Electrode mixture film, method for manufacturing electrode mixture film, and lithium secondary battery including electrode mixture film.

Abstract

This invention relates to an electrode mixture membrane comprising an adhesive having a three-dimensional fiber network structure and an electrode active material contained within the fiber network structure, wherein the electrode mixture membrane has an R-value defined by the density and tensile strength of the electrode mixture membrane, the R-value being in the range of 5.0 to 10.0. By improving the sheet integrity of the electrode mixture membrane, the R-value can meet this range, thereby providing an electrode mixture membrane with excellent mechanical strength and surface appearance, and stable performance during lamination with a current collector.

Description

Technical Field

[0001] This disclosure relates to electrode mixture films, methods for manufacturing electrode mixture films, and lithium secondary batteries including electrode mixture films. Background Technology

[0002] Secondary batteries are used in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable gaming devices, power tools, and electric bicycles, as well as large products that require high power, such as electric vehicles or hybrid vehicles, and in power storage devices for storing surplus electricity or renewable energy and for backup power.

[0003] Typically, secondary batteries are manufactured by applying an electrode active material slurry to a positive current collector and a negative current collector to form an electrode active material layer, then performing a drying and rolling process on it to manufacture the positive and negative electrodes, then stacking the positive and negative electrodes on both sides of a separator to form an electrode assembly with a predetermined shape, and then housing the electrode assembly in a battery case, then injecting electrolyte into it and sealing the case.

[0004] Meanwhile, during the drying process of the electrode active material, the solvent contained in the slurry evaporates, which may lead to defects such as pinholes or cracks forming on the electrode active material layer on the current collector. In addition, since the interior and exterior of the electrode active material slurry are not dried uniformly during the drying process, there is a risk of a decrease in electrode quality due to powder floating caused by differences in solvent evaporation rates. Powder floating refers to the phenomenon where powder in the first dried section rises, thus creating gaps with the relatively later dried sections.

[0005] To address the aforementioned issues, drying equipment capable of adjusting the solvent evaporation rate is being considered to ensure uniform drying of the inside and outside of the electrode active material slurry. However, such drying equipment is very expensive and consumes a significant amount of money and time during operation, thus hindering manufacturing processability.

[0006] On the other hand, the solvent included in typical electrode active material slurries is N-methyl-2-pyrrolidone (NMP), which has a high boiling point. Therefore, it requires high thermal energy and a very long drying oven to dry the solvent, making it very unfavorable for large-scale production. In addition, N-methyl-2-pyrrolidone (NMP) is a toxic substance, harmful to living organisms, and therefore has the disadvantage of being environmentally unfriendly.

[0007] Therefore, research on dry electrodes, which manufacture electrodes without the use of solvents, has recently been actively pursued. Dry electrodes are typically manufactured by laminating a self-supporting electrode mixture film onto a current collector. This electrode mixture film comprises an electrode active material, a binder, a conductive material, etc. The aforementioned electrode mixture film involves the following process: first, the electrode active material, a carbon material as a conductive material, and a fiberizable binder are mixed together using a mixer or the like; then, shear force is applied to the binder through a process such as jet milling or kneading to fiberize the binder; finally, the resulting mixture is calendered into a film form to manufacture a self-supporting film.

[0008] Meanwhile, in the process of manufacturing electrode mixture films, electrode powder is introduced into calendering rolls and rolled to manufacture electrode mixture films. It is difficult to control the roll-to-roll process of using the roll-to-roll process. If the number of calendering operations and the roll gap are not properly controlled, there is a problem of increased film defect rate. Furthermore, the electrode mixture films manufactured in this way have poor appearance characteristics and resistivity properties.

[0009] Therefore, there is a need to develop a dry electrode in which the mechanical strength of the electrode mixture film is maintained during the calendering process performed by the roll-to-roll process, and the final manufactured electrode has excellent properties. Summary of the Invention

[0010] Technical issues

[0011] To address the aforementioned problems, this disclosure provides an electrode mixture film with excellent mechanical properties, as well as excellent appearance and electrical properties, by controlling the compressive density of the electrode mixture film and its tensile strength in the MD and TD directions.

[0012] In addition, in order to provide an electrode mixture film with the above-mentioned properties to solve the above-mentioned problems, this disclosure provides a method for manufacturing an electrode mixture film, wherein the method controls the roll gap reduction rate of the roll pressing roller and the compression density increase rate of the film before and after pressing when using a roll pressing roller to press the electrode powder into an electrode mixture film during a roll-to-roll process.

[0013] In addition, to solve the above problems, this disclosure provides a dry electrode using the above-mentioned electrode mixture film, which has excellent resistive properties and excellent durability due to its excellent mechanical properties, thereby providing a lithium secondary battery with improved output and life properties.

[0014] Technical solution

[0015] [1] In one aspect, an electrode mixture membrane is provided, the electrode mixture membrane comprising an adhesive having a three-dimensional fiber network structure and an electrode active material contained in the three-dimensional fiber network structure, wherein the R value defined by Equation 1 below is from 5.0 to 10.0.

[0016] [Equation 1]

[0017] R=[dx (TS M )] / [(TS T )]

[0018] In Equation 1 above, d is the compressible density of the electrode mixture film, and the unit of d is g / cc, TS M It is the tensile strength of the electrode mixture film in the MD direction, and TS T It is the tensile strength of the electrode mixture film in the TD direction.

[0019] [2] In [1] above, the R value defined by Equation 1 above can be 6.5 to 9.5.

[0020] [3] In [1] and / or [2] above, the tensile strength TS of the electrode mixture film in the MD direction M With tensile strength TS in the TD direction T The ratio of TS M / TS T It can be between 1.5 and 3.5.

[0021] [4] In at least one of [1] to [3] above, the tensile strength TS of the electrode mixture film in the MD direction M With tensile strength TS in the TD direction T The ratio of TS M / TS T It can be from 2.0 to 3.2.

[0022] [5] In at least one of [1] to [4] above, the compressibility density of the electrode mixture film can be from 2.4 g / cc to 3.4 g / cc.

[0023] [6] In at least one of [1] to [5] above, the electrode active material may include a lithium transition metal compound containing one or more of the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe).

[0024] [7] In at least one of [1] to [6] above, the adhesive may include polytetrafluoroethylene (PTFE).

[0025] [8] In another aspect, a method for manufacturing the above-mentioned electrode mixture film is provided, the method comprising: in a roll-to-roll process comprising two or more pairs of pressing rollers, step S1: manufacturing a preformed mixture film by powder pressing an electrode powder comprising an electrode active material and an adhesive, and step S2: pressing the preformed mixture film three or more times, while reducing the gap between the pressing rollers as the number of pressing rollers increases.

[0026] [9] In [8] above, step S2 can perform tableting so that the tensile strength of the electrode mixture film in the MD direction is greater than or equal to 0.65 MPa.

[0027]

[10] In [8] and / or [9] above, step S2 can be controlled such that the increase in compressibility of the preformed mixture film by pressing is less than or equal to 5.0%.

[0028]

[11] In at least one of [8] to

[10] above, step S2 may be controlled such that the gap of the first round of tableting is reduced by 60% to 80% relative to the gap of the powder tableting in step S1.

[0029]

[12] In at least one of [8] to

[11] above, step S2 may be controlled such that the gap of the Nth pressing round is reduced by 30% to 60% relative to the gap of the (N-1)th pressing round, wherein N can be an integer from 2 to 5.

[0030]

[13] In another aspect, a lithium secondary battery including a dry electrode is provided, wherein the dry electrode includes the above-described electrode mixture film.

[0031]

[14] In

[13] above, the dry electrode can be a dry positive electrode.

[0032] Beneficial effects

[0033] The electrode mixture film disclosed in this disclosure controls the reduction rate of the gap of the roller pressing rollers and the increase rate of the compressibility density of the film before and after pressing by controlling the roller pressing rollers during the roller-to-roll process to press the electrode powder into an electrode mixture film. This controls the compressibility density of the electrode mixture film and its tensile strength in the MD and TD directions, thereby enabling it to have excellent mechanical properties, appearance characteristics, and electrical properties.

[0034] Furthermore, the lithium secondary battery disclosed in this disclosure can have improved output and lifetime properties by including a dry electrode that has excellent durability due to the excellent mechanical properties of the electrode mixture film and improved electrode resistance due to its excellent appearance characteristics. Detailed Implementation

[0035] It will be understood that the terms or words used in this disclosure and claims should not be construed as having the meanings defined in commonly used dictionaries, but should be construed as having meanings and concepts consistent with the technical concept of the invention, based on the principle that the inventors may appropriately define the concepts of the terms to best interpret the invention.

[0036] In this disclosure, machine orientation (MD) refers to the longitudinal direction of the electrode mixture film, and transverse direction (TD) refers to the width direction of the electrode mixture film.

[0037] In this disclosure, "volume cumulative average particle size D" 50 "" refers to the particle size corresponding to 50% volume accumulation in the particle size distribution curve. 50 This can be measured using methods such as laser diffraction. Laser diffraction can typically measure particle sizes from the submicron region to a few millimeters, thus providing results with high reproducibility and high resolution.

[0038] In this disclosure, a "mixture composition" refers to a mixture comprising an electrode active material and a binder (selectively, including a conductive material), which has been physically mixed into a homogeneous dispersed phase, and may be a mixture in the form of a powder phase as a product of a mixing process (mixing technique) according to this disclosure, and may be a mixture in which there is substantially no solvent. Here, "substantially no solvent" means that when the mixture composition is obtained by mixing, no solvent or only trace amounts of solvent are introduced.

[0039] In this disclosure, "mixed aggregate" is a product of a kneading process (kneading process) according to this disclosure, in which the mixed composition is subjected to shear forces, thereby causing the binder to become fibrous, so as to allow the powdered mixture to bond or connect with each other and be transformed into aggregate in a dough-like state, wherein the product is 100% solid.

[0040] In this disclosure, "powder for electrodes" can refer to a material in a powder phase state where the mixed aggregate has been crushed and thus has a small particle size.

[0041] In this disclosure, the "electrode mixture film" can be formed without the presence of a solvent and can be fabricated into a self-supporting monolithic form using the aforementioned electrode powder. In this disclosure, the term "self-supporting" means that it can maintain its independent form without relying on other components and that it can move or manipulate itself. As described below, the electrode mixture film can be formed by pressing electrode powder and can, for example, have a layered structure shape formed by integration through compression.

[0042] In this disclosure, "pre-formed mixture film" refers to the film from the moment electrode powder is formed into a sheet through a powder pressing process in a roll-to-roll process until the sheet passes through the final pressing roller in that process. In the powder pressing process, the electrode powder first passes through the pressing roller, and the film can be a self-supporting sheet, which may be a sheet with relatively weak holding force. This term is used interchangeably with "powder-pressed film." Here, "powder pressing" means manufacturing electrode powder into a self-supporting sheet form by calendering, where "pressing" can refer to the calendering process performed during the manufacturing of the pre-formed mixture film into an electrode mixture film.

[0043] In this disclosure, "three-dimensional fiber network structure" can refer to a structure formed by the fiberization of the adhesive during the molding of an electrode mixture membrane from a sheet containing a mixture of electrode active materials and an adhesive. Specifically, the three-dimensional fiber network structure can refer to various structures in which microfibers formed by the fiberization of the adhesive form a framework, thereby providing support and making the electrode mixture membrane a self-supporting membrane. In this case, the electrode active material, and selectively conductive material, can be accommodated in the pores formed in the three-dimensional fiber network structure.

[0044] Electrode mixture membrane

[0045] In one aspect, the electrode mixture membrane is characterized by comprising a binder having a three-dimensional fiber network structure and an electrode active material contained within the three-dimensional fiber network structure, wherein the R value, as defined by Equation 1 below, is from 5.0 to 10.0.

[0046] [Equation 1]

[0047] R=[dx (TS M )] / [(TS T )]

[0048] In Equation 1 above, d is the compressible density of the electrode mixture film, and the unit of d is g / cc, TS M It is the tensile strength of the electrode mixture film in the MD direction, and TS T It is the tensile strength of the electrode mixture film in the TD direction.

[0049] Because electrode mixture films undergo various processes, including mixing to form a mixture composition, kneading to form a mixed aggregate, pulverizing the mixed aggregate in the form of kneaded mixture composition, and pressing the pulverized mixed aggregate into sheets, the mechanical, appearance, and performance properties of the electrodes are affected by various factors. In particular, the process of pressing electrodes into sheets using powder is a roller-to-roll process using rollers, which is challenging. Furthermore, because it involves preparing powder into sheet form without the use of special solvents, significant differences in the mechanical and appearance properties of the resulting films exist.

[0050] Since rolling is performed from the powder pressing process to the subsequent pressing process, it is necessary to control these processes to ensure that the electrode loading and density reach the target level. Furthermore, the mechanical properties of the preformed mixture film are significantly affected by the initial powder pressing in order to enable continuous processing in this process.

[0051] Therefore, in this disclosure, in order to ensure the mechanical strength of the electrode mixture film, including not only the appearance characteristics visible to the naked eye, but also all possible cracks, etc., R is defined using the tensile strength of the electrode mixture film in the MD direction, the tensile strength in the TD direction, and the compressive density, so as to allow the R value to meet 5 to 10, thereby providing an electrode mixture film with excellent mechanical strength and excellent appearance characteristics.

[0052] R value in Equation 1: tensile strength ratio and compressive density

[0053] According to the embodiment, the electrode mixture film has an R value of 5 to 10 as defined by Equation 1 above. The R value is defined as the tensile strength TS in the MD direction. M The product of compressibility density d and tensile strength TS in the TD direction T The ratio of the tensile strength in the MD direction to the tensile strength in the TD direction may mean that the tensile strength in the MD direction meets a sufficient level, but the ratio of the tensile strengths mentioned above can be adjusted according to the compressive density of the electrode mixture film.

[0054] The electrode composite film is manufactured in the form of a self-supporting sheet because the fibrillable adhesive is fiberized through the aforementioned process, and the fiberized adhesive forms a three-dimensional fiber network structure. The orientation of the adhesive plays a crucial role in the manufacturing process of the sheet-like film. Depending on the adhesive orientation, the tensile strength can vary according to the film's direction, and for the stability of the self-supporting film, it is preferable that the tensile strength in the MD direction is greater than that in the TD direction.

[0055] Meanwhile, since the sheet is manufactured through a roll-to-roll process, it is difficult to control the tensile strength in the TD direction. Therefore, attempts are made to ensure the tensile strength in the MD direction by controlling process conditions. However, during this process, the film is damaged due to excessive rolling. However, this trend may change depending on the film's compressibility density. That is, even if the tensile strength in the MD direction is sufficient relative to the tensile strength in the TD direction, if the compressibility density is low, even with good orientation, the durability may be weak due to the low density. Furthermore, even with good compressibility density, if the tensile strength in the MD direction is too large relative to the tensile strength in the TD direction, the preformed mixture film may crack or break during the rolling process. Therefore, it is necessary to determine the strength stability or durability of the electrode mixture film by establishing relational equations, such as an equation defining the R value.

[0056] If the R value is less than 5, then TS M / TS T The ratio of the powder to the compressive density is less than or equal to 2 due to the low tensile strength in the MD direction, or the low compressive density. This may mean a failure to control the continuous process of a series of powder tableting and pressing via a roll-to-roll process. Even if the continuous process is controlled, the low compressive density may require additional rolling pressure, thus increasing the possibility of film rupture. Electrode mixture films thus manufactured may have poor appearance characteristics, and in particular, tearing at the ends in the width direction of the electrode mixture film may be significant. Therefore, the difference between the maximum and minimum values ​​in the width direction is significantly increased, which may lead to very low utilization as an electrode.

[0057] Furthermore, if the R value is greater than 10, it can be said that there are pinholes or potential cracks that are almost invisible to the naked eye in the electrode mixture film. That is, the tensile strength in the MD direction may be too high compared to the tensile strength in the TD direction, or the compressive density may be quite high. In this case, the linear pressure during rolling is too high, which rapidly increases the possibility of breakage due to shear force or external impact. This may ultimately lead to problems such as damage during the lamination process with the current collector or the battery assembly process, or breakage in either direction during the battery charging and discharging process. Therefore, the R value needs to be adjusted so that it does not become too large.

[0058] Therefore, the R value needs to be adjusted to 5 to 10, and preferably, the R value can be greater than or equal to 5.5, greater than or equal to 5.7, greater than or equal to 6.0, greater than or equal to 6.5, or greater than or equal to 6.8, and can also be less than or equal to 9.8, less than or equal to 9.6, less than or equal to 9.5, less than or equal to 9.4, or less than or equal to 9.2.

[0059] On one hand, the tensile strength TS of the electrode mixture film in the MD direction.M With tensile strength TS in the TD direction T The ratio of TS M / TS T The ratio can be from 1.5 to 3.5. The ratio of tensile strength in the MD direction to tensile strength in the TD direction is a fundamental factor determining the mechanical strength of the electrode, and the tensile strength in the MD direction should be higher than that in the TD direction. However, if this value becomes too high, the anisotropy of the electrode mixture film may become too strong, increasing the incidence of defects in one direction compared to the strength of the film itself. Therefore, it is preferable that the tensile strength in the MD direction and the tensile strength in the TD direction satisfy the above-mentioned range, and the lower limit can be greater than or equal to 1.7, greater than or equal to 1.9, greater than or equal to 2.0, or greater than or equal to 2.2, and the upper limit can be less than or equal to 3.4, less than or equal to 3.2, or less than or equal to 3.0.

[0060] On one hand, the compressive density of the electrode mixture film can be from 2.4 g / cc to 3.4 g / cc, preferably greater than or equal to 2.5 g / cc, greater than or equal to 2.6 g / cc, or greater than or equal to 2.7 g / cc, or less than or equal to 3.2 g / cc, less than or equal to 3.1 g / cc, or less than or equal to 3.0 g / cc. In some cases, the compressive density corresponds to the basic properties to be achieved when manufacturing the electrode, and the value of the compressive density to be achieved for each target can vary, but careful consideration needs to be given to satisfying the defined R value together with the ratio of tensile strength in the MD direction to tensile strength in the TD direction mentioned above.

[0061] In other words, even if the desired compressive density value is achieved, if the R value is not met due to the tensile strength ratio, it is expected that problems may occur in the mechanical strength or appearance characteristics of the electrode mixture film. Even if the value is slightly lower than the target value, it is preferable to consider the value together with the tensile strength ratio rather than considering it alone, because the tensile strength ratio can compensate for the characteristics of mechanical strength or appearance characteristics.

[0062] On one hand, the electrode mixture film includes an electrode active material and a fiberizable binder, and may optionally also include a conductive material.

[0063] Electrode active materials

[0064] On the one hand, the electrode active material is not particularly restricted, as long as it is a commonly used electrode active material, and for example, the electrode active material can be a positive electrode active material or a negative electrode active material.

[0065] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and may include a lithium transition metal compound, which contains one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

[0066] Specifically, the positive electrode active material may include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium 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.), a lithium nickel manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium nickel cobalt-based oxide (e.g., LiNi 1- Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium manganese cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2- Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium nickel manganese cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2), etc.), or a lithium nickel cobalt transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), and may include any one thereof or may include a compound of two or more thereof.

[0067] In addition, the positive electrode active material may include iron-containing lithium metal phosphate-based compounds, such as lithium iron phosphate, and may be represented, for example, by the following chemical formula 1.

[0068] [Chemical Formula 1]

[0069] Li 1+a Fe 1-x M x PO4

[0070] In the above chemical formula 1, M is selected from one or more of Mn, Co, Ni, Al, Mg and Ti, and -0.5≤a≤0.5, and 0≤x<1.

[0071] If the positive electrode active material is a lithium metal phosphate-based compound, especially lithium iron phosphate, the safety of the positive electrode active material is guaranteed. However, compared with lithium nickel-based oxides, the disadvantage of this positive electrode active material is that it has a relatively small capacity. However, according to the embodiments of the present invention, since a dry electrode with high load capacity can be realized, a lithium secondary battery with improved capacity, excellent safety, and excellent unit price competitiveness can be realized.

[0072] In terms of increasing battery capacity and stability, lithium metal oxides can be LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxides (e.g., Li(Ni)O2). 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, Li(Ni) 0.8 Mn 0.1 Co 0.1 (O2) etc.), lithium nickel cobalt aluminum oxides (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 O2, etc.), lithium nickel manganese cobalt aluminum oxides (e.g., Li(Ni) 0.86 Co 0.05 Mn 0.07 Al 0.02 Materials such as lithium iron phosphate (e.g., LiFePO4) and lithium iron phosphate (e.g., LiFePO4) can be used, and any one of them or a mixture of two or more of them can be used, or materials doped with one or more transition metals can be applied.

[0073] The negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly inserting / extracting lithium ions, a metal or an alloy of a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0074] As the carbon material capable of reversibly inserting / extracting lithium ions, a carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used without particular limitation, and representative examples thereof may include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon may include graphite, such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon may include soft carbon (carbon fired at low temperature), hard carbon, mesophase pitch carbide, fired coke, etc.

[0075] As the metal or the alloy of a metal and lithium, a metal or an alloy of a metal and lithium 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 can be used.

[0076] As the metal composite oxide, one selected from the group consisting of 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 Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements in Group 1, Group 2, and Group 3 of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) can be used.

[0077] The material capable of doping and dedoping lithium may be Si, SiO xWhen \(0 < x\leqslant2\), Si - Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but excluding Si), Sn, \(SnO_2\), Sn - Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but excluding Sn), etc., or at least one of them can be mixed and used with \(SiO_2\). The element Y can be selected from the group consisting of 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, and combinations thereof.

[0078] The transition metal oxide can be a lithium - containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0079] Meanwhile, according to an embodiment of the present invention, the electrode active material can be included in an amount of 80 wt% to 99 wt% based on the total weight of the electrode mixture film, and preferably, the electrode active material can be included in an amount of greater than or equal to 85 wt%, greater than or equal to 88 wt%, greater than or equal to 90 wt%, greater than or equal to 92 wt%, greater than or equal to 93 wt%, or greater than or equal to 95 wt%, or less than or equal to 98.5 wt%, less than or equal to 98 wt%, or less than or equal to 97.5 wt%. If included within the above range, it can be preferred in terms of increasing the capacity and energy density of the electrode, as well as optimizing the functions of the conductive material and the binder as auxiliary materials.

[0080] conductive materials

[0081] In one aspect, the electrode mixture film can selectively include a conductive material, where the conductive material is a component for further improving the conductivity of the electrode active material, and the conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery.

[0082] For example, as conductive materials, the following can be used: carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; fluorocarbon powder; graphite materials, such as crystalline natural graphite or artificial graphite; fibrous carbon materials, such as carbon fibers, carbon nanotubes, or carbon nanofibers; metal fibers; metal powders, such as aluminum powder or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; conductive polymers, such as polyphenylene derivatives, etc. Specifically, in order to uniformly mix and improve the conductivity of the conductive material, one or more of the following can be included: graphite materials, carbon black, and carbon nanotubes (CNTs).

[0083] The content of the conductive material can be from 0.1 wt% to 10.0 wt% based on the total weight of the electrode mixture film. Preferably, the content of the conductive material can be greater than or equal to 0.2 wt%, greater than or equal to 0.3 wt%, greater than or equal to 0.5 wt%, or greater than or equal to 0.7 wt%, and the content of the conductive material can be less than or equal to 8.0 wt%, less than or equal to 6.0 wt%, or less than or equal to 5.0 wt%. A larger amount of conductive material is more conducive to the formation of conductive pathways, but the capacity may be reduced due to the relatively smaller amount of active material. Although it is not easy to control the amount of material added due to dispersion issues, the effect of forming conductive pathways can be maximized by optimizing the dispersion within the above range. Therefore, it is preferable to apply the conductive material within the above range.

[0084] adhesives

[0085] In one aspect, the adhesive has the function of forming a three-dimensional fiber network structure, so that the electrode mixture membrane can be self-supporting, and the adhesive is not specified as a particular adhesive, as long as it is fiberizable, that is, capable of forming a three-dimensional fiber network structure in the electrode mixture membrane by fiberization, and provides pores that can accommodate electrode active materials and optional conductive materials.

[0086] Fibrinization of adhesives refers to the process of subdividing a polymer used as an adhesive into segments, and can be performed, for example, by applying mechanical shear force, thereby loosening and fibrousting the surface, thereby forming multiple microfibers, which may include a three-dimensional fiber network structure.

[0087] The fiber-forming adhesive may preferably include one or more of the group consisting of polytetrafluoroethylene (PTFE) and polyolefins, and more preferably, halogenated polyethylene comprising polytetrafluoroethylene may be applied, and for example may include polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, polytrichlorofluoroethylene or polytetrachloroethylene, and more preferably, may include polytetrafluoroethylene (PTFE).

[0088] Specifically, the content of polytetrafluoroethylene (PTFE) can be 60 wt% based on the total weight of the adhesive. In this case, the adhesive may also include one or more of polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polyolefin-based adhesives.

[0089] The binder content can be from 0.1 wt% to 10.0 wt% based on the total weight of the electrode mixture film, and preferably, the binder content can be greater than or equal to 0.2 wt%, greater than or equal to 0.3 wt%, greater than or equal to 0.5 wt%, greater than or equal to 0.7 wt%, or greater than or equal to 1.0 wt%, or less than or equal to 9.0 wt%, less than or equal to 8.0 wt%, less than or equal to 7.0 wt%, or less than or equal to 5.0 wt%. In the case of a fibrous binder, if it is included in the above range, there is no problem of the binder acting as a resistor, or the problem of requiring the binder to be manufactured in the form of a self-supporting sheet with a high degree of fibrousness.

[0090] The electrode mixture membrane can have a porosity of 17 vol% to 30 vol%, preferably greater than or equal to 19 vol%, or greater than or equal to 20 vol%, and can also have a porosity of less than or equal to 29 vol%, less than or equal to 28 vol%, less than or equal to 27 vol%, or less than or equal to 26 vol%. If the above ranges are met, electrolyte solution impregnation is excellent, which can improve lifetime and output properties, and the energy density can be excellent.

[0091] Porosity can be calculated using the following equation A.

[0092] [Equation A]

[0093] Porosity (vol%) = {1 - (electrode density / actual density)} × 100

[0094] In Equation A above, the true density is the density of the electrode mixture film measured by collecting the electrode mixture film into a certain size and then pressing the electrode mixture film with a pressing device until the thickness of the film remains constant, and the electrode density is the density of the electrode mixture film measured by collecting the film into a certain size.

[0095] Method for manufacturing electrode mixture films

[0096] A method for manufacturing an electrode mixture film is characterized by comprising: in a roll-to-roll process comprising two or more pairs of pressing rollers, step (S1): manufacturing a preformed mixture film by powder pressing of an electrode powder comprising an electrode active material and a binder or optionally also comprising a conductive material, and step (S2): pressing the preformed mixture film three or more times, while reducing the gap between the pressing rollers as the number of pressing rollers increases.

[0097] The roll-to-roll process applied to steps S1 and S2 is a process that includes two or more pairs of rollers, wherein step S1 can be referred to as a powder pressing process and step S2 can be referred to as a calendering process, and can be a process of applying a method of hot pressing the supplied material using multiple rollers.

[0098] The calendering apparatus may include a pressing section, in which pressing rolls may be arranged in pairs and facing each other, wherein multiple pressing rolls may be continuously arranged in the pressing section. If multiple pressing rolls are continuously arranged, the temperature and circumferential speed ratio (the rotational speed ratio of a pair of rolls) of each roll may be the same, or the temperature of the calendering rolls may be satisfied. In this case, the rotational speed ratio of the pressing rolls may be adjusted independently within the range of 1:1 to 1:10.

[0099] Step S1

[0100] Since the descriptions of the electrode active material, conductive material, and fiber-forming binder are the same as those described above, their detailed descriptions will be omitted, and an electrode powder comprising the electrode active material, conductive material, and fiber-forming binder can be prepared as follows.

[0101] 1) Preparation of electrode powder

[0102] In the process of obtaining electrode powder according to an embodiment of the present invention, an electrode active material and a binder are first mixed, and a conductive material is selectively mixed in to obtain a mixture composition. At this time, the above mixing is performed so that the electrode active material, the optional conductive material, and the binder are uniformly distributed. Since the electrode active material, the conductive material, and the binder are mixed into a powder phase, various methods can be used without limitation, as long as these methods can easily mix the electrode active material, the conductive material, and the binder. However, in the manufacturing method according to an embodiment of the present invention, a solvent-free dry method is applied, allowing mixing to be performed by dry mixing, and the above materials can be introduced into equipment such as a mixer or agitator for mixing.

[0103] Mixing can be performed in a mixer at 3,000 rpm to 20,000 rpm, and preferably at 5,000 rpm to 15,000 rpm. If performed within the above range, the materials can be uniformly mixed, which can improve battery performance. For example, the mixing rate can be greater than or equal to 5,500 rpm, greater than or equal to 6,000 rpm, or greater than or equal to 6,500 rpm, and can also be less than or equal to 14,000 rpm, less than or equal to 13,000 rpm, or less than or equal to 12,000 rpm. When applying the above mixing rates, mixing can be performed in a mixer for 0.5 minutes to 60 minutes, preferably 1 minute to 30 minutes, 1 minute to 20 minutes, or 1 minute to 10 minutes.

[0104] Next, a fiberization process to fiberize the adhesive can be performed on the mixture obtained from the above mixing.

[0105] The fiberization process is not particularly limited, as long as it is performed normally; however, it is preferably performed by high-temperature, low-shear kneading, and for example, by a dough-making machine, such as a kneader. The fiberizable binder is fiberized by the aforementioned kneading, thereby bonding or connecting the electrode active material and conductive material powders to each other to form a mixed aggregate with a solids content of 100%.

[0106] Kneading can be performed at a rate of 10 rpm to 100 rpm, preferably greater than or equal to 20 rpm, greater than or equal to 30 rpm, greater than or equal to 40 rpm, or greater than or equal to 45 rpm, and can also be performed at a rate of less than or equal to 80 rpm, less than or equal to 70 rpm, or less than or equal to 60 rpm. Furthermore, kneading can be performed for 3 minutes to 60 minutes, preferably greater than or equal to 4 minutes, or greater than or equal to 5 minutes, and can also be performed for less than or equal to 40 minutes, less than or equal to 30 minutes, less than or equal to 25 minutes, or less than or equal to 20 minutes. If the above ranges are met, appropriate fiberization can be achieved to improve battery performance.

[0107] In addition, kneading can be performed at high temperatures and pressures above atmospheric pressure, and specifically, it can be performed at pressures above atmospheric pressure.

[0108] More specifically, kneading can be performed at temperatures ranging from 50°C to 230°C, preferably from 90°C to 200°C, and more preferably above or equal to 100°C, above or equal to 110°C, or above or equal to 120°C, and can also be performed at temperatures below or equal to 180°C, below or equal to 170°C, or below or equal to 160°C. If kneading is performed at high temperatures within the aforementioned ranges, the fiberization of the adhesive and agglomeration through kneading can be readily achieved, and the problem of the fiberized adhesive breaking apart can be appropriately prevented.

[0109] Additionally, kneading can be performed at pressures equal to or higher than atmospheric pressure, specifically between 1 atm and 3 atm, and more specifically between 1.1 atm and 3 atm. Performing kneading within these ranges can appropriately prevent the problem of fibrous binder breaking apart and prevent the aggregate density from becoming too high.

[0110] In other words, according to the present invention, performing a high-temperature and low-shear kneading process under conditions of high temperature and pressure equal to or higher than atmospheric pressure, rather than performing a high-shear kneading process, can help achieve the intended effects of the present invention.

[0111] Next, the mixed aggregate prepared by the above kneading step can be pulverized to obtain electrode powder.

[0112] The mixed aggregate prepared by the above kneading process can be directly subjected to calendering (sheet pressing). However, in this case, the mixed aggregate needs to be pressed under high pressure and high temperature to form a film. Therefore, there may be problems such as the film density becoming too high or the film not being uniform. Therefore, the mixed aggregate prepared as described above is pulverized to prepare a powder phase for electrodes.

[0113] The equipment used in the above-mentioned pulverization is not particularly limited, but equipment such as mixers or grinders is preferred.

[0114] The grinding can be performed at a rate of 1,000 rpm to 15,000 rpm for 5 seconds to 30 minutes, preferably at a rate of 3,000 rpm to 8,000 rpm for 30 seconds to 15 minutes. If grinding is performed within the above range, sufficient grinding is achieved, thereby preparing powder of appropriate size for tableting, and fine powder is not generated in large quantities from the aggregate.

[0115] The average particle size of the electrode powder can be from 10 μm to 3000 μm, specifically from 50 μm to 1500 μm, and more specifically from 100 μm to 700 μm. If the above range is met, an electrode mixture film with uniform thickness and density can be formed, and the excellent physical properties of the electrode mixture film can be ensured.

[0116] Additionally, although not strictly necessary, the electrode powder according to the invention may also include fillers to suppress electrode expansion. The fillers are not particularly limited, as long as they are fibrous materials that will not cause chemical changes in the battery, but may be, for example, selected from at least one of olefin-based polymers such as polyethylene and polypropylene, and fibrous materials such as glass fiber and carbon fiber.

[0117] 2) Powder pressing of electrode powder

[0118] Step S1 is the following process: the electrode powder obtained as described above is introduced into a roll-to-roll process comprising two or more pairs of rolls, thereby producing a preformed hybrid film in the form of a self-supporting sheet. That is, this is the first step in manufacturing a self-supporting sheet, and the film form can be manufactured by powder pressing; however, its strength and appearance may not be suitable for use as an electrode, and even with additional pressing processes performed after powder pressing, the state of the preformed hybrid film after powder pressing rarely changes its relative advantages, even after final pressing. Therefore, this process may also require careful control.

[0119] In the above-described powder tableting process, the gap between the rollers can be 250 μm to 500 μm, preferably 280 μm to 450 μm, and more preferably 280 μm to 400 μm. Roller gaps within this range minimize damage to the edge portions of the preformed mixture film and also minimize cracks in the edge and central portions of the preformed mixture film. Therefore, it is preferable to perform the first powder tableting within this range.

[0120] Step S2

[0121] Step S2 is characterized by performing three or more tableting operations on the preformed mixture film after powder tableting, wherein the gap between the rollers gradually decreases during the three tableting operations.

[0122] At least three compressions are required. The number of compressions is ultimately intended to gradually increase the compression density, thereby adjusting to the target film thickness in a non-abrupt manner, and increasing the tensile strength in the MD direction, which may be difficult to achieve without reducing the roll gap.

[0123] During tableting, the increase in compression density can be controlled to be less than 5.0%. This means that when the pre-formulated mixture film, after being tableted from powder, is sequentially tableted, the change in compression density before and after tableting should not be too large. Preferably, the roll gap is controlled such that the increase is less than or equal to 5.0%. Since the aforementioned control of the compression density increase rate affects the mechanical strength and appearance characteristics of the electrode mixture film, and may affect not only visually identifiable damage to the edge portions, but also potential cracks that may occur during battery assembly, charging, and discharging, it is preferable to appropriately control the increase in compression density. Here, the increase in compression density can be defined as the ratio of the change in compression density before and after tableting to the compression density before tableting.

[0124] In addition to controlling the increase rate of compression density, the roll gap reduction rate of the pressing rollers can be 30% to 80% during the roll-to-roll process applied in steps S1 and S2. Preferably, the roll gap reduction rate is controlled in relation to the increase rate of compression density, and in order to manufacture an electrode mixture film that satisfies the above-mentioned R value, the first round of pressing in step S2 can preferably be performed in a pressing roller whose roll gap is reduced by about 60% to 80% relative to the roll gap of the powder pressing in step S1 performed thereon; that is, preferably, the roll gap reduction rate is controlled to be 60% to 80%.

[0125] Furthermore, after the first round, step S2 can be controlled to reduce the roller gap of the Nth round of tablet pressing by 30% to 60% relative to the roller gap of the (N-1)th round of tablet pressing (the previous round), where N can be an integer from 2 to 5. Here, the roller gap reduction rate can be defined as the ratio of the roller gap difference between the (N-1)th round and the Nth round to the roller gap of the Nth round.

[0126] It may be important to apply all the process control conditions described above, but it may be most preferable to have an R value of 5 to 10, defined by the ratio of tensile strength in the MD direction to tensile strength in the TD direction and the ratio of compressive density.

[0127] The three-round pressing process allows for controlling the roll gap during the first pressing round to be 100 μm to 250 μm, preferably 100 μm to 200 μm, 100 μm to 180 μm, or 100 μm to 150 μm. Furthermore, the roll gap during the second pressing round can be 50 μm to 100 μm, 60 μm to 100 μm, or 70 μm to 100 μm, and in the third pressing round, the roll gap can be controlled to be 10 μm to 70 μm, 15 μm to 70 μm, or 20 μm to 70 μm. Within these ranges, if the roll gap is controlled to satisfy the aforementioned increase in compression density and decrease in roll gap, an electrode mixture film with excellent mechanical strength and appearance properties can be manufactured.

[0128] Three or more tablet compressions may be performed, but the number of compressions must be controlled to no more than 10, and at least three compressions should be performed. If the above conditions are met and three or more compressions are performed, the above restrictions are not particularly important.

[0129] dry electrode

[0130] The dry electrode according to the present invention comprises the electrode mixture membrane described above according to an embodiment of the present invention. Specifically, the dry electrode may include a current collector and the electrode mixture membrane of the present invention formed on the current collector.

[0131] In addition, the dry electrode according to the present invention can be manufactured by stacking electrode mixture films on one or both sides of a current collector and laminating the resulting product.

[0132] Lamination can be a rolling process, thereby attaching the electrode mixture film to the current collector. Lamination can be performed by using a rolling method with laminating rollers, and in this case, the laminating rollers can be maintained at a temperature of 20°C to 200°C.

[0133] If the dry electrode is the positive electrode, the current collector can be any current collector that is conductive but does not cause a chemical change in the corresponding battery, and is not particularly limited. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as current collectors.

[0134] If the dry electrode is the negative electrode, the current collector is not particularly restricted, as long as it has high conductivity and does not cause changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel, aluminum-cadmium alloys, etc., can be used.

[0135] The thickness of the current collector can be from 3 μm to 500 μm, preferably greater than or equal to 8 μm, greater than or equal to 10 μm, or greater than or equal to 20 μm, and can be less than or equal to 200 μm, less than or equal to 100 μm, or less than or equal to 80 μm, but is not limited thereto. In addition, micro-irregular structures can be formed on the surface of the current collector to improve the adhesion of the mixture film.

[0136] The current collector may be wholly or partially coated with a conductive primer to reduce resistance and improve surface adhesion. In this document, the conductive primer may include conductive materials and adhesives, wherein the conductive materials are not limited as long as they are conductive, but may be, for example, carbon-based materials. The adhesives may include fluoropolymer adhesives (including PVDF and PVDF copolymers), acrylic adhesives, and water-based adhesives, etc., which are soluble in solvents.

[0137] Lithium secondary batteries

[0138] The lithium secondary battery according to the present invention includes a dry electrode as described above, and the dry electrode includes an electrode mixture membrane as described above located on a current collector. For example, the lithium secondary battery may include a secondary battery containing a liquid electrolyte and an all-solid-state battery containing a solid electrolyte.

[0139] If the lithium secondary battery according to an embodiment of the present invention is a secondary battery containing a liquid electrolyte, a separator may be included between the multiple electrodes. The separator is used to separate the negative and positive electrodes and provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is a separator commonly used in lithium secondary batteries. In particular, separators with excellent electrolyte moisture retention and low resistance to ion movement in the electrolyte are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers formed from porous polymer membranes can be used. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, separators including coatings of ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0140] In addition, if the lithium secondary battery is an all-solid-state battery, a solid electrolyte membrane can be manufactured to perform the function of a separator.

[0141] In addition, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which can be used to manufacture lithium secondary batteries, but is not limited to these.

[0142] Specifically, the electrolyte may include organic solvents and lithium salts. As organic solvents, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which the ions involved in the electrochemical reactions of the battery can move. Specifically, organic solvents that can be used include: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane, etc. Among these solvents, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate-based compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) that can improve the charge / discharge performance of the battery are even more preferred.

[0143] As a lithium salt, any compound can be used without particular restrictions, as long as it can provide the lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from 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 -At least one of the constituent groups, and as a lithium salt, can be used, such as LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt can be used in a concentration range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and more preferably 1.0 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, and lithium ions can move efficiently.

[0144] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also include one or more additives, such as alkylene carbonate compounds, including ethylene difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In this case, the content of the additives can be from 0.1 wt% to 10.0 wt% based on the total weight of the electrolyte.

[0145] In addition, the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output performance and capacity retention, and can therefore be used in portable devices such as mobile phones, laptops and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0146] Therefore, according to another embodiment of the present invention, a battery module including a lithium secondary battery as a unit battery and a battery pack including the battery module are provided.

[0147] Battery modules or battery packs can be used as a power source for power tools, electric vehicles including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs), or for one or more medium to large-sized devices in a system for energy storage.

[0148] Examples

[0149] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments set forth herein.

[0150] Examples 1 to 4 and Comparative Examples 1 to 6: Fabrication of Electrode Mixture Films

[0151] 96 g of LiNi will be used as the positive electrode active material 0.81 Co 0.05 Mn 0.12 Al 0.02 O2, 1.8 g of carbon black as a conductive material and 2.2 g of polytetrafluoroethylene (PTFE) as a fiberizable binder were mixed to prepare a mixture composition. The mixture composition was then introduced into a kneader and kneaded for 5 minutes at 1.1 atmospheres, 150°C and 50 rpm to prepare aggregate. The aggregate was then pulverized to prepare electrode powder.

[0152] Subsequently, the electrode powder is pre-pressed with calendering rolls during the roll-to-roll process to produce a pre-mixed film, and the pre-mixed film is pressed under the conditions shown in Table 1 below to produce an electrode mixture film (roller diameter: 200 mm, roll speed ratio: 2:3.1).

[0153] The tensile strength and compressive density in the MD direction of the preformed mixture films manufactured by powder compression in the example and comparative examples above were measured and are shown in Table 1 below.

[0154] After the membrane was cut into 50 mm (MD) × 10 mm (TD) pieces, the tensile strength (MPa) in the MD direction was measured using a UTM instrument (ZwickRoell Ltd.) according to ASTM 638, under conditions of a preload of 0.01 kg / cm and a rate of 50 mm / min. The maximum force (MPa) applied relative to the MD direction until the sample did not break was then obtained.

[0155] The compressive density (g / cc) was obtained by using the ratio of the weight of the introduced mixture composition to the volume of the film rolled by the powder tablet and each round of tableting, and the density increase rate (%) was obtained using the following equation.

[0156] Density increase rate (%) = [(compressed density after tableting) - (compressed density before tableting)] / (compressed density before tableting)

[0157] [Table 1]

[0158] Experimental Example 1: Measuring the physical properties of an electrode mixture film

[0159] For the electrode mixture films manufactured in the examples and comparative examples above, the tensile strength in the MD and TD directions was measured, the elongation was obtained by the following methods, and their appearance characteristics were evaluated.

[0160] 1) Tensile strength (MPa) and elongation (%): After cutting the electrode mixture film into 50 mm (MD) × 10 mm (TD) pieces, the tensile strength was measured using a UTM instrument (ZwickRoell Ltd.) according to ASTM 638, under a preload of 0.01 kg / cm and a rate of 50 mm / min. The tensile strength (MPa) was obtained using the maximum force applied relative to each of the MD and TD directions until the sample did not break, and the elongation (%) was obtained using the ratio of the increase in length of the sample until breakage to the initial length of the sample (the percentage of the length before breakage to the initial length).

[0161] 2) Compressibility density (g / cc): The compressibility density is obtained by using the ratio of the weight of the introduced mixture composition to the volume of the film rolled by each round of powder tableting and tableting.

[0162] [Table 2]

[0163] Referring to Table 2 above, it can be seen that in Examples 1 to 4, where the roll gap reduction rate and density increase rate are well controlled, the mechanical properties are excellent, and thus an electrode mixture film meeting the R-value range can be obtained. However, in Comparative Examples 1 to 4, where the tableting process was not performed three or more times, the mechanical properties are poor, and therefore, the R-value is less than 5 or greater than 10. Furthermore, it can be confirmed that in Comparative Examples 5 and 6, where tableting was performed three times, the roll gap reduction rate was not sufficiently controlled, resulting in poor mechanical properties, and therefore, the R-value is less than 5.

[0164] Experimental Example 2: Evaluation of Electrode Mixture Membranes

[0165] For the appearance of the electrode mixture films of each example and each comparative example, the degree of tearing at the edge portions was observed to assess the appearance, and the electrode resistance was measured.

[0166] 1) Appearance assessment (cm): Measure the length of the portion of the electrode mixture film with a length of 30 cm that is the deepest tear and therefore has the shortest length in the width direction, perpendicular to the longitudinal direction.

[0167] 2) Electrode layer resistance (Ωcm): The electrode mixture film manufactured in each of the examples and comparative examples was placed on an aluminum foil (15 μm thick) equipped with a conductive primer layer and laminated by a roll press maintained at 150°C to manufacture a dry electrode. After each manufactured dry electrode was cut into 100 mm × 100 mm pieces, a current of 100 uA was applied to the electrode using the MP resistance measurement method, and the resistance between the electrode mixture film and the current collector layer was measured using the potential difference measured in 46 probes.

[0168] [Table 3]

[0169] Referring to Table 3 above, it can be confirmed that in Examples 1 to 4, the tearing at both ends of the film is reduced, resulting in the measured width of the normal product being significantly longer than that of the comparative examples, and the resistance of the electrode layer is also at an excellent level. However, in Comparative Examples 1 to 6, which do not meet the R-value requirements, it can be confirmed that in the appearance evaluation, the width of the normal product is significantly narrower, thus the quality is very poor, and the resistance is at a very high level. This can be expected to be due to the failure to properly control the process, thereby preventing the adhesive from being properly dispersed during sheet molding, and the failure to control the tensile strength and density values ​​in the MD and TD directions.

Claims

1. An electrode mixture membrane, comprising: Adhesives with a three-dimensional fiber network structure; as well as Electrode active material contained within the fiber network structure The value of R, as defined by Equation 1 below, ranges from 5.0 to 10.0: [Equation 1] R=[d x (TS M )] / [(TS T )] In Equation 1 above, d is the compressive density of the electrode mixture film, and the unit of d is g / cc, TS M TS is the tensile strength of the electrode mixture film in the MD direction. T It is the tensile strength of the electrode mixture film in the TD direction.

2. The electrode mixture film according to claim 1, wherein, R, as defined by Equation 1 above, ranges from 6.5 to 9.

5.

3. The electrode mixture film according to claim 1, wherein, The tensile strength (TS) of the electrode mixture film in the MD direction M ) and tensile strength (TS) in the TD direction T The ratio of (TS) M / TS T The value ranges from 1.5 to 3.

5.

4. The electrode mixture film according to claim 1, wherein, The tensile strength (TS) of the electrode mixture film in the MD direction M ) and tensile strength (TS) in the TD direction T The ratio of (TS) M / TS T The value ranges from 2.0 to 3.

2.

5. The electrode mixture film according to claim 1, wherein, The compressible density of the electrode mixture film is between 2.4 g / cc and 3.4 g / cc.

6. The electrode mixture film according to claim 1, wherein, The electrode active material includes a lithium transition metal compound containing one or more elements selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

7. The electrode mixture film according to claim 1, wherein, The adhesive comprises polytetrafluoroethylene (PTFE).

8. A method for manufacturing an electrode mixture film, said electrode mixture film being the electrode mixture film according to claim 1, the method comprising: In a roll-to-roll process involving two or more pairs of pressure rolls Step (S1) involves manufacturing a preformed mixture film by powder pressing an electrode powder, including an electrode active material and a binder. as well as Step (S2) involves pressing the pre-formed mixture film three or more times, while simultaneously reducing the gap between the rollers as the number of pressing rollers increases.

9. The method for manufacturing an electrode mixture film according to claim 8, wherein, Step S2 involves pressing the film so that the tensile strength of the electrode mixture film in the MD direction is greater than or equal to 0.65 MPa.

10. The method for manufacturing an electrode mixture film according to claim 8, wherein, Step S2 is controlled such that the increase in compressibility of the preformed mixture film as a result of pressing is less than or equal to 5.0%.

11. The method for manufacturing an electrode mixture film according to claim 8, wherein, The step S2 is controlled such that the roller gap of the first round of tableting is reduced by 60% to 80% relative to the roller gap of the powder tableting in step S1.

12. The method for manufacturing an electrode mixture film according to claim 8, wherein, Controlling step S2 reduces the roller gap of the Nth pressing round by 30% to 60% relative to the roller gap of the (N-1)th pressing round, where N is an integer from 2 to 5.

13. A lithium secondary battery, the lithium secondary battery comprising a dry electrode, wherein, The dry electrode comprises the electrode mixture membrane according to claim 1.

14. The lithium secondary battery according to claim 13, wherein, The dry electrode is a dry positive electrode.

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