Electrode sheet tandem rolling apparatus and tandem rolling method

Abstract

According to an embodiment of the present invention, provided is a tandem rolling apparatus for rolling an electrode sheet including a coated portion which is coated with an electrode active material slurry on one surface or both surfaces of a current collector and an uncoated portion which is not coated with the electrode active material slurry. The tandem rolling apparatus comprises: a rolling unit including primary rolling rolls disposed above and below the electrode sheet to primarily roll the electrode sheet, and secondary rolling rolls disposed above and below the electrode sheet to secondarily roll the primarily rolled electrode sheet; two or more transfer rolls for transferring the electrode sheet; a load cell for monitoring tension of the electrode sheet that has passed through the secondary rolling rolls; a cooling unit including a plurality of cooling rolls installed to be spaced apart along the direction of transfer of the electrode sheet to cool the electrode sheet, and a nip roll disposed in contact with a rear end cooling roll positioned rearmost in the direction of transfer among the cooling rolls; and a control unit for adjusting the upper limit torque of the cooling rolls in consideration of the rate of transfer of the electrode sheet.

Description

Tandem rolling device for electrode sheets, and tandem rolling method

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0172129 filed November 27, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0003] The present invention relates to a tandem rolling apparatus for electrode sheets and a tandem rolling method.

[0004] In modern society, as the use of portable devices such as mobile phones, laptops, camcorders, and digital cameras, as well as energy storage systems (ESS), has become commonplace, the development of technologies in related fields is becoming active. Furthermore, rechargeable secondary batteries are being utilized as power sources for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (P-HEVs) as a solution to address air pollution caused by conventional gasoline vehicles using fossil fuels; consequently, the need for the development of secondary batteries is increasing.

[0005] Currently commercialized rechargeable batteries include nickel-cadmium, nickel-hydrogen, nickel-zinc, and lithium-ion batteries. Among these, lithium-ion batteries are receiving the most attention due to their advantages of free charging and discharging, low self-discharge rate, and high energy density.

[0006] The manufacturing process of such lithium secondary batteries is broadly divided into three stages: electrode process, assembly process, and formation process. The electrode process is further divided into active material mixing process, electrode coating process, rolling process, slitting process, and winding process.

[0007] Among these, the rolling process is a process in which the electrode substrate is passed between a pair of high-temperature heated rolling rolls to compress it to a desired thickness in order to reduce the thickness of the electrode substrate after the coating process to increase capacity density and to increase the adhesion between the electrode current collector and the electrode active material.

[0008] At this time, the above rolling process is divided into single rolling, which performs rolling only once, and tandem rolling, which performs rolling twice; however, recently, as the development of high-capacity batteries is actively progressing, the tandem rolling process is predominant.

[0009] However, in the case of the above tandem rolling, the elongation rate is higher than that of single rolling, and accordingly, the difference in elongation rate between the retained part coated with the active material layer and the uncoated part where the active material layer is not formed increases, which increases the tension burden on the uncoated part and raises the risk of wire breakage.

[0010] In this regard, a cooling roll exists between the secondary rolling roll and the outfeed section in the tandem rolling device, but conventionally, the outfeed tension section was maintained as a single section, making it impossible to control the tension between the cooling rolls immediately after secondary rolling.

[0011] To explain this, FIG. 1 schematically illustrates a part of a conventional tandem rolling device (10), specifically a subsequent device including a secondary rolling roll.

[0012] Referring to FIG. 1, a conventional tandem rolling device (10) includes a secondary rolling roll (11) that rolls an electrode sheet (10-1), and the electrode sheet (10-1) that has passed through the secondary rolling roll (11) is transferred to a cooling roll (12) by a transfer roll (14). At this time, tension is applied to the electrode sheet (10-1) by the torque value of the cooling roll (12) and the transfer speed of the electrode sheet (10-1), but since the nip roll (13) exists only at the end of the tandem rolling device (10), tension control between the secondary rolling roll (11) and the cooling roll (12) is not possible.

[0013] In addition, since the conventional tandem rolling device (10) operates with the upper torque limit of the cooling roll (12) fixed, there is a problem that the tension is high immediately after rolling and there is a variation in tension depending on the feed speed.

[0014] Therefore, there is a need to develop rolling process technology that can improve the breakage of the electrode sheet by adjusting the tension immediately after this secondary rolling.

[0015] The present invention aims to provide an electrode sheet tandem rolling apparatus and a tandem rolling method capable of improving the breakage of an electrode sheet by tandem rolling.

[0016] However, the problems that the embodiments of the present invention aim to solve are not limited to the problems described above and can be expanded in various ways within the scope of the technical ideas included in the present invention.

[0017] According to one embodiment of the present invention,

[0018] A tandem rolling device for rolling an electrode sheet comprising a retaining portion having an electrode active material slurry coated on at least one surface of the current collector and a non-retaining portion not coated with the electrode active material slurry,

[0019] A rolling unit comprising a primary rolling roll disposed on the upper and lower sides of the electrode sheet to perform primary rolling of the electrode sheet, and a secondary rolling roll disposed on the upper and lower sides of the electrode sheet to perform secondary rolling of the primary rolled electrode sheet,

[0020] Two or more transfer rollers for transferring the electrode sheet,

[0021] A load cell for monitoring the tension of the electrode sheet that has passed through the second rolling roll,

[0022] A cooling unit equipped with a plurality of cooling rolls spaced apart along the transport direction of the electrode sheet to cool the electrode sheet, and a nip roll in contact with a rear cooling roll located at the end of the transport direction among the cooling rolls;

[0023] A tandem rolling device is provided that includes a control unit for adjusting the upper limit torque of the cooling roll by taking into account the tension of the electrode sheet measured by the load cell.

[0024] At this time, the control unit can adjust the upper limit torque of the cooling roll, and adjust the tension value of the electrode sheet measured by the load cell immediately after passing through the secondary rolling roll to be 130N to 170N.

[0025] At this time, the upper torque limit of the cooling roll may be adjusted within a range of 0.8% to 3%.

[0026] The transfer speed of the electrode sheet by the above transfer roll may be 5 m / min to 110 m / min.

[0027] Meanwhile, the first rolling roll shear section and the second rolling roll shear section may each further include a first preheating roll and a second preheating roll.

[0028] In addition, the tandem rolling device may further include an unwinder that unwinds the electrode sheet, which is wound in a roll shape, to transfer it to a rolling section, and a rewinder that winds the electrode sheet back into a roll shape after passing it through the cooling section.

[0029] Furthermore, the tandem rolling device may further include an induction heating unit that heats the current collector before the electrode sheet is transferred to the rolling unit.

[0030] Meanwhile, the surface temperatures of the first rolling roll and the second rolling roll may each be 25°C to 90°C, and the surface temperature of the cooling roll may be lower than the surface temperatures of the first rolling roll and the second rolling roll, and may be 10°C to 30°C.

[0031] According to another embodiment of the present invention, a tandem rolling method for rolling an electrode sheet comprising a retaining portion coated with an electrode active material slurry on one or both sides of a current collector and an uncoated portion not coated with the electrode active material slurry, wherein

[0032] The above electrode sheet is first rolled by a first rolling roll, and

[0033] The above first-rolled electrode sheet is secondarily rolled by a second-rolling roll, and

[0034] After the above secondary rolling, the electrode sheet is cooled by a cooling roll, and

[0035] A tandem rolling method is provided in which the upper limit torque of the cooling roll is adjusted considering the tension of the electrode sheet after the second rolling, and the tension value of the electrode sheet is adjusted to be 130N to 170N immediately after passing through the second rolling roll.

[0036] At this time, the upper torque limit of the cooling roll can be adjusted within a range of 0.8% to 3%.

[0037] Here, the transfer speed of the electrode sheet may be 5 m / min to 110 m / min.

[0038] The above tandem rolling method may separate the tension section by applying a nip roll to a rear cooling roll located at the end of the cooling roll based on the conveying direction of the electrode sheet.

[0039] The surface temperatures of the first rolling roll and the second rolling roll may each be 25°C to 90°C, and the surface temperature of the cooling roll may be lower than the surface temperatures of the first rolling roll and the second rolling roll, and may be 10°C to 30°C.

[0040] Meanwhile, it may further include an induction heating process for heating the current collector before the first rolling process.

[0041] Figure 1 is a schematic diagram of a part of a conventional tandem rolling device.

[0042] FIG. 2 is a schematic diagram of a tandem rolling device according to one embodiment of the present invention.

[0043] FIG. 3 is a partial flowchart of a tandem rolling method according to one embodiment of the present invention.

[0044] Figure 4 is a graph showing the tension of the electrode sheet immediately after secondary rolling according to the electrode sheet transfer speed of the comparative example according to Experimental Example 1, measured by a load cell.

[0045] Figure 5 is a graph showing the tension of the electrode sheet immediately after secondary rolling according to the electrode sheet transfer speed of the embodiment according to Experimental Example 1, measured by a load cell.

[0046] Figure 6 is a graph showing the frequency of wire breakage according to electrode sheet tension in Experimental Example 2.

[0047] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0048] To clearly explain the present invention, parts unrelated to the explanation have been omitted, and the same reference numerals are used for identical or similar components throughout the specification.

[0049] Furthermore, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and thus the present invention is not necessarily limited to what is illustrated. Thicknesses have been enlarged in the drawings to clearly represent various layers and regions. Additionally, for convenience of explanation, the thickness of some layers and regions has been exaggerated in the drawings.

[0050] Furthermore, when a part such as a layer, membrane, region, or plate is said to be "on" or "on" another part, this includes not only the case where it is "directly above" the other part, but also the case where there is another part in between. Conversely, when a part is said to be "directly above" another part, it means that there is no other part in between. Also, saying that a part is "on" or "on" a reference part means that it is located above or below the reference part, and does not necessarily mean that it is located "on" or "on" facing the opposite direction of gravity.

[0051] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0052]

[0053] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0054] FIG. 2 schematically illustrates a tandem rolling apparatus for an electrode sheet according to one embodiment of the present invention, and FIG. 3 also illustrates a part of a tandem rolling method for an electrode sheet in sequence.

[0055] Hereinafter, a rolling device applied to an electrode sheet according to the present invention and a method thereof will be described in detail together with reference to FIG. 1 and FIG. 2.

[0056] Referring to FIG. 1 and FIG. 2 together, the tandem rolling device (100) according to the present invention comprises two or more conveying rolls (130) that convey an electrode sheet (101) in its entirety, a primary rolling roll (110) that is positioned above and below the electrode sheet (101) conveyed by the conveying rolls (130) and performs primary rolling of the electrode sheet (101), and a secondary rolling roll (120) that is positioned above and below the electrode sheet (101) and performs secondary rolling of the electrode sheet (101) that has passed through the primary rolling rolls (110).

[0057] A rolling method performed two or more times in this manner is called tandem rolling. As explained above, this tandem rolling causes a large difference in elongation between the retaining part where the active material layer is formed and the unretaining part where the active material layer is not formed, resulting in a high frequency of wire breakage.

[0058] Accordingly, the inventors of the present application, after conducting in-depth research, have come to complete a tandem rolling device and a method thereof that can significantly reduce the frequency of wire breakage of the electrode sheet (101).

[0059] Here, the electrode sheet (101) includes a retaining portion coated with an electrode active material slurry on at least one surface of the current collector, which is not shown in detail in the drawing, and a non-retaining portion not coated with the electrode active material slurry.

[0060] The above current collector may be determined differently depending on whether it is a positive or negative electrode, but generally, it may have a thickness of 3 to 500 μm. In addition, it is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, etc., on the surface of copper, aluminum, or stainless steel may be used. The current collector may also form fine irregularities on its surface to increase the adhesion of the electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0061] The type of active material in the above electrode active material slurry is determined depending on whether it is a positive electrode or a negative electrode, and when the electrode (101) sheet is a positive electrode, the electrode active material slurry may include a positive electrode active material, a binder, a conductive material, and other additives.

[0062] The above-mentioned cathode active material is, for example, a compound capable of reversible intercalation and deintercalation of lithium, such as a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese 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.), lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )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 the atomic fractions of independent elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO4-b )X b (Here, M is one or more selected from Al, Mg and Ti, X is one or more selected from F, S and N, and -0.5≤a≤+0.5, 0≤x≤0.5, 0≤b≤0.1) etc. may be further included.

[0063] The above conductive material is a component for further improving the conductivity of the active material, and such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders 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 materials such as polyphenylene derivatives may be used. Among these, the above conductive material may include conductive nanomaterials such as carbon nanotubes or carbon nanofibers to further lower the resistance of the secondary battery and further improve output characteristics.

[0064] Typically, the conductive material may be included in an amount of 1 to 20 weight%, or 1 to 15 weight%, or 1 to 10 weight% based on the total weight of the solids included in the electrode active material slurry.

[0065] The above binder is a component that assists in the bonding of the active material and the conductive material, etc., and in the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile-based rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0066] Typically, the binder may be included in an amount of 1 to 20 weight%, or 1 to 15 weight%, or 1 to 10 weight% based on the total weight of the solids included in the electrode active material slurry.

[0067] In addition, the above-mentioned other additives may further include, for example, fillers as components that inhibit expansion. The above-mentioned filler is not particularly limited as long as it can inhibit the expansion of the electrode without causing chemical changes in the battery, and, for example, olifin-based polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. may be used.

[0068] When the electrode sheet (101) is a negative electrode, the electrode active material slurry may include, in addition to the negative electrode active material, a binder such as the one described in the positive electrode, a conductive material, and other additives.

[0069] The above-mentioned cathode active material comprises one or more carbon-based materials selected from the group consisting of graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon, Si-based materials, and Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me1-x Me y 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) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO2, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물; 리튬 티타늄 산화물 등을 포함할 수 있지만, 당업계에 알려진 것이라면 이들만으로 한정되지 않는다.

[0070] Again, looking specifically at the tandem rolling device (100) and the tandem rolling method, the electrode sheet (101) is first rolled by the primary rolling roll (110), that is, the upper primary rolling roll (111) located above the electrode sheet (101) and the lower primary rolling roll (112) located below it, thereby performing primary rolling (S1).

[0071] Afterwards, secondary rolling is performed to roll the electrode sheet (101) by means of a secondary rolling roll (120), that is, an upper secondary rolling roll (121) located above the electrode sheet (101) and a lower secondary rolling roll (122) located below it, so as to have a final target thickness or density (S2).

[0072] Here, the first rolling and the second rolling are processes of rolling the entire electrode sheet (101) in the width direction, that is, rolling the retaining portion and the unretaining portion of the electrode sheet (101) entirely.

[0073] However, during such rolling, the uncoated portion is not rolled well due to the difference in thickness between the retained portion and the uncoated portion, that is, the difference in thickness according to the thickness of the active material slurry coating.

[0074] Accordingly, the tandem rolling apparatus and tandem rolling method according to the present invention, although not illustrated in the drawings, may further include a first non-rolling process in which only the non-rolling portion is rolled after the first rolling, and a second non-rolling process in which only the non-rolling portion is rolled after the second rolling, in each of the first rolling and second rolling processes, and may further include non-rolling rolling rolls that perform such processes.

[0075] From this, the difference in elongation between the above-mentioned retained portion and the unretained portion can be reduced.

[0076] Additionally, rolling according to the present invention can also be performed as hot tandem rolling, and thus, the surface temperature of the rolling rolls (110, 120) can be increased so that heat can be applied to the electrode sheet (101) along with the rolling.

[0077] For example, the surface temperature of the first rolling roll (110) and the second rolling roll (120) that perform the first rolling and the second rolling may each be 25°C to 90°C, more specifically 60°C to 90°C, and even more specifically 70°C to 90°C.

[0078] Here, the surface temperature can be measured by temperature sensors located near the upper and lower rolling rolls (111, 112, 121, 122) of the first rolling roll (110) and the second rolling roll (120). Specifically, the temperature sensors can measure the temperature by detecting the temperature by irradiating a laser onto the surface of the rolling rolls (111, 112, 121, 122).

[0079] When the first rolling roll (110) and the second rolling roll (120) are at 25°C, it means that no separate heat is applied. However, when performing hot tandem rolling by applying heat to raise the surface temperature of the first rolling roll (110) and the second rolling roll (120), it is desirable to apply a model with a large possible target thickness range and a high rolling rate, as this has the effect of reducing the equipment load due to increased rolling load.

[0080] At this time, when performing hot tandem rolling to raise the surface temperature of the first rolling roll (110) and the second rolling roll (120), although not shown in the drawing, a preheating roll that applies heat to the electrode sheet (101) immediately before performing each of the first rolling and second rolling processes may be further included, and a process of preheating by the preheating roll may be additionally performed.

[0081] Here, preheating can be performed such that the surface temperature of the preheating roll is lower than the surface temperature of the first rolling roll (110) and the second rolling roll (120) and is between 30°C and 50°C.

[0082] Meanwhile, the tandem rolling device (100) according to the present invention includes a cooling section equipped with a plurality of cooling rolls (140) spaced apart along the conveying direction of the electrode sheet (101) so as to cool the electrode sheet (101) after the second rolling is completed, and a nip roll (150) in contact with a rear cooling roll located at the end of the conveying direction among the cooling rolls (140).

[0083] That is, according to the present invention, a nip roll (150) is applied and provided to the rear cooling roll, thereby separating the tension section after secondary rolling into two.

[0084] When the tension section is separated in this way, it is easy to control the tension applied to the secondary rolling roll (120) and the cooling roll (140). Accordingly, the present invention is provided with a nip roll (150) that contacts the rear cooling roll, so that the tension applied to the electrode sheet (101) immediately after passing through the secondary rolling roll (120) can be easily controlled through the control unit (170).

[0085] Specifically, the tension of the electrode sheet (101) immediately after passing through the secondary rolling roll (120) can be measured and monitored by a load cell (160) (S3).

[0086] At this time, the tension of the electrode sheet (101) measured by the load cell (160) is the value of the force applied to the electrode sheet (101) at the transfer roll immediately after the secondary rolling where the load cell (160) is located.

[0087] And the control unit (170) adjusts the upper torque of the cooling roll (140) based on the tension of the electrode sheet (101) measured by the load cell (160) (S4).

[0088] Specifically, the control unit (170) can adjust the upper limit torque of the cooling roll (140) so that the tension value of the electrode sheet (101) measured by the load cell (160) immediately after passing through the secondary rolling roll (120) is 130N to 170N, more specifically 130N to 160N, and even more specifically 130N to 150N.

[0089] It is difficult to maintain tension outside the above range and smaller than the above range, and it is not desirable if it becomes larger than the above range because the frequency of wire breakage increases.

[0090] Accordingly, the control unit (170) continuously receives the tension of the electrode sheet (101) from the load cell (160) and performs the role of continuously changing and adjusting the upper limit torque of the cooling roll (140) so that this tension has the above range, so S3 and S4 are continuously repeated during the rolling process of the electrode sheet (101).

[0091] At this time, the control unit (170) can adjust the upper limit torque of the cooling roll (140) to a range of 0.8% to 3%, specifically 0.9% to 2.9%, and accordingly, the tension applied to the electrode sheet (101) immediately after secondary rolling can be adjusted to the above range.

[0092] The tension of the electrode sheet (101) is determined by various factors such as the upper limit torque of the cooling roll (140), the transport speed of the electrode sheet (101), and the travel speed of the secondary rolling roll (120).

[0093] For example, when the transfer speed of the electrode sheet (101) is high, the upper limit torque of the cooling roll (140) is increased together, and when the transfer speed of the electrode sheet (101) is low, the upper limit torque of the cooling roll (140) is lowered together, thereby reducing the tension applied to the electrode sheet (101).

[0094] The transfer speed of the electrode sheet (101) can be, for example, 5 m / min to 110 m / min, and more specifically, 10 m / min to 100 m / min.

[0095] In this way, according to the present invention, immediately after passing through the secondary rolling roll (120), the tension value of the electrode sheet (101) is adjusted to be 130N to 170N, and then it passes through the cooling roll (140), and the cooling of the electrode sheet (101) is completed (S5).

[0096] For such cooling, the surface temperature of the cooling roll (140) is lower than the surface temperature of the first rolling roll and the second rolling roll, and may be 5°C to 25°C, and more specifically, 5°C to 20°C.

[0097] These cooling rolls (140) can be controlled by passing cooling water or cooling air, etc., through the flow path inside the cooling rolls (140).

[0098] If the above cooling is not performed, electrode damage due to heating may occur and the electrode material may also be affected, which is undesirable.

[0099] Meanwhile, the tandem rolling device (100) according to the present invention further includes an induction heating unit (190) that heats a current collector before the electrode sheet (101) is transferred to the rolling unit, thereby further performing an induction heating process.

[0100] At this time, the induction heating unit (190) refers to a process that heats only the current collector portion, and the induction heating temperature can be specifically, in detail, 200°C to 300°C, and more specifically, 200°C to 260°C.

[0101] The above induction heating temperature may be a temperature set in the induction heating unit (190).

[0102] If the induction heating temperature is too low outside the above range, the elongation of the uncoated portion is not properly performed, which increases the likelihood of wire breakage or the formation of wrinkles; if it is too high, the tensile strength of the uncoated portion decreases and the likelihood of wrinkles increases, making it impossible to obtain the required electrode quality, which is undesirable.

[0103] Meanwhile, the tandem rolling device (100) of the present invention may further include an unwinder (181) that unwinds the electrode sheet (101) in a roll-like shape and transfers it to a rolling section when rolling is performed, and a rewinder (182) that winds the electrode sheet (101) back into a roll-like shape after passing it through a cooling section.

[0104]

[0105] In the following, embodiments are disclosed to aid in understanding the present invention, and the difference in the frequency of wire breakage occurrence when the conditions according to the present invention are satisfied versus when they are not is explained through experimental examples. However, the following embodiments are intended to illustrate the present invention and the scope of the present invention is not limited thereto.

[0106]

[0107] <Comparative Example>

[0108] While performing rolling using a tandem rolling device as shown in Fig. 1 below, the tension of the electrode sheet measured by the load cell immediately after the second rolling was measured.

[0109]

[0110] <Example>

[0111] Rolling was performed using a tandem rolling apparatus according to the present invention as shown in Fig. 2 below, while varying the cooling roll torque value and measuring the tension of the electrode sheet measured by the load cell immediately after the second rolling. The change in the cooling roll torque value was applied in a direction that maintains the tension of the electrode sheet measured by the load cell immediately after rolling at a constant target tension using a torque table.

[0112]

[0113] <Experimental Example 1>

[0114] Graphs of the change in tension of the electrode sheet measured in the above comparative example and example are shown in Figures 4 and 5 below.

[0115] Referring to FIGS. 4 and 5, when a conventional fixed torque value is used and a nip roll is not applied to the cooling roll, it can be seen that the tension of the electrode sheet immediately after secondary rolling has a value in the range of about 190 N to 210 N, regardless of the electrode sheet transfer speed.

[0116] On the other hand, when the upper limit torque value of the cooling roll is changed in real time considering the transfer speed of the electrode sheet according to the present invention, it can be confirmed that the tension of the electrode sheet is maintained at approximately 145N immediately after secondary rolling.

[0117]

[0118] <Experimental Example 2>

[0119] As in the example, the tandem rolling apparatus according to the present invention was used, and the upper limit torque of the cooling roll was adjusted so that the tension immediately after the second rolling was about 175N, about 145N, and about 130N, and electrode sheet rolling was performed.

[0120] In addition, as in the comparative example, electrode sheet rolling was performed using a conventional tandem rolling device so that the tension became about 190N immediately after secondary rolling.

[0121] In addition, the frequency of wire breakage in the electrode sheet was investigated and is shown in Fig. 6 below.

[0122] The above frequency of wire breakage is obtained by dividing the number of times an item corresponding to wire breakage occurred in the equipment alarm history when continuous production was performed for about 24 hours under each condition by the actual electrode production volume ([times] / production volume [10km]).

[0123] Referring to Fig. 6, it can be seen that the frequency of wire breakage increases rapidly as the tension of the electrode sheet increases immediately after the second rolling, and in particular, when the tension is about 190N or 175N, a fairly high frequency of wire breakage is observed, whereas when the tension is 145N and 130N, the frequency of wire breakage decreases significantly.

[0124]

[0125] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

[0126] [Explanation of the symbol]

[0127] 10, 100: Tandem rolling device,

[0128] 110: Primary rolling roll,

[0129] 11, 120: Secondary rolling roll,

[0130] 130: Transfer roll,

[0131] 140: Cooling roll,

[0132] 150: Niproll,

[0133] 160: Electrode sheet tension measuring load cell,

[0134] 170: Control unit,

[0135] 181: Unwinder,

[0136] 182: Rewinder,

[0137] 190: Induction heating device.

[0138] According to the present invention, when process conditions in the rolling process of an electrode sheet are adjusted to satisfy specific conditions, the effect of significantly improving rolling defects without degrading electrode quality is achieved.

Claims

1. A tandem rolling apparatus for rolling an electrode sheet comprising a retaining portion coated with an electrode active material slurry on at least one surface of the current collector and an uncoated portion not coated with the electrode active material slurry, A rolling unit comprising a primary rolling roll disposed on the upper and lower sides of the electrode sheet to perform primary rolling of the electrode sheet, and a secondary rolling roll disposed on the upper and lower sides of the electrode sheet to perform secondary rolling of the primary rolled electrode sheet, Two or more transfer rollers for transferring the electrode sheet, A load cell for monitoring the tension of the electrode sheet that has passed through the second rolling roll, A cooling unit equipped with a plurality of cooling rolls spaced apart along the transport direction of the electrode sheet to cool the electrode sheet, and a nip roll in contact with a rear cooling roll located at the end of the transport direction among the cooling rolls; A tandem rolling device comprising a control unit that adjusts the upper torque limit of the cooling roll by taking into account the tension of the electrode sheet measured by the load cell.

2. In Paragraph 1, A tandem rolling device in which the control unit adjusts the upper limit torque of the cooling roll, but adjusts the tension value of the electrode sheet measured by the load cell immediately after passing through the secondary rolling roll to be 130N to 170N.

3. In Paragraph 1, A tandem rolling device in which the transfer speed of the electrode sheet by the above transfer roll is 5 m / min to 110 m / min.

4. In Paragraph 3, A tandem rolling device in which the upper torque limit of the cooling roll according to the transfer speed of the electrode sheet is adjusted in the range of 0.8% to 3%.

5. In Paragraph 1, A tandem rolling apparatus comprising a first preheating roll and a second preheating roll, respectively, in the first rolling roll shear section and the second rolling roll shear section.

6. In Paragraph 1, The above tandem rolling device comprises an unwinder in which the electrode sheet is wound in a roll shape and which unwinds the electrode sheet to transfer it to a rolling section, and A tandem rolling device further comprising a rewinder that winds the electrode sheet into a roll shape again after passing through the cooling section above.

7. In Paragraph 1, The above tandem rolling device further includes an induction heating unit that heats a current collector before the electrode sheet is transferred to the rolling unit.

8. In Paragraph 1, A tandem rolling apparatus in which the surface temperatures of the first rolling roll and the second rolling roll are each 25℃ to 90℃.

9. In Paragraph 1, A tandem rolling device in which the surface temperature of the cooling roll is 10℃ to 30℃.

10. A tandem rolling method for rolling an electrode sheet comprising a retaining portion coated with an electrode active material slurry on one or both sides of a current collector and an uncoated portion not coated with the electrode active material slurry, wherein The above electrode sheet is first rolled by a first rolling roll, and The above first-rolled electrode sheet is secondarily rolled by a second-rolling roll, and After the above secondary rolling, the electrode sheet is cooled by a cooling roll, and A tandem rolling method that adjusts the upper limit torque of the cooling roll considering the tension of the electrode sheet after the second rolling, and adjusts the tension value of the electrode sheet to be 130N to 170N immediately after passing through the second rolling roll.

11. In Paragraph 10, A tandem rolling method in which the transfer speed of the electrode sheet is 5 m / min to 110 m / min.

12. In Paragraph 10, A tandem rolling method in which the upper limit torque of the cooling roll according to the transfer speed of the electrode sheet is controlled within the range of 0.8% to 3%.

13. In Paragraph 10, The above tandem rolling method is a tandem rolling method that separates the tension section by applying a nip roll to a rear cooling roll located at the end of the cooling roll based on the conveying direction of the electrode sheet.

14. In Paragraph 10, A tandem rolling method in which the surface temperatures of the first rolling roll and the second rolling roll are each 25°C to 90°C, and the surface temperature of the cooling roll is lower than the surface temperatures of the first rolling roll and the second rolling roll, and is 10°C to 30°C.

15. In Paragraph 10, A tandem rolling method further comprising an induction heating process for heating the current collector before the first rolling above.

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