Method and apparatus for producing secondary battery electrode including rolling undried electrode active material slurry

Abstract

The present invention provides a method and apparatus for manufacturing an electrode for a secondary battery, the method and apparatus including a rolling step of applying a load to an electrode active material slurry when the solid content of the undried electrode active material slurry is 70 wt% to 98 wt% during a step of drying the electrode active material slurry coated on a current collector in one or more layers.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0061936 dated May 13, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method and an apparatus for producing an electrode for a secondary battery, the method including a step of rolling an undried electrode active material slurry. [Background technology]

[0003] The rapid increase in the use of fossil fuels has led to an increased demand for alternative and clean energy, and one of the most actively researched fields in this area is the field of power generation and storage using electrochemistry.

[0004] At present, secondary batteries are a typical example of electrochemical elements that use such electrochemical energy, and the range of their use is tending to expand more and more.

[0005] Recently, with technological development and increasing demand for portable devices such as portable computers, portable phones, and cameras, the demand for secondary batteries as energy sources has increased rapidly. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and working potential, long cycle life, and low self-discharge rate, have been the subject of much research and are now commercially available and in wide use.

[0006] Furthermore, as interest in environmental issues grows, much research is being conducted on electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Nickel-metal hydride batteries are mainly used as the power source for such electric vehicles and hybrid electric vehicles, but research into using lithium secondary batteries with high energy density and discharge voltage is being actively conducted, and some of them are already at the commercialization stage.

[0007] Electrodes, which are components of lithium secondary batteries, are manufactured by coating an electrode active material slurry, which is a mixture of an active material, a conductive agent, a binder, a thickener, and the like, in a solvent, on a current collector and drying the resulting slurry.

[0008] In this case, the solvent is removed during a drying process, and the active material and the other components form an electrode mixture, and the structural characteristics of the electrode mixture are determined only by the composition of the slurry and the target loading amount.

[0009] On the other hand, electrodes that have completed the drying process are too thick to be used in secondary batteries that require high energy density, so they are rolled to densify the electrodes to a target thickness.

[0010] Generally, such a rolling process is performed so that the rolling ratio, which indicates the change in thickness before and after rolling, is 20 to 40%, and a load of about 10 tons is applied to the electrode to achieve this rolling ratio. However, the higher the load applied to the electrode, the more defects such as cracking of the active material, electrode breakage, and waviness occur.

[0011] Therefore, there is a pressing need for development of a manufacturing technique for secondary battery electrodes that can solve these problems, reduce the probability of defects occurring in the rolling process, and improve processability. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to solve the above problems by manufacturing an electrode with a higher density than a structure formed naturally through a drying process, thereby minimizing the rolling load for rolling the electrode to a target thickness in the rolling process, thereby minimizing the probability of occurrence of defects. [Means for solving the problem]

[0013] The terms and words used in this specification and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical ideas of the present invention, based on the principle that the inventor can appropriately define the concepts of terms in order to best describe his / her invention.

[0014] Hereinafter, according to one embodiment of the present invention, there is provided a method for manufacturing an electrode for a secondary battery, the method including a rolling process of applying a load to an electrode active material slurry when the solid content of the undried electrode active material slurry is 70 wt% to 98 wt% during a process of drying the electrode active material slurry coated on a current collector in one or more layers.

[0015] At this time, the rolling process is carried out when the solid content of the wet electrode active material slurry is 80wt% to 90wt%.

[0016] The rolling step is carried out by a press roll that applies a linear pressure onto the undried electrode active material slurry.

[0017] Specifically, the rolling step is performed under a linear pressure load of 0.5 kgf / cm to 0.1 ton / cm.

[0018] In addition, in the method for producing an electrode for a secondary battery, after the rolling step, additional drying may be performed until the solid content of the electrode active material slurry becomes 99 to 100 wt %.

[0019] More specifically, the method for producing an electrode for a secondary battery includes the steps of: (a) coating one or more layers of an electrode active material slurry on a current collector; (b) drying the electrode active material slurry to a solid content of 70 wt% to 98 wt%; (c) a wetting rolling step of applying a load to the electrode active material slurry having a solid content of 70 wt% to 98 wt%; (d) a further drying step of forming an electrode mixture by further drying the electrode active material slurry until the solid content of the electrode active material slurry becomes 99 to 100 wt %; and (e) a dry rolling step of rolling the electrode mixture after drying.

[0020] According to another embodiment of the present invention, there is provided an apparatus for manufacturing an electrode for a secondary battery, comprising: a roller-shaped unwinder around which a sheet-shaped current collector is wound; a transfer unit that continuously transfers the sheet-like current collector; a coating unit that applies one or more layers of electrode active material slurry to at least one surface of the sheet-like current collector; a drying section for drying the electrode active material slurry to form an electrode mixture on at least one surface of a sheet-shaped current collector; and a roller-shaped rewinder that winds up the electrode sheet in which the electrode mixture is formed on the sheet-shaped current collector, The drying section includes a wetting rolling section that applies a load onto the electrode active material slurry when the solid content of the undried electrode active material slurry is 70 wt % to 98 wt %.

[0021] At this time, the coating unit may be a coating die, a coating roll, or a slide-slot.

[0022] Meanwhile, the drying section may include a hot air nozzle that generates hot air in a drying oven, an IR (infrared) lamp, or both of these, and the wetting rolling section may be a press roll, and may be provided in a section inside or outside the drying oven where the solid content of the electrode active material slurry becomes 70 wt% to 98 wt%.

[0023] Here, the hot air nozzles and the IR lamps may be arranged alternately. [Brief description of the drawings]

[0024] [Figure 1]1 is a schematic diagram of an apparatus for manufacturing an electrode for a secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention will now be described in further detail.

[0026] According to one embodiment of the present invention, there is provided a method for manufacturing an electrode for a secondary battery, the method including a rolling process of applying a load to an electrode active material slurry when a solid content of the undried electrode active material slurry is 70 wt% to 98 wt% during a process of drying the electrode active material slurry coated on a current collector in one or more layers.

[0027] According to another embodiment of the present invention, there is provided an apparatus for manufacturing an electrode for a secondary battery, comprising: a roller-shaped unwinder around which a sheet-shaped current collector is wound; a transfer unit that continuously transfers the sheet-like current collector; a coating unit that applies one or more layers of electrode active material slurry to at least one surface of the sheet-like current collector; a drying section for drying the electrode active material slurry to form an electrode mixture on at least one surface of a sheet-shaped current collector; and a roller-shaped rewinder that winds up the electrode sheet in which the electrode mixture is formed on the sheet-shaped current collector, The drying section includes a wetting rolling section that applies a load onto the electrode active material slurry when the solid content of the undried electrode active material slurry is 70 wt % to 98 wt %.

[0028] Hereinafter, the present invention will be described in detail with reference to the drawings so that a person skilled in the art can easily carry out the present invention. However, the drawings are merely examples, and the present invention can be realized in various different forms within the scope of the present invention, and is not limited to the drawings.

[0029] Specifically, an electrode manufacturing apparatus for a secondary battery according to an embodiment of the present invention is illustrated in Fig. 1. The electrode manufacturing apparatus for a secondary battery according to the present invention includes a roller-shaped unwinder 110 around which a sheet-shaped current collector 101 is wound, a transport unit 120 for continuously transporting the sheet-shaped current collector 101, a coating unit 130 for applying one or more layers of electrode active material slurry 102 on at least one surface of the sheet-shaped current collector 101, a drying unit 140 for drying the electrode active material slurry 102 to form an electrode mixture 103 on at least one surface of the sheet-shaped current collector 101, and a roller-shaped winder 150 for winding up the electrode sheet in which the electrode mixture 103 is formed on the sheet-shaped current collector 101.

[0030] At this time, the drying section 140 includes a wetting rolling section 143 that applies a load onto the electrode active material slurry 102 when the solid content of the undried electrode active material slurry 102 is 70 wt % to 98 wt %.

[0031] Hereinafter, the components of the electrode manufacturing apparatus will be described in detail, and the method for manufacturing an electrode for a secondary battery according to the present invention will also be described.

[0032] First, the unwinder 110 has a structure in which a sheet-like current collector 101 is wound around a roll.

[0033] The unwinder 110 unwinds the sheet-shaped current collector 101 so that the sheet-shaped current collector 101 is transported by the transport unit 120 .

[0034] The conveying unit 120 receives the sheet-shaped current collector 101 unwound from the unwinder 110 and conveys the sheet-shaped current collector 101 through the coating unit 130 and the drying unit 140 to the winder 150 .

[0035] Here, the transport section 120 may be a roll.

[0036] Next, the sheet-shaped current collector 101 is unwound from the unwinder 110 and transferred by the transfer section 120 to the coating section 130 by the transfer section 120 .

[0037] The coating unit 130 coats the sheet-shaped current collector 101 with one or more layers of electrode active material slurry 102 .

[0038] At this time, the coating unit 130 is not limited as long as it can coat the electrode active material slurry 101, and can be determined according to the number of layers of the electrode active material slurry 102 by coating using a conventionally known coating device such as a coating die, a coating roll, or a slide slot, and the specific configuration differs depending on whether double-sided coating or single-sided coating is performed. However, since various coating forms have been disclosed in the art, FIG. 1 shows only a structure in which the electrode active material slurry is coated using a coating die as an example.

[0039] Specifically, the coating unit 130 includes a coating die 131 having an outlet slot through which the electrode active material slurry 102 flows out toward the sheet-shaped current collector 101, and a coater roll 132 that is spaced a predetermined distance from the outlet slot of the die 131 and transports the sheet-shaped current collector 101 by rotation so that the electrode active material slurry 102 can be applied to the sheet-shaped current collector 101 by the coating die 131.

[0040] Thereafter, the sheet-shaped current collector 101 coated with the electrode active material slurry 102 is transferred to the drying unit 140 by the transfer unit 120 .

[0041] The drying section 140 in this embodiment is not limited to any device that can evaporate the solvent from the electrode active material slurry 102 to form the electrode mixture 103, and may have any conventionally known structure, and may be, for example, a heating type and / or a hot air type.

[0042] Therefore, the drying section 140 includes a hot air nozzle 141 that generates hot air in the drying oven 144, and an IR (infrared) lamp 142. Meanwhile, in FIG. 1, the secondary battery electrode manufacturing apparatus 100 according to the present invention also includes a wetting rolling section 143 as a press roll in the drying oven 14.

[0043] Meanwhile, FIG. 1 below shows a configuration in which the wetting rolling section 143 is formed within the drying oven 144, but this is not limited thereto. Even if the wetting rolling section 143 is included in the drying section 140, it is not formed within the drying oven 144. Alternatively, the drying oven 144 may be formed of two or more units, each of which includes a hot air nozzle 141 and an IR lamp 142, and the wetting rolling section 143 may be included between the units having a solid content of 70 wt% to 98 wt%.

[0044] The drying process of the electrode active material slurry 102 in the drying section 140 is carried out in the following manner.

[0045] First, when drying of the electrode active material slurry 102 starts in the drying section 140, the electrode active material slurry 102 is dried so that the solid content of the electrode active material slurry 102 becomes 70 wt% to 98 wt%. Thereafter, wetting rolling is performed to apply a load to the electrode active material slurry 102 having a solid content of 70 wt% to 98 wt%, and thereafter, additional drying is performed to form the electrode mixture 103 by performing additional drying until the solid content of the electrode active material slurry 102 becomes 99 to 100 wt%.

[0046] For this purpose, the wetting rolling section 143 may be provided in a section inside or outside the drying oven 144 where the solid content of the electrode active material slurry 102 is 70 wt% to 98 wt%, and more specifically, the wetting rolling section 143 according to this embodiment may be provided in a section where the solid content of the undried electrode active material slurry 102 is 80 wt% to 90 wt%.

[0047] The solid content can be expressed as the solid content by measuring the change in weight of the slurry before and after drying, or by measuring the moisture content in the electrode in-line using a NIR (near infrared) moisture measuring sensor or the like.

[0048] At this time, the wetting rolling step is carried out by a press roll that applies a linear pressure onto the undried electrode active material slurry.

[0049] Specifically, the wetting rolling step is performed under a linear pressure load of 0.5 kgf / cm or more, specifically 0.8 kgf / cm or more and 5 ton / cm or less, specifically 1 ton / cm, and further specifically 0.1 ton / cm or less.

[0050] If the line pressure is too low beyond the above range, the benefits of the wetting rolling cannot be obtained, and the effects of the present invention cannot be achieved. If the line pressure is too high, cracks in the active material may occur during the wetting rolling, which is undesirable.

[0051] Meanwhile, as other components included in the drying section 140, the configuration of the hot air nozzle 141 and IR lamp 142 that perform drying is not limited, and only one component may be included, or both of the two components may be included, or a configuration may be provided in which the hot air nozzle 141 is included on one side of the wetting rolling section 143 and the IR lamp 142 is included on the other side, but the hot air nozzle 141 and the IR lamp 142 may be arranged alternately so that both hot air and heat drying can be performed.

[0052] After passing through the drying section 140, the solvent is almost completely evaporated on the sheet-shaped current collector 101, forming an electrode mixture 103 having a solid content of 99 to 100 wt %, and the electrode sheet having the electrode mixture 103 formed on the sheet-shaped current collector is then wound up by a roller-shaped winding machine 150.

[0053] The winder 150, like the unwinder 110, has a structure for winding the electrode sheet into a roll.

[0054] Although not shown, the electrode sheet is then unwound again for rolling, and is rolled by a dry rolling unit to have an appropriate porosity and electrode density.

[0055] The dry rolling section is also not limited in terms of its device or structure as long as it can roll the electrode mixture. For example, the dry rolling section may be configured to roll the electrode mixture by adjusting the separation distance between a pair of rollers.

[0056] According to the present invention, since one wetting rolling is performed when the electrode active material slurry is not completely dried, the rolling rate is relatively low in the subsequent dry rolling process performed after the electrode active material slurry is completely dried.

[0057] More specifically, when wetting rolling is not performed, the rolling ratio in the dry rolling stage generally cannot be set high. However, when wetting rolling is performed according to the present invention, the electrode mixture is dried at a reduced thickness, so that rolling can be performed at a lower load, and the desired thickness, porosity, etc. of the electrode mixture can be obtained even if the rolling ratio is not high.

[0058] Here, the rolling ratio means a ratio of a thickness difference of the electrode mixture before and after rolling to a thickness of the electrode mixture before rolling. Therefore, a smaller rolling ratio means a smaller thickness difference before and after dry rolling.

[0059] Various electrode materials contained in the electrode active material slurry, such as active materials, conductive agents, binders, fillers, etc., are known in the art, and all of these are included in the scope of the present invention, and the present invention is not limited to the composition of the electrode active material slurry.

[0060] Meanwhile, the sheet-shaped current collector on which the electrode active material slurry is coated is not particularly limited as long as it is conductive and does not induce chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The sheet-shaped current collector can have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesive strength of the active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0061] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a semiconductor memory device according to an embodiment of the present invention;

[0062] <Example 1> Artificial graphite was used as the active material, SBR (styrene butadiene rubber) as the binder, carbon black as the conductive agent, and CMC (carboxymethyl cellulose) as the additive. The electrode active material slurry was added to water in a weight ratio of 96:0.5:2.5:1, and the solid content was 48 wt%. The loading amount after complete drying was 266 mg / 25 cm. 2 The slurry was coated on a current collector of Cu foil (thickness: 20 μm) so that the solid content reached 90 wt%, and then dried at 100° C. The electrode active material slurry was taken out of the drying furnace at the moment when the solid content reached 90 wt%, and rolled at a linear pressure of 0.8 kgf / cm by a roll press process, and then further dried at 100° C. until the solid content reached about 100 wt%, to prepare an electrode.

[0063] The solids content was measured by the change in weight of the slurry before and after drying.

[0064] <Example 2> An electrode was manufactured in the same manner as in Example 1, except that the solid content of the electrode active material slurry was 80 wt % when the roll pressing process was performed.

[0065] <Comparative Example 1> An electrode was manufactured in the same manner as in Example 1, except that the solid content of the electrode active material slurry was 60 wt % when the roll pressing process was performed.

[0066] <Comparative Example 2> An electrode was produced in the same manner as in Example 1, except that the roll press step was carried out at a linear pressure of 0.2 kgf / cm.

[0067] <Comparative Example 3> An electrode was manufactured in the same manner as in Example 1, except that the roll press process was not performed.

[0068] <Experimental Example 1> The thickness of the electrode mixture of the electrodes manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 was measured by a thickness gauge. Specifically, the thickness was measured using a μ-Hite height gauge manufactured by TESA.

[0069] The thickness of the electrode mixture was determined by subtracting the thickness of the Cu foil as the current collector from the value measured by such a thickness meter, and the results are shown in Table 1 below.

[0070] [Table 1]

[0071] Referring to Table 1, it can be seen that when wet rolling according to the present invention is performed, the thickness of the electrode dried before the dry rolling process is reduced by a certain amount compared to Comparative Example 3 where wet rolling is not performed.

[0072] In contrast, when drying is insufficient, that is, when the solid content is less than 70 wt% (Comparative Example 1), the electrode layer is destroyed during rolling, and when the line pressure of the wetting rolling is excessively weak (Comparative Example 2), there is no rolling effect, which is not preferable.

[0073] According to the present invention, when the solid content of the electrode active material slurry before it is completely dried satisfies certain conditions, in the case where a wetting rolling process is performed in which a load is applied to the undried electrode active material slurry, a structure that is structurally denser can be secured when drying is completed than when rolling is not performed. Thereafter, in the dry rolling process after drying is completed, a target rolling ratio is reduced, and thus the rolling load for rolling the electrode to a target thickness can be reduced, which has the effect of minimizing defects such as cracking, breakage, and waviness of the active material. [Explanation of symbols]

[0074] 100: Electrode manufacturing equipment 101: Sheet-shaped current collector 102: Electrode active material slurry 110: Unwinding machine 120:Transfer section 130: Coating section 140:Drying section 150: Winding machine

Claims

1. A method for producing an electrode for a secondary battery, comprising the steps of: A method for manufacturing an electrode for a secondary battery, comprising: drying an electrode active material slurry coated on a current collector in one or more layers such that the solid content of the undried electrode active material slurry is 80 wt % to 90 wt %; and applying a load to the electrode active material slurry in a drying oven when the solid content of the undried electrode active material slurry is 80 wt % to 90 wt %. The method further comprises performing additional drying after the rolling step.

2. The method for producing an electrode for a secondary battery according to claim 1 , wherein the rolling step is performed by using a press roll that applies a linear pressure onto the undried electrode active material slurry.

3. The method for producing an electrode for a secondary battery according to claim 2 , wherein the rolling step is performed under a linear pressure load of 0.5 kgf / cm to 0.1 ton / cm.

4. 2. The method for producing an electrode for a secondary battery according to claim 1, further comprising the step of drying the electrode active material slurry after the rolling step until the solid content of the electrode active material slurry reaches 99 to 100 wt %.

5. (a) coating one or more layers of an electrode active material slurry on a current collector; (b) drying the electrode active material slurry to a solid content of 80 wt % to 90 wt %; (c) a wetting rolling step of applying a load onto the electrode active material slurry having a solid content of 80 wt % to 90 wt %; (d) additionally drying the electrode active material slurry until the solid content of the electrode active material slurry is 99 to 100 wt % to form an electrode mixture; 2. The method of claim 1, further comprising: (e) a dry rolling step of rolling the electrode mixture after the drying step.

6. An apparatus for manufacturing an electrode for a secondary battery, comprising: a roller-shaped unwinder around which a sheet-shaped current collector is wound; a transfer unit that continuously transfers the sheet-like current collector; a coating unit that applies one or more layers of electrode active material slurry to at least one surface of the sheet-like current collector; a drying section for drying the electrode active material slurry to form an electrode mixture on at least one surface of a sheet-shaped current collector; and a roller-shaped winding machine that winds up the electrode sheet in which the electrode mixture is formed on the sheet-shaped current collector, The drying unit dries the undried electrode active material slurry so that the solid content of the undried electrode active material slurry is 80 wt % to 90 wt %, and includes a wetting rolling unit in a drying oven that applies a load onto the electrode active material slurry when the solid content of the undried electrode active material slurry is 80 wt % to 90 wt %.

7. The apparatus for manufacturing an electrode for a secondary battery according to claim 6 , wherein the coating unit is a coating die, a coating roll, or a slide slot.

8. 7. The secondary battery electrode manufacturing apparatus according to claim 6, wherein the drying section includes one or both of a hot air nozzle for generating hot air in a drying oven and an infrared lamp.

9. 9. The apparatus for manufacturing an electrode for a secondary battery according to claim 8, wherein the hot air nozzles and the infrared lamps are arranged alternately.

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