JP2013139889A - Electrode drying method and electrode drying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode drying method and an electrode drying device by which desirable drying conditions can be set while continuous drying state of an electrode layer are recognized.SOLUTION: An electrode drying method, for drying an electrode layer 40 formed by applying electrode slurry 20 containing a solvent 21 to current collecting foil 30 in a drying furnace 50, includes: setting drying reference values A1, A2 defined by a locus of an evaporation volume of the solvent 21 from the electrode layer 40 relative to time in advance; detecting drying factors including a temperature in the drying furnace 50, a wind speed, and a solvent concentration, and calculating a solvent evaporation volume M based on the drying factors; and drying the electrode layer 40 while controlling a heating part 80 for heating the inside of the drying furnace 50 and an air blowing part 70 for blowing air to the inside of the drying furnace 50 such that the solvent evaporation volume M follows the drying reference values A1, A2.

Description

  The present invention relates to an electrode drying method and an electrode drying method.

  Lithium ion secondary batteries are widely used as power sources for automobiles and home appliances because they have a high storage density and maintain good storage performance even after repeated charging and discharging.

  In the process of forming an electrode of a lithium ion secondary battery, first, an electrode layer is formed by applying a certain weight of a slurry slurry containing a solvent on an electrode foil such as a positive electrode aluminum foil or a negative electrode copper foil. To do. Next, in the drying furnace, the solvent contained in the electrode layer is evaporated and dried to fix the solid content of the electrode layer and the electrode foil. In the electrode drying step, a method of blowing hot air to the electrode layer on the electrode foil in a drying furnace is common (see, for example, Patent Document 1).

JP 2006-107780 A

  If the evaporation rate of the solvent in the electrode drying step is too high, the binder contained in the electrode slurry is remarkably moved along with the movement of the solvent in the electrode layer, and the binder is unevenly distributed in the upper layer of the electrode layer. When such binder segregation occurs, the amount of binder between the solid content of the electrode layer and the electrode foil decreases, so that the adhesion strength decreases, the resistance value in the battery increases, and the electrode performance decreases. become.

  In addition, if the evaporation rate of the solvent in the electrode drying process is slow, the adhesion strength increases, but the material may be unevenly distributed in the electrode slurry, and as a result, the resistance value in the battery increases and the electrode performance is reduced. It will cause a decline.

  Therefore, it is desirable to maintain the solvent evaporation rate appropriately, but it is not easy to maintain the desired evaporation rate because the solvent evaporates and thus the amount of solvent in the electrode layer changes. For this reason, in Patent Document 1, for example, the electrode drying process is divided into a plurality of regions depending on the degree of drying, and the drying conditions (temperature, wind speed) in each region are changed, so that drying is performed according to the degree of drying of the electrode layer. The condition has been changed.

  However, since the method described in Patent Document 1 cannot measure the evaporation rate of the solvent, the drying conditions are initially set based on experience and trial and error, and the set conditions are fixed. Therefore, it only defines the reaching point of the dry state at the end of the electrode drying process in each region, and does not grasp the continuous dry state that affects the quality.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an electrode drying method and an electrode drying apparatus capable of setting desirable drying conditions while grasping the continuous drying state of the electrode layer. To do.

  The electrode drying method according to the present invention is an electrode drying method in which an electrode layer formed by applying an electrode slurry containing a solvent to a current collector is dried in a drying furnace. In the electrode drying method, a drying reference value defined by a trajectory of the evaporation amount of the solvent from the electrode layer with respect to time is set in advance, and a drying factor including a temperature, a wind speed, and a solvent concentration in the drying furnace is detected. The amount of evaporation of the solvent is calculated based on the drying factor. And the said electrode layer is dried, controlling the heating part which heats the inside of a drying furnace, and the ventilation part which ventilates in a drying furnace so that the evaporation amount of the said solvent follows a dry reference value.

  According to the electrode drying method of the present invention, the heating part and the air blowing part are controlled so that the evaporation amount of the solvent calculated based on the drying factor follows the drying reference value. This makes it possible to set desirable drying conditions.

It is a schematic block diagram which shows the electrode drying apparatus which concerns on embodiment. It is a schematic diagram which shows the state which has dried the electrode layer with the drying system of embodiment. It is a schematic block diagram which shows one of the drying zones provided in the electrode drying apparatus which concerns on embodiment. FIG. 4 is a schematic cross-sectional view taken along line 4-4 of FIG. It is a graph which shows the amount of solvent evaporation with respect to drying furnace passage time. It is a graph which shows the amount of solvent evaporation with respect to the drying furnace passage time after changing drying conditions. It is a schematic sectional drawing which shows when the solvent evaporated with the air discharged from the nozzle for collection is guide | induced to a collection pipe, (A) shows the case where a laminar flow is produced, (B) shows the case where a vortex is produced. It is a schematic block diagram which shows one of the drying zones at the time of operating an additional heating part. It is a schematic sectional drawing which shows the other example of a solvent concentration detection part. It is a schematic block diagram which shows the other example of an additional heating part. It is a schematic block diagram which shows the further another example of an additional heating part.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The dimensional ratios in the drawings are exaggerated for convenience of explanation, and are different from the actual ratios.

  As shown in FIGS. 1 to 3, the electrode drying apparatus 10 uses an electrode layer 40 formed by applying an electrode slurry 20 containing a solvent 21 to an electrode foil 30 (corresponding to a current collector) in a drying furnace 50. It is a device for drying inside. The electrode drying apparatus 10 includes a transport unit 60 that transports the electrode foil 30 on which the electrode layer 40 is formed in a drying furnace 50, a heating unit 80 that applies heat to dry the electrode layer 40, and heated air. It has the ventilation part 70 which ventilates in the drying furnace 50, and the additional heating part 90 different from the heating part 80. Furthermore, the electrode drying apparatus 10 includes a plurality of measuring means, an electrode temperature detection unit 100 that measures the temperature of the electrode layer 40, a wind speed detection unit 110 that measures the wind speed in the drying furnace 50, It has a furnace temperature detector 120 that measures the ambient temperature, and a solvent concentration detector 130 that measures the concentration of the evaporated solvent. In the electrode drying apparatus 10, each part of the electrode drying apparatus 10 is comprehensively controlled by the control unit 160. Details will be described below.

  The electrode foil 30 is used as a current collector. The electrode foil 30 can be made of an appropriate material such as aluminum, copper, nickel, iron, and stainless steel. Specifically, for example, an electrode foil 30 such as aluminum can be used for the positive electrode current collector, and an electrode foil 30 such as copper can be used for the negative electrode current collector. Although there is no restriction | limiting in particular about the specific thickness of the electrode foil 30, For example, in the case of aluminum, it is a thin film of about 20 micrometers, and in the case of copper, it is about 10 micrometers.

  The electrode slurry 20 includes a positive electrode slurry used for forming a positive electrode and a negative electrode slurry used for forming a negative electrode.

  The positive electrode slurry has, for example, a positive electrode active material 22, a conductive auxiliary agent 24, and a binder 23, and has a predetermined viscosity by adding a solvent 21. The positive electrode active material 22 is, for example, lithium manganate. The conductive auxiliary agent 24 is, for example, acetylene black. The binder 23 is, for example, PVDF (polyvinylidene fluoride). The solvent 21 is, for example, NMP (normal methyl pyrrolidone). The positive electrode active material 22 is not particularly limited to lithium manganate, but it is preferable to apply a lithium-transition metal composite oxide from the viewpoint of capacity and output characteristics. For example, carbon black or graphite can be used as the conductive assistant 24. The binder 23 and the solvent 21 are not limited to PVDF and NMP. Water can also be used as the solvent 21.

The negative electrode slurry has, for example, a negative electrode active material 22, a conductive auxiliary agent 24, and a binder 23, and has a predetermined viscosity by adding the solvent 21. The negative electrode active material 22 is, for example, graphite. The conductive auxiliary agent 24, the binder 23, and the solvent 21 are, for example, acetylene black, PVDF, and NMP. The negative electrode active material 22 is not particularly limited to graphite, and hard carbon or a lithium-transition metal composite oxide can also be used. For example, carbon black or graphite can be used as the conductive assistant 24. The binder 23 and the solvent 21 are not limited to PVDF and NMP.
Water can also be used as the solvent 21.

  The positive electrode layer 40 formed by applying the positive electrode slurry to the electrode foil 30 and the negative electrode layer 40 formed by applying the negative electrode slurry are dried in a drying furnace 50 to form the positive electrode and the negative electrode. At this time, NMP as the solvent 21 contained in the electrode slurry 20 is removed from the electrode slurry 20 by evaporating.

  The drying furnace 50 of the electrode drying apparatus 10 includes a casing 140 that forms a hot air passage and a conveyance path for the electrode foil 30. The inside of the drying furnace 50 is composed of drying zones 51 to 56 divided into a plurality (six in the illustrated example). For convenience of explanation, the first drying zone 51, the second drying zone 52, in order from the upstream side in the direction in which the electrode foil 30 is transported (hereinafter sometimes referred to as the transport direction) (in order from the left side in FIG. 1), The third drying zone 53, the fourth drying zone 54, the fifth drying zone 55, and the sixth drying zone 56 are referred to. By providing the partition wall 141 in the casing 140, the first to sixth drying zones 51 to 56 are formed. In order to arrange the transport unit 60, an opening is provided in the end surface of the casing 140 and the partition wall 141. In each of the first to sixth drying zones 51 to 56, hot air is supplied from an upper nozzle 142 for supplying hot air from an upper position of the conveyed electrode foil 30 and from a lower position of the conveyed electrode foil 30. A lower nozzle 143 for exhausting air and an exhaust port 144 for exhausting air from the inside of the drying zones 51 to 56 through the exhaust pipe 190 are provided.

  And the heating part 80, the ventilation part 70, and the additional heating part 90 are provided for each of the drying zones 51-56. Further, an electrode temperature detection unit 100, a wind speed detection unit 110, a furnace temperature detection unit 120, and a solvent concentration detection unit 130 are provided for each of the drying zones 51 to 56.

  A hot air supply pipe 150 is connected to the upper nozzle 142 and the lower nozzle 143, and a heating unit 80 and a blower unit 70 are connected to the hot air supply pipe 150. The heating unit and the air blowing unit 70 are connected to the control unit 160 and can arbitrarily control the heating temperature and the air flow rate. An intake pipe 170 that takes in air from the outside and a circulation pipe 180 for reusing the air in the drying zones 51 to 56 are connected to the blower unit 70, and a valve 181 provided in the circulation pipe 180 opens and closes. As a result, the air discharged from the circulation pipe 180 can be mixed with the air from the intake pipe 170 at an arbitrary ratio and reused. By reusing the exhaust, mass production at low cost becomes possible.

  The air blowing unit 70 has a fan 71 for air blowing. The heating unit 80 is a heat exchanger, and heats the air by exchanging heat with a heat medium (for example, steam or steam reflux water). The heating unit 80 may not be a heat exchanger as long as air can be heated. The temperature of the hot air is not particularly limited because it varies depending on the environmental temperature, the type of the electrode slurry 20, and the like, but is 100 ± 40 ° C., for example.

  The additional heating unit 90 includes an irradiation unit 91 that irradiates the electrode layer 40 with infrared rays from a position above the conveyed electrode foil 30 and a shutter 92 that can cover the irradiation unit 91. The shutter 92 can be opened and closed by a driving source such as a motor. When the shutter 92 is closed, the infrared rays from the irradiation unit 91 are not irradiated to the electrode layer 40 and are opened, so that the width direction perpendicular to the transport direction is obtained. The slits 93 are formed at regular intervals extending in the depth direction of the paper in FIGS. 1 and 3 (hereinafter also referred to as the width direction) (see FIG. 8). The infrared rays irradiated through the slit 93 heat the electrode layer 40. At this time, the irradiation rate is uniform in the extending direction (width direction) of the slit 93, and the center in the gap direction (conveying direction) of the slit 93. Irradiation rate decreases in both directions with the part at the top.

  The solvent concentration detection unit 130 includes a collection tube 131 (exhaust path) for collecting the evaporated solvent, a collection nozzle 132 that forms a flow toward the collection tube 131 in the drying furnace 50, and a collection. And a solvent concentration meter 134 provided in the tube 131. The collection tube 131 and the collection nozzle 132 are arranged to face each other in the width direction so as to sandwich the electrode layer 40 therebetween. The collection nozzle 132 is connected to a hot air supply pipe 150 having a valve 151 so that heated air can be discharged, and a flow of air along the upper surface of the electrode layer 40 is formed to the collection pipe 131. Introduce air. The collection pipe 131 guides the collected air to the exhaust pipe 190. The solvent concentration meter 134 detects the concentration of the solvent contained in the collected air and transmits the detected signal to the control unit 160.

  The electrode temperature detection unit 100 is, for example, a radiation thermometer, detects the temperature of the electrode layer 40 from a separated position, and transmits the detected signal to the control unit 160.

  The wind speed detection unit 110 detects the wind speed in the drying furnace and transmits the detected signal to the control unit 160.

  The furnace temperature detection unit 120 is, for example, a thermocouple, a resistance thermometer, or the like, detects the atmospheric temperature in the drying furnace 50, and transmits the detected signal to the control unit 160.

  The transport unit 60 includes a supply roll 61 that supplies the electrode foil 30 before the electrode slurry 20 is applied, a winding roll 62 that winds up the electrode foil 30 after the electrode layer 40 is dried, a supply roll 61 and a winding roll. A plurality of support rolls 63 that are arranged between the take-up roll 62 and hold the lower surface of the electrode foil 30. The electrode foil 30 is wound around the supply roll 61 in advance. A motor M that rotationally drives the winding roll 62 is connected to the winding roll 62. When the motor M is driven and the take-up roll 62 is rotationally driven, the electrode foil 30 is unwound from the supply roll 61, conveyed in the drying furnace 50, and taken up by the take-up roll 62. Thus, the conveyance part 60 conveys the elongate electrode foil 30 continuously by a roll-to-roll system.

  Application | coating of the electrode slurry 20 is performed by the application part 145, conveying the electrode foil 30. FIG. The application unit 145 includes a coater 146 that applies the slurry-like electrode slurry 20 containing the solvent 21 to the electrode foil 30. The coater 146 faces the electrode foil 30 and intermittently applies the electrode slurry 20 while conveying the electrode foil 30. Thereby, the electrode slurry 20 is intermittently arranged with a gap of a constant interval. In the intermittent coating method using the coater 146, the electrode slurry 20 is uniformly coated with a film thickness of about 30 to 300 μm on a current collector foil supplied by a roll-to-roll method, and continuous production is performed.

  The control unit 160 is composed mainly of a CPU and a memory, and a program for controlling the operation is stored in the memory. The control unit 160 controls the operation of the application unit 145 to adjust the application amount and application thickness of the electrode slurry 20, and controls the operation of the heating unit 80 and the air blowing unit 70 for each of the drying zones 51 to 56. Then, adjust the temperature of the supply air, the air volume, etc. The controller 160 also controls the operation of the motor M to adjust the conveyance speed of the electrode foil 30.

  Furthermore, the control unit 160 calculates the solvent evaporation amount M from signals transmitted from the solvent concentration detection unit 130, the furnace temperature detection unit 120, the wind speed detection unit 110, and the electrode temperature detection unit 100. That is, since the solvent evaporation amount M in the furnace is determined by the conditions of the solvent concentration in the atmosphere, the furnace temperature, the wind speed in the furnace, and the temperature of the electrode layer 40, it is based on the measured values of these drying factors. The solvent evaporation amount M, which is the total amount of the solvent 21 evaporated from the electrode layer 40, is calculated. The solvent evaporation amount M increases as the solvent concentration in the atmosphere is lower, the furnace temperature is higher, the furnace wind speed is higher, and the temperature of the electrode layer 40 is higher. The solvent evaporation amount M based on these drying factors can be determined experimentally.

  Further, as shown in FIG. 5, the control unit 160 stores in advance a drying reference value A <b> 1 defined by a locus of the solvent evaporation amount with respect to time. Then, the control unit 160 automatically adjusts the heating unit 80, the additional heating unit 90, and the air blowing unit 70 so that the solvent evaporation amount M calculated from the measured drying factor is always within the range of the drying reference value A1. To do. The solvent evaporation amount M increases as the heating amount by the heating unit 80 and the additional heating unit 90 is increased and the blowing amount by the blowing unit 70 is increased.

  In the present embodiment, the drying reference value A1 is defined as a band-shaped range having a width as shown in FIG. 5, but is defined and calculated by a line having no width. The solvent evaporation amount M may be controlled so as to follow the line as much as possible. The drying reference value A1 is determined by experiments or the like.

  A plurality (two in this embodiment) of reference drying values are provided according to the time required for drying. FIG. 6 shows a drying reference value A2 when drying is performed over a longer time than the drying reference value A1 shown in FIG.

  Before describing the operation of the present embodiment, a problem that occurs when the temperature and air volume of the supply air supplied to the drying furnace 50 are not appropriate will be described.

  When the drying rate is improved in the drying furnace 50 using hot air, the hot air temperature is increased and the air volume is increased, and the amount of solvent 21 (NMP) removed at the interface portion between the surface of the electrode layer 40 and the atmosphere 57 is increased. Increase. In such a case, drying is accelerated and the binder 23 (PVDF) is segregated near the surface of the electrode layer 40. For this reason, it becomes impossible to obtain a coating film strongly adhered to the electrode foil 30, that is, a strongly adhered electrode layer 40.

  The following can be cited as causes of segregation of the binder 23 when the hot air temperature is increased. That is, since the electrode layer 40 contains the binder 23 dissolved in the solvent 21 at the time of drying, the solvent 21 itself convects in the electrode layer 40 when the electrode layer 40 is exposed to a high temperature environment. Wake up. As a result, the dissolved binder 23 is segregated.

  Moreover, the following can be mentioned as a cause of the segregation of the binder 23 when the air volume is increased. That is, only the solvent 21 (NMP) in the vicinity of the surface of the electrode layer 40 is preferentially evaporated and only the vicinity of the surface is dried first (surface pre-drying), and the capillary phenomenon due to cracks or holes generated in the surface pre-drying portion. The NMP is sucked from the depth toward the surface. As a result, the dissolved binder 23 is segregated.

  Under drying conditions that can cause segregation of the binder 23 at the time of drying, the surface roughness is large and the adhesion is weak, so the contact amount or contact area between the electrode foil 30 and the electrode layer 40 is reduced. For this reason, not only the resistance value in the battery in the initial stage, but also the resistance value in the battery after repeated charge / discharge increases, leading to a decrease in electrode performance.

  In order to eliminate the segregation of the generated binder 23, there is a method in which the dried electrode is compressed by a roll press or the like. However, since the structure is forcibly changed after the drying is completed and the electrode layer 40 is fixed, the adhesion strength of the electrode layer 40 is not improved so much. Moreover, it is desirable to avoid adding a compression step after the drying step from the viewpoint of realizing mass production at a low cost.

  Next, the operation of this embodiment will be described.

  The motor M is driven to rotationally drive the take-up roll 62, and the electrode foil 30 is unwound from the supply roll 61 and taken up on the take-up roll 62. The coater 146 applies the electrode slurry 20 intermittently to the surface of the moving electrode foil 30. The control unit 160 controls the operation of the application unit 145 and adjusts the application amount and application thickness of the electrode slurry 20. The heating unit 80 and the air blowing unit 70 supply hot air from the upper and lower nozzles 142 and 143 into the hot air passage. After applying the electrode slurry 20 containing the solvent 21 to the surface of the electrode foil 30, the electrode layer 40 is sequentially transported to the first drying zone 51 to the sixth drying zone 56, and dried in each of the drying zones 51 to 56. In the furnace 50, the solvent 21 contained in the electrode layer 40 is evaporated.

  Further, in each drying furnace 50, heated air supplied from the hot air supply pipe 150 is discharged from the collection nozzle 132 to form a flow of air along the upper surface of the electrode layer 40, thereby capturing the air. Air is introduced into the collecting tube 131. The air flow can be, for example, a laminar flow along the electrode layer 40 as shown in FIG. 7A, or a vortex having straightness as shown in FIG. 7B. The collection pipe 131 guides the collected air to the solvent concentration meter 134 and then discharges it to the exhaust pipe 190. Thus, by providing the collection nozzle 132 and the collection tube 131, the solvent evaporated from the electrode layer 40 can be collected effectively, and the vicinity of the electrode layer 40 that affects the evaporation of the solvent 21 can be collected. The solvent concentration can be accurately measured by the solvent concentration meter 134.

  In each of the drying zones 51 to 56, the solvent concentration detector 130, the furnace temperature detector 120, the wind speed detector 110, and the electrode temperature detector 100 allow the solvent concentration in the atmosphere, the furnace temperature, and the wind speed in the furnace. , And the temperature of the electrode layer 40 are sequentially detected, and the detected signal is transmitted to the controller 160. The controller 160 sequentially calculates the solvent evaporation amount M from the electrode layer 40 that is being transported from the received signal. Thus, since the solvent evaporation amount M in the drying furnace 50 is determined by the conditions of the solvent concentration in the atmosphere, the furnace temperature, the wind speed in the furnace, and the temperature of the electrode layer 40, these drying factors are measured. Thus, the solvent evaporation amount M evaporated from the electrode layer 40 can be calculated. Note that the furnace temperature and the temperature of the electrode layer 40 can be approximated to be substantially the same, and only one of them can be measured and used to calculate the solvent evaporation amount M.

  Then, the control unit 160 controls the heating unit 80 and the air blowing unit 70 so that the solvent evaporation amount M calculated from the measured drying factor is always within the range of the preset drying reference value A1. Adjust automatically.

  The calculated solvent evaporation amount M is set in advance in the drying furnace 50 of each of the drying zones 51 to 56 while sequentially transporting the electrode layer 40 to the first drying zone 51 to the sixth drying zone 56. The solvent 21 contained in the electrode layer 40 is evaporated so that it always falls within the range of the dry reference value A1. Thus, by constantly monitoring the solvent concentration in the atmosphere, which is a drying factor, the furnace temperature, the wind speed in the furnace, and the temperature of the electrode layer 40, and adjusting the solvent evaporation amount M within the drying reference value A1, The desired solvent evaporation amount M can be maintained so as to follow the drying reference value A1 that changes with the passage of time. For this reason, an electrode having high peel strength and high performance can be produced stably.

  When the time required for the drying process needs to be changed, the drying reference value A1 is switched to another drying reference value A2 shown in FIG.

  The electrode manufacturing process includes a step of dispersing the solid content of the electrode slurry 20 in the solvent 21, a step of applying the electrode slurry 20 to the electrode foil, a step of drying the electrode slurry 20, a step of pressing the dried electrode layer 40, and A step of cutting the electrode into a predetermined shape is included, and a high production rate of the electrode is exhibited by performing these steps continuously. However, each process has an individual production speed, and waiting time, cleaning time, etc. accompanying the delivery of materials and products occur between the processes. However, since the electrode drying apparatus 10 takes time to start again once it is stopped, it is desirable that the electrode drying apparatus 10 has the ability to absorb the increase and decrease in production time without stopping. By providing a plurality of drying reference values A1 and A2 having different drying times, the drying time can be freely changed, and the increase or decrease in production time between the previous and subsequent steps can be absorbed.

  Therefore, for example, when replacing the container of the electrode slurry 20 that is supplied in a constant amount in a container, the electrode drying apparatus 10 is switched to the drying reference value A2 without stopping the electrode drying apparatus 10, and the time taken for the electrode drying process is changed. And you can earn time to change containers.

  When switching to the drying reference value A2, the control unit 160 controls the motor M to change the conveyance speed.

  Then, the control unit 160 controls the heating unit 80 and the air blowing unit 70 so that the solvent evaporation amount M calculated from the measured drying factor is always within the range of the preset drying reference value A2. Adjust automatically. And the solvent evaporation amount M calculated in the drying furnace 50 of each drying zone 51-56 is changed, conveying the electrode layer 40 to the 1st drying zone 51-the 6th drying zone 56 sequentially. The solvent 21 contained in the electrode layer 40 is evaporated so as to be always within the range of the dry reference value A2.

  And when it becomes necessary to raise the furnace temperature in any one of the drying zones 51 to 56 with the switching to the drying reference value A2, the heating by the heating unit 80 raises the temperature inside the drying furnace 50. Therefore, the additional heating unit 90 is also activated while increasing the amount of heating by the heating unit 80. The additional heating unit 90 can heat the electrode layer 40 at the same time as opening the shutter 92 as shown in FIG. 8 by operating the irradiation unit 91 with the shutter 92 closed. When the shutter 92 is opened, infrared rays are emitted from the slit 93. At this time, since the irradiation rate is uniform in the extending direction (width direction) of the slit 93, the electrode layer 40 is uniformly heated in the width direction. be able to. Moreover, since the irradiation rate of the infrared rays irradiated from the slit 93 decreases in both directions (upstream and downstream directions of the transport direction) with the central portion at the apex in the gap direction (transport direction) of the slit 93, When the moving electrode layer 40 enters the infrared irradiation range, it is not heated rapidly and the solvent can be kept dry well. Thereafter, as the temperature in the drying furnace 50 rises as a whole due to heating by the heating unit 80, the amount of heating by the additional heating unit 90 is reduced and finally the additional heating unit 90 is stopped.

  In this way, by constantly monitoring the solvent concentration in the atmosphere, which is a drying factor, the temperature in the furnace, the wind speed in the furnace, and the temperature of the electrode layer 40, and adjusting the solvent evaporation amount M within the drying reference value A2, Even if the drying time is changed, a desirable solvent evaporation amount M can be maintained so as to follow the drying reference value A2. For this reason, since a desirable dry state can always be maintained, it can prevent that the segregation of the binder 23 arises. Since the electrode layer 40 is dried under conditions that do not cause segregation of the binder 23, the adhesion between the electrode foil 30 and the electrode layer 40 is improved, and the contact amount or contact area between the electrode foil 30 and the electrode layer 40 is increased. Become big enough. For this reason, not only the resistance value in the battery in the initial stage, but also the resistance value in the battery after repeated charging and discharging is reduced, and the electrode performance can be improved.

  When the replacement of the electrode slurry 20 container is completed, the electrode is dried by returning to the original drying reference value A1 having a short drying time (high drying speed). Also in this case, when it becomes necessary to raise the furnace temperature in any of the drying zones 51 to 56, the heating amount by the heating unit 80 is increased and the additional heating unit 90 is operated. Then, as the temperature in the drying furnace 50 rises as a whole due to heating by the heating unit 80, the amount of heating by the additional heating unit 90 is reduced and finally the additional heating unit 90 is stopped.

<Experimental example>
Using a drying furnace having a length X (m) in the conveying direction in the furnace, a drying experiment was performed at a conveying speed of 0.5 X (m / min). The inside of the drying furnace was divided into a plurality of drying zones, and the temperature and wind speed could be set individually for each drying zone. Each drying zone is equipped with a solvent concentration detector, furnace temperature detector, wind speed detector, and electrode temperature detector to monitor the solvent concentration, furnace temperature, furnace wind speed, and electrode layer temperature in the atmosphere. And recorded. Then, the amount of solvent evaporation was calculated based on the measured drying factor, and the time course of the solvent evaporation amount was obtained. At this time, the equipment conditions were changed so as to change the drying factor, and as shown in Experimental Examples 1 to 5 in Table 1, a plurality of time courses of solvent evaporation were obtained. And the electrode was produced on the conditions of Experimental Examples 1-5, and the resistance value in a battery after repeating peeling strength and charging / discharging 100 times was evaluated. The results are shown in Table 1.

  As a result, in Experimental Example 1 and Experimental Example 5, the peel strength was low and the resistance value was high, and the quality as a battery was not satisfied. On the other hand, Experimental Example 2 to Experimental Example 4 had high peel strength and low resistance, satisfying the quality as a battery. As described above, it was possible to obtain a plurality of solvent evaporation trajectories in which the produced battery exhibited good performance. Therefore, it is possible to set a drying reference value for establishing the quality of the battery within the range of the conditions of Experimental Example 2 to Experimental Example 4.

  Next, using the same drying furnace, a drying experiment was performed at a conveyance speed of 0.25 × (m / min), which is half of the previous experiment. The drying conditions were the same as in the previous experiment except for the conveyance speed. And the temperature and wind speed were controlled for every drying zone so that the amount of solvent evaporation in each drying zone might become the same as that of Experimental Examples 1-5, and the result of Experimental Examples 6-10 was obtained. That is, in Experimental Examples 6 to 10, the electrodes were produced using the trajectory of the solvent evaporation amount obtained from Experimental Examples 1 to 5 as the drying reference value. The results are shown in Table 2.

  As a result, in Experimental Example 6 and Experimental Example 10 corresponding to Experimental Example 1 and Experimental Example 5, the peel strength was low and the resistance value was high, and the quality as a battery was not satisfied. On the other hand, Experimental Example 7 to Experimental Example 9 corresponding to Experimental Example 2 to Experimental Example 4 had high peel strength and low resistance value, satisfying the quality as a battery. Thus, it was confirmed that a preferable electrode can be obtained by using a drying reference value that establishes quality even if the transport speed changes and the time for passing through each drying zone in the furnace changes.

  As described above, according to the present embodiment, the drying reference values A1 and A2 defined by the trajectory of the evaporation amount of the solvent 21 from the electrode layer 40 with respect to time are set in advance, and the temperature and wind speed in the drying furnace 50 are set. Then, a drying factor including the solvent concentration is detected, and the solvent evaporation amount M is calculated based on the drying factor. Then, the electrode layer 40 is dried while controlling the heating unit 80 and the air blowing unit 70 so that the solvent evaporation amount M follows the drying reference values A1 and A2. Therefore, desirable drying conditions can be set while grasping the continuous drying state of the electrode layer 40. For this reason, since the electrode layer 40 is dried under desirable drying conditions that are continuously provided, segregation of the binder 23 can be prevented. Since the electrode layer 40 is dried under conditions that do not cause segregation of the binder 23, the adhesion between the electrode foil 30 and the electrode layer 40 is improved, and charge / discharge is performed as well as the resistance value in the battery in the initial stage. The resistance value in the battery after the repetition is reduced, and the electrode performance can be improved.

  When the drying time for holding the electrode layer 40 in the drying furnace 50 is changed, the solvent evaporation amount M calculated based on the drying factor is a predetermined drying reference value A1, A2 corresponding to the changed drying time. The heating unit 80 and the air blowing unit 70 are controlled so as to follow the above. Therefore, it is possible to freely change the drying time, and it is possible to absorb the increase or decrease in production time between the previous and subsequent processes.

  When the drying time for holding the electrode layer 40 in the drying furnace 50 is changed, the electrode layer 40 is heated using an additional heating unit 90 different from the heating unit 80 in addition to the heating unit 80. For this reason, it becomes possible to heat the electrode layer 40 rapidly, and it can transfer to the changed dry conditions rapidly.

  When changing the drying time for holding the electrode layer 40 in the drying furnace 50, after the additional heating unit 90 is operated while increasing the heating amount by the heating unit 80, the heating amount by the additional heating unit 90 is gradually decreased. Let For this reason, after responding quickly to the drying conditions changed using the additional heating unit 90, the heating by the additional heating unit 90 can be reduced as the heating by the heating unit 80 is effective, and desirable drying conditions can be set. Can be maintained.

  A dedicated collection tube 131 (exhaust path) for exhausting the solvent 21 evaporated from the electrode layer 40 is provided, and a solvent concentration detector 130 is disposed in the collection tube 131 to detect the concentration of the solvent. For this reason, the solvent 21 evaporated from the electrode layer 40 can be collected effectively, and the solvent concentration in the vicinity of the electrode layer 40 that affects the evaporation of the solvent 21 can be detected more accurately.

  Since the flow of the fluid which goes to the exclusive collection pipe | tube 131 (exhaust path | route) is produced in the drying furnace 50 and the evaporated solvent 21 is guide | induced to the collection pipe | tube 131, the evaporated solvent 21 can be collected more effectively.

  A collection nozzle 132 for generating a fluid flow toward the dedicated collection pipe 131 (exhaust path) is provided, and the solvent 21 that has evaporated to the collection pipe 131 is guided by the collection nozzle 132, so that a desired flow can be easily generated. The evaporated solvent 21 can be collected more effectively.

(Modification example)
Although the embodiment in which the inside of the drying furnace 50 is divided into a plurality of (six) drying zones 51 to 56 has been shown, the number of drying zones may not be six, or the present invention can be applied to only one drying furnace. Can do.

  In the additional heating unit 90, when the infrared irradiation range is linear, the drying rate is likely to increase rapidly only within the irradiation range, so that the irradiation rate gradually changes toward the transport direction of the electrode layer 40. Infrared rays may be irradiated through an infrared reflecting film capable of setting infrared transmittance. Alternatively, an infrared reflecting film can be used as a material constituting the shutter 92.

  In addition, as shown in FIG. 9, the solvent concentration detectors are not provided in the collection tube, but the solvent concentration detectors 200 and 201 are arranged at a plurality of locations in the drying furnace 50 at different distances from the electrode layer 40. Also good. At this time, the solvent concentration detector 200 is positioned above the gas-liquid boundary layer formed above the electrode layer 40, and the solvent concentration detector 201 is positioned below the gas-liquid boundary layer of the electrode layer 40. Yes. Accordingly, by averaging the detection results of the plurality of solvent concentration detection units 200 and 201, it is possible to calculate the accurate solvent evaporation amount M without being influenced by the deviation of the solvent concentration depending on the location. Of course, it can also be comprised only with one solvent concentration detection part which is not provided in a collection tube.

  Moreover, an additional heating part is not limited to the structure which irradiates infrared rays. For example, as shown in FIG. 10, the support roll 211 is provided with a heating source 212 for heating the support roll 211 itself, and a cooling means 213 for circulating the refrigerant in the support roll 211 to cool the support roll 211. The additional heating unit 210 can be used. The configuration of the heating source 212 is not limited as long as it can be heated. For example, a heating wire, infrared rays, a heat exchanger, electromagnetic induction heating, or the like can be used. By setting it as such a structure, the electrode layer 40 can be heated via the electrode foil 30 which touches the support roll 211 directly. Further, by providing the cooling means 213, when the heating by the additional heating unit 210 becomes unnecessary, the support roll 211 can be quickly cooled, and the followability to the target temperature is improved. Further, when electromagnetic induction heating is used for the heating source 212, the metal electrode foil 30 may be directly heated instead of heating the support roll 211.

  As shown in FIG. 11, an additional heating unit 220 that is provided in parallel with the heating unit 80 and heats the air blown into the drying furnace 50 similarly to the heating unit 80 may be provided. The additional heating unit 220 can switch between supply and stop of hot air to the hot air supply pipe 150 by opening and closing the valve 221 by the control unit 160.

  Moreover, although the additional heating part 90 of the same structure is provided in each drying zone 51-56, you may provide the additional heating part of a different structure in each drying zone 51-56.

  Moreover, although the form which conveys the electrode foil 30 continuously was illustrated, the form conveyed by a batch type may be sufficient.

  Further, the present invention is not limited to the case where the electrode slurry 20 is intermittently applied, and it goes without saying that the present invention can also be applied to the case where the electrode slurry 20 is continuously applied.

10 electrode drying device,
20 electrode slurry,
21 solvent,
40 electrode layers,
50 drying ovens,
51-56 first and second drying zones,
60 transport section,
70 Blower,
80 heating section,
90,210 Additional heating section,
100 electrode temperature detector,
110 wind speed detector,
120 furnace temperature detector,
130, 200, 201 solvent concentration detector,
131 Collection pipe (exclusive exhaust route),
132 Nozzle for collection,
134 solvent concentration meter,
145 application part,
160 control unit,
A1, A2 dry standard value,
M Solvent evaporation.

Claims (15)

An electrode drying method for drying an electrode layer formed by applying an electrode slurry containing a solvent to a current collector in a drying furnace,
A drying reference value defined by a trajectory of the amount of solvent evaporation from the electrode layer with respect to time is set in advance, and a drying factor including temperature, wind speed, and solvent concentration in the drying furnace is detected and based on the drying factor. Calculate the evaporation amount of the solvent, and control the heating unit that heats the inside of the drying furnace and the blowing unit that blows air into the drying furnace so that the evaporation amount of the solvent follows the drying reference value. An electrode drying method for drying a layer.   When changing the drying time for holding the electrode layer in the drying furnace, the evaporation amount of the solvent calculated based on the drying factor becomes a predetermined drying reference value corresponding to the changed drying time. The electrode drying method according to claim 1, wherein the heating unit and the air blowing unit are controlled so as to follow.   The said electrode layer is heated using the additional heating part different from the said heating part in addition to the said heating part, when changing the drying time which hold | maintains the said electrode layer in the said drying furnace. The method for drying an electrode according to 1.   When changing the drying time for holding the electrode layer in the drying furnace, after the additional heating unit is operated while increasing the heating amount by the heating unit, the heating amount by the additional heating unit is gradually decreased. The electrode drying method according to claim 3.   A dedicated exhaust path for exhausting the solvent evaporated from the electrode layer is provided, and a solvent concentration detection unit that detects the concentration of the solvent is disposed in the exhaust path to detect the concentration of the solvent. 5. The electrode drying method according to any one of 4 above.   The electrode drying method according to claim 5, wherein a flow of fluid toward the dedicated exhaust path is generated in the drying furnace to guide the evaporated solvent to the dedicated exhaust path.   The electrode drying method according to claim 6, wherein a collecting nozzle that generates a flow of fluid toward the dedicated exhaust path is provided, and the solvent evaporated to the dedicated exhaust path is guided by the collecting nozzle.   In the drying furnace, a solvent concentration detection unit for detecting the concentration of the solvent evaporated from the electrode layer is disposed at a plurality of locations at different distances from the electrode layer, and the concentration of the solvent is obtained by averaging a plurality of detection results. The method for drying an electrode according to any one of claims 1 to 4, wherein An electrode drying apparatus for drying an electrode layer formed by applying an electrode slurry containing a solvent to a current collector in a drying furnace,
A temperature detector for detecting the temperature in the drying furnace;
A wind speed detector for detecting the wind speed in the drying furnace;
A solvent concentration detection unit for detecting the solvent concentration of the atmosphere in the drying furnace;
A heating unit for heating the inside of the drying furnace;
An air blower for blowing air into the drying furnace;
Receiving signals detected from the temperature detection unit, the wind speed detection unit, and the solvent concentration detection unit, calculate the evaporation amount of the solvent based on the detection value, the evaporation amount of the solvent from the electrode layer with respect to time An electrode drying apparatus comprising: a control unit that controls the heating unit and the air blowing unit so as to follow a preset drying reference value defined by a trajectory of the evaporation amount of the solvent.   The control unit calculates the solvent calculated based on the detection values received from the temperature detection unit, the wind speed detection unit, and the solvent concentration detection unit when changing the drying time for holding the electrode layer in the drying furnace. The electrode drying apparatus according to claim 9, wherein the heating unit and the air blowing unit are controlled so that an evaporation amount of the slag follows a predetermined drying reference value corresponding to the drying time after the change. An additional heating part different from the heating part,
11. The electrode drying according to claim 9, wherein the control unit operates the additional heating unit in addition to the heating unit when changing a drying time for holding the electrode layer in the drying furnace. apparatus.   When changing the drying time for holding the electrode layer in the drying furnace, the control unit operates the additional heating unit while increasing the amount of heating by the heating unit, and then heats by the additional heating unit The electrode drying apparatus according to claim 11, wherein the amount is gradually decreased.   The electrode drying apparatus according to any one of claims 9 to 12, further comprising a dedicated exhaust path for exhausting the solvent evaporated from the electrode layer, in which the solvent concentration detection unit is disposed.   The electrode drying apparatus according to claim 13, further comprising a collection nozzle that generates a flow of fluid toward the dedicated exhaust path.   The electrode drying apparatus according to any one of claims 9 to 12, wherein the solvent concentration detection unit is provided at a plurality of locations in the drying furnace at different distances from the electrode layer.

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