Electrode and secondary battery comprising same

Abstract

The present specification relates to an electrode comprising: an electrode mixture film including an electrode active material and a binder having a three-dimensional fiber network structure; and a current collector having the electrode mixture film disposed on at least one surface thereof, wherein the electrode has a low-intensity region of 15.0% or more on the basis of area with respect to the entire region on the surface thereof, and the low-intensity region is defined as a region in which IB, the intensity of a peak appearing in the range of wave numbers of 1190 cm-1 to 1260 cm-1, is 1.0 or less in an IR spectrum derived by analyzing the surface of the electrode by attenuated total reflection infrared spectroscopy (ATR-FTIR). Through this, structural characteristics such as fiber thickness, fiber amount, and arrangement state of the fibrous binder on the electrode surface are controlled, so that calendering processability is excellently performed, thereby providing an electrode having excellent appearance characteristics, and providing a secondary battery, a battery box, and an electric device having excellent durability, lifespan characteristics, output, and rapid charging performance.

Description

Electrode and secondary battery including the same

[0001] The present specification discloses technology relating to an electrode and a secondary battery including said electrode.

[0002]

[0003] Secondary batteries are used not only in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and E-bikes, but also in large products requiring high output such as electric vehicles and hybrid vehicles, as well as in power storage devices that store surplus power or new and renewable energy and backup power storage devices.

[0004] Typically, a secondary battery is manufactured by applying an electrode active material slurry to a positive electrode current collector and a negative electrode current collector to form an electrode active material layer, then manufacturing a positive electrode and a negative electrode through drying and rolling processes, and then stacking them on both sides of a separator to form an electrode assembly of a predetermined shape, and then housing the electrode assembly in a battery case, injecting an electrolyte, and sealing.

[0005] Meanwhile, during the drying process of the electrode active material slurry, defects such as pinholes or cracks may be induced in the electrode active material layer formed on the current collector as the solvent contained in the slurry evaporates. In addition, since the inner and outer parts of the electrode active material slurry are not dried uniformly during the drying process, there is a risk that the electrode quality may deteriorate due to a powder floating phenomenon caused by the difference in solvent evaporation rates, that is, powders in the parts that dry first rise and form a gap with the parts that dry relatively later.

[0006] To solve the above problem, drying devices capable of controlling the evaporation rate of the solvent are being considered so that the inside and outside of the electrode active material slurry can be dried uniformly; however, these drying devices are very expensive and require significant cost and time to operate, which is disadvantageous in terms of manufacturing processability.

[0007] On the other hand, the solvent included in conventional electrode active material slurries is N-methyl-2-pyrrolidone (NMP), which has a high boiling point and requires high thermal energy and a very long drying oven to dry, making it very unfavorable for mass production. In addition, N-methyl-2-pyrrolidone (NMP) is a toxic substance and is harmful to living organisms, so it has the disadvantage of not being environmentally friendly.

[0008] Therefore, there has recently been a trend of active research on dry electrodes that manufacture electrodes without using solvents. The above-mentioned dry electrode is generally manufactured by laminating a free-standing type electrode composite film, which is manufactured in a sheet form and includes an electrode active material, a binder, a conductive material, etc., onto a current collector. This electrode composite film includes a process of first fiberizing the electrode active material, a carbon material as a conductive material, and a fiberizable binder, and then calendering the obtained mixture into a film form to manufacture a free-standing film.

[0009] The aforementioned dry electrode can be manufactured through various routes and methods, and the conditions requiring control differ for each method. Furthermore, even minute differences in process conditions or subtle variations in the composition and particle size of the electrode materials can significantly affect the fabrication feasibility, appearance characteristics, durability, and cell performance of the electrode. Therefore, there is a need to develop a dry electrode that possesses excellent appearance characteristics while ensuring cell performance.

[0010]

[0011] In this specification, by determining the fiber thickness, density, and arrangement relationship of electrode materials, such as fibrous binders, on the surface of the electrode through an analysis method applying attenuated total reflection infrared spectroscopy, high-intensity regions and low-intensity regions are defined according to the analysis, thereby providing an electrode with excellent resistance characteristics and appearance characteristics.

[0012] In addition, the present specification aims to provide a secondary battery with excellent durability and lifespan characteristics by applying an electrode that has excellent appearance characteristics, superior mechanical properties, and improved resistance characteristics.

[0013]

[0014] [1] According to one embodiment, an electrode comprises: an electrode composite film comprising an electrode active material and a binder having a three-dimensional fiber network structure; and a current collector having the electrode composite film disposed on at least one surface thereof, wherein the electrode has a low-intensity region of 15.0% of the total surface area, and the low-intensity region has a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the surface of the electrode by attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 The integral value of the peak appearing in the range, I B An electrode is provided, defined as a region where α is 1.0 or less.

[0015] [2] In the electrode of [1] above, the low-intensity region of the entire surface area of ​​the electrode is 15.0% to 85.0% in terms of area, and the low-intensity region has a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the surface of the electrode by attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 The integral value of the peak appearing in the range, I B It may be defined as an area where is 1.0 or less.

[0016] [3] In the electrode of [1] and / or [2] above, the high-intensity region of the entire surface area of ​​the electrode is 15.0% or less in terms of area, and the high-intensity region has a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the surface of the electrode by attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity appearing in the range, I B It may be defined as an area where is 1.75 or higher.

[0017] [4] In at least one of the electrodes [1] to [3] above, the high-intensity region of the entire surface area of ​​the electrode is 10.0% or less in terms of area, and the high-intensity region has a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the surface of the electrode by attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity appearing in the range, I B It may be defined as an area where is 1.75 or higher.

[0018] [5] In at least one of the electrodes [1] to [4] above, the electrode active material may comprise a lithium transition metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe).

[0019] [6] In at least one of the electrodes [1] to [5] above, the electrode active material may include a lithium iron phosphate-based compound, and the lithium iron phosphate-based compound may include a compound represented by the following chemical formula 1.

[0020] [Chemical Formula 1]

[0021] Li 1+a [Fe 1-x M x ]PO4

[0022] In the above chemical formula 1, M comprises one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤x≤0.5, 0≤y<1.

[0023] [7] In at least one of the electrodes [1] to [6] above, the binder may be included in an amount of 3.5% by weight or less relative to the total weight of the electrode composite film.

[0024] [8] In at least one of the electrodes [1] to [7] above, the binder may include polytetrafluoroethylene (PTFE).

[0025] [9] At least one of the electrodes [1] to [8] above may be an anode.

[0026]

[0027]

[0010] In another aspect, a secondary battery is provided that includes at least one electrode of [1] to [9] above.

[0028]

[0011] A battery box containing the secondary battery of

[0010] above is provided.

[0029]

[0012] An electric device including the battery box of

[0011] above is provided.

[0030]

[0031] In one aspect, the electrode can improve the processability of the calendering process and achieve the effect of improving the appearance characteristics and durability of the electrode by identifying and controlling the surface distribution state according to fiber thickness of the fibrous binder from the area ratio of the low-intensity region defined by an analysis method applying attenuated total reflection infrared spectroscopy. In addition, by including an appropriate amount or more of the low-intensity region on the surface, resistance characteristics can be improved through increased electrical conductivity resulting from increased contact area between active materials and contact area between the conductive material and the active material.

[0032] In another aspect, by applying the electrode, the above secondary battery can have excellent durability and improved lifespan characteristics, and as resistance characteristics are improved, improved output performance can be expected.

[0033]

[0034] Figure 1 is an IR spectrum derived by attenuated total reflection infrared spectroscopy (ATR-FTIR).

[0035] Figure 2 is an example of an image in which the IR spectrum mapping results of Figure 1 are standardized.

[0036]

[0037] The present invention will be described in more detail below.

[0038] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0039] In this specification, "volume cumulative n% particle size Dn" refers to the particle size corresponding to n% of the volume cumulative amount in the particle size distribution curve, where n may be an integer between 1 and 99, and usually D 10 , D 50 and D 90 This can be primarily used. The above D n For example, it can be measured using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the sub-micron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0040] In this specification, "average particle size" refers to the arithmetic mean of the particle sizes of at least 30 particles observed in a scanning electron microscope image when the cross-section of the electrode is observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope. In this case, particle size refers to the diameter of the longest axis of the particle. The above "volume cumulative 50% particle size D" 50 Although " and "average particle size" differ in measurement method, their values ​​can be derived to be substantially the same, and the cumulative 50% particle size D measured in the powder state 50 After the powder is manufactured into an electrode, it may have a value similar to the average particle size observed in the scanning electron microscope image of the electrode and the error range level.

[0041] In this specification, "composite composition" refers to a mixture comprising an electrode active material and a binder (optionally including a conductive material) that is physically mixed to form a uniform dispersed phase. As a product of the mixing process according to this specification, it may be a powdered mixture and may substantially not involve a solvent. Here, "substantially not involving a solvent" means that no solvent is introduced or only a very small amount of solvent is introduced during the mixing of the composite composition.

[0042] In this specification, “mixed aggregate” refers to a product of a mixing process (kneading process) according to this specification in which the powdered mixture is converted into a dough-like aggregate as the binder is fiberized under shear force, and the product may have a solid content of 100%.

[0043] In this specification, “powder for electrode” refers to a material in which the mixed aggregate is crushed to form a powder with a smaller particle size, and may mean an electrode material in powder form comprising an electrode active material, a binder, and optionally a conductive material.

[0044] In this specification, the term "electrode composite film" may refer to a free-standing type single sheet manufactured using an "electrode composite" comprising an electrode active material and a binder without the involvement of a solvent, or an electrode composite layer laminated onto a current collector. In this specification, the term "free-standing type" means that it can maintain an independent form without relying on other components and can be moved or handled on its own. As described below, the electrode composite film may be formed by accumulating electrode powders by compression.

[0045] In this specification, “powder-sheeting film” refers to a sheet-shaped film manufactured through a powder-sheeting process in which powder for an electrode passes through a rolling roll for the first time in a roll-to-roll process, and may be a self-standing sheet. Here, “powder-sheeting” means that the powder for the electrode is formed into a self-standing sheet shape by a rolling roll of a roll-to-roll process, and “sheeting” may have substantially the same meaning as calendering, and may refer to a process performed during the process of manufacturing the powder-sheeting film into an electrode composite film, which may refer to a process of rolling the powder-sheeting film.

[0046] In this specification, the “three-dimensional fiber network structure” refers to a structure formed by the fiberization of a binder during the process of sheet forming from a composite composition comprising an electrode active material and a binder into an electrode composite film, wherein a plurality of fibers are connected in any direction at a plurality of points. The three-dimensional fiber network structure may refer to various forms of structures capable of functioning as a support that enables the electrode composite film to be a self-standing film, by having a fine fibrous binder form a framework. At this time, the electrode active material and, optionally, a conductive material may be accommodated within the pores formed in the three-dimensional fiber network structure.

[0047] In this specification, the term "dry electrode" may refer to an electrode manufactured from a process in which a solvent is substantially not involved in the manufacturing process, wherein an electrode composite layer on a current collector, i.e., an electrode composite film, is manufactured by including an electrode active material and a binder (optionally, a conductive material). Here, "substantially not involved in the manufacturing of the electrode" means that no solvent is introduced or only a very small amount of solvent is introduced during the manufacturing of the electrode.

[0048] In this specification, each of the electrode and the secondary battery including the same comprises one or more of the technical features and / or technical configurations described below, and these technical features and / or technical configurations may be combined in various ways.

[0049]

[0050] electrode

[0051] In one aspect, an electrode comprising: an electrode composite film comprising an electrode active material and a binder having a three-dimensional fiber network structure; and a current collector having said electrode composite film disposed on at least one surface thereof, wherein the electrode has a low-intensity region of at least 15.0% in area relative to the entire surface area, and said low-intensity region has a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the surface of the electrode by attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 The integral value of the peak appearing in the range, I B An electrode characterized by being defined as a region where is 1.0 or less may be provided.

[0052]

[0053] The above electrode composite film requires precise control of the conditions of the mixing, kneading, and calendering processes to uniformly disperse and fiberize the binder in the active material in order to secure the appearance and mechanical properties of the electrode. For example, the powder in a mixed state of electrode materials obtained through kneading is formed into a sheet by roll rolling. The powder sheeting film, which is the film immediately after the powder is formed into a sheet, may require precise control of the calendering process conditions (roll rolling and lamination with the current collector) depending on its physical properties and the dispersion state of the electrode materials within the film. If these conditions are not precisely controlled, the powder may not attach or detach properly from the roll at the appropriate time, which can cause appearance defects, and a reduction in the battery's lifespan due to minute appearance defects may also become a problem.

[0054] Furthermore, since the dispersion / distribution state of electrode materials in the powder sheeting film tends not to change significantly in the dry electrode after final lamination with the current collector, it may be important to check the dispersion state early and properly control the calendering process to maintain this dispersion state, while also understanding the correlation between the dispersion state and the performance of the dry electrode.

[0055] However, since there is currently no method to quantitatively analyze the dispersion state of electrode materials within the film, performing the calendering process on powder sheeting films with poor dispersion reduces process efficiency and makes it difficult to optimize calendering process conditions. Furthermore, it is difficult to identify the correlation between the dispersion state of high-performance dry electrodes.

[0056]

[0057] Meanwhile, to provide a more detailed example, the above dry electrode forms a three-dimensional fiber network structure through the fiberization of the binder and can be formed into a film. In this respect, the fiberization process of the binder plays a significantly important role in the dry electrode manufacturing process, and how this process is controlled can have a significant impact on the ease of optimizing the subsequent film forming process and on whether the appearance characteristics and mechanical properties of the film can be secured at an excellent level. Additionally, the dry electrode manufacturing process includes a process of forming the electrode powder into a film, and the success or failure of this process depends on the detachability of the powder and the roll.

[0058] In this specification, the aim is to provide an electrode that facilitates the optimization of the film forming process by controlling the entire process, such as the particle size and type of active material, the type and content of binder, the fiberization process of the binder, and the sheeting process, in the dry electrode manufacturing process; exhibits excellent durability due to superior appearance characteristics and mechanical properties; and enables improved ionic and electrical conductivity as the distribution of coarse and fine fibers is controlled. Furthermore, through such an electrode, a secondary battery with improved resistance and lifespan characteristics can be realized, and such an electrode and secondary battery can be determined by the area ratio of a low-intensity region defined using attenuated total reflection infrared spectroscopy.

[0059]

[0060] In one aspect, the electrode may have an area ratio of a binder-poor region relative to the entire surface area of ​​15.0% or more. In the electrode, the low-intensity region may be an area where relatively thin fibers exist within the entire area, which is an area where hyperfibrosis has progressed, or an area with a low proportion of binder. Generally, the surface distribution characteristics of the binder, such as these low-intensity regions, do not change abruptly even during calendering and lamination from the powder-sheeting film to the electrode composite film, and the characteristics can be maintained at a similar level.

[0061] If such a low-intensity region can be properly distributed from the powder sheeting film onto the surface, it can maximize roll adhesion during the calendering process, thereby minimizing problems such as edge defects or detachment during the process, and ultimately provide flexibility to the electrode and reduce resistance. The aforementioned low-intensity region is defined as having a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the surface of the electrode using attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 The integral value of the peak appearing in the range I B It can be defined as an area where is 1.0 or less.

[0062] If the area ratio of the above low-strength region is less than 15.0%, some powder from the film may detach during calendering, causing folds or cracks on the inner side of the film, and some regions may not adhere well to the roll and run, resulting in defects such as tearing of the edge or cracks even if they are not torn, so it is desirable to have the above-mentioned range.

[0063] The area ratio of the above low-intensity region may be 15.0% or more, 20.0% or more, 22.0% or more, or 25.0% or more, or 85.0% or less, 84.0% or less, 83.0% or less, 82.0% or less, or 81.5% or less. When the electrode is manufactured to fall within this desirable range, there is an advantage in that the likelihood of it becoming a dry electrode that satisfies all appearance characteristics, mechanical properties, and resistance characteristics as described above can be greatly increased.

[0064]

[0065] The electrode may be characterized in that the high-intensity region is 15.0% or less of the total region. The high-intensity region is defined as having a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity I appearing in the range B A region with a value of 1.5 or higher may refer to a region on the surface of the electrode where fibrous binders are relatively dense compared to other regions, or where there are many relatively thick fibers.

[0066] The high-strength region may, for example, be a coarse fiber region. The high-strength region may have various technical implications and can serve as a measure for evaluating how robust the three-dimensional fiber network structure forming the fibrous binder in a self-supporting film is, and whether a high proportion of specific regions where the binder is clumped or thick fibers exist impedes electrolyte impregnation or lithium ion mobility. For example, the high-strength region can provide mechanical strength to the electrode and can serve as a part that forms an appropriately sized void within the electrode, providing a pathway for ion movement.

[0067] In the above electrode, if the area ratio of the high-strength region is 15.0% or less, it means that binders with thick fiber thickness are distributed less on the surface, so adhesion with the roll during the calendering process can be guaranteed, and the effect of improving processability can be expected, and defects in the edge part or inner film in the electrode state can be minimized, so the appearance characteristics of the electrode can be excellent.

[0068] It is desirable to adjust the electrode composition or process conditions so that the area ratio of the high-intensity region to the total region is controlled to a range of 15.0% or less. The area ratio of the high-intensity region may preferably be 13.0% or less, 11.0% or less, 10.0% or less, 8.0% or less, or 5.0% or less, and may be 0.5% or more, or 1.0% or more.

[0069]

[0070] In one aspect, the electrode may have a medium-intensity region of 15.0% to 85.0% in terms of area relative to the entire surface area. It may be desirable to control the electrode so that the medium-intensity region has an appropriate area. The medium-intensity region is defined as having a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the surface of the electrode using attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity appearing in the range, I B It can be defined as an area greater than 1.0 and less than 1.75.

[0071] The above medium-strength region can act as an anchor between the high-strength region and the low-strength region, and compared to the case where only the rich region and the poor region exist in excess, it can improve the flexibility of the electrode and prevent unexpected cracks in the electrode, thereby contributing to the improvement of the overall durability of the electrode, which can be optimally achieved when the area ratio of the medium-strength region is within the above range.

[0072] The area ratio of the above-mentioned medium strength region may be 20.0% or more, 25.0% or more, or 30.0% or more, and may also be 80.0% or less, 75.0% or less, 70.0% or less, 65.0% or less, or 60.0% or less, and if the electrode is manufactured to be included in such a desirable range, the effect of improved electrode durability as described above can be expected.

[0073]

[0074] In one aspect, the total area ratio of each of the low-intensity region, high-intensity region, and medium-intensity region can be analyzed by applying attenuated total reflection infrared spectroscopy to the electrode surface.

[0075] This analysis method has the advantage of enabling the manufacture of electrodes with superior characteristics by analyzing the film surface, thereby allowing for the quantification of structural surface properties regarding the fiber thickness, density, and arrangement relationships of the fibrous binder, in addition to analyzing the mechanical properties or appearance characteristics of the electrode and resistance characteristics. This is achieved by analyzing the film surface to more easily control the conditions or number of roll rolling operations in the subsequent calender roll based on the binder distribution of the initially formed powder-sheet film.

[0076] The above analysis method comprises the step of cutting the electrode into a size of 4 mm x 4 mm to 5 cm x 5 cm based on the surface and extracting it as a sample (A1); the step of analyzing the surface of the sample using attenuated total reflection infrared spectroscopy (ATR-FTIR) and mapping the derived IR spectrum (A2); wherein, by a commercial image program, the IR spectrum mapping result obtained in step A2 is 1190 cm⁻¹ -1 to 1260 cm -1 The intensity of the peak appearing in the wavenumber range (integral value of the peak) I BA step (A3) in which is normalized to 0.5 to 2.0; the above I B The area where α is 1.5 or higher is the high-intensity area, I B The region where α is 1.0 or less is the low-intensity region, I B It can be calculated by an analysis method comprising: a step (A4) of defining a region where the value is less than 1.5 and greater than 1.0 as a medium-intensity region and calculating the ratio occupied by each region; and a step (A5) of obtaining an average value of the ratio of the high-intensity region, the ratio of the medium-intensity region, and the ratio of the low-intensity region by repeating steps A1 to A4 five or more times using a sample extracted at a different location from the sample within the same electrode as the electrode.

[0077] For example, in step A1 above, the electrode surface sample may be 4 mm x 4 mm to 5 cm x 5 cm. When measuring the IR spectrum, the actual measured range may be 4 mm x 4 mm, but for the accuracy of the measuring instrument, it may be desirable to cut the sample larger than the measurement range.

[0078] Step A2 above may involve dividing the sample into at least 10x10 to 20x20 grids within the measurement range of the sample (e.g., 4 mm x 4 mm), preferably into 20x20 grids, and mapping an IR spectrum for each grid. FIG. 1 is an example of an IR spectrum for a sample containing a fibrous binder, which may be a graph that can be obtained when Step A2 is performed.

[0079] In the above A3 step, the result of mapping the IR spectrum by a commercial image program (e.g., Omnic, Image J, etc.) can be standardized, and the standardization is performed at a wavenumber of 1190 cm⁻¹ in the IR spectrum. -1 to 1260 cm -1The intensity of the peak appearing within the range may be displayed as a value between 0.5 and 2.0. The above standardization may be a process of ensuring that peak intensities of 0.5 or less appearing on each IR spectrum are represented identically, and that peak intensities of 2.0 or more appearing identically are also represented identically. Furthermore, the above standardization may also involve a process of aligning baselines by adjusting tilt, etc., so that the intensity values ​​of the peaks in each IR spectrum can be derived from the same standard. This series of processes may be performed using the commercial image program.

[0080] In addition, in the above standardization process, for example, the above I B Depending on the value, values ​​of 0.5 or less correspond to blue, and values ​​of 2.0 or more correspond to red, and values ​​in between can also be converted to corresponding color coordinate values. For example, an image such as that shown in Fig. 2 can be obtained, which may be an image obtained according to standardization after performing step A3 on a sample containing a fibrous binder, and is a result image measured in a range of 4 mm x 4 mm within a 5 cm x 5 cm sample.

[0081] The ratio of each region to the total area may be the ratio of the area of ​​each region to the area of ​​the total area, and grids of 10x10 to 20x20 may be divided into high-intensity, medium-intensity, and low-intensity regions, and the ratio of the number of grids of the corresponding region to the total grid may be the ratio of the area to the total area. In addition, if one wishes to use an intensity value in the image as a reference, for example, 1.5, the part corresponding to 1.5 on the scale bar of FIG. 2 can be set as a threshold point to derive the area above or below that value.

[0082] The above analysis method is based on the observation that when a manufactured electrode is cut to a specific size and the surface of the cut sample is analyzed by infrared spectroscopy, the peak intensity of the IR spectrum varies depending on the structural characteristics regarding the thickness, content, or arrangement of the fibrous binder up to a depth of about 1 μm from the surface. This method can be used to determine what structural characteristics the fibrous binder has on the surface, as the peak intensity, or integral value, increases when the fiber thickness of the fibrous binder in a specific region is thick or numerous, and conversely, the integral value decreases when the fiber thickness is thin or few.

[0083] The above analysis method can determine the intensity of a peak at a specific point from a peak attributed to a binder present on the surface, and through this determination, map the level of peak intensity across the entire surface. Through this mapping, image data can be obtained regarding the structural characteristics of the fibrous binder on the surface of the electrode, such as fiber thickness, arrangement, and quantity. In the case of this analysis method, since a sample is taken from a portion of the entire dry electrode for analysis, it is difficult to consider a single measurement as representative of the entire electrode. Therefore, it may be necessary to check for reliability by repeating this analysis at least five times to confirm whether the same results are obtained. In this regard, the above attenuated total reflection infrared spectroscopy has the advantage of being able to determine how the binder is distributed across the entire electrode.

[0084]

[0085] An electrode according to one embodiment of the present invention comprises an electrode active material and a binder, and may optionally further comprise a conductive material.

[0086] There are no special limitations on the electrode active material as long as it is a commonly used electrode active material. For example, the electrode active material may be a positive electrode active material or a negative electrode active material, and preferably, it may be a positive electrode active material.

[0087] The above-mentioned positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium complex metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

[0088] Specifically, it may include a lithium composite transition metal oxide comprising lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite transition metal oxide may be a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 Ms2 )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.) any one or more of these compounds may be included.

[0089] Among these, the lithium metal oxides mentioned above include LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), lithium nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), or lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 It may be )O2), etc., and any one of these or a mixture of two or more of them may be used.

[0090] The above positive active material may include a lithium iron phosphate-based compound, and, for example, may include a compound represented by the following chemical formula 1.

[0091] [Chemical Formula 1]

[0092] Li 1+a Fe 1-xM x PO4

[0093] In the above chemical formula 1, M comprises one or more selected from Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤a≤0.5, 0≤x<1.

[0094] When the above-mentioned positive electrode active material is a lithium iron phosphate-based compound, the disadvantage is that while safety is guaranteed, the capacity is relatively smaller compared to lithium nickel-based oxides; however, since it is possible to realize an electrode capable of high loading, it is possible to implement a lithium secondary battery with excellent cost competitiveness and a lithium iron phosphate-based compound with improved capacity and superior safety.

[0095] Furthermore, in the case of the aforementioned electrode, the distribution of the binder was precisely quantified using attenuation-total reflection spectroscopy to realize an electrode with improved performance; when lithium iron phosphate-based compounds are applied, greater synergy can be achieved in terms of performance enhancement. For example, because lithium iron phosphate-based compounds have small particle sizes and large specific surface areas, they are difficult to disperse dry; depending on the degree of fibrillation, electrode fabrication itself may not be possible, appearance characteristics and durability may vary significantly, and even fabricated electrodes may exhibit considerable performance variability. However, for electrodes where the distribution of the binder on the surface is precisely defined, significant performance differences can be observed depending on whether the area ratio is satisfied in electrodes using lithium iron phosphate-based compounds, which can be more meaningful compared to cases where other active materials are applied.

[0096] In one aspect, preferably, the lithium iron phosphate-based compound has a volume-based particle size distribution with a volume-cumulative 50% particle size D. 50 This may be 0.60 μm to 2.00 μm. Preferably, it may be 0.70 μm or more, 0.90 μm or more, 1.80 μm or less, or 1.50 μm or less.

[0097] The above lithium iron phosphate-based compound has a volume cumulative 10% particle size D in the volume-based particle size distribution. 10 This may be 0.10 μm to 1.20 μm. Preferably, it may be 0.15 μm or more, 0.20 μm or more, and also 1.00 μm or less, 0.80 μm or less, 0.60 μm or less.

[0098] The above lithium iron phosphate-based compound has a volume-based particle size distribution with a cumulative 90% particle size D. 90 This may be 2.00 μm to 7.00 μm. Preferably, it may be 2.50 μm or more, 3.00 μm or more, 6.50 μm or less, 6.00 μm or less, 5.00 μm, or 4.50 μm or less.

[0099] Meanwhile, the above lithium iron phosphate-based compound is D 50 This is a small particle, D, having a diameter of 0.60 μm to 2.00 μm. 50 This heavy particle having a diameter of 1.00 μm to 4.00 μm and D 50 It may have a bimodal particle size distribution including two or more particles selected from large particles ranging from 6.00 μm to 20.0 μm, or it may have a trimodal particle size distribution including small particles, medium particles, and large particles. Additionally, preferably, the D50 of the small particles may be 0.70 μm or more, 0.75 μm or more, or 0.80 μm or more, and may also be 1.70 μm or less, or 1.50 μm or less, and the D50 of the medium particles may be 1.50 μm or more, or 2.00 μm or more, and may also be 3.80 μm or less, or 3.50 μm or less. The above-mentioned allele may have a D50 of 7.00 μm or more, 8.00 μm or more, or 9.00 μm or more, and may be 18.00 μm or less, 16.00 μm or less, 15.00 μm or less, or 13.00 μm or less.

[0100] In the case of a lithium iron phosphate-based compound having the aforementioned particle size distribution, a greater synergy can be obtained based on the surface distribution characteristics of the aforementioned binder, thereby enabling the realization of a secondary battery with excellent durability and superior resistance and lifespan characteristics.

[0101] In addition, the lithium iron phosphate-based compound may have a tap density of 0.500 g / cc to 2.000 g / cc, preferably 0.600 g / cc or more, 0.700 g / cc or more, or 0.750 g / cc or more, and may be 1.500 g / cc or less, 1.300 g / cc or less, or 1.000 g / cc or less. When a lithium iron phosphate-based compound having a tap density within the above range is applied, it can contribute to realizing surface distribution characteristics of the electrode by controlling the degree of fibrillation of the binder.

[0102] Meanwhile, the electrode active material may include a negative electrode active material, and the negative electrode active material may be a material capable of reversibly intercalating / deintercalating lithium ions, and may include, for example, at least one selected from the group consisting of lithium metal; carbon-based active material; metalloid active material including Si or Sn; metal-based active material including a metal or an alloy of these metals and lithium; metal composite oxide; and transition metal oxide.

[0103] The above carbon-based active material may be used without particular limitation as long as it is commonly used in lithium-ion secondary batteries, and representative examples include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the above crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the above amorphous (or low-crystallinity) carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0104] The above metalloid active material may include silicon-based active materials and / or tin-based active materials, and silicon-based active materials include Si and SiO x (0 <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님)으로 이루어진 군에서 선택될 수 있다. 또한 주석계 활물질은, Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0105] As the above-mentioned metal-based active material, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of these metals and lithium may be used.

[0106] The above metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Sn x Me 1-x Mey O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0107] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0108] Meanwhile, according to one embodiment of the present invention, the electrode active material may comprise 80% to 99% by weight based on the total weight of the electrode composite film, preferably 85% or more by weight, 88% or more by weight, 90% or more by weight, 92% or more by weight, 93% or more by weight, or 95% or more by weight, and may also comprise 98.5% or less by weight, 98% or less by weight, or 97.5% or less by weight. When included within the above range, it may be desirable in terms of increasing the capacity and energy density of the electrode, as well as optimizing the functions of the auxiliary materials, such as the conductive material and the binder.

[0109]

[0110] In one aspect, the binder functions to form a three-dimensional fiber network structure so that the electrode composite film can stand on its own, and the binder is not specified as being capable of fiberization, that is, if it can form a three-dimensional fiber network structure within the electrode composite film through fiberization and provide a void capable of accommodating an electrode active material and optionally a conductive material.

[0111] The fiberization of the above binder refers to a treatment that divides the polymer applied as a binder into smaller fibers, which can be performed, for example, by applying mechanical shear force, and as a result, the surface is loosened and fiberized, forming multiple microfibers, and thereby can include a three-dimensional fiber network structure.

[0112] The fiber-forming binder may preferably comprise one or more selected from the group consisting of polytetrafluoroethylene (PTFE) and polyolefins, more preferably may comprise polytetrafluoroethylene (PTFE), and even more preferably may comprise polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) may be included in an amount of 60% by weight or more based on the total weight of the binder. At this time, the binder may additionally comprise one or more of polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-cohexafluoropropylene (PVdF-HFP), and polyolefin-based binders.

[0113] The binder may be included in an amount of 0.1% to 10.0% by weight relative to the total weight of the electrode composite film, and preferably, may be included in an amount of 0.2% or more, 0.3% or more, 0.5% or more, 0.7% or more, or 1.0% or more by weight, and may also be included in an amount of 9.0% or less, 8.0% or less, 7.0% or less, 5.0% or less, 4.0% or less, 3.5% or less, or 3.0% or less by weight. In the case of a binder mixture, if it is included within the above range, problems acting as resistance or problems with the degree of fiberization for manufacturing into a self-supporting sheet form may not occur.

[0114]

[0115] The above conductive material is a component for further improving the conductivity of the electrode active material, and can be optionally included in the electrode composite film and accommodated in the pores within the three-dimensional fiber network structure formed by the binder, and such conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery.

[0116] For example, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite or artificial graphite with a highly developed crystal structure; conductive fibers such as carbon-based fibers (e.g., carbon nanotubes, carbon nanofibers, carbon fibers) or metallic fibers; fluorocarbon powder; metallic powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives may be used. Specifically, to ensure uniform mixing of the conductive material and to improve conductivity, one or more selected from the group consisting of graphite powder, carbon black, and carbon nanotubes may be included.

[0117] The conductive material may be included in an amount of 0.1% to 10.0% by weight relative to the total weight of the electrode composite film. Preferably, it may be included in an amount of 0.2% or more, 0.3% or more, 0.5% or more, or 0.7% or more by weight, and may also be included in an amount of 8.0% or less, 6.0% or less, or 5.0% or less by weight. Although a higher amount of the conductive material may be advantageous for forming a conductive path, the capacity may be reduced due to a relative decrease in the amount of active material, and controlling the amount of material is not easy due to dispersion issues; however, since the effect of forming a conductive path can be maximized by optimizing dispersibility within the above range, it may be desirable to apply the conductive material within the aforementioned range.

[0118]

[0119] In one aspect, the electrode may be highly loaded, for example, the electrode has a loading amount of 620 mg / 25 cm 2 It may be abnormal, 630 mg / 25cm 2 Above, 650 mg / 25cm 2 Above, 670 mg / 25cm 2 Above, 700 mg / 25cm 2 Above, 720 mg / 25cm 2 Above, 750 mg / 25cm 2 Above, 780 mg / 25cm 2 800 mg / 25cm or more 2 It may be above. Even if the loading amount is increased to the above range, if the degree of surface distribution of the binder is well controlled, it is possible to provide an electrode that satisfies both durability and lifespan.

[0120] The electrode composite film of the above electrode may have a porosity of 17 volume% to 30 volume%, preferably 19 volume% or more, or 20 volume% or more, and may also be 29 volume% or less, 28 volume% or less, 27 volume% or less, 26 volume% or less, 24 volume% or less, or 23 volume% or less. When the above range is satisfied, the electrolyte impregnation is excellent, so lifespan characteristics and output characteristics can be improved, and it may be excellent in terms of energy density.

[0121] The porosity can be calculated using the following mathematical formula A.

[0122] [Mathematical Formula A]

[0123] Porosity (Volume%) = {1 - (Electrode Density / True Density)} × 100

[0124] In the above mathematical formula A, true density is the density of the electrode composite film measured when the electrode composite film is taken in a certain size and pressed with a press machine until the thickness of the film does not change, and the electrode density is the density of the electrode composite film measured when the film is taken in a certain size.

[0125]

[0126] In one aspect, the electrode comprises an electrode composite film and a current collector having the electrode composite film disposed on at least one surface.

[0127] When the above electrode is a positive electrode, the above current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, the above current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0128] When the above electrode is a negative electrode, the above current collector is not particularly limited as long as it has high conductivity without causing changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used.

[0129] The thickness of the above current collector may be 3 μm to 100 μm, preferably 8 μm to 80 μm, but is not limited thereto. In addition, fine irregularities may be formed on the surface of the above current collector to increase the adhesion of the composite film.

[0130]

[0131] The above-mentioned current collector may be used with a conductive primer coated wholly or partially on the surface to lower resistance and improve adhesion. Here, the conductive primer may comprise a conductive material and a binder, and the conductive material is not limited to any material that exhibits conductivity, but may be, for example, a carbon-based material. The binder may include solvent-soluble fluorine-based (including PVDF and PVDF copolymers), acrylic binders, and water-based binders.

[0132]

[0133] Method for manufacturing an electrode

[0134] In one aspect, the method for manufacturing the electrode comprises the steps of: mixing an electrode active material and a binder to prepare a composite composition (S1); introducing the composite composition into a mixing machine and mixing to obtain a mixed aggregate (S2); crushing the mixed aggregate to obtain an electrode powder (S3); and rolling the electrode powder to produce an electrode composite film (S4).

[0135] Since the description regarding the electrode active material and binder, in particular the binder capable of forming a three-dimensional fiber network structure, and the description regarding the area ratio of at least one of the high-intensity region, low-intensity region, and medium-intensity region determined by attenuated total reflection spectral analysis of the surface and interior of the dry electrode, as well as the description regarding the conductive material that may be optionally included, are identical to those described above, a detailed description is omitted, and the manufacturing process for each step is described below.

[0136] Since the process of manufacturing dry electrodes involves mixing electrode materials without a solvent, dispersing them through a predetermined process, and then forming them into a film, problems regarding the dispersibility of the electrode materials, processability during film forming, and the appearance and mechanical properties of the film always arise, which affects the performance of the electrode and cell. These problems frequently occur when controlling the degree of dispersion of the composition during the mixing process, controlling the degree of fiberization of the binder during the kneading process, and forming the powder into a sheet through powder sheeting. Consequently, it can be said that control over the entire dry electrode manufacturing process is required to ensure the success or failure of film forming during the calendering process, as well as the appearance and mechanical properties of the dry electrode.

[0137] Furthermore, factors such as the particle size of the active material and the characteristics and content of the binder can determine the success or failure of fabrication and the superiority or inferiority of performance of the final electrode composite film when designing the electrode composition. When the particle size is small, the sensitivity of controlling the degree of fiberization increases and the difficulty of sheet formation rises, while even slight increases or decreases in the binder content affect changes in resistance or the durability of the electrode.

[0138] By designing the electrode composition and controlling the manufacturing process, the area ratio of the low-intensity region of the electrode can be made to have a specific value.

[0139] Below, the method for manufacturing the above dry electrode is described in detail for each step.

[0140]

[0141] S1 stage

[0142] In one aspect, the method for manufacturing the electrode comprises step S1 of mixing an electrode active material and a binder, and optionally adding a conductive material to prepare an electrode composite composition.

[0143] The above mixing is performed so that the electrode active material and binder can be uniformly distributed, and since they are mixed in powder form without a solvent, they can be mixed by various methods that enable simple mixing, without limitation. However, since the present invention is manufactured as a dry electrode that does not use a solvent, the above mixing can be performed as a dry mixing, and the materials can be mixed by introducing them into a device such as a mixer or blender.

[0144] At this time, the mixing can be performed in a mixer at 3,000 rpm to 20,000 rpm for 1 minute to 60 minutes, and preferably at 5,000 rpm to 15,000 rpm for 3 minutes to 30 minutes. When performed within the above range, the materials can be uniformly mixed, thereby improving battery performance. More specifically, the mixing speed may be 5,500 rpm or higher, 6,000 rpm or higher, or 6,500 rpm or higher, and may also be 14,000 rpm or lower, 13,000 rpm or lower, or 12,000 rpm or lower.

[0145] The control conditions of the above mixing process can determine how uniformly the binder is fiberized in the subsequent mixing process of step S2. If the mixing is not uniform, even if fiberization occurs uniformly, uneven areas may occur on the entire surface of the film. Therefore, by applying an appropriate mixing speed and mixing time, the binder distribution characteristics on the surface of the electrode can be satisfied.

[0146]

[0147] S2 stage

[0148] In the method for manufacturing the electrode above, the S2 step comprises applying a shear force to the composite composition obtained from the mixing of the S1 step to form a mixed aggregate. That is, the S2 step may be a fiberization process of a binder mixture using a binder capable of forming a matrix.

[0149] The above fiberization process can be performed, for example, through mechanical milling or kneading, and there are no special limitations as long as it is performed generally, but preferably, it can be performed by high-temperature, low-shear kneading, and can be performed through a kneader such as a twin-screw extruder, for example. Through such kneading, the fiberizable binder is fiberized, and the electrode active material and conductive material powders are combined or connected to form a mixed aggregate with 100% solid content.

[0150] The above mixing can be performed at a speed of 10 rpm to 300 rpm, preferably at a speed of 20 rpm or more, 30 rpm or more, or 40 rpm or more, and also preferably at a speed of 280 rpm or less, 270 rpm or less, 260 rpm or less, 250 rpm or less, 240 rpm or less, 230 rpm or less, 220 rpm or less, 210 rpm or less, 200 rpm or less, or 190 rpm or less. In addition, the mixing time can be 10 minutes to 30 minutes, preferably 15 minutes to 25 minutes or 17 minutes to 25 minutes. When the above range is satisfied, appropriate fiberization can proceed, and a structurally stable matrix can be formed while being fiberized uniformly throughout.

[0151] Furthermore, the content of the composite composition introduced into the mixer during the above mixing process can also be controlled. For example, the composite composition discharged from the above mixing process can be introduced in an amount of 80 volume% to 250 volume% relative to the internal volume of a mixer such as a kneader, and preferably 90 volume% or more, 100 volume% or more, 110 volume% or more, 120 volume% or more, or 130 volume% or more, and also 240 volume% or less, 230 volume% or less, 220 volume% or less, 210 volume% or less, or 200 volume% or less.

[0152] The volume ratio of the composite composition to the internal volume of the above-mentioned mixer may be measured when the volume of the composite composition is at atmospheric pressure. For example, the bulk density of the above-mentioned composite composition in powder form may be less than 1.0 kg / L. If, for instance, the bulk density of the powder is assumed to be 0.46 kg / L, then when 10 kg is input, the input volume becomes 21.7 L, and in this case, when the internal volume of the mixer is 10 L, the volume percentage may be 217 volume%. Due to the low bulk density of the above-mentioned composite composition in powder form, it may be compressed by more than twice, and accordingly, the volume percentage can be controlled by considering the bulk density of the powder, the internal volume of the mixer, the degree of compression of the powder, etc.

[0153] As described above, the fiberization of the binder can be controlled by controlling the amount of composite composition added during mixing. By simultaneously adjusting the conditions of the mixing process, the extent to which the binder network structure formed according to the degree of binder fiberization affects the contact area between active materials can be controlled, and the surface distribution characteristics of the binder can be controlled. In other words, by controlling the shear force applied to the composite composition, it can serve as a measure to prevent over-fiberization and induce appropriate fiberization so that the powder does not detach.

[0154] The above mixing can be performed under high temperature and pressure conditions above atmospheric pressure, and more specifically, under pressure conditions higher than atmospheric pressure.

[0155] The above mixing can be performed at a temperature of 50°C to 230°C, preferably 90°C to 200°C, and may be 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, or 140°C or higher, and may also be 190°C or lower or 180°C or lower. When mixing is performed at a high temperature such as within the above range, the fiberization of the binder and agglomeration by mixing can be effectively achieved, and the problem of breakage of the fiberized binder can be appropriately prevented.

[0156] It can be performed at atmospheric pressure or higher, specifically at a pressure of 1 atm to 3 atm, and more specifically at 1.1 atm to 3 atm. When performed within the above range, the problem of breakage of the binder undergoing fiberization can be adequately prevented, and the problem of the density of the aggregate becoming too high can be prevented.

[0157] As described above, when a high-temperature, low-shear mixing process is performed under high temperature and pressure conditions greater than atmospheric pressure instead of high-shear mixing, and when the aforementioned mixing speed, mixing time, mixing temperature, and pressure are satisfied, an electrode satisfying the surface binder distribution characteristics can be realized.

[0158]

[0159] S3 stage

[0160] In the above method for manufacturing the electrode, the S3 step is a step of obtaining a powder for the electrode by crushing a mixed aggregate produced through a kneading step.

[0161] Although the mixed aggregate produced through the above kneading process may be immediately pressurized to form a sheet (sheeting, e.g., a calendering process), this may require pressing the aggregate under high pressure and high temperature to produce a thin film; consequently, problems may arise such as the film density becoming too high or the inability to obtain a uniform film. Therefore, the mixed aggregate produced as described above is crushed to produce a powder for electrodes.

[0162] The device used for the above grinding is not particularly limited, but preferably can be performed with a device such as a blender or a grinder.

[0163] The grinding above can be performed at a speed of 1,000 rpm to 15,000 rpm for 5 seconds to 30 minutes, preferably at a speed of 3,000 rpm to 8,000 rpm for 30 seconds to 15 minutes. When performed within the above range, sufficient grinding can be achieved to produce powder of a size suitable for film formation, and a large amount of fine powder may not be generated in the aggregate.

[0164] In the case of the aforementioned grinding process, it serves to help form a powder sheeting film in the subsequent sheet forming process, and at the same time, since the binder distribution characteristics on the electrode surface may be affected by how much the aggregated binder is crushed and how well the fibrous binder is maintained during the grinding process, it may be desirable to appropriately control the grinding speed and time of the grinding process.

[0165] The average particle size of the above electrode powder may be 10㎛ to 3,000㎛, more specifically 50㎛ to 1,500㎛, and even more specifically 100㎛ to 700㎛. When the above range is satisfied, an electrode composite film with uniform thickness and density can be formed, and excellent electrode composite film properties can be secured.

[0166] The above-mentioned electrode powder may additionally include fillers to suppress the expansion of the electrode, although this is not essential. The fillers are not particularly limited as long as they are fibrous materials that do not cause chemical changes in the battery, but examples include at least one selected from olefinic polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers.

[0167] In one aspect, the degree of crystallization of the electrode powder may be 1.0% to 15.0%, preferably 1.5% or more, and 14.0% or less, 13.0% or less, 12.0% or less, or 11.0% or less. The degree of crystallization may be defined by the following Formula 1.

[0168] [Equation 1]

[0169] X C = [(△H m ) / (△H m0 )] x 100

[0170] In Equation 1 above, △H m The actual melting enthalpy of the binder is derived by differential scanning calorimetry, and △H m0 is the theoretical enthalpy of melting when the binder is in a 100% crystalline state.

[0171] The above degree of crystallization (Xc) can be measured using differential scanning calorimetry (DSC) and is based on the temperature at the point where the highest enthalpy is observed during crystallization (peak temperature). Specifically, the above degree of crystallization is the melting enthalpy (△H) measured by DSC. m The ) value is the enthalpy of melting (△H) of a theoretically perfect crystal (degree of crystallization 100%). m0 It is expressed as a percentage by dividing by the value of )(equilibrium heat of fusion), and can be calculated by Equation 1 above. Here, the theoretical enthalpy of melting value of a perfect crystal (△H m0 For this, you can refer to polymer handbooks or related academic papers. For example, the theoretical melting enthalpy value of perfect crystals of PTFE is 85.4 J / g. Meanwhile, thermal analysis of polymers, such as DSC, can typically be measured and calculated according to ASTM D3418-21.

[0172] As mentioned above, the degree of crystallinity can serve as a criterion for measuring the degree of fiberization of the binder, but since it is estimated from the overall average value, it is difficult to determine the distribution of the electrode surface and the ratio of coarse fibers to fine fibers. Therefore, by controlling the high-intensity region, which defines the electrode surface distribution characteristics using IR as described above, it is possible to realize an electrode with superior performance and high reproducibility.

[0173]

[0174] S4 stage

[0175] In the above method for manufacturing the electrode, the above step S4 is a step of manufacturing an electrode composite film by thermally pressing the electrode powder through roll rolling.

[0176] The above S4 step may be a process of manufacturing an electrode composite film in the form of a self-standing sheet by heat-pressing the electrode powder obtained as described above using rolling rolls in a roll-to-roll process (calendering process, sheeting process) that includes two or more pairs of rolling rolls.

[0177] The above roll-to-roll process (calendar process) may include a roll press section, and the roll press section may have rolling rolls arranged in pairs facing each other, or three or more rolls arranged in contact with each other, and such rolling rolls may be arranged in a plurality of consecutively in the roll press section. When the rolling rolls are arranged in a plurality of consecutively, the temperature of each roll and the peripheral speed ratio (ratio of rotational speeds of a pair of rolls) may be the same or different.

[0178] The above step S4 may include a step of obtaining a powder-sheeting film by powder-sheeting the powder for the electrode (S4a); and a step of manufacturing an electrode composite film by sheeting the powder-sheeting film two or more times (S4b). That is, in step S4a, the powder may be converted into a sheet, and then in step S4b, it may be rolled to improve strength and satisfy the porosity and loading amount required for the electrode.

[0179] It may be desirable to control the temperature of the rolling roll in which the powder-sheeting film is manufactured in step S4a as the temperature of the rolling roll in which the above electrode powder is first fed, and the temperature of the rolling roll may be 60°C to 110°C, and preferably 70°C to 100°C.

[0180] The rotational speed ratio of the rolling rolls equipped in the roll-to-roll process of the above S4 step can each be independently and appropriately adjusted within a range of 1:1 to 1:10. In addition, the manufactured electrode composite film can be fed back into the roll press section to be adjusted to an appropriate thickness and subjected to 1 to 10 heat pressings.

[0181] The binder distribution characteristics on the surface of the electrode can be controlled by controlling the conditions of the aforementioned S4 step, for example, the temperature of the roll during powder-sheeting, the number of calendering cycles, the peripheral speed ratio between rolling rolls, and the roll gap.

[0182]

[0183] In one aspect, the electrode composite film manufactured according to the above manufacturing method can be laminated and placed on one or both sides of a current collector through a lamination process immediately following step S4, and finally, a dry electrode can be manufactured.

[0184] The above lamination may be a step of attaching the electrode composite film by rolling it onto a current collector. The above lamination may be performed by a roll press method using a lamination roller, wherein the lamination roller may be maintained at a temperature of 20°C to 200°C.

[0185] The method for manufacturing the electrode described above may further perform a post-rolling process after the lamination. Through the post-rolling process, the porosity can be controlled, and the degree of fiberization of the binder can also be finely controlled by applying additional shear force; thus, by selectively performing the post-rolling process, the binder distribution characteristics on the surface of the electrode can be controlled.

[0186]

[0187] secondary battery

[0188] In one aspect, a secondary battery may include an electrode as described above. For example, the secondary battery may include a secondary battery including a liquid electrolyte and an all-solid-state battery including a solid electrolyte, and may include a lithium secondary battery and a sodium secondary battery.

[0189]

[0190] In one aspect, if the secondary battery is a secondary battery containing a liquid electrolyte, a separator may be included between a plurality of electrodes. The separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0191] In addition, if the secondary battery is an all-solid-state battery, the solid electrolyte membrane can be manufactured to perform the function of the separator.

[0192]

[0193] In addition, for non-aqueous electrolyte secondary batteries, organic liquid electrolytes or inorganic liquid electrolytes may be applied as the electrolyte, and for solid electrolyte secondary batteries, polymer-based solid electrolytes, gel polymer solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, or oxide-based solid electrolytes may be used, but are not limited to these.

[0194] The above liquid electrolyte may include an organic solvent. The above organic solvent may be used without special limitations as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0195]

[0196] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may be at least one selected from the group consisting of, and the lithium salt is, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc. may be used. It is preferable to use the lithium salt within a concentration range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0197]

[0198] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10.0 weight% based on the total weight of the electrolyte.

[0199]

[0200] Battery box and electrical device

[0201] In another aspect, a battery box including the secondary battery may be provided. The battery box may include at least one secondary battery and may include a package that accommodates the secondary battery. Herein, the battery box may be, for example, a battery cell, a battery module, or a battery pack.

[0202] Since the above battery box stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it can be used as one or more power devices selected from the group consisting of: portable electronic devices such as mobile phones, laptops, and digital cameras; power tools such as electric drills and electric saws; electric powered vehicles such as electric bicycles, electric scooters, electric motorcycles, battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0203] In another aspect, an electric / electronic device may be provided that includes the battery box, wherein the battery box is included as a power source. The electric device or electronic device may include one or more selected from the group consisting of portable electronic devices, power tools, electric power vehicles, and power storage systems.

[0204]

[0205] Examples

[0206] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0207]

[0208] Example 1

[0209] 496 wt% of LiFePO4 with a D50 of 1.2 μm as the positive active material, 1 wt% of carbon black as the conductive material, and 3 wt% of polytetrafluoroethylene (PTFE) as the binder were put into a blender and mixed to prepare a composite composition.

[0210] Next, the above composite composition was introduced into a kneader in an amount of 200 volume% relative to the capacity (volume basis) of the kneader, and the mixture was kneaded for 13 minutes at 1.1 atm and 150°C to produce an aggregate, and the aggregate was crushed to produce a powder for electrodes.

[0211] After that, the temperature of the roll into which the electrode powder is fed in the above roll-to-roll process was set to 100°C to powder-sheet the electrode powder to form a powder-sheeting film, and then the powder-sheeting film was additionally sheeted twice and laminated with aluminum foil to manufacture an electrode having an electrode composite film placed on an aluminum current collector.

[0212]

[0213] Example 2

[0214] A dry electrode was manufactured in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 170 volume% relative to the capacity (volume basis) of the kneader and manufactured at 170°C for 13 minutes.

[0215]

[0216] Example 3

[0217] A dry electrode was manufactured in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 180 volume% relative to the capacity (volume basis) of the kneader and manufactured for 15 minutes.

[0218]

[0219] Example 4

[0220] A dry electrode was prepared in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 160 volume% relative to the capacity (volume basis) of the kneader and prepared at 190°C for 17 minutes.

[0221]

[0222] Example 5

[0223] A dry electrode was manufactured in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 160 volume% relative to the capacity (volume basis) of the kneader and manufactured for 15 minutes.

[0224]

[0225] Comparative Example 1

[0226] A dry electrode was manufactured in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 170 volume% relative to the capacity (volume basis) of the kneader and manufactured for 10 minutes.

[0227]

[0228] Comparative Example 2

[0229] A dry electrode was prepared in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 160 volume% relative to the capacity (volume basis) of the kneader and prepared at 130°C for 12 minutes.

[0230]

[0231] Comparative Example 3

[0232] A dry electrode was prepared in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 180 volume% relative to the capacity (volume basis) of the kneader and prepared at 130°C for 13 minutes.

[0233]

[0234] Comparative Example 4

[0235] A dry electrode was manufactured in the same manner as in Example 1, except that the above composite composition was introduced into a kneader in an amount of 160 volume% relative to the capacity (volume basis) of the kneader and manufactured for 10 minutes.

[0236]

[0237] Experimental Example 1: Spectroscopic analysis of attenuated total reflection infrared for a dry electrode

[0238] For the electrodes of the above examples and comparative examples, the binder dispersion state on the surface and internal cross-section was quantified by the following method.

[0239] Each electrode was cut to a size of 5 cm x 5 cm relative to the surface to serve as a sample, and an area corresponding to a measurement range of 4 mm x 4 mm on the surface of the sample was divided into 20 x 20 grids, and for each grid, the IR spectrum was mapped by analyzing it using attenuated total reflection infrared spectroscopy (Thermo Fischer, iN10).

[0240] Using a commercial imaging program (Omnic), the wavenumber is 1190 cm -1 to 1260 cm -1 Peak intensity I appearing in the range B After normalizing the values ​​so that values ​​0.5 or lower were standardized into the blue region and values ​​2.0 or higher were standardized into the red region, images were obtained in which intermediate values ​​were also converted into color coordinates corresponding to the intensity. Simultaneously, the region with a peak intensity of 1.0 or lower was defined as the low-intensity region, the region with a peak intensity of 1.75 or higher as the high-intensity region, and the region with a peak intensity of less than 1.75 and greater than 1.0 as the medium-intensity region. The ratio occupied by each region to the total area was calculated. This process was repeated by extracting samples 10 times from the same electrode, and the area ratio for each was calculated to obtain the average value of the calculated area ratios.

[0241]

[0242] High Intensity Range (%) Low Intensity Range (%) Example 1 2.25 23.00 Example 2 1.25 59.00 Example 3 3.00 39.25 Example 4 1.50 81.50 Example 5 10.75 20.75 Comparative Example 1 1.25 10.00 Comparative Example 2 14.00 5.25 Comparative Example 3 1.25 8.25 Comparative Example 4 21.5 6.75

[0243] Referring to Table 1 above, it can be seen that in the case of Examples 1 to 5, the low-intensity region satisfies a value of 15% or more, whereas in Comparative Examples 1 to 4, the low-intensity region does not satisfy the above range.

[0244] Experimental Example 2: Dry Electrode Evaluation

[0245] In the above examples and comparative examples, the processability of calendering during manufacturing and the appearance characteristics of the final electrode were measured by the following method.

[0246] 1) Appearance characteristics: After cutting the electrodes manufactured in the examples and comparative examples to a length of 30 cm, the defective length (cm) of the edge portion caused by tearing or cracking in the width direction (TD direction) and whether there was internal tearing, and if so, the length (cm), were measured and shown in Table 2 below.

[0247] 2) Calendering processability: While calendering the powder sheeting film two or more times, it was observed whether the film adhered well to the roll and ran, and whether problems such as detachment or breakage occurred. It was evaluated as O if the film adhered well to the roll and there were no problems with running, as if part of the film detached from the roll or cracks occurred on part of the side, and as X if the film detached from the roll and caused problems with running or cracks occurred in the center of the film.

[0248] Calendering Processability Internal Defect Length (cm) Edge Defect Length (cm) Edge Crack Rate (%) Example 1: 2.2 1.5 7.5 Example 2: 0 1.4 7.0 Example 3: 0 1.6 8.0 Example 4: 0 1.3 6.5 Example 5: 0 1.1 2.8 14.0 Comparative Example 1: 3.0 5.0 25.0 Comparative Example 2: 3.5 4.3 21.5 Comparative Example 3: 2.6 4.5 22.5 Comparative Example 4: 3.5 4.8 24.0

[0249] Referring to Table 2 above, it can be confirmed that in the case of Examples 1 to 5, no significant problems occurred during the calendering process, and accordingly, the area of ​​the low-strength region was achieved at least 15%, and as a result, there were no internal defects or only minor ones, and the defect rate of the edge portion was also significantly low. It can be confirmed that, preferably, the larger the area ratio of the low-strength region—for example, 15% or more, preferably 20% or more, 22% or more, and more preferably 25% or more—the more perfect and flawless the electrode can be manufactured.

Claims

1. An electrode comprising: an electrode composite film comprising an electrode active material and a binder having a three-dimensional fiber network structure; and a current collector having the electrode composite film disposed on at least one surface thereof; The above electrode has a low-intensity region of 15.0% or more in terms of area relative to the entire surface area, and The aforementioned low-intensity region is at a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the electrode surface using attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity appearing in the range, I B An electrode defined as a region where α is 1.0 or less.

2. In Paragraph 1, The above electrode has a low-intensity region of 15.0% to 85.0% of its total surface area based on area, and The aforementioned low-intensity region is at a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the electrode surface using attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity appearing in the range, I B An electrode defined as a region where α is 1.0 or less.

3. In Paragraph 1, The above electrode has a high-intensity region of 15.0% or less based on area for the entire surface area, and The aforementioned high-intensity region is defined as having a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the electrode surface using attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity appearing in the range, I B An electrode defined as a region where α is 1.75 or higher.

4. In Paragraph 1, The above electrode has a high-intensity region of 10.0% or less based on area for the entire surface area, and The aforementioned high-intensity region is defined as having a wavenumber of 1190 cm⁻¹ in the IR spectrum derived by analyzing the electrode surface using attenuated total reflection infrared spectroscopy (ATR-FTIR). -1 to 1260 cm -1 Peak intensity appearing in the range, I B An electrode defined as a region where α is 1.75 or higher.

5. In Paragraph 1, The electrode active material comprises a lithium transition metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

6. In Paragraph 1, The electrode active material may include a lithium iron phosphate-based compound, and the lithium iron phosphate-based compound includes a compound represented by the following chemical formula 1, electrode: [Chemical Formula 1] Li 1+a Fe 1-x M x PO4 In the above chemical formula 1, M comprises one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤a≤0.5, 0≤x<1.

7. In Paragraph 1, The electrode, wherein the binder is included in an amount of 3.5 weight% or less relative to the total weight of the electrode composite film.

8. In Paragraph 1, The above binder comprises polytetrafluoroethylene (PTFE), an electrode.

9. In Paragraph 1, The above electrode is an electrode that is a positive electrode.

10. A secondary battery comprising the electrode of claim 1.

11. A battery box comprising the secondary battery of claim 10.

12. An electric device comprising the battery box of paragraph 11.

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