Patent Publication Number: US-2021167456-A1

Title: Battery pack

Description:
TECHNICAL FIELD 
     The present invention relates to a battery pack in which a plurality of battery cells is connected in series or in parallel to increase the capacity. 
     BACKGROUND ART 
     A battery pack having a plurality of battery cells housed in a case is used as a power source for portable devices and cordless devices. In this battery pack, a plurality of battery cells is connected in series or in parallel to increase the capacity. In particular, in recent years, battery packs are required to increase in capacity and also decrease in size and weight from the viewpoint of portability. Therefore, each battery cell has been increased in capacity, and there is employed a configuration of a battery pack in which the battery cells are arranged without a gap therein. 
     On the other hand, the battery cells may exhibit thermal runaway due to various causes such as internal short circuit and overcharge. If any one of a plurality of arranged battery cells overheats and ignites, adjacent battery cells may be heated and induce thermal runaway, which propagates and causes thermal runaway of many of the battery cells in some cases. Therefore, it is required that even if any one of the battery cells produces abnormal heat, it does not affect the other battery cells. 
     In addition, a plastic holder is used for the battery pack to arrange the battery cells in place. This holder is formed into a structure in which each battery cell is guided and arranged in a fixed position. This holder allows the battery cells to be arranged at fixed positions, but would melt under the temperature of a battery cell that might have generated abnormal heat. Due to the melting, the holder may no longer partition the battery cells adjacent to the battery cell that has generated abnormal heat but cause these battery cells to burn from the heat. There has been developed a battery pack in which a mica plate is disposed between adjacent battery cells to insulate heat. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Unexamined Japanese Patent Publication No. 2008-218210 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The mica plate disposed between the battery cells can thermally insulate the battery cells from each other unless the holder does not melt. However, once the holder gets melted due to abnormal heat generation by any one of the battery cells, the mica plate cannot prevent burning of the battery cells. 
     The present invention was developed to eliminate the above drawback. An object thereof is to provide a battery pack that can avoid induction of thermal runaway while using a plurality of battery cells. 
     Solution to Problem and Advantageous Effect of Invention 
     The battery pack of the present invention includes a plurality of battery cells  1  and holder  2  that has battery cells  1  arranged in a parallel posture. Holder  2  has partition wall  23  between adjacent battery cells  1  for arranging battery cells  1  at fixed positions. Partition wall  23  has a surface facing battery cells  1  as resin molded layer  12  shaped to arrange battery cells  1  at the fixed positions. Partition wall  23  has a three-layer structure that non-melting plate  13  is disposed inside and resin molded layer  12  is laminated on both surfaces of non-melting plate  13 . Holder  2  is formed in a single-piece structure by molding resin molded layer  12  from a synthetic resin. 
     The above battery pack is characterized in that the holder and the non-melting plate can avoid induction of thermal runaway of the battery cells while arranging the plurality of battery cells at fixed positions in the holder. In particular, the above battery pack has a feature that the holder can effectively prevent induction of thermal runaway while the holder for arranging the plurality of battery cells at fixed position can be mass-produced inexpensively as a single-piece plastic structure. The above feature can be achieved because the partition wall is provided between the battery cells, the partition wall has a three-layer structure of the resin molded layers and the non-melting plate, the surface facing the battery cell has the plastic resin molded layer shaped to arrange the battery cell at the fixed position, and the non-melting plate is disposed inside the resin molded layer. In the partition wall of the three-layer structure in which the resin molded layers are laminated on both sides of the non-melting plate, the plastic of the resin molded layer in contact with the battery pack having generated abnormal heat would melt but the plastic of the resin molded layer on the opposite side would not melt in the presence of the non-melting plate. The non-melting plate and the non-melting resin molded layer remain as a partition wall of a two-layer structure, and this partition wall prevents burning of the adjacent battery cells. When any of the battery cells generates abnormal heat, the resin molded layer laminated on one surface of the non-melting plate will thermally melt with the battery cell having generated abnormal heat and absorbs the heat of melting, but the resin molded layer laminated on the other surface will not thermally melt due to protection by the non-melting plate. Thus, the non-melting plate and the resin molded layer on the one surface protect the adjacent battery cells, thereby preventing induction of thermal runaway. 
     In the battery pack of the present invention, battery cells  1  are cylindrical batteries, and holder  2  comprises plastic, and the plastic has insertion gap  25  for disposing non-melting plate  13  at a fixed position inside resin molded layer  12 . The plastic has the surface facing corresponding battery cell  1 , the surface being curved along surface of the corresponding battery cell  1  and allows non-melting plate  13  to be disposed into insertion gap  25 . 
     In this battery pack, the insertion gap is provided in the process of molding the holder from plastic so that the non-melting plate can be inserted into the insertion gap and placed at a fixed position after molding. Thus, the battery pack can be easily assembled by disposing the non-melting plate at the correct position without a positional shift in the holder and also arranging the cylindrical batteries at the fixed positions by the resin molded layer. Since the surfaces of the holder facing the battery cells on the resin molded layer are curved along the cylindrical batteries, the non-melting plate can be disposed inside to make the resin molded layer thick so that it is possible to efficiently absorb heat energy of the battery cell having generated abnormal heat by the melting heat of the thick resin molded layer and to prevent induction of thermal runaway of the battery cells particularly in an efficient manner. 
     In the battery pack of the present invention, non-melting plate  13  can be an inorganic plate. In this battery pack, the non-melting plate is the inorganic plate to improve the heat resistance of the non-melting plate and securely block abnormal heat generated by any of the battery cells. Thus, the battery pack can reliably prevent induction of thermal runaway of the battery cells without becoming deformed even if it is heated at a high temperature. 
     In the battery pack of the present invention, non-melting plate  13  can be a mica plate. This battery pack can reliably prevent induction of thermal runaway of the battery cells with the non-melting plate as a plate material that is inexpensive and has excellent heat insulating properties. 
     In the battery pack of the present invention, holder  2  can have holding tube  22  in which battery cell  1  is disposed, and can include inflow spaces  24  and  27  outside holding tube  22  into which a heat-melted portion of holding tube  22  is to flow. 
     The above battery pack can cool the plastic of the resin molded layer melted with the battery cell having generated abnormal heat by flowing into the inflow spaces. Further, the above battery pack can prevent induction of thermal runaway of the battery cells in a more effective manner by flowing the melted resin molded layer into the inflow spaces to provide an air layer between the battery cell and the non-melting plate for heat insulating. 
     In the battery pack of the present invention, holder  2  can have holding tubes  22  arranged in multiple stages and multiple rows, include cross-shaped partition wall  23  provided between holding tubes  22  arranged vertically and horizontally, and include inflow space  24  extending in the longitudinal direction of battery cell  1  in a central portion of cross-shaped partition wall  23 . 
     In the above battery pack, the inner volume of the inflow space provided in the central portion of the holder is large, and the melted resin molded layer can be efficiently flowed into the inflow space, and it is possible to prevent induction of thermal runaway of the battery cells more effectively. 
     In the battery pack of the present invention, holder  2  can include insertion gap  25  having inflow space  27  in partition wall  23  between adjacent holding tubes  22 , insertion gap  25  can include holding gap  26  for disposing non-melting plate  13  at a fixed position with a central portion sandwiched in holding gap  26 , and the inflow space, a lateral width of holding gap  26  can be narrower than a lateral width of non-melting plate  13 , and inflow space  27  can be provided on both side portions of non-melting plate  13 . 
     In the above battery pack, since the inflow space is provided on both sides of the holding gap of the non-melting plate, the melted resin molded layer of the holding tube can efficiently flow into the inflow spaces, so that it is possible to further effectively prevent induction of thermal runaway of the battery cells. 
     In the battery pack of the present invention, non-melting plate  13  can be disposed so as to be freely placed into and taken out of the insertion gap  25 . 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a battery pack according to an exemplary embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the battery pack shown in  FIG. 1  taken along line II-II. 
         FIG. 3  is an exploded perspective view of the battery pack shown in  FIG. 1 . 
         FIG. 4  is a perspective view of a battery block. 
         FIG. 5  is an exploded perspective view of the battery block shown in  FIG. 4 . 
         FIG. 6  is a perspective view of a core pack in which two battery blocks and a circuit board are coupled. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Hereinafter, the present invention will be described in detail with reference to the drawings. In the following description, terms to denote specific directions or positions (e.g., “top”, “bottom”, and other terms including those terms) are used as necessary for easy understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meanings of the terms. The parts having the same reference numerals appearing in a plurality of drawings indicate the same or equivalent parts or members. 
     The exemplary embodiment described below is specific examples of the technical idea of the present invention, and the present invention is not limited to the following exemplary embodiment. The dimensions, materials, shapes, relative arrangements, and the like of the components described below are not intended to limit the scope of the present invention thereto but are intended for exemplification, unless specifically stated. The contents described in relation to one exemplary embodiment and example can be applied to other exemplary embodiments and examples. The sizes and positional relationships of members shown in the drawings may be exaggerated in order to clarify the explanation. 
       FIGS. 1 to 5  show a battery pack according to one exemplary embodiment of the present invention.  FIG. 1  is a perspective view of the battery pack,  FIG. 2  is a vertical cross-sectional view of the battery pack, and  FIG. 3  is an exploded perspective view of the battery pack.  FIG. 4  is a perspective view of a battery block built in the battery pack,  FIG. 5  is an exploded perspective view of the battery block, and  FIG. 6  is a perspective view of a battery core pack in which two battery blocks and a circuit board are coupled. Battery pack  100  shown in  FIGS. 1 to 6  includes a plurality of battery cells  1  and holder  2  in which battery cells  1  are arranged in a parallel posture. Battery pack  100  shown in  FIGS. 2 and 3  includes exterior case  9  that houses two sets of battery blocks  10  arranged in the longitudinal direction, and circuit board  4 . 
     Battery pack  100  is used as a power source for a mobile device such as a vacuum cleaner. However, the present invention does not limit the use of the battery pack to a mobile device. The battery pack is also applicable to other mobile devices such as an electric tool and an assisted bicycle, for example. The battery pack shown in the drawings is structured to be detachably coupled to a portable device. However, the battery pack of the present invention can also be used by being incorporated in a portable device in a non-detachable state. 
     (Exterior Case  9 ) 
     Battery pack  100  is formed in a rectangular tubular box shape as shown in  FIGS. 2 and 3 . Exterior case  9  shown in the drawings is divided into two parts, case body  9 A and closing part  9 B. Exterior case  9  has connector  19  drawn to the outside for connecting with a portable device that is to be supplied power from battery pack  100 . Exterior case  9  is made of a material having excellent electrical insulating properties and thermal insulating properties, for example, resin such as polycarbonate. 
     Inside exterior case  9  stores, as shown in  FIG. 3 , two sets of battery blocks  10 , insulating plate part  11  disposed between battery blocks  10 , and circuit board  4  connected to battery blocks  10 . As shown in  FIGS. 4 and 5 , battery block  10  has a plurality of battery cells  1  arranged in parallel posture in holder  2 . In illustrated battery block  10 , four battery cells  1  are arranged in two rows and two stages in holder  2 . Battery cell  1  uses a cylindrical battery having a cylindrical exterior can. In illustrated battery block  10 , four battery cells  1  are arranged in two rows and two stages, and battery cells  1  are connected in series by lead plates  3 . In illustrated battery block  10 , four battery cells  1  are arranged in two rows and two stages and connected in series. However, a number and connection form of battery cells can be freely changed. 
     Battery cell  1  is a lithium ion secondary battery. However, battery cell  1  can be a non-aqueous electrolyte secondary battery other than a lithium-ion secondary battery. The cylindrical battery cell may be a rechargeable secondary battery such as a nickel metal hydride battery or a nickel cadmium battery, especially a battery that generates heat at high temperatures when being used. 
     Battery cells  1  are electrically connected in series by lead plates  3 . Lead plate  3  is formed by bending a metal plate having excellent conductivity. Lead plate  3  is welded to an electrode on an end surface of battery cell  1 . Lead plate  3  with battery cell  1  is connected to circuit board  4 . Circuit board  4  has a charge/discharge circuit and a protection circuit mounted thereon. Circuit board  4  is connected to output lead part  3   x  for inputting positive or negative output of each battery block  10 , or is connected to intermediate potential lead part  3   y  for measuring intermediate potential in order to detect a voltage of each battery cell  1 . In addition, circuit board  4  may be connected to potential of a temperature detector (not illustrated) for detecting a temperature of each battery cell  1 . The temperature detector can be a thermistor or the like. 
     (Insulation Plate Part  11 ) 
     As shown in  FIG. 3 , inside exterior case  9  has insulating plate part  11  disposed between battery blocks  10 . Insulating plate part  11  is disposed between battery blocks  10  arranged side by side in the longitudinal direction of exterior case  9 . Insulating plate part  11  is an inorganic plate made from a material having excellent insulating properties and heat insulating properties, for example, such as a mica plate. 
     (Battery Block  10 ) 
     Battery block  10  has four battery cells  1  arranged at fixed positions in plastic holder  2 . Battery block  10  shown in  FIGS. 4 and 5  has holder  2  divided into first holder  2 A and second holder  2 B in the longitudinal direction of battery cells  1 . First holder  2 A and second holder  2 B are separately manufactured by molding plastic, and battery cells  1  are inserted and coupled to each other. First holder  2 A and second holder  2 B each have cylindrical holding part  21  for inserting cylindrical battery cells  1  and arranging the same at fixed positions. An inner shape of holding part  21  is substantially the same as an outer shape of battery cell  1 , and to be exact, the inner shape of holding part  21  is slightly larger to smoothly insert and arrange battery cells  1  at fixed positions. First holder  2 A and second holder  2 B of this structure are coupled to each other at fixed positions with battery cells  1  therebetween in a state where both ends of cylindrical battery cells  1  are inserted. First holder  2 A and second holder  2 B can be more accurately coupled to each other with opposing surfaces as a fitting structure, and are also coupled together at fixed positions with a non-melting plate described later. 
     (Holder  2 ) 
     In order to arrange four battery cells  1  in a parallel posture, holder  2  shown in  FIGS. 3 and 4  is molded into a shape in which four sets of holding tubes  22  are coupled in two rows and two stages in a parallel posture, and holding part  21  is formed such that an inside of each holding tube  22  is made substantially equal to the outer shape of battery cell  1 . Holding tube  22  defines partition wall  23  between adjacent battery cells  1 . In illustrated holder  2 , since battery cells  1  are arranged in two rows and two stages, cross-shaped partition wall  23  is provided between the four sets of battery cells  1  arranged vertically and horizontally. Partition wall  23  has a three-layer structure of non-melting plate  13  and resin molded layers  12  in which resin molded layer  12  is provided on the surface facing battery cell  1  and non-melting plate  13  is disposed inside resin molded layer  12 . Partition wall  23  has a three-layer structure in which resin molded layers  12  are laminated on both sides of internal non-melting plate  13 . Resin molded layer  12  has a surface molded into a curved surface along a surface of cylindrical battery cell  1  to arrange battery cell  1  at a fixed position. 
     Holder  2  of  FIGS. 4 and 5  has inflow spaces  24  and  27  for heat-melted holding tube  22  outside holding tube  22 . In holder  2  of  FIGS. 4 and 5 , holding tubes  22  are arranged in multiple stages and multiple rows, in two rows and two stages in these drawings, cross-shaped partition wall  23  is provided between holding tubes  22  arranged vertically and horizontally, and inflow space  24  is provided in the center of cross-shaped partition wall  23 . Inflow space  24  is provided in a hollow part of cross-shaped partition wall  23 , as a rectangular hollow part extending in the longitudinal direction of battery cell  1 . Inflow space  24  provided in this part has a large internal volume so that the heat-melted resin of holding tube  22  can smoothly flow into this space. 
     Holder  2  of  FIG. 4  further has inflow spaces  27  provided on both sides of insertion gap  25  for disposing non-melting plate  13  at a fixed position. Inflow spaces  27  each are provided such that flat-surface parts facing each other are placed at portions of an outer surfaces of adjacent cylindrical holding tubes  22 , holding gap  26  for non-melting plate  13  is provided between the facing flat-surface parts, and a lateral width of holding gap  26  is made narrower than a lateral width of non-melting plate  13 , in other words, an entire width of insertion gap  25 . Insertion gap  25  has inflow spaces  27  on both sides of holding gap  26  of non-melting plate  13 . Holding gap  26  sandwiches non-melting plate  13  between both sides and holds at a fixed position. Inflow spaces  27  are on both sides of insertion gap  25  and allow the heat-melted resin of holding tube  22  to flow in. 
     Holder  2  described above has inflow spaces  24  and  27  into which the heat-melted synthetic resin of holding tube  22  is to flow at the both sides of insertion gap  25  and the hollow parts of cross-shaped partition wall  23 . In this holder  2 , when battery cell  1  generates abnormal heat and holding tube  22  is heat-melted, the heat-melted synthetic resin flows into inflow spaces  27  on the both sides of insertion gap  25 . Melted synthetic resin flowing into these spaces melts the synthetic resin between inflow spaces  27  and inflow space  24  provided in the hollow part of the cross-shaped partition wall  23 , and then flows into inflow space  24  provided in the hollow part of cross-shaped partition wall  23  as shown by arrows A. The heat-melted synthetic resin flows into inflow space  24  and is cooled. When the synthetic resin is heat-melted and flows into inflow space  24 , an air layer is formed between battery cell  1  and non-melting plate  13 , and a heat insulation effect of this air layer prevents induction of thermal runaway to adjacent battery cells  1 . Since holder  2  of  FIG. 2  also has inflow space  27  outside lower holding tubes  22 , when any of battery cells  1  inside lower holding tubes  22  generates abnormal heat and holding tube  22  is heat-melted, the melted synthetic resin flows into inflow spaces  27  provided below holding tube  22  and is cooled. In addition, the air layer is provided between battery cell  1  and non-melting plate  13  to insulate the heat and prevent thermal runaway. 
     (Non-Melting Plate  13 ) 
     Non-melting plate  13  is a plate that does not deform at the temperature of battery cell  1  having generated abnormal heat, and preferably an inorganic plate such as a mica plate. As the inorganic plate, instead of the mica plate, one obtained by sintering or molding inorganic powder into a plate shape, or a plate-shaped inorganic material, or a plate-shaped inorganic fiber material can be used. As the non-melting plate, a plate material slightly thinner than the insertion gap is used such that it can be detachably disposed in the insertion gap. 
     Battery pack  100  described above is assembled in the following steps. 
     (1) Battery cells  1  and non-melting plates  13  are arranged and coupled at fixed positions in first holder  2 A and second holder  2 B. First holder  2 A and second holder  2 B are coupled in a state where battery cells  1  are inserted into corresponding holding parts  21  and non-melting plates  13  are inserted into corresponding insertion gaps  25  of partition wall  23 . First holder  2 A and second holder  2 B are coupled by a locking structure, and are also coupled at fixed positions via built-in battery cells  1  and non-melting plates  13 . 
     (2) Lead plates  3  are connected to end surface electrodes of battery cells  1  exposed from both end surfaces of holder  2  so that all battery cells  1  housed in holder  2  are connected in series. Lead plates  3  are electrically connected and fixed by welding to the end surface electrodes of battery cells  1 . 
     Battery block  10  is manufactured through the above steps. 
     (3) Two battery blocks  10  are coupled with insulating plate part  11  sandwiched therebetween. Two battery blocks  10  are arranged side by side in the axial direction of battery cells  1 , and are insulated by insulating plate part  11  interposed therebetween. 
     (4) Circuit board  4  is coupled to two battery blocks  10 . Holder  2  shown in  FIGS. 3 to 6  includes projecting part  29  on an upper surface, and projecting part  29  is guided to concave part  4   a  provided on an outer peripheral edge of circuit board  4  to dispose circuit board  4  at a fixed position. Further, holder  2  shown in the diagrams includes locking hook  30  protruding from the upper surface, and this locking hook  30  is locked to circuit board  4  and is coupled at a fixed position by a locking structure. Circuit board  4  is fixed to holder  2  by screwing set screws  18  penetrating circuit board  4  into fixing bosses  28  provided on the upper surface of holder  2 . 
     (5) Output lead parts  3   x  and intermediate potential lead parts  3   y  drawn from lead plates  3  are electrically coupled to circuit board  4  connected to battery block  10 . Output lead parts  3   x  and intermediate potential lead parts  3   y  are disposed so as to project from an upper surface of battery block  10 , are inserted into connection holes  4   b  provided in circuit board  4  and disposed at fixed positions, and are electrically connected and physically coupled to circuit board  4  by soldering. 
     In the above state, as shown in  FIG. 6 , battery core pack  20  in which circuit board  4  is coupled to two battery blocks  10  is manufactured. 
     (6) Battery core pack  20  is stored in exterior case  9 . Circuit board  4  shown in the diagram is connected to output connector  19 . Battery core pack  20  is stored in case body  9 A of exterior case  9  such that connector  19  passes through open window  9   a  in case body  9 A, and then case body  9 A is closed with closure part  9 B. Then, open window  9   a  of case body  9 A is closed by closure lid  17 . 
     INDUSTRIAL APPLICABILITY 
     The battery pack of the present invention is suitably used as a power source for portable devices such as vacuum cleaners, electric power tools, and assisted bicycles. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           100  battery pack 
           1  battery cell 
           2  holder 
           2 A first holder 
           2 B second holder 
           3  lead plate 
           3   x  output lead part 
           3   y  intermediate potential lead part 
           4  circuit board 
           4   a  concave part 
           4   b  connection hole 
           9  exterior case 
           9 A case body 
           9   a  open window 
           9 B closing part 
           10  battery block 
           11  insulation plate part 
           12  resin molded layer 
           13  non-melting plate 
           17  closure lid 
           18  set screw 
           19  connector 
           20  core pack 
           21  holding part 
           22  holding tube 
           23  partition wall 
           24  inflow space 
           25  insertion gap 
           26  holding gap 
           27  inflow space 
           28  fixing boss 
           29  projecting part 
           30  locking hook