JP2015046410A - Device of manufacturing battery electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device of manufacturing a battery electrode suitable for achieving a higher capacity of a battery while a mixture crack or the like is hard to occur in the electrode material after a drying process even if the electrode material is thickly coated on a current collector foil of a vehicular battery.SOLUTION: Disclosed is a device of manufacturing a battery electrode P including a drying step in which, after a slurry-like paste obtained by dissolving an electrode material into a solvent is coated on the upper surface of a web-like current collector foil S, the coated paste is dried in a drying oven 10. In the drying step, in a constant drying region (B) where the solvent linearly decreases, a curvature part PW is arranged in which the coated surface side of the current collector foil is curved upward in a feeding direction.

Description

  The present invention relates to a battery electrode manufacturing apparatus mounted on a vehicle, and more particularly to a drying apparatus that applies a paste obtained by dissolving an electrode material in a solvent to form a slurry on a web-shaped current collector foil.

For example, an electrode (positive electrode and negative electrode) of a lithium ion secondary battery is prepared by collecting an active material, which is an electrode material, and a paste obtained by dissolving a binder resin or a thickener in a solvent into a slurry, such as an aluminum foil or a copper foil. It is manufactured by coating on an electric foil and drying. Lithium ion secondary batteries have recently been required to have higher capacities for electric vehicles (EV) and plug-in hybrid vehicles (PHV). In order to increase the capacity, it has been studied to make the battery electrode a thick film electrode (for example, a film thickness of about 80 to 100 μm).
However, if the electrode material is applied thickly on the current collector foil and dried to produce a thick film electrode, thermal shrinkage during drying increases, resulting in cracks in the electrode material after drying. Prone to occur. As an anti-cracking measure, increasing the binder resin has little effect, and if high-speed drying is attempted to reduce the drying furnace equipment cost, thermal shrinkage is accelerated, and defects such as cracking increase further. Product yield decreases.

In general, in the drying period, as shown in FIG. 6, the material preheating period (region (A)) in which the material that has been at room temperature is heated to the temperature in the drying furnace, and the constant rate drying in which the solvent decreases linearly. There is a period (region (B)) and a decreasing rate drying period (region (C)) in which the decrease in the solvent is slow. In particular, in the constant rate drying period, it exists between the active material and the binder resin. Tensile stress tends to remain inside the film due to shrinkage of the coating film caused by rapid evaporation of the solvent. FIGS. 7A to 7C are diagrams schematically illustrating the occurrence of residual tensile stress due to evaporation of the solvent. FIG. 7A is a schematic view showing a state immediately after coating in which a mixture g1 as an electrode material is dissolved in a solvent w1 and applied onto the current collector foil s. The mixture g1 is in the form of particles and is a solvent. Distributed in w1. The material preheating period is in this state.
Thereafter, when heated in a constant rate drying period, as shown in FIG. 7B, the solvent w2 is evaporated from the surface of the coating film t2 to be reduced, and the particulate mixture g2 is close to each other and partially contracted. It becomes.
Furthermore, when the drying progresses and the solvent w2 is evaporated, the process proceeds to a decreasing rate drying period, and the tensile stress f accompanying shrinkage increases between the mixture g3 as shown in FIG. 7C. When this tensile stress f increases inside the coating film, cracks (hereinafter, also referred to as “mixture cracking”) are likely to occur due to gaps between the mixture g3 that is the electrode material. If there is a crack in the mixture, lithium may deposit on the portion during charge / discharge, causing an internal short circuit. Further, when the mixture cracking progresses, the electrode material may peel from the current collector foil s.
For example, Patent Literature 1 and Patent Literature 2 disclose techniques for dealing with such a problem.
Patent Document 1 discloses a technique for improving productivity by controlling a drying process without generating fine cracks on the surface of an electrode when an electrode material is applied on a current collector and dried. ing. The technique of Patent Document 1 reaches the critical moisture content, which is the moisture content of the electrode material when the diffusion rate in the electrode material on almost the entire surface of the electrode material becomes smaller than the evaporation rate of water from the free water surface in the drying process. A first drying step (which corresponds to a “fixed rate drying period”) and a second drying step (which corresponds to a “decreasing rate drying period”) after which the first drying step is performed. The drying process is characterized in that the heat transfer rate is higher than that of the second drying process.

In Patent Document 2, a material slurry obtained by kneading a powder material on a long sheet-shaped current collector is applied and dried to produce wrinkles and cracks in the process of producing a long sheet-shaped electrode plate. A technique for producing a high-quality electrode plate with less occurrence is disclosed. In the technique of Patent Document 2, an arc-shaped nozzle having a structure in which air is blown from the inside to the outside in the latter half when the drying conditions are divided into two or more stages (the “decreasing drying period” corresponds). It is characterized in that it is installed so as to blow air from the coating surface side so that the coating surface is along the arc surface of the nozzle and is in non-contact.

JP 2007-227831 A JP 2010-232123 A

However, since the technique of Patent Document 1 increases the heating rate during the constant rate drying period, the evaporation speed of the solvent is increased, and cracking of the mixture and peeling of the mixture from the current collector foil are more likely to increase. There was a problem.
In the technique of Patent Document 1, when the heat transfer rate in the first drying step is increased, the active material and the binder resin are liberated by thermal convection in the solvent, and migration in which the binder resin is segregated toward the film surface tends to occur. Become. The segregation on the surface of the binder resin film hinders the movement of lithium ions during charging and discharging, and a new problem of battery performance degradation occurs.
In particular, in the case of a thick film electrode, since the binder resin content also increases relatively, the segregated binder resin layer tends to be thick. Therefore, the movement of lithium ions is further hindered, and there is a problem that the demand for increasing the capacity of the battery cannot be achieved.
Moreover, in the technique of patent document 2, since it is a structure which blows air to the coating surface which adjoined from the circular-arc-shaped nozzle which has a structure which blows | winds air from the inside to the outside, a wave etc. arise on the coating-film surface of an electrode material. There is a risk of hindering the smoothing of the film thickness. If the film thickness cannot be smoothed, variations occur in the gap with the separator, which inhibits the uniform movement of lithium ions and lowers the battery performance. Therefore, also in this case, there is a problem that the demand for high capacity by the thick film electrode of the battery cannot be achieved.

  The present invention has been made to solve the above problems, and even when the electrode material is thickly applied to the current collector foil of a vehicle battery, the electrode material after drying is less likely to cause cracking of the mixture, etc. An object of the present invention is to provide a battery electrode manufacturing apparatus suitable for increasing the capacity of the battery.

In order to solve the above problems, the battery electrode manufacturing apparatus of the present invention has the following configuration.
(1) In the battery electrode manufacturing apparatus including a drying step of drying in a drying furnace after applying a paste in which an electrode material is dissolved in a solvent to form a slurry on the upper surface of the web-shaped current collector foil, the drying step Among them, in the constant rate drying region where the solvent decreases linearly, a curved portion where the application surface side of the current collector foil curves upward along the feeding direction is disposed, and the curved portion is disposed at a position where the curved portion is disposed. A barrel-shaped transport roller is provided at a predetermined interval.

Next, the operation and effect of the battery electrode manufacturing apparatus according to the present invention will be described.
(1) In a battery electrode manufacturing apparatus including a drying step of drying in a drying furnace after applying a paste in which an electrode material is dissolved in a solvent to form a slurry on the upper surface of a web-shaped current collector foil, Among them, in the constant rate drying region where the solvent decreases linearly, the application surface side of the current collector foil is provided with a curved portion that curves upward along the feed direction. Even if it is applied thickly, the electrode material after drying is less likely to cause cracking of the mixture and is suitable for increasing the capacity of the battery.

  Specifically, in the drying step, in the constant rate drying region where the solvent decreases linearly, a curved portion where the application surface side of the current collector foil is curved upward along the feeding direction is arranged. By extending the length of the coating in advance along the line, it is possible to cope with the shrinkage of the coating that occurs as the solvent evaporates. In other words, in the constant-rate drying region where the solvent decreases linearly, the film is stretched while curving the coating length in advance, so the tensile stress between the electrode materials generated by the contraction of the coating due to the evaporation of the solvent is reduced. It can be canceled by the compressive stress generated when the curved portion is returned to the flat state after drying. As a result, tensile stress is unlikely to remain in the dried film. Therefore, even if the electrode material is thickly applied to the current collector foil, tensile stress does not easily remain inside the dried film, so that a mixture crack or the like hardly occurs in the dried electrode material. Therefore, a thick film electrode for increasing the capacity of the battery can be produced without causing a mixture crack or the like inside the film.

In addition, because the curved portion is arranged in the constant rate drying region of the drying process, the internal residual tensile stress accumulated during the constant rate drying period during which the solvent between the electrode material mixture evaporates and the film shrinks easily occurs is determined by the constant rate drying period. In the subsequent reduced rate drying period, the curved portion can be made flat and relaxed. Therefore, relaxation of internal residual stress can be realized in one drying chamber.
Moreover, since the application surface side of the current collector foil is curved along the feeding direction, the bending portion can similarly relieve the internal residual tensile stress in any part in the feeding direction.
Moreover, since the application surface side is curved upward in the constant rate drying region, the curved portion effectively passes the heat source disposed above the drying furnace during the constant rate drying period, thereby effectively making the thermal energy in the drying furnace. Can be used.
Furthermore, since the present invention is a method of arranging the curved portion in the constant rate drying region, segregation of the binder resin, which is a new problem in the technique of Patent Document 1, is unlikely to occur, which is a problem in the technique of Patent Document 2. Rippling of film thickness is also difficult to occur. Therefore, the effect that it becomes easier to achieve high capacity by the thick film electrode can be achieved.
Therefore, according to the invention of (1), even when the electrode material is thickly applied to the current collector foil of the vehicle battery, the electrode material after drying is less likely to cause cracking of the mixture, which is suitable for increasing the capacity of the battery. An apparatus for manufacturing a battery electrode can be provided.

In addition, since all or part of the curved portion is curved further upward along the width direction on the application surface side of the current collector foil, the internal residual tensile stress generated in the width direction of the current collector foil can be relaxed.
In general, in coating on a metal foil, which is a current collector constituting an electrode of a lithium ion secondary battery, the width of the coating film is about 150 to 200 mm and slit to a required size after drying. Therefore, contraction of the coating film occurs also in the width direction of the current collector foil. By bending the bending portion further upward along the width direction, the tensile stress in the width direction can be relaxed together with the tensile stress in the feed direction.
In addition, the magnitude | size of the tensile stress of the width direction changes with width dimensions, thickness, etc. of a coating film. Accordingly, the range in which the coating surface side curves upward along the width direction of the current collector foil may be a part in the feeding direction of the curved portion.

  Furthermore, since the drying furnace is provided with barrel-shaped transport rollers at predetermined intervals at the position where the curved portion is formed, even if the electrode material is thickly applied to the current collector foil, the dried electrode material It is possible to provide a drying furnace that is less susceptible to cracking of the mixture and is suitable for increasing the capacity of the battery. The lower surface of the current collector foil is in contact with the transport roller. Therefore, by forming the outer shape of the transport roller into a barrel shape whose center is convexly curved, it is possible to easily form a curved portion corresponding to the contraction of the coating film caused by the evaporation of the solvent. The barrel-shaped curved surface includes an arc curved surface, an elliptic curved surface, a continuous polygon curved surface, and the like.

It is a typical cross-sectional view of the drying furnace in the manufacturing apparatus of the battery electrode which is embodiment which concerns on this invention. It is a typical top view of the conveyance roller used for the fixed rate drying area | region of the drying furnace shown in FIG. 1, (a) shows a wrinkle, (b) shows no wrinkle. It is explanatory drawing of the method of forming the curved part in the fixed rate drying area | region of the drying furnace shown in FIG. 1, (a) shows the curvature when the electrode material is applied to the collector foil cut | disconnected in the rectangular sheet shape, and it dries. , (B) shows when the warp is extended, and (c) shows the dimensional relationship of the curved portion. It is a figure which illustrates typically the dispersion state of the mixture of the electrode material in a curved part, (a) shows the state immediately after coating, (b) shows the state of a fixed rate drying period, (c) is The state after drying is shown. It is the graph which compared the peeling strength of the electrode material at the time of making it dry by embodiment which concerns on this invention, and the conventional method. It is a graph which shows the relationship between a drying period and the content rate of a solvent. It is a figure which illustrates typically the dispersion state of the mixture of electrode material in a conventional method, (a) shows the state immediately after coating, (b) shows the state of a fixed rate drying period, (c) is The state after drying is shown.

Next, an embodiment of a battery electrode manufacturing apparatus according to the present invention will be described in detail with reference to the drawings.
The battery electrode manufacturing apparatus 100 includes a paste in which an active material, which is an electrode material, and a binder resin, a thickener, and the like, which are bound to the upper surface of a web-shaped current collector foil, are dissolved in a solvent to form a slurry. A coating device 20 for coating in a thin film, a drying furnace 10 for drying the current collector foil coated with the electrode material, and a winding device 30 for winding the dried current collector foil into a coil shape. (The coating device 20 and the winding device 30 are not shown).
The coating device 20 and the winding device 30 use the prior art as they are, and a detailed description thereof is omitted. Here, the description will focus on the drying furnace 10 which is a feature of the present invention.

<Basic structure of drying oven>
First, the basic structure of the drying furnace in the battery electrode manufacturing apparatus according to the present invention will be described. In FIG. 1, the typical cross-sectional view of the drying furnace in the manufacturing apparatus of the battery electrode which is embodiment which concerns on this invention is shown. FIG. 2 is a schematic top view of a conveying roller used in the constant rate drying region of the drying furnace shown in FIG. 1, wherein (a) shows wrinkles and (b) shows no wrinkles.
As shown in FIG. 1, in the drying furnace 10 of the present embodiment, a web-like battery electrode P coated with an electrode material passes over conveying rollers 1, 2, and 3 arranged at predetermined intervals. A drying chamber 4 is provided. Above the drying chamber 4, a plurality of air outlets 7 are continuously provided, and hot air is discharged downward from each air outlet 7. The temperature of the hot air is about 80 to 90 ° C. The transport rollers 1, 2, and 3 are driven rollers.
When the coating film applied to the upper surface of the web-like battery electrode P enters the drying chamber 4 from the inlet 5, it is dried by hot air from the blower port 7. The dried battery electrode P is fed out from the outlet 6 and wound around the winding device 30 (not shown) until a predetermined diameter is reached. The feeding speed of the battery electrode P varies depending on the thickness, width, type of solvent, etc. of the coating film, but is, for example, about several hundred cm to several m / sec.

  In the drying chamber 4, the solvent in the coating film evaporates from the surface. In general, the solvent content varies according to the curve M shown in FIG. From the change in the solvent content, the material preheating period (region (A)) in which the material at room temperature is heated to the temperature in the drying furnace 10 and the constant rate drying period ((B) in which the solvent decreases linearly. And a decreasing rate drying period (region (C)) in which the decrease in the solvent is slow. In the material preheating period, the solvent hardly decreases, and in the decreasing rate drying period, the decreasing rate of the solvent is greatly reduced. Therefore, the drying is performed most efficiently during the constant rate drying period, and the shrinkage of the coating film accompanying the decrease in the solvent greatly proceeds.

As shown in FIG. 1, in the constant rate drying region (B) corresponding to the constant rate drying period, a curved portion PW in which the application surface side of the battery electrode P is curved upward along the feeding direction is formed. In order to form the curved portion PW of the battery electrode P in the constant rate drying region (B), the transport roller 2 is arranged at a predetermined interval at a position that supports the lower surface side of the curved portion PW. The conveyance roller 2 is arranged in an arch shape in a side view.
The electrode material applied to the battery electrode P is curved and extended in the feeding direction by the conveying roller 2 arranged in an arch shape in the constant rate drying region (B).
On the other hand, in the reduced rate drying region (C) corresponding to the reduced rate drying period, no curved portion is formed. Therefore, the electrode material curved and extended in the feeding direction in the constant rate drying region (B) is returned to the original flat state in the decreasing rate drying region (C).
Further, in the constant rate drying region (B), the curved portion PW of the battery electrode P passes through a position close to the air blowing port 7 disposed above the drying chamber 4. Therefore, the thermal energy from the blower port 7 can be more effectively given to the curved portion PW.
In addition, the conveyance rollers 1 and 3 that support the lower surface side of the battery electrode P in the material preheating region (A) and the reduction rate drying region (C) are inclined on the extension of the conveyance roller 2 in the constant rate drying region (B). It is arranged linearly downward. Therefore, in the material preheating region (A) and the reduction rate drying region (C), the amount of heat energy supplied from the blower port 7 is reduced as compared with the constant rate drying region (B).

As shown in FIG. 2, the conveyance roller 2 in the constant rate drying region (B) has outer shapes 21 and 23 that are in contact with the lower surface side of the battery electrode P in a barrel shape whose center is curved in a convex shape. The barrel-shaped curved surface corresponds to an arcuate curved surface, an elliptical curved surface, a continuous polygonal curved surface, or the like.
Moreover, the barrel-shaped transport roller 2 may be a roller with a hook having flat surfaces 22 at both ends as shown in FIG. 2A, or may be a roller without a hook as shown in FIG. 2B. Good. In the case of a roller with a flange, the flat surfaces 22 at both ends have a function of regulating the meandering of the battery electrode P. In the present embodiment, a roller with a hook is used.
Since the barrel-shaped transport roller 2 has a curved center, the electrode material applied to the battery electrode P can be curved not only in the feed direction but also in the width direction.
However, the outer shape of the conveying rollers 1 and 3 in the material preheating region (A) and the reduction rate drying region (C) contacting the lower surface side of the battery electrode P is cylindrical. Therefore, the battery electrode P returns to a flat surface in the rate-decreasing drying region (C), and the electrode material curved and extended in the feed direction and the width direction in the constant-rate drying region (B) In C), the original flat state is restored.

<Formation method of curved part>
Next, a forming method for forming the curved portion PW of the battery electrode P in the constant rate drying region (B) will be described. FIG. 3 is an explanatory view of a method of forming a curved portion in the constant rate drying region of the drying furnace shown in FIG. 1, and (a) shows a case where an electrode material is applied to a current collector foil cut into a rectangular sheet and dried. A warp is shown, (b) shows when the warp is extended, and (c) shows a dimensional relationship of the curved portion.
First, a thin paste is prepared by dissolving a mixture G1 in which an active material, which is an electrode material, and a binder resin, a thickener, and the like, are dissolved in a solvent on a current collecting foil S1 cut into a rectangular sheet of about A4 size in a solvent. And then dried. The drying conditions are the same as those of the drying furnace 10 shown in FIG.

As shown to Fig.3 (a), as for the rectangular sheet S1 after drying, a coating film shrink | contracts with evaporation of a solvent, and it curves to the application surface side. The string R2 with respect to the curved surface of the rectangular sheet S1 is measured without constraining the curved state. The string R2 corresponds to the linear distance of the curved portion PW.
Thereafter, as shown in FIG. 3B, the curved rectangular sheet S1 is forcibly flattened, and the linear distance R1 at both ends of the rectangular sheet S1 is measured. The straight line distance R1 corresponds to the circumferential length of the curved portion PW.
Next, the position and linear distance of the constant rate drying region (B) of the drying furnace 10 shown in FIG. 1 are obtained. The position and linear distance of the constant rate drying region (B) can be obtained from a range in which the solvent content rate decreases linearly by measuring the correlation curve M between the solvent content rate and the drying period shown in FIG. As a result, the linear distance L1 of the constant rate drying region (B) shown in FIG.
Finally, the circumference L2 = L1 × R1 / R2 of the bending portion PW is obtained by proportional calculation from the above-described R1, R2, and L1.
As apparent from the above proportional calculation formula, the idea of the curved portion PW of the battery electrode P in the constant rate drying region (B) is that the contraction state of the coating film obtained under the unconstrained condition is proportionally calculated by the proportional calculation. ) Is reproduced in a similar manner.

<Tensile stress relaxation mechanism>
Next, a mechanism for relieving the tensile stress generated in the coating film in the constant rate drying region (B) will be described. FIG. 4 is a diagram schematically explaining the dispersion state of the electrode material mixture in the curved portion, (a) showing the state immediately after coating, (b) showing the state of the constant rate drying period, (C) shows the state after drying.
As shown in FIG. 4 (a), the coating film T1 immediately after being applied to the upper surface of the current collector foil S is mainly composed of an electrode material mixture G1 in which an active material and a binder resin are bound together. Distributed in. The battery electrode P <b> 1 forms a curved portion whose application surface side curves upward along the feeding direction. Accordingly, the coating film T1 is also extended and curved in the feeding direction.
As shown in FIG. 4B, in the constant rate drying region (B), the coating film T2 is heated by the hot air from the blower port 7, and the solvent W2 in the coating film evaporates from the surface and linearly decreases. . At this time, the temperature of the coating film T2 and the current collector foil S is kept constant by the heat of vaporization accompanying the evaporation of the solvent W2. Since the temperature of the coating film T2 does not increase, surface solidification hardly proceeds. Since the temperature of the current collector foil S does not increase, the current collector foil S hardly expands or contracts.

However, as shown in FIG. 4B, since the solvent W2 in the coating film T2 evaporates from the surface and decreases linearly, the coating film T2 contracts by the amount of the decrease in the solvent W2. This shrinkage occurs not only in the thickness direction of the coating film T2 but also in the surface direction (arrow direction). In particular, the shrinkage in the surface direction is increased because it is accumulated in the feeding direction of the battery electrode P2. At this time, since the current collector foil S itself hardly expands or contracts, the electrode material mixture G2 in the coating film T2 or between the electrode material mixture G2 and the current collector foil S has a coating film T2. Tensile stress accompanying shrinkage occurs.
As shown in FIG. 4 (c), in the decreasing rate drying region (C) that passes after the constant rate drying region (B), the curved portion of the battery electrode P3 returns to a flat surface. When the battery electrode P3 returns to the flat surface, the coating film is forcibly shortened in the feed direction. By shortening the coating film, between the mixture G3 inside the coating film and between the mixture G3 and the current collector foil S, the compressive stress in the direction opposite to the tensile stress F generated in the constant rate drying region (B). H is generated. Since this compressive stress H is the compressive stress when the curvature previously obtained under the unconstrained condition is restored, the magnitudes of the compressive stress H and the tensile stress F are substantially equal.
Therefore, the tensile stress generated inside the coating film in the constant rate drying region (B) is offset by the compressive stress generated by returning the curved portion PW to the original flat surface in the decreasing rate drying region (C), and the internal residual The tensile stress is relaxed to a substantially zero state.
Even in the width direction of the current collector foil P, the tensile stress generated in the constant rate drying region (B) is relaxed in the decreasing rate drying region (C) by passing through the barrel-shaped transport roller 2.
As described above, since the tensile stress hardly remains inside the dried coating film, even if the electrode material is applied thickly to the battery electrode P, the electrode material after drying is not easily cracked.
Therefore, a thick film electrode for increasing the capacity of the battery can be produced without causing cracks or the like inside the coating film.

<Evaluation of peel strength>
Next, the result of measuring the peel strength of the electrode material after drying in the drying furnace 10 described above will be described. FIG. 5 shows a graph comparing the peel strength of the electrode material when dried according to an embodiment of the present invention with a drying method of the prior art.
For measurement of peel strength, a peel peel test was employed, and an autograph was used as the tensile tester. The test piece of the present invention was prepared by kneading a mixture of about 10 to 20 μm in average particle diameter with a copper stay having a thickness of about 10 μm at a solvent content of about 45% and applying a coating film having a thickness of about 100 μm for 40 seconds. Made by drying. The drying temperature is about 90 ° C. The test piece of the comparative example was prepared by dividing the drying time into 40 seconds and 90 seconds, which were applied under the same conditions. The drying method is float type drying. The drying temperature is about 90 ° C.
As shown in FIG. 5, the peel strength of the test piece according to the present invention is improved by about 3 to 5 times compared to the comparative example of the prior art. The reason why the peel strength is improved in this manner is that, in the constant rate drying region (B) where the solvent decreases linearly, the length of the coating is increased in advance while curving the coating. It can be estimated that the tensile stress between the electrode materials generated by the shrinkage of the material can be canceled by the compressive stress generated when the curved portion is returned to the flat state after drying.

<Effect>
As described above in detail, according to the battery electrode manufacturing apparatus according to the present embodiment, after the paste in which the electrode material is dissolved in a solvent and applied in the form of a slurry is applied to the upper surface of the web-shaped current collector foil S. In the battery electrode P manufacturing apparatus including a drying process for drying in the drying furnace 10, the application surface side of the current collector foil S is in the constant rate drying region (B) where the solvent decreases linearly in the drying process. Since the curved portion PW that curves upward along the feed direction is arranged, even if the electrode material is applied thickly on the current collector foil S, the electrode material after drying is not easily cracked and the like. Suitable for high capacity.

  Specifically, in the constant rate drying region (B) in which the solvent decreases linearly in the drying step, a curved portion PW in which the application surface side of the current collector foil S is curved upward along the feed direction is disposed. Therefore, by extending the coating film length in advance along the feeding direction, it is possible to cope with the contraction of the coating film caused by the evaporation of the solvent. In other words, in the constant rate drying region (B) where the solvent linearly decreases, the coating length is extended while curving in advance, so that the electrode material generated due to the contraction of the coating due to evaporation of the solvent is between The tensile stress can be canceled by the compressive stress generated when the curved portion PW is returned to a flat state after drying. As a result, tensile stress is unlikely to remain in the dried film. For this reason, even if the electrode material is applied thickly to the current collector foil P, tensile stress does not easily remain in the dried film, so that the electrode material after drying is not easily cracked. Therefore, a thick film electrode for increasing the capacity of the battery can be produced without causing cracks or the like inside the film.

Further, according to the present embodiment, since the curved portion PW is arranged in the constant rate drying region (B) of the drying process, the internal residual tensile stress accumulated during the constant rate drying period is curved in the decreasing rate drying period after the constant rate drying period. The curve of the part PW can be relaxed by returning to the original flatness. Therefore, relaxation of internal residual stress can be realized in one drying chamber 4.
Moreover, since the application surface side of the current collector foil S is curved along the feed direction, the curved portion PW can similarly relieve the internal residual tensile stress at any part in the feed direction.
Further, since the curved portion PW is curved upward on the coating surface side in the constant rate drying region (B), the curved portion PW passes through the vicinity of the heat source disposed above the drying oven 10 during the constant rate drying period. The thermal energy of can be used effectively.
Furthermore, according to the present embodiment, since the curved portion PW is disposed in the constant rate drying region (B), segregation of the binder resin, which is a new problem in the technique of Patent Document 1, is difficult to occur. The film thickness undulation that was a problem with this technology is also unlikely to occur. Therefore, the effect that it becomes easier to achieve high capacity by the thick film electrode can be achieved.

In addition, according to the present embodiment, all or part of the curved portion PW is characterized in that the application surface side of the current collector foil S is further curved upward along the width direction. Internal residual tensile stress generated in the direction can also be relaxed.
In general, in coating on a metal foil, which is a current collector constituting an electrode of a lithium ion secondary battery, the width of the coating film is about 150 to 200 mm and slit to a required size after drying. Therefore, the contraction of the coating film also occurs in the width direction of the current collector foil S. By bending the bending portion PW further upward along the width direction, the tensile stress in the width direction can be relaxed together with the tensile stress in the feed direction.
In addition, the magnitude | size of the tensile stress of the width direction changes with width dimensions, thickness, etc. of a coating film. Therefore, the range in which the coating surface side curves upward along the width direction of the current collector foil S may be a part in the feeding direction of the curved portion PW.

  Moreover, according to this embodiment, since the drying furnace 10 is provided with the barrel-shaped transport roller 2 at a predetermined interval at a position where the curved portion PW is formed, the electrode foil is made thick on the current collector foil S. Even if it is applied, the electrode material after drying is unlikely to crack, and the drying furnace 10 suitable for increasing the capacity of the battery can be obtained. The lower surface of the current collector foil S abuts on the transport roller 2. Therefore, by forming the outer shape of the transport roller 2 into a barrel shape with the center curved in a convex shape, the curved portion PW corresponding to the contraction of the coating film caused by the evaporation of the solvent can be easily formed.

<Modification>
A modification to the above-described embodiment will be described.
In the present embodiment, the curved portion PW of the battery electrode P is disposed in the constant rate drying region (B), but may be disposed in the material preheating drying region (A) and the constant rate drying region (B). This is because the range of the curved portion PW can be expanded, so that the compressive stress when returning to the flatness in the reduction rate drying region (C) increases, and the stress relaxation can be performed more effectively.
In the present embodiment, the conveying roller 2 is arranged in an arch shape to form the curved portion PW of the battery electrode P. However, the conveying roller 2 is not limited to the conveying roller but may be a conveying belt. Moreover, the combination may be sufficient. This is because the curved surface of the curved portion PW can be a gently curved surface if it is a conveyor belt. Further, if the curved surface is gentle, it is easy to maintain a state where the mixture G of the electrode material is uniformly dispersed.

  The present invention can be used as an electrode manufacturing apparatus suitable for a lithium ion secondary battery used in, for example, an electric vehicle or a hybrid vehicle.

DESCRIPTION OF SYMBOLS 1 Cylindrical conveyance roller of material preheating drying area 2 Barrel-shaped conveyance roller of fixed rate drying area 3 Cylindrical conveyance roller of reduction rate drying area 4 Drying chamber 5 Inlet 6 Outlet 7 Blowing port 10 Drying furnace 20 Coating device 30 Winding device DESCRIPTION OF SYMBOLS 100 Battery electrode manufacturing apparatus P Battery electrode PW Curved part S Current collector foil

Claims (1)

In a battery electrode manufacturing apparatus comprising a drying step of drying in a drying furnace after applying a paste in which an electrode material is dissolved in a solvent to form a slurry on the upper surface of a web-shaped current collector foil,
In the drying step, in the constant rate drying region where the solvent linearly decreases, a curved portion in which the application surface side of the current collector foil curves upward along the feeding direction is disposed,
An apparatus for manufacturing a battery electrode, comprising a barrel-shaped transport roller at a predetermined interval at a position where the curved portion is disposed.

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