Secondary battery

Abstract

Presented are a secondary battery and an energy storage device, the secondary battery comprising: a single-cell group having one or more single cells; and an outermost electrode disposed outside the one or more single cells of the single-cell group, wherein: the outermost electrode comprises a current collector, an electrode active material layer provided on one side of the current collector, and a flame-retardant layer provided on the other side of the current collector; the electrode active material layer of the outermost electrode is disposed to face the outer surface of the single-cell group; and the flame-retardant layer comprises a plurality of capsules including a flame retardant and a binder for a flame-retardant layer, which connects and fixes the plurality of capsules to each other.

Description

secondary battery

[0001] The present invention relates to a secondary battery, and specifically, to a secondary battery with improved stability.

[0002] This application claims priority based on Korean application No. 10-2025-0049775 filed on April 16, 2025, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] Due to the rapid increase in the use of fossil fuels, there is a growing demand for alternative and clean energy. As part of this trend, the field of power generation and energy storage utilizing electrochemistry is currently the most actively researched area. Lithium-ion batteries are a representative example of electrochemical devices that utilize such electrochemical energy, and their scope of application is steadily expanding.

[0004] Lithium-ion batteries are not only used as an energy source for mobile devices, but recently, their use as a power source for electric and hybrid electric vehicles is becoming a reality, capable of replacing fossil fuel-powered vehicles such as gasoline and diesel cars, which are one of the major causes of air pollution. Furthermore, their scope of application is continuously expanding, including their role as auxiliary power sources integrated with power grid systems.

[0005] While lithium-ion batteries can store larger amounts of energy and operate for longer periods as their energy density increases, such high energy density can increase the likelihood of rapid internal electrochemical reactions, potentially leading to safety issues. In particular, if conditions such as internal short circuits or overcharging occur, the internal temperature of the battery can rise sharply, causing thermal runaway. This thermal runaway can trigger battery ignition and, in large battery systems, lead to a chain of explosions.

[0006] To address this, methods involving the addition of fire retardants to the electrolyte have been studied; however, as the concentration of the fire retardant increases, the ionic conductivity within the electrolyte decreases, leading to a deterioration in the electrochemical performance of the cell. Due to these issues, the use of excessive amounts of fire retardants has been restricted, and there have been limitations in ensuring sufficient fire resistance from a practical standpoint. To improve this, a technology has been developed to encapsulate fire retardants and introduce them into the separator and electrolyte. When applied to the separator, the capsules are released by heat, allowing for effective response in the event of a fire; however, there is a problem in that the presence of the capsules reduces the porosity of the separator, thereby lowering ionic conductivity. Meanwhile, when applied to the electrolyte, the fire retardant is uniformly distributed, which helps reduce the risk of ignition; however, there is still a limitation in that a certain level of ionic conductivity decreases depending on the solubility and diffusion characteristics of the fire retardant.

[0007] To solve these problems, the development of technology to optimize the capsule placement and release mechanisms is required.

[0008] The present invention aims to solve the aforementioned problem and provides a secondary battery with improved stability by delaying or mitigating the thermal runaway phenomenon that occurs when the internal temperature of the battery rises rapidly.

[0009] In order to solve the problem of the present invention, according to one aspect of the present invention, an electrode of the following embodiment is provided.

[0010] According to the first embodiment,

[0011] A single cell group comprising one or more single cells; and an outermost electrode disposed on the outer side of one or more of the single cell group, and

[0012] The outermost electrode comprises a current collector, an electrode active material layer provided on one side of the current collector, and a flame retardant layer provided on the other side of the current collector.

[0013] The electrode active material layer of the outermost electrode is positioned opposite the outer surface of the single cell group, and

[0014] The flame retardant layer comprises a plurality of capsules containing a flame retardant and a binder for the flame retardant layer that connects and fixes the plurality of capsules to each other.

[0015] A secondary battery is provided, characterized in that the electrode active material layer of the outermost electrode comprises an active material and a binder, wherein the binder is fiberized to bind the active material, or the electrode active material layer of the outermost electrode comprises a plurality of granules having an active material and a binder.

[0016] According to the second embodiment, in the first embodiment,

[0017] The above capsule may include a flame retardant and a shell surrounding the flame retardant.

[0018] According to the third embodiment, in the first embodiment or the second embodiment,

[0019] The flame retardant may include an organic phosphorus compound, a fluorinated carbon compound, a brominated methane compound, or two or more of these.

[0020] According to the fourth embodiment, in any one of the first to third embodiments,

[0021] When the temperature of the secondary battery rises above the self-heating temperature, the shell of the capsule is damaged, and the flame retardant contained inside the shell may be released.

[0022] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0023] The average particle size of the above capsule may be 30 to 170 μm.

[0024] According to the 6th embodiment, in any one of the 1st to 5th embodiments,

[0025] The weight ratio of the capsule and the binder for the flame retardant layer in the above flame retardant layer may be 49:1 to 10:1.

[0026] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0027] The above single cell group may include one single cell or two or more stacked single cells.

[0028] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0029] In the case where the above single cell group has one single cell, a separator is interposed between the single cell and the outermost electrode, and in the case where the above single cell group has two or more single cells, a separator may be interposed between the single cell group and the outermost electrode, and between each of the single cells stacked within the above single cell group.

[0030] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0031] The above separator may include a separator for stacking, a separator for folding, or both.

[0032] According to the 10th embodiment, in any one of the 1st to 9th embodiments,

[0033] A half cell may be further interposed between the above single cell group and the outermost electrode.

[0034] According to the 11th embodiment, in any one of the 1st to 10th embodiments,

[0035] The above-mentioned fibrous binder may include a fluorine-containing polymer.

[0036] According to the 12th embodiment, in any one of the 1st to 11th embodiments,

[0037] The above granules may be secondary particles in which one or more active material particles are connected and fixed by a binder.

[0038] According to the 13th embodiment, in any one of the 1st to 12th embodiments,

[0039] The granules may comprise a central part containing one or more active materials; and a surface part containing a binder located on all or part of the outer side of the central part and binding the active materials.

[0040] According to the 14th embodiment, in any one of the 1st to 13th embodiments,

[0041] The electrode active material layer of the outermost electrode may include a plurality of granules having an active material and a binder; and a fibrous binder that connects and fixes the plurality of granules to each other.

[0042] According to the 15th embodiment,

[0043] An energy storage device comprising a secondary battery of any one of the first to fourth embodiments is provided.

[0044] A secondary battery according to one embodiment of the present invention has a structure comprising a group of single cells consisting of one or more single cells and an outermost electrode disposed on the outside thereof, wherein the outermost electrode comprises a current collector, an electrode active material layer formed on one side of the current collector, and a flame retardant layer formed on the opposite side thereof, wherein the flame retardant layer comprises a plurality of capsules containing a flame retardant and a binder for the flame retardant layer that connects the capsules to each other and fixes them to the surface of the electrode, and is disposed to face the outer direction of the secondary battery.

[0045] As a result, the flame retardant layer of a secondary battery according to one embodiment of the present invention can be designed so that, under normal operating conditions, the flame retardant is stably preserved within the capsule without affecting the electrochemical performance of the secondary battery, while the shell of the capsule ruptures at a certain temperature or higher and the flame retardant is released when ideal heat generation occurs inside the secondary battery or an external heat source is applied. Accordingly, the flame retardant can be released at a high local concentration in a specific area of ​​the outermost electrode where the heat source is concentrated, thereby suppressing thermal runaway reactions more effectively than conventional flame retardant addition methods.

[0046] In addition, in one embodiment of the present invention, since the flame retardant is protected within a capsule under conditions where it is not needed, the risk of causing performance degradation by directly reacting with the electrolyte and other battery components can be minimized. At the same time, effective flame retardant performance can be achieved without the need for additional flame retardant coating or protective devices while improving the thermal stability of the secondary battery, thereby contributing to the lightweighting of the battery and the simplification of the manufacturing process.

[0047] Accordingly, a secondary battery according to one embodiment of the present invention implements an active flame retardant mechanism in which a flame retardant acts selectively only under conditions of abnormal heat rise, thereby exhibiting a localized flame retardant effect during the initial stage of thermal runaway to suppress diffusion and significantly improve the safety of the battery. Through these features, the secondary battery according to one embodiment of the present invention can be effectively applied to high-energy-density battery systems requiring stability in various application fields, such as electric vehicles, energy storage systems (ESS), and portable electronic devices.

[0048] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the aforementioned description; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0049] FIG. 1 is a schematic diagram of the outermost electrode of a secondary battery according to one embodiment of the present invention.

[0050] FIG. 2 is a schematic diagram of a capsule provided in the flame-retardant layer of the outermost electrode of a secondary battery according to one embodiment of the present invention.

[0051] FIG. 3 is a schematic diagram of a secondary battery according to one embodiment of the present invention.

[0052] FIG. 4 is a schematic diagram of an assembly of a secondary battery according to one embodiment of the present invention.

[0053] FIG. 5 is a schematic diagram of a secondary battery according to one embodiment of the present invention.

[0054] Figure 6 is a schematic diagram of the outermost electrode of the secondary battery of Figure 5.

[0055] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0056] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0057] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0058] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0059] Conventional secondary batteries have a problem in that the outermost electrode active material layer of the double-sided electrodes, which does not face the electrode active material layer of another electrode, cannot be utilized in the actual battery, thus failing to meet the technical requirement to maximize the energy density of the secondary battery.

[0060] To solve this, there have been attempts to apply single-sided electrodes to the outermost layer, but in the case of single-sided electrodes, bending occurs significantly compared to double-sided electrodes, and there was a problem that defects increased during the assembly process when single-sided electrodes with large bending were applied.

[0061] In a secondary battery according to one embodiment of the present invention, the outermost electrode is provided with an electrode active material layer on one side of the current collector and a flame retardant layer on the other side of the current collector, thereby increasing the energy density of the secondary battery and resolving the bending problem that occurs when using a single-sided electrode in which the electrode active material layer is provided only on one side of the current collector and the other side is left as an uncoated portion.

[0062] Furthermore, the flame retardant layer of a secondary battery according to one embodiment of the present invention can effectively suppress a thermal runaway reaction by stably preserving the flame retardant within the capsule in a normal operating environment of the secondary battery without affecting the electrochemical performance of the secondary battery, while allowing the shell of the capsule to rupture at a certain temperature or higher and releasing the flame retardant at a high local concentration in a specific area of ​​the outermost electrode where the heat source is concentrated when ideal heat generation occurs inside the secondary battery or when an external heat source is applied.

[0063]

[0064] According to one aspect of the present invention,

[0065] A single cell group comprising one or more single cells; and an outermost electrode disposed on the outer side of one or more of the single cell group, and

[0066] The outermost electrode comprises a current collector, an electrode active material layer provided on one side of the current collector, and a flame retardant layer provided on the other side of the current collector.

[0067] The electrode active material layer of the outermost electrode is positioned opposite the outer surface of the single cell group, and

[0068] A secondary battery is provided, characterized in that the flame retardant layer comprises a plurality of capsules containing a flame retardant and a binder for the flame retardant layer that connects and fixes the plurality of capsules to each other.

[0069] According to one embodiment of the present invention, the single cell group may include one single cell or two or more stacked single cells.

[0070] At this time, the term "mono cell" refers to a unit assembly having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and both the positive electrode and the negative electrode are double-sided electrodes, that is, electrodes having a current collector and electrode active material layers on both sides of the current collector.

[0071] According to one embodiment of the present invention, a separator may be further interposed between the single cell group and the outermost electrode.

[0072] In addition, according to one embodiment of the present invention, a half cell may be further interposed between the single cell group and the outermost electrode. In this case, the term "half cell" refers to a unit assembly having only one type of electrode among a positive electrode and a negative electrode as an electrode, and the electrode of the half cell is a double-sided electrode having electrode active material layers on both sides of a current collector.

[0073] In the case where the above single cell group has one single cell, a separator is interposed between the single cell and the outermost electrode, and in the case where the above single cell group has two or more single cells, a separator may be interposed between the single cell group and the outermost electrode, and between each of the single cells stacked within the above single cell group.

[0074] A secondary battery according to one embodiment of the present invention may include, depending on the method of combining a group of single cells and a separator interposed therein, a stacked battery having a stacked electrode assembly in which two or more single cells are stacked in one direction, a stacked / folded battery having a stacked / folded electrode assembly obtained by placing two or more single cells in a predetermined pattern on a long sheet-type separator and folding the separator into various roll shapes, or a composite battery including all of these.

[0075] Accordingly, a separator for a secondary battery according to one embodiment of the present invention may include a separator for a stack, a separator for a folding, or both, depending on the shape of the secondary battery.

[0076] In cases where a half-cell is additionally interposed between the above single cell group and the outermost electrode, a separator may be interposed between the single cell group and the half-cell, and between the half-cell and the outermost electrode.

[0077] According to one embodiment of the present invention, the secondary battery may be configured by stacking in the order of "single cell group / separator / outermost electrode", or by stacking in the order of "single cell group / separator / inverted battery (double-sided electrode) / separator / outermost electrode", or by stacking in the order of "outermost electrode / separator / single cell group / separator / outermost electrode", or by stacking in the order of "outermost electrode / separator / single cell group / separator / inverted battery (double-sided electrode) / separator / outermost electrode", or by stacking in the order of "outermost electrode / separator / inverted battery (double-sided electrode) / single cell group / separator / inverted battery (double-sided electrode) / separator / outermost electrode".

[0078] Referring to FIG. 1, the outermost electrode (100) comprises a current collector (10), an electrode active material layer (20) provided on one side of the current collector (10), and a flame retardant layer (30) provided on the other side of the current collector (10). The flame retardant layer (30) may comprise a plurality of capsules (50) containing a flame retardant (not shown) and a binder (40) for the flame retardant layer that connects and fixes the plurality of capsules (50) to each other.

[0079] Referring to FIG. 2, the capsule (50) may include a flame retardant (52) and a shell (51) surrounding the flame retardant (52).

[0080] According to one embodiment of the present invention, the flame retardant is a compound added to improve the thermal stability of a secondary battery and reduce the risk of ignition, and has a specific chemical structure and excellent chemical compatibility with the electrolyte. Depending on its chemical structure, such a flame retardant may include an organic phosphorus compound, a fluorocarbon compound, a brominated methane compound, or two or more of these, and the characteristics and specific examples of each flame retardant are described below.

[0081] First, the above-mentioned organic phosphorus compound is a flame retardant containing phosphorus (P) and serves to block flames by forming a flame-retardant phosphate compound upon combustion. In addition, some organic phosphorus compounds can maintain stable properties without decomposing within the electrolyte, thereby contributing to the maintenance of long-term performance of the secondary battery. Examples of organic phosphorus compounds that can be used in one embodiment of the present invention include dimethyl thiophosphate (DMTP), tris(2-chloroisopropyl) phosphate (TCPP), triethyl phosphate (TEP), and triphenyl phosphate (TPP). These compounds may be used individually or may be used in combination with multiple compounds.

[0082] Next, the above-mentioned fluorinated carbon compound is a flame retardant containing carbon (C) and fluorine (F) atoms, possessing high thermal stability and low flammability, and excellent compatibility with the electrolyte, which can contribute to extending the lifespan of the secondary battery. Examples of fluorinated carbon compounds that can be used in the present invention include dodecafluoro-2-methylpentan-3-one, methyl nonafluoroisobutyl ether, and perfluoropolyether (PFPE) series compounds, and these can play a role in preventing performance degradation of the secondary battery by maintaining low viscosity in the electrolyte while simultaneously possessing flame retardancy.

[0083] In addition, the above-mentioned brominated methane-based compound is an organic compound containing bromine (Br), and plays a role in imparting flame retardancy by suppressing free radical reactions by releasing bromine radicals (Br·) upon combustion. Examples of brominated methane-based compounds that can be used in one embodiment of the present invention include dibromomethane (DBM), tetrabromobisphenol A (TBBA), and decabromodiphenyl ethane (DBDPE), and these can impart high flame retardancy along with certain heat dissipation characteristics.

[0084] As such, the flame retardant used in one embodiment of the present invention may include organic phosphorus compounds, fluorinated carbon compounds, and brominated methane compounds, and these compounds may be used alone or in combination. Furthermore, the flame retardant of the present invention is not limited thereto, and various modified compounds belonging to the above series or functionally similar flame retardants may be used.

[0085] According to one embodiment of the present invention, the capsule may comprise a flame retardant and a shell surrounding the same. The shell stably preserves the flame retardant under normal conditions, but when the temperature of the secondary battery rises above a certain temperature (e.g., above the self-heating temperature), the shell of the capsule is damaged, and the flame retardant contained within the shell may be released.

[0086] Rechargeable batteries may generate some heat even during normal operation, and their temperature can be maintained stably if the heat is released externally through appropriate heat dissipation pathways. However, if a certain temperature is exceeded, heat generated internally accumulates, causing the battery temperature to rise rapidly. The temperature at which the battery begins to generate heat on its own, without the need for external heat application, is called the Self-Heating Temperature (SHT).

[0087] The above self-heating temperature may vary depending on the chemical composition and design of the secondary battery, and generally may occur in the range of about 100°C to 160°C. For example, in the case of a secondary battery containing a lithium cobalt oxide (LCO) cathode active material, self-heating may begin at about 100°C to 130°C, and in the case of a secondary battery containing a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) series cathode active material, self-heating may begin at about 120°C to 160°C. In addition, a secondary battery containing a lithium iron phosphate (LFP) cathode active material has relatively high thermal stability and may begin self-heating at about 180°C to 250°C.

[0088] When the self-heating temperature is reached, the following heat generation reaction may proceed rapidly inside the secondary battery.

[0089] Heat may be generated as the solid electrolyte interphase (SEI) layer decomposes at approximately 80°C to 120°C. At approximately 100°C to 150°C, the electrolyte may thermally decompose and release flammable gases, which may induce additional exothermic reactions. Subsequently, at approximately 150°C to 250°C, the positive electrode active material releases oxygen, which reacts with the electrolyte to induce additional heat generation. Furthermore, side reactions may occur between the negative electrode active material and the current collector (copper, aluminum, etc.) at high temperatures, which may further accelerate the thermal runaway phenomenon.

[0090] According to one embodiment of the present invention, the shell of the capsule may be designed to be damaged at a temperature lower than the self-heating temperature of the secondary battery. For example, the shell may be formed to rupture or decompose at approximately 80°C to 120°C, thereby allowing a flame retardant to be released before the thermal runaway reaction begins, which can delay or suppress the exothermic reaction.

[0091] The above-described shell can be designed to protect the flame retardant from being released under unnecessary conditions within the secondary battery, while enabling the rapid and effective release of the flame retardant when the temperature of the secondary battery rises. To this end, the shell can release the flame retardant by at least one of a thermal decomposition method, a physical destruction method, or a dissolution method. The thermal decomposition method is a method in which the flame retardant is released as the shell thermally decomposes at a specific temperature; the physical destruction method is a method in which the flame retardant is released as the shell cracks due to rapid thermal expansion or mechanical stress; and the dissolution method is a method in which the flame retardant is released as the shell dissolves by reacting with the electrolyte or components within the secondary battery at a specific temperature.

[0092] In addition, the damage mechanism of the shell can be adjusted according to the material and thickness of the shell.

[0093] For example, if the shell is made of a polymer such as polyurethane, polylactic acid, or polyurea, the shell has thermoresponsive properties and can release a flame retardant by thermally decomposing at a specific temperature. Additionally, if the shell is made of an inorganic material such as silicon dioxide (silica), alumina, or zirconia, the flame retardant may be released as cracks occur due to rapid thermal expansion or thermal stress.

[0094] In one embodiment of the present invention, the flame retardant release temperature can be controlled by adjusting the thickness of the shell of the capsule. The thickness of the shell can be set, for example, in the range of 0.1 μm to 10 μm. Specifically, when the thickness of the shell is 0.1 μm or more and 1.0 μm or less, the shell may rupture at a temperature of about 80°C to 120°C; when the thickness of the shell is 1.0 μm or more and 5.0 μm or less, it may rupture at a temperature of about 120°C to 180°C; and when the thickness of the shell is 5.0 μm or more and 10 μm or less, it may rupture at a temperature of about 180°C or higher.

[0095] The shell may be made of a material insoluble in the electrolyte and may be made of a polymer material, an inorganic material, or a composite material thereof. The polymer material is a material having heat-sensitive properties, and may undergo structural deformation or thermal decomposition at a certain temperature. For example, the shell may include one or more of polyurethane, polyurea, polylactic acid, polyvinyl alcohol, polylactic acid, melamine-formaldehyde, polyolefin (polyethylene, polypropylene, etc.), polystyrene, polyamide (nylon, etc.), polycaprolactone, polyester (polyethylene terephthalate, etc.), gelatin, chitosan, cellulose, and derivatives thereof. Additionally, the shell may be made of an inorganic material with excellent heat resistance and may include one or more of silicon dioxide, alumina, magnesia, zirconia, or silicate compounds.

[0096] In order to maintain a balance between the preservation and release characteristics of the flame retardant within the capsule, the ratio of the shell to the total weight of the capsule may be adjusted. For example, the weight ratio of the flame retardant in the capsule may be 50% by weight or more and 80% by weight or less, and the weight ratio of the shell may be 20% by weight or more and 50% by weight or less. When the weight ratio of the flame retardant satisfies these ranges, the strength of the shell is adequately secured, which can increase the likelihood of the flame retardant being released at the target temperature, and the flame retardant can be contained in a sufficient amount within the capsule, thereby providing more effective flame retardant performance.

[0097] According to one embodiment of the present invention, the average particle size of the capsule may be 30 to 170 μm, or 50 μm to 150 μm, 30 to 107 μm, or 30 to 76 μm, or 76 to 170 μm, or 107 to 170 μm, or 76 to 107 μm. When the average particle size of the capsule satisfies these ranges, sufficient space inside the capsule where the flame retardant can be stored is secured to secure the storage capacity of the flame retardant, and it may be advantageous to select a flame retardant effective for the safety improvement reaction of the secondary battery so that the shell of the capsule is destroyed in a timely manner at the self-heating temperature of the secondary battery to release the flame retardant.

[0098] According to one embodiment of the present invention, by optimizing the type and content of the aforementioned flame retardant, the average particle size of the capsule, and the material and thickness of the capsule shell, the flame retardant can be stably preserved in a normal secondary battery operating environment, and the flame retardant can be effectively released as the shell is destroyed when thermal runaway occurs, thereby enabling effective control of the operating temperature of the secondary battery.

[0099] In the case where the operating temperature of a secondary battery is controlled by releasing the flame retardant contained in the capsule as the shell of the capsule included in the flame retardant layer of the outermost electrode is destroyed during thermal runaway of the secondary battery, the explanation can be made more effectively by the type of flame retardant, the boiling point of the flame retardant, and the average particle size, size, and thickness of the capsule.

[0100] A flame-retardant layer according to one embodiment of the present invention may be composed of a capsule and a binder for the flame-retardant layer, and the weight ratio of the capsule to the binder for the flame-retardant layer in the flame-retardant layer may be 49:1 to 10:1, or 49:1 to 19:1, or 19:1 to 10:1. When the weight ratio satisfies these ranges, the capsule is included in a sufficient proportion within the flame-retardant layer to maximize the flame-retardant effect, the mechanical strength of the flame-retardant layer is improved, thereby allowing the flame-retardant layer to be stably attached to the electrode surface, and the structural stability of the electrode can be maintained by uniformly distributing the flame-retardant layer on the electrode surface.

[0101] FIG. 3 illustrates a schematic diagram of a secondary battery according to one embodiment of the present invention, and more specifically, a schematic diagram of an electrode assembly having an outermost electrode in the secondary battery.

[0102] The electrode assembly (200) according to FIG. 3 is configured by stacking in the order of a single cell group / separator / inverted battery (double-sided electrode) / separator / outermost electrode.

[0103] Specifically, an electrode assembly (200) according to one embodiment of the present invention according to FIG. 3 comprises: a single cell group having one or more single cells (220) each having a double-sided positive electrode layer (223) / positive current collector (221) / positive electrode layer (222), a double-sided negative electrode layer (228) / negative current collector (226) / negative electrode layer (227), and a separator (224) interposed between the double-sided positive electrode and the double-sided negative electrode; and an outermost electrode (negative electrode) (210) disposed on one side of the outermost side of the single cell group and composed of a negative electrode layer (216) / negative current collector (217) / flame retardant layer (218), and a double-sided positive electrode layer (213) / positive current collector (211) / positive electrode layer (212) between the outermost electrode and the single cell group. A half-cell (210') including an anode may be further provided. A separator (214) may be interposed between the single-sided cathode and the double-sided anode. The flame retardant layer (218) may include a capsule (218a) containing a flame retardant and a binder (218b) for the flame retardant layer that connects and fixes the capsules to each other.

[0104] At this time, a separator (separator for stacking) (215, 225) may be placed between the single cells within the single cell group and between the single cell group and the half cell.

[0105] According to one embodiment of the present invention, the secondary battery comprises a single cell group having one or more single cells; and an outermost electrode disposed on the outer side of one or more of the single cell group, wherein the single cell group and the outermost electrode may be provided in the form of a stack / folding type electrode assembly.

[0106] Referring to FIGS. 4 to 6, a stack / folding type electrode assembly (310) provided in a secondary battery according to one embodiment of the present invention has a structure in which single cells (311, 312, 313, 314) are placed in a predetermined pattern on a long sheet-type separator (folding separator) (316), and the separator is folded into a roll shape. At this time, on the outer side of the series of single cells, a half-cell (315p) including a double-sided positive electrode, a separator (315s), and an outermost electrode having a single-sided negative electrode active material layer (315n) and a flame retardant layer (315f) are provided. As a result, the flame retardant layer (315f) of the outermost electrode (315) can be positioned at the outermost point in the stack / folding type electrode assembly (310). Here, the double-sided positive electrode (315p) is provided with positive active material layers (315a, 315c) on both sides of the current collector (315b), the single-sided negative electrode (315n) is provided with a negative active material layer (315d) on one side of the current collector, and a flame retardant layer (315f) is provided on the other side of the current collector where the negative active material layer is not provided.

[0107] At this time, the separator (316) surrounding the series of single cells can be folded by being placed between the single cells in various ways applicable in the field of technology other than the method shown in FIG. 5.

[0108] According to one embodiment of the present invention, the electrode active material layer of the outermost electrode may include an active material and a binder. The electrode active material layer may optionally further include a conductive material. The electrode active material layer of the outermost electrode is positioned opposite to the outer surface of the single cell group. At this time, the electrode active material layer positioned at the outermost side of the single cell group and the electrode active material layer of the outermost electrode may be positioned to have an opposite electrode relationship with each other.

[0109] The current collector included in the outermost electrode above is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may also form fine irregularities on its surface to increase the adhesion of the active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0110] Furthermore, the above-mentioned current collector may be used with a conductive primer layer coated wholly or partially on the surface to lower resistance and improve adhesion. Here, the conductive primer layer may comprise a conductive material and a binder for the primer layer. The conductive material is not limited to any material that exhibits conductivity and may be, for example, a carbon-based material, a metallic material (metal powder or metal fiber), a conductive whisker, a conductive metal oxide, a conductive polymer, etc. Carbon-based materials include natural graphite, artificial graphite, graphene, carbon black, Denka black, acetylene black, Ketjen black, Super-P, Channel black, furnace black, lamp black, thermo black, carbon nanotubes, graphite nanofibers, carbon nanofibers, etc. Metal materials include copper, nickel, aluminum, silver, etc. Conductive whiskers include zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, alumina whiskers, etc. Conductive metal oxides include titanium oxide, etc. Conductive polymers include polyphenylene derivatives, etc. These can be used alone or as a mixture of two or more types.

[0111] The binder for the primer layer above may be a solvent-soluble fluorine-based binder (including PVDF and PVDF copolymer) or an acrylic-based binder, and may include water-based binders such as styrene butadiene rubber (SBR).

[0112] The active material included in the electrode active material layer of the outermost electrode may be a positive electrode active material or a negative electrode active material.

[0113] The above-mentioned cathode active material may include, for example, lithium transition metal oxide; lithium metal iron phosphate; lithium nickel-manganese-cobalt oxide; an oxide in which a portion of lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these, but is not limited thereto. Specifically, the above-mentioned cathode active material may include, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; and a compound with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides represented as O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, a+b+c=1); an oxide in which a portion of lithium nickel-manganese-cobalt oxide is substituted with aluminum (lithium nickel-manganese-cobalt-aluminum oxide) Li a [Ni b Coc Mn d Al e ] 1-f M 1 f O 2 ( The above M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8≤a≤1.2, 0.5≤b≤0.99, 0 <c<0.5, 0<d<0.5, 0.01≤e≤0.1, 0≤f≤0.1임), 디설파이드 화합물; Fe2(MoO4)3등을 들 수 있지만, 이들만으로 한정되는 것은 아니다. 구체적으로, 상기 리튬 니켈-망간-코발트-알루미늄 산화물은 Li[Ni 0.87 Co 0.05 Mn 0.07 Al 0.01 It could be ]O2)) etc.

[0114] In addition, the above-mentioned cathode active material is a carbon-based active material such as non-graphitizable carbon, graphite-based carbon (synthetic graphite, natural graphite, etc.); Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z Metal complex oxides of (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0≤x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloy; tin alloy; silicon (Si), silicon oxide (SiOx (0 <x≤2), Si / C 복합체, 규소계 합금 등의 규소계 활물질; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 사용할 수 있다.

[0115] The above Si / C composite (silicon-carbon composite) comprises silicon-based particles (e.g., silicon (Si) and silicon oxide (SiOx)) within a carbon-based support (carbon matrix). <x≤2) 등)가 물리적으로 분산되거나 화학적으로 결합된 구조를 포함할 수 있다. 상기 탄소 담지체는 비정질 탄소(카본블랙, 활성탄, 하드 카본 등), 흑연, 카본나노튜브, 카본나노파이버, 그래핀 등을 포함할 수 있고, 또는 이들 중 2 이상을 포함할 수 있다. 또한, 상기 탄소 담지체는 비정질 탄소, 흑연, 카본나노튜브, 카본나노파이버, 그래핀 등으로 이루어질 수 있고, 또는 이들 중 2 이상으로 이루어질 수 있다.

[0116] According to one embodiment of the present invention, the content of silicon-based particles relative to 100 parts by weight of the carbon support may be 5 to 45 parts by weight, or 10 to 40 parts by weight, or 15 to 35 parts by weight, or 20 to 30 parts by weight, or 5 to 20 parts by weight, or 20 to 45 parts by weight. According to one embodiment of the present invention, the carbon support may include activated carbon, and the silicon-based particles may include pure Si particles. The granules may further include other types of negative electrode active materials in addition to the silicon-based active material.

[0117] When silicon-based particles satisfy this content range relative to the carbon support, sufficient electrical conductivity is maintained while increasing lithium storage capacity, and the carbon support effectively buffers the volume expansion of silicon to suppress cracking and detachment of the electrode structure, and as a result, the mechanical stability of the electrode and the charge / discharge characteristics (lifetime characteristics) of the secondary battery can be improved.

[0118] Specific examples of such silicon-based active materials include Si, SiO, Si / C, SiO / C, SiO2, etc., but are not limited thereto.

[0119] According to one embodiment of the present invention, the active material of the outermost electrode may, in detail, be a negative electrode active material, and more specifically, be carbon such as graphite-based carbon (artificial graphite, natural graphite, etc.), lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; silicon-based oxide such as Si, SiO, Si / C, SiO / C, SiO2, etc.

[0120] According to one embodiment of the present invention, the electrode active material layer may further include a conductive material, and may include an active material, a conductive material, and a binder.

[0121] The above conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, silver; needle-shaped or branched conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, alumina whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. In detail, to ensure uniform mixing of the conductive material and to improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may include activated carbon.

[0122] The binder may include a fluorine-containing binder, a non-fluorine-containing binder, or two or more of these. As the fluorine-containing binder, a fluorine-containing polymer may be used, and it may include polytetrafluoroethylene (PTFE); PVdF-based copolymers such as polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP), or two or more of these. Specifically, the fluorine-containing binder may include polytetrafluoroethylene (PTFE). Additionally, the fluorine-containing binder may include polytetrafluoroethylene alone, or additionally include one or more PVdF-based copolymers such as polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) in addition to polytetrafluoroethylene. The above-mentioned non-fluorine-containing binder may include polyolefin, polyethylene oxide (PEO), etc.

[0123] According to one embodiment of the present invention, the electrode active material layer of the outermost electrode may be manufactured in a dry manner using a mixed powder (or granules, etc.) containing an active material, a binder, or optionally a conductive material, without using a liquid medium. In this case, the step of drying the liquid medium may not be performed.

[0124] Compared to the case where the electrode active material layer of the outermost electrode is manufactured by a wet method in which an electrode slurry comprising an active material, a binder, and a liquid medium that dissolves or disperses the binder is applied and dried on at least one side of a current collector, the following advantages are provided when the electrode active material layer is formed on one cross-section of the current collector of the outermost electrode in a dry method without a liquid medium using a mixed powder comprising an active material, a binder (fibrous binder), or optionally a conductive material, or granules in which the active material, binder, or optionally a conductive material is pre-compounded.

[0125] In conventional wet methods, binder migration and concentration gradients are prone to form due to the flow and drying processes of the slurry during the process of forming a single-sided coating structure. Additionally, the slurry may penetrate in the direction of the current collector thickness or spread to the opposite side. As a result, compositional non-uniformity of the electrode layer may occur.

[0126] In particular, in a structure where a flame-retardant layer is formed on the other side of the outermost electrode using a slurry-based wet method, there is a possibility that the solvent or dispersion medium of the flame-retardant layer slurry may seep into the electrode active material layer on one side through the current collector or along the edge path. In this case, the liquid medium of the flame-retardant layer slurry may redissolve or swell the binder within the electrode active material layer. As a result, the particle binding structure of the already formed electrode active material layer may become loose or collapse. Additionally, there is a risk that the electrode structure may be damaged due to deformation of the pore structure and composition distribution.

[0127] In addition, curling or warping deformation of the current collector is prone to occur due to drying shrinkage. This can adversely affect the uniform formation of the flame-retardant layer formed on the opposite side. Furthermore, there is a risk that the flame-retardant layer on the opposite side may be contaminated by slurry components or solvents, or that process interference may occur. Problems such as non-uniform thickness and mass loading distribution may also arise.

[0128] In contrast, in the dry method, a fibrous binder can directly connect active material particles to form a three-dimensional binding network. Alternatively, a granular structure in which the active material, binder, and conductive material are uniformly composited in advance can be applied. Through such a structure, compositional and structural uniformity is ensured throughout the electrode active material layer.

[0129] Furthermore, since a liquid medium is absent, component migration or penetration essentially does not occur. Consequently, high mechanical bonding stability and electrical contact reliability are maintained even with a single electrode layer formed on only one side of the current collector. Structural and process independence from the flame-retardant layer on the opposite side is also ensured.

[0130] Furthermore, since solvent and drying processes are unnecessary, drying shrinkage, deformation, contamination, and process interference are suppressed. As a result, it is highly advantageous in that the electrode active material layer and the flame retardant layer can be stably and co-formed on the outermost electrode of a single-plane structure.

[0131] According to one embodiment of the present invention, the outermost electrode comprises a current collector; and an electrode active material layer located on the current collector and comprising an active material and a binder, wherein the binder can be fiberized to bind the active material.

[0132] According to one embodiment of the present invention, the binder can be fiberized to bind the active material, and when the electrode active material layer further includes a conductive material, the binder can be fiberized to bind the active material and the conductive material.

[0133] The outermost electrode may include a fibrous binder as a means for binding an active material or an active material and a conductive material. This fibrous binder exhibits less breakage compared to conventional non-fibrous binders and has excellent elongation properties in the longitudinal direction, thereby improving the flexibility of the electrode active material layer and the electrode itself containing it. The fiberization process of the binder will be examined in detail in the electrode manufacturing method described later.

[0134] The above-mentioned fibrillated binder may be derived from a fibrillable binder. The above-mentioned fibrillable binder is not particularly limited as long as it is capable of microfiber formation by the step of preparing a mixed powder during the electrode manufacturing process described later. A fluorine-containing binder may be more preferable as the above-mentioned fibrillable binder. Microfiber formation refers to a process of finely splitting a polymer, and can be performed, for example, using mechanical shear force. Specific examples of such fibrillated binders may include fluorine-containing polymers. Specifically, the above-mentioned fibrillated binder may include polytetrafluoroethylene (PTFE). The above-mentioned fibrillated binder may include polytetrafluoroethylene alone, or may additionally include one or more PVdF-based copolymers such as polyvinylidene fluoride (PVdF) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene) in addition to polytetrafluoroethylene. The above-mentioned fiberized binder may be polytetrafluoroethylene.

[0135] According to one embodiment of the present invention, the content of the active material may be 85 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, and the content of the binder may be 0.5 to 10 parts by weight.

[0136] In addition, the content of the active material may be 90 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, and the content of the binder may be 0.5 to 5 parts by weight.

[0137] When the content of the active material, conductive material, and binder satisfies these ranges, the binder can be sufficiently fiberized in the subsequent mixing process to form a mixture mass, and an electrode film can be easily manufactured through the molding of the mixed powder formed through the grinding process, the physical properties of the electrode film can be secured, the content of the active material is secured to prevent the problem of capacity reduction, and sufficient conductivity can be secured.

[0138] According to one embodiment of the present invention, the outermost electrode comprises a current collector; and an electrode active material layer comprising a granule and a binder, wherein the granule is located on the current collector and comprises an active material and a binder for the granule, and the binder included together with the granule is fiberized as described above to bind the active material.

[0139] At this time, regarding the granules, one may refer to the description of the granules included in the electrode active material layer of the outermost electrode according to one embodiment of the present invention described later.

[0140] Meanwhile, in some cases, a filler that inhibits the expansion of the electrode may be additionally introduced into the electrode active material layer. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery, and for example, olefin-based polymers such as polyethylene and polypropylene; or fibrous materials such as glass fibers and carbon fibers are used.

[0141] In one embodiment of the present invention, the degree of crystallization of the binder in the electrode active material layer may be 10% or less.

[0142] In one embodiment of the present invention, the degree of crystallization (Xc) can be measured using differential scanning calorimetry (DSC) and is based on the temperature (peak temperature) at the point where the highest enthalpy is observed during crystallization. Specifically, the degree of crystallization is the melting enthalpy (△H) measured by DSC.m The ) value is the enthalpy of melting (△H) of a theoretically perfect crystal (degree of crystallization 100%) m0 It is expressed as a percentage by dividing by the value of the equilibrium heat of fusion, and can be calculated by the following Equation 1. Here, the theoretical enthalpy of melting value of a perfect crystal can be found in the polymer handbook for known polymers, and for unknown or newly synthesized materials, it can be calculated by extrapolation by extending the degree of crystallization at two or more points.

[0143] [Relationship 1]

[0144] Xc(%) = (△H m ÷ △H m0 ) x 100

[0145] According to one embodiment of the present invention, the binder included in the electrode active material layer of the outermost electrode may include a fluorine-containing binder, and the electrode active material layer may have a Quantified Binder Ratio (QBR) of 1.1 or less.

[0146] The above QBR is defined by the following mathematical formula.

[0147] QBR = Bs / Bf

[0148] In the above mathematical formula, Bs represents the average value of the fluorine content in the surface region of the electrode active material layer from the outermost surface of the electrode active material layer up to within 15% of the total thickness of the electrode active material layer, and Bf represents the average value of the fluorine content in the bottom region of the electrode active material layer from the interface of the electrode active material layer facing the current collector up to within 15% of the total thickness of the electrode active material layer.

[0149] At this time, QBR can be calculated using the following method.

[0150] First, an electrode to be tested for QBR is selected, and a cross-section of the selected electrode is fabricated using argon ion milling. Subsequently, the components within the electrode active material layer of the fabricated electrode cross-section are mapped using an Energy Dispersive X-ray Spectroscopy (EDS) detector of a Scanning Electron Microscope (SEM).

[0151] A line profile is extracted in the direction of the electrode active material layer thickness from the EDS mapping results, and among the extracted line profile results, the average value of the fluorine content in the surface region of the electrode active material layer (Bs) and the average value of the fluorine content in the bottom region of the electrode active material layer (Bf) are extracted, and the QBR value is calculated using the following formula.

[0152] QBR = Bs / Bf

[0153] At this time, the surface region of the electrode active material layer is a region from the outermost surface in the thickness direction of the electrode active material layer to within 15% of the total thickness of the electrode active material layer, and the bottom region of the electrode active material layer is a region from the interface of the electrode active material layer facing the current collector to within 15% of the total thickness of the electrode active material layer.

[0154] The above QBR value is 1.1 or less, and according to one embodiment of the present invention, the QBR value may be 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and may also be 0.95 to 1.05, and may be set as a numerical range with lower and upper limits by selecting and combining each of the lower and upper limits listed herein.

[0155] When the above QBR value satisfies the range of 1.1 or less, the problem of the fluorine-containing binder migrating to the electrode surface and the fluorine-containing binder content in the surface region becoming higher than the fluorine-containing binder content in the bottom region of the electrode active material layer does not occur, and as a result, the distribution of the binder in the thickness direction of the electrode active material layer becomes even, so the binder content in the part close to the current collector does not decrease, thereby improving the adhesion between the current collector and the electrode active material layer, and the conductivity on the surface of the electrode active material layer and the charge / discharge speed accordingly can also be improved.

[0156] Specifically, the above fluorine-containing binder may include polytetrafluoroethylene (PTFE); PVdF-based copolymers such as polyvinylidene fluoride (PVdF) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), or two or more of these. Additionally, the above fluorine-containing binder may include polytetrafluoroethylene alone, or additionally include one or more PVdF-based copolymers such as polyvinylidene fluoride (PVdF) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene) in addition to polytetrafluoroethylene.

[0157] The above electrode active material layer may be derived from a dry electrode film. The term "dry electrode film" refers to a film manufactured by a dry manufacturing method that does not use a dispersion medium, unlike the conventional wet electrode manufacturing method in which an active material and a binder (which may optionally further include a conductive material) are dissolved and / or dispersed in a dispersion medium such as water or an organic solvent to obtain a slurry, which is then applied onto a current collector and dried. The electrode film manufactured in this way is subsequently laminated onto a current collector to finally be manufactured into an electrode. Specific manufacturing methods for the electrode film and the electrode are described below.

[0158] According to one embodiment of the present invention, the electrode active material layer in the outermost electrode may be formed by a manufacturing method comprising: a step of preparing a mixture including an active material and a binder; a step of preparing a mixture lump by kneading the mixture at a pressure greater than or equal to atmospheric pressure and at a temperature of 70°C to 200°C; a step of crushing the mixture lump to obtain a mixed powder for electrodes; a step of feeding the mixed powder for electrodes between a plurality of rolls and calendering it to form an electrode film; and a step of laminating the electrode film onto a current collector.

[0159] The method for manufacturing a single-sided electrode applied to an electrode assembly according to the present invention will be described in more detail below. According to one embodiment of the present invention, in addition to the electrode active material layer of the outermost electrode applied to a secondary battery according to the present invention, a double-sided electrode included in a single cell group or a half cell can also be manufactured by the following method.

[0160] First, a mixture containing an active material and a binder is prepared. As previously described, a conductive material may be optionally included, and embodiments in which a conductive material is additionally included are also described below, even if the conductive material is not explicitly specified.

[0161] At this time, the mixing for preparing the above mixture is performed so that the active material and binder can be uniformly distributed, and since they are mixed in powder form, the mixing is not limited to any method that enables simple mixing and can be performed by various methods. However, since the electrode of the present invention is manufactured by a dry manufacturing method that does not use a dispersion medium, the mixing can be performed by dry mixing and can be performed by introducing the materials into a device such as a blender.

[0162] In addition, the above mixture may be prepared by mixing in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute to ensure uniformity.

[0163] According to one embodiment of the present invention, a super mixer or the like may be used in the mixing step for preparing the mixture, and specifically, a method of mixing in a super mixer at 1,000 to 2,000 rpm for 5 to 10 minutes may be applied.

[0164] The above binder can be microfiberized by the step of preparing the above-mentioned mixed powder. The microfiberization refers to a process of dividing the polymer into fine fibers, and can be performed, for example, using mechanical shear force. Specific examples of such a binder are as described above.

[0165] Next, the above mixture is kneaded at a temperature of 70°C to 200°C and under a pressure higher than atmospheric pressure to produce a mass of the mixture.

[0166] In conventionally known techniques, high-shear mixing, such as in a jet mill, was performed to fiberize the binder. However, problems such as the active material being finely pulverized and the formed fibers being cut occurred due to this mixing. In the present invention, these problems were resolved by a low-shear mixing method instead of high-shear mixing.

[0167] The above mixing is not limited to a specific method. In a specific embodiment of the present invention, the mixing may be performed using a dough mixer, such as a kneader, for example.

[0168] This mixing step is to form a mixture mass of 100% solid content by combining or connecting the active material, or the active material and the conductive material, as the binder becomes fiberized.

[0169] Specifically, the mixing can be controlled at a speed of 10 rpm to 100 rpm. For example, the mixing can be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The mixing can be performed for 1 minute to 30 minutes. For example, it can be performed for 3 minutes to 10 minutes at a speed of 20 rpm to 50 rpm within the above range. Meanwhile, the mixing can be controlled at a shear rate in the range of 10 / s to 500 / s. In a specific embodiment of the present invention, the mixing can be performed for 1 minute to 30 minutes, and the shear rate can be controlled at a range of 30 / s to 100 / s.

[0170] In addition, this mixing step can be performed at high temperature and pressure conditions above atmospheric pressure, and more specifically, at pressure conditions higher than atmospheric pressure.

[0171] More specifically, the mixing can be performed on the mixture in a range of 70°C to 200°C, specifically, 90°C to 180°C.

[0172] If performed outside the above temperature range at a low temperature, the fiberization of the binder and clumping by mixing do not occur well, so film formation is not easily achieved during calendering, and if performed at too high a temperature, the fiberization of the binder occurs rapidly and there is a problem that the already formed fibers may be cut by excessive shear force thereafter, which is undesirable.

[0173] In addition, it can be performed at atmospheric pressure or higher, or under a pressure of 1 atm to 60 atm, or under a pressure of 1 atm to 30 atm, or under a pressure of 1 atm to 10 atm, or under a pressure of 1 atm to 8 atm, or under a pressure of 1.1 atm to 7 atm, or under a pressure of 1.1 atm to 6 atm.

[0174] When the above pressure range is satisfied, problems such as fibers being cut or the density of the mixture lumps becoming too high due to excessive shear force and pressure can be prevented. That is, according to the present invention, when a low-shear mixing process is performed under high temperature and pressure conditions above atmospheric pressure instead of high-shear mixing, the effect intended by the present invention can be achieved.

[0175] Next, the above mixture lump is crushed to obtain a mixed powder for electrodes.

[0176] Specifically, the mixture mass produced through the above kneading may be calendered immediately, but in this case, the mixture mass may need to be pressed to produce a thin film, and consequently, a problem may arise in that a uniform film cannot be obtained. According to the present invention, the mixture mass produced undergoes the grinding step. That is, if the electrode mixture powder obtained by grinding is too large or clumped together, bridges may be formed during the calendering process, resulting in defects in the film's appearance such as pinholes or a film having non-uniform surface characteristics. Therefore, the electrode mixture powder having a uniform size is obtained by grinding, and calendering is performed.

[0177] At this time, the grinding step may be performed using a device such as a blender or a grinder, although it is not limited to this method. Specifically, the grinding step may be performed for 30 seconds to 10 minutes at a speed of 5,000 rpm to 20,000 rpm, and more specifically, for 30 seconds to 2 minutes at a speed of 10,000 rpm to 18,000 rpm.

[0178] When the above grinding speed and time are satisfied, sufficient grinding is performed to form powder of a size suitable for film formation, and the problem of excessive fine powder generation in the mixture lumps can be prevented. If necessary, a classification process may be performed to filter out powder that exceeds a certain size or is smaller than a certain size.

[0179] According to one embodiment of the present invention, a cutter mill, a fine mill, etc., may be used in the grinding step. At this time, the cutter mill may be used to coarsely grind the lump of the mixture prepared by kneading to a size of several mm by operating at a condition of 400 to 500 rpm for several seconds. In addition, the fine mill may be used to uniformly grind the coarsely ground powder to a size of a certain level or smaller, and may be used at a condition of 3,000 to 8,000 rpm.

[0180] Next, the above electrode mixture is fed between a plurality of rolls and calendered to form an electrode film.

[0181] According to one embodiment of the present invention, the process of forming the electrode film comprises a plurality of spaced-apart rolls, an electrode mixture obtained in a previous step is introduced between adjacent rolls, and the rolls are rotated in a facing direction so that the mixture is rolled and formed into a sheet or film shape through a powder sheeting step, and subsequently, an electrode film having a target thickness can be obtained through a plurality of calendering steps.

[0182] According to one embodiment of the present invention, in a process for forming an electrode film, the spacing between a plurality of rolls can be appropriately controlled by considering the specifications or physical properties of the electrode film being manufactured. For example, the spacing between the second and third rolls and the spacing between the fourth and fifth rolls can be controlled to be larger.

[0183] Specifically, this calendering process may be a step of processing the mixed powder for the electrode into a film form, for example, by manufacturing it into a film form having an average thickness of 50 μm to 300 μm.

[0184] At this time, the calendering may be performed, for example, by a roll existing in a face-to-face manner. According to one embodiment of the present invention, the calendering may be performed repeatedly one or more times, for example, 1 to 5 times, or 3 to 4 times, or 4 times.

[0185] At this time, the roll temperature may be 50℃ to 200℃.

[0186] The rotational speed ratio of the above roll can be appropriately controlled according to the size of the roll, the number of calendering cycles, and the thickness of the electrode film, for example, in a range of 1 to 10 times, or 1 to 8 times, or 1 to 7 times, or 1.2 to 5 times.

[0187] In addition, the gap between a pair of facing rolls can be variably adjusted according to the thickness and density of the film to be obtained.

[0188] Specifically, narrowing the gap between the aforementioned pair of facing rolls increases the pressure, while widening the gap decreases the pressure. Since the gap between the aforementioned pair of facing rolls may vary depending on the film thickness, equipment tolerances, etc., it may be more appropriate to express it as a force applied to a predetermined length or area.

[0189] According to one embodiment of the present invention, the force applied by the pair of facing rolls may be 100 to 500 kgf, or 150 to 450 kgf, or 170 to 300 kgf, or 170 to 250 kgf, or 180 to 230 kfg per 1 cm of roll width.

[0190] By proceeding to such a calendering step, a dry electrode film that performs the role of an electrode composite can be manufactured. In the past, such a dry electrode film was also referred to as a free standing film.

[0191] The electrode film manufactured in this manner does not contain a solvent, so it has almost no fluidity, making it easy to handle and allowing it to be processed into a desired shape and used to manufacture electrodes of various shapes. Furthermore, if the electrode film of the present invention is used in the manufacture of electrodes, the drying process for solvent removal can be omitted, thereby significantly improving the processability of electrode manufacturing, and also resolving problems such as breakage of the active material or breakage of the fibrous contained binder, which were issues in the manufacture of conventional dry electrodes.

[0192] Next, the above electrode film is laminated onto a metal current collector.

[0193] The above lamination step may be a step of rolling and attaching the electrode film obtained in the preceding step onto a current collector to a predetermined thickness. The lamination may also be performed by a lamination roll, and at this time, the lamination roll may be maintained at a temperature of 25 to 250°C.

[0194] According to one embodiment of the present invention, the compression ratio of the electrode film may be 30 to 50%, or 35 to 50%, or 40 to 50%.

[0195] The compression ratio of the above electrode film can be defined as the ratio of the thickness of the electrode film that is compressed at the moment of lamination, and can be expressed by the following Equation 1.

[0196] [Equation 1]

[0197] Compression ratio (%) = T p / T1×100

[0198] In Equation 1,

[0199] T p represents the pressure thickness of the electrode film during the lamination stage, and

[0200] T1 refers to the thickness of the electrode film before the lamination step.

[0201] In the present invention, by adjusting the compression ratio to satisfy a specific range during the lamination step, it is possible to provide appropriate density and porosity of the electrode film and excellent adhesion between the electrode film and the current collector.

[0202] When the compression ratio of the electrode film satisfies the range of 30 to 50%, the pressure applied to the electrode film is sufficient to improve the adhesion between the electrode film and the current collector, and the problem of the electrode film peeling off from the current collector after the lamination process can be prevented, and the problem of the electrode film increasing in density more than necessary, resulting in a porosity lower than the target porosity or damage to the current collector can be resolved.

[0203] In one embodiment of the present invention, when electrode films are laminated on both sides of the current collector, the compression ratio (%) of Equation 1 may mean Equation 2 below.

[0204] [Equation 2]

[0205] 30 ≤ (T1 + 0.5T c - 0.5T gap ) / T1×100 ≤ 50

[0206] In Equation 2, T1 represents the thickness of the electrode film before the lamination step, and T crepresents the thickness of the entire house, and T gap represents the gap between the first and second rolling rolls.

[0207] In addition, the rolling rate of the electrode film that has undergone the lamination step during the manufacture of the double-sided electrode may be in the range of 20% or less, or 18% or less, or 15% or less, or 5% to 15%, or 6% to 15%, or 7% to 15%, or 9% to 13%.

[0208] In one embodiment of the present invention, the rolling rate of the electrode film that has undergone a lamination step when forming the electrode active material layer of the outermost electrode may be in the range of 10% or less, or 3% to 10%, or 3.5% to 10%, or 3.7% to 7.1%, or 3.7% to 4.9%, or 4.9% to 7.1%.

[0209] Here, the rolling rate can be defined as the ratio of the thickness of the electrode film after the lamination step to the thickness of the electrode film before the lamination step, and can be expressed by the following Equation 3.

[0210] [Equation 3]

[0211] Rolling rate (%) = (T1-T2) / T1×100

[0212] In the above Equation 3,

[0213] T1 refers to the thickness of the electrode film prior to the lamination step, and

[0214] T2 represents the thickness of the electrode film after the lamination step.

[0215] When the above rolling rate satisfies the range described above, appropriate density and porosity of the electrode film and adhesion between the electrode film and the current collector can be achieved.

[0216] The apparent density increase rate before and after lamination of the above electrode film with the current collector can be expressed by the following Equation 4:

[0217] [Equation 4]

[0218] Apparent density growth rate (%) = (D2-D1) / D1×100

[0219] D1 is the apparent density (g / cm³) of the electrode film prior to the lamination step. 3 Representing ),

[0220] D2 is the apparent density (g / cm³) of the electrode film after the lamination step. 3 It represents ).

[0221] The apparent density increase rate before and after lamination of the electrode film with the current collector may be 5 to 30%, or 7 to 25%, or 10 to 20%.

[0222] D1 and D2, representing the apparent densities of the electrode film, can be varied depending on the type of active material, and according to one embodiment of the present invention, the active material is lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, a+b+c=1); or an oxide in which a portion of lithium nickel-manganese-cobalt oxide is substituted with aluminum (lithium nickel-manganese-cobalt-aluminum oxide) Li a [Ni b Co c Mn d Al e ] 1-f M 1 f O 2 ( The above M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8≤a≤1.2, 0.5≤b≤0.99, 0 <c<0.5, 0<d<0.5, 0.01≤e≤0.1, 0≤f≤0.1임) 등 인 경우에, 상기 D1및 D2는 2.75 g / cm 3 Up to 3.8 g / cm² 3It can be a range.

[0223] Meanwhile, if the apparent density increase rate of the electrode film satisfies the above range, the adhesion between the electrode film and the current collector can be improved, and problems such as the porosity deviating from the target range or damage to the active material or current collector can be prevented.

[0224] The apparent density of the electrode film before and after lamination with the current collector can be calculated by measuring the weight and thickness of the electrode film before lamination, measuring the weight and thickness of the electrode after lamination, and determining the weight and thickness of the film after subtracting the weight and thickness of the current collector.

[0225] In addition, the active material loading amount of the electrode film is 3 mAh / cm² 2 Up to 15mAh / cm 2 It could be, and specifically 4mAh / cm 2 Up to 10mAh / cm 2 It could be.

[0226] Here, the loading amount of the active material is the value calculated by the following Equation 5.

[0227] [Equation 5]

[0228] Loading amount of active material (mAh / cm²) 2 ) = Capacity of active material (mAh / g) x Weight content ratio of active material in dry electrode film (wt%) x Weight per unit area of ​​dry electrode film (g / cm²) 2 )

[0229] In addition, the interfacial resistance between the electrode film and the current collector is 5 Ω·cm 2 Below, in detail, 2Ω·cm 2 The above interface resistance may be less than or equal to the following. Here, the above interface resistance can be calculated by applying a current of 100 μA to the electrode using a Multi-Probe (MP) resistance measurement method and measuring the resistance value between the dry electrode film and the contact layer using the potential difference measured between multiple probes. If the above range of interface resistance is satisfied, the battery performance of the secondary battery manufactured thereafter can be improved.

[0230] According to one embodiment of the present invention, an electrode film is rolled to a predetermined thickness and attached to one surface of a current collector using a pair of lamination rolls, thereby finally forming an electrode active material layer of the outermost electrode.

[0231] According to one embodiment of the present invention, the electrode active material layer of the outermost electrode may include a plurality of granules having an active material and a binder.

[0232] The above granules may be secondary particles in which one or more active material particles are connected and fixed by a binder.

[0233] The above granules may further include additional components, such as conductive materials, as needed.

[0234] According to one embodiment of the present invention, the active material included in the granules may include a silicon-based active material. The silicon-based active material is silicon (Si) and silicon oxide (SiOxide). <x≤2), Si / C 복합체, 또는 이들 중 2 이상을 포함할 수 있다. 상기 규소계 활물질의 구체적인 예로는 Si, SiO, SiO / C, SiO2등이 있고, 여기에 한정되지는 않는다.

[0235] In addition, according to one embodiment of the present invention, the conductive material included in the granules may include a linear conductive material.

[0236] According to one embodiment of the present invention, the granules may include a silicon-based active material and a linear conductive material.

[0237] A negative electrode active material containing a silicon-based active material, which has excellent capacity but has limited application due to large volume changes, is manufactured into a granule of a predetermined shape according to one embodiment of the present invention, wherein the silicon-based active material is connected and fixed by a linear conductive material and a binder uniformly dispersed within the granule, so that even if there is a volume change of the silicon-based active material within the negative electrode active material layer later, a conductive network within the negative electrode active material layer can be stably formed by the linear conductive material that connects the silicon-based active material uniformly through linear contact, and as a result, electrical properties such as the lifespan characteristics of an electrochemical device such as a secondary battery employing such a negative electrode can be significantly improved.

[0238] The above linear conductive material may include single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers, or two or more of these.

[0239] The carbon nanotubes described above include allotropes of carbon having sp2 bonding structures, in which a graphite sheet has a cylindrical shape with a nano-sized diameter, and aggregates thereof. The carbon nanotube aggregate refers to a secondary structure formed by the arrangement or aggregation of multiple carbon nanotubes. For example, the carbon nanotube aggregate may be a bundle-type carbon nanotube in the form of a bundle or rope in which multiple carbon nanotubes are arranged or aligned in a certain direction, or an entangled-type carbon nanotube in the form of a sphere or potato in which multiple carbon nanotubes are entangled without a certain direction.

[0240] At this time, the multi-walled carbon nanotube is a small hollow tube composed of a coaxial cylindrical surface sleeve of several hexagonal lattices of carbon atoms, and the single-walled carbon nanotube may be composed of a single carbon cylindrical surface. The walls of this tubular structure are composed of a hexagonal lattice similar to a graphite sheet, the intersections of the hexagonal lattice are where carbon atoms are located, and each carbon atom is adjacent to a surrounding carbon atom, and at the same time, both ends (end caps) of the tube can be closed with a polygonal structure composed of pentagonal carbon rings.

[0241] The above linear conductive material, in particular single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), is 500m 2 / g or more, or 500m 2 / g to 5,000m 2 / g, or 800m 2 / g or more, or 800m 2 / g to 5,000m 2 / g, or 900 m 2 / g to 2000 m 2 It can have a BET specific surface area of ​​ / g. When a linear conductive material having a BET specific surface area as described above is used, excellent formation of a conductive network between silicon-based negative electrode active materials can be achieved, thereby further improving the cycle characteristics of the secondary battery.

[0242] The linear conductive material may have a length of 0.5 μm to 100 μm. For example, the single-walled carbon nanotube may have an average length of 2 μm to 100 μm, and the multi-walled carbon nanotube may have an average length of 0.3 μm to 30 μm. Meanwhile, the linear conductive material may have a cross-sectional diameter of 1 nm to 100 nm.

[0243] The amount of binder contained in the surface portion of the granules may be greater than the amount of binder contained in the center of the granules. The amount of binder may refer to weight or volume.

[0244] In conjunction with or independently thereof, the granules may have a greater amount of binder (wt%) (Bs / Gt) contained in the surface portion of the granules compared to the amount of binder (wt%) (Bc / Gt) contained in the center of the granules relative to 100 wt% of the total weight of the granules. Here, Bc represents the weight of the binder contained in the center, Bs represents the weight of the binder contained in the surface portion, and Gt represents the total weight of the granule particles.

[0245] In conjunction with or independently thereof, the granules may have a higher content of binder (vol%) (Bs / Gt) contained in the surface portion of the granules compared to the content of binder (vol%) (Bc / Gt) contained in the center of the granules relative to 100 vol% of the total volume of the granules. Here, Bc is the volume of binder contained in the center, Bs is the volume of binder contained in the surface portion, and Gt may represent the total volume of the granule particles.

[0246] Here, the surface portion refers to an area near the surface of the granules up to a predetermined depth from the surface of the granules in the direction of the center of the granules, and the center may refer to a part other than the surface portion. In one embodiment of the present invention, the surface portion may refer to an area extending from the center of the granules toward the outer side of the granules to the surface of the granules after 70% of the radius. In one embodiment of the present invention, the surface portion may refer to, for example, an area extending to the surface of the granules after 80%, 85%, 90%, or 95% of the radius.

[0247] In one embodiment of the present invention, the center of the granules may mean half the longest diameter of the granules.

[0248] In one embodiment of the present invention, in the region from the center of the granule particle to the surface of the granule after 90% radius, the content of the binder relative to 100 wt% of the total weight of the granule in the said region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0249] In another embodiment of the present invention, in the region from the center of the granule to the surface of the granule after 95% of the particle radius, the content of the binder relative to 100 wt% of the total weight of the granule in the said region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0250] In another embodiment of the present invention, in the region from the center of the granule particle to the surface of the granule after the radius of 99%, the content of the binder relative to the total weight of the granule in the region of 100 wt% may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0251] In one embodiment of the present invention, in the region from the center of the granule particle to the surface of the granule after a radius of 90%, the content of the binder relative to the total volume of the granule in the region (100 vol%) may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0252] In another embodiment of the present invention, in the region from the center of the granule to the surface of the granule after 95% of the particle radius, the content of the binder relative to the total volume of the granule in the region (100 vol%) may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0253] In another embodiment of the present invention, in the region from the center of the granule particle to the surface of the granule after the radius of 99%, the content of the binder relative to the total volume of the granule in the region of 100 vol% may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0254] To describe the granules in more detail, the granules may comprise a central part containing one or more active materials; and a surface part containing a binder located on all or part of the outer side of the central part and binding the active materials. That is, in the central part of the granules, a plurality of active materials form an aggregate by making surface contact, line contact, point contact, or two or more of these contacts with each other, and in the surface part of the granules, a binder is located on part or all of the outer side of the aggregate, thereby fixing and binding the plurality of active materials in the central part of the granules to each other.

[0255] According to one embodiment of the present invention, a small amount of binder is additionally included in the center of the granules, which can serve to connect and fix a plurality of active materials in the center to each other.

[0256] Meanwhile, in one embodiment of the present invention, the granules may have an aspect ratio of 0.5 to 1.0, preferably 0.75 to 1.0. The aspect ratio may refer to the ratio of the major axis length to the minor axis length of the granules. In another embodiment of the present invention, the average aspect ratio of the granules may have a value of 0.5 to 1.0, preferably 0.75 to 1.0, in which case the average aspect ratio may refer to the ratio of the average major axis length to the average minor axis length of the granule particles. Here, the average minor axis length represents the average value of the length in the axial direction having the shortest length of the granules, and the average major axis length represents the average value of the length in the axial direction having the longest length of the granules. When the aspect ratio of the granules satisfies this range, it is advantageous in terms of having sufficient fluidity suitable for the process.

[0257] In one embodiment of the present invention, the particle size of the granules may have a range of 0.1 to 1,000 μm based on the longest diameter of the particle. In another embodiment of the present invention, the average particle size (D50) of the granules may have a range of 0.1 to 1,000 μm.

[0258] According to one embodiment of the present invention, the granules may comprise 80 to 98 parts by weight of an active material, 0.5 to 10 parts by weight of a conductive material, and 0.5 to 10 parts by weight of a binder. Alternatively, the granules may comprise 85 to 95 parts by weight of an active material, 0.5 to 5 parts by weight of a conductive material, and 0.5 to 8 parts by weight or 0.5 to 7 parts by weight or 0.5 to 6 parts by weight or 0.5 to 5 parts by weight or 0.5 to 4 parts by weight or 1 to 8 parts by weight or 1 to 7 parts by weight or 1 to 6 parts by weight or 1 to 5 parts by weight or 1 to 4 parts by weight of a binder.

[0259] When the content of the above active material, conductive material, and binder satisfies these ranges, the cohesive force between the active materials in the cathode is increased, and the dispersibility of the conductive material and binder can be significantly improved.

[0260] In one embodiment of the present invention, the binder may include one or more of a linear binder and a point binder.

[0261] The above-mentioned linear binder acts as a binder within a composition containing an active material and may refer to a polymer compound characterized by a structure in which polymer chains are arranged linearly. Such a linear binder has flexible polymer chains, thereby stably binding the active material and the conductive material to the current collector, and absorbing the volume expansion and contraction of the electrode that occur during the charging and discharging process, so as to maintain the mechanical stability and electrical contact of the electrode.

[0262] The above-mentioned point-shaped binder refers to a binder that does not completely dissolve in a solvent when dispersed therein, maintains a point-shaped form with a size of several hundred nanometers, has good dispersibility so that it can effectively surround the surface of the active material, and has low viscosity relative to the solid content, making it easy to control the binder content relative to the active material. By using such a point-shaped binder together with the active material and the linear conductive material within the granules, the surface of the active material can be sufficiently covered while maintaining the dispersibility of the linear conductive material.

[0263] Although there are no particular restrictions on the shape of the above-mentioned point binder, it is preferable that it be in a particulate form because it provides good binding properties and can suppress the reduction of the capacitance of the prepared electrode or deterioration caused by repeated charging and discharging. Examples of particulate point binders include those in which dispersed binder particles, such as latex, are dispersed in a solvent such as water, or powdered binders obtained by drying such a dispersion.

[0264] The above linear binder may include an acrylate-based polymer.

[0265] Examples of the above acrylate-based polymers include polymers comprising monomer units derived from acrylic acid esters and / or methacrylic acid esters. The proportion of monomer units derived from acrylic acid esters and / or methacrylic acid esters in the acrylate-based polymer may be at least 40% by weight, preferably at least 50% by weight, and more preferably at least 60% by weight. Specific examples of acrylate-based polymers include cross-linked acrylate-based polymers such as acrylamide-acrylate copolymer, 2-ethylhexyl-methacrylic acid-acrylonitrile-ethylene glycol dimethacrylate copolymer, 2-ethylhexyl-methacrylic acid-methacrylonitrile-diethylene glycol dimethacrylate copolymer, 2-ethylhexyl-styrene-methacrylic acid-ethylene glycol dimethacrylate copolymer, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer, and butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymer; Examples include copolymers of ethylene and (meth)acrylic acid esters, such as ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-ethyl methacrylate copolymer; and graft polymers obtained by grafting a radical polymerizable monomer onto the copolymers of ethylene and (meth)acrylic acid esters. Meanwhile, examples of radical polymerizable monomers used in the graft polymers include methyl methacrylate, acrylonitrile, and methacrylic acid. Additionally, copolymers of ethylene and (meth)acrylic acid, such as ethylene-acrylic acid copolymers and ethylene-methacrylate copolymers, can be used as dispersion-type binders.

[0266] According to one embodiment of the present invention, the acrylate-based polymer may include an acrylamide-acrylate copolymer.

[0267] The above point binder may include a diene-based polymer, a styrene-based polymer, or two or more of these.

[0268] Examples of the above-mentioned diene-based polymers include polymers containing monomer units derived from conjugated dienes such as butadiene and isoprene, and hydrogenated products thereof. The proportion of monomer units derived from conjugated dienes in the diene-based polymer may be at least 40% by weight, preferably at least 50% by weight, and more preferably at least 60% by weight. Specifically, examples include conjugated diene homopolymers such as polybutadiene or polyisoprene; aromatic vinyl-conjugated diene copolymers such as styrene-butadiene copolymer (SBR), which may be carboxy-modified; cyanated vinyl-conjugated diene copolymers such as acrylonitrile-butadiene copolymer (NBR); hydrogenated SBR, hydrogenated NBR, etc.

[0269] The above styrene-based polymer is a polymer having repeating units derived from styrene monomers, and may include styrene homopolymers (polystyrene), styrene copolymers, etc. Examples of the above styrene copolymers may include block copolymers such as styrene-ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-isoprene copolymer, styrene-n-butyl-itaconic acid-methyl-acrylonitrile methacrylate copolymer, styrene-n-butyl-itaconic acid-methyl-acrylonitrile methacrylate copolymer, styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-isoprene block copolymer, and styrene-ethylene-propylene-styrene block copolymer.

[0270] In addition, in one embodiment of the present invention, the binder may include a linear binder and a point binder. In one embodiment of the present invention, the binder may include an acrylate-based polymer (e.g., acrylamide-acrylate copolymer, acrylamide-acrylic acid-acrylonitrile copolymer, etc.) as the linear binder and a diene-based polymer or a styrene-based polymer (e.g., styrene-butadiene copolymer (SBR), etc.) as the point binder.

[0271] According to one embodiment of the present invention, the electrode active material layer of the outermost electrode may be formed by a method comprising: a step of preparing a slurry by mixing an active material and a binder with a dispersion medium; a step of preparing an initial granule by spray-drying the slurry; a step of applying the initial granule onto a current collector; and a step of forming an electrode active material layer comprising rolled granules by rolling the applied initial granules.

[0272] The granules included in the electrode active material layer of the outermost electrode are the result of rolling the initial granules produced by a method comprising the steps of: mixing an active material and a binder with a dispersion medium to prepare a slurry; and spray-drying the slurry; and this can be referred to as rolled granules.

[0273] According to one embodiment of the present invention, the slurry may further include a conductive material.

[0274] First, the active material, binder, and optionally a conductive material and additional additives can be dispersed or dissolved in a dispersion medium (a solvent for the negative electrode binder) to obtain a slurry in which the active material, binder, an optional component conductive material, and other additives are dispersed or dissolved.

[0275] Water is most suitable as the dispersion medium used to obtain the above slurry, but an organic solvent may also be used. Examples of organic solvents include alkyl alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, and diglyme; amides such as diethylformamide, dimethylacetoamide, N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and dimethylimidazolidinone; and sulfur-based solvents such as dimethyl sulfoxide and sulfolain, but alcohols are preferred. If an organic solvent with a boiling point lower than that of water is used in combination, the drying speed during flow granulation can be accelerated. In addition, since the dispersibility or solubility of the cathode binder can be changed, the viscosity or fluidity of the slurry can be adjusted according to the amount or type of dispersion medium, thereby improving production efficiency.

[0276] The amount of dispersion medium used when preparing the above slurry may be an amount such that the solid content concentration of the slurry is usually in the range of 1 to 50 weight%, or 5 to 50 weight%, or 10 to 30 weight%.

[0277] The method or sequence of dispersing or dissolving the active material and binder in the dispersion medium is not particularly limited, and examples include a method of adding and mixing the active material and binder in the dispersion medium, or a method of dissolving or dispersing the binder in the dispersion medium and then finally adding and mixing the active material. At this time, as described above, a conductive material, other additives, etc., may be optionally added to the dispersion medium.

[0278] Mixing means may include, for example, mixing devices such as ball mills, sand mills, bead mills, pigment dispersers, stone mills, ultrasonic dispersers, homogenizers, and planetary mixers. Mixing can usually be performed for 10 minutes to several hours in the range of room temperature to 80°C.

[0279] Next, the above slurry can be spray-dried to produce the initial granules.

[0280] Spray drying is a method of drying by spraying a slurry into hot air. Spraying methods used in the spray drying device include the rotary disc method and the nozzle pressurization method. The rotary disc method is a method in which a slurry is introduced near the center of a high-speed rotating disc, and due to the centrifugal force of the disc, the slurry is placed outside the disc and then dried in a mist form. The rotation speed of the disc depends on the size of the disc, but is usually 5,000 rpm to 35,000 rpm, preferably 15,000 rpm to 30,000 rpm. On the other hand, the nozzle pressurization method is a method of drying by passing the slurry through a thin nozzle while simultaneously spraying a high-pressure fluid, such as air or another liquid, to spray it in a mist form.

[0281] In one embodiment of the present invention, the temperature of the hot air can be controlled to 80°C to 250°C based on the reactor inlet temperature (at the time of input) in terms of forming a granular structure with a high electrode binder content on the surface. In the present invention, considering the binder content gradient and aspect ratio, it can preferably be controlled to 175°C to 220°C, and more preferably to 180°C to 220°C. In the spray drying method, the method of inhaling the hot air is not particularly limited, and examples include a method in which the hot air and the spray direction flow parallel in the transverse direction, a method in which the spray is sprayed at the top of the drying tower and descends together with the hot air, a method in which the sprayed droplets come into countercurrent contact with the hot air, and a method in which the sprayed droplets flow parallel with the initial hot air and then fall by gravity to come into countercurrent contact. Meanwhile, in one embodiment of the present invention, the outlet temperature of the reactor (temperature of the hot air discharged from the reactor) during the spray drying can be controlled to 90°C to 130°C.

[0282] If the outlet temperature and / or ΔT, which is the difference between the inlet and outlet temperatures, is low, drying does not occur properly, resulting in the formation of particles with a large amount of residual solvent; consequently, uniform spherical particles are not formed, and the granules may clump together or become irregular. On the other hand, if the inlet temperature is too high and ΔT is large, over-drying prevents granulation, and particles with a very small D50 and low aspect ratio may be produced. Therefore, to achieve high sphericity, minimize binder clumping, and control particle size to an appropriate level, it is necessary to control the inlet and outlet temperatures within an appropriate range.

[0283] In addition, the surface of the product obtained by optional spray drying, i.e., the granules, can be heat-treated to harden it, and the heat treatment temperature can usually be 80°C to 300°C.

[0284] According to one embodiment of the present invention, the electrode active material layer of the outermost electrode may be formed by a method comprising: a step of applying a plurality of granules onto a current collector; and a step of rolling the applied plurality of granules to form a negative active material layer.

[0285] Granules manufactured by the method described above are applied onto a current collector, and at this time, a primer layer comprising a conductive material and a binder as described above may be provided on all or part of at least one surface of the current collector.

[0286] According to one embodiment of the present invention, a plurality of prepared granules can be supplied to a roll-type pressure molding device, such as a screw feeder, to form an active material layer. At this time, a negative electrode active material layer can be directly laminated on a negative electrode current collector by sending the negative electrode current collector to the roll of the pressure molding device simultaneously with the supply of granules. Alternatively, the granules can be scattered on a negative electrode current collector, the granules can be evenly distributed with a blade or the like to adjust the thickness, and then formed with a pressure device to form an active material layer of the outermost electrode.

[0287] In these methods, the temperature during roll pressure forming is typically 0 to 200°C, which may be higher than the melting point or glass transition temperature of the binder, or may be 20°C or higher than the melting point or glass transition temperature. The forming speed during roll pressure forming may typically be 0.1 to 20 m / min, or 1 to 10 m / min. Additionally, the linear press pressure between the rolls may typically be 0.2 to 30 kN / cm, or 0.5 to 10 kN / cm.

[0288] In order to eliminate thickness variations in the formed cathode and increase the density of the active material layer to achieve high capacity, additional pressure may be applied as needed. The post-pressing method may be a press process using rolls. In a roll press process, two cylindrical rolls are arranged vertically in parallel with a narrow gap, and each is rotated in opposite directions to interlock an electrode between them and apply pressure. The rolls may also be temperature-controlled, such as by heating or cooling.

[0289] According to one embodiment of the present invention, the electrode active material layer of the outermost electrode may include a plurality of granules and a fibrous binder that connects and fixes the granules to each other. In this case, the granules and the fibrous binder may be adapted from the foregoing.

[0290] According to one embodiment of the present invention, the electrode active material layer in the outermost electrode may be formed by a manufacturing method comprising: a step of preparing a mixture comprising granules and a fiberizable binder; a step of kneading the mixture at a pressure greater than or equal to atmospheric pressure and at a temperature of 70°C to 200°C to prepare a mixture lump; a step of crushing the mixture lump to obtain a mixed powder for electrodes; a step of feeding the mixed powder for electrodes between a plurality of rolls and calendering it to form an electrode film; and a step of laminating the electrode film onto a current collector.

[0291] The electrode active material layer of the outermost electrode may further include an active material in addition to a plurality of granules and a fibrous binder that connects and fixes the granules to each other. For example, the granules may include a silicon-based active material, and the additional active material may include a carbon-based active material.

[0292] According to one embodiment of the present invention, the electrode active material layer in the outermost electrode may be formed by a manufacturing method comprising: a step of preparing a mixture comprising granules, additional active material, and a fiberizable binder; a step of kneading the mixture at a pressure greater than or equal to atmospheric pressure and at a temperature of 70°C to 200°C to prepare a mixture lump; a step of crushing the mixture lump to obtain a mixed powder for electrodes; a step of feeding the mixed powder for electrodes between a plurality of rolls and calendering it to form an electrode film; and a step of laminating the electrode film onto a current collector.

[0293] At this time, instead of introducing granules into the step of preparing a mixture in the method of manufacturing the electrode active material layer at the outermost electrode, they may be introduced into the step of preparing a mixture mass by kneading, or they may be introduced after the step of obtaining a mixed powder for the electrode and calendering process may be carried out.

[0294] According to one embodiment of the present invention, the electrode active material layer of the outermost electrode applied to the secondary battery according to the present invention, and the electrode active material layer based on one side of the double-sided electrode included in a single cell group or half cell, is 0.02 to 0.06 g / cm² 2 , or 0.03 to 0.05 g / cm³ 2 , or 0.033 to 0.048 g / cm³ 2 It can have a loading amount. Here, the loading amount of the electrode active material layer refers to the total weight of the solid components constituting the electrode active material layer per unit area of ​​the electrode active material layer.

[0295] A secondary battery according to one aspect of the present invention may be provided by housing a group of single cells having one or more of the aforementioned single cells; and an outermost electrode disposed on the outside of one or more of the group of single cells in a battery case (cylindrical case, prismatic case, pouch, etc.) and injecting a lithium-containing non-aqueous electrolyte.

[0296] The separator provided in the secondary battery of the present invention may be a porous polymer film made of a polyolefin-based polymer, such as a conventional porous polymer film used as a separator, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, used alone or in a laminated form. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc., may be used, but is not limited thereto.

[0297] The above-mentioned non-aqueous electrolyte comprises a lithium salt as an electrolyte and an organic solvent for dissolving it.

[0298] The above lithium salt may be used without limitation as long as it is one commonly used in electrolytes for secondary batteries, for example, as the anion of the above lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF -, (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0299] The organic solvent included in the above electrolyte may be any commonly used solvent without limitation, and one or more selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran may be used.

[0300] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts in the electrolyte, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0301] Optionally, the electrolyte stored according to the present invention may further include additives such as an overcharge prevention agent included in conventional electrolytes. Additionally, according to one aspect of the present invention, an energy storage device comprising the secondary battery is provided.

[0302] At this time, since the specific structure, etc. of the above secondary battery and energy storage device is as previously known, a description is omitted in this specification.

[0303]

[0304] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0305]

[0306] Example 1

[0307] (1) Manufacturing of the outermost electrode

[0308] 1) Manufacture of a single-sided electrode (cathode)

[0309] 97 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) as cathode active materials, 1 part by weight of polytetrafluoroethylene (PTFE) and 1.5 parts by weight of polyvinylidene fluoride (PVDF) as binders, and 0.5 parts by weight of carbon black were put into a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture, which was then put into a kneader.

[0310] The temperature of the kneader was stabilized at 150°C, and the mixture was placed into the kneader. The lid was then operated at a speed of 40 rpm for 5 minutes under a pressure of 1.1 atm to obtain a lump of the mixture. The lump of the mixture was fed into a blender and ground at 10,000 rpm for 30 seconds, and classified through a sieve with pores of 1 mm to obtain a mixed powder for electrodes. Subsequently, the prepared mixed powder for electrodes was fed three times into a lab calender (roll diameter: 160 mm, roll temperature: 100°C) to produce an electrode film. By adjusting the gap during calendering, it was possible to produce an electrode film having a desired density (porosity).

[0311] A single electrode film was placed on one side of a current collector (a copper foil (thickness 10㎛) coated with a conductive primer layer of 0.5㎛ on each side, in which carbon black and PVDF binder are mixed in a weight ratio of 1:2) and laminated using a room temperature compression roll (lamination roll) to manufacture a single-sided cathode.

[0312] At this time, the conditions of the lamination were that the diameter of a pair of facing compression rolls was 160 phi, the peripheral speed ratio of a pair of compression rolls was 1:1, and the process speed was 5 mpm (meters per minute).

[0313]

[0314] 2) Manufacture of the outermost electrode having a flame-retardant layer

[0315] A capsule (average particle size: 107 μm) was prepared having a flame retardant (1,1,1,2,2,4,5,5,5-Nonafluoro-4-(trifluoromethyl)-3-pentanone) and a shell made of urea-formaldehyde-resorcinol material surrounding the flame retardant. At this time, the content of the flame retardant was 98.5 parts by weight based on 100 parts by weight of the capsule. The thickness of the shell was 1.35 μm.

[0316] A flame-retardant layer slurry was prepared by homodispering 100 parts by weight of the above capsule with 0.83 parts by weight of carboxymethylcellulose (CMC), 4.71 parts by weight of styrene-butadiene rubber (SBR), and a liquid medium as binders for the flame-retardant layer, with a weight ratio of capsule to CMC / SBR of 19:1. At this time, carboxymethylcellulose (CMC) was added as a 1.5% by weight aqueous solution and SBR as an 8.5% by weight aqueous dispersion.

[0317] Subsequently, a flame-retardant layer was formed by coating and drying a flame-retardant layer slurry on the side (bare side, uncoated side) of the previously manufactured single-sided electrode where the active material layer was not formed, thereby finally manufacturing the outermost electrode.

[0318]

[0319] (2) Manufacturing of secondary batteries

[0320] A cathode composite was prepared by mixing 97.6 parts by weight of synthetic graphite and natural graphite (weight ratio: 90:10) as cathode active materials, 1.2 parts by weight of styrene-butadiene rubber (SBR) functioning as a binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC). A cathode composite slurry was prepared by dispersing this cathode composite in ion-exchanged water functioning as a solvent. A double-sided cathode was manufactured by coating this slurry onto both sides of a copper foil with a thickness of 10 μm, drying, and pressing. At this time, the loading amount of the electrode active material layer on one side of the double-sided cathode was 0.033 g / cm³. 2 It was.

[0321] Li[Ni as a positive electrode active material 0.88 Co 0.07 Mn 0.04 ]Al 0.01O2), a pre-dispersion of carbon black as the anode conductor, and polyvinylidene fluoride (PVdF) as the anode binder were added to NMP, a dispersion medium, in a weight ratio of 96.5:1.5:2, and a homogenizer was stirred at 3500 rpm for 1 hour to prepare an anode active material slurry. The solid content of the carbon black pre-dispersion was 16%, and the final solid content of the slurry was prepared to be 68%. The above slurry was coated on both sides of an aluminum current collector with a thickness of 12 μm, and the coated slurry was dried using a drying device equipped with a hot air blower and an IR heater to form an anode active material layer. Subsequently, the anode active material layer was rolled using a roll pressing method to manufacture a double-sided anode. At this time, the loading amount of the electrode active material layer on one side of the double-sided anode was 0.048 g / cm³. 2 It was.

[0322] Single cells (311, 312, 313, 314) prepared by stacking a double-sided positive electrode, a double-sided negative electrode, and a first separator (separator for stacking) (polyethylene film (thickness: 9 μm)) manufactured by the above method, and a half-cell (315p) of a double-sided positive electrode stacked on one side of an outermost electrode having a flame-retardant layer (315f) and a single-sided electrode (315n) are placed on a second separator (separator for folding) (316) (polyethylene film (thickness: 9 μm)), and an electrode assembly having the structure of FIG. 5 is manufactured by rolling it in a folding manner according to FIG. 4 and inserted into a pouch.

[0323] Subsequently, a secondary battery was manufactured by using a liquid electrolyte in which LiPF6 is dissolved at 1M in a solvent mixed with ethylene carbonate, dimethylene carbonate, and diethyl carbonate in a 1:2:1 (volume ratio), injecting the solution into a pouch into which the electrode assembly is inserted, sealing it, and forming it.

[0324]

[0325] Comparative Example 1

[0326] (1) Manufacturing of the outermost electrode (cathode)

[0327] 97 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) as cathode active materials, 1 part by weight of polytetrafluoroethylene (PTFE) and 1.5 parts by weight of polyvinylidene fluoride (PVDF) as binders, and 0.5 parts by weight of carbon black were put into a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture, which was then put into a kneader.

[0328] The temperature of the kneader was stabilized at 150°C, and the mixture was placed into the kneader. The lid was then operated at a speed of 40 rpm for 5 minutes under a pressure of 1.1 atm to obtain a lump of the mixture. The lump of the mixture was fed into a blender, ground at 10,000 rpm for 30 seconds, and classified using a sieve with pores of 1 mm to obtain a mixed powder for electrodes. Subsequently, the prepared mixed powder for electrodes was fed three times into a lab calender (roll diameter: 160 mm, roll temperature: 100°C) to manufacture an electrode film. By adjusting the gap during calendering, an electrode film having the desired density (porosity) could be manufactured. The pressure applied by a pair of opposing rolls during calendering was 221 kgf per 1 cm of film width.

[0329] Two electrode films were placed on both sides of a current collector (an aluminum foil (thickness 15㎛) coated with a conductive primer layer of carbon black and PVDF binder mixed in a weight ratio of 1:2, with 0.5㎛ on each side) and laminated using a room temperature compression roll (lamination roll) to manufacture a double-sided cathode.

[0330] At this time, the conditions of the lamination were such that the diameter of a pair of facing compression rolls was 200 phi, the peripheral speed ratio of a pair of compression rolls was 1:1, and the force applied by the compression rolls was 155 kgf per 1 cm of film width.

[0331]

[0332] (2) Manufacturing of secondary batteries

[0333] A secondary battery was manufactured in the same manner as in Example 1, except that the outermost electrode (negative electrode) manufactured in Comparative Example 1 was used.

[0334]

[0335] Performance evaluation

[0336] The following evaluation was performed on the secondary batteries prepared in Example 1 and Comparative Example 1, and the results are shown in Table 1.

[0337]

[0338] Self-heating temperature

[0339] The self-heating temperature refers to the temperature at which a secondary battery begins to generate heat on its own without the application of heat, and an evaluation was conducted using an Accelerating Rate Calorimeter (ARC) to simulate the self-heating situation.

[0340] First, two identical secondary batteries were placed inside an ARC chamber, and the experiment was performed with the secondary batteries in a 100% SOC (State of Charge) state. Temperature gauges were connected to the two secondary batteries, and the two secondary batteries were fixed with a jig.

[0341] The temperature inside the ARC chamber was increased at a rate of 0.02°C per minute starting from a temperature of 50°C, and the temperature change was monitored to observe whether self-heating occurred.

[0342] At this time, if the self-heating rate increased to 0.02℃ / min or more, it was determined to be a self-heating temperature.

[0343]

[0344] thermal runaway temperature

[0345] After finding the self-heating temperature, heating was stopped to allow self-heating without external heat, and the self-heating status of the secondary battery was continuously monitored.

[0346] The thermal runaway temperature refers to the temperature at which the temperature of a secondary battery begins to rise rapidly on its own. In the self-heating temperature evaluation above, if the self-heating rate increases by 1℃ / min or more using an ARC (Accelerating rate calorimeter), it is determined to be the thermal runaway temperature.

[0347]

[0348] Heat runaway time

[0349] In the self-heating temperature evaluation, the time taken from the start of the evaluation to the thermal runaway temperature was measured using ARC.

[0350]

[0351] Maximum temperature

[0352] In the self-heating temperature evaluation, the maximum temperature observed in the ARC was measured after the secondary battery started thermal runaway.

[0353]

[0354] Self-heating temperature T1(°C) Thermal runaway temperature T2(°C) Thermal runaway time t2(min) Maximum temperature T3(°C) Reference :[0.02°C / min] Reference :[1°C / min] Reference :[1°C / min] Comparative Example 1121.2158.51495810.7 Example 1116.4157.81613763,5

[0355]

[0356] Referring to Table 1, it was confirmed that the secondary battery of Example 1 had a thermal runaway time delayed by 118 minutes and a maximum temperature reduced by 47.2°C compared to the secondary battery of Comparative Example 1.

[0357] From this, it was found that the secondary battery of Example 1 effectively suppresses the thermal runaway reaction by causing the shell of the capsule containing the flame-retardant layer of the outermost electrode to rupture at a temperature above a certain level and releasing the flame retardant.

Claims

A single cell group comprising one or more single cells; and an outermost electrode disposed on the outer side of one or more of the single cell group, and The outermost electrode comprises a current collector, an electrode active material layer provided on one side of the current collector, and a flame retardant layer provided on the other side of the current collector. The electrode active material layer of the outermost electrode is positioned opposite the outer surface of the single cell group, and The flame retardant layer comprises a plurality of capsules containing a flame retardant and a binder for the flame retardant layer that connects and fixes the plurality of capsules to each other. A secondary battery characterized in that the electrode active material layer of the outermost electrode comprises an active material and a binder, wherein the binder is fiberized to bind the active material, or wherein the electrode active material layer of the outermost electrode comprises a plurality of granules having an active material and a binder. In paragraph 1, A secondary battery characterized by comprising a flame retardant and a shell surrounding the flame retardant. In paragraph 1, A secondary battery characterized in that the flame retardant comprises an organic phosphorus compound, a fluorinated carbon compound, a brominated methane compound, or two or more of these. In paragraph 1, A secondary battery characterized by the fact that when the temperature of the secondary battery rises above the self-heating temperature, the shell of the capsule is damaged and the flame retardant contained inside the shell is released. In paragraph 1, A secondary battery characterized by the average particle size of the capsule being 30 to 170 μm. In paragraph 1, A secondary battery characterized in that the weight ratio of the capsule and the binder for the flame retardant layer in the flame retardant layer is 49:1 to 10:

1. In paragraph 1, A secondary battery characterized in that the above single cell group comprises one single cell or two or more stacked single cells. In Paragraph 7, A secondary battery characterized in that, when the above-mentioned single cell group comprises one single cell, a separator is interposed between the single cell and the outermost electrode, and when the above-mentioned single cell group comprises two or more single cells, a separator is interposed between the single cell group and the outermost electrode and between each of the single cells stacked within the single cell group. In paragraph 8, A secondary battery characterized in that the above-mentioned separator comprises a stack separator, a folding separator, or both. In paragraph 1, A secondary battery characterized by having a half cell further interposed between the above single cell group and the outermost electrode. In paragraph 1, A secondary battery characterized in that the above-mentioned fiberized binder comprises a fluorine-containing polymer. In paragraph 1, A secondary battery characterized in that the above granules are secondary particles in which one or more active material particles are connected and fixed by a binder. In paragraph 1, A secondary battery characterized by comprising: a central part containing one or more active materials; and a surface part containing a binder located on all or part of the outer side of the central part and binding the active materials. In paragraph 1, A secondary battery characterized in that the electrode active material layer of the outermost electrode comprises a plurality of granules having an active material and a binder; and a fibrous binder connecting and fixing the plurality of granules to each other. An energy storage device comprising a secondary battery according to any one of claims 1 to 14.

Images