separator substrate refers to a polymer substrate manufactured according to a dry process without using a diluent, unlike the manufacturing method of the first separator substrate described above. Although the second separator substrate manufactured by the dry method has non-uniform pore sizes compared to the first separator substrate, it has the advantage of exhibiting a favorable effect in improving the output performance of the battery due to the uniform distribution of pores compared to the first separator substrate.

[0176] In one embodiment of the present invention, according to the dry method, when stretching the polymer sheet, a phenomenon occurs in which the separator splits due to the crystallization of the polymer fibers, so there may be a problem in that it is not easy to make the thickness of the substrate thin compared to the wet method. However, since the electrode assembly according to one aspect of the present invention uses two types of separator substrates with different manufacturing methods, it may be preferable to use one in which the difference in electrical resistance between the first separator substrate and the second separator substrate is within 30% in order to reduce the difference in physical properties between the two types of separators and improve the output characteristics of the electrochemical device.

[0177] To this end, in one embodiment of the present invention, the thickness of the second separator substrate may be the same as the thickness of the first separator substrate.

[0178] In another embodiment of the present invention, when the thickness of the second separator substrate is thicker than the thickness of the first separator substrate, a thickness deviation of 40% or less according to Formula 1 below may be used.

[0179] [Equation 1]

[0180] Thickness deviation (△d) = [(T2-T1) / T1] X 100 (%)

[0181] In the above Equation 1,

[0182] T1 is the thickness of the first separator substrate, and

[0183] T2 is the thickness of the second separator substrate.

[0184] In one embodiment of the present invention, the thickness deviation according to Formula 1 may be, for example, 5% to 40%, 10% to 35%, or 11% to 33%, but the present invention is not limited thereto.

[0185] In this specification, the method for measuring the thickness of the first separator substrate and the second separator substrate is based on the method for measuring the thickness of the first separator substrate as described above.

[0186] In one embodiment of the present invention, the thickness of the second separator substrate may be, for example, 10 μm to 14 μm, 10 μm to 13 μm, 10 μm to 12 μm, 10 μm to 11 μm, or 11 μm to 12 μm, but the present invention is not limited thereto.

[0187] In one embodiment of the present invention, the second membrane substrate may preferably have a porosity of 70 volume% or less to improve the inherently low mechanical strength of the dry membrane. For example, the porosity of the second membrane substrate may be 40 volume% to 70 volume%, 40 volume% to 60 volume%, 45 volume% to 55 volume%, or 50 volume% to 55 volume%, but the present invention is not limited thereto.

[0188] In this specification, the method for measuring the thickness and porosity of the second separator substrate is based on the description of the first separator substrate.

[0189] In one embodiment of the present invention, in order for the second separator substrate to exhibit excellent mechanical strength while exhibiting the porosity described above, it may be preferable that the average size of the pores within the second separator substrate be, for example, 40 nm or less. For example, the average size of the pores within the second separator substrate may be 10 nm or more and 40 nm or less, 15 nm or more and 35 nm or less, 20 nm or more and 30 nm or less, 23 nm or more and 27 nm or less, or 24 nm or more and 26 nm or less, but the present invention is not limited thereto.

[0190] In this specification, the method for measuring the average pore size of the second separator substrate is based on the description of the first separator substrate.

[0191] A dry method for manufacturing a second separation membrane substrate according to one embodiment of the present invention may include the following steps.

[0192] S2-1) A step of feeding a polymer resin into an extruder to obtain an extruded product,

[0193] S2-2) A step of obtaining a polymer sheet by thermoforming the above extruder,

[0194] S2-3) A step of stretching the polymer sheet at a low temperature, followed by stretching at a high temperature, and

[0195] S2-4) Step of heat-fixing the stretched sheet.

[0196] In one embodiment of the present invention, the polymer resin may typically be a polyolefin-based resin, such as the first separator substrate.

[0197] In one embodiment of the present invention, the polyolefin-based resin for manufacturing the second separator substrate preferably includes polypropylene resin to improve the mechanical strength of the dry separator, but the present invention is not limited thereto.

[0198] In one embodiment of the present invention, the second separator substrate may be composed solely of polypropylene resin in terms of mechanical strength. To this end, the polymer resin may include polypropylene resin, and the step (S2-1) may include the step of introducing polypropylene resin into an extruder and melt-kneading it.

[0199] According to one embodiment of the present invention, a polymer sheet can be obtained by extruding a molten-mixed polymer resin through step (S2-1) and molding the extruded product through step (S2-2). For the extrusion, a flat die such as a T die or a coat hanger die may be used, and a roll-to-roll molding machine may be used for the molding.

[0200] Next, the molded polymer sheet can be stretched at least twice under different temperature conditions.

[0201] Specifically, the above step (S2-3) includes the step of stretching the polymer sheet at a low temperature (low-temperature stretching) and then stretching it at a high temperature (high-temperature stretching). The above step (S2-3) can increase the amount of pores formed by rapidly cooling the polymer sheet by first stretching the obtained polymer sheet at a low temperature, and then increase the size of the pores formed during low-temperature stretching by performing secondary stretching at a higher temperature. By doing so, the porosity of the second separator substrate obtained through the above step (S2-3) can be increased, but the mechanism of the present invention is not limited thereto.

[0202] In one embodiment of the present invention, the mechanical strength and puncture strength of the polymer sheet can be improved through the stretching process. In this case, according to one embodiment of the present invention, the second separator substrate is uniaxially stretched, and it is preferable that the low-temperature stretching and the high-temperature stretching be performed in directions parallel to each other. More specifically, the low-temperature stretching and the high-temperature stretching may each be performed in the machine direction (MD).

[0203] In one embodiment of the present invention, the stretching can be performed by a roll method or a tenter method, sequentially or simultaneously.

[0204] According to one embodiment of the present invention, in order to increase porosity while maintaining the mechanical strength of the second membrane substrate obtained, it may be preferable to perform low-temperature stretching at a stretching ratio lower than the high-temperature stretching ratio.

[0205] In this specification, the 'stretch ratio' represents the ratio of the length of the polymer sheet after stretching to the length of the polymer sheet before stretching. That is, the stretch ratio can be calculated as the ratio of (length of the polymer sheet after stretching / length of the polymer sheet before stretching).

[0206] In one embodiment of the present invention, the low-temperature stretching may be a decisive step in determining the number of pores in the second separator substrate being formed. Specifically, after the polymer sheet is obtained, the initial stretching process is performed at a low temperature to tear the amorphous structure of the fibers and form micropores. At this time, if the low-temperature stretching ratio is too high, the polymer sheet may tear or damage may occur in terms of the porosity of the second separator substrate being formed; therefore, it may be preferable for the low-temperature stretching ratio to be performed within a range lower than the high-temperature stretching ratio.

[0207] In one embodiment of the present invention, the low-temperature stretching may be performed at a stretching ratio of, for example, 1.05 to 1.1 times, but the present invention is not limited thereto.

[0208] In one embodiment of the present invention, the high-temperature stretching may be a decisive step in determining the size of the pores within the second separator substrate. Specifically, the pore size can be increased by further stretching a sheet in which micropores were formed during a low-temperature stretching process at a high temperature to enlarge the size of the already formed micropores. At this time, since a high-temperature stretching ratio lower than the low-temperature stretching ratio may cause a problem of increasing the resistance of the second separator, it may be preferable for the high-temperature stretching ratio to be performed within a range greater than the low-temperature stretching ratio as described above.

[0209] In one embodiment of the present invention, the high-temperature stretching may be performed at a stretching ratio of, for example, 1.75 to 2.1 times, but the present invention is not limited thereto.

[0210] In one embodiment of the present invention, the stretching temperature may vary depending on the melting point of the polymer used, for example, polypropylene resin, and the present invention is not limited thereto.

[0211] The heat setting (S2-4) above may be performed to remove residual stress within the polymer sheet after stretching of the preceding stage. For example, it may be preferable to perform the heat setting at a higher temperature than the thermoforming, low-temperature stretching, and high-temperature stretching processes of the preceding stage.

[0212] According to one embodiment of the present invention, the step (S2-1) may be performed at a temperature of 200°C or higher to melt the polymer resin.

[0213] According to one embodiment of the present invention, the subsequent step (S2-2) may be performed at a temperature of, for example, 200°C to 250°C or 210°C to 230°C to cool the obtained extruder so that the extruder can be formed into a sheet shape.

[0214] According to one embodiment of the present invention, the low-temperature stretching of step (S2-3) may be performed at a temperature of, for example, 90°C to 135°C, for example, 90°C to 120°C, 95°C to 110°C, or 100°C to 110°C in order to increase the amount of pores formed while rapidly cooling the thermoformed polymer sheet.

[0215] According to one embodiment of the present invention, the high-temperature stretching of step (S2-3) may be performed at a temperature of, for example, 140°C to 160°C, for example, 140°C to 150°C, or 145°C to 150°C in order to increase the pore size by secondarily stretching the low-temperature stretched polymer sheet at a higher temperature.

[0216] According to one embodiment of the present invention, step (S2-4) may involve heat-setting at a temperature higher than that of (S2-1) to (S2-3) to remove residual stress within the stretched polymer sheet and increase mechanical strength, and the heat-setting temperature may be performed, for example, at 150°C to 170°C, 150°C to 165°C, 150°C to 160°C, or 155°C to 160°C, but the present invention is not limited thereto.

[0217] In one embodiment of the present invention, the second separation membrane substrate manufactured by the dry method may have a structure comprising a main chain of a polymer resin used, microfibrils extending in one direction not parallel to the direction in which the main chain extends, and pores formed between the microfibrils.

[0218] Specifically, the second separator substrate may be uniaxially stretched as described above, and the orientation direction of the polymer fibers may be formed in a single direction.

[0219] That is, according to one embodiment of the present invention, the first separator substrate may be biaxially stretched, and the second separator substrate may be uniaxially stretched.

[0220] In this specification, the orientation direction of the fibers of the first and second separator substrates can be confirmed through microscopic observation of the cross-section of the separator substrate or through a known method for confirming the elongation direction of the separator.

[0221] In one embodiment of the present invention, the second separator may be composed solely of a second separator substrate, but may further include a porous coating layer provided on one or both sides of the first separator substrate, similar to the first separator.

[0222] FIG. 3 shows a schematic diagram of the structure of a second separator (103) according to one embodiment of the present invention.

[0223] In this specification, regarding the porous coating layer in the second separator, the description of the first separator is adopted.

[0224]

[0225] adhesive binder

[0226] In one embodiment of the present invention, the electrode assembly may further include one or more adhesive binders at at least one of the interface between the first separator and the first electrode, the interface between the first electrode and the second separator, and the interface between the second separator and the second electrode.

[0227] FIG. 4 illustrates a schematic diagram of an electrode assembly according to one embodiment of the present invention. Referring to FIG. 4, in one embodiment of the present invention, at least one of the interfaces between the first separator and the first electrode, the interface between the first electrode and the second separator, and the interface between the second separator and the second electrode may include one or more adhesive binders (107).

[0228] In one embodiment of the present invention, the one or more adhesive binders may be used without particular limitation as long as they are capable of imparting adhesive force between the electrode and the separator. For example, the adhesive binder may include a fluorine-based binder, a non-fluorine-based binder, or a mixture thereof, and regarding the fluorine-based binder and the non-fluorine-based binder, the description regarding the porous coating layer may be applied.

[0229] In one embodiment of the present invention, when one or more adhesive binders are included in the above-described at least one interface, the one or more adhesive binders may be included by coating an adhesive binder on the surface of an adjacent separator and then laminating an electrode onto the adhesive binder coating layer. Alternatively, the one or more adhesive binders may be included by coating an adhesive binder on the surface of an adjacent electrode and then laminating a separator onto the adhesive binder coating layer. Alternatively, the one or more adhesive binders may be included by coating an adhesive binder on both the surface of an adjacent electrode and the surface of a separator, and then laminating an electrode and a separator so that their respective adhesive binder coating layers come into contact. The method of coating the adhesive binder on the surface of the electrode and / or separator is not particularly limited.

[0230] In one embodiment of the present invention, the method of coating one or more adhesive binders on the surface of the electrode and / or separator may use conventional coating methods known in the art, such as dip coating, die coating, roll coating, comma coating, or a combination thereof. In addition, the drying may be performed using conventional drying methods, such as natural drying or air drying, without any particular limitations.

[0231] In one embodiment of the present invention, in order to coat one or more adhesive binders on the surface of the electrode and / or separator, an adhesive binder coating solution may be prepared by dispersing or dissolving the adhesive binder in a suitable solvent, and non-limiting examples of the solvent may include one or more mixtures selected from the group consisting of water, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane, but the present invention is not limited thereto.

[0232] In one embodiment of the present invention, the adhesive binder described above may be derived from a porous coating layer formed on a separation membrane adjacent to the interfaces.

[0233] In one embodiment of the present invention, the adhesive binder may be formed by applying a slurry containing the adhesive binder onto a separator and then drying it by a humidification separation method. At this time, a concentration gradient may be formed from the surface of an adjacent electrode to the surface of an adjacent separator so that the concentration of the adhesive binder included in the at least one interface becomes lower as it approaches the adjacent separator, but the present invention is not limited thereto.

[0234]

[0235] According to another aspect of the present invention, a method for manufacturing the electrode assembly can be provided.

[0236] A method for manufacturing an electrode assembly according to another aspect of the present invention may include the step of preparing an electrode assembly by sequentially stacking a first separator, a first electrode, a second separator, and a second electrode in the thickness direction. At this time, as described above, the first separator comprises a first separator substrate manufactured by a wet method, and the second separator comprises a second separator substrate manufactured by a dry method, wherein the first separator substrate has a thickness of 10 μm or less and a porosity of 45 volume% or more.

[0237]

[0238] According to another aspect of the present invention, an electrochemical device comprising the electrode assembly and the electrolyte can be provided.

[0239] The above electrochemical device may be manufactured by including a process of loading the electrode assembly into a suitable case and injecting an electrolyte, but the present invention is not limited thereto.

[0240] In one embodiment of the present invention, the positive and negative electrodes may each have an electrode active material coated on a current collector, or they may be in the form of a self-supporting metal plate or a film containing an active material without a current collector, and their size, shape, or type of active material is not particularly limited.

[0241] For example, an electrochemical device according to one embodiment of the present invention may include an NCM-based active material as a positive electrode and a graphite-based active material as a negative electrode, but the present invention is not limited thereto.

[0242] In one embodiment of the present invention, the electrolyte can be used without particular limitation as long as it is an electrolyte commonly used for implementing an electrochemical device.

[0243] In addition, in one embodiment of the present invention, the electrochemical element may be an example of a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. More specifically, the secondary battery may be a lithium secondary battery.

[0244] In one embodiment of the present invention, the case may be one that is conventionally used as a battery case, and is not particularly limited in its external shape according to the use of the battery. For example, the case may be a cylindrical, prismatic, pouch, or coin type using a can.

[0245] As described above, an electrode assembly according to one aspect of the present invention can exhibit excellent insulation characteristics and charge / discharge characteristics.

[0246] According to one embodiment of the present invention, the electrochemical element can achieve a capacity retention rate of 90% or more according to Formula 2 below, although not limited thereto.

[0247] [Equation 2]

[0248] Capacity retention rate (%) = (C m+200 / C m ) X 100 (%)

[0249] In the above Equation 2,

[0250] Cm represents the discharge capacity measured during m charge-discharge cycles, and

[0251] Cm+200 represents the discharge capacity measured during m+200 charge-discharge cycles, and

[0252] m represents an integer greater than or equal to 1.

[0253] In one embodiment of the present invention, m in Equation 2 is an integer greater than or equal to 1. The m may be, for example, an integer greater than or equal to 1,000, an integer greater than or equal to 800, an integer greater than or equal to 1,600, or an integer greater than or equal to 1,500, but the present invention is not limited thereto.

[0254] In one embodiment of the present invention, when m is 1, the capacity retention rate may be, for example, 90% or more, 92% or more, 94% or more, or 95% or more. In one embodiment, the capacity retention rate of the electrochemical element may be in the range of 94% to 95%, but the present invention is not limited thereto.

[0255] In this specification, the capacity retention rate according to the charge-discharge cycle of the electrochemical element may be measured by obtaining a cycle-discharge capacity graph by performing 1C rate charging and 1C rate discharging (CC / CC) within a voltage range of 2.5V to 4.2V at room temperature (25℃) as one cycle, but the present invention is not limited thereto.

[0256]

[0257] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0258] [Manufacturing and Physical Property Evaluation of Separator Membranes]

[0259] Preparation of the first separator substrate (wet method)

[0260] Preparation Example 1.

[0261] 9 kg of high-density polyethylene (HDPE) (Daehan Petrochemical, VH035) was fed into an extruder (Korea EM, φ32 twin-screw extruder L / D = 56) together with 21 kg of diluent (Kukdong Petrochemical LP350F) and melt-extruded at 200°C to obtain a polyethylene melt extruder. The obtained melt extruder was passed through a T-die, cooled and formed into a sheet using a cooling casting device at a temperature of 40°C with a travel speed of 7 m / min, and then stretched in MD and then TD using a tenter-type sequential stretching machine. The diluent was extracted from the stretched sheet using methylene chloride to form a porous membrane, and then heat-set to obtain a separator substrate with a thickness of 9 μm.

[0262]

[0263] Preparation Examples 2 to 4.

[0264] A first separator substrate was manufactured using the same method as in Manufacturing Example 1, except that the process was changed according to the conditions of Table 1 below.

[0265] However, in the case of Manufacturing Example 4, the thickness of the extruded material was increased by adjusting the T-die gap to produce a separation membrane substrate with a thickness of 12 μm.

[0266]

[0267] (Temperature / Stretch Ratio) MD Stretch TD Stretch Heat Fixation Manufacturing Example 1112℃ / 6.0131.5℃ / 7.0132℃ Manufacturing Example 2112℃ / 6.0130.5℃ / 7.0132℃ Manufacturing Example 3112℃ / 6.0129℃ / 7.0132℃ Manufacturing Example 4112℃ / 6.0130.5℃ / 7.0131℃

[0268] Preparation of the second separator substrate (dry method)

[0269] Preparation Example 5.

[0270] Polypropylene resin (PP, melt index (MI) 0.3) was fed as a raw material into an extruder (Korea EM, φ32 twin-screw extruder L / D = 56), melted at 230°C, and extruded. The extruded material was thermoformed in a temperature range of 145°C using a roll-to-roll uniaxial stretcher to obtain a polypropylene film, then stretched once at a stretching ratio of 1.05 times in a low-temperature stretching range of 100°C, then stretched a second time at a stretching ratio of 1.8 times in a high-temperature stretching range of 145°C, and then heat-set at a temperature of 155°C to produce a second separator substrate with a thickness of 10 μm.

[0271]

[0272] Preparation Example 6.

[0273] A second separator substrate with a thickness of 12 μm was prepared by making the thickness of the film formed by extrusion thicker when polypropylene was extruded, and a separator substrate was prepared in the same manner as in Preparation Example 5.

[0274]

[0275] Formation of a porous coating layer

[0276] A porous coating layer was formed by applying a slurry of PVDF-HFP binder (Mw 500,000 g / mol, HFP 15 wt%) and inorganic particles (Al2O3) mixed in a solvent at a weight ratio of 20:80 to both sides of each of the separator substrates prepared above, and then drying under humid conditions.

[0277]

[0278] Evaluation of separator substrate thickness

[0279] The thickness of each separator substrate was measured using a thickness gauge from Mitutoyo.

[0280]

[0281] Evaluation of porosity of separation membrane substrates

[0282] The porosity of the membrane substrate was measured using Micrometrics’ Autopore IV 9500 in a pressure range of 0.5 to 60,000 psi according to ASTM D4284-92 standards.

[0283]

[0284] Evaluation of average pore size within the separator substrate

[0285] Each of the membrane substrates prepared above was die-cut into a size of (MD X TD) 5 cm to prepare samples. For the prepared samples, a dry-up curve was obtained using a Perm-porometer (CFP-1500A) from Porous Materials Inc., and a wet-up curve was obtained using a wet-up method. For the wet-up method, the membrane substrate was filled with Galwick solution (PMI) and a pressure in the range of 50 to 350 psi was applied. Using the obtained dry and wet curves, the average pore size was measured by a known formula that converts the pore diameter from the pressure at the point where the curve representing half the slope of the dry curve intersects the wet curve.

[0286]

[0287] Measurement of electrical resistance of separator substrate

[0288] Each of the separator substrates prepared above was placed in a CR2016 battery case along with an electrolyte composed of 1M LiPF6, ethyl carbonate (EC) and ethyl methyl carbonate (EMC) (3 / 7 v / v), and 2 wt% vinylene carbonate (VC), and then sealed to prepare a measurement sample. The electrical resistance values ​​of each separator substrate were measured using a Solartron analytical EIS instrument from Solartron under frequency conditions of 100,000 to 10,000 Hz.

[0289]

[0290] Measurement of electrical resistance of the separator

[0291] Using the separator with the porous coating layer formed above, the electrical resistance was measured in the same manner as the 'method for measuring the electrical resistance of the separator substrate' above.

[0292]

[0293] Separator Classification Separator Substrate Porous Coating Layer Manufacturing Method Thickness Porosity Average Pore Size Electrical Resistance Manufacturing Example 1 Wet 9 µm 52 vol% 46 nm 0.65 Ω Manufacturing Example 2 Wet 9 µm 48 vol% 45 nm 0.75 Ω Manufacturing Example 3 Wet 9 µm 42 vol% 42 nm 1.0 Ω Manufacturing Example 4 Wet 12 µm 45 vol% 44 nm 1.1 Ω Manufacturing Example 5 Dry 10 µm 50 vol% 24 nm 0.7 Ω Manufacturing Example 6 Dry 12 µm 50 vol% 26 nm 0.8 Ω

[0294] [Fabrication of Electrode Assemblies and Performance Evaluation of Electrochemical Devices]

[0295] Preparation of the anode

[0296] Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), a conductive material (carbon black), and a binder resin (PVDF) were mixed with water in a weight ratio of 97.5:0.7:1.8 to prepare a slurry for an anode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to produce an anode having an anode active material layer (thickness 60 μm).

[0297]

[0298] Preparation of the cathode

[0299] A graphite-based active material, carbon black, carboxymethylcellulose (CMC), and binder resin (SBR) were mixed with water in a weight ratio of 97.5:0.7:1.1:0.7 to prepare a slurry for a negative electrode active material layer with a concentration of 50 wt% of the components excluding water. At this time, a 9:1 mixture of artificial graphite and natural graphite was used as the graphite-based active material. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to produce a negative electrode having a negative electrode active material layer (thickness 60 μm).

[0300]

[0301] Manufacturing of electrode assemblies and lithium secondary batteries

[0302] Using the first separator substrate and the second separator substrate manufactured above, an electrode laminate was manufactured by stacking them in the thickness direction in the order of lower separator / cathode / central separator / anode and then taping the long side.

[0303] An electrode assembly was prepared by stacking 25 manufactured electrode laminates, placing the prepared electrode assembly into a pouch, injecting an electrolyte composed of 1M LiPF6, ethyl carbonate (EC) and ethylmethyl carbonate (EMC) (3 / 7 v / v), and 2 wt% vinylene carbonate (VC), and sealing it to manufacture a lithium secondary battery.

[0304]

[0305] Resistance evaluation

[0306] The prepared pouch-type battery was discharged in 3C-rate CC mode (voltage 2.5 V cut condition) and the resistance was measured at 10 seconds during the discharge process.

[0307]

[0308] Capacity retention rate evaluation

[0309] After performing charge-discharge cycles on the pouch-type battery prepared above using the following method, the discharge capacity after 200 cycles was evaluated based on the single discharge capacity, and the capacity retention rate (%) during 200 cycles was measured. The charge-discharge cycle was performed by charging at a 1C rate and discharging at a 1C rate (CC / CC) within a voltage range of 2.5V to 4.2V at room temperature (25℃) as one cycle.

[0310]

[0311] Short circuit defect rate evaluation (Hi-pot test)

[0312] After sequentially stacking the [bottom separator / cathode / central separator / anode] in the manner described above, an electrode assembly was obtained by laminating using a hot press at 60°C and 6.5 MPa for 10 seconds.

[0313] The short-circuit failure rate was evaluated by performing a Hi-pot test on 2,000 obtained electrode assemblies. The Hi-pot test was performed using a tester (Chroma, Model 19052) under conditions of 50 V, <0.5 mA (Charge time: 50 ms, test time: 50 ms).

[0314] Classification Lower Separator Central Separator Electrical Resistance Deviation (△ER, %) Between Separator Substrates Cell Resistance (mΩ) Capacitance Retention Rate (%) Short Circuit Defect Rate (%) Example 1 Manufacturing Example 1 Manufacturing Example 5 7.1 2.8 9 40.10 Example 2 Manufacturing Example 2 Manufacturing Example 6 6.3 3.0 9 30.15 Comparative Example 1 Manufacturing Example 6 Manufacturing Example 6 0 2.9 9 35.0 Comparative Example 2 Manufacturing Example 3 Manufacturing Example 5 4 2.9 3.8 8 20.10 Comparative Example 3 Manufacturing Example 4 Manufacturing Example 6 3 7.5 4.0 8 10.10 Comparative Example 4 Manufacturing Example 1 Manufacturing Example 1 10 3.8 9 00.10

[0315] As confirmed by the evaluation results above, in the case of Comparative Example 1, in which dry separators are applied as both the lower and central separators of the electrode assembly, it was confirmed that while the cell resistance is kept low, the short circuit failure rate is high.

[0316] On the other hand, in the case of Comparative Example 4, in which wet separators are applied as both the lower and central separators of the electrode assembly, the short circuit failure rate is low and the capacity retention rate is 90%, but it was confirmed that there is a problem in that it is not suitable for high-power batteries due to high cell resistance.

[0317] Furthermore, Comparative Examples 2 and 3, in which a wet separator was applied to the lower separator and a dry separator was applied to the central separator, were also found to have an inferior effect in terms of capacity retention rate because the thickness of the wet separator substrate was thick or the porosity was less than 45 volume%, and the difference in electrical resistance between the separator substrates exceeded 30%.

[0318] [Explanation of the symbol]

[0319] 1: Electrode assembly

[0320] 10: Electrode laminate

[0321] 101: First separator

[0322] 102: First electrode

[0323] 103: Second separator

[0324] 104: Second electrode

[0325] 1010: First separator substrate

[0326] 1011, 1012: First porous coating layer

[0327] 1030: Second separator material

[0328] 1031, 1032: Second porous coating layer

[0329] 107: Adhesive binder

Claims

1. One or more electrode stacks comprising a first separator, a first electrode, a second separator, and a second electrode sequentially stacked in the thickness direction, and The first separator above comprises a first separator substrate manufactured by a wet method, and The above second separator comprises a second separator substrate manufactured by a dry method, and The above-mentioned first separator substrate has a thickness of 10 μm or less and a porosity of 45 volume% or more, forming an electrode assembly.

2. In Claim 1, An electrode assembly in which the thickness of the second separator substrate is equal to or thicker than the thickness of the first separator substrate.

3. In Claim 2, An electrode assembly having a thickness deviation of 40% or less according to the following Formula 1 of the second separator substrate and the first separator substrate: [Equation 1] Thickness deviation (△d) = [(T2-T1) / T1] X 100 (%) In the above Equation 1, T1 is the thickness of the first separator substrate, and T2 is the thickness of the second separator substrate.

4. In Claim 1, An electrode assembly having a porosity of 40 volume% to 70 volume% of the second separator substrate.

5. In Claim 1, An electrode assembly having a difference in electrical resistance (△ER) between the first separator substrate and the second separator substrate of 30% or less.

6. In Claim 1, An electrode assembly having an average pore size of 40 nm or more of the first separator substrate.

7. In Claim 1, An electrode assembly having an average pore size of 40 nm or less of the second separator substrate.

8. In Claim 1, An electrode assembly wherein the first separator and the second separator each independently comprise a porous coating layer containing inorganic particles and a binder resin on one or both sides of a separator substrate.

9. In Claim 1, The interface between the first separator and the first electrode, The interface between the first electrode and the second separator, and An electrode assembly comprising at least one adhesive binder at at least one interface between the second separator and the second electrode.

10. In Claim 9, An electrode assembly having a concentration gradient formed from the surface of an adjacent electrode to the surface of an adjacent separator so that the concentration of an adhesive binder included in at least one interface becomes lower as it approaches the adjacent separator.

11. In Claim 9, The above adhesive binder comprises a fluorine-based binder, forming an electrode assembly.

12. In Claim 1, The above-mentioned first separator substrate is manufactured by biaxial stretching, and The electrode assembly wherein the second separator substrate is manufactured by uniaxial stretching.

13. In Claim 1, The above electrode assembly is a stacked electrode assembly.

14. An electrochemical device comprising an electrode assembly and an electrolyte according to any one of claims 1 to 13.

15. In Claim 14, The above electrochemical device is an electrochemical device that exhibits a capacitance retention rate of 90% or more according to the following Equation 2: [Equation 2] Capacity retention rate (%) = (C m+200 / C m ) X 100 (%) In the above Equation 2, Cm represents the discharge capacity measured during m charge-discharge cycles, and Cm+200 represents the discharge capacity measured during m+200 charge-discharge cycles, and m represents an integer greater than or equal to 1.

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