Patent Publication Number: US-2023163404-A1

Title: Manufacturing apparatus and method of manufacturing electrochemical cell

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-189535 filed on Nov. 22, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a manufacturing apparatus, and a method of manufacturing electrochemical cells. 
     2. Description of Related Art 
     Japanese Unexamined Patent Application Publication No. 2018-106850 (JP 2018-106850 A) discloses an injection device and an injecting method that can improve the production efficiency of power storage modules. 
     SUMMARY 
     Generally, electrochemical cells (which can be abbreviated to “cells”) are manufactured by enclosing, for example, power generating elements and electrolyte in an exterior body. During use of the cells, gas may be generated in the exterior body due to deterioration of the electrolyte, for example. As the gas is generated, the internal pressure in the exterior body can be increased. Considering later gas generation, it is desirable to reduce gas in the exterior body as much as possible during the manufacturing stage. Thus, the pressure in the exterior body may be reduced. For example, the pressure in the exterior body may be reduced by, for example, a vacuum pump, etc. After the pressure (degree of pressure reduction) in the exterior body reaches a target value, the exterior body is sealed. 
     In some cases, an exterior body having low rigidity is used. For example, a sheet-like exterior body, such as a metal foil laminate film, may be used. When the rigidity of the exterior body is low, the exterior body can be pushed by the external pressure and deformed when the pressure in the exterior body is reduced. With the exterior body thus deformed, a gas channel can be blocked. If the gas channel is blocked, there is a possibility that the target degree of pressure reduction in the exterior body has not been reached even if a value indicated by a pressure gauge reaches a target value. 
     The disclosure provides a manufacturing apparatus and a method of manufacturing an electrochemical cell, which guarantee the internal pressure in an exterior body by reducing blockage of a gas channel when the pressure in the exterior body is reduced. 
     A manufacturing apparatus according to a first aspect of the disclosure is a manufacturing apparatus for manufacturing an electrochemical cell having an exterior body under reduced pressure. The manufacturing apparatus includes a chamber, a pressure reducing device, and a return pipe. The pressure reducing device is configured to reduce a pressure in the chamber. The return pipe includes a first opening, a conduit, and a second opening. The first opening and the second opening are respectively and independently open to an interior of the chamber. The first opening is configured to be connected to the exterior body. The conduit connects the first opening and the second opening. The conduit is configured to once draw a gas in the exterior body out of the chamber when the pressure in the chamber is reduced, and then return the gas into the chamber. 
     In the manufacturing apparatus according to the first aspect, the return pipe may include a plurality of return pipes that are independent of each other. Each of the return pipes may include the first opening, the conduit, and the second opening. 
     The manufacturing apparatus according to the first aspect may further include a pressure gauge. The pressure gauge may be connected to the conduit. 
     The manufacturing apparatus according to the first aspect may further include a flow meter. The flow meter may be connected to the conduit. 
     The manufacturing apparatus according to the first aspect may further include a sealing device. The sealing device may be configured to seal the exterior body in the chamber. 
     A method of manufacturing an electrochemical cell according to a second aspect of the disclosure includes preparing the manufacturing apparatus according to the first aspect of the disclosure, preparing a workpiece by enclosing a power generating element in the exterior body, placing the workpiece in the chamber, connecting the exterior body and the first opening. and reducing a pressure in the chamber, to reduce a pressure in the exterior body via the return pipe. 
     In the method according to the second aspect, in preparing the manufacturing apparatus, the manufacturing apparatus including a plurality of return pipes that are independent of each other may be prepared. In preparing the workpiece, a cell module including a plurality of electrochemical cells may be prepared as the workpiece. The electrochemical cells may respectively and independently include internal spaces. In connecting the exterior body and the first opening, the return pipes that are separate from each other may be respectively connected to the internal spaces. 
     In the method according to the second aspect, in preparing the manufacturing apparatus, the manufacturing apparatus including a pressure gauge may be prepared. In reducing the pressure in the exterior body, the pressure in the exterior body may be reduced such that a value indicated by the pressure gauge becomes equal to or lower than a reference value. 
     In the method according to second aspect, in preparing the manufacturing apparatus, the manufacturing apparatus including a flow meter may be prepared. In reducing the pressure in the exterior body, the pressure in the exterior body may be reduced such that an integrated value of measurement values of the flow meter is equal to or larger than a reference value after the pressure stops being reduced. 
     The method according to the second aspect may further include injecting an electrolyte into the exterior body, through an injection port formed in the exterior body. In connecting the exterior body and the first opening, the first opening of the return pipe may be connected to the injection port. 
     The method according to the second aspect, the exterior body may contain at least one type selected from the group consisting of a metal foil and a metal foil laminate film. 
     In the method, in preparing the workpiece, a bipolar cell module may be prepared as the workpiece. 
     The method according to the second aspect may further include sealing the exterior body under reduced pressure. 
     In the following, an embodiment of this disclosure (which can be abbreviated to “this embodiment”) and an example of this disclosure (which can be abbreviated to “Example”) will be described. However, the technical scope of this disclosure is not limited to this embodiment and Example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and w % herein: 
         FIG.  1    is a first conceptual diagram of a reduced pressure condition; 
         FIG.  2    is a second conceptual diagram of a reduced pressure condition: 
         FIG.  3    is a conceptual diagram showing one example of a cell module: 
         FIG.  4    is a conceptual diagram showing one example of a manufacturing apparatus of the embodiment; 
         FIG.  5    is a schematic flowchart of a method of manufacturing an electrochemical cell according to the embodiment: 
         FIG.  6    is a schematic cross-sectional view of a first unit, a second unit, and a third unit in the embodiment; 
         FIG.  7    is a schematic cross-sectional view of a bipolar cell module in the embodiment: 
         FIG.  8    is a schematic top view of the bipolar cell module in the embodiment, and 
         FIG.  9    is a conceptual diagram showing Comparative Example. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Definition of Terms, Etc 
     In this specification, the terms “comprising”, “including”, “having”, and their variations (e.g., “be comprised of”) are in open-ended form. The open-ended form may or may not further include additional elements in addition to the essential elements. The term “consisting of” is in closed form. However, even the closed form does not exclude additional elements that are normally incidental impurities or irrelevant to the disclosed technology. The term “consisting substantially of . . . ” is in semi-closed form. In the semi-closed form, addition of elements having substantially no influence on the basic and novel characteristics of the disclosed technology is permitted. 
     In this specification, expressions such as “may do” and “can do” are used in the permissive sense “have the possibility of doing”, rather than in the obligatory sense “must do”. 
     In this specification, the order of execution of a plurality of steps, actions, and operations included in various method is not limited to the order of description unless otherwise noted. For example, two or more steps may be executed at the same time. For example, two or more steps may be executed before or after each other. 
     Geometric terms (e.g., “parallel”, “perpendicular”. “orthogonal”, etc.) in this specification should not be interpreted in a strict sense. For example, “parallel” may deviate somewhat from “parallel” in a strict sense. The geometric terms in this specification can include, for example, tolerances, errors, etc. in design, operation, manufacturing, etc. The dimensional relationships in each figure may not match the actual dimensional relationships. In some cases, the dimensional relationships (length, width, thickness, etc.) in each figure are changed to aid understanding of the disclosed technology. In addition, some configurations may be omitted. 
     In this specification, “electrochemical cell” denotes a single device that converts chemical energy into electrical energy. The electrochemical cells include primary batteries and secondary batteries. The electrochemical cells include lithium-ion batteries and nickel-metal-hydride batteries. The lithium-ion batteries include liquid batteries and all solid-state batteries. In this specification. “cell module” denotes a collection of a plurality of electrochemical cells. The electrochemical cells may or may not be electrically connected to each other. The electrochemical cells may form a series circuit or a parallel circuit. 
     In this specification, the “degree of pressure reduction” denotes the magnitude of the pressure of gas remaining in an exterior body after pressure reduction. The degree of pressure reduction can also be referred to as “degree of vacuum”. 
     SUMMARY OF EMBODIMENT 
     Initially, the summary of this embodiment will be described. The operation mechanism of this specification includes presumption. The operation mechanism does not limit the embodiment. 
     1. A manufacturing apparatus can manufacture an electrochemical cell in which the pressure in an exterior body is reduced. The manufacturing apparatus includes a chamber, a pressure reducing device, and a return pipe. The pressure reducing device is configured to reduce the pressure in the chamber. The return pipe includes a first opening, a conduit, and a second opening. The first opening and the second opening are respectively and independently open to the interior of the chamber. The first opening is configured to be connected to the exterior body. The conduit connects the first opening and the second opening. The conduit extends to once draw gas in the exterior body out of the chamber when the pressure in the chamber is reduced, and then return the drawn gas into the chamber. 
       FIG.  1    is a first conceptual diagram of a reduced pressure condition. As the gas in the exterior body  210  is discharged, the internal pressure P 1  in the exterior body  210  becomes lower than the external pressure P E . Namely, the inside of the exterior body  210  is brought into a negative-pressure state relative to the ambient atmosphere. The internal space of the exterior body  210  may be crushed by the external pressure P E , which may result in blockage of a gas channel. 
       FIG.  2    is a second conceptual diagram of a reduced pressure condition. In  FIG.  2   , the white arrows indicate gas flow. In the manufacturing apparatus of item “I” above, the gas in the exterior body  210  can be discharged via the return pipe  140 . As the pressure in the chamber  110  is reduced, the pressure of the chamber  110  (external pressure P E ) is reduced. In the return pipe  140 , a pressure loss can be generated. As a result, the internal pressure P 1  in the exterior body  210  can become larger than the external pressure P E . Namely, the inside of the exterior body  210  can be brought into a positive-pressure state, relative to the ambient atmosphere (atmosphere in the chamber  110 ). As the positive-pressure state is maintained during pressure reduction, the internal space of the exterior body  210  is considered to be less likely or unlikely to be crushed by the external pressure P E . Namely, blockage of the gas channel is considered to be less likely or unlikely to take place. 
     2. The manufacturing apparatus may include a plurality of return pipes. Each of the return pipes that are independent of each other includes the first opening, conduit, and second opening. 
     The manufacturing apparatus of item “1” above can produce a single cell, for example. The manufacturing apparatus of item “2” above can produce a cell module. The manufacturing apparatus of item “2” above is considered suitable for the manufacture of cell modules. 
       FIG.  3    is a conceptual diagram showing one example of a cell module. The cell module  250  includes partitions  230 . The partition  230  divides adjacent cells  200  from each other. When any gas channel is blocked due to deformation of the exterior body  210  in an outer cell  200 , the occurrence of the blockage can be detected by exterior appearance. The white arrows in  FIG.  3    indicate one example of the deformation direction. When any gas channel is blocked due to deformation of the partition  230  in an inner cell  200 , for example, it is difficult to detect the occurrence of the blockage by exterior appearance. 
     By connecting separate return pipes to the individual cells, it is considered possible to reduce the pressure in each of the cells while keeping the cell in the positive-pressure state. Thus, blockage of gas channels in the inner cells is considered to be reduced. 
     In the manufacturing apparatus of item “2” above, the object of which the pressure is reduced is a single chamber. Thus, the pressures in a plurality of cells can be reduced at the same time by a single pressure reducing device. 
     3. The manufacturing apparatus may further include a pressure gauge. The pressure gauge is connected to the conduit. 
     The pressure gauge may be used to check the degree of pressure reduction of each of the cells. 
     4. The manufacturing apparatus may further include a flow meter. The flow meter is connected to the conduit. 
     For example, the total amount of the gas discharged may be obtained by integrating the measurement values of the flow meter. For example, the degree of pressure reduction in the individual cells may be determined from the total amount of the gas discharged and the internal space (volume) of the exterior body. 
     5. The manufacturing apparatus may further include a sealing device. The sealing device may be configured to seal the exterior body in the chamber. 
     6. A method of manufacturing an electrochemical cell includes the following steps (a) to (e). 
     (a) Prepare the manufacturing apparatus of item “I” above.
 
(b) Prepare a workpiece by enclosing power generating elements in the exterior body.
 
(c) Place the workpiece in the chamber.
 
(d) Connect the exterior body to the first opening.
 
(e) Reduce the pressure in the chamber, thereby to reduce the pressure in the exterior body via the return pipe.
 
     The manufacturing apparatus of item “1” above can be used in the procedure of item “6” above, for example. 
     7. In step (a) above, a manufacturing apparatus including a plurality of independent return pipes, for example, may be prepared. In step (b) above, a cell module including a plurality of electrochemical cells may be prepared as the workpiece. The electrochemical cells respectively and independently include internal spaces. In step (d) above, separate return pipes may be connected to the respective internal spaces. 
     In the manufacturing method of item “7” above, the cell module can be produced. The cell module may be of bipolar type or monopolar type. In the bipolar type, each electrode has two polarities. For example, the front side of the electrode is a positive electrode, and the rear side is a negative electrode. The electrode can also be referred to as “bipolar electrode”. In the monopolar type, each electrode has a single polarity. Namely, the electrode is a positive electrode or a negative electrode. 
     8. In step (a) above, a manufacturing apparatus including a pressure gauge, for example, may be prepared. In step (e) above, the pressure in the exterior body may be reduced so that the value indicated by the pressure gauge becomes equal to or lower than a reference value. 
     For example, the degree of pressure reduction may be checked by the pressure gauge. 
     9. In step (a) above, a manufacturing apparatus including a flow meter may be prepared. In step (e) above, the pressure in the exterior body may be reduced so that the integrated value of the measurement values of the flow meter is equal to or larger than a reference value after the pressure stops being reduced. 
     For example, the degree of pressure reduction may be checked by the flow meter. For example, the degree of pressure reduction may be checked by both the pressure gauge and the flow meter. 
     10. An injection port may be formed in the exterior body. Electrolyte can be injected into the exterior body via the injection port. In step (d) above, the first opening of the return pipe may be connected to the injection port. 
     For example, gas may be discharged from the injection port of the exterior body. 
     11. The exterior body may include at least one type selected from the group consisting of metal foil, and metal foil laminate film. 
     The metal foil and metal foil laminate film can have low rigidity. The manufacturing method of item “6” above is considered suitable for the case where the rigidity of the exterior body is low. 
     12. In step (b) above, a bipolar cell module may be prepared as the workpiece. 
     The manufacturing method of item “7” above is considered suitable for the manufacture of bipolar cell modules. 
     13. The method of manufacturing the electrochemical cell may further include step (f) below. 
     (f) Seal the exterior body under reduced pressure. 
     DETAILS OF THE EMBODIMENT 
     Next, details of the embodiment will be described. 
     Manufacturing Apparatus 
       FIG.  4    is a conceptual diagram showing one example of the manufacturing apparatus of this embodiment. The “manufacturing apparatus of this embodiment” can be simply referred to as “the manufacturing apparatus”. The manufacturing apparatus  100  includes a chamber  110 , a pressure reducing device  130 , and return pipes  140 . The manufacturing apparatus  100  may further include, for example, sealing devices  120 , pressure gauges  150 , flow meters  160 , etc. 
     The chamber  110  can provide a stable sealed space under a reduced pressure condition. The chamber  110  may be, for example, a metal container. The chamber  110  may include an exhaust port  111 , for example. The exhaust port  111  can be connected to the pressure reducing device  130 . For example, a stage, holder, or the like (not shown in  FIG.  4   ) may be provided in the chamber  110 . The workpiece  201  may be held by the stage, holder, or the like. 
     The sealing device  120  may be configured to seal the exterior body  210 , inside the chamber  110 , for example. The sealing device  120  may be configured to seal the exterior body  210 , outside the chamber  110 , for example. The sealing device  120  can seal the exterior body  210  by any given method. The sealing device  120  may include, for example, a thermal welding device, ultrasonic welding device, etc. The sealing device  120  may be located, for example, in the chamber  110 . For example, a part of the sealing device  120  may be located in the chamber  110 . For example, a portion of the sealing device  120  that actually performs sealing may be located in the chamber  110 . The portion that actually performs sealing may include, for example, a press unit, heat bar, heat plate, ultrasonic hom, anvil, etc. The sealing device  120  may be located, for example, outside the chamber  110 . 
     The pressure reducing device  130  may be configured to reduce the pressure in the chamber  110 . The pressure reducing device  130  may include, for example, a vacuum pump, compressor, etc. 
     The return pipe  140  can be strong enough not to be deformed when pushed by external pressure during pressure reduction. The return pipe  140  may be made of, for example, metal. The return pipe  140  includes a first opening  141 , conduit  143 , and second opening  142 . The first opening  141  and the second opening  142  respectively and independently open to the interior of the chamber  110 . The positions of the first opening  141  and second opening  142  may be determined as desired provided that they are not the same position. The first opening  141  is configured to be connected to the exterior body  210 . For example, a jig for connecting the return pipe  140  to the exterior body  210  may be attached to the first opening  141 . 
     The conduit  143  connects the first opening  141  to the second opening  142 . The first opening  141  is located at one end of the conduit  143 . The second opening  142  is located at the other end of the conduit  143 . In  FIG.  4   , the white arrows indicate flow of gas. The conduit extends to once draw the gas in the exterior body  210  out of the chamber  110  when the pressure in the chamber  110  is reduced, and then return the drawn gas into the chamber  110 . Namely, when the pressure in the chamber  110  is reduced, the gas in the exterior body  210  is sucked from the first opening  141 . The sucked gas passes through the conduit  143 , and is released to the interior of the chamber  110  via the second opening  142 . In the conduit  143 , a pressure loss is considered to be generated in the conduit  143 . Due to the pressure loss, the interior of the exterior body  210  can be in a positive-pressure state relative to the atmosphere in the chamber  110 . The pressure in the exterior body  210 , which is in the positive-pressure state, is reduced, so that blockage of the gas channel in the exterior body  210  can be reduced. 
     For example, the conduit  143  may have an inside diameter of 1 to 10 mm, or may have an inside diameter of 2 to 6 mm. When the inside diameter of the conduit  143  is in the range of 1 to 10 mm, a suitable pressure loss can be generated. The inside diameter of the conduit  143  may be constant or varied. The pressure loss may be generated due to change of the inside diameter. The conduit  143  may have two or more elbows. The pressure loss may occur at the elbows. 
     The manufacturing apparatus  100  may include a single return pipe  140 . The manufacturing apparatus  100  may include two or more return pipes  140 . In  FIG.  4   , three retum pipes  140  are illustrated as one example. Each of the two or more return pipes  140 , which are independent of each other, includes the first opening  141 , conduit  143 , and second opening  142 . With the manufacturing apparatus  100  including the two or more return pipes  140 , the cell module  250  can be produced. The number of the return pipes  140  can correspond to the number of the cells  200  included in the cell module  250 . 
     The manufacturing apparatus  100  may further include a pressure gauge  150 . The pressure gauge  150  is connected to the conduit  143 . Depending on the target degree of pressure reduction, the pressure gauge  150  having an appropriate pressure range can be selected. The degree of pressure reduction in the exterior body  210  can be determined from the value indicated by the pressure gauge  150 . When the manufacturing apparatus  100  includes two or more return pipes  140 , the pressure gauge  150  may connected to each of the return pipes  140 . 
     The manufacturing apparatus  100  may further include a flow meter  160 . The flow meter  160  is connected to the conduit  143 . Depending on the gas flow rate, the flow meter  160  having an appropriate flow range can be selected. The gas flow rate is measured by the flow meter  160 . The integrated value of the measurement values is considered as the total amount of discharged gas. The degree of pressure reduction in the exterior body  210  can be determined from the total amount of the discharged gas and the internal space of the exterior body  210 . When the manufacturing apparatus  100  includes two or more return pipes  140 , the flow meter  160  may be connected to each of the return pipes  140 . 
     Method of Manufacturing Electrochemical Cell 
       FIG.  5    is a schematic flowchart of a method of manufacturing an electrochemical cell according to this embodiment. In the following description, the “method of manufacturing an electrochemical cell according to this embodiment” will be briefly referred to as “the manufacturing method”. The manufacturing method includes (a) preparation of manufacturing apparatus, (b) preparation of workpiece, (c) placement of workpiece, (d) connection to return pipe, and (e) pressure reduction. The manufacturing method may further include, for example, (0) sealing, etc. The order of description in  FIG.  5    is mere formality. For example, the order of (a) preparation of manufacturing apparatus and (b) preparation of workpiece may be reversed. 
     (a) Preparation of Manufacturing Apparatus 
     The manufacturing method includes preparation of the manufacturing apparatus  100 . The details of the manufacturing apparatus  100  have been described above. 
     (b) Preparation of Workpiece 
     The manufacturing method includes preparing the workpiece  201  by enclosing the power generating elements  220  in the exterior body  210 . The workpiece  201  is so-called “pre-sealed cell”. For example, a bipolar cell module may be prepared as the workpiece  201 . The bipolar cell module includes a plurality of cells. The bipolar cell module may include, for example, 1 to 100 cells, or may include 10 to 50 cells, or may include 20 to 40 cells. Here, the “bipolar cell module” is simply referred to as “cell module”. 
       FIG.  6    is a schematic cross-sectional view of a first unit, a second unit, and a third unit in this embodiment. The first unit  251 , second unit  252 , and third unit  253  can constitute the cell module  250 . The first unit  251  and the third unit  253  are located at opposite ends in the stacking direction (Z-axis direction) The second units  252  are stacked between the first unit  251  and the third unit  253 . 
     The exterior body  210  is in the form of a sheet. The exterior body  210  may function as a current collector. The exterior body  210  may include at least one type selected from the group consisting of metal foil and metal foil laminate film. The metal foil laminate film can be formed by covering metal foil with a resin layer. The resin layer may include, for example, polypropylene (PP), polyethylene terephthalate (PET), etc. The metal foil may include at least one type selected from the group consisting of aluminum (Al) foil, stainless steel (SUS) foil, nickel (Ni) foil, titanium (Ti) foil, and copper (Cu) foil. For example, the metal foil may be plated. For example, the SUS foil may be plated with Ni. The exterior body  210  may include at least one type selected from the group consisting of Al foil and Al foil laminate film, for example. 
     The first unit  251  is prepared by forming the positive electrode layer  10  on one surface of one exterior body  210 . The positive electrode layer  10  contains a positive-electrode active material. The positive-electrode active material may include, for example, lithium nickel cobalt manganate and lithium iron phosphate. The positive electrode layer  10  may further contain, for example, a conductive material, binder, solid electrolyte, etc. 
     The negative electrode layer  20  is formed on one surface of the other exterior body  210 . The negative electrode layer  20  contains a negative-electrode active material. The negative-electrode active material may include, for example, graphite, silicon, silicon oxide, etc. The negative electrode layer  20  may further contain, for example, a conductive material, binder, solid electrolyte, etc. The third unit  253  is prepared by attaching the separator  30  to one surface of the negative electrode layer  20 . The separator  30  may include, for example, a porous film. The porous film may contain, for example, polyolefins, etc. The separator  30  may include, for example, a solid electrolyte layer. 
     The partition  230  is in the form of a sheet. The partition  230  may be formed of the same material as the exterior body  210  or may be formed of a different material than the exterior body  210 . The partition  230  may function as a current collector. The partition  230  may include, for example, metal foil. The partition  230  may include, for example, Al foil, etc. The positive electrode layer  10  is formed on one surface of the partition  230 . The negative electrode layer  20  is formed on the surface opposite to the surface on which the positive electrode layer  10  is formed. The positive electrode layer  10 , partition  230  and negative electrode layer  20  are combined to form a bipolar electrode. In the bipolar electrode, the separator  30  is attached to one surface of the negative electrode layer  20 , so that the second unit  252  is prepared. 
       FIG.  7    is a schematic cross-sectional view of the bipolar cell module in this embodiment. The first unit  251 , second unit  252 , . . . , second unit  252 , and third unit  253  are stacked together to form the cell module  250 . A set of the positive electrode layer  10 , separator  30 , and negative electrode layer  20  form the power generating element  220 . The power generating element  220  is sandwiched by two partitions  230 , so that the cell  200  is formed. At the opposite ends in the stacking direction, the power generating element  220  is sandwiched between the partition  230  and the exterior body  210 , so that the cell  200  is formed. Each of the cells  200  independently includes an internal space. 
     The exterior body  210  includes a sealing material  240 . For example, the sealing material  240  may be located so as to fill the periphery of the power generating elements  220 . The sealing material  240  may contain, for example, thermoplastic resin (such as PP). The injection ports  241  may be formed in a part of the sealing material  240 . Namely, the injection ports  241  may be formed in the exterior body  210 . The injection port  241  is a hole that can provide a liquid channel and a gas channel. The electrolyte may be injected into each cell  200  through the injection port  241 . Namely, the electrolyte may be injected into the exterior body  210  through the injection port  241 . 
       FIG.  8    is a schematic top view of the bipolar cell module in this embodiment. The planar shape of the cell module  250  may be selected as desired. The planar shape of the cell module  250  may be, for example, a rectangular shape. The sealing material  240  can be located so as to surround the perimeter of the exterior body  210 .  FIG.  7    is a cross-sectional view taken along line A-A in  FIG.  8   . 
     For example, a monopolar cell module may be prepared as the workpiece  201 . For example, the partition  230  may consist of two or more sheet-like members. In this case, the positive electrode layer  10  is formed on one surface of one of the sheet-like members of the partition  230 . The negative electrode layer  20  is formed on one surface of the other sheet-like member of the partition  230 . The monopolar cell is formed by superposing the one sheet-like member on the other sheet-like member so that the positive electrode layer  10  and the negative electrode layer  20  are opposed to each other. Between adjacent monopolar cells, the surface opposite to the surface on which the positive electrode layer  10  of the one sheet-like member included in one cell is formed is superposed on the surface opposite to the surface on which the negative electrode layer  20  of the other sheet-like member included in the other cell is formed, so that the monopolar cell module is formed. 
     (c) Placement of Workpiece 
     The manufacturing method includes placing the workpiece  201  in the chamber  110 . For example, the workpiece  201  into which the electrolyte has been injected can be placed in the chamber  110  (see  FIG.  4   ). 
     (d) Connection to Retum Pipe 
     The manufacturing method includes connecting the exterior body  210  and the first opening  141  (return pipe  140 ) (see  FIG.  4   ). For example, the injection port  241  may be connected to the first opening  141 . In the case of the cell module  250 , separate return pipes  140  can be connected to the injection ports  241  of the respective cells  200 . The exterior body  210  may be provided with a gas exhaust port (not shown), separately from the injection ports  241 . The gas exhaust port can function as a gas channel. 
     (e) Pressure Reduction 
     The manufacturing method includes reducing the pressure in the chamber  110 , thereby to reduce the pressure in the exterior body  210  via the return pipes  140  (see  FIG.  4   ). The pressure in the chamber  110  can be reduced by the pressure reducing device  130 . A pressure loss can be generated in the return pipe  140 . 
     The completion of the pressure reduction may be determined by the value indicated by the pressure gauge  150 , for example. When the value indicated by the pressure gauge  150  is equal to or lower than a reference value, for example, it may be determined that the target degree of pressure reduction has been reached. Namely, the pressure in the exterior body  210  may be reduced so that the value indicated by the pressure gauge  150  becomes equal to or lower than the reference value. 
     The completion of the pressure reduction may be determined by the flow meter  160 , for example. When the integrated value of the measurement values of the flow meter  160  (the total amount of discharged gas) is equal to or larger than the reference value after the pressure reducing device  130  is stopped, for example, it may be determined that the target degree of pressure reduction has been reached. When the target degree of pressure reduction has not been reached, the pressure reducing device  130  can be started again. 
     The reference values of the pressure and the flow rate can be set as appropriate according to the target degree of pressure reduction, the shape of the conduit  143 , etc. The target degree of pressure reduction may be, for example, 5 to 50 kPa. 
     (f) Sealing 
     The manufacturing method may include sealing the exterior body  210  under reduced pressure. Thus, the cell module  250  is sealed. The cell module  250  includes a plurality of cells  200 . For example, in the chamber  110 , the injection ports  241  may be sealed by the sealing devices  120 . For example, heat pressing melts and solidifies the sealing material  240 . The sealing material  240  can block the injection ports  241  (see  FIG.  7   ). The injection ports  241  may be blocked outside the chamber  110 , for example. 
     Experiment 
     In this experiment, the cell module  250  was prepared as the workpiece  201 . The cell module  250  was of bipolar type. The cell module  250  included five cells  200 . 
     EXAMPLE 
     In Example, the manufacturing apparatus  100  was used (see  FIG.  4   ). Separate return pipes  140  were respectively connected to the five cells  200 . The pressure in the chamber  110  was reduced, so that the pressure in the exterior body  210  was reduced via the retum pipes  140 . The exterior body  210  was sealed at the target degree of pressure reduction. Whether the target degree of pressure reduction has been reached was determined by using both the pressure gauges  150  and the flow meters  160 . 
     COMPARATIVE EXAMPLES 
       FIG.  9    is a conceptual diagram showing Comparative Example. In Comparative Example, the cell module  250  was placed in a chamber  310 . The pressure in the chamber  310  was reduced, so that the pressure in the exterior body  210  was reduced. As the pressure in the chamber  310  was reduced, the pressures in the five cells  200  were reduced all together. After the pressure reduction, the exterior body  210  was sealed. The required time of pressure reduction was the same as that of Example. For example, another pressure gauge may be provided at an exhaust port  311  of the chamber  310 , and whether the target degree of pressure reduction has been reached may be determined by use of the pressure gauge. 
     Evaluation 
     For each of the five cells  200 , the presence or absence of blockage of a gas channel was visually checked. When a bulge due to residual air was observed in any of the cells  200 , blockage of a gas channel was considered to have occurred. When no bulge due to residual air was observed in the cells  200 , it was considered that no blockage of a gas channel occurred. 
     In Example, blockage of a gas channel was not observed. In Example, the internal pressure is considered to be guaranteed with respect to all of the cells. 
     In Comparative Example, blockage of the gas channel was observed. In Comparative Example, the internal pressure is not considered to be guaranteed with respect to all of the cells. 
     The embodiment and Example are exemplary in all respects. The embodiment and Example are not restrictive. The technical scope of this disclosure encompasses all modifications within the meaning and scope of the claims and equivalents. For example, it is expected from the outset to extract any configurations from the embodiment and Example, and arbitrarily combine the configurations.