Patent Publication Number: US-2023155240-A1

Title: Battery module

Description:
This application is based on and claims the benefit of priority from Japanese Patent Application No. 2021-186321, filed on 16 Nov. 2021, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a battery module. 
     Related Art 
     In order to have a battery module serving as the power source of an electric vehicle or the like function appropriately, it is necessary to apply pressure in the lamination direction so as to pressurize the laminated battery cells. In particular, in a solid-state secondary battery made using a solid electrolyte as the electrolyte, it is necessary to apply somewhat large pressure compared to a liquid secondary battery made using a liquid electrolyte. As the pressurizing method, there is a method of joining an end plate and side plate at both end faces and lateral faces of a laminate, in a state preloading the laminate from both end faces of the laminate of battery cells. 
     In the above-mentioned pressurizing method, it is necessary to perform greater preloading than the target pressure on the laminate. In addition, since there is variation in the elastic modulus in the lamination direction of the laminate, there is a problem in that the residual load becomes non-uniform. Furthermore, as a result of the strength and rigidity of the end plate and side plate becoming necessary, there is also a problem in that the space of the member enlarges, and the occupancy of the battery cells in the battery module reduces. As another pressurizing method, technology which sandwiches the laminate by a pair of pressure plates, and pressurizing the pair of pressure plates by connection rods is disclosed (for example, refer to Patent Document 1).
     Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2008-293771   

     SUMMARY OF THE INVENTION 
     The technology disclosed in Patent Document 1 arranges a plurality of oblong lithium ion batteries on the same plane, and connects a pair of pressure plates by a central connection rod and peripheral connection rods. The pair of pressure plate are pressurized so as to approach each other, by fastening threaded members installed at both ends of the peripheral connection rods. However, in the above-mentioned technology, since displacement in the cell lamination direction arises upon the lithium ion battery expanding or contracting accompanying discharge/charge, it is difficult to fix the pressure plate of the lamination direction end of the lithium ion battery laminate to the case, during use in a lithium ion battery. 
     The present invention has been made taking account of the above, and has an object of providing a battery module which can appropriately pressurize the laminate, absorb displacement of the applied load accompanying charge and discharge of the laminated battery cells during use of the lithium ion battery, and fix pressure plates at ends in the lamination direction of the lithium ion battery laminate to a case. 
     A first aspect of the present invention relates to a battery module including: a cell laminate in which a plurality of battery cells having a power generation element and external body covering the power generation element are laminated; a fastening member which fastens the cell laminate; end plates disposed at both ends in a lamination direction of the cell laminate; a fastening nut which fastens the fastening member and the end plate at an outer side of the cell laminate; a stay fastened by the fastening nut; and a case accommodating the cell laminate, in which the cell laminate is fixed to the case by the stay. 
     According to the first aspect of the present invention, it is possible to provide a battery module which can absorb displacement accompanying expansion and contraction of cell laminates by way of stays. 
     According to a second aspect of the present invention, in the battery module as described in the first aspect, rigidity in the lamination direction of the stay is lower than rigidity in a direction orthogonal to the lamination direction of the stay. 
     According to the second aspect of the present invention, it is possible absorb displacement accompanying expansion and contraction of cell laminates by way of stays. 
     According to a third aspect of the present invention, in the battery module as described in the first or second aspect, the stay has a first sloped part which slopes in a widening direction downwards when viewing from the lamination direction. 
     According to the third aspect of the present invention, it is possible absorb displacement accompanying expansion and contraction of cell laminates by way of stays. 
     According to a fourth aspect of the present invention, in the battery module as described in any one of the first to third aspects, the stay has a second sloped part which slopes downward towards an outer side in the lamination direction of the cell laminate, from a fastening part with the fastening nut. 
     According to the fourth aspect of the present invention, it is possible absorb displacement accompanying expansion and contraction of cell laminates by way of stays. 
     According to a fifth aspect of the present invention, in the battery module as described in any one of the first to fourth aspects, a plurality of the fastening members is arranged, and the stay includes a plurality of holes through which a part of the fastening member inserts, and is formed integrally. 
     According to a fifth aspect of the present invention, it is possible to more precisely design the rigidity of the stay, and possible to improve the reliability of the battery module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a partial cross-sectional view showing a battery module according to a first embodiment of the present invention shown in a side view; 
         FIG.  2    is an exploded view showing the structure of the battery module in  FIG.  1   ; 
         FIG.  3    is a view showing principle parts in  FIG.  2    to be enlarged; 
         FIG.  4    is a partial cross-sectional view showing a battery module according to a second embodiment of the present invention in a top view; 
         FIG.  5    is a partial cross-sectional view showing the battery module in  FIG.  4    in a side view; 
         FIG.  6    is a drawing viewing the battery module in  FIG.  4    from one lamination direction side; 
         FIG.  7    is a drawing viewing the battery module in  FIG.  4    from one lamination direction side; 
         FIG.  8    is a drawing viewing a stay of the battery module in  FIG.  7    from a lateral face; 
         FIG.  9    is a drawing viewing the overall configuration of a stay of the battery module in  FIG.  7    from one lamination direction side; 
         FIG.  10    is a view showing a modified example of a stay of the battery module in  FIG.  7   ; and 
         FIG.  11    is a drawing viewing the stay in  FIG.  10    from a lateral face. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     A battery module according to a first embodiment of the present invention will be explained by referencing  FIGS.  1  to  3   . In each of the drawings shown below, the same reference symbols are assigned to identical portions and corresponding portions. 
     (Cell Laminate) 
     A battery module  10  according to a first embodiment has cell laminates  11   a ,  11   b  in which a plurality of battery cells  1  having a power generation element  2  and external body  3  covering the power generation element  2  are laminated, as shown in  FIG.  1   . The power generation element  2 , for example, is a solid-state battery made by a positive electrode layer, solid electrolyte layer and negative electrode layer being repeatedly laminated in this order. In the following explanation, the power generation element  2  is explained as a solid-state battery; however, the power generation element  2  may be an electrolytic solution-type battery including a liquid electrolyte. The battery module  10 , in addition to the above, has a fastening member  4 , center fixing member  5 , end plates  6 , pressure plates  7 , stay  8  and fastening nuts f 1 . 
     As the materials constituting the positive electrode layer, solid electrolyte layer and negative electrode layer serving as the power generation element  2 , it is possible to use known materials as materials constituting a solid-state battery. 
     The external body  3  accommodates the power generation element  2  inside. The external body  3  is not particularly limited; however, it is preferably a laminate film. By configuring the external body  3  with a laminate film, it is possible to reduce the volume of the external body  3 , and possible to improve the energy density of the battery module. The laminate cell, for example, has a multi-layer structure in which a heat bonding resin layer such as polyolefin is laminated on the outside of a metal layer consisting of aluminum, stainless steel (SUS) or the like. As the external body  3 , it is possible to use a metallic can. 
     The plurality of battery cells  1  constitute the cell laminates  11   a ,  11   b  by a plurality thereof being laminated in the same direction (lamination direction L 1  shown in  FIG.  1   ) as the lamination direction of the electrode layers constituting the power generation element  2 . The cell laminates  11   a ,  11   b  are retained to be compressed by the end plates  6  from both end sides in the lamination direction L 1 . In the plurality of battery cells  1 , as shown in  FIG.  2   , at the central part in a vertical-direction cross section along the lamination direction L 1 , first through holes h 1  (hereinafter, may be described simply as “through hole h 1 ”) are respectively provided in a direction passing through each electrode layer constituting the power generation element  2 . The through hole h 1  is a hole part passing through the battery cell  1  with the external body  3 . Although the shape of the through hole h 1  is not limited, it preferably has a circular cross-sectional shape similarly to the cross-sectional shape of the fastening member  4  described later. As the formation method of the through hole h 1 , for example, it is possible to form by forming a laminate with the through hole in each of the respective electrode layers and solid-state electrolyte layers constituting the power generation element  2 , enclose the above-mentioned laminate in the external body  3 , join external bodies  3  at locations corresponding to the above-mentioned through hole by welding of the laminate film, and forming a through hole one size smaller than the above-mentioned through hole in the inner circumferential side of the above-mentioned through hole in the external body  3  by punch blanking or the like. 
     So that the through hole h 1  passes through each, the plurality of battery cells  1  are arranged, and the fastening member  4  fastening the cell laminates  11   a ,  11   b  is arranged in the through hole h 1 . A pair of end plates  6  are fastened in a direction sandwiching the gap therebetween by the fastening members  4 . It is thereby possible to pressurizing the cell laminates  11   a ,  11   b  without initial pressurizing (preloading). 
     (Fastening Member) 
     The fastening member  4  has a shaft forming the main body, a male screw part  41  formed at both ends of the shaft, an expanding diameter part  42  formed at the central part in the axial direction, and a locking part  43  arranged between the male screw part  41  and shaft. The expanding diameter part  42  is arranged within a second through hole h 2  of a central fixing member  5  described later. The fastening member  4  has the shaft inserted in the through hole h 1  of the cell laminates  11   a ,  11   b , the male screw parts  41  extend from the hole parts h 3 , h 4 , h 5  provided in the end plate  6 , pressure plate  7  and stay  8 , respectively, at both ends of the cell laminates  11   a ,  11   b , and are threaded with the fastening nuts f 1 . The cross-sectional shape of the fastening member  4  is preferably circular from the viewpoint of making the cross-sectional stress uniform. 
     By inserting the fastening member  4  in the through hole h 1  provided at the central part of the lamination surface of the cell laminates  11   a ,  11   b , and pressurizing the cell laminates  11   a ,  11   b  using the pair of end plates  6  and fastening nuts f 1 , it is possible to make the surface pressure applied to the cell laminates  11   a ,  11   b  uniform. In addition, an outer frame fixing the cell laminate becomes unnecessary, and it is possible to improve the volume ratio of the power generation element  2  in the battery module  10 ; therefore, it is possible to improve the energy density of the battery module  10 . It should be noted that, in the present invention, the fastening member  4  is not limited to being inserted in the through hole h 1  provided at the central part of the lamination surface of the cell laminate. The fastening member  4  may be arranged at a location other than the central part of the lamination surface of the cell laminate. 
     The locking part  43 , as shown in  FIG.  1   , is arranged inside of the hole part h 3  formed in the end plate  6 , which is in the vicinity of the fastening nut f 1 . The locking part  43 , for example, is a member having a polygonal shape or sawtooth shape in a cross-sectional view. The locking part  43  may be formed integrally with the fastening member  4 , or may be configured by a separate member from the fastening member  4 , and adhered to the fastening member  4 . 
     The locking part  43  has a function of accepting the torsional stress in the axial direction of the fastening member  4 , by engaging in the hole part h 3  formed in the end plates  6 , and having an in-plane shape corresponding to the cross-sectional shape of the locking part  43 . The torsional stress upon screwing the male screw part  41  with the fastening nut f 1  is only transferred to the male screw part  41  of the fastening member  4  and the locking part  43 , and is not transferred to the inner side of the cell laminates  11   a ,  11   b  from the locking part  43 . Therefore, it is possible to prevent slack of the fastening nut f 1  during use of the battery module  10  over a long period. In addition, by the tightening of the fastening nut f 1 , it is possible to apply larger axial force to the fastening member  4 . In addition to the above, it becomes possible finely adjust the surface pressure applied to the cell laminates  11   a ,  11   b  according to the tightening degree of the fastening nut f 1 . 
     The diameter of a cross section in an axial direction of the shaft  44  of the fastening member  4  shown in  FIG.  2    can be designed according to the surface pressure to be applied to the cell laminates  11   a ,  11   b . By reducing the above-mentioned diameter, since the stress per unit area applied to the shaft  44  increases, it becomes possible to decrease the elastic modulus maintaining the distance between the end plates  6  in the compressing direction, and the variation width of surface pressure to be applied to the cell laminates  11   a ,  11   b  can be decreased. 
     (Central Fixing Member) 
     The central fixing member  5  is a member arranged between the plurality of battery cells  1 , and is a member arranged at the center in the lamination direction L 1  of the battery module  10 , as shown in  FIG.  1   . The surface pressure applied to the cell laminates  11   a ,  11   b  is made uniform in the lamination direction L 1 , by the central fixing member  5 . The central fixing member  5  only receives force by being compressed in the lamination direction L 1 ; therefore, it is possible to configure by a light-weight metal such as aluminum, for example. 
     The central fixing member  5  is provided with the second through hole h 2  (hereinafter may be described simply as “through hole h 2 ”) in which the diameter expanding part  42  of the fastening member  4  is arranged. As shown in  FIG.  2   , the central fixing member  5  is arranged so that the through hole h 2  communicates with the through hole h 1 . The through hole h 2  may be able to fix at a vertical face relative to the axial direction by the inlay fixing or the like with the diameter expanding part  42 . It thereby becomes possible to position and fix the central fixing member  5  and fastening member  4 , and it is possible to easily arrange the central fixing member  5  at the center in the lamination direction L 1  of the battery module  10 . 
     (End Plate) 
     The end plates  6  are a pair of members arranged at both ends in the lamination direction L 1  of the cell laminates  11   a ,  11   b . In the end plates  6 , a hole part h 3  into which the fastening member  4  can be inserted is formed, as shown in  FIG.  2   . The fastening member  4  is inserted in the hole part h 3 , and fastened by the fastening nut f 1 , whereby the end plates  6  clamp and retain the cell laminates  11   a ,  11   b.    
     The end plate  6  has a sloped part  61  and a load point  62 , as shown in  FIG.  3   . The load point  62  is a surface continuous with the sloped part  61 , and is a substantially vertical surface relative to the lamination direction L 1 . The end plate  6  abuts the pressure plate  7  at a plurality of the load points  62 . The surface pressure applied to the cell laminates  11   a ,  11   b  from the end plates  6  is thereby made uniform relative to the lamination plane. 
     (Pressure Plate) 
     The pressure plates  7  are a pair of members fastened by the fastening nut f 1  together with the end plate  6 . The pressure plate  7  is arranged at the outer side in the lamination direction L 1  of the end plate  6  at both ends in the lamination direction L 1  of the cell laminates  11   a ,  11   b . The pressure plate  7  is an elastically deformable member, and is a member of leaf spring shape made of metal, for example. The hole part h 4  into which the fastening member  4  can be inserted is formed in the pressure plate  7 , as shown in  FIG.  2   . By the fastening member  4  being inserted in the hole part h 4 , and fastened by the fastening nut f 1 , the axial force from tightening of the fastening nut f 1  is transferred to the end plate  6  via the pressure plate  7 . 
     The pressure plate  7  has a sloped part  71  and load point  72 , as shown in  FIG.  3   . The sloped part  71  is a surface sloping along the sloped part  61 . The load point  72  is a surface continuous with the sloped part  71 , and is a substantially vertical surface relative to the lamination direction L 1 . 
     (Stay) 
     The stays  8  are a pair of members fastened by the fastening nut f 1  together with the end plate  6  and pressure plate  7 . The stay  8  is a member for fixing the cell laminates  11   a ,  11   b . The stay  8  is arranged at the outer side in the lamination direction L 1  of the pressure plate  7 , at both ends in the lamination direction L 1  of the cell laminates  11   a ,  11   b . In the stay  8 , as shown in  FIG.  2   , a hole part h 5  into which the fastening member  4  can be inserted is formed. The fastening member  4  is inserted into the hole part h 5 , and fastened by the fastening nut f 1 . By fixing the stay  8  using the fastening member  4 , it is possible to decrease the installation space and parts count of the stay  8 . The details of the configuration of the stay  8  will be explained in the following second embodiment. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be explained by referencing  FIGS.  4  to  9   . In the following explanation, the same reference symbols are attached in the drawings for configuration which are similar to the above first embodiment, and explanations thereof may be omitted. 
       FIG.  4    is a top view of a battery module  100  according to the second embodiment. The battery module  100  is a module made into a larger size battery module by combining the battery modules  10 . As shown in  FIGS.  4  and  5   , in the plurality of battery cells  1   a , a plurality of hole parts are formed at the central part in a vertical direction cross section along the lamination direction L 1 , and a plurality of fastening members  4  (three in the present embodiment) are respectively inserted and arranged. The arranged number of fastening members  4  is not limited as described above, and may be two or four, for example. The battery module  100  includes a case  9  accommodating the laminate of the battery cells  1   a , as shown in  FIGS.  5  and  6   . 
     A central fixing member  5   a  according to the present embodiment has a plurality of the through holes h 2  into which the fastening member  4  is inserted. In addition, the central fixing member  5   a  has a connection part  51  with the case  9 . The fastening bolt f 2  is threaded to the connection part  51 , and the central fixing member  5   a  and case  9  are connected. It is thereby possible to further raise the rigidity of the laminate of the battery cells  1   a.    
     Three of the pressure plates  7  according to the present embodiment are arranged in a direction L 2 , which is a direction orthogonal to the lamination direction L 1 , as shown in  FIG.  6   . In addition, the load points  72   a ,  72   b ,  72   c  and  72   d  at which the pressure plate  7  abuts the end plate  6  are arranged at the four symmetrical positions with the fastening nut f 1  as reference, in the present embodiment. 
     (Stay) 
     The stay  8   a  according to the present embodiment has a connection part  83  with the case  9  at both ends in the direction L 2  orthogonal to the lamination direction L 1  and/or between fastening members  4 , as shown in  FIGS.  6  and  7   . The fastening bolt f 3  is threaded to the connection part  83 , and the stay  8   a  and case  9  are connected. It is thereby possible to further raise the rigidity of the laminate of the battery cells  1   a . In addition, the stay  8   a  is configured by an elastically deformable member, and the rigidity in the lamination direction L 1  is set to be lower than the rigidity in a direction orthogonal to the lamination direction L 1 . The stay  8   a  can thereby absorb the displacement accompanying expansion and contraction of the laminate of the battery cells  1   a . Therefore, irrespective of the battery cells  1   a  expanding and contracting during use of the battery module  10 , it is possible to fix the pressure plate  7  to the case  9  via the stay  8   a.    
       FIG.  7    is a drawing viewing part of the stay  8   a  arranged at the lamination end side of the battery module  100  from the lamination direction L 1 , which is the same viewpoint as  FIG.  6   . The stay  8   a  has a first sloped part  81  which slopes in a direction widening downward, viewing from the lamination direction L 1 , as shown in  FIG.  7   . In addition, as shown in  FIG.  8   , the stay  8   a  has a second sloped part  82  which slopes downwards toward the outer side in the lamination direction L 1  from the hole part h 5 , which is a fastening part with the fastening nut f 1 . According to the above configuration, the stay  8   a  can absorb the displacement accompanying expansion and contraction of the laminate of the battery cells  1   a , by bending deformation in the lamination direction L 1 . On the other hand, the rigidity relative to the lamination surface of the battery cell  1   a  rises, and the laminate of battery cells  1   a  can be preferably fixed. 
       FIG.  9    is a drawing viewing the entirety of the stay  8   a  used in the battery module  100 , in the same viewpoint as  FIG.  6   . The stay  8   a  is not provided independently according to the number of fastening members  4  and hole parts h 5 , and is preferably the stay  8   a  integrally molded irrespective of the number of fastening members  4  and hole parts h 5 , as shown in  FIG.  9   . By integrally molding the stay  8   a , it is possible to make the connection part  83   a  with the case  9  provided between each hole part h 5  into a single unit. Therefore, compared to a case of providing the stay  8   a  independently, then superimposing connection parts  83   a  and jointly tightening by the fastening bolt f 3 , a level difference will not arise in the connection part  83   a . Therefore, since it is possible to more precisely design the rigidity of the stay  8   a  for absorbing displacement accompanying the expansion and contraction of each cell laminate, the reliability of the battery module  100  can be improved. In addition, the parts count of the battery module  100  can be reduced, and the assembly workability can be improved. Furthermore, by the fastening member  4  being inserted in the plurality of hole parts h 5 , and fastening by the fastening nut f 1 , since similar effects as the locking part  43  of the above-mentioned fastening member  4  are obtained, it is possible to configure the fastening member  4  without providing the locking part  43 . 
     Third Embodiment 
       FIG.  10    is a drawing viewing part of a stay  8   b  according to the third embodiment in the same viewpoint as  FIG.  7   . The stay  8   b  can be applied to a battery module similar to the battery module  100  in which the stay  8   a  is applied. 
     The stay  8   b , similarly to stay  8   a , has the connection part  83  with the case  9 , at both ends in the direction L 2  orthogonal to the lamination direction L 1  and/or between fastening members  4 . The fastening bolt f 3  is threaded to the connection part  83 , and the stay  8   b  and case  9  are connected. In addition, as shown in  FIG.  10   , it has a first sloped part  81   a .  FIG.  11    is a drawing viewing the stay  8   b  from a direction along the lamination direction L 1 , similarly to  FIG.  8   . The stay  8   b  has a second sloped part  82  similarly to the stay  8   a.    
     The stay  8   b  has a hole part h 6 , as shown in  FIG.  10   . By providing the hole part h 6  in the stay  8   b , the rigidity in the lamination direction L 1  of the stay  8   b  is easily designed. This is because, by adjusting the size of the hole part h 6 , it is possible to adjust the rigidity in the lamination direction L 1  of the stay  8   b . In addition to the above, it is possible to increase the deflection allowance in the lamination direction L 1 , by the stay  8   b  having the hole part h 6 . For this reason, it is possible to more preferably absorb displacement accompanying expansion and contraction of the laminate of the battery cells  1   a . The shape of the hole part h 6  in  FIG.  10    has an opening of substantially square shape; however, the shape of the hole part h 6  is not particularly limited. 
     Although preferred embodiments of the present invention have been explained above, the present invention is not to be limited to the above embodiments, and appropriate modifications are possible. 
     The above embodiments explain the locking part  43  as engaging in the hole part h 3  having the in-plane shape corresponding to the cross-sectional shape of the locking part  43  formed in the end plate  6 , for example. It is not limited to the above. The locking part  43  may be provided at an end of the male thread part  41 , and fix the end of the male thread part  41 . 
     In the above embodiments, the stays  8 ,  8   a  are explained as having formed therein the hole part h 5  into which the fastening member  4  can be inserted, and is fastened by the fastening nut f 1 . It is not limited to the above. The stay of the present invention may be connected at one location or a plurality of locations with the pressure plate. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
         
           
               10 ,  100  battery module 
               1 ,  1   a  battery cell 
               11   a ,  11   b  cell laminate 
               2  power generation element 
               3  external body 
               4  fastening member 
               43  locking part 
               5 ,  5   a  central fixing member 
               51  connection part 
               6  end plate 
               8  stay 
               81  first sloped part 
               82  second sloped part 
               9  case 
             f 1  fastening nut 
             h 1  first through hole 
             h 2  second through hole 
             h 5  hole part 
             L 1  lamination direction