Electrode for secondary battery, secondary battery comprising the electrode, and method of manufacturing electrode

Abstract

An electrode for a secondary battery according to one embodiment of the present disclosure includes an electrode current collector; and an electrode layer on the electrode current collector, wherein the electrode layer includes an electrode composition in which an active material, a conductive material, and a binder are dry-mixed, wherein the binder includes a first binder and a second binder, the first binder and the second binder are different from each other, and wherein the second binder is attached to a surface of the first binder.

Description

Technical Field

[0001] Cross Reference to Related Applications

[0002] This application claims the benefits of Korean Patent Application No. 10-2020-0139305, filed with the Korean Intellectual Property Office on October 26, 2020, and Korean Patent Application No. 10-2021-0137513, filed with the Korean Intellectual Property Office on October 15, 2021, the disclosures of which are incorporated herein by reference in their entirety.

[0003] This disclosure relates to an electrode for a secondary battery, a secondary battery including the electrode, and a method for manufacturing the electrode, and more specifically, to an electrode for a secondary battery having improved tensile strength and reduced electrical resistance, a secondary battery including the electrode, and a method for manufacturing the electrode. Background Technology

[0004] With the development of mobile device technology and increasing demand, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and high voltage, long cycle life and low self-discharge rate, are commercially available and widely used.

[0005] In particular, secondary batteries are attracting attention as an energy source for power-driven devices such as electric bicycles, electric cars, and hybrid electric vehicles, as well as for mobile devices such as mobile phones, digital cameras, laptops, and wearable devices.

[0006] Furthermore, with increasing attention to environmental issues, research on electric vehicles and hybrid electric vehicles is becoming more frequent. These vehicles can replace fossil fuel-powered cars such as gasoline and diesel vehicles, which are major contributors to air pollution. While nickel-metal hydride batteries are primarily used as power sources for electric and hybrid electric vehicles, research is actively underway to utilize high-energy-density lithium-ion batteries, some of which are already in the commercialization stage.

[0007] Conventional electrodes for secondary batteries are manufactured using wet processes. However, wet manufacturing inherently requires high-temperature heat treatment processes and carries the risk of damage to metal oxides. Therefore, there is a growing need to develop electrodes manufactured using dry processes. Summary of the Invention

[0008] Technical issues

[0009] The purpose of this disclosure is to provide an electrode for a secondary battery with improved tensile strength and reduced electrical resistance, a secondary battery including the electrode, and a method for manufacturing the electrode.

[0010] The purpose of this disclosure is not limited to the above-described purposes, and those skilled in the art should clearly understand other purposes not described herein through the following detailed description and accompanying drawings.

[0011] Technical solution

[0012] According to one embodiment of the present disclosure, an electrode for a secondary battery is provided, comprising: an electrode current collector; and an electrode layer located on the electrode current collector, wherein the electrode layer comprises an electrode composition in which an active material, a conductive material, and an adhesive are dry-mixed, wherein the adhesive comprises a first adhesive and a second adhesive, the first adhesive and the second adhesive being different from each other, and wherein the second adhesive is attached to the surface of the first adhesive.

[0013] The glass transition temperature (T) of the second adhesive g The temperature can be greater than the glass transition temperature (T) of the first adhesive. g ).

[0014] The glass transition temperature (Tg) of the first adhesive can be above 15 degrees Celsius and below 100 degrees Celsius, and the glass transition temperature (Tg) of the second adhesive can be above 25 degrees Celsius and below 115 degrees Celsius. The content of the adhesive can be above 0.51% by weight and below 11.99% by weight based on the total weight of the electrode composition.

[0015] The content ratio of the first adhesive to the second adhesive can be from 0.1:10 to 10:0.1.

[0016] The first adhesive may include polytetrafluoroethylene (PTFE), and the second adhesive may include an acrylic polymer material.

[0017] The active material may include at least one selected from the group consisting of: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium copper oxide (Li2CuO2), vanadium oxide, Ni-site lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide having a spinel structure, LiMn2O4 in which the Li in the formula is partially replaced by alkaline earth metal ions, disulfide compounds, Fe2(MoO4)3, and lithium manganese oxide (LMO, Lithium Manganese Oxide). The electrode composition is manufactured as a self-supporting film, and the self-supporting film can be attached to the electrode current collector.

[0018] The self-supporting membrane can have a strength of 5 kgf / cm². 2Above and 50 kgf / cm 2 The following tensile strengths.

[0019] According to another embodiment of this disclosure, a method for manufacturing an electrode for a secondary battery is provided, the method comprising the steps of: dry mixing an active material, a conductive material and an adhesive to prepare a mixture; applying a shear force to the mixture to prepare an electrode composition; manufacturing a self-supporting membrane with the electrode composition; and attaching the self-supporting membrane to an electrode current collector to form an electrode for a secondary battery, wherein the adhesive comprises a first adhesive and a second adhesive, the first adhesive and the second adhesive being different from each other, and wherein the second adhesive is attached to the surface of the first adhesive.

[0020] The glass transition temperature (T) of the second adhesive g The temperature can be greater than the glass transition temperature (T) of the first adhesive. g ).

[0021] The glass transition temperature (Tg) of the first adhesive can be above 15 degrees Celsius and below 100 degrees Celsius, and the glass transition temperature (Tg) of the second adhesive can be above 25 degrees Celsius and below 115 degrees Celsius. The step of dry mixing the active material, conductive material and adhesive to prepare the mixture can be carried out at room temperature, and the step of applying shear force to the mixture to prepare the electrode composition can be carried out at a temperature of 100 degrees Celsius or higher.

[0022] The content of the adhesive can be more than 0.51% by weight and less than 11.99% by weight based on the total weight of the electrode composition.

[0023] The content ratio of the first adhesive to the second adhesive can be from 0.1:10 to 10:0.1.

[0024] The first adhesive may include polytetrafluoroethylene (PTFE), and the second adhesive may include an acrylic polymer material.

[0025] The active material may include at least one selected from the group consisting of: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium copper oxide (Li2CuO2), vanadium oxide, Ni-position lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide having a spinel structure, LiMn2O4 wherein the Li in the formula is partially replaced by alkaline earth metal ions, disulfide, Fe2(MoO4)3, and lithium manganese oxide (LMO, Lithium Manganese Oxide).

[0026] According to another embodiment of this disclosure, a secondary battery is provided, which includes the electrodes described above for a secondary battery.

[0027] Beneficial effects

[0028] According to embodiments of this disclosure, by using electrode compositions comprising different binders to manufacture an electrode for a secondary battery and a secondary battery including the electrode, the tensile strength of the electrode can be increased and the resistance reduction effect of the secondary battery including the electrode can be improved.

[0029] The effects of this disclosure are not limited to those described above, and those skilled in the art will clearly understand from the description of the appended claims other additional effects not described above. Attached Figure Description

[0030] Figure 1 This is a diagram illustrating an electrode composition for an electrode of a secondary battery according to an embodiment of the present disclosure;

[0031] Figure 2 This is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to an embodiment of the present disclosure;

[0032] Figure 3 In the embodiments and comparative examples of this disclosure, the tensile strength and initial discharge capacity are compared based on the adhesive content of the electrodes used in the secondary battery.

[0033] Figure 4 In the embodiments and comparative examples of this disclosure, curves comparing tensile strength and initial discharge capacity are presented based on the content ratio of the first adhesive and the second adhesive for the electrodes of the secondary battery; and

[0034] Figure 5 In the embodiments and comparative examples of this disclosure, curves comparing tensile strength and initial discharge capacity are presented based on the glass transition temperatures of the first and second adhesives used for the electrodes of the secondary battery. Detailed Implementation

[0035] In the following description, various embodiments of this disclosure will be illustrated with reference to the accompanying drawings to enable those skilled in the art to readily implement them. This disclosure can be modified in various ways and is not limited to the embodiments set forth herein.

[0036] Electrodes for secondary batteries according to embodiments of this disclosure will now be described.

[0037] An electrode for a secondary battery according to an embodiment of this disclosure includes: an electrode current collector; and an electrode layer formed of a free-standing film located on the electrode current collector. The electrode layer includes an electrode composition in which an active material, a conductive material, and a binder are dry-mixed.

[0038] A self-supporting membrane can be first fabricated, then attached to the electrode current collector, and subsequently, an electrode layer is formed through a lamination process. Here, the self-supporting membrane can have a strength of 5 kgf / cm². 2 Above and 50 kgf / cm 2 The following tensile strengths.

[0039] Therefore, the self-supporting film can be in a state where the active material, conductive material, first binder, and second binder included in the electrode composition are mixed together with high bonding strength, and the self-supporting film can be easily stored in roll form. Thus, productivity and electrode flexibility can be effectively improved. However, when the tensile strength of the self-supporting film is less than 5 kgf / cm²... 2 During charging and discharging, cracks can form between the active materials in the electrodes, leading to increased resistance, decreased conductivity, and reduced lifespan.

[0040] Next, the components included in the electrodes for a secondary battery according to embodiments of this disclosure will be described in detail.

[0041] Figure 1 This is a diagram illustrating an electrode composition for an electrode of a secondary battery according to an embodiment of the present disclosure.

[0042] Reference Figure 1 The electrode for a secondary battery according to this embodiment may include a first adhesive 100 and a second adhesive 200 as adhesives. The first adhesive 100 and the second adhesive 200 may be different from each other. Here, the first adhesive 100 and the second adhesive 200 serve to improve the adhesion between active material particles and the adhesion between the active material and the current collector. Here, the second adhesive 200 may be attached to the surface of the first adhesive 100.

[0043] Therefore, in the electrode for a secondary battery according to an embodiment of the present disclosure, the first adhesive 100 can be spaced apart from each other by the second adhesive 200. This prevents contact between the first adhesives 100 and reduces agglomeration of the first adhesives 100. Furthermore, without interfering with the bridging effect of the first adhesives 100 between active material particles or between active material particles and the current collector, the dispersibility of the first adhesives 100 can be improved, and the tensile strength and flexibility of the electrode can also be improved.

[0044] In one example, the first adhesive 100 may include polytetrafluoroethylene (PTFE). Here, PTFE has the property of pulling fibers out of the particles when a shear force is applied. That is, in the electrode for a secondary battery according to an embodiment of this disclosure, a strong shear force is applied to the electrode composition containing PTFE, thereby mixing the electrode composition by a physical mixing method according to the fiberization of the PTFE.

[0045] Therefore, in the electrode for a secondary battery according to the embodiments of the present disclosure, the electrode composition can be dry-mixed without separate solvents or additives, which is very effective for bridging between active material particles or between active material particles and current collectors, and can also prevent damage to the active material during high-temperature heat treatment according to existing mixing methods.

[0046] In one example, the second adhesive 200 may comprise an acrylic polymer material. Here, the acrylic polymer material includes acrylic-based polymers and acrylate-based polymers, and at least one of these may be selected and used. In one example, the second adhesive 200 may be at least one selected from the group consisting of polyacrylic acid (PAA), methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), ethylhexyl acrylate (EHA), and methyl methacrylate (MMA).

[0047] In addition, the glass transition temperature (T) of the second adhesive 200 g The glass transition temperature (T) can be greater than that of the first adhesive (100). g Here, the glass transition temperature (T) of the second adhesive 200 is... g It can be higher than room temperature. Room temperature is typically defined as a temperature with a 5-degree Celsius margin of error based on a standard temperature of 20 degrees Celsius.

[0048] More specifically, the glass transition temperature (T00) of the first adhesive 100 g The temperature can be above 15 degrees Celsius and below 100 degrees Celsius, and the glass transition temperature (T) of the second adhesive 200 is... g The temperature can be above 25 degrees Celsius and below 115 degrees Celsius. In one example, the glass transition temperature (T00) of the first adhesive 100 is... g The temperature is above 15 degrees Celsius and below 95 degrees Celsius, and the glass transition temperature (T) of the second adhesive 200 is... g The temperature can be above 30 degrees Celsius and below 110 degrees Celsius.

[0049] Here, the glass transition temperature (Tg) can typically be measured using methods such as DSC, DMA, and TMA. g For example, in this embodiment, the glass transition temperature (T) g The glass transition temperature (Tg) is measured using the DSC method, with applicable standard ISO 11357-2. Alternatively, a TA Instrument Q20 can be used as the measuring device, and measurements can be performed over a temperature range of -50 to 200°C at a heating rate of 20°C / min. Analysis is performed using a secondary heating curve, where the inflection point method can be employed to determine the glass transition temperature (Tg). g ).

[0050] Therefore, in the electrode for a secondary battery according to an embodiment of the present disclosure, the first adhesive 100 and the second adhesive 200 have glass transition temperatures within the aforementioned range, and the second adhesive 200 is attached to the surface of the first adhesive 100 in a state where the second adhesive 200 is not melted at room temperature, thus preventing the aggregation of the first adhesive 100.

[0051] Furthermore, when the temperature rises during subsequent electrode manufacturing and becomes higher than the glass transition temperature (T00) of the second binder 200, g When the second adhesive 200 is melted, the first adhesive 100 can be fiberized, thereby bridging between active material particles or between active material particles and current collectors.

[0052] In other words, the first adhesive 100 and the second adhesive 200 can be within the glass transition temperature (T) range mentioned above. g Effectively regulates the fiberization time of the first adhesive 100.

[0053] On the other hand, when the glass transition temperature (T) of the second adhesive 200 g The glass transition temperature (T) is lower than that of the first adhesive 100. g When the glass transition temperature (T00) of the first adhesive 100 is reached, the second adhesive 200 melts before the first adhesive 100, thus reducing or eliminating the second adhesive 200 remaining on the surface of the first adhesive 100. In this case, there is no problem of not being able to adjust the fiberization timing of the first adhesive 100, when the glass transition temperature (T00) of the first adhesive 100 is reached. g When the temperature is below room temperature, there is a problem that the first adhesive 100 will fibrose at room temperature, and it is difficult to prevent the first adhesive 100 from agglomerating.

[0054] Furthermore, when the glass transition temperatures (T) of the first adhesive 100 and the second adhesive 200 are... gBelow the aforementioned temperature range, at least a portion of the second adhesive 200 melts at room temperature, and the first adhesive 100 undergoes fibrosis at room temperature, making it difficult to prevent the aggregation of the first adhesive 100. Therefore, the bridging effect between particles within the electrode composition may decrease, and the tensile strength may also be significantly reduced.

[0055] Conversely, when the glass transition temperatures (T) of the first adhesive 100 and the second adhesive 200 are... g When the temperature is above the above-mentioned range, the following problems exist in the electrode manufacturing process: additional manufacturing time, manufacturing equipment, etc. are required in the process of raising the temperature to melt the first adhesive 100 and the second adhesive 200, and the fiberization of the first adhesive 100 cannot be carried out.

[0056] Furthermore, the content of binders 100 and 200 can be more than 0.51% by weight and less than 11.99% by weight based on the total weight of the electrode composition. More preferably, the content of binders 100 and 200 can be more than 1% by weight and less than 11% by weight based on the total weight of the electrode composition. In one example, the content of binders 100 and 200 can be more than 1% by weight and less than 10% by weight based on the total weight of the electrode composition.

[0057] Therefore, the electrode for a secondary battery according to this embodiment contains a binder within the aforementioned range, thereby maximizing the fiberization of the binder and achieving excellent bridging effects between particles within the electrode composition, resulting in excellent tensile strength. Furthermore, it prevents binder aggregation and improves dispersibility, thus the electrode containing the aforementioned electrode composition exhibits excellent resistance reduction.

[0058] In contrast, when the total content of binders 100 and 200 is less than 0.51% by weight, the bridging effect between particles within the electrode composition decreases, and therefore the tensile strength may also be significantly reduced. Furthermore, when the content of binders 100 and 200 is greater than 11.9% by weight, the first and second binders act as resistors in the electrode comprising the electrode composition, leading to problems with predicting high output.

[0059] Furthermore, the content ratio of the first adhesive 100 and the second adhesive 200 can be from 0.1:10 to 10:0.1. More preferably, the content ratio of the first adhesive 100 and the second adhesive 200 can be from 0.5:10 to 10:0.5. In one example, the content ratio of the first adhesive 100 and the second adhesive 200 can be from 1:10 to 10:1.

[0060] Therefore, the electrode for a secondary battery according to this embodiment contains a first binder 100 and a second binder 200 within the above-mentioned range, thereby maximizing the fiberization of the binder, resulting in excellent bridging effect between particles within the electrode composition, and thus excellent tensile strength. Furthermore, it prevents binder aggregation and improves dispersibility, thus the electrode containing the above-mentioned electrode composition exhibits excellent resistance reduction.

[0061] In contrast, when the content ratio of the first binder 100 to the second binder 200 is less than 0.1, the degree of fiberization of the binder decreases, and when only the second binder 200 is included, there is a problem that the electrode cannot be manufactured. Furthermore, when the content ratio of the first binder 100 to the second binder 200 is greater than 10, the binder is prone to agglomeration, which may reduce the resistance reduction effect of the electrode and degrade the battery performance.

[0062] The active material can be a positive electrode active material. Positive electrode active materials may include, for example: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide, lithium copper oxide (Li2CuO2), vanadium oxide, Ni-site lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide with spinel structure, LiMn2O4 in which the Li in the formula is partially replaced by alkaline earth metal ions, disulfide compounds, Fe2(MoO4)3 and the like.

[0063] In one example, the active material may include lithium manganese oxide (LMO). Here, the active material may be included in an amount of 85% to 99% by weight based on the total weight of the electrode composition. More preferably, the active material may be included in an amount of 87% to 98% by weight based on the total weight of the electrode composition. In one example, the active material may be included in an amount of 89% to 97% by weight based on the total weight of the electrode composition.

[0064] Conductive materials are used to impart conductivity to the electrodes, and there are no particular limitations on the types of conductive materials that can be used, as long as they are electronically conductive and do not cause chemical changes in the battery to be constructed. Specific examples of conductive materials include: carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon graphene, and carbon fibers; graphite such as natural graphite and artificial graphite; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. These conductive materials can be used alone or as a mixture of two or more. Here, the conductive material can be included in an amount from 1% to 10% by weight based on the total weight of the electrodes.

[0065] The electrodes described above for a secondary battery may be included as the positive electrode in a secondary battery according to another embodiment of the present disclosure. More specifically, a secondary battery according to another embodiment of the present disclosure may include an electrode assembly and an electrolyte, the electrode assembly including a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode.

[0066] Similar to the electrodes used in secondary batteries, a negative electrode can be manufactured by applying a negative electrode slurry, including a negative electrode active material, a polymer material, a conductive material, etc., to a negative electrode current collector.

[0067] The negative electrode can also be manufactured by attaching or applying a negative electrode slurry, which includes a negative electrode active material, to a negative electrode current collector, and the negative electrode slurry may further include, together with the negative electrode active material, the conductive material and polymer material as described above.

[0068] The negative electrode active material can be any material commonly used in the art for lithium secondary batteries. In one example, materials such as lithium metal, lithium alloy, petroleum coke, activated carbon, graphite, silicon, tin, metal oxides, or other carbon materials can be used.

[0069] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatments of carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, and similar materials can be used.

[0070] The separator separates the negative and positive electrodes and provides a channel for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with excellent electrolyte retention capabilities and low resistance to electrolyte ion migration are preferred. Furthermore, the electrolyte solution used herein may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, or the like that can be used in the preparation of lithium secondary batteries.

[0071] Specifically, the electrolyte solution may include organic solvents and lithium salts. As an organic solvent, any solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reactions of the battery can migrate. Lithium salts can be used without particular limitation, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries.

[0072] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, in addition to the electrolyte components described above, the electrolyte solution may further include, for example, one or more additives, such as haloalkyl carbonate compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, ethylene glycol dimethyl ether (glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the additives may be included in an amount from 0.1% to 5% by weight, based on the total weight of the electrolyte solution.

[0073] Figure 2 This is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to an embodiment of the present disclosure. (Refer to...) Figure 2 The method for manufacturing an electrode for a secondary battery according to this embodiment includes: a premixing step (S10) of mixing an active material, a conductive material and a binder; a mixing step (S20) of applying a high shear force to prepare an electrode composition; a step of manufacturing a self-supporting film using a second electrode composition (S30); and a step of manufacturing an electrode by a lamination process after attaching the self-supporting film to an electrode current collector (S40).

[0074] Here, in the premixing step (S10), the active material, conductive material, and adhesive can be dry-mixed. The adhesive includes a first adhesive and a second adhesive, which are different from each other. The second adhesive is attached to the surface of the first adhesive.

[0075] The present disclosure will be described below through more specific embodiments. However, the following embodiments are for illustrative purposes only, and the scope of the present disclosure is not limited thereto.

[0076] <Example 1>

[0077] Perform a premixing step (S10) to prepare a mixture in which the active material, conductive material, first binder, and second binder are dry-mixed using a Waring blender. Here, the active material is 92% by weight of lithium manganese oxide (LMO), and the conductive material is 2% by weight of Super C65.

[0078] The total content of polytetrafluoroethylene (PTFE) as the first binder and the acrylic polymer as the second binder is 6% by weight. Here, the content ratio of the first binder 100 to the second binder 200 is 70:30. Furthermore, the glass transition temperature (Tg) of the first binder 100 is... g The glass transition temperature (T) of the second adhesive 200 is 34 degrees Celsius. g The temperature is 55 degrees Celsius. At this time, the premixing step (S10) is carried out at 5000 rpm for 1 minute at room temperature.

[0079] Subsequently, a mixing step (S20) was performed using a Bench Kneader PBV-0.1L apparatus (purchased from Irie Shokai), in which shear force was applied to the mixture prepared in the premixing step (S10) to prepare the electrode composition. At this time, the mixing step (S20) was carried out at 100 degrees Celsius and 30 rpm for 5 minutes.

[0080] <Example 2>

[0081] In Example 2, the content ratio of the first adhesive 100 and the second adhesive 200 is 40:60. Furthermore, the glass transition temperature (Tg) of the second adhesive 200 is... g The temperature was 40 degrees Celsius. Apart from this, the electrode composition was prepared in the same manner as in Example 1.

[0082] <Example 3>

[0083] In Example 3, the active material was 97% by weight of lithium manganese oxide (LMO), and the total content of the first binder 100 and the second binder 200 was 1% by weight. Except for this, the electrode composition was prepared in the same manner as in Example 1.

[0084] <Example 4>

[0085] In Example 4, the active material was 88% by weight of lithium manganese oxide (LMO), and the total content of the first binder 100 and the second binder 200 was 10% by weight. Except for this, the electrode composition was prepared in the same manner as in Example 1.

[0086] <Example 5>

[0087] In Example 5, the glass transition temperature (T) of the first adhesive 100 g The glass transition temperature (T) of the second adhesive 200 is 90 degrees Celsius. g The temperature was 106 degrees Celsius. Apart from this, the electrode composition was prepared in the same manner as in Example 1.

[0088] <Comparative Example 1>

[0089] In Comparative Example 1, the active material was 97.5% by weight of lithium manganese oxide (LMO), and the total content of the first binder 100 and the second binder 200 was 0.5% by weight. Except for this, the electrode composition was prepared in the same manner as in Example 1.

[0090] <Comparative Example 2>

[0091] In Comparative Example 2, the active material was 86% by weight of lithium manganese oxide (LMO), and the total content of the first binder 100 and the second binder 200 was 12% by weight. Except for this, the electrode composition was prepared in the same manner as in Example 1.

[0092] <Comparative Example 3>

[0093] In Comparative Example 3, the content ratio of the first adhesive 100 and the second adhesive 200 was 100:0. Furthermore, the glass transition temperature (Tg) of the first adhesive 100 was... g The temperature was 25 degrees Celsius. Apart from this, the electrode composition was prepared in the same manner as in Example 1.

[0094] <Comparative Example 4>

[0095] In Comparative Example 4, the content ratio of the first binder 100 and the second binder 200 was 0:100. Apart from this, the electrode composition was prepared in the same manner as in Example 1.

[0096] <Comparative Example 5>

[0097] In Comparative Example 5, the glass transition temperature (T) of the first adhesive 100 gThe glass transition temperature (T) of the second adhesive 200 is -10 degrees Celsius. g The temperature is -40 degrees Celsius. Apart from this, the electrode composition is prepared in the same manner as in Example 1.

[0098] <Comparative Example 6>

[0099] In Comparative Example 6, the glass transition temperature (T) of the first adhesive 100 g The glass transition temperature (T) of the second adhesive 200 is 11 degrees Celsius. g The temperature is -12 degrees Celsius. Apart from this, the electrode composition is prepared in the same manner as in Example 1.

[0100] <Comparative Example 7>

[0101] In Comparative Example 7, the glass transition temperature (T) of the first adhesive 100 g The glass transition temperature (T) of the second adhesive 200 is 110 degrees Celsius. g The temperature was 120 degrees Celsius. Apart from this, the electrode composition was prepared in the same manner as in Example 1.

[0102] <Experimental Example 1 (Determination of Tensile Strength)>

[0103] Reference Figure 2 For the electrode compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 6, a self-supporting membrane manufacturing step (S30) was performed using a rolling mill (purchased from Inoue MFG) to manufacture self-supporting membranes with a length of 20 mm and a width of 20 mm. For each manufactured self-supporting membrane, both ends were fixed with clamps, and the tensile strength of the self-supporting membrane was measured using an Instron UTM device at a speed of 50 mm / min. The results are shown in Table 1 below.

[0104] [Table 1]

[0105]

[0106] <Experimental Example 2 (Determination of Discharge Capacity)>

[0107] Reference Figure 2 For Examples 1 to 5 and Comparative Examples 1 to 6, the self-supporting film roller manufactured in Test Example 1 was pressed onto a current collector serving as aluminum foil, and then the load value was set to 5 mAh / cm². 2The porosity was set to 30%. Under these conditions, the electrode fabrication step (S40) for manufacturing the positive electrode was performed. Then, a coin-shaped half-cell was fabricated together with each fabricated positive electrode using lithium metal with a thickness of 200 μm as the negative electrode. Then, for each fabricated coin-shaped half-cell, the discharge capacity value after the first cycle of charging and discharging was calculated under 0.1C / 0.1C conditions within a voltage range of 3.0-4.3V, and the results are shown in Table 2 below.

[0108] [Table 2]

[0109]

[0110] <Experimental Results Analysis>

[0111] Figure 3 In the embodiments and comparative examples of this disclosure, curves comparing tensile strength and initial discharge capacity are presented based on the binder content of the electrodes used in secondary batteries. Specifically, Figure 3 These are graphs showing the tensile strength and initial discharge capacity of Examples 1, 3, 4, Comparative Example 1, and Comparative Example 2, respectively, used to compare the results shown in Tables 1 and 2. In Comparative Example 1, Example 3, Example 1, Example 4, and Comparative Example 2, the content ratio of the first adhesive and the second adhesive is the same, wherein the total content of the first adhesive 100 and the second adhesive 200 increases in the order of Comparative Example 1, Example 3, Example 1, Example 4, and Comparative Example 2.

[0112] In Comparative Example 1, the total content of the first adhesive 100 and the second adhesive 200 was 0.5% by weight, which was less than the content in the Example. In Comparative Example 2, the total content of the first adhesive 100 and the second adhesive 200 was 12% by weight, which was greater than the content in the Example.

[0113] Reference Figure 3 It can be confirmed that as the total content of the first adhesive 100 and the second adhesive 200 increases, the tensile strength becomes excellent, but the initial discharge capacity decreases. That is, when the total content of the first adhesive 100 and the second adhesive 200 is too low, there is a problem of reduced tensile strength. Furthermore, when the total content of the first adhesive 100 and the second adhesive 200 is too high, the resistance of the adhesive also increases with the increase of the adhesive content, which leads to a problem of reduced initial discharge capacity. Therefore, when the total content of the first adhesive 100 and the second adhesive 200 is as in Examples 1, 3, and 4, it can be confirmed that both the tensile strength and the initial discharge capacity are excellent overall.

[0114] Figure 4In the embodiments and comparative examples of this disclosure, curves comparing tensile strength and initial discharge capacity are presented based on the content ratio of the first and second adhesives for the electrodes of the secondary battery. Specifically, Figure 4 These are graphs showing the tensile strength and initial discharge capacity of Examples 1, 2, 3, and 4, respectively, used to compare the results shown in Tables 1 and 2. In Examples 1, 2, 3, and 4, the total content of the first adhesive 100 and the second adhesive 200 is the same, but their content ratios differ. Here, in the order of Comparative Example 4, Example 2, Example 1, and Comparative Example 3, the content of the first adhesive gradually increases, and the content of the second adhesive gradually decreases.

[0115] Reference Figure 4 First, as in Comparative Example 4, when only the second binder is included in the binder, it is difficult to manufacture the electrode during dry mixing, and therefore it is impossible to measure the tensile strength and initial discharge capacity. Thus, it can be confirmed that the first binder must be included in the electrode for a secondary battery according to this disclosure.

[0116] In addition, refer to Figure 4 As in Comparative Example 3, when only the first adhesive is included in the adhesive, it can be confirmed that both tensile strength and initial discharge capacity are reduced. This is because when the first adhesive is used alone, it will aggregate at room temperature, thereby reducing the bridging effect between particles and increasing the resistance.

[0117] Therefore, with the content ratio of the first adhesive 100 and the second adhesive 200 as in Examples 1 and 2, it can be confirmed that the tensile strength and initial discharge capacity are excellent overall.

[0118] Figure 5 In the embodiments and comparative examples of this disclosure, curves comparing tensile strength and initial discharge capacity are presented based on the glass transition temperatures of the first and second adhesives used in the electrodes of the secondary battery. Specifically, Figure 5 These are graphs showing the tensile strength and initial discharge capacity of Examples 1, 5, Comparative Examples 5, and 6, respectively, used to compare the results shown in Tables 1 and 2. In Examples 1, 5, 5, 6, and 7, the content and ratio of the first adhesive 100 and the second adhesive 200 are the same, but the glass transition temperatures of the first adhesive 100 and the second adhesive 200 are different. Here, the glass transition temperatures of the first adhesive 100 and the second adhesive 200 increase in the order of Comparative Examples 5, 6, 1, 5, and 7. Figure 5 Comparative Example 7 is omitted because tensile strength and initial discharge capacity could not be measured.

[0119] Reference Figure 5 It can be confirmed that as the glass transition temperature of the first adhesive 100 and the second adhesive 200 increases, the tensile strength and initial discharge capacity gradually increase.

[0120] That is, as in Comparative Examples 5 and 6, when the glass transition temperatures of the first adhesive 100 and the second adhesive 200 are too low, the second adhesive 200 melts at room temperature, and therefore the second adhesive 200 may not easily adhere to the surface of the first adhesive 100. Therefore, when a second adhesive 200 with an excessively low glass transition temperature is included, there is a problem that it is difficult to prevent the first adhesive 100 from agglomerating at room temperature.

[0121] Furthermore, as in Comparative Examples 5 and 6, when the glass transition temperature of the second adhesive 200 is lower than that of the first adhesive 100, the second adhesive 200 melts before the first adhesive 100, which causes the following problem: it is difficult to further prevent the coagulation of the first adhesive 100.

[0122] Furthermore, referring to Tables 1 and 2, as in Comparative Example 7, when the glass transition temperatures of the first adhesive 100 and the second adhesive 200 are too high, it can be confirmed that the first adhesive 100 does not fibrose at the processing temperature, and therefore, the tensile strength and initial discharge capacity cannot be measured. Therefore, when the first adhesive 100 and the second adhesive 200 have glass transition temperatures as in Examples 1 and 5, it can be confirmed that agglomeration of the first adhesive 100 is effectively prevented, while fibrosis progresses smoothly; thus, the overall tensile strength and initial discharge capacity are excellent.

[0123] Although the invention has been shown and described above with reference to preferred embodiments, the scope of this disclosure is not limited thereto, and those skilled in the art can design many other variations and modifications using the principles of the invention as defined in the appended claims, which will also fall within the spirit and scope of this disclosure.

Claims

1. An electrode for a secondary battery, comprising: Electrode current collector; and The electrode layer located on the electrode current collector, The electrode layer comprises an electrode composition in which active materials, conductive materials, and binders are dry-mixed. The adhesives mentioned above include a first adhesive and a second adhesive, wherein the first adhesive and the second adhesive are different from each other. The second adhesive is attached to the surface of the first adhesive. The glass transition temperature (T) of the second adhesive g The glass transition temperature (T) of the first adhesive is greater than that of the first adhesive. g ), The first adhesive has a glass transition temperature (Tg) of 15 degrees Celsius or higher and 100 degrees Celsius or lower, and the second adhesive has a glass transition temperature (Tg) of 25 degrees Celsius or higher and 115 degrees Celsius or lower. The binder content is between 0.51% by weight and 11.99% by weight, based on the total weight of the electrode composition. The content ratio of the first adhesive to the second adhesive is from 0.1:10 to 10:0.

1.

2. The electrode for a secondary battery according to claim 1, wherein: The first adhesive comprises polytetrafluoroethylene, and The second adhesive comprises an acrylic polymer material.

3. The electrode for a secondary battery according to claim 1, wherein: The active material includes at least one selected from the group consisting of: lithium cobalt oxide, lithium nickel oxide, lithium copper oxide, vanadium oxide, Ni-site lithium nickel oxide, lithium manganese composite oxide, and Fe2(MoO4)3.

4. The electrode for a secondary battery according to claim 1, wherein: The electrode composition is fabricated into a self-supporting film, and The self-supporting membrane is attached to the electrode current collector.

5. The electrode for a secondary battery according to claim 4, wherein: The self-supporting membrane has a strength greater than 8 kgf / cm². 2 And 50 kgf / cm 2 The following tensile strengths.

6. A method for manufacturing an electrode for a secondary battery, the method comprising the following steps: The active material, conductive material and adhesive are dry-mixed to prepare a mixture; Shear force is applied to the mixture to prepare the electrode composition; A self-supporting membrane is manufactured using the electrode composition described above; and The self-supporting membrane is attached to an electrode current collector to form an electrode for a secondary battery. The adhesive comprises a first adhesive and a second adhesive, wherein the first adhesive and the second adhesive are different from each other, and The second adhesive is attached to the surface of the first adhesive. The glass transition temperature (T) of the second adhesive g The glass transition temperature (T) of the first adhesive is greater than that of the first adhesive. g ), The first adhesive has a glass transition temperature (Tg) of 15 degrees Celsius or higher and 100 degrees Celsius or lower, and the second adhesive has a glass transition temperature (Tg) of 25 degrees Celsius or higher and 115 degrees Celsius or lower. Based on the total weight of the electrode composition, the sum of the contents of the first binder and the second binder is 0.51% by weight or more and 11.99% by weight or less, and The content ratio of the first adhesive to the second adhesive is from 0.1:10 to 10:0.

1.

7. The method for manufacturing an electrode for a secondary battery according to claim 6, wherein: The step of dry-mixing the active material, conductive material, and binder to prepare the mixture is carried out at room temperature, and The step of applying shear force to the mixture to prepare the electrode composition is carried out at a temperature of 100 degrees Celsius or higher.

8. The method for manufacturing an electrode for a secondary battery according to claim 6, wherein: The first adhesive comprises polytetrafluoroethylene, and The second adhesive comprises an acrylic polymer material.

9. The method for manufacturing an electrode for a secondary battery according to claim 6, wherein: The active material includes at least one selected from the group consisting of: lithium cobalt oxide, lithium nickel oxide, lithium copper oxide, vanadium oxide, Ni-site lithium nickel oxide, lithium manganese composite oxide, and Fe2(MoO4)3.

10. A secondary battery comprising the electrodes for a secondary battery as described in claim 1.

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