Patent Publication Number: US-2023163426-A1

Title: Battery cell

Description:
This application is based on and claims the benefit of priority from Chinese Patent Application No. 202111412042.2, filed on 25 Nov. 2021, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to battery cells. 
     Related Art 
     Conventionally, secondary batteries such as a lithium-ion secondary battery which have a high energy density are widely spread. In recent years, in terms of improving energy efficiency, reducing negative impacts on the global environment by increasing the share of renewable energy and reducing CO 2 , the use of secondary batteries has been considered for various applications such as in-vehicle use. A secondary battery has a structure in which a solid electrolyte (separator) is provided between a positive electrode and a negative electrode and which is filled with a liquid or solid electrolyte (electrolytic solution). 
     In a lithium-ion secondary battery using any one of a liquid electrolyte and a solid electrolyte, a positive electrode including a positive electrode current collector, the electrolyte and a negative electrode including a negative electrode current collector are repeatedly stacked. Then, in each of the positive electrode and the negative electrode, a plurality of current collectors are drawn in the same direction, are then bundled and are thereafter connected to a lead terminal (see, for example, Patent Document 1). 
     When as in a technique disclosed in Patent Document 1, a plurality of current collectors are bundled and connected to a lead terminal, since the foil-shaped current collectors are bent to generate stress, the current collectors may be damaged or cut by vibrations or the like. Hence, it is considered that the current collectors are individually brought into contact with the lead terminal which is extended in the stacking direction of the current collectors. 
     Examples of a technique for bringing the current collectors into contact with the lead terminal which is extended in the stacking direction of the current collectors include a method of collecting the bundled current collectors at one end portion in the stacking direction, extending the lead terminal to the portion alone and bringing the lead terminal into contact with the current collectors (see, for example, Patent Document 2). 
     Patent Document 1: Japanese unexamined Patent Application, Publication No. 2008-159592 
     Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2010-027494 
     SUMMARY OF THE INVENTION 
     In a technique disclosed in Patent Document 2, as in the technique disclosed in Patent Document 1, a plurality of current, collectors are collected to be bent by an amount corresponding to a coating thickness, with the result that the current collectors may be damaged or cut. Disadvantageously, if a terminal is inserted into holes formed in current collectors, and an axial force is only generated by a rivet to press the current collectors to the terminal, only an end surface of the current collectors is brought into contact with the terminal, with the result that it is likely that conductivity between the current collectors and the terminal cannot be reliably ensured. 
     The present invention is made in view of the problem described above, and an object thereof is to provide a battery cell which can prevent current collectors from being damaged or cut and can reliably ensure conductivity between the current collectors and a terminal. 
     (1) The present invention relates to a battery cell which includes: a power generation element that includes a plurality of current collectors; and a terminal that is extended in a stacking direction of the current collectors and is electrically connected to the current collectors, and in which the terminal is inserted through holes formed in the current collectors, bent portions are formed at abutment parts of the current collectors that abut on the terminal and a distance holder is arranged between the current collectors and around the abutment parts. 
     According to the invention of (1), it is possible to provide a battery cell which can prevent the current collectors from being damaged or cut and can reliably ensure conductivity between the current collectors and the terminal. 
     (2) The battery cell described in (1) which includes: an exterior that includes a hole into which the terminal is inserted, and in which an end portion of the terminal in the stacking direction is extended outside the exterior. 
     According to the invention of (2), an electrode for the battery cell can be provided at the end portion in the stacking direction of the current collectors. 
     (3) The battery cell described in (2) in which a bent portion is formed at an abutment part of an end surface of the hole in the exterior that abuts on the terminal. 
     According to the invention of (3), it is possible to enhance the sealing property of the exterior. 
     (4) The battery cell described in (3) in which the amount of bending in the bent portion of the exterior is smaller than the amount of bending in one of the bent portions of one of the current collectors. 
     In the invention of (4), the entry of the exterior between the current collector and the terminal can be prevented, and thus it is possible to reliably bring the current collector into contact with the terminal. 
     (5) The battery cell described in (3) or (4) in which one of the end portions of the terminal in the stacking direction that, is arranged outside the exterior is larger in diameter than the terminal arranged within the exterior, and in which a lead terminal or a gap filler is arranged between the end portion of the terminal and the exterior. 
     According to the invention of (5), a current, is easily extracted from the battery cell, and it is possible to enhance the sealing property of the exterior. 
     (6) The battery cell described in (5) in which the end portion of the terminal and the lead terminal or the second distance holder are fitted together with any one of a concavo-convex portion, a screw shape and a rivet. 
     According to the invention of (6), it is possible to further enhance the sealing property of the exterior. 
     (7) The battery cell described in (1) which includes the exterior that stores the power generation element and the terminal therewithin, and in which the exterior includes a conductive layer on an abutment surface that abuts on a stacking end surface of the power generation element. 
     According to the invention of (7), it is possible to reduce the resistance of the battery cell and to enhance airtightness. 
     (8) The battery cell described in (7) in which the exterior includes a resin layer, that covers an outer perimeter of the conductive layer on the abutment surface, and in which the conductive layer on the abutment surface is larger in area than the resin layer on the abutment, surface. 
     According to the invention of (8), it is possible to reduce the resistance of the battery cell and to enhance airtightness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a top view of a battery cell according to a first, embodiment of the present invention; 
         FIG.  2    is a cross-sectional view taken along line A-A in  FIG.  1   ; 
         FIG.  3    is a cross-sectional view taken along line B-B in  FIG.  1   ; 
         FIG.  4    is a cross-sectional view of a battery cell according to a second embodiment of the present invention; and 
         FIG.  5    is a schematic view when an exterior in the second embodiment of the present invention is seen from an abutment surface. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described below with reference to drawings. The details of the present invention are not limited to the following embodiments. Although in the following embodiments, a battery cell is described as a lithium-ion solid secondary battery, the present invention is not limited to the configuration described above, and the present invention can also be applied to solid secondary batteries other than the lithium-ion secondary battery. 
     First Embodiment 
     Overall Configuration of Battery Cell 
     As shown in  FIGS.  1  to  3   , a battery cell  1  according to the present embodiment includes a negative electrode lead terminal  20  and a positive electrode lead terminal  30  serving as lead terminals, and an exterior  6 . As shown in  FIGS.  2  and  3   , the battery cell  1  includes, as a power generation element, a multilayer in which negative electrode current collectors  22 , negative electrode active material layers  23 , solid electrolyte layers  4 , positive electrode current collectors  32  and positive electrode active material layers  33  stored within the exterior  6  are stacked. As shown in  FIG.  2   , a plurality of negative electrode current collectors  22  are drawn from the end surface of the multilayer in the same direction to individually abut on a negative electrode terminal  21   a  or  21   b.  Likewise, as shown in  FIG.  3   , a plurality of positive electrode current collectors  32  are drawn from the end surface of the multilayer in the same direction to individually abut on a positive electrode terminal  31   a  or  31   b.    
     In the multilayer serving as the power generation element, on both surfaces of each of the negative electrode current collectors  22 , the negative electrode active material layers  23  are stacked, and on the surfaces of each of the positive electrode current collectors  32 , the positive electrode active material layers  33  are stacked. These may be separate layers or the current collectors and the active material layers may be integrally formed. The solid electrolyte layer  4  is stacked between the negative electrode current collector  22  and the negative electrode active material layer  23 , and between the positive electrode current collector  32  and the positive electrode active material layer  33 . A plurality of stacking units described above may be repeatedly stacked, and the number of layers stacked is not particularly limited. 
     Negative Electrode Current Collector 
     The negative electrode current collector  22  is not particularly limited, and a known current collector which can be used for the negative electrode of a secondary battery can be applied. As the negative electrode current collector  22 , a foil-shaped metal foil is used. Examples thereof include metal foils such as a stainless steel (SUS) foil and a copper (Cu) foil. 
     Negative Electrode Active Material Layer 
     The negative electrode active material of the negative electrode active material layer  23  is not particularly limited, and a known material used as a negative electrode active material for a secondary battery can be applied. The composition thereof is also not particularly limited, and may include a solid electrolyte, a conductivity aid, a binder and the like. Examples of the negative electrode active material include metal lithium, lithium alloys such as a Li—Al alloy and a Li—In alloy, lithium titanates such as Li 4 Ti 5 O 12 , carbon materials such as carbon fiber and graphite and the like. 
     Positive Electrode Current Collector 
     The positive electrode current collector  32  is not particularly limited and a known current collector which can be used for the positive electrode of a secondary battery can be applied. As the positive electrode current collector  32 , a foil-shaped metal foil is used. Examples thereof include metal foils such as a stainless steel (SUS) foil and an aluminum (Al) foil. 
     Positive Electrode Active Material Layer 
     The positive electrode active material of the positive electrode active material layer  33  is not particularly limited, and a known material used as a positive electrode active material for a secondary battery can be applied. The composition thereof is also not particularly limited, and may include a solid electrolyte, a conductivity aid, a binder and the like. Examples of the positive electrode active material include transition metal chalcogenides such as titanium disulfide, molybdenum disulfide and niobium selenide, transition metal oxides such as lithium nickelate (LiNiO 2 ), lithium manganate (LiMnO 2 , LiMd 2 O 4 ) and lithium cobaltate LiCoO 2 ) and the like. 
     Negative Electrode Terminal and Positive Electrode Terminal 
     The negative electrode terminals  21   a  and  21   b  are conductive members which are substantially cylindrical, and are formed with, for example, two members which are coupled within the exterior  6  through a coupling member C. The negative electrode terminals  21   a  and  21   b  are extended in the stacking direction of a plurality of negative electrode current collectors  22  in the multilayer, and are electrically connected to the negative electrode current collectors  22  drawn from the multilayer within the exterior  6 . One end portion of the negative electrode terminal  21   a  is arranged outside the exterior  6 , and is larger in diameter than the negative electrode terminal  21   a  arranged within the exterior  6 . The configuration of the negative electrode terminal is not limited to the configuration using the two members described above, and may be a configuration using one member. However, by forming the negative electrode terminal of two members, the negative electrode terminal can be easily inserted into holes formed in the negative electrode current collectors  22  and be fixed. 
     Between the one end portion of the negative electrode terminal  21   a  and the exterior  6 , the negative electrode lead terminal  20  serving as the lead terminal is arranged. The negative electrode lead terminal  20  is fitted with a concavo-convex portion  211  to the negative electrode terminal  21   a.  In this way, the sealing property of the multilayer described above can be enhanced. Instead of the negative electrode lead terminal  20 , a gap filler which is a separate member may be arranged. The gap filler described above is not particularly limited as long as it can be electrically connected to the negative electrode lead terminal  20  and the negative electrode terminal  21   a  and is conductive. The negative electrode lead terminal  20  and the negative electrode terminals  21  may be fitted together with a screw shape or a rivet instead of the concavo-convex portion described above. 
     The positive electrode terminals  31   a  and  31   b  have the same configuration as the negative electrode terminals  21   a  and  21   b.    
     Solid Electrolyte Layer 
     Although the solid electrolyte of the solid electrolyte layer  4  is not particularly limited, examples thereof include sulfide solid electrolyte materials, oxide solid electrolyte materials, nitride solid electrolyte materials, halide solid electrolyte materials and the like. 
     Lead Terminal 
     The negative electrode lead terminal  20  and the positive electrode lead terminal  30  are not particularly limited, and are preferably a linear plate-shaped member of aluminum (Al), copper (Cu) or the like which is flexible. 
     Exterior 
     The exterior  6  stores the multilayer which is the power generation element. Intrusion of air and moisture into the multilayer can be prevented by the exterior  6 . The exterior  6  is formed with, for example, a laminate film including an inorganic thin film such as an aluminum foil and a resin layer and the like. 
     Connection Structure of Current Collectors and Terminals 
     As shown in  FIG.  2   , in a plurality of negative electrode current collectors  22  drawn from the end surface of the multilayer, holes into which the negative electrode terminals  21   a  and  21   b  are inserted are formed. In a state before the negative electrode terminals  21   a  and  21   b  are inserted, the holes formed in the negative electrode current collectors  22  are smaller in diameter than the negative electrode terminals  21   a  and  21   b  arranged within the exterior  6 . The negative electrode terminals  21   a  and  21   b  are inserted into the holes formed in the negative electrode current collectors  22  while the diameters of the holes are being pressed and expanded. In this way, bent portions  221  are formed at abutment parts of the negative electrode current collectors  22  which abut on the negative electrode terminals  21   a  and  21   b.    
     Since the diameters of the holes formed in the negative electrode current collectors  22  which are metal foils are pressed and expanded, and thus the bent portions  221  are formed, the bent portions  221  have stress acting in a direction in which the negative electrode current collectors  22  abut on the negative electrode terminals  21   a  and  21   b.  In this way, it is possible to increase the contact areas of the negative electrode current collectors  22  and the negative electrode terminals  21   a  and  21   b,  as well as to reliably bring the negative electrode current collectors  22  into contact with the negative electrode terminals  21   a  and  21   b,  which makes it possible to reliably ensure conductivity between the negative electrode current collectors  22  and the negative electrode terminals  21   a  and  21   b.  Although in  FIGS.  1  to  3   , the bent portions  221  are formed around the end portions of the negative electrode current collectors  22  of the metal foils on a short side, the bent portions  221  may be formed around the end portions of the negative electrode current collectors  22  of the metal foils on a long side. In this way, a current distribution can be made uniform. 
     In the exterior  6 , a hole into which the negative electrode terminal  21   a  is inserted is formed. In a state before the negative electrode terminal  21   a  is inserted the hole formed in the exterior  6  is smaller in diameter than the negative electrode terminal  21   a  formed within the exterior  6 . The negative electrode terminal  21   a  is Inserted into the hole formed in the exterior  6  while the diameter of the hole formed in the exterior  6  is being pressed and expanded. In this way, a bent portion is formed at an abutment part of the end surface of the hole which abuts on the negative electrode terminal  21   a.  Hence, it is possible to reliably bring the end surface of the hole into contact with the negative electrode terminal  21   a.  Although conventionally, for example, moisture permeates a part where the exterior formed with a laminate film and the like and a metal terminal extended from an end portion of the exterior are thermally welded, and this contributes to a decrease in the life of the battery cell, the configuration described above makes it possible to enhance the sealing property of the exterior  6 , with the result that it is possible to increase the life of the battery cell. 
     Moreover, the amount of bending in the bent portion formed in the exterior  6  is preferably smaller than the amount of bending in the bent portions  221  formed in the negative electrode current collectors  22 . In this way, in the adjacent negative electrode current collectors  22  within the exterior  6 , the entry of the exterior  6  between the negative electrode terminal  21   a  and the negative electrode current collectors  22  can be prevented, and thus it is possible to reliably ensure conductivity between the negative electrode terminal  21   a  and the negative electrode current collectors  22 . The configuration described above can be achieved by decreasing the diameters of the holes formed in the negative electrode current collectors  22  in the state before the negative electrode terminal  21   a  is inserted as compared with the diameter of the hole formed in the exterior  6 . 
     As shown in  FIG.  2   , shims  5   a  serving as distance holders are arranged between the negative electrode current collectors  22  drawn from the end surface of the multilayer and around the bent portions  221  serving as abutment portions which abut on the negative electrode terminals  21   a  and  21   b.  The thickness of the shim  5   a  in the stacking direction is substantially equal to the distance between the adjacent negative electrode current collectors  22  in the multilayer. Hence, the negative electrode current collectors  22  drawn from the end surface of the multilayer can be arranged substantially parallel to each other without being bent at parts other than the bent portions  221  of the abutment parts which abut on the negative electrode terminals  21   a  and  21   b.  In this way, it is possible to prevent the negative electrode current collectors  22  from being damaged and cut. 
     As shown in  FIG.  3   , in a plurality of positive electrode current collectors  32  drawn from the end surface of the multilayer, holes into which the positive electrode terminals  31   a  and  31   b  are inserted are formed. The positive electrode current collectors  32  and the positive electrode terminals  31   a  and  31   b  have the same configurations as the negative electrode current collectors  22  and the negative electrode terminals  21   a  and  21   b,  and bent portions  321  are formed at abutment parts of the positive electrode current collectors  32  which abut on the positive electrode terminals  31   a  and  31   b.  In this way, the same effects as in the negative electrode current collectors  22  and the negative electrode terminals  21   a  and  21   b  can be obtained. 
     As shown in  FIG.  3   , the shims  5   a  serving as the distance holders are arranged between the positive electrode current collectors  32  drawn from the end surface of the multilayer and around the bent portions  321 . The thickness of the shim  5   a  is substantially equal to the distance between the adjacent positive electrode current collectors  32  in the multilayer. On the other hand, since in the multilayer of the present embodiment, the negative electrode current collector  22  is arranged at an end portion in the stacking direction on the side of the positive electrode terminal  31   a,  a shim  5   b  is arranged, in this part, between the exterior  6  and the positive electrode current collector  32 . The thickness of the shim  5   b  is smaller than that of the shim  5   a.  Since at an end portion in the stacking direction on the side of the positive electrode terminal  31   b,  an end portion of the positive electrode terminal  31   b  having a predetermined thickness on the side of the exterior  6  is sealed into the exterior  6 , the shim  5   b  having a smaller thickness than the shim  5   a  is arranged between the positive electrode current collectors  32  at the end portion in the stacking direction on the side of the positive electrode terminal  31   b.    
     Battery Module 
     When a plurality of battery cells  1  having the configuration described above are combined to form a battery module, the battery cells  1  are arranged such that the negative electrode lead terminals  20  and the positive electrode lead terminals  30  which are arranged to be extended in the stacking direction of the multilayer are aligned side by side, with the result that the battery module can be formed without the formation of wasting space. Here, the negative electrode lead terminals  20  and the positive electrode lead terminals  30  in the battery cells  1  are preferably arranged in a staggered arrangement when they are seen in plan view from the stacking direction of the multilayer. When in the use of the battery module, each of the battery cells  1  may be expanded to cause a change in thickness, since in the configuration described above, the positions of the positive electrode lead terminals  30  whose thicknesses are easily changed can be dispersed, the thicknesses of the battery modules can be made uniform. 
     Second Embodiment 
     A second embodiment of the present invention will then be described. Configurations common to the first embodiment may be identified with the same reference numerals in drawings, and descriptions thereof may be omitted. 
     Exterior 1 
     As shown in  FIG.  4   , a battery cell  1   a  according to the present embodiment includes: a multilayer serving as a power generation element in which negative electrode current collectors  22 , negative electrode active material layers  23 , solid electrolyte layers  4 , positive electrode current collectors  32  and positive electrode active material layers  33  are stacked; and an exterior  6   a  which stores negative electrode terminals  22   a  and  21   b  therewithin. Although  FIG.  4   , shows the exterior  6   a  which stores the negative electrode terminals  21   a  and  21   b  therewithin, the exterior  6   a  stores positive electrode terminals  31   a  and  31   b  in the same configuration. 
     The exterior  6   a  includes a resin layer  61 , a metal layer  62  which is a conductive layer and a resin layer  63 . The resin layer  61  is an outermost layer in the battery cell  1   a,  and the resin layer  63  is an innermost layer in the battery cell  1   a.  As shown in  FIG.  5   , a part of the metal layer  62  is extended outside the battery cell  1   a  to form a lead terminal  62   a.  The lead terminal  62   a  is preferably electrically connected to the metal layer  62 , and may be formed with a member different from the metal layer  62 . Instead of the metal layer  62 , a conductive material other than metal may be used. 
     As shown in  FIG.  4   , the metal layer  62  abuts on a negative electrode current collector  22   a  arranged on one stacking end surface of the multilayer. In this way, a current collected by the negative electrode terminals  21   a  and  21   b  can be passed through the negative electrode current collector  22   a  and the metal layer  62  to the lead terminal  62   a  shown in  FIG.  5   . The metal layer  62  likewise abuts on a positive electrode current collector  32   a  arranged on the other stacking end surface of the multilayer. 
       FIG.  5    is a schematic view when the exterior  6   a  is seen from the side of an abutment surface which abuts on the multilayer. As shown in  FIG.  5   , the metal layer  62  is arranged in a center portion of the abutment surface of the exterior  6   a.  The outer, perimeter of the metal layer  62  is covered by the resin layer  63 . The area of the metal layer  62  on the abutment surface is increased, and thus it is possible to reduce electrical resistance. On the other hand, the resin layer  63  can preferably insulate an area between the negative electrode terminals  21   a  and  21   b  and the metal layer  62 , and the area on the abutment surface is preferably minimized. In terms of the above description, the area of the metal layer  62  on the abutment surface is preferably larger than the area of the resin layer  63 . 
     The exterior  6   a  having the configuration described above can be produced by removing, in a laminate film formed by stacking, for example, a resin layer, a metal layer and a resin layer in this order, the resin layer on one surface side. Instead of forming the lead terminal  62   a  in the exterior  6   a,  a part of the resin layer  61  may be removed to provide a lead terminal which is connected to the metal layer  62 . In a conventional laminate cell, voids may be formed between a laminate film and a lead terminal, and this contributes to a decrease in airtightness. However, in the configuration of the lead terminal described above, as compared with the conventional laminate cell, the airtightness of the battery cell  1   a  can be enhanced. Instead of the configuration of the lead terminal described above, a part of the metal layer  62  may be extended to be exposed from, one end of the exterior  6   a  so as to form a lead terminal. 
     Since in the multilayer described above, a current is concentrated in the negative electrode current collector  22   a  and the positive electrode current collector  32   a  which abut on the metal layer  62 , the negative electrode current collector  22   a  and the positive electrode current collector  32   a  are preferably greater in thickness than the negative electrode current collector  22  and the positive electrode current collector  32 . 
     Although the preferred embodiments of the present invention have been described above, the details of the present, invention are not limited to the embodiments described above, and can be changed as necessary. 
     Although in the description of the above embodiments, the negative electrode current collectors  22  and the positive electrode current collectors  32  are extended from the respective current collectors, the present invention is not limited to this configuration. The negative electrode current collector  22  and the positive electrode current collector  32  are preferably drawn from the end surface of the multilayer, and may be drawn by being electrically connected to a different member. 
     EXPLANATION OF REFERENCE NUMERALS 
       1 ,  1   a  battery cell 
       20  negative electrode lead terminal (lead terminal) 
       30  positive electrode lead terminal (lead terminal) 
       21   a,    21   b  negative electrode terminal (terminal) 
       31   a,    31   b  positive electrode terminal (terminal) 
       22  negative electrode current collector (current collector) 
       32  positive electrode current collector (current collector) 
       221 ,  321  bent portion 
       5   a,    5   b  shim (distance holder) 
       6 ,  6   a  exterior 
       62  conductive layer (metal layer) 
       63  resin layer