JP7731397B2 - Method for manufacturing an electricity storage device - Google Patents

Description

The technology disclosed herein relates to a method for manufacturing an electricity storage device.

Currently, energy storage devices such as lithium-ion secondary batteries and nickel-metal hydride batteries are widely used in a variety of fields, including vehicles and mobile terminals. For example, this type of energy storage device is constructed by housing an electrode assembly and an electrolyte solution inside a case. In manufacturing this type of energy storage device, an assembly is first created in which the electrode assembly is housed inside the case. The assembly is then dried before the electrolyte solution is injected. This prevents localized increases in resistance due to moisture contamination.

Technology related to the drying process of this electrode assembly is disclosed in Patent Document 1. The manufacturing method described in Patent Document 1 involves creating an assembly in which the electrode assembly is housed in a case, gripping the outer surface of the assembly with a gripping tool, and heating the gripped assembly to dry the interior. In the manufacturing method described in Patent Document 1, during the gripping process, a greater confining pressure is applied to a central region of the rectangular surface of the electrode assembly, including the center line in the long side direction, than to other regions of the rectangular surface excluding the central region. This makes it possible to suppress uneven drying within a single electricity storage device.

Japanese Patent Application Laid-Open No. 2022-139499

In recent years, at manufacturing sites for energy storage devices, it has become common to place multiple assemblies in a drying oven and simultaneously dry them. This improves the manufacturing efficiency of energy storage devices. However, such drying ovens are prone to uneven temperature distribution within the oven. In this case, there is a risk of uneven drying among multiple assemblies being dried simultaneously. The technology disclosed here has been developed to solve this problem.

The method for manufacturing an electricity storage device disclosed herein includes a preparation step of preparing an assembly in which an electrode body is housed in a case, and a drying step of housing a plurality of assemblies in a drying oven and drying the interior of the case. The drying step includes a measurement step of measuring a drying coefficient K for each of the plurality of assemblies based on the following formula (1), and a condition change step of individually changing the drying conditions for each of the plurality of assemblies based on the drying coefficient K. Note that in formula (1), Mi is the weight (g) of the assembly at a first measurement time, and Mc is the weight (g) of the assembly at a second measurement time that is a predetermined time after the first measurement time.
K=(Mi-Mc)/Mi (1)

In the technology disclosed herein, the drying coefficient K is measured for each of multiple assemblies subjected to the drying process. This drying coefficient K is the rate of weight loss (water evaporation rate) of the assembly per unit time during drying. By measuring this drying coefficient K, the progress of the drying process for each assembly can be determined. For example, an assembly placed in a high-temperature environment will have a large drying coefficient K because the water evaporates rapidly and the weight decreases significantly. On the other hand, an assembly placed in a low-temperature environment will have a small drying coefficient K because the water evaporates slowly and the weight loss is limited. In the manufacturing method disclosed herein, the drying conditions for each assembly are individually changed based on this drying coefficient K. This allows the progress of the drying process for multiple assemblies to be equalized. As a result, uneven drying among multiple assemblies can be prevented, even when using a drying oven with uneven temperature distribution within the oven.

FIG. 1 is a plan view schematically showing the internal structure of a drying furnace used in the drying step of the manufacturing method according to the first embodiment. FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 3 is a flowchart showing the manufacturing method according to the first embodiment. FIG. 4 is a cross-sectional view showing a schematic diagram of the assembly. FIG. 5 is a flowchart showing the drying process in the first embodiment. FIG. 6 is a side view illustrating the condition changing step in the first embodiment. FIG. 7 is a side view illustrating the condition changing step in the first embodiment. FIG. 8 is a side view illustrating the condition changing step in the first embodiment. FIG. 9 is a side cross-sectional view schematically showing the internal structure of a drying furnace used in the drying step of the manufacturing method according to the second embodiment. FIG. 10 is a cross-sectional side view that schematically shows the internal structure of a drying furnace used in the drying step of the manufacturing method according to the third embodiment.

Below, several preferred embodiments of the technology disclosed herein will be described with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (e.g., the configuration of the power storage device, other manufacturing processes, etc.) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

Note that the symbols L, R, F, Rr, U, and D in the drawings referenced in this specification represent left, right, front, rear, top, and bottom, respectively. Also, the symbols X, Y, and Z in the drawings represent the width, depth, and height directions of the drying oven, respectively. However, these are merely predetermined directions for the convenience of explanation and do not limit the technology disclosed herein.

In addition, the term "electricity storage device" in this specification refers to a device in which an electrode assembly and an electrolyte are housed in a case. In this electricity storage device, charge carriers move between a pair of electrodes (positive and negative electrodes) via the electrolyte, resulting in a charge-discharge reaction. In the technology disclosed herein, electricity storage devices include secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, as well as capacitors such as lithium-ion capacitors and electric double-layer capacitors. In addition, the term "assembly" in this specification refers to a structure assembled to a state prior to the injection of electrolyte during the manufacture of an electricity storage device. In other words, the term "assembly" in the technology disclosed herein refers to an electricity storage device in which no electrolyte is present in the case and part of the case (such as an injection hole) is open.

First Embodiment
A first embodiment of the manufacturing method disclosed herein will be described below with reference to FIGS. 1 to 8. FIG. 1 is a plan view schematically illustrating the internal structure of a drying furnace used in the drying step of the manufacturing method according to the first embodiment. FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. FIG. 3 is a flowchart illustrating the manufacturing method according to the first embodiment. FIG. 4 is a cross-sectional view schematically illustrating an assembly. FIG. 5 is a flowchart illustrating the drying step in the first embodiment. FIGS. 6 to 8 are side views illustrating the condition changing step in the first embodiment. For ease of explanation, in FIG. 1, assemblies A1 to A4 are represented by dotted lines, and the structure D below the assemblies A1 to A4 is shown in perspective. Similarly, in FIG. 2, the structure L to the left of the assemblies A1 to A4 is shown in perspective.

1. Configuration of the Drying Oven First, the drying oven used in the manufacturing method according to this embodiment will be described. As shown in Figures 1 and 2, this drying oven 100 includes a furnace body 10, a roller conveyor 20, a heating device 30, a position changing device 40, a weight measuring means 50, and a control device 60.

(1) Furnace Body As shown in FIGS. 1 and 2, the furnace body 10 of the drying furnace 100 is a tunnel-shaped furnace body. In other words, the furnace body 10 has an internal space (furnace interior 10i) extending along the depth direction Y. The furnace interior 10i can accommodate multiple assemblies A1 to A4 (four in the figure). An inlet 12 is provided at the rear Rr end of the furnace body 10. An openable/closable inlet shutter 12a is provided at the inlet 12. An outlet 14 is provided at the front F end of the furnace body 10. An outlet shutter 14a is attached to the outlet 14. As will be described in more detail below, the drying furnace 100 is a batch-type drying furnace that seals the furnace interior 10i and performs a drying process while accommodating multiple assemblies A1 to A4.

(2) Roller Conveyor The roller conveyor 20 is a device that transports the assemblies A1 to A4 from the rear Rr to the front F. As shown in FIG. 1 , the roller conveyor 20 includes a first conveyor 20A and a second conveyor 20B. The first conveyor 20A extends along the depth direction Y on the left side L of the furnace chamber 10i. Meanwhile, the second conveyor 20B extends along the depth direction Y on the right side R of the furnace chamber 10i. That is, the roller conveyor 20 includes two conveyors that extend parallel to each other. A predetermined gap S1 is provided between the first conveyor 20A and the second conveyor 20B. Each of the first conveyor 20A and the second conveyor 20B is composed of a plurality of rollers 22. As shown in FIG. 2 , the rollers 22 are continuously arranged along the depth direction Y so that their positions in the height direction Z are aligned. A predetermined gap S2 is provided between each of the rollers 22. In this drying oven 100, the assemblies A1 to A4 are placed on a roller conveyor 20 (plurality of rollers 22). Then, by rotating each of the rollers 22, the assemblies A1 to A4 can be transported forward F in the depth direction Y.

(3) Heating Device The heating device 30 heats the assemblies A1 to A4 in the furnace interior 10i. The drying furnace 100 includes a side heating device 32, a top heating device 34, and a bottom heating device 36. As shown in FIG. 1, the drying furnace 100 includes four side heating devices 32 on the side wall (the side wall on the left side L in FIG. 1) of the furnace body 10. Each side heating device 32 is positioned to face the side of each of the four assemblies A1 to A4 on the roller conveyor 20. Each side heating device 32 also includes a side fan 32a and a side heater 32b. This allows hot air to be supplied to the side of each of the assemblies A1 to A4. Next, as shown in FIG. 2, four top heating devices 34 are provided on the ceiling of the furnace body 10. Each top heating device 34 is positioned to face the top of each of the four assemblies A1 to A4. Each top heating device 34 is equipped with a top fan 34a and a top heater 34b. This allows hot air to be supplied to the top surfaces of the assemblies A1 to A4. A bottom heating device 36 is provided on the bottom surface of the furnace body 10. The bottom heating device 36 is equipped with a bottom heater 36a that heats the assemblies A1 to A4 from below D. Note that the heating device only needs to be capable of heating the assemblies in the furnace, and the specific number and configuration of the devices can be changed as appropriate.

(4) Position Changing Device The position changing device 40 changes the placement positions of the assemblies A1 to A4 within the furnace interior 10i. As will be described in detail later, the position changing device 40 in this embodiment changes the placement positions of the assemblies A1 to A4 on the roller conveyor 20. The position changing device 40 includes a first shaft 42, a second shaft 44, a third shaft 46, and a drive mechanism 48. As shown in FIG. 2 , the first shaft 42 is a columnar member extending upward from the drive mechanism 48 in the height direction Z toward the upper U. The second shaft 44 is a rod-shaped member extending from the upper end of the first shaft 42 toward both sides (the front F and the rear Rr) in the depth direction Y. As shown in FIG. 1 , the third shaft 46 is a plurality of rod-shaped members extending in the width direction X so as to intersect with the second shaft 44. The drive mechanism 48 has a lifting function that elevates the second shaft 44 and the third shaft 46 by extending and retracting the first shaft 42 in the height direction Z. The drive mechanism 48 also has a rotation function that rotates the second shaft 44 and the third shaft 46 by rotating the first shaft 42. As shown in FIG. 1 , the first shaft 42 and the second shaft 44 of the position changer 40 are disposed in the gap S1 between the first conveyor 20A and the second conveyor 20B in a plan view. Each of the plurality of third shafts 46 is disposed in the gap S2 between the plurality of rollers 22 in a plan view. This prevents interference with the roller conveyor 20 when the first shaft 42, the second shaft 44, and the third shaft 46 are raised and lowered. As shown in FIGS. 1 and 2 , the drying oven 100 in this embodiment has two position changers 40. Specifically, one position changer 40 is disposed at the rear Rr in the depth direction Y. The rear Rr position changer 40 is located at D below the assemblies A3 and A4. The other position changer 40 is disposed at F in the depth direction Y. The front F position changer 40 is located at D below the assemblies A1 and A2.

(5) Weight Measuring Means The weight measuring means 50 individually measures the weights of the assemblies A1 to A4 during the drying process. The specific configuration of the weight measuring means is not particularly limited, and any conventionally known measuring device can be used without particular limitation. For example, the weight measuring means 50 shown in FIG. 2 is a load cell attached to some of the rollers 22. This allows the weights of the assemblies A1 to A4 placed on the roller conveyor 20 to be measured. As will be described in detail later, these weights of the assemblies A1 to A4 are used to calculate the drying coefficient K. The number and positions of the weight measuring means are not particularly limited as long as they can individually measure the weight of each of the multiple assemblies. For example, a weight measuring means may be attached to each of the multiple rollers supporting one assembly, and an average value, etc., may be calculated. This allows for more accurate measurement of the weight of each assembly.

(6) Control Device The control device 60 controls the operation of the drying furnace 100. The control device 60 is a microcomputer capable of storing and performing calculations on various types of data. Although not shown, the control device 60 is connected to each device (such as the roller conveyor 20 and the heating device 30) that constitutes the drying furnace 100. The control device 60 controls the operation of each device to perform the drying process on the assemblies A1 to A4. The control device 60 is also connected to the weight measuring means 50. The control device 60 in this embodiment stores a control program that individually changes the drying conditions for each of the assemblies A1 to A4 based on the measurement results of the weight measuring means 50. A method for manufacturing an electricity storage device that is executed based on this control program will be described below.

2. Method for Manufacturing an Electricity Storage Device As shown in FIG. 3, the method for manufacturing an electricity storage device according to this embodiment includes a preparation step S10 and a drying step S20.

(1) Preparation step S10
In the preparation step S10, assemblies A1 to A4 (see FIG. 4 ) are prepared, each having an electrode body 2 housed in a case 1. A liquid inlet 3 is formed in the case 1 of each of the assemblies A1 to A4. The liquid inlet 3 is an opening used to inject an electrolyte into the case 1. Therefore, in the assemblies A1 to A4 before the liquid inlet step, the inside and outside of the case 1 are in communication with each other via the liquid inlet 3. Note that this step is not limited to a specific procedure as long as it is possible to prepare the assemblies A1 to A4. For example, in the preparation step S10, the assemblies A1 to A4 may be prepared according to a conventionally known procedure, or pre-fabricated battery assemblies A1 to A4 may be prepared.

(2) Drying step S20
In the drying process S20, the multiple assemblies A1 to A4 are housed inside the drying furnace 100, and the inside of the case 1 is dried. As shown in Fig. 5, the drying process S20 in this embodiment includes a drying start process S21, a measurement process S22, a difference calculation process S23, a difference determination process S24, and a condition change process S25. Each process will be described below.

(2-1) Drying start step S21
In this process, multiple assemblies A1 to A4 are placed in the furnace chamber 10i and the drying process begins. Specifically, the carry-in shutter 12a is opened to open the carry-in entrance 12. Next, the roller conveyor 20 is operated. Four assemblies A1 to A4 are sequentially placed on the operating roller conveyor 20. This allows the assemblies A1 to A4 to be carried into the furnace chamber 10i. The roller conveyor 20 is then stopped when the first assembly A1 reaches the end of the furnace chamber 10i on the front F side (just before the carry-in exit 14). This allows the four assemblies A1 to A4 to be placed in the furnace chamber 10i. Next, the carry-in shutter 12a is closed to seal the furnace chamber 10i, and the heating device 30 is then operated. This starts the drying process for the assemblies A1 to A4.

(2-2) Measurement step S22
In this step, the drying coefficient K is measured for each of the multiple assemblies A1 to A4 based on the following formula (1): "Mi" in formula (1) is the weight (g) of each of the assemblies A1 to A4 at a first measurement time. "Mc" is the weight (g) of the assembly at a second measurement time, which is a predetermined time after the first measurement time.
K=(Mi-Mc)/Mi (1)

Specifically, the weight measurement means 50 sequentially transmits the current weights of the assemblies A1 to A4 to the control device 60 in FIG. 2 . The control device 60 stores the weights _Mi1 to _Mi4 of the assemblies A1 to A4 at a predetermined first measurement time. After a certain time has elapsed, the control device 60 acquires the weights _Mc1 to _Mc4 of the assemblies A1 to A4 at a second measurement time. Next, the control device 60 substitutes the weight _Mi1 of the assembly A1 at the first measurement time and the weight _Mc1 of the assembly A1 at the second measurement time into the above formula (1). This allows the drying coefficient _K1 of the assembly A1 to be calculated. The control device 60 also calculates the drying coefficients _K2 to _K4 of the other assemblies A2 to A4 following a similar procedure. Here, the drying coefficients _K1 to _K4 indicate the moisture evaporation rates of the assemblies A1 to A4 from the first measurement time to the second measurement time. For example, an assembly placed in a high-temperature environment will have a large drying coefficient K because moisture evaporates rapidly. On the other hand, an assembly placed in a low-temperature environment will have a small drying coefficient K because moisture evaporates less easily. In other words, by performing this process, the progress of the drying process in each of the multiple assemblies A1 to A4 can be detected.

The first measurement time and the second measurement time in this step can be set to any timing. For example, the first measurement time can be set to the time when the drying start step S21 is performed. The second measurement time can be set to a time 60 to 180 minutes (e.g., 120 minutes) after the first measurement time. Multiple second measurement times may be set in this step. For example, the weights _Mc1 to _Mc4 of the assemblies A1 to A4 at the second measurement time may be obtained each time a predetermined time (e.g., 120 minutes) has elapsed since the first measurement time.

(2-3) Difference calculation step S23
In this step, the control device 60 calculates the difference (K _max - K _min ) between the maximum value K _max and the minimum value K _min of the multiple drying coefficients K ₁ to K ₄ measured in the measurement step S22. Specifically, the control device 60 first compares the drying coefficients K ₁ to K ₄ of each of the assemblies A1 to A4 and selects the maximum value K _max and the minimum value K _min . Next, the control device 60 calculates the difference (K _{max -} K _min ) between the maximum value K _max and the minimum value K min . This difference (K _max - K _min ) serves as an index of the variation in the progress of the drying process among the multiple assemblies A1 to A4. Specifically, if the difference (K _max - K _min ) is small, there is not a large difference in the moisture evaporation rate among the multiple assemblies A1 to A4. Based on this, it can be determined that the drying process is progressing uniformly. On the other hand, if the difference (K _max - K _min ) is large, there is a large difference in the rate of water evaporation among the assemblies A1 to A4, which indicates that there is variation in the progress of the drying process.

(2-4) Difference determination step S24
In the difference determination step S24, the difference (K _max - K _min ) is compared with a predetermined threshold value _KD , and when the difference (K _max - K _min ) exceeds the threshold value _KD , the condition change step S25 is initiated. Specifically, the control device 60 compares the difference (K _max - K _min ) calculated in the difference calculation step S23 with the threshold value _KD . If the difference exceeds the threshold value (K _max - K _min > K _D ), it is determined that there is variation in the progress of the drying process among the multiple assemblies A1 to A4. In this case, the control device 60 proceeds to the condition change step S25 in order to correct the variation in the degree of drying (Yes in S24). On the other hand, if the difference is equal to or less than the threshold ( _Kmax - _Kmin ≦ _KD ), it is determined that the progress of the drying process for the multiple assemblies A1 to A4 is approximately uniform. In this case, the control device 60 maintains the current drying conditions and returns the process to the measurement process S22 (No in S24). In this way, by performing the difference determination process S24, the condition change process S25 can be started at an appropriate time.

(2-5) Condition change step S25
In this process, the drying conditions for each of the assemblies A1 to A4 are individually changed based on the drying coefficient K. This allows the progress of the drying process for the assemblies A1 to A4 to be equalized. As a result, even if there is a bias in the temperature distribution inside the furnace 10i, uneven drying can be prevented from occurring among the assemblies A1 to A4.

The specific means for changing the drying conditions for the assemblies A1 to A4 is not particularly limited, and various means can be employed. For example, in the manufacturing method according to this embodiment, the positions of the assemblies A1 to A4 within the drying furnace 100 are changed based on the drying coefficients _K1 to _K4 . Specifically, in a tunnel-shaped furnace body 10 as shown in FIG. 1 , the drying temperature tends to be relatively low near the inlet 12 and the outlet 14 (the outermost regions in the depth direction Y). As a result, the drying coefficients _K1 and _K4 of the assemblies A1 and A4 located on the outermost regions in the depth direction Y are relatively low, while the drying coefficients _K2 and _K3 of the assemblies A2 and A3 located in the center in the depth direction Y are relatively high. In response to this, in the condition changing step S25 according to this embodiment, the positions of the central assemblies A2 and A3 and the outermost assemblies A1 and A4 are swapped using a position changing device 40. Hereinafter, the details of the position change using the position change device 40 will be described using the assemblies A1 and A2 arranged on the exit 14 side as an example.

First, as shown in FIG. 6, in a normal position change device 40, the second shaft 44 and the third shaft 46 are located at D below the roller conveyor 20. On the other hand, when the condition change process S25 is started, the control device 60 activates the lifting function of the drive mechanism 48 of the position change device 40 to extend the first shaft 42 upward U (see FIG. 7). As a result, the second shaft 44 and the third shaft 46 rise above U above the roller conveyor 20, lifting assemblies A1 and A2. Next, the control device 60 activates the rotation function of the drive mechanism 48 to rotate the first shaft 42 180° (see FIG. 8). This swaps the positions of assemblies A1 and A2 in the depth direction Y. The control device 60 then lowers the second shaft 44 and the third shaft 46. As a result, assemblies A1 and A2 are placed back on the roller conveyor 20. As described above, the position changing device 40 of this embodiment can swap the assembly A1, which was placed in a relatively low-temperature area (outside in the depth direction Y), with the assembly A2, which was placed in a relatively high-temperature area (towards the center in the depth direction Y). By continuing the drying process in this state, the progress of the drying process for the assembly A1 and the assembly A2 can be equalized.

In this embodiment, the control device 60 is preset with a time (drying time) for performing the drying step S20. The control device 60 repeatedly performs the above-described measurement step S22 through condition change step S25 until this drying time has elapsed. This allows the drying process to be carried out while appropriately leveling the dryness of the multiple assemblies A1 to A4. As a result, uneven drying among the assemblies A1 to A4 after the drying step S20 can be more effectively prevented. Then, once the drying time has elapsed, the control device 60 opens the discharge shutter 14a and operates the roller conveyor 20. This allows the dried assemblies A1 to A4 to be transported outside the furnace body 10.

As described above, in the manufacturing method according to this embodiment, the drying coefficients _K1 to _K4 are measured to determine the progress of the drying process for each of the assemblies A1 to A4. Then, the drying conditions (here, the installation positions) for the assemblies A1 to A4 are individually changed based on these drying coefficients _K1 to _K4 . This allows the progress of the drying process for the multiple assemblies A1 to A4 to be equalized, preventing uneven drying among the multiple assemblies A1 to A4 even when using a furnace body 10 in which the temperature distribution inside the furnace 10i is uneven.

<Other Embodiments>
One embodiment of the technology disclosed herein has been described above. Note that the technology disclosed herein is not limited to the above embodiment, and includes other embodiments with various configuration changes. Other embodiments of the technology disclosed herein will be described below.

1. Means for Changing Drying Conditions As described above, the means for changing the drying conditions in the condition changing step is not particularly limited, and various means can be adopted. Other examples of the means for changing the drying conditions will be described below.

(1) Installation of Rails For example, the drying furnace 100 in the first embodiment uses two position changers 40 to change the installation positions of the assemblies A1 to A4. However, the number of position changers 40 is not particularly limited. For example, in the drying furnace 100A in the second embodiment shown in FIG. 9, a rail 70 extending along the depth direction Y is installed on the bottom surface of the furnace interior 10i. In this drying furnace 100A, one position changer 40 is slidably attached to the rail 70. With this configuration, even with only one position changer 40, the positions of all the assemblies A1 to A4 can be changed. In particular, with the configuration shown in FIG. 9, the positions of the assemblies A2 and A3 located in the center of the depth direction Y can be swapped. As a result, even slight drying unevenness in the center of the depth direction Y can be effectively prevented.

(2) Heater Control In the first and second embodiments, the drying conditions are changed by changing the positions of the assemblies A1 to A4. However, the drying conditions for the assemblies can also be changed by other means. For example, as shown in FIG. 10 , a drying oven 100B in a third embodiment does not include a position change device. Instead, the drying oven 100B includes multiple heaters (side heater 32b, top heater 34b, and bottom heater 36a) that heat each of the assemblies A1 to A4. In the condition change process using the drying oven 100B configured as described above, the temperature of each of the multiple heaters may be individually changed based on the drying coefficient K. Specifically, in the condition change process in the third embodiment, the temperature of the heater adjacent to the assembly with the small drying coefficient K is increased, and the temperature of the heater adjacent to the assembly with the large drying coefficient K is decreased. This allows the progress of the drying process for the multiple assemblies A1 to A4 to be equalized.

(3) Fan Control The drying oven 100 shown in FIG. 10 also includes multiple fans (side fan 32a, top fan 34a) that supply warm air to each of the assemblies A1 to A4. In this case, the condition change process may individually change the airflow of each of the multiple fans based on the drying coefficient K. Specifically, in this condition change process, the airflow of the fan adjacent to the assembly with a small drying coefficient K is increased, and the airflow of the fan adjacent to the assembly with a large drying coefficient K is decreased. This allows the progress of the drying process of the multiple assemblies A1 to A4 to be equalized. Note that the condition change process of the manufacturing method disclosed herein may also be performed by combining the above-described assembly position change, heater control, and fan control.

2. Drying Process Procedure As shown in FIG. 5 , the drying process S20 in the first embodiment includes a difference calculation process S23 and a difference determination process S24. In other words, the manufacturing method according to the first embodiment determines the timing for starting the condition change process S25 based on the difference (K _max −K _min ) between the maximum value K _max and the minimum value K _min of the drying coefficient K. However, the start condition for the condition change process S25 does not limit the technology disclosed herein. For example, the manufacturing method disclosed herein may employ timer control to start the condition change process when a preset condition change time is reached. By conducting a preliminary experiment to determine the time at which variations in the progress of the drying process begin to occur among multiple assemblies, the condition change process can be started at an appropriate time even when timer control is employed. Furthermore, the timing for starting the condition change process may be determined by the operator rather than the control device. In this case, a display may be provided in the drying oven, and the drying coefficient K of each assembly may be displayed on the display. This allows the operator to instruct the start of the condition change process at an appropriate time.

3. Furnace Size In the above-described embodiment, the number of assemblies A1 to A4 that can be accommodated in the furnace chamber 10i is four. However, the manufacturing method disclosed herein can be applied without particular limitation to drying furnaces that can accommodate multiple (two or more) assemblies. As the number of assemblies accommodated increases, the furnace body becomes larger, which tends to result in uneven drying due to uneven temperature distribution. In contrast, the manufacturing method disclosed herein can appropriately prevent uneven drying even when a large furnace body is used. Therefore, the manufacturing method disclosed herein is particularly suitable for large drying furnaces that can accommodate six or more assemblies (more preferably eight or more, and particularly preferably ten or more). The upper limit of the number of assemblies that can be accommodated is not particularly limited and may be 20 or less, or 16 or less. As in the above embodiment, the number of assemblies that can be accommodated may be six or less (e.g., four).

4. Furnace Structure The drying furnaces 100, 100A, and 100B described above each have a tunnel-shaped furnace body 10, and the assemblies A1 to A4 undergoing drying are placed on a roller conveyor 20. However, the shape of the furnace body and the location where the assemblies are stored are not limited to the manufacturing method disclosed herein. For example, the drying furnace may include a storage shelf with multiple partitions and a box-shaped furnace body in which the storage shelf is installed. In a drying furnace with such a configuration, multiple assemblies can be dried simultaneously by placing the assemblies on the partitions of the storage shelf. In this case, the drying coefficient K of each assembly can be measured by attaching a weight measuring device to each of the partitions of the storage shelf. The progress of the drying process for multiple assemblies can be equalized by switching the assemblies between the different tiers using a robot arm or the like.

The technology disclosed herein has been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above. In other words, the technology disclosed herein encompasses the aspects described in items 1 to 6 below.

<Item 1>
a preparation step of preparing an assembly in which an electrode body is housed in a case;
a drying step of housing a plurality of the assemblies in a drying oven and drying the inside of the case,
The drying step includes:
a measuring step of measuring a drying coefficient K based on the following formula (1) for each of the plurality of assemblies;
and a condition changing step of individually changing the drying conditions for each of the plurality of assemblies based on the drying coefficient K.
K=(Mi-Mc)/Mi (1)
In the above formula (1), Mi is the weight (g) of the assembly at the first measurement time, and Mc is the weight (g) of the assembly at the second measurement time after a predetermined time has elapsed since the first measurement time.

<Item 2>
The drying step includes:
a difference calculation step of calculating a difference (K _max −K _min ) between a maximum value K _max and a minimum value K _min of the plurality of drying coefficients K measured in the measurement step;
2. The method for manufacturing an electricity storage device according to item 1, further comprising a difference determination step of comparing a predetermined threshold value _KD with the difference ( _{K max} −K _min ) and starting the condition change step when the difference (K _max −K _min ) exceeds the threshold value KD.

<Item 3>
2. The method for manufacturing an electricity storage device according to item 1, wherein the condition changing step is started when a preset condition changing time is reached.

<Item 4>
4. The method for manufacturing an electricity storage device according to any one of items 1 to 3, wherein the condition changing step changes a position of the assembly in the furnace based on the drying coefficient K.

<Item 5>
the drying oven includes a plurality of heaters that heat each of the assemblies;
5. The method for manufacturing an electricity storage device according to any one of items 1 to 4, wherein the condition changing step changes the temperature of each of the plurality of heaters individually based on the dryness coefficient K.

<Item 6>
the drying oven includes a plurality of fans that supply hot air to each of the assemblies;
6. The method for manufacturing an electricity storage device according to any one of items 1 to 5, wherein the condition changing step changes the airflow rate of each of the plurality of fans individually based on the dryness coefficient K.

10: Furnace body 20: Roller conveyor 30: Heating device 40: Position changing device 50: Weight measuring means 60: Control device 70: Rail 100: Drying furnaces A1 to A4: Assembly

Claims (6)

a preparation step of preparing an assembly in which an electrode body is housed in a case;
a drying step of housing a plurality of the assemblies in a drying oven and drying the inside of the case,
The drying step includes:
a measuring step of measuring a drying coefficient K based on the following formula (1) for each of the plurality of assemblies;
and a condition changing step of individually changing the drying conditions for each of the plurality of assemblies based on the drying coefficient K.
K=(Mi-Mc)/Mi (1)
In the above formula (1), Mi is the weight (g) of the assembly at the first measurement time, and Mc is the weight (g) of the assembly at the second measurement time after a predetermined time has elapsed since the first measurement time. The drying step includes:
a difference calculation step of calculating a difference (K _max −K _min ) between a maximum value K _max and a minimum value K _min of the plurality of drying coefficients K measured in the measurement step;
_2. The method for manufacturing an electricity storage device according to claim 1, further comprising a difference determination step of comparing a predetermined threshold value _KD with the difference (K _max −K _min ) and starting the condition change step when the difference (K _max −K _min ) exceeds the threshold value KD. The method for manufacturing an electricity storage device described in claim 1, wherein the condition change process is initiated when a preset condition change time is reached. The method for manufacturing an electricity storage device described in any one of claims 1 to 3, wherein the condition changing step changes the placement position of the assembly in the furnace based on the drying coefficient K. the drying oven includes a plurality of heaters that heat each of the assemblies;
4. The method for manufacturing an electricity storage device according to claim 1, wherein the condition changing step changes the temperature of each of the plurality of heaters individually based on the dryness coefficient K. the drying oven includes a plurality of fans that supply hot air to each of the assemblies;
4. The method for manufacturing an electricity storage device according to claim 1, wherein the condition changing step changes the air volume of each of the plurality of fans individually based on the dryness coefficient K.