Patent Publication Number: US-2020303689-A1

Title: Case and method for manufacturing the same, method for inserting stacked body, and cell stack

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2019-54179, filed on Mar. 22, 2019, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present disclosure relates to a case and a method for manufacturing the same, a method for inserting a stacked body, and a cell stack. 
     In an all-solid-state battery, in order to advance its cell reaction, it is necessary to apply a pressure of, for example, about 0.8 to 40 MPa in the stacking direction of the layers constituting the all-solid-state battery. 
     Japanese Unexamined Patent Application Publication No. 2018-14286 discloses, as a restraining member that applies a restraining pressure in the stacking direction of a stacked body constituting an all-solid-state battery, a restraining member including two plate-like parts that sandwich both surfaces of the stacked body, a rod-like part that connects the two plate-like parts to each other, and an adjusting part that is connected to the rod-like part and adjusts the restraining pressure by using a screw structure or the like. 
     Japanese Unexamined Patent Application Publication No. 2018-107003 discloses a technique for hermetically housing a stacked body of an all-solid-state battery in an exterior can. In the technique disclosed in Japanese Unexamined Patent Application Publication No. 2018-107003, the stacked body of the all-solid-state battery is hermetically housed in the exterior can by putting the stacked body of the all-solid-state battery in a main body of the exterior can and then welding a lid constituting an upper surface part of the exterior can to the main body thereof. 
     Further, Japanese Unexamined Patent Application Publication No. 2017-212120 discloses, as a technique for improving in-plane uniformity of a restraining load applied to battery cells, a battery including a plurality of battery cells and spacers each of which is disposed between two respective adjacent battery cells, in which each of the spacers includes low spring-constant convex parts and high spring-constant convex parts that come into contact with a battery case. 
     SUMMARY 
     It has been known that an all-solid-state battery expands and contracts depending on the operating condition and/or the operating environment. The shape of the restraining member disclosed in Japanese Unexamined Patent Application Publication No. 2018-14286 and that of the exterior can disclosed in Japanese Unexamined Patent Application Publication No. 2018-107003 substantially do not change. Therefore, when the all-solid-state battery expands, an excessively high restraining pressure may occur. Since a high restraining pressure acts as a load on both the all-solid-state battery and the restraining member, at least one of them may deteriorate and hence the battery performance may deteriorate. Further, when the all-solid-state battery contracts, a satisfactory restraining pressure may not be applied. 
     The present disclosure has been made in order to solve the above-described problem and one of the objects thereof is to provide a case having elasticity corresponding to expansion and contraction of a stacked body housed therein and a method for manufacturing the same, a method for inserting the stacked body into the case, and a cell stack using the case. 
     A first exemplary aspect is a case configured to house a stacked body, including: 
     two opposed contact parts in contact with the stacked body; and 
     two spring structures connecting the two contact parts with each other. 
     According to the case having the above-described configuration, the spring structures deform according to a force applied to the contact parts. For example, when the housed stacked body expands, the spring structures expand, thus preventing the pressure applied to the stacked body from excessively increasing. On the other hand, when the housed stacked body contracts, the spring structures contract and hence the contact between the stacked body and the contact parts is maintained, thus preventing or reducing the decrease in the pressure applied to the stacked body. 
     The case may be made of fiber reinforced plastic. The case made of fiber reinforced plastic has a higher strength. 
     Another exemplary aspect is a method for manufacturing a case, including: winding a carbon fiber impregnated with a resin around a mold; and curing the resin. 
     According to the above-described method for manufacturing a case, it is possible to manufacture a case that is made of fiber reinforced plastic and hence has a high strength. 
     In the above-described method for manufacturing a case, the carbon fiber impregnated with the resin may be in the form of a sheet. The manufacturing time can be reduced by using the sheet-like carbon fiber. 
     In the above-described method for manufacturing a case, in the winding of the carbon fiber around the mold, the carbon fiber may be wound around the mold while being pressed to the mold so as to conform to a shape thereof. According to the above-described manufacturing method, the case can be easily manufactured even when the spring structures of the case have a concave part. 
     The above-described method for manufacturing a case may further include, after the winding of the mold around the mold, using the mold as a core mold and pressing the carbon fiber by using an outer mold. According to the above-described manufacturing method, the case can be easily manufactured even when the spring structures of the case have a concave part. 
     Further, a method for manufacturing a case according to an embodiment may include injection-molding the case from a resin composition containing a carbon fiber. 
     Another exemplary aspect is a method for inserting a stacked body into a case, including preparing the case and the stacked body, and inserting the stacked body into the case in a state where the spring structures of the case are forcibly expanded. By inserting the stacked body into the case in the above-described manner, the pressing from the case to the stacked body can be maintained even when the stacked body contracts from its initial state. 
     Further, another exemplary aspect is a method for inserting a stacked body into a case, including preparing the case and the stacked body, and inserting the stacked body into the case in a state where the stacked body is forcibly compressed in a stacking direction. By inserting the stacked body in the above-described manner, the pressing from the case to the stacked body can be maintained even when the stacked body contracts from its initial state. 
     Another exemplary aspect is a cell stack including: 
     a case including two opposed contact parts and two spring structures connecting the two contact parts with each other; and 
     a stacked body in which at least two all-solid-state fuel-cell unit cells are stacked, in which 
     the stacked body is inserted into the case and both ends of the stacked body in a stacking direction come into contact with the two contact parts, respectively, and 
     the two contact parts are pressed in the stacking direction of the stacked body. 
     According to the cell stack having the above-described configuration, the spring structures of the case expand or contract when each battery cell in the stacked body expands or contracts, so that the change in the pressure exerted from the case to the stacked body is reduced. As a result, the pressure applied to the stacked body is maintained within an appropriate range. 
     In the above-described cell stack, the all-solid-state fuel-cell unit cell may be a sulfide battery cell containing silicon in its negative electrode. According to the cell stack in accordance with an embodiment, even in the case of a sulfide battery cell containing silicon in its negative electrode, which has a relatively large expansion coefficient during the charging, it is possible to apply an appropriate pressure to the stacked body in response to expansion and contraction of the stacked body. 
     According to the present disclosure, it is possible to provide a case having elasticity corresponding to expansion and contraction of a stacked body housed therein and a method for manufacturing the same, a method for inserting the stacked body into the case, and a cell stack using the case. 
     The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing an example of a case according to an embodiment; 
         FIG. 2  is a perspective view showing an example of a cell stack according to an embodiment; 
         FIG. 3  is a front view of the cell stack shown in  FIG. 2 ; 
         FIG. 4  is a front view for explaining changes in the case when the stacked body has expanded; 
         FIG. 5  is a front view showing a modified example of the case; 
         FIG. 6  is a front view showing another modified example of the case; 
         FIG. 7  is a front view for explaining a first method for inserting a stacked body; and 
         FIG. 8  is a front view for explaining a second method for inserting a stacked body. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, the present disclosure will be explained through embodiments of the present disclosure. However, they are not intended to limit the scope of the present disclosure according to the claims. Further, the following descriptions and drawings are simplified as appropriate for clarifying the explanation. 
     Note that in the present disclosure, the term “curing” includes a case where resins are cured through a chemical reaction, a case where a resin and a crosslinking agent are cured through a chemical reaction, and a case where a resin is cured by cooling it to its glass transition temperature or lower without undergoing any chemical reaction. 
     Firstly, a structure of a case according to this embodiment will be described.  FIG. 1  is a cross section schematically showing a case according to this embodiment. In the following description, a three-dimensional (XYZ) coordinate system will be used to clarify the description. Note that the scale in each axial direction may be different from one another. 
     A case  10  shown in  FIG. 1  is a case for housing a stacked body. The case  10  includes two contact parts  11  that respectively come into contact with both ends of the stacked body in the stacking direction after the stacked body is housed in the case, and two spring structures  12  that connect the two contact parts  11  with each other. The two contact parts  11  are disposed in places where they are opposed to each other, and the two spring structures  12  are disposed so as to be opposed to each other. The two contact parts  11  and the two spring structures  12  constitute the cylindrical case  10  as a whole. A stacked body  20  is disposed inside the cylinder (see  FIG. 2 ). 
     The case  10  can be made of any material with which a required strength can be achieved. In the case of a cell stack, which will be described later, the stacked body repeatedly expands and contracts in a state where a high restraining pressure is applied to the stacked body. Therefore, the case is required to have a strength by which the case can withstand the repeated expansion and contraction. In this case, metal or fiber reinforced plastic (e.g., CFRP (Carbon Fiber Reinforced Plastic)) may be used as the material for the case. Further, in view of the strength, the contact parts  11  and the spring structures  12  of the case  10  may be integrally molded. Note that a method for manufacturing a case will be described later. 
       FIG. 2  is a perspective view showing an example of a cell stack according to this embodiment. Further,  FIG. 3  is a front view of the cell stack shown in  FIG. 2 . The two contact parts  11  are in contact with the end parts of the stacked body  20  in the stacking direction. The contact parts  11  are pressed in the stacking direction of the stacked body  20  by the restoring forces of the spring structures  12 . 
     In this embodiment, the spring structures  12  expand and contract according to forces of the spring structures  12  in the longitudinal direction (an X-axis direction), and generate the restoring forces. For example, in the case of metal or CFRP, since the elongation rate of the material itself is small, the spring structure  12  is achieved by using its shape. Specific examples of the shape of the spring structure  12  include a curved shape as shown in the example of  FIG. 1 , a bent shape as shown in an example of  FIG. 5 , and a corrugated shape (a concavo-convex shape) as shown in an example of  FIG. 6 . 
     The stacked body  20  is formed by stacking at least two plate-like members. Any type of plate-like members may be used as the above-described plate-like members. In this embodiment, since the case has elasticity corresponding to expansion and contraction of the stacked body, the all-solid-state battery cells  21  that expand or contract according to the operating environment can be suitably used as the plate-like members. In this embodiment, even sulfide battery cells containing silicon in their negative electrodes having a high expansion coefficient can be suitably used. 
     The stacked body  20  may be a stacked body composed of the all-solid-state battery cells  21 , or may be a stacked body further including end plates  22  at both ends in the stacking direction of the stacked body of the all-solid-state battery cells  21 . Examples of the material for the end plates  22  include metal, CFRP, etc. Further, the edges of the contact surfaces of the end plates  22  that come into contact with the case  10  may be chamfered (R-machining). By disposing such end plates, it is possible to prevent the load on the case  10  from being concentrated at parts of the case  10 . 
     Note that a distance between the contact parts  11  (hereinafter, also referred to as a major axis) is represented by “a”. In  FIG. 1 , “a 0 ” represents a distance between the contact parts  11  when no force is applied to the case  10  (hereinafter, also referred to as an initial state). 
     Further, a thickness of the stacked body in the stacking direction (hereinafter, also simply referred to as a thickness) is represented by “b”. In  FIG. 3 , “b m ” is a thickness of the stacked body  20  in a state where the stacked body  20  contracts as much as possible. 
     The major axis “a” of the case  10  in a state where the stacked body  20  is housed therein is equal to the thickness “b” of the stacked body  20 . As shown in  FIG. 3 , the case  10  according to this embodiment may press the stacked body even when the thickness of the stacked body has the minimum value “b m ”. Because of this feature, the distance “a 0 ” between the contact parts  11  in the initial state may be smaller than the minimum value “b m ” for the thickness of the stacked body. 
     The case  10  according to this embodiment may be designed while taking the thickness “b m ” of the stacked body to be housed into consideration. 
       FIG. 4  is a front view for explaining changes in the case when the stacked body has expanded. As shown in  FIG. 4 , the stacked body  20  housed in the case  10  may expand according to the operating environment. If the restraining member is not substantially deformed as in the case of Japanese Unexamined Patent Application Publication Nos. 2018-14286 and 2018-107003, the stacked body  20  cannot easily expand in the stacking direction and hence an excessively high restraining pressure may occur. 
     In contrast, when the stacked body  20  housed in the case  10  according to this embodiment expands, the spring structure  12  is forcibly expanded and the length of the major axis “a” of the case  10  increases to the after-expansion thickness “b” of the stacked body. As a result, the change in pressure is reduced and hence it is possible to prevent an excessively high restraining pressure from being applied to the stacked body  20 . 
     Next, two different methods for inserting a stacked body  20  into a case  10  according to this embodiment will be described. According to the below-shown insertion methods, a stacked body that satisfies a relation (Initial major axis “a 0 ” of case  10 )&lt;(Minimum thickness “b m ” of stacked body  20 ) can be inserted into the case. 
     The first insertion method is described with reference to  FIG. 7 .  FIG. 7  is a front view for explaining the first method for inserting a stacked body into a case. In  FIG. 7 , “b 0 ” indicates a thickness of the stacked body in its initial state. In the first insertion method, the spring structure  12  of the case  10  is forcibly expanded and the stacked body  20  is inserted into the case  10  in a state where the major axis “a” of the case  10  is increased to the thickness “b 0 ” or longer. According to this method, the stacked body  20  can be easily inserted. This insertion method can be suitably used, in particular, when the spring structure has a convex shape as shown in  FIG. 1 or 5 . However, in the case of a concavo-convex shape as shown in an example of  FIG. 6 , the case may not be forcibly expanded sufficiently. In such a case, the below-shown second insertion method may be used. 
     The second insertion method is described with reference to  FIG. 8 .  FIG. 8  is a front view for explaining a second method for inserting a stacked body into a case. In the second insertion method, the stacked body  20  is inserted into the case  10  in a state where the stacked body  20  is forcibly compressed to the thickness “a 0 ” or shorter by a compressing mechanism  23 . The insertion is completed by removing the compressing mechanism  23  after the insertion. According to this method, it is possible to insert the stacked body  20  into the case  10  even when the case  10  has a shape due to which the case  10  cannot be forcibly expanded with ease. 
     Further, the above-described first and second insertion methods may be combined with each other. That is, by forcibly expanding the case  10  and forcibly compressing the stacked body  20 , the stacked body  20  is inserted into the case  10  in a state where a relation (Thickness “b” of stacked body)&lt;(Major axis “a” of case) holds. According to this method, it is possible to insert the stacked body into the case without imposing an excessive load on the stacked-body side. 
     Next, an example method for manufacturing a case according to this embodiment is described. Firstly, a method for manufacturing a case made of fiber reinforced plastic will be described. After that, a method for manufacturing a case made of metal will be described. 
     The first manufacturing method includes winding carbon fibers impregnated with a resin around a mold, and curing the resin. 
     The resin with which the carbon fibers are impregnated may be a thermosetting resin or a thermoplastic resin. In the case of the thermosetting resin, a crosslinking agent (a thermosetting agent) is usually used in combination with the resin. 
     In this manufacturing method, a mold (a mandrel) for a case  10  is prepared. Separately from the preparation of the mold, carbon fibers are immersed in a thermosetting resin, or a thermoplastic resin fluidized by heating, so that the carbon fibers are impregnated with the resin. Next, the carbon fibers are wound around the mold by a filament winding method (an FW method) while rotating the mold so that the wound carbon fibers have a predetermined thickness. Next, the case  10  can be manufactured by curing the resin. According to the first manufacturing method, since long carbon fibers are wound around the case  10 , the case  10  having an excellent mechanical strength can be obtained. 
     The second manufacturing method is a method in which: sheet-like carbon fibers (prepreg) are prepared as carbon fibers impregnated with a resin; the sheet-like carbon fibers are wound around a mold by a sheet winding method (an SW method); and then the resin is cured. According to this method, the productivity is improved as compared to that of the first manufacturing method. 
     The first and second manufacturing methods can be suitably used, in particular, when the spring structure has a convex shape as shown in  FIGS. 1 and 5 . In contrast, in the case of a concavo-convex shape as shown in an example of  FIG. 6 , it is difficult to form concave parts  13 . 
     In a third manufacturing method, in the step of winding carbon fibers around a mold, the carbon fibers are wound around the mold while being pressed to the mold so as to conform to the shape thereof. According to this method, it is possible to suitably manufacture a case  10  of which spring structures have a concavo-convex shape. Specifically, in the above-described FW method or the SW method, a pressing mechanism is disposed at a place where the mold and carbon fibers come into contact with each other, and the carbon fibers are made to conform to the shape of the mold by pressing the carbon fibers onto the mold. In this manufacturing method, a local heating mechanism may be used so that the carbon fibers are not detached from the concave parts. When the resin is a thermoplastic resin, the thermoplastic resin is fluidized by heating the carbon fibers before they are brought into contact with the mold. Further, when the resin is a thermosetting resin, it is heated after the carbon fibers are brought into contact with the mold. As the heating means, for example, a laser, an IR lamp, etc. can be used. 
     In a fourth manufacturing method, after carbon fibers are wound around a mold by the FW method or the SW method, the mold is used as a core mold and the carbon fibers are pressed by using an outer mold. In this method, the carbon fibers enter the concave parts during the pressing. Therefore, the carbon fibers do not necessarily have to conform to the concave parts when they are wound around the mold. 
     According to the third or fourth manufacturing method described above, it is possible to suitably manufacture a case having a concavo-convex shape. 
     Further, a fifth manufacturing method is, for example, a method for injection-molding a case from a resin composition containing carbon fibers. Although the strength of the case is slightly poorer than those of the above-described first to fourth manufacturing methods because the length of the carbon fibers is short, the productivity is excellent. Therefore, this manufacturing method can be adopted according to the use of the case. 
     Further, in the case of manufacturing a case made of metal, firstly, a metal plate having a predetermined size is prepared. Then, after an external shape of the case is formed by pressing the metal plate, the pressed metal plate is formed into a cylindrical shape by welding end parts thereof to each other. 
     Next, a cell stack according to this embodiment is described with reference to  FIG. 2 . A cell stack  100  according to this embodiment includes a case  10  including two opposed contact parts  11  and two spring structures  12  connecting the two contact parts  11  with each other; and a stacked body  20  in which at least two all-solid-state battery cells  21  are stacked, in which: the stacked body  20  is inserted into the case  10  and both ends of the stacked body  20  in a stacking direction come into contact with the two contact parts  11 , respectively; and the two contact parts  11  are pressed in the stacking direction of the stacked body  20 . 
     According to the cell stack  100  in accordance with this embodiment, the spring structures  12  of the case  10  expand or contract when each battery cell  21  in the stacked body  20  expands or contracts, so that the change in the pressure exerted from the case  10  to the stacked body  20  is reduced. As a result, the pressure applied to the stacked body is maintained within an appropriate range (e.g., about 0.8 to 40 MPa). This embodiment can be suitably applied to a sulfide battery cell containing silicon in its negative electrode having a high expansion coefficient. 
     From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.