Lithium-ion secondary battery containing electrodes manufactured by a dry process

Abstract

The dry electrode according to the present invention has a uniform distribution of binder resin and / or electrode active material in the thickness direction of the electrode active material layer, resulting in excellent adhesion between the electrode active material layer and the current collector, and improving the shape stability of the electrode active material layer. Furthermore, in the dry electrode, the electrode active material within the electrode active material layer does not align in a specific direction but has an irregular orientation. The secondary battery according to the present invention, including the dry electrode, has a decrease in ohm resistance with changes in the charge state of charge (SOC), resulting in low heat generation even when high currents such as fast charging are applied, high safety of battery operation, and advantages from the viewpoint of battery thermal management.

Description

Technical Field

[0001] The present invention relates to a secondary battery including a dry electrode manufactured by a dry method.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0101870 filed on August 3, 2023, and all the contents disclosed in the specification of the application are incorporated into this application.

Background Art

[0003] With the rapid increase in the use of fossil fuels, the demand for the use of alternative energy and clean energy has been increasing. As part of this, the fields of power generation and power storage using electrochemistry are the most actively studied. Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its application areas are continuously expanding. Among these secondary batteries, a typical lithium-ion secondary battery is not only used as an energy source for mobile devices but has also been commercialized as a power source for electric vehicles and hybrid electric vehicles that can replace fossil fuel vehicles such as gasoline vehicles and diesel vehicles, which are major causes of air pollution. Furthermore, its applications are expanding as a power auxiliary source through grid connection.

[0004] Such a lithium-ion secondary battery is manufactured through an electrode manufacturing process, an electrode assembly manufacturing process, and a forming process. Generally, in the electrode manufacturing process, after manufacturing an electrode slurry, the slurry is coated on an electrode current collector and dried. Also, subsequent processes such as a rolling process, a slitting process, and a winding process follow after drying. Here, the electrode slurry manufacturing process is a process of blending components for forming an electrode active material layer where actual electrochemical reactions occur in the electrode. More specifically, it is a process of mixing an electrode active material, which is an essential component of the electrode, a conductive material and a filler, which are other additives, a binder for binding between powders and adhesion to the current collector, and a solvent for imparting viscosity and dispersing powders, and manufacturing them in the form of a slurry having fluidity.

[0005] Thus, in electrodes where a slurry coating method has been conventionally applied to form the electrode active material layer, the binder material within the electrode is not uniformly distributed in the thickness direction of the electrode, but rather is concentrated more on the surface side of the electrode active material layer. As a result, there is a problem in that sufficient bonding force is not secured between the electrode active material layer and the current collector. This is due to a migration phenomenon in which the binder material moves to the surface side during the evaporation process of the solvent when the slurry dries.

[0006] To solve this problem, drying devices that can adjust the evaporation rate of the solvent while ensuring uniform drying of the inside and outside of the electrode active material layer are being considered. However, these drying devices are very expensive and require considerable cost and time to operate, making them unfavorable from a manufacturing process standpoint. Furthermore, during slurry drying, the electrode active material settles downwards, causing the electrode active material particles to become densely packed. This results in the formation of an electrode structure that is unfavorable for rapid charging, particularly at the negative electrode.

[0007] Therefore, in recent years, research into manufacturing dry electrodes without using solvents has been actively conducted. The dry electrode can be manufactured by scattering composite particles (electrode granules) containing an active material and a binder resin onto a current collector and then pressing the scattered electrode granules onto it. The electrode granules can be manufactured by a spray drying method, which involves uniformly dispersing electrode components (electrode active material, conductive material, binder, etc.) in a spray solution and then atomizing it. Alternatively, the electrode can also be manufactured by shear mixing the electrode active material and the binder resin under dry conditions without a solvent, and then scattering the composite powder formed by the compounding of the active material and binder resin onto a current collector and pressing it onto it. In this method, the shear force applied by the shear mixing under the dry conditions causes the binder resin to be subdivided and fibrousized, forming a composite material of the fibrous active material and the binder resin. [Overview of the project] [Problems that the invention aims to solve]

[0008] The problem that the present invention aims to solve is to provide a dry electrode and a secondary battery containing the same, in which the distribution of binder, the distribution of electrode active material, or both of these distributions in the thickness direction of the electrode active material layer is uniform. Furthermore, the present invention aims to provide a secondary battery in which at least one of the positive or negative electrode is a dry electrode manufactured by a dry manufacturing method, and in which the ohm resistance (ohm resistance, Ω) changes depending on the charge state of charge (SOC) interval.

[0009] It will be readily apparent that any other objectives and advantages of the present invention can be achieved by the means or methods and combinations thereof described in the claims. [Means for solving the problem]

[0010] This invention relates to a lithium-ion secondary battery including a dry electrode.

[0011] The aforementioned dry electrode was manufactured by a dry manufacturing method. It comprises an electrode active material layer containing an electrode active material and an electrode binder, The electrode active material layer includes granules obtained from the result of spray-drying a composition containing an electrode active material and an electrode binder, or includes a composite material in which the electrode active material and a fibrous electrode binder are compounded, or includes both thereof. The ohm resistance of the aforementioned lithium-ion secondary battery changes in accordance with the change in the State of Charge (SOC).

[0012] A second aspect of the present invention is that, in the above-described embodiment, the change in ohm resistance is such that the ohm resistance decreases as the State of Charge (SOC) increases.

[0013] A third aspect of the present invention is that, in any one of the above-described aspects, the lithium-ion secondary battery has a larger rate of change (amount of change) of ohm resistance in the initial SOC section compared to the subsequent sections.

[0014] A fourth aspect of the present invention is that, in any one of the above-described aspects, the rate of change of ohms is greater in the section before SOC 50% than in the section after SOC 50%.

[0015] A fifth aspect of the present invention is that, in any one of the above-described aspects, the electrode active material includes a negative electrode active material, and the dry electrode is the negative electrode.

[0016] A sixth aspect of the present invention is, in any one of the above-described aspects, the dry electrode comprises a current collector and an electrode active material layer located on the current collector, wherein the electrode active material layer is formed by the accumulation of granules, and the granules have an electrode binder content at the surface that is greater than the electrode binder content at the center, relative to 100% by weight of the total weight of the electrode active material and electrode binder, the surface is a region from the surface of the electrode granule to 20% of the radius toward the center of the electrode granule, and the center is the portion other than the surface.

[0017] A seventh aspect of the present invention is that, in any one of the above-described aspects, the surface portion is a region extending from the surface of the electrode granule toward the center of the electrode granule by 10% of the radius.

[0018] An eighth aspect of the present invention is that, in any one of the above-described aspects, the electrode granule has an aspect ratio (length-to-width ratio) of 0.75 to 1.0.

[0019] A ninth aspect of the present invention is, in any one of the above-described aspects, the electrode granule has a particle size (D 50 These are particles with a size of 0.1 to 1,000 μm.

[0020] A tenth aspect of the present invention is that, in any one of the above-described aspects, the electrode active material comprises two or more electrode active material materials.

[0021] An eleventh aspect of the present invention is that, in any one of the above-described aspects, the lithium-ion secondary battery has an average value of ohm resistance in the SOC 0% to SOC 20% range that is higher than the average value of ohm resistance in the SOC 80% and above range.

[0022] A twelfth aspect of the present invention is that, in any one of the above-described aspects, the lithium-ion secondary battery has lower ohm resistance in the section after 10% SOC compared to the section before 10% SOC.

[0023] A thirteenth aspect of the present invention is that, in any one of the above-described aspects, the difference between the ohm resistance value at the 80% SOC point and the 5% SOC point of the lithium-ion secondary battery is 1% or more of the difference between the minimum and maximum ohm resistance values ​​over the entire SOC measurement period.

[0024] A fourteenth aspect of the present invention is that, in any one of the above-described aspects, the lithium-ion secondary battery may have at least one tangent line with a negative slope in the graph of the rate of change of resistance over the entire SOC measurement period.

[0025] Each of the above embodiments may be implemented independently, or two or more of them may be implemented in combination. [Effects of the Invention]

[0026] The dry electrode according to the present invention has a uniform distribution of binder resin and / or electrode active material in the thickness direction of the electrode active material layer, resulting in excellent adhesion between the electrode active material layer and the current collector, and improving the morphological stability of the electrode active material layer. Furthermore, in the dry electrode, the electrode active material within the electrode active material layer does not align in a specific direction but has an irregular orientation. The secondary battery according to the present invention, including the dry electrode, has a decrease in ohm resistance with changes in the charge state of charge (SOC), resulting in low heat generation even when high currents such as fast charging are applied, high safety of battery operation, and advantages from the viewpoint of battery thermal management.

[0027] The drawings accompanying this specification illustrate preferred embodiments of the present invention and are intended to further illustrate the technical idea of ​​the invention along with the content of the invention; therefore, the present invention shall not be construed as being limited only to what is shown in the drawings. [Brief explanation of the drawing]

[0028] [Figure 1] This shows SEM images of the electrode granules confirmed in this example. [Figure 2] This shows a cross-section of an electrode manufactured by the manufacturing method according to Example 1 of the present invention. [Figure 3] This graph shows the distribution of binder content along the thickness direction of the electrode active material layer in an electrode manufactured by the manufacturing method according to Example 1 of the present invention. [Figure 4] This shows a cross-section of an electrode manufactured by the manufacturing method according to Comparative Example 3 of the present invention. [Figure 5] This graph shows the distribution of binder content along the thickness direction of the electrode active material layer in an electrode manufactured by the manufacturing method according to Comparative Example 3 of the present invention. [Figure 6] This is a schematic diagram of an electrode relating to one embodiment of the present invention. [Figure 7] This is a schematic diagram for calculating the QBR value of the electrode layer. [Figure 8] This image shows a cross-sectional view of the electrode granules produced in Example 1. [Figure 9] This image shows a cross-sectional view of the electrode granules produced in Example 2. [Figure 10] This image shows a cross-sectional view of the electrode granules produced in Example 3. [Figure 11] This image shows a cross-sectional view of the electrode granules produced in Comparative Example 1. [Figure 12] This image shows a cross-sectional view of the electrode granules produced in Comparative Example 2. [Figure 13]This graph shows the binder resin content from the center to the surface of the electrode granule particles obtained in Example 1, Example 2, and Comparative Examples 1 to 3. [Figure 14] This graph shows the binder resin content from the center to the surface of the electrode granule particles obtained in Example 1, Example 2, Comparative Example 1, and Comparative Example 2. [Figure 15] This is a photographic image showing a group of electrode granules fixed within a cured epoxy resin. [Figure 16] This is a schematic diagram illustrating the distinction between the surface and central part of the electrode granules of the present invention. [Figure 17] This shows the measured ohm resistance (ohm resistance, Ω) for each SOC interval in the battery according to each embodiment of the present invention. [Figure 18] This shows the rate of change in ohm resistance (ohm resistance, Ω resistance) for each SOC interval in batteries according to the embodiments and comparative examples of the present invention. [Figure 19] This shows the charge transfer (CT) resistance and ohm resistance for each state of charge (SOC) in batteries according to each embodiment of the present invention. [Modes for carrying out the invention]

[0029] The present invention will be described in detail below. However, the present invention is not limited to the following, and each component may be modified or selectively mixed as needed. Therefore, it should be understood that this includes all modifications, equivalents or substitutes that fall within the spirit and technical scope of the present invention.

[0030] Throughout this specification, when a configuration is described as "including" a component, this does not mean that it excludes other components, unless otherwise specified, but rather that it may include other components.

[0031] Furthermore, terms such as “about” and “substantially” used throughout this specification are used to mean, when manufacturing and material tolerances specific to the meaning mentioned are presented, in or near that value, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that mention precise or absolute numerical values ​​in order to aid in understanding the invention.

[0032] Throughout this specification, the phrase "A and / or B" means "A or B or both."

[0033] The specific terms used herein are for convenience only and are not limiting. Terms such as “up,” “down,” “left,” “right,” “front,” “back,” “inside,” and “outside” are used to describe the relative position or direction between components, rather than absolute position, or to indicate position or direction in the referenced drawings. These terms include not only the terms themselves, but also words containing them, their derivatives, and words with similar meanings.

[0034] The "glass transition temperature (Tg)" as used herein is measured by conventional methods known in the art, and may be measured by differential scanning calorimetry (DSC), for example.

[0035] In this specification, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume in a given structure, with the unit vol%, and can be used interchangeably with terms such as void ratio and porosity. In the present invention, the measurement of porosity is not particularly limited, but according to one embodiment of the present invention, it can be measured, for example, by the Brunauer-Emmett-Teller (BET) measurement method using nitrogen gas, or by the mercury infiltration method (Hg porosimeter) and based on the American Society for Testing and Materials (ASTM) D-2873. Alternatively, the true density can be calculated from the density (apparent density) of the object to be measured, the composition ratio of the materials contained in the object, and the density of each component, and the porosity can be calculated from the difference between the apparent density and the true density.

[0036] The term "average particle size (D)" used in this specification 50 )" refers to the particle size at the 50% point of the cumulative particle number distribution by particle size. 50 Laser diffraction can be used to measure particle sizes such as those of [specific particles]. Specifically, the powder to be measured is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns corresponding to particle size as the particles pass through the laser beam is measured to calculate the particle size distribution. By calculating the particle size at the 50% point of the cumulative particle number distribution by particle size in the measuring device, D 50 The particle size can be measured.

[0037] In this specification, the "thickness" of each layer contained in the electrode may refer to a value measured by a known method for measuring thickness. The method for measuring thickness is not limited to this, but for example, it may be a value measured using a thickness measuring instrument (Mitutoyo Corporation, VL-50S-B).

[0038] As used herein, "specific surface area" may refer to a value measured by a known method for measuring specific surface area. The method for measuring specific surface area is not limited to, but may include, for example, a flow-type or fixed-type method.

[0039] The present invention relates to a secondary battery comprising a dry electrode manufactured by a dry manufacturing method. The secondary battery may be a lithium-ion secondary battery.

[0040] The dry electrode may include an electrode active material layer comprising an electrode active material and an electrode binder. The electrode may further include a current collector, and the electrode active material layer may be arranged on one or both sides of the current collector.

[0041] In one embodiment of the present invention, the dry electrode includes an electrode active material layer, which may be formed by the accumulation of electrode granules under pressure. Alternatively, the electrode active material layer may be formed by compressing an electrode powder, which is a composite of the electrode active material and a fibrous electrode binder, into a film. Furthermore, the electrode active material layer may be formed by mixing the granules and the electrode powder and accumulating them under pressure.

[0042] In this invention, the term "dry electrode" means a product manufactured by accumulating the electrode granules and / or electrode powder into a layered structure by pressurization, i.e., including the electrode active material layer. Specifically, the granules and / or electrode powder can be sprayed to a predetermined thickness on the surface of a current collector and then pressed together with the current collector to manufacture an electrode, or the material itself can be accumulated into a layered structure of a predetermined thickness by pressurization (or made into a film) and then bonded to the current collector. Here, the spraying and pressurizing steps of the granules and / or electrode powder are performed dry without the addition of a solvent, and are distinguished from the prior art in that a solvent is not used in the manufacturing process of the electrode active material layer, unlike the prior art in which a slurry mixed with a solvent is applied and dried.

[0043] A lithium-ion secondary battery according to one embodiment of the present invention can be manufactured by forming an electrode assembly by placing an insulating film between a positive electrode and a negative electrode, housing the electrode assembly in, for example, a pouch-type battery case, a cylindrical battery case, or a rectangular battery case, and then injecting an electrolyte. Alternatively, it can be manufactured by stacking the electrode assemblies, impregnating them with an electrolyte, housing the resulting product in a battery case, and sealing it. The insulating film may be a separator, a solid electrolyte membrane, or both.

[0044] In one embodiment of the present invention, the secondary battery according to the present invention can change its ohm resistance in response to changes in the State of Charge (SOC).

[0045] In the present invention, the secondary battery is not limited to a charge / discharge rate, and changes in ohm resistance, as described below, can be observed within the range. For example, the secondary battery can be charged and discharged at a rate of 0.001C to 10C or 0.001C to 5C.

[0046] In one embodiment of the present invention, the secondary battery, which includes at least one dry electrode among a negative electrode and a positive electrode, may exhibit a tendency for its ohm resistance to decrease as the State of Charge (SOC) increases. Figure 17 shows the results of measuring the ohm resistance at different SOC intervals using the lithium-ion secondary battery according to the present invention. Furthermore, referring to Figure 18, the lithium-ion secondary battery according to the present invention may exhibit a tendency for the rate of change of the battery's ohm resistance to become negative (-) as the SOC increases during charging. In the present invention, the rate of change of ohm resistance may be greater in the interval before SOC 50% than in the interval after SOC 50%. That is, the rate of change of ohm resistance may show a pattern of decreasing more sharply in the interval from the first measured SOC point to SOC 20%, or to SOC 30%, or to SOC 50%, than in the interval from SOC 20% to the final measured SOC point, or from SOC 30% to the final measured SOC point, or from SOC 50% to the final measured SOC point.

[0047] In this specification, the initial SOC measurement point may be any point between SOC 0% and SOC 10%. For example, it may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The initial SOC measurement point may also be a point where ohm resistance can be separated. On the other hand, the final SOC measurement point may be any point after SOC 70%, 75%, 80%, or 90%. For example, it may be 75%, 80%, 85%, or 90%.

[0048] Ohm resistance, one of the resistive components of electrochemical elements such as batteries, has the property of hindering the flow of current and tends to change in resistance value depending on the magnitude of the applied current. In the case of dry electrodes, there is no process that induces particle orientation, as in the drying of wet slurries, so the active material particles in the electrode active material layer tend not to be oriented in a consistent direction. For this reason, during charging and discharging of the battery, the direction of volume change of the electrode active material particles becomes non-uniform, and separation may occur between the electrode active material particles. The change in ohm resistance during charging in batteries containing dry electrodes may be due to this non-uniform direction of volume change of the electrode active material particles. (Despite the change in ohm resistance,) Also, when manufacturing electrodes by the dry method, there are many exposed basal planes in the electrode active material particles, so the overall resistance, including ohm resistance, decreases, and the kinetics of the electrode tend to become faster. In one embodiment of the present invention, the dry electrode may be a negative electrode, and the negative electrode may include a negative electrode active material that exhibits volume expansion during charging and discharging, such as a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a tin-based negative electrode active material.

[0049] Referring to Figure 18, such a significant decrease in ohmic resistance is not observed in the electrode manufactured by the wet method of Comparative Example 3. This is because, when electrodes are manufactured by drying a wet slurry, the electrode active material settles to the bottom of the slurry and accumulates densely during the slurry drying process, potentially leading to a high degree of orientation, such as parallel arrangement of particles. In particular, carbon materials such as graphite tend to accumulate in a manner that increases orientation. Therefore, the volume change of the electrode active material during battery charging and discharging may exhibit a specific direction, but in such volume changes, the change in spacing between active material particles is small. As described above, it is presumed that wet electrodes exhibit a low rate of separation between electrode active material particles even during volume changes during charging and discharging, resulting in a small or no change in ohmic resistance. Furthermore, wet electrodes have the characteristic of having very little exposure of the base surface during such a drying process.

[0050] In one embodiment of the present invention, the average value of the ohm resistance of the secondary battery from the initial measured SOC point to the 20% SOC interval may be higher than the average value of the ohm resistance in the interval from 80% SOC onward. In this specification, "subsequent interval" means the interval up to the final measured SOC point. For example, the initial measurement point may be 0% SOC, and the interval from 80% SOC onward may be up to 100% SOC, but is not limited to this. On the other hand, the average value of the resistance means the average value calculated after measuring the ohm resistance at predetermined intervals, for example, 1% SOC intervals, and summing up the ohm resistance values ​​at each SOC in said interval.

[0051] In one embodiment of the present invention, the ohm resistance value of the secondary battery at any point in the interval before SOC 10% may be higher than the ohm resistance value at any point in the interval after SOC 10%, or after SOC 20%, or after SOC 30%, or after SOC 40%, or after SOC 50%, or after SOC 60%, or after SOC 70%, or after SOC 80%.

[0052] In one embodiment of the present invention, the ohm resistance value of the secondary battery at any point in the interval before SOC 20% may be higher than the ohm resistance value at any point in the interval after SOC 20%, or after SOC 30%, or after SOC 40%, or after SOC 50%, or after SOC 60%, or after SOC 70%, or after SOC 80%.

[0053] In one embodiment of the present invention, the ohm resistance value of the secondary battery at any point in the interval before SOC 30% may be higher than the ohm resistance value at any point in the interval after SOC 30%, or after SOC 40%, or after SOC 50%, or after SOC 60%, or after SOC 70%, or after SOC 80%.

[0054] In one embodiment of the present invention, the ohm resistance of the secondary battery may be lower in the section after SOC 10% compared to the section before SOC 10%. In one embodiment of the present invention, the ohm resistance of the secondary battery may be lower in the section after SOC 20% compared to the section before SOC 20%. In one embodiment of the present invention, the ohm resistance of the secondary battery may be lower in the section after SOC 30% compared to the section before SOC 30%.

[0055] In one embodiment of the present invention, the difference between the ohm resistance value at the 80% SOC point and the ohm resistance value at the 5% SOC point or the first point where ohm resistance can be separated may be 1% or more, 3% or more, 5% or more, 10% or more, 20% or more, or 30% or more relative to the difference between the minimum and maximum ohm resistance values ​​over the entire SOC measurement period.

[0056] In one embodiment of the present invention, the difference between the ohm resistance value at the 50% SOC point and the ohm resistance value at the 5% SOC point or the first point where ohm resistance can be separated is 1% or more, 3% or more, 5% or more, 10% or more, 20% or more, or 30% or more relative to the difference between the minimum and maximum ohm resistance values ​​over the entire SOC measurement period.

[0057] In one embodiment of the present invention, the difference between the ohm resistance value at the 30% SOC point and the ohm resistance value at the 5% SOC point or the first point where ohm resistance can be separated is 1% or more, 3% or more, 5% or more, 10% or more, 20% or more, or 30% or more relative to the difference between the minimum and maximum ohm resistance values ​​over the entire SOC measurement period.

[0058] In one embodiment of the present invention, when the rate of change (amount of change) of the resistive component, particularly the ohm resistance, over the entire SOC measurement period of the lithium-ion secondary battery is observed, any one or more tangents may show a negative slope. In one embodiment of the present invention, the rate of change (amount of change) of the ohm resistance in the initial SOC period of the secondary battery, specifically the lithium-ion secondary battery, may be larger than that in subsequent periods. Preferably, the rate of change (amount of decrease) of the ohm resistance means the rate of decrease (amount of decrease) of the ohm resistance, and the rate of decrease (amount of decrease) of the ohm resistance in the initial period may be larger than that in subsequent periods. In one specific embodiment, the rate of decrease (amount of decrease) of the ohm resistance in the period from the first measured SOC point (e.g., SOC 0%) to SOC 20% may be larger than that in the period after SOC 20%. Also, the rate of decrease of the ohm resistance in the period from the first measured SOC point (e.g., SOC 0%) to SOC 30% may be larger than that in the period after SOC 30%. Alternatively, the ohm resistance reduction rate of the battery may be greater in the section from the initially measured SOC point (e.g., SOC 0%) to the SOC 40% section compared to the section after SOC 40%. Alternatively, the ohm resistance reduction rate of the battery may be greater in the section from the initially measured SOC point (e.g., SOC 0%) to the SOC 50% section compared to the section after SOC 50%.

[0059] On the other hand, in the present invention, the rate of change of ohm resistance can be calculated based on the following formula 1.

[0060] (Equation 1) Ohmic Resistance Change = (R) soc / R i ) × 100%

[0061] In the above formula 1, R i R is the ohm resistance at the lowest SOC at which it is possible to separate ohm resistance and charge transfer resistance from the Nyquist plot. soc This represents the ohm resistance at each SOC.

[0062] As described above, dry electrodes exhibit the aforementioned ohm resistance change in both fibrous binder electrodes and granular binder electrodes, due to the non-uniform orientation of the electrode active material particles contained in the electrode active material layer. In particular, the ohm resistance change is more pronounced in the granular binder type, as can be seen in the examples described later, and is even more pronounced in granular binder electrodes where the binder resin is unevenly distributed on the surface.

[0063] On the other hand, according to Joule's Law, power is proportional to the product of the square of the current and the resistance, so the amount of heat generated increases as the current and resistance increase during battery operation. In the case of a secondary battery to which the dry electrode of the present invention is applied, the ohm resistance decreases in the range where rapid charging is mainly performed, such as SOC 15% to SOC 85% or SOC 20% to SOC 80%, which is advantageous from the viewpoint of battery heat management and safety improvement.

[0064] In this invention, the resistance value to SOC can be confirmed by measurement using in situ EIS (Electrochemical Impedance Spectroscopy). This method involves connecting two channels to a single jig, allowing charging to proceed in one channel, and measuring EIS in the other channel at predetermined time intervals or predetermined SOC intervals, thereby enabling simultaneous measurement of EIS. The EIS measurement interval can be 1% intervals of SOC. In one embodiment, multiple charge-discharge cycles can be performed, and the average value of the EIS results measured at each SOC can be used as a representative value. Here, the EIS measurement method can be the EIS measurement method for electrochemical elements that is commonly applied in this art. On the other hand, the charging and discharging of the battery and the EIS measurement can be performed at room temperature. From the Nyquist plot obtained at this time, the ratio of ohm resistance and charge transfer (CT) resistance can be calculated, respectively. Figure 19 shows the ohm resistance and charge transfer resistance values ​​and their ratios for different states of charge (SOCs) measured using the batteries of Examples 1, 2, and 4. Referring to this figure, it was confirmed that the ohm resistance of the secondary battery according to the present invention decreases with increasing SOC. It was also confirmed that the charge transfer resistance decreases along with it. However, it was confirmed that the battery including the wet electrode according to Comparative Example 3 showed a slight decrease in charge transfer resistance, but the degree of change in ohm resistance with respect to SOC changes was significantly lower compared to the present invention.

[0065] On the other hand, in the present invention, the State of Charge (SOC) is expressed as a percentage (%) by dividing the currently usable battery capacity by the total capacity, in order to indicate the remaining capacity of the battery. The SOC can be calculated using the current integration method. According to the current integration method, the SOC can be calculated by integrating the input and output currents of the battery and adding or subtracting this from the initial capacity. Here, the current can be measured by a current sensor provided in the battery's charge and discharge path.

[0066] The components of the lithium-ion secondary battery according to the present invention will be described in detail below.

[0067] <Granules for electrodes> In the present invention, the electrode granule may have the form of a composite particle containing an electrode active material, an electrode binder, and optional components that may be added as needed. In one embodiment of the present invention, the electrode granule may be a secondary particle formed by granulating two or more electrode active material particles bound together by the electrode binder. In the present invention, the electrode active material may mean an aggregate of particles, where the diameter of each particle of the electrode active material may be 0.05 μm to 2 μm. In one embodiment of the present invention, the electrode active material may be 80% or more by weight or 90% or more by weight of the total weight of the electrode granule, and the electrode binder may be included in an amount of 20% or less by weight or 10% or less by weight. In one embodiment of the present invention, the electrode granule may further include an electrode conductive material as an optional component, as needed. The electrode conductive material may be included in an amount of 0.1% to 20% by weight, preferably 0.1% to 10% by weight, based on 100% by weight of the electrode granule. For example, the conductive material in the electrode granule may be present in an amount ranging from approximately 0.1% to 5% by weight.

[0068] According to one embodiment of the present invention, the content of the electrode active material in the electrode granule may be 85% to 98% by weight. Within this range, the content of the electrode binder may be 0.5% to 10% by weight, and the content of the electrode conductive material may be 0.5% to 5% by weight. According to another embodiment, the content of the electrode active material may be 90% to 98% by weight, the content of the electrode binder may be 0.5% to 5% by weight, and the content of the electrode conductive material may be 0.5% to 5% by weight.

[0069] FIG. 16 schematically shows the surface portion and the central portion of the granule for an electrode of the present invention. Referring to the figure, in the present invention, in the granule for an electrode, the amount of the electrode binder contained in the surface portion 102 of the granule for an electrode can be larger than the amount of the electrode binder contained in the central portion 101 of the granule for an electrode. Alternatively, the granule for an electrode may show a tendency that the content of the binder resin increases from the central portion toward the surface portion. The amount of the binder may mean weight or volume.

[0070] Together with or independently of this, with respect to 100% by weight of the total weight of the granule for an electrode, the content (% by weight) (B c / G t ) of the electrode binder contained in the central portion 101 of the granule for an electrode, the content (% by weight) (B s / G t ) of the electrode binder contained in the surface portion (102) of the granule for an electrode can be higher. Here, the B c is the weight of the binder contained in the central portion, B s is the weight of the binder contained in the surface portion, and G t means the weight of the entire granule for an electrode particle.

[0071] Together with or independently of this, with respect to 100% by volume of the total volume of the granule for an electrode, the content (% by volume) (B c / G t ) of the electrode binder contained in the central portion 101 of the granule for an electrode, the content (% by volume) (B s / G t ) of the electrode binder contained in the surface portion 102 of the granule for an electrode can be higher. Here, the B[[ID=3I]] c is the volume of the binder contained in the central portion, B s is the volume of the binder contained in the surface portion, and G t means the volume of the entire granule for an electrode particle.

[0072] Here, the surface portion may mean the area near the surface of the electrode granule from the surface of the electrode granule to a predetermined depth toward the center of the electrode granule. The center portion means the portion other than the surface portion. In one embodiment of the present invention, the surface portion may mean the surface area extending inward from the surface of the electrode granule, specifically toward the center of the electrode granule, up to 30% of the radius. In one embodiment of the present invention, the surface portion may mean the surface area from the surface of the electrode granule to 30% of the radius, the surface area up to 20% of the radius, the surface area up to 15% of the radius, the surface area up to 10% of the radius, or the surface area up to 5% of the radius. Preferably, the surface portion may mean the surface area from the surface of the electrode granule to 20% of the radius.

[0073] In one embodiment of the present invention, the surface portion may mean the region from the center of the electrode granule outward from the electrode granule to the electrode granule surface beyond 70% of the radius. In one embodiment of the present invention, the surface portion may mean, for example, the region from the center of the electrode granule to the electrode granule surface beyond 80% of the radius, beyond 85% of the radius, beyond 90% of the radius, or beyond 95% of the radius.

[0074] In one embodiment of the present invention, the center of the electrode granule may mean the point at half the longest diameter of the electrode granule. In the present invention, the radius may mean the distance from the center of the electrode granule to each point on the surface of the electrode granule. In one embodiment of the present invention, along each radius, the surface and the center can be divided based on points equal to the distance from the surface of the electrode granule, specifically, points up to 30% of the radius from the surface, up to 20% of the radius, up to 10% of the radius, up to 5% of the radius, or up to 1% of the radius.

[0075] In one embodiment of the present invention, in the region from the center of the electrode granule to the electrode granule surface beyond 90% of the radius, the content of the electrode binder relative to 100% of the total weight of the electrode granule in that region may be 50% or more by weight, 60% or more by weight, 70% or more by weight, 80% or more by weight, or 90% or more by weight.

[0076] In another embodiment of the present invention, in the region from the center of the electrode granule to the electrode granule surface at a radius of 95% or more, the content of the electrode binder relative to 100% by weight of the total weight of the electrode granule in that region may be 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0077] In yet another embodiment of the present invention, in the region from the center of the electrode granule to the electrode granule surface at 99% or more of its radius, the content of the electrode binder relative to 100% by weight of the total weight of the electrode granule in that region may be 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0078] In one embodiment of the present invention, in the region from the center of the electrode granule to the electrode granule surface at a radius of 90% or more, the content of the electrode binder relative to 100% of the total volume of the electrode granule in that region may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0079] In another embodiment of the present invention, in the region from the center of the electrode granule to the electrode granule surface at a radius of 95% or more, the content of the electrode binder relative to 100% of the total volume of the electrode granule in that region may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0080] In yet another embodiment of the present invention, in the region from the center of the electrode granule to the electrode granule surface at 99% or more of its radius, the content of the electrode binder relative to 100% of the total volume of the electrode granule in that region may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0081] In one embodiment of the present invention, in the surface region of the electrode granule from the surface of the electrode granule to 10% of the radius, the content of the electrode binder relative to 100% of the total mass of the electrode granule in that region may be 50% or more by weight, 60% or more by weight, 70% or more by weight, 80% or more by weight, or 90% or more by weight.

[0082] In another embodiment of the present invention, in the surface region of the electrode granule up to 5% of the radius from the surface of the electrode granule, the content of the electrode binder relative to 100% by weight of the total mass of the electrode granule in that region may be 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0083] In yet another embodiment of the present invention, in the surface region of the electrode granules up to 1% of the radius from the surface of the electrode granules, the content of the electrode binder relative to 100% by weight of the total mass of the electrode granules in that region may be 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0084] In one embodiment of the present invention, in the surface region of the electrode granule from the surface of the electrode granule to 10% of the radius, the content of the electrode binder relative to 100% of the total volume of the electrode granule in that region may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0085] In another embodiment of the present invention, in the surface region of the electrode granule up to 5% of the radius from the surface of the electrode granule, the content of the electrode binder relative to 100% of the total volume of the electrode granule in that region may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0086] In yet another embodiment of the present invention, in the surface region of the electrode granule up to 1% of the radius from the surface of the electrode granule, the content of the electrode binder relative to 100% of the total volume of the electrode granule in that region may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0087] Figure 1 schematically shows an SEM image of electrode granule particles according to an embodiment of the present invention. Referring to the figure, in the electrode granules, a surface region with a high binder content is observed from the surface toward a predetermined depth towards the particle center, and in the part other than the surface, i.e., the central part (core) surrounded by the surface, the binder distribution is less than in the surface.

[0088] More specifically, the electrode granule may comprise a central part containing multiple electrode active materials, and a surface part located on all or part of the outside of the central part, containing an electrode binder that binds the electrode active materials together. That is, in the central part of the electrode granule, the multiple electrode active materials form aggregates 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 electrode granule, the electrode binder is located on part or all of the outside of such aggregates, fixing and binding the multiple electrode active materials in the central part to each other.

[0089] According to one embodiment of the present invention, the central part also contains a small amount of electrode binder, which can serve to connect and fix the multiple electrode active materials in the central part to each other. However, as mentioned above, it is desirable that the ratio of electrode binder content in the surface part is higher than that in the central part.

[0090] On the other hand, in one embodiment of the present invention, the electrode granule may preferably have an aspect ratio of more than 0.75 and more than 1.0. The aspect ratio may mean the ratio of the minor axis length to the major axis length of the electrode granule. In another embodiment of the present invention, the average aspect ratio of the electrode granule may have a value of 0.5 to 1.0, preferably 0.75 to 1.0, in which case the average aspect ratio may mean the ratio of the average minor axis length to the average major axis length of the electrode granule particles. In this case, the average minor axis length may represent the average length in the axial direction having the shortest length of the electrode granule, and the average major axis length may represent the average length in the axial direction having the longest length of the electrode granule. When the aspect ratio of the electrode granule satisfies such a range, it is advantageous from the viewpoint of having sufficient fluidity suitable for the process.

[0091] On the other hand, in one embodiment of the present invention, the particle size of the electrode granule may be in the range of 0.1 to 1000 μm based on the longest diameter of the particle. In another embodiment of the present invention, the average particle size (D50) of the electrode granule may be in the range of 0.1 to 1000 μm.

[0092] <Electrode powder and method for manufacturing the same> In the present invention, the electrode powder comprises an electrode active material and an electrode binder, and may further contain optional components such as a conductive material as needed. The electrode powder comprises a finely fibrous electrode binder as described below, and may have a form in which electrode materials such as electrode active material particles are bound together by the fine fibers of the electrode binder.

[0093] In one specific embodiment, the electrode powder may be obtained by a manufacturing method comprising: (a) a step of manufacturing a powdery blend containing an electrode active material, a conductive material, and a binder resin; (b) a step of kneading the powdery blend to manufacture a mixture mass; and (c) a step of crushing the mixture mass to obtain a mixed powder for electrodes.

[0094] First, the electrode active material and the electrode binder are mixed to obtain a uniform dry powder blend (a). The powder blend may further contain optional materials such as conductive materials as needed. The mixing is not particularly limited as long as it is a dry mixing method, and can be carried out by putting the electrode material into a device such as a mixer or blender. In one embodiment of the present invention, the mixing is preferably carried out so that the degree of crystallinity of the binder resin in the obtained dry powder blend is 50% or less, and the process conditions can be controlled to achieve such a degree of crystallinity. For example, the mixing time can be controlled in the range of 1 second to 20 minutes. The temperature of the mixture can be controlled in the range of 20°C to 70°C. The mixing can also be carried out in a mixer under process conditions of 500 rpm to 20,000 rpm, 5,000 rpm to 20,000 rpm, or 1,000 rpm to 15,000 rpm, or 10,000 rpm to 15,000 rpm.

[0095] Next, the powdered blend obtained above is applied to a kneading process to fibrousize the electrode binder (b). Through this kneading process, the binder resin is fibrousized while the electrode active material and conductive material powder are bonded or linked together, forming a mass-like blend. The fibrousization refers to the process of finely dividing a polymer, and for example, by applying mechanical shear force, a large number of fine fibers (fibrils) are generated.

[0096] The kneading described above is not limited to any particular method. In one specific embodiment of the present invention, the kneading may be carried out using a mixing machine such as a kneader. For example, the kneader may be a twin-screw extruder, a single-screw extruder, a batch kneader, a continuous kneader, etc.

[0097] In one embodiment of the present invention, the kneading can be controlled at a speed of 10 rpm to 100 rpm. For example, the kneading can be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. On the other hand, in one embodiment of the present invention, the kneading process can be controlled at a shear rate in the range of 5 / sec to 1000 / sec. In one specific embodiment of the present invention, the kneading can be carried out for 1 minute to 30 minutes, and the shear rate can be controlled in the range of 10 / sec to 500 / sec. On the other hand, the kneading can be carried out at a temperature in the range of 70°C to 200°C, more specifically 90°C to 150°C. The temperature may be the temperature inside the kneader, the temperature of the object being kneaded, or both temperatures may be controlled within the above range.

[0098] If the process is carried out at a temperature outside the aforementioned range, the fibrous formation of the binder and the agglomeration by kneading are not sufficiently achieved during the kneading process, resulting in the problem that film formation does not occur easily during calendering. On the other hand, if the process is carried out at an excessively high temperature, the fibrous formation of the binder proceeds rapidly, and there is a problem that the already formed fibers may be cut by the excessive shear force thereafter, which is undesirable. As mentioned above, since the kneading process is carried out at a high temperature and with a relatively low shear force, there is no concern about pulverization / damage of the electrode active material or cutting of the binder fibers, and an electrode powder containing finely fibrous binder resin can be obtained. Furthermore, the fibrous binder resin has high uniformity in fiber thickness and / or length.

[0099] On the other hand, although the binder resin may undergo fibrous formation in step (a), the fibers formed in step (a) are large in diameter and difficult to finen to the extent necessary to achieve the tensile strength and tensile elongation required by the dry electrode. In the present invention, preferably, the fine fibrous formation of the binder resin is carried out mainly through step (b).

[0100] Non-limiting examples of binder resins suitable for the fiberization process include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or mixtures of two or more of these, more specifically, polytetrafluoroethylene (PTFE), and even more specifically, polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) may be present in an amount of 30% by weight or more based on the total weight of the binder resin. On the other hand, it goes without saying that the binder resin may further contain, in addition to the above-mentioned components, polyethylene oxide (PEO) and / or polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), etc.

[0101] Next, the lump-like blend produced by the kneading process is pulverized again to obtain a mixed powder for electrodes. At this time, the pulverization is not particularly limited and can be carried out using known pulverizing equipment such as a blender or grinder. In one embodiment of the present invention, from the viewpoint of film formation, the particle size of the obtained mixed powder for electrodes may preferably be in the range of 30 μm to 180 μm.

[0102] On the other hand, in the present invention, the degree of crystallinity (c) of the binder resin contained in the electrode mixed powder may be 20% or less. Such a degree of crystallinity can be adjusted by adjusting at least one of the process conditions, namely the kneading time, kneading temperature, rotation speed (rpm), and shear rate.

[0103] <Dry Electrode> A dry electrode according to one aspect of the present invention is an electrode for an electrochemical element comprising a current collector and an electrode active material layer located on the current collector. The electrode active material layer may be formed by accumulating an electrode granule or electrode powder, or both thereof, containing an electrode active material and an electrode binder, having the aforementioned structural characteristics, into a layered structure by pressurization.

[0104] The electrode active material layer and current collector will be explained in more detail below.

[0105] <Electrode active material layer> The electrode active material layer contains an electrode active material and an electrode binder. In the present invention, the electrode active material layer may have a form in which the electrode granules, electrode powder, or both are pressurized and accumulated in a layered structure. When the electrode granules are introduced into an electrode, the aspect ratio or particle size range may not be maintained in its initial state due to the calendering process described later. The electrode active material layer may contain 80% or more, 90% or more, 95% or more, or 99% or more of the electrode granules based on 100% by weight of the electrode active material layer. On the other hand, in one embodiment, the electrode active material layer may further contain electrode active material, electrode binder, and electrode conductive material that have undergone a granulation process but are not incorporated into the electrode granules and exist in a free state. It may also further contain electrode granule particles whose aspect ratio and / or particle size range do not fall within the above-mentioned ranges.

[0106] In one embodiment of the present invention, the electrode active material layer preferably has a porosity of 20% to 40% by volume from the viewpoint of electrolyte impregnation, morphological stability, and ionic conductivity. In one embodiment of the present invention, the electrode active material layer into which the electrode granules are introduced has pores provided by the interstitial volume, which is the space between the electrode granules, and may exhibit porous characteristics derived from such a structure.

[0107] On the other hand, according to one embodiment, the thickness of the electrode active material layer may be, for example, 30 μm to 300 μm, but is not limited thereto.

[0108] According to another embodiment of the present invention, the electrode active material layer may be configured as a single layer comprising one unit active material layer.

[0109] According to yet another embodiment of the present invention, the electrode active material layer may have a multilayer structure in which two or more unit active material layers are stacked. In this case, the electrode materials contained in each unit active material layer, such as electrode active material and electrode binder, may be the same or different from each other in each layer, and are not limited to this. Furthermore, each layer may optionally contain an electrode conductive material, and in this case, the electrode conductive material may also be the same or different from each other in each layer.

[0110] Furthermore, in one embodiment of the present invention, the electrode active material layer has a uniform binder distribution in the thickness direction. In a specific embodiment, the electrode active material layer may have a difference of 10% by weight or less between the binder content (by weight) in the upper 100% by weight and the binder content (by weight) in the lower 100% by weight, based on the point where the electrode active material layer is 50% from the current collector. Also, based on the thickness of the electrode active material layer, the difference in binder content between the region from the current collector to the electrode surface layer up to 15% thickness and the region from the electrode active material layer surface layer to the current collector up to 15% thickness may be 10% by weight or less.

[0111] Such binder distribution may be due to the fact that the electrode active material layer according to the present invention is manufactured by pressing the electrode granules and / or electrode powder. As described below, the electrode manufacturing method of the present invention is characterized by manufacturing electrode granule particles or electrode powder containing electrode material, then scattering them to a predetermined thickness on a current collector or release paper, and then pressurizing them to accumulate. In the case of an electrode manufacturing method involving slurry manufacturing, binder migration is induced by solvent evaporation during slurry drying, causing the binder to concentrate and distribute on the surface of the electrode. However, in the present invention, since a method is applied in which dry electrode granule particles and / or electrode powder are pressed and accumulated without using a solvent, the binder migration phenomenon does not occur. As a result, the binder shows a uniform distribution in the thickness direction in each unit layer.

[0112] <Electrode material> According to one embodiment, the electrode active material layer may include an electrode active material and an electrode binder, and may further include an electrode conductive material as needed. For example, the mixing ratio of the electrode active material, electrode conductive material and electrode binder in the electrode active material layer may be 80 to 99 parts by weight: 0.5 to 10 parts by weight: 0.5 to 10 parts by weight of electrode active material: electrode conductive material: electrode binder, and more specifically, 90 to 99 parts by weight: 0.5 to 5 parts by weight: 0.5 to 10 parts by weight.

[0113] The electrode may be a positive electrode or a negative electrode.

[0114] When the electrode is the positive electrode, the positive electrode active material is a lithium transition metal oxide or lithium metal phosphate, and is not particularly limited as long as it is in the form of a metal oxide, 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; chemical formula Li 1+x Mn 2-xO4 (where x = 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3), Ni-site type lithium nickel oxide represented by; chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); a part of Li in the chemical formula is substituted with aluminum ion, Li 1+x (Ni a Co b Mn c Al d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1); lithium metal phosphate LiM<00​​​​​​​​​​​​​​​​​​(0 < x ≤ 2), silicon-based materials such as SiO, SiO / C, and SiO2; tin-based materials such as SnO and SnO2; metal oxides such as PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. are used, but not limited thereto. On the other hand, in order to exhibit the above-described change pattern of ohmic resistance, the electrode active material may include one or more of graphite-based carbon materials, silicon, silicon-based alloys, silicon-based materials, tin, tin-based alloys, and tin-based materials having a high volume expansion rate associated with charge and discharge.

[0116] On the other hand, in one embodiment of the present invention, the electrode active material may include two or more different electrode active material materials. Specifically, the granular particles for electrodes may include two or more different electrode active material materials within one particle. The electrode active material material is not particularly limited as long as it is the above-described component. For example, the granular particles for electrodes may include artificial graphite and natural graphite as the electrode active material, and the artificial graphite and natural graphite may be mixed at a predetermined ratio.

[0117] The electrode conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. More specifically, to ensure uniform mixing of the electrode conductive material and improve conductivity, it may contain one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may contain activated carbon. On the other hand, in one embodiment of the present invention, the electrode granule particles may contain two or more different conductive materials within a single particle. For example, the electrode granule may contain a mixture of carbon black and carbon nanotubes as conductive materials in a predetermined ratio.

[0118] In the present invention, the electrode binder is not particularly limited as long as it is used as a binder material for electrochemical elements, and may include, for example, diene polymers, acrylate polymers, olefin polymers, fluorine polymers, styrene polymers, or two or more of these.

[0119] Examples of the diene polymer include polymers containing monomer units derived from conjugated dienes such as butadiene and isoprene, and hydrogenated versions thereof. The proportion of monomer units derived from conjugated dienes in the diene polymer is usually 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more.

[0120] Specific examples of the aforementioned diene polymers include conjugated diene homopolymers such as polybutadiene and polyisoprene; aromatic vinyl-conjugated diene copolymers such as styrene-butadiene copolymer (SBR), which may be carboxylated; cyanated vinyl-conjugated diene copolymers such as acrylonitrile-butadiene copolymer (NBR); and hydrogenated SBR, hydrogenated NBR, etc.

[0121] The styrene-based polymer is a polymer having repeating units derived from styrene monomers, and examples include styrene homopolymers (polystyrene) and styrene copolymers. Examples of the styrene-based copolymer include styrene-ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-isoprene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile 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.

[0122] Examples of the acrylate polymer include polymers containing 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 polymer is usually 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more.

[0123] Specific examples of acrylate polymers include crosslinked acrylate polymers such as 2-ethylhexyl acrylate-methacrylic acid-acrylonitrile-ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-diethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-styrene-methacrylic acid-ethylene glycol dimethacrylate copolymer, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer, and butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymer; 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 radical polymerizable monomers onto the ethylene-(meth)acrylic acid ester copolymers. Examples of radical polymerizable monomers used in the graft polymers include methyl methacrylate, acrylonitrile, and methacrylic acid. In addition, copolymers of ethylene and (meth)acrylic acid, such as ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer, can be used as dispersible binders.

[0124] The olefin polymer may contain at least one of polyethylene, polypropylene, and polybutylene. In one embodiment of the present invention, the electrode powder containing the fibrous binder may contain the polyethylene polymer.

[0125] The fluorine-based polymer may include polyvinylidene fluoride copolymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP), and more specifically, it may include polytetrafluoroethylene (PTFE), and even more specifically, it may be polytetrafluoroethylene (PTFE). In one embodiment of the present invention, the electrode powder containing the fibrous binder may contain polytetrafluoroethylene.

[0126] On the other hand, in one embodiment of the present invention, the binder resin may contain two or more different materials. Specifically, the electrode granule particles may contain two or more different binder materials within a single particle. For example, the electrode granule may be a mixture of styrene-butadiene rubber (SBR) and an acrylate polymer in a predetermined ratio as the binder material.

[0127] In one embodiment of the present invention, when the electrode is a fibrous electrode powder type electrode, the electrode binder may contain a fluorine copolymer. In a specific embodiment, the electrode may contain PTFE among the fluorine copolymers, and more preferably PTFE may be present in an amount of 60% by weight or more based on the total binder weight. On the other hand, it goes without saying that the electrode binder may further contain fluorine copolymers other than PTFE, styrene copolymers, polyolefin copolymers, polyethylene oxide (PEO), acrylate copolymers, and the like.

[0128] On the other hand, in one embodiment of the present invention, when the electrode is formed by the accumulation of granules, the electrode binder may contain at least one of diene polymers and styrene polymers, and this may be present in an amount of 60% by weight or more based on the total binder weight. In one specific embodiment, the electrode binder may contain 60% by weight or more of styrene-butadiene block copolymer based on the total binder weight. On the other hand, it goes without saying that the electrode binder may also further contain fluorine copolymers, polyolefin copolymers, polyethylene oxide (PEO), acrylate copolymers, and the like.

[0129] On the other hand, according to one embodiment of the present invention, when the electrode binder includes an electrode binder having a double bond, for example, when the electrode is a negative electrode, the negative electrode active material layer may have a first QBR (Quantified Binder Ratio) of 2.0 or less.

[0130] The first QBR is defined by the following formula 2.

[0131] (Equation 2) First QBR = ABs / ABf

[0132] In the above formula 2, ABs represents the average value of the double bond content in the surface region of the negative electrode active material layer from the outermost surface to within 15% of the total thickness of the negative electrode active material layer, and ABf represents the average value of the double bond content in the bottom region of the negative electrode active material layer from the interface of the negative electrode active material layer facing the current collector to within 15% of the total thickness of the negative electrode active material layer.

[0133] Figure 6 is a schematic diagram of an electrode according to one embodiment of the present invention. Referring to Figure 6, the electrode 10 comprises an electrode current collector 12 and an electrode active material layer 11 located on the electrode current collector 12 and containing an electrode active material and a fluorine-containing electrode binder.

[0134] The electrode active material layer 11 has, with respect to its overall thickness d, an electrode active material layer surface region 11s from the outermost surface of the electrode active material layer to within 15% of the overall thickness d of the electrode active material layer, and an electrode active material layer bottom region 11f from the electrode active material layer interface facing the electrode current collector to within 15% of the overall thickness d of the electrode active material layer.

[0135] In the first QBR of the above formula, ABs represents the average value of the double bond content of the binder in the electrode active material layer surface region 11s, and ABf represents the average value of the double bond content of the binder in the electrode active material layer bottom region 11f.

[0136] At this time, the first QBR can be calculated by the following method.

[0137] First, an electrode to be used to confirm the first QBR is selected, and a cross-section of the selected negative electrode is prepared using argon ion milling. Then, the components within the negative electrode active material layer of the prepared electrode cross-section are mapped using an energy dispersive X-ray spectroscopy (EDS) detector on a scanning electron microscope (SEM).

[0138] From the EDS mapping results, a line profile along the thickness direction of the negative electrode active material layer is extracted. From the extracted line profile results, the average value Bs of the binder double bond content in the electrode layer surface region and the average value Bf of the binder double bond content in the electrode layer bottom region are extracted, and the first QBR value is calculated using the following formula.

[0139] The first QBR = ABS / ABf

[0140] In this case, the electrode active material layer surface region is the 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 electrode active material layer bottom region is the region from the electrode active material layer interface facing the current collector to within 15% of the total thickness of the electrode active material layer.

[0141] The first QBR value is a numerical value that indicates the uniformity of the electrode binder distribution in the thickness direction within the electrode active material layer, based on the ratio of the electrode binder content in the surface region to the electrode binder content in the bottom region of the electrode active material layer. In this case, the electrode binder content can be estimated based on the double bond components of the electrode binder used.

[0142] The first QBR value may be 2.0 or less, or 0.6 to 2.0, or 0.9 to 2.0, or 0.6 to 1.4, or 0.6 to 1.4, or 0.9 to 1.4, or 0.9 to 1.1.

[0143] When the first QBR value satisfies the above range, the binder migrates to the electrode surface, preventing the content of electrode binder in the surface region from becoming excessively large compared to the content of electrode binder in the bottom region of the electrode active material layer, resulting in a uniform distribution of binder in the thickness direction of the electrode active material layer. As a result, the adhesion between the current collector and the electrode active material layer is improved, and the conductivity on the surface of the electrode active material layer is enhanced, which in turn can improve the charge-discharge rate, thus offering advantages.

[0144] On the other hand, in one embodiment of the present invention, the electrode may contain an electrode binder having a double bond as a binder material, for example, a styrene-butadiene copolymer, in which case the second QBR value may be 2.0 or less.

[0145] According to one embodiment of the present invention, when the electrode contains a fluorine-based binder as the binder material, the electrode active material layer has a second QBR (Quantified Binder Ratio) of 1.1 or less, and the second QBR can be defined by the following formula 3.

[0146] (Equation 3) Second QBR = CBs / CBf

[0147] In the above formula 3, CBs represents the average value of the fluorine content of the electrode binder in the electrode layer surface region from the outermost surface of the electrode active material layer to within 15% of the total thickness of the electrode layer, and CBf represents the average value of the fluorine content of the electrode binder in the electrode active material layer bottom region from the electrode active material layer interface facing the electrode current collector to within 15% of the total thickness of the electrode active material layer.

[0148] The second QBR value is 1.1 or less, and according to one embodiment of the present invention, the second QBR value may be 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and may also be between 0.95 and 1.05.

[0149] When the second QBR value is within the range of 1.1 or less, the fluorine-containing electrode binder migrates to the electrode surface, preventing the amount of fluorine-containing electrode binder in the surface region from becoming excessive compared to the amount in the bottom region of the electrode active material layer, resulting in a uniform binder distribution in the thickness direction of the electrode active material layer. As a result, the adhesion between the current collector and the electrode active material layer is improved, and the conductivity on the surface of the electrode active material layer is enhanced, which can also improve the charge-discharge rate, thus offering advantages.

[0150] In one embodiment of the present invention, the electrode may contain a fluorine-based binder resin, in which case the second QBR value may be 1.1 or less.

[0151] Figure 7 is a schematic diagram for calculating the first or second QBR value of the electrode active material layer. Referring to Figure 7, the X-axis represents the thickness of the electrode active material layer, i.e., the distance from the surface towards the current collector, and the Y-axis represents the measured intensity of the binder component, i.e., the fluorine component intensity or the double bond intensity. Line A shows the intensity of the double bond component of binders containing double bonds, extracted by EDS mapping of the binder component within the electrode active material layer in the electrode cross-section, and line B is a trend line showing the trend of line A, and is a line smoothed using the LOWESS smoothing method, i.e., the Locally-Weighted Scatterplot Smoother method. In Figure 7, Bs represents the binder intensity at the electrode surface, and Bf represents the binder intensity at the bottom of the electrode (opposing the current collector).

[0152] On the other hand, in the present invention, the electrode binder may include diene polymers and crosslinked acrylate polymers, from the viewpoint of obtaining an active material layer with excellent adhesion to the current collector and surface smoothness, and further enabling the production of electrodes for electrochemical elements having high capacitance and low internal resistance.

[0153] The electrode binder is not particularly limited in shape, but it is preferably particulate in order to have good binding properties and to suppress the decrease in capacitance of the fabricated electrode and deterioration due to repeated charging and discharging. Examples of particulate electrode binders include those in which dispersed binder particles, such as latex, are dispersed in water, or powders obtained by drying such dispersions. Such particulate binders can preferably be included in the negative electrode.

[0154] On the other hand, in some cases, a filler, which is a component that suppresses the expansion of the electrode active material layer, may be further added to the electrode active material layer. The filler does not cause any chemical changes in the battery and is not particularly limited as long as it is a fibrous material. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers can be used.

[0155] The current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used. The current collector can also have fine irregularities formed on its surface to increase adhesion to the electrode active material, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0156] On the other hand, in one embodiment of the present invention, a conductive primer may be coated on the current collector, either entirely or partially.

[0157] The primer layer comprises a primer layer binder (hereinafter referred to as "second binder") and a primer layer conductive material (hereinafter referred to as "second conductive material"), and the total content of the second binder and the second conductive material in the primer layer may be 90% by weight or more.

[0158] An electrode according to one embodiment of the present invention comprises an electrode active material layer containing electrode granules, and includes a primer layer containing a second binder and a second conductive material, wherein the total content of the second binder and the second conductive material is 90% by weight or more. This ensures the long-term stability of the primer layer, and as a result, can exhibit excellent physical properties such as adhesive strength and lifespan characteristics, but the present invention is not limited thereto.

[0159] According to one embodiment of the present invention, the primer layer comprises a second binder and a second conductive material, and may further comprise a dispersant.

[0160] According to another embodiment of the present invention, the primer layer may include a second binder and a second conductive material, but may substantially omit a dispersant.

[0161] According to one embodiment of the present invention, the second binder can be any known binder used for a primer layer, without any particular limitations.

[0162] According to another embodiment of the present invention, the second binder may preferably be a polymer capable of ensuring the temporal stability of the primer layer. Specifically, the second binder may have a glass transition temperature (Tg) of 45°C or lower.

[0163] According to yet another embodiment of the present invention, the second binder is, for example, styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile-butadiene rubber (NBR), styrene-butadiene-styrene block polymer (SBS), styrene-ethylene-butadiene block polymer (SEB), styrene-(styrene-butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), ethylene-propylene-diene ternary copolymer (EPDM), poly(ethylene-co-propylene-co-5-methylene-2-norbornene), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-hexafluoropropylene It may contain fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene, polypropylene, ethylene vinyl acetate copolymer, polyethylene oxide, polypropylene oxide, polyarylate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, or two or more of these.Specifically, the binder may contain styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, or two or more of these.

[0164] According to yet another embodiment of the present invention, the second binder may be one or more types selected from the aforementioned types, having the aforementioned glass transition temperature values.

[0165] According to yet another embodiment of the present invention, the second binder may be styrene-butadiene rubber (SBR) having a glass transition temperature (Tg) of -40°C to 45°C, nitrile-butadiene rubber (NBR) having a glass transition temperature (Tg) of -40°C to 45°C, or a mixture thereof.

[0166] According to one embodiment of the present invention, the second conductive material has a specific surface area of ​​30 m². 2 / g~1,400m 2 The particle size is / g and may have a spherical shape. In this case, the primary particle size of the spherical conductive material may be, for example, 10nm to 100nm, specifically 15nm to 70nm, but is not limited to this.

[0167] According to yet another embodiment of the present invention, the second conductive material has a specific surface area of ​​10 m². 2 / g~400m 2 The conductive material may have a tubular shape with a density of / g. In this case, the conductive material having a tubular shape may have a cross-sectional diameter in the direction perpendicular to the length direction of 0.1 to 3 nm, specifically 0.3 to 1.5 nm, but is not limited to this.

[0168] The second conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite or artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. More specifically, activated carbon, graphite, carbon black, carbon nanotubes, or mixtures of two or more of these may be included for uniform mixing of the conductive material and improvement of conductivity, and more preferably activated carbon may be included.

[0169] According to one embodiment of the present invention, the primer layer contains the above-mentioned composition and may have a thickness of 300 nm to 1.5 μm, specifically 700 nm to 1.3 μm, but is not limited thereto.

[0170] <Method for manufacturing electrode granules> According to one embodiment of the present invention, the electrode granules may be manufactured by a method comprising the steps of mixing an electrode active material and an electrode binder with a dispersion medium to produce a slurry, and spray-drying the slurry.

[0171] First, the electrode active material and electrode binder, along with additional conductive materials and additives as needed, are dispersed or dissolved in a dispersion medium (solvent in the case of the negative electrode binder) to obtain a slurry in which the electrode active material and electrode binder, along with the electrode conductive material and / or other additives, are dispersed or dissolved.

[0172] Water is the most suitable dispersion medium used to obtain the slurry, but organic solvents can 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, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and dimethylimidazolidinone; sulfur-based solvents such as dimethyl sulfoxide and sulfolane; and others, but alcohols are preferred. Using an organic solvent with a lower boiling point than water in combination can increase the drying rate during fluid granulation. Furthermore, since the dispersibility or solubility of the negative electrode binder may change, the viscosity and fluidity of the slurry can be adjusted according to the amount or type of dispersion medium, thereby improving production efficiency.

[0173] The amount of dispersion medium used when preparing the slurry may be such that the solid content concentration of the slurry is typically in the range of 1 to 50% by weight, 5 to 50% by weight, or 10 to 30% by weight.

[0174] The method or sequence for dispersing or dissolving the electrode active material and electrode binder in the dispersion medium is not particularly limited. Examples include adding the electrode active material and electrode binder to the dispersion medium and mixing them, or dissolving or dispersing the electrode binder in the dispersion medium first, and then adding the electrode active material at the end and mixing it. If the slurry contains conductive material and / or additives, these components may be added at the same time as the electrode active material. Examples of mixing means include mixing equipment such as ball mills, sand mills, bead mills, pigment dispersers, stone mills, ultrasonic dispersers, homogenizers, and planetary mixers. Mixing may be carried out, for example, at room temperature to 80°C for 10 minutes to several hours.

[0175] Next, the slurry is spray-dried. The spray-drying method involves spraying the slurry into hot air to dry it. The spraying methods used in the spray-drying apparatus include the rotating disc method and the nozzle pressurization method. The rotating disc method involves introducing the slurry to approximately the center of a rapidly rotating disc, and using the centrifugal force of the disc to push the slurry out to the outer circumference of the disc, drying it in the process as a mist. 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 involves passing the slurry through a narrow nozzle while simultaneously injecting a high-pressure fluid such as air or another liquid, spraying it in a mist to dry it.

[0176] 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), from the viewpoint of forming an electrode granule structure with a high electrode binder content on its surface. In the present invention, considering the gradient of binder content and aspect ratio, the temperature can be preferably controlled to 175°C to 220°C, more preferably to 180°C to 220°C. In the spray drying method, the method of drawing in the hot air is not particularly limited, and examples include a method in which the hot air and spray direction are parallel in the lateral direction, a method in which the hot air is sprayed from the top of the drying tower and descends together with the hot air, a method in which the sprayed droplets and hot air come into contact in a countercurrent, and a method in which the sprayed droplets initially flow parallel with the hot air and then fall by gravity and come into contact in a countercurrent. On the other hand, in one embodiment of the present invention, the reactor outlet temperature (temperature of the hot air discharged from the reactor) during spray drying can be controlled to 90°C to 130°C.

[0177] If the outlet temperature and / or the difference between the inlet and outlet temperatures (ΔT) is small, drying will be insufficient, resulting in the formation of particles with a large amount of residual solvent. Uniform spherical particles cannot be obtained, and electrode granules may aggregate or be formed in an amorphous state. On the other hand, if the inlet temperature is excessively high and ΔT is large, granulation will not occur due to over-drying, and particles with an extremely small D50 and a low aspect ratio may be produced. Therefore, in order to achieve a high aspect ratio, minimize binder aggregation, and control the particle size at an appropriate level, it is necessary to control the inlet and outlet temperatures within an appropriate range.

[0178] Furthermore, the surface of the product obtained by selective spray drying, i.e., the electrode granules, may be heat-treated to harden it, and the heat treatment temperature at this time is usually 80°C to 300°C.

[0179] <Method of manufacturing electrodes> According to one embodiment of the present invention, the method for manufacturing the electrode may include the steps of scattering an electrode material containing the aforementioned plurality of electrode granules or electrode powders or both onto a current collector, and pressurizing the scattered electrode material to form an electrode active material layer.

[0180] One of the electrode materials manufactured by the method described above is scattered onto the current collector. At this time, at least one surface of the current collector may be provided with a primer layer containing the second conductive material and the second binder as described above.

[0181] According to one embodiment of the present invention, the prepared electrode granules can be supplied to a roll-type pressure molding device by a supply device such as a screw feeder to form an active material layer. At this time, by sending the current collector to the roll of the pressure molding device at the same time as the supply of the electrode granules, the active material layer can be directly laminated on the current collector. Alternatively, the electrode granules can be scattered on the current collector, the thickness can be adjusted uniformly with a blade or the like, and then molded with a pressure device to form the electrode active material layer.

[0182] In these methods, the temperature during roll pressure forming is typically 0°C to 200°C, preferably higher than the melting point or glass transition temperature of the electrode binder, and more preferably 20°C or more higher than the melting point or glass transition temperature. The forming speed during roll pressure forming is typically 0.1 m / min to 20 m / min, or 1 m / min to 10 m / min. The press line pressure between the rolls is typically 0.2 kN / cm to 30 kN / cm, or 0.5 kN / cm to 10 kN / cm.

[0183] To eliminate variations in the thickness of the molded electrodes and increase the density of the electrode active material layer to achieve higher capacity, further pressurization may be performed as needed. The most common post-pressurization method is a roll press process. In the roll press process, two cylindrical rolls are placed parallel to each other vertically with a narrow gap between them, and they are rotated in opposite directions, sandwiching the electrode between them and applying pressure. The rolls can also be heated or cooled to control their temperature.

[0184] Alternatively, a dry electrode can be manufactured by calendering the manufactured electrode material to produce a dry electrode film, and then laminating the dry electrode film with a current collector.

[0185] Such calendering processes the electrode material into a film shape, for example, by pressurizing it into a film with an average thickness of 50 μm to 300 μm. In one embodiment of the present invention, the calendering may be performed using a calendering apparatus that includes a roll press section in which two rollers are arranged facing each other. The calendering apparatus may include at least one roll press section. For example, multiple roll press sections may be arranged in a series, allowing for multi-stage compression of the electrode mixture powder. Meanwhile, one or more rollers in the calendering apparatus may be independently temperature-controlled to 50°C to 200°C. With or independently of this, the rotation speed ratio of two rollers in the one or more roll press sections may be controlled to a ratio of 1:1 to 1:3. By proceeding to such a calendering process, a dry electrode film that serves as an electrode mixture can be produced. Such a dry electrode film is also called a free-standing film or a self-supporting film. Such dry electrode films may have sufficient mechanical strength to be used in the manufacturing process of energy storage devices without any external support elements such as current collectors, support webs, or other structures. Alternatively, they may be used in battery manufacturing in combination with a support such as a current collector. On the other hand, in one embodiment of the present invention, the obtained dry electrode film has a degree of crystallinity d of the binder resin in the dry electrode film of 10% or less. If the degree of crystallinity of the obtained dry electrode film exceeds 10%, the degree of crystallinity can be adjusted by adjusting the gap between the two rollers of the roll press section or by controlling the speed ratio. For example, the degree of fibrous formation of the binder can be increased by reducing the gap and / or increasing the speed ratio.

[0186] According to another embodiment of the present invention, a secondary battery is provided in which an electrode assembly including the positive electrode, negative electrode, and insulating film is housed in a battery case (cylindrical case, rectangular case, pouch, etc.), and an energy storage device is provided which includes the same as a unit battery. In this case, at least one of the positive electrode and negative electrode may be the aforementioned electrode. For example, the negative electrode may be a dry electrode. On the other hand, the battery may further include a lithium-containing non-aqueous electrolyte.

[0187] If the electrode assembly includes a separator, the separator may be a conventional porous polymer film used as a separator, such as a porous polymer film made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, either alone or in a laminated configuration. Alternatively, an insulating thin film with high ion permeability and mechanical strength may be used. The separator may include a safety-reinforced separator (SRS) in which a thin layer of ceramic material is coated on the surface of the separator. Furthermore, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used, but is not limited thereto.

[0188] Alternatively, if the insulating film is a solid electrolyte film, the solid electrolyte film may contain a solid electrolyte material, and the solid electrolyte material may contain one or more of oxide-based solid electrolytes, sulfide-based solid electrolytes, and polymer-based solid electrolytes. Furthermore, if the lithium-ion secondary battery is an all-solid-state battery, the dry electrode of the present invention may further contain the aforementioned solid electrolyte material.

[0189] The electrolyte solution comprises a lithium salt as the electrolyte and an organic solvent for dissolving it.

[0190] The lithium salt can be any lithium salt commonly used in electrolytes for secondary batteries, and for example, as the anion of the 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 can be selected from the group consisting of the following.

[0191] The organic solvent contained in the electrolyte can be any commonly used one or more, and typically one or more selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran can be used.

[0192] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents with high dielectric constants that can effectively dissociate lithium salts in the electrolyte. Furthermore, by mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, an electrolyte with high electrical conductivity can be prepared, making it even more suitable for use.

[0193] Selectively, the electrolyte used in the present invention may further contain additives such as overcharge inhibitors that are typically found in electrolytes.

[0194] A lithium-ion secondary battery according to one embodiment of the present invention can be completed by forming an electrode assembly by placing a separator between the positive electrode and the negative electrode, housing the electrode assembly in, for example, a pouch-type battery case, a cylindrical battery case, or a rectangular battery case, and then injecting an electrolyte. Alternatively, a lithium-ion secondary battery can be completed by stacking the electrode assemblies, impregnating them with an electrolyte, housing the resulting product in a battery case, and sealing it.

[0195] On the other hand, since the specific structure of the lithium-ion secondary battery and energy storage device in the present invention is known, a description of them is omitted in this specification.

[0196] In the present invention, each of the embodiments described above can be implemented independently. It goes without saying that two or more of the embodiments described above can also be implemented in combination.

[0197] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0198] [Example 1] 1.Negative electrode (1) Preparation of a current collector equipped with a primer layer Carbon black is used as the second conductive material (specific surface area: 30 m²). 2 / g, particle size: 70nm) 30 parts by weight, styrene-butadiene rubber (SBR) (T) as the second binder. g A slurry for the primer layer was prepared by mixing 69 parts by weight of (-15℃) and 1 part by weight of carboxymethylcellulose (CMC) as a dispersant with water, which was the dispersion medium. At this time, the proportions of conductive material, binder, and dispersant in the slurry were the same as the proportions of conductive material, binder, and dispersant in the primer layer that was subsequently formed. The solid content ratio of the slurry for the primer layer was 7% by weight.

[0199] The prepared primer layer slurry was applied to one surface of a copper current collector (thickness: 10 μm), and dried at 130°C to form a primer layer over the entire surface of the copper current collector.

[0200] (2) Preparation of granules for the electrode of the negative electrode active material layer A slurry with a viscosity of approximately 1000 cPs was prepared by mixing 1.91 parts by weight of natural graphite with a spheroidization degree of 0.95 and 76.5 parts by weight of artificial graphite with an average spheroidization degree of 0.9 as negative electrode active materials, carbon black (SuperC65) as a negative electrode conductive material, carboxymethylcellulose (daicel2200, aqueous solution form, solid content concentration 1.5% by weight) as a negative electrode dispersant, and modified styrene-butadiene copolymer (grade name: AX-B119) as a negative electrode binder with water as a dispersion medium in a weight ratio of 95.6:1.0:1.1:2.3. At this time, the solid content in the slurry was 30% by weight. The carboxymethylcellulose in the above weight ratio was calculated based on the solid content.

[0201] The prepared slurry was introduced into a spray dryer along with hot air under a pressure range of -40 mmH2O and dried. At this time, the spray dryer conditions were controlled to an inlet temperature of 180°C, an outlet temperature of 90°C, and a rotation speed of 18000 rpm. The obtained electrode granules were then subjected to an industrial sieve to remove coarse powder larger than 150 μm, and further separated to remove fine powder smaller than 40 μm. The separated fine powder was mixed with the electrode granules from which only the coarse powder had been removed to finally prepare a negative electrode granule containing a larger amount of fine powder than conventional electrode granules. The electrode granules comprised a central part containing multiple negative electrode active materials and negative electrode conductive materials, and a surface part located outside the central part containing a negative electrode binder that binds the negative electrode active materials and negative electrode conductive materials. The average particle size (D50) of the obtained electrode granules was 66.5 μm, and the aspect ratio was 0.96. Figure 8 shows a cross-sectional image of the electrode granules manufactured in Example 1, processed using the EPMA (electron probe microanalysis) method described later. The closed curves shown in the image connect points that are at the same distance from the surface.

[0202] (3) Manufacturing of the negative electrode On one surface of the current collector equipped with the primer layer, a thickness adjustment bar is used to adjust the current collector 25 cm 2 The prepared electrode granules were uniformly applied in an amount of 400 mg per unit, and a negative electrode active material layer was formed by applying pressure at a rate of 2 m / min under conditions of 0.7 tons per cm, 60°C, and a sheeting machine (roll-to-roll hot rolling forming machine), thereby manufacturing the negative electrode.

[0203] [Example 2] Electrode granules were manufactured in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 180°C and the outlet temperature to 130°C. The average particle size (D50) of the obtained electrode granules was 61.4 μm, and the aspect ratio was 0.99. Figure 9 shows a cross-sectional image of the electrode granule particles manufactured in Example 2, processed using the EPMA method described later. The closed curves in the image connect points that are at the same distance from the surface.

[0204] [Example 3] Electrode granules were manufactured in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 200°C and the outlet temperature to 110°C. The average particle size (D50) of the obtained electrode granules was 35.8 μm, and the aspect ratio was 0.77.

[0205] Figure 10 shows a cross-sectional image of the electrode granules manufactured in Example 3, processed using the EPMA method described later. The closed curves in the image connect points that are the same distance from the surface to the center of the electrode granule.

[0206] [Example 4] 96g of natural graphite, 1g of carbon black as a conductive material, and 3g of polytetrafluoroethylene (PTFE) as a binder were placed in a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture. After stabilizing the kneader temperature at 80°C, the mixture was placed in the kneader and operated at a speed of 25 rpm for 5 minutes under a lid pressure of 1.1 atmospheres to obtain a mixture mass. The mixture mass was placed in a blender and pulverized at 10,000 rpm for 30 seconds to obtain an electrode mixed powder. The obtained electrode mixed powder was classified into particles between 150 μm and 1000 μm using a multi-stage classifier. The classified electrode powder was placed in a laboratory calender (with a roll diameter of 200 mm, a roll temperature of 100°C, and a roll speed ratio of 1.5) and electrode films were manufactured through several calendering processes.

[0207] The two electrode films were placed on both sides of a current collector coated with the primer layer, and the negative electrode was manufactured by laminating them using a compression roll maintained at 100°C. At this time, the rolling ratio of the electrode film in the lamination process was 39%. The rolling ratio of the electrode film was calculated as the ratio of the electrode film thickness after the lamination process to the electrode film thickness before the lamination process.

[0208] [Comparative Example 1] Electrode granules were manufactured in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 170°C and the outlet temperature to 70°C. The average particle size (D50) of the obtained electrode granules was 42.8 μm, and the aspect ratio was 0.75. Furthermore, the negative electrode was manufactured in the same manner as in Example 1, except that the electrode granules manufactured in Comparative Example 1 were used instead of the electrode granules manufactured in Example 1. In Comparative Example 1, there was some over-drying, resulting in an aspect ratio of 0.75 or less, and uniform spherical particles were not formed, with large variations between particles. Figure 11 shows a cross-sectional image of the electrode granule particles manufactured in Comparative Example 1, processed using the EPMA method described later. Referring to the figure, it was confirmed that the binder resin (light color) was distributed throughout the entire cross-section of the electrode granules. The closed curve in the image connects points that are at the same distance from the surface.

[0209] [Comparative Example 2] Electrode granules were manufactured in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 170°C and the outlet temperature to 140°C. The average particle size (D50) of the obtained electrode granules was 78.0 μm, and the aspect ratio was 0.37. In Comparative Example 2, the difference between the inlet and outlet temperatures was small, and the solvent was not sufficiently removed, resulting in the formation of particles with a large amount of residual solvent. As a result, uniformly shaped spherical particles were not obtained, the moisture absorption was high, and aggregation between particles was observed.

[0210] Figure 12 shows a cross-sectional image of the electrode granules produced in Comparative Example 2, processed using the EPMA method described later. Referring to this figure, it can be confirmed that the binder resin (light color) is distributed throughout the entire cross-section of the electrode granules. The closed curves in the image connect points at the same distance from the surface.

[0211] [Comparative Example 3] A slurry with a solid content of 47% by weight was prepared by mixing 19.1 parts by weight of natural graphite with an average spheroidization degree of 0.95 and 76.5 parts by weight of artificial graphite with an average spheroidization degree of 0.9 as negative electrode active materials, 1 part by weight of carbon black (Super-C65) as a negative electrode conductive material, 2.3 parts by weight of styrene-butadiene rubber (SBR) as a negative electrode binder, 1.1 parts by weight of carboxymethylcellulose (CMC) as a binder and thickener, and water as a dispersion medium.

[0212] A copper (Cu) thin film, which is a 10 μm thick negative electrode current collector, is coated with the slurry on one side. The upper and lower active material layers thus formed are then rolled simultaneously using a roll pressing method with a drying apparatus equipped with a hot air blower and an IR heater, resulting in a dried weight of 400 mg / 25 cm² per unit area. 2 A negative electrode was manufactured that has a negative electrode active material layer with a loading amount of [amount].

[0213] [Confirmation of binder distribution in the negative electrode active material layer] The negative electrodes produced in Example 1, Example 4, and Comparative Example 3 were placed together in a glass container with OsO4 crystals or aqueous solution, and allowed to undergo a sufficient chemical reaction (deposition) for at least 3 hours by evaporating the reagent. Subsequently, cross-sections of the negative electrodes from the Examples and Comparative Examples were prepared using argon ion milling.

[0214] Using an energy dispersive X-ray spectroscopy (EDS) detector on a scanning electron microscope (SEM), the constituent components within the negative electrode active material layer in the cross-section in the thickness direction of the negative electrode of Example 1, Example 4, and Comparative Example 3 were mapped using EDS.

[0215] Figure 2 shows the EDS mapping results for the electrode of Example 1, and Figure 4 shows the EDS mapping results for the electrode of Comparative Example 3. Referring to these figures, it was confirmed that in the electrode of Example 1, the binder resin was distributed more towards the surface of the electrode granule than towards the center of the electrode granule. Furthermore, the electrode of Example 1 was manufactured by a method of pressing the electrode granule, and it was confirmed that the binder was uniformly distributed in the electrode thickness direction. In contrast, in the electrode of Comparative Example 3, it was confirmed that the binder content was high in the electrode surface layer. Unlike the electrode manufacturing method of Example 1, the electrode of Comparative Example 3 was manufactured by a coating and drying method of the electrode slurry, and this binder distribution is due to binder migration due to the evaporation of the solvent.

[0216] On the other hand, Figures 3 and 5 are graphs showing the average value of the Os content of the binder bound to Os in the Os-bound binder

[0217] On the other hand, the electrode in Example 4 contained a fluorine-based binder, and as described above, EDS mapping was performed and the QBR was calculated, resulting in a QBR value of 1.1 or less.

[0218] [Measurement of ohm resistance and its rate of change (amount of change) in response to changes in charge state of charge (SOC)] Lithium-ion secondary batteries were manufactured using the electrodes of Example 1, Example 2, Example 4, and Comparative Example 3, and the ohm resistance and its rate of change (amount of change) associated with the State of Charge (SOC) were identified for each battery.

[0219] LiNi as a positive electrode active material 0.8 Co 0.1 Mn 0.1 A cathode active material slurry was prepared by adding O2, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 96:2:2 to the solvent N-methylpyrrolidone (NMP). The cathode active material slurry was coated onto a sheet-shaped aluminum current collector and dried, resulting in a final cathode loading of 4.0 mAh / cm². 2 The positive electrode was prepared in such a way.

[0220] A separator was interposed between the positive electrode manufactured as described above and the negative electrodes manufactured in Examples 1, 2, 4, and Comparative Example 3, and the electrode assembly was manufactured by pressurizing it at 70°C and 6.5 MPa for 20 seconds. After assembling the electrode assembly into a coin cell, a non-aqueous electrolyte prepared by dissolving LiPF6 in an organic solvent (Ethylene carbonate:Diethyl carbonate = 1:1 (v:v)) to a concentration of 1 M was injected to manufacture a lithium secondary battery.

[0221] Next, the resistance value relative to the State of Charge (SOC) was measured for each battery. First, the obtained batteries were charged from 2.5V to 4.2V in CC-CV mode at a 0.33C rate (0.05C cut-off), and after a 10-minute rest, they were discharged from 4.2V to 2.5V in CC mode at a 0.33C rate. This was repeated three times. The charging and discharging were performed at 25°C. After discharging, the batteries were rested for 30 minutes, and then the resistance value was confirmed by in situ electrochemical impedance spectroscopy (EIS). Each battery was connected to two channels, and charging proceeded on one channel while EIS was measured at regular time intervals on the other channel, so that EIS was measured simultaneously with charging. The measurements were performed at room temperature (25°C) while charging at a rate of 0.33 (C rate), in 1% increments of SOC from 0% to 100%. The SOC was based on the battery capacity confirmed by the charging and discharging of the batteries.

[0222] For electrochemical impedance spectroscopy (EIS) measurements, a Solartron 1470E cell test system and 1255B frequency response analyzer were used. Electrochemical impedance spectroscopy analysis was performed at 25°C under the conditions of a scan range of 10,000 Hz to 100,000 Hz and an amplitude of 10 mV, and the resistance was calculated from the results.

[0223] From the Nyquist plot obtained at this time, the ohm resistance, charge transfer (CT) resistance, and rate of change (amount of change) were calculated for each state of charge (SOC). The ratio of ohm resistance to charge transfer resistance was measured in 1% increments of SOC. The rate of change of ohm resistance was calculated based on the following formula 1.

[0224] (Equation 1) Rate of change of ohm resistance (mic Resistance change) = (R SOC / R i ) × 100

[0225] In the above formula 1, R i R is the ohm resistance at the lowest SOC at which ohm resistance and charge transfer resistance can be separated from the Nyquist plot. SOC This represents the ohm resistance at each SOC.

[0226] Figure 19 shows the ratio of ohm resistance to charge transfer resistance for different states of charge (SOC) measured using the batteries of Examples 1, 2, and 4. SOC, on the other hand, represents the remaining capacity of the battery, and is expressed as a percentage (%) by dividing the currently usable battery capacity by the total capacity. Referring to Figure 19, a tendency was observed for ohm resistance to decrease with increasing SOC in the batteries of Examples 1, 2, and 4.

[0227] On the other hand, Figure 17 shows the ohm resistance measured for each SOC interval for the batteries of Example 1, Example 2, and Example 4. Figure 18 shows the rate of decrease in ohm resistance for each SOC interval for Example 1, Example 2, Example 4, and Comparative Example 3. The lithium-ion secondary battery according to the present invention may show a tendency for the ohm resistance of the battery to decrease as the SOC increases during charging. Furthermore, it was confirmed that the rate of change of ohm resistance of the lithium-ion secondary battery according to the present invention shows a negative (-) tendency as the SOC increases during charging. Referring to the above figures, it was confirmed that in the batteries of Example 1, Example 2, and Example 4, the rate of change of ohm resistance was larger in the initial interval and in the intervals before SOC 20%, SOC 30%, SOC 40%, and SOC 50%, respectively, than in the intervals after SOC 20%, SOC 30%, SOC 40%, and SOC 50%, respectively. In contrast, it was confirmed that the battery of Comparative Example 3 (composed only of wet electrodes) had a smaller rate of change of resistance with respect to SOC compared to the examples.

[0228] As is clear from the above, the secondary battery according to the present invention improves process convenience because the slurry drying step can be omitted during electrode manufacturing, and because the binder resin and electrode active material are uniformly distributed in the thickness direction in the electrode active material layer, sufficient bonding force can be ensured between the electrode active material layer and the current collector. In addition, the rate of decrease in ohm resistance increases as the charge state of charge (SOC) increases, which is advantageous in terms of thermal management during rapid charging of the battery.

[0229] [Confirmation of binder distribution in electrode granules] Using EPMA (JXA-8350F, -15kV, 20nA, stage mapping conditions), the cross-section of the electrode granules was analyzed by radial profile to confirm the binder distribution within the electrode granules. First, the binder within each electrode granule obtained in Examples 1 to 3 was stained with OsO4. This staining was performed by placing the electrode granules in a glass container with OsO4 crystals or aqueous solution and allowing the reagent to react by evaporating it. Subsequently, the mixture was fixed in a silicone mold and cured to obtain an electrode granule matrix (see Figure 15). Next, cross-sectional samples were prepared from the electrode granule matrix using an ion milling (Ar ion milling) apparatus (Hitachi IM5000, acceleration voltage: 6kV). For cross-sectional preparation, the acceleration voltage was set to 6kV, the emission current to 400μA, and the milling time was appropriately adjusted so that the entire mask was not engraved. The prepared cross-sectional sample was fixed to the EPMA apparatus, the electrode granule was positioned in the center of the display, and a cross-sectional scan was performed using the stage mapping method. Once the scan was complete, an image was created in the form of a mass map, taking into account the atomic number effect, absorption effect, and fluorescence excitation effect. From the obtained mass map, elements in the range of 0-4 wt% were specified with a contrast of 0-255, and an Os map was extracted. The conventional backscatter electron image obtained during the EPMA analysis process and the Os map were combined into a single layer using Photoshop®, and closed curves were drawn in 30-pixel increments from the boundary of the electrode granule obtained from this layer. The Os content at each closed curve was then analyzed. The Os content was corrected by introducing the surface area of ​​the closed curve at each position so that the relative amounts at each position could be compared. Figure 13 shows the distribution (content) of binder resin in each portion along the radius of the electrode granules for each example and comparative example. Figure 14 shows the cumulative distribution of binder resin along the radius of the electrode granules for each example and comparative example.Referring to the figure, it was confirmed that the electrode granules of Examples 1, 2, and 4 had a higher binder content in the surface portion leading to the electrode granule surface from 70% radius onward, particularly from 80% radius onward, compared to the center portion. In contrast, it was confirmed that the electrode granules obtained in Comparative Examples 1 and 2 had a higher binder content in the center portion than in the surface portion.

Claims

1. A lithium-ion secondary battery comprising a dry electrode manufactured by a dry manufacturing method, The dry electrode includes an electrode active material layer containing an electrode active material and an electrode binder, The electrode active material layer includes granules obtained from the result of spray-drying a composition containing an electrode active material and an electrode binder, or includes a composite material in which the electrode active material and a fibrous electrode binder are compounded, or includes both thereof. The lithium-ion secondary battery is a lithium-ion secondary battery in which the ohm resistance changes in response to a change in the state of charge (SOC).

2. The lithium-ion secondary battery according to claim 1, wherein the change in ohm resistance is such that the ohm resistance decreases as the charge state of charge (SOC) increases.

3. The lithium-ion secondary battery according to claim 1, wherein the rate of change of the ohm resistance is greater in the section before SOC 50% than in the section after SOC 50%.

4. The lithium-ion secondary battery according to claim 1, wherein the electrode active material includes a negative electrode active material, and the dry electrode is a negative electrode.

5. The dry electrode includes a current collector and an electrode active material layer located on the current collector, wherein the electrode active material layer is formed by the accumulation of the granules. The lithium-ion secondary battery according to claim 1, wherein the granule has a higher content of electrode binder in the surface portion than in the center portion, relative to 100% by weight of the total weight of the electrode active material and electrode binder, the surface portion is the region from the surface of the granule to 20% of the radius toward the center of the granule, and the center portion is the portion other than the surface portion.

6. The lithium-ion secondary battery according to claim 5, wherein the surface portion is a region extending from the surface of the granule to 10% of the radius toward the center of the granule.

7. The lithium-ion secondary battery according to claim 5, wherein the aspect ratio of the granules is 0.75 to 1.

0.

8. The particle size of the granule (D ５０ The lithium-ion secondary battery according to claim 5, wherein the ) is 0.1 to 1,000 μm.

9. The lithium-ion secondary battery according to claim 1, wherein the electrode active material layer comprises two or more electrode active material materials.

10. The lithium-ion secondary battery according to claim 1, wherein the average value of the ohm resistance in the interval from SOC 0% to SOC 20% is higher than the average value of the ohm resistance in the interval from SOC 80% onwards.

11. The lithium-ion secondary battery according to claim 1, wherein the ohm resistance in the section after 10% SOC is lower than in the section before 10% SOC.

12. The lithium-ion secondary battery according to claim 1, wherein the difference between the ohm resistance value at the 80% SOC point and the ohm resistance value at the 5% SOC point is 1% or more of the difference between the minimum and maximum ohm resistance values ​​over the entire SOC measurement period.

13. The lithium-ion secondary battery according to claim 1, wherein in the graph of the rate of change of resistance over the entire SOC measurement period, at least one tangent line has a negative slope (-).

14. The lithium-ion secondary battery according to claim 1, wherein the rate of change of ohm resistance in the initial SOC section is larger than in subsequent sections.

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