Patent Publication Number: US-2019173074-A1

Title: Battery

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-232611, filed Dec. 4, 2017; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a battery. 
     BACKGROUND 
     In a battery pack, such as a secondary battery, a battery module, which is an aggregation of a plurality of battery cells (electric cells), is housed inside a battery case. During use of the battery pack, there is a possibility that the battery cells inside the case may exhibit thermal runaway due to short circuiting or other reasons. 
     Assuming such a situation, the battery pack is equipped with a safety mechanism configured to prevent explosion of the battery cells. As an example of this safety mechanism, a pressure relief portion for pressure release is provided in the battery cell. If, for example, a high temperature combustible gas is generated inside the battery cell and an internal pressure of the battery cell increases, the pressure relief portion of the battery cell is operated. 
     As a safety mechanism, a gas discharge portion for gas venting is also formed in the battery case. A combustible vent gas discharged from the pressure relief portion of the battery cell is discharged to the outside of the battery pack from the gas discharge portion of the battery case. At this time, the vent gas discharged from the pressure relief portion is a high temperature combustible gas. Accordingly, unless the gas is discharged to the outside of the battery pack safely, there is a possibility that the battery case of the battery pack may explode or ignite even if the explosion of the battery cell can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view depicting a general configuration of an entire battery according to an embodiment. 
         FIG. 2  is an exploded perspective view of the battery of  FIG. 1 . 
         FIG. 3  is a longitudinal cross sectional view depicting a vent path structure of an inner portion of the battery of  FIG. 1 . 
         FIG. 4  is a perspective view depicting the vent path structure of  FIG. 3 . 
         FIG. 5  is a perspective view depicting a reverse side of a case of the vent path structure of  FIG. 4 . 
         FIG. 6  is a perspective view depicting a modification of a vent path structure of a battery. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, a battery includes: a battery case, an inner portion of which is sealed; a gas discharge portion for gas venting formed in the battery case; a battery module housed in the battery case, the battery module being an aggregation of a plurality of battery cells; a pressure relief portion formed in a part of the battery cell and allowing a vent gas expelled from an inner portion of the battery cell to flow out; and a vent path structure configuring a vent gas path through which the vent gas flows between the pressure relief portion and the gas discharge portion, and a liquid trap portion facilitating liquefaction of the vent gas flowing in the vent gas path and trapping the liquefied liquid. 
     Hereinafter, an embodiment will be explained with reference to  FIGS. 1-5 .  FIG. 1  is a perspective view depicting a general configuration of the entire battery  11 A according to an embodiment.  FIG. 2  is an exploded perspective view of the battery  11 A of  FIG. 1 .  FIG. 3  is a longitudinal sectional view depicting a vent path structure  26  of an inner portion of the battery  11 A of  FIG. 1 .  FIG. 4  is a perspective view depicting the vent path structure  26  of  FIG. 3 .  FIG. 5  is a perspective view depicting a lower surface  27   b , which is a reverse side of a case  27  of the vent path structure of  FIG. 4 . 
     The battery  11 A of the present embodiment comprises a battery case  11 , a vent gas release portion (gas discharge portion)  25 , a battery module  15 , a pressure relief portion  16  that is a safety valve, and a vent path structure  26 . 
     The battery case  11  comprises an upper case  12  and a lower case  13 . As shown in  FIG. 2 , the lower case  13  is a housing shaped like a rectangular box in which an upper surface opening  13   a  is formed. This lower case  13  comprises a bottom plate  13   b  shaped like a rectangular flat plate, and side wall portions  13   c ,  13   d ,  13   e , and  13   f  providing four surfaces including a front surface, a rear surface, a right surface, and a left surface. 
     Inside the lower case  13 , the battery module  15 , which is an aggregation of a plurality of battery cells  14 , is housed as shown in  FIG. 2 . In the present embodiment, an example of the battery module  15 , in which five battery cells  14  are arranged in juxtaposition, is indicated. 
     The battery cells  14  have, for example, a housing  14   a  such as an approximately rectangular parallelepiped cell can configured by a metal container such as aluminum, or laminate film. Inside the housing  14   a , for example, an electrode main body (coil) (not shown) that is spirally wound, an electrolyte solution, etc. are housed. 
     On a top plate  14   b  of the housing  14   a , a pair of cell terminals, and the pressure relief portion  16  that is a safety valve, are arranged. The cell terminals of the adjacent battery cells  14  are connected by a bus bar  22 . In the present embodiment, the cell terminals of the five battery cells  14  are connected in series by four bus bars  22 . 
     A positive electrode cell terminal  23  is connected to a cell terminal of one battery cell  14  arranged on the outer side. A negative electrode cell terminal  24  is respectively connected to a cell terminal of the other battery cell  14  arranged on the outer side. 
     The pressure relief portion  16  is a thin-walled portion  16   a , which is a part of the top plate  14   b  of the housing  14   a  that is formed thinner in thickness than the other parts, as shown in  FIG. 3 . In other words, the pressure relief portion  16  is a fragile portion formed on a part of the top plate  14   b . In the present embodiment, the pressure relief portion  16  is formed into a shape in which a part of the top surface of the top plate  14   b  is dented with respect to that which surrounds it. 
     The thin-walled portion  16   a  is formed by, for example, a cross-shaped groove in which a plurality of linear grooves are arranged in a cross shape on a surface of the top plate  14   b . Note that the thin-walled portion  16   a  may be provided on the reverse side of the top plate  14   b , or may be provided on both surfaces of the top plate  14   b.    
     This pressure relief portion  16  releases inside the space of the battery cell  14  by the thin-walled portion  16   a  rupturing if the internal pressure of the housing  14   a  exceeds a preset pressure to let the internal vent gas of the battery cell  14  to flow out. 
     The upper case  12  is a housing which is shaped like a rectangular box and in which a lower surface opening  12   a  is formed. This upper case  12  comprises a top plate portion  12   b , and side wall portions  12   c ,  12   d ,  12   e , and  12   f  configuring four surfaces including a front surface, a rear surface, a right surface, and a left surface. 
     Then, in a state where an upper end portion of the lower case  13  (an end portion on the upper surface opening  13   a  side) and a lower end portion of the upper case  12  (an end portion on the lower surface opening  12   a  side) are abutted, the upper case  12  and the lower case  13  are fixed by a screw (not shown). Thereby, the upper case  12  and the lower case  13  are joined. At this time, in between the lower case  13  and the upper case  12  is sealed by a packing (not shown). Thus, the inner portion of the battery case  11  is sealed. 
     The upper case  12  is provided with the upper plate portion  12   b  with a hole through which a positive electrode terminal  18  is inserted, a hole through which a negative electrode terminal  19  is inserted, two vent gas release portions  25 , etc. The vent gas release portion  25  comprises a hole  25   a  formed on the upper case  12 , and a waterproof vent filter  25   b  provided in the hole  25   a  to allow the air inside the battery case  11  and the air outside the battery case  11  to flow out from and into the battery case  11 , respectively, while keeping the inside of the battery case  11  water tight. 
     This waterproof vent filter  25   b  comprises, for example, a porous PTFE film. Then, the vent gas release portion  25  is configured, when the internal pressure of the battery case  11  changes as a result of a change in surrounding atmospheric pressure, a rise in temperature, etc., to allow the air inside the battery case  11  and the air outside the battery case  11  to flow out from and into (be exchanged) the battery case  11 , with the battery case  11  kept water tight. This inhibits a possible difference in pressure between the inside and outside of the battery case  11 . 
     In addition, the vent path structure  26 , a control substrate  17 , other structural members, etc. are arranged on an upper side of the battery module  15 . A positive electrode tab  20  and a negative electrode tab  21  of the battery module  15  are connected to the control substrate  17 . A positive electrode terminal  18  is connected to an upper end portion of the positive electrode tab  20 . The positive electrode cell terminal  23  of the battery module  15  is connected to a lower end portion of the positive electrode tab  20 . A negative electrode terminal  19  is connected to an upper end portion of the negative electrode tab  21 . The negative electrode cell terminal  24  of the battery module  15  is connected to a lower end portion of the negative electrode tab  21 . 
     In addition, the vent path structure  26  is formed by the case  27  arranged on an upper side of the battery module  15 , as shown in  FIG. 3 . This case  27  comprises a lower side member  28  on an upper surface of which the upper surface opening  28   a  is formed, and a plate-like upper side member  29  that becomes a lid to seal the upper surface opening  28   a , as shown in  FIG. 4 . The lower side member  28  and upper side member  29  are formed by, for example, an insulator, such as resin. 
     The lower side member  28  comprises approximately the same length as that of the five battery cells  14  of the battery module  15  in a juxtaposition direction. As shown in  FIG. 5 , five communicating holes  30  are formed on a bottom surface  27   a  of the lower side member  28 . Each of the five communicating holes  30  is communicating with each pressure relief portion  16  of the five battery cells  14 . Note that the bottom surface  27   a  is a lower surface of an internal space of the case  27 . 
     To explain specifically, in the present embodiment, the pressure relief portion  16  is configured by a part of an upper surface of the top plate portion  14   b  being formed into a dented shape with respect to that which surrounds it. A communicating hole  30  is opposed to the pressure relief portion  16 , and a peripheral portion of the communicating hole  30  is in contact with and sealed by a peripheral portion of the pressure relief portion  16 , and thereby the pressure relief portion  16  and the communicating hole  30  are communicated. Note that the lower side member  28  is fixed to the battery module  15  by a fixing means, such as an adhesive or fixing member, in a state where the lower surface  27   b  of the lower side member  28  is in contact with an upper surface of the battery module  15 . 
     In the upper side member  29 , the communicating hole  31  is formed at a position corresponding to each of the two vent gas release portions  25  of the upper case  12 . Note that in the present embodiment, the corresponding position is, as an example, an opposed position with the control substrate  17  therebetween. 
     The control substrate  17  is arranged on the upper surface of the upper side member  29 . Furthermore, two intermediate communicating holes  32  are formed in the control substrate  17 . The intermediate communicating holes  32  penetrate the control substrate  17  in its thickness direction. One intermediate communicating hole  32  is communicated to one communicating hole  31  and the hole  25   b  of one vent gas release portion  25 . The other intermediate communicating hole  32  is communicated to the other communicating hole  31  and the hole  25   b  of the other vent gas release portion  25 . 
     To explain specifically, on the lower surface of the control substrate  17 , a peripheral portion of the intermediate communicating hole  32  and a peripheral portion of the communicating hole  31  are in contact with each other so as to be sealed therebetween, and the intermediate communicating hole  32  is communicated to the communicating hole  31 . On the upper surface of the control substrate  17 , the peripheral portion of the intermediate communicating hole  32  and the peripheral portion of the hole  25   b  of the vent gas release portion  25  are in contact with each other so as to be sealed therebetween, and the intermediate communicating hole  32  is communicated to the hole  25   b.    
     Thereby, the vent gas path  33 , through which a vent gas flows between the pressure relief portion  16  and the vent gas release portion  25  by an internal space of the case  27  and the intermediate communicating hole  32  of the control substrate  17 , is formed. Then, a part of the vent gas path  33  is surrounded by the case  27 . The vent gas path  33  is provided extended in a direction orthogonal to the gravity direction. 
     Furthermore, the vent path structure  26  comprises a liquid trap portion  34  which facilitates liquefaction of the vent gas flowing inside the vent gas path  33 . The liquid trap portion  34  traps the liquefied liquid. Herein, on the bottom surface  27   a  of the lower side member  28 , a plurality of fine convex portions  35  protruding upward, and a first heat sink portion  36  in which concave portions between adjacent convex portions  35  are aligned in a direction in which a plurality of battery cells  14  are aligned, are formed. 
     A plurality of convex portions  35  are configured by, for example, fixing another plate-like member to the lower side member  28  by a fixing means, such as an adhesive agent. Note that the convex portions  35  may be formed integrally with the lower side member  28 . Each of a plurality of convex portions  35  is, for example, formed into a rectangular plate shape extending from one inner side surface to the other inner side surface along a direction in which the battery cells  14  are aligned. An upper end of the plurality of convex portions  35  are disposed on the same plane. Namely, the height of each of a plurality of convex portions  35  with respect to the bottom surface  27   a  is the same. The height of a plurality of convex portions  35  is set to configure a main path  33   a  between with a lower end of a convex portion  37 , to be described later, of the upper side member  29 . Note that a concave portion between two convex portions  35  communicates with the main path  33   a . The main path  33   a  extends in a direction orthogonal to a direction in which the gravity is applied in a state where the batteries  14  are installed. 
     In addition, on the upper side member  29 , a plurality of fine convex portions  37  protruding downward in an inner surface  29   a  (a lower surface in  FIG. 3 ), and a second heat sink portion  38 , in which concave portions between adjacent convex portions  37  are aligned in a direction in which a plurality of battery cells  14  are aligned, are formed. 
     A plurality of convex portions  37  may be, for example, configured by fixing another plate-like member to the upper side member  29  by a fixing means, such as an adhesive agent. Note that the convex portion  37  may be formed integrally with the upper side member  29 . Each of a plurality of convex portions  37  is, for example, formed into a rectangular plate shape extending from one edge to the other edge along a direction in which the battery cells  14  are aligned. Lower ends of a plurality of convex portions  37  are arranged on the same plane. Concave portions between two adjacent convex portions  37  communicate with the main path  33   a.    
     In the first heat sink portion  36  of the lower side member  28 , a space between two adjacent convex portions  35  is set to generate capillarity. In other words, the width of a concave portion between the adjacent convex portions  35  is set to generate capillarity. In the second heat sink portion  38  of the upper side member  29 , a space of two adjacent convex portions  37  is set to generate capillarity. In other words, the width of a concave portion between the adjacent convex portions  37  is set to generate capillarity. Then, in the present embodiment, the liquid trap portion  34  is formed by the first heat sink portion  36  of the lower side member  28  and the second heat sink portion  38  of the upper side member  29 . 
     In the present embodiment, a suitable space is formed between the first heat sink portion  36  of the lower side member  28  and the second heat sink portion  38  of the upper side member  29 . This space configures the main path  33   a.    
     Next, a working effect of the battery  11 A of the present embodiment with the above configuration will be described. At the time of an abnormality of the battery  11 A of the present embodiment, for example, if a high temperature combustible gas is generated in the inner portion of the battery cell  14  due to thermal runway of the battery cell  14  and an internal pressure of the battery cell  14  increases, the pressure relief portion  16  of the battery cell  14  operates. 
     Namely, the pressure relief portion  16  is set in advance so that the thin-walled portion  16   a  will be cut if the internal pressure of the housing  14   a  becomes a set pressure or higher. Thereby, a vent gas expelled from the inner portion of the battery cell  14  is allowed to flow out through a slit of the thin-walled portion  16   a.    
     At this time, a combustible vent gas released from the pressure relief portion  16  of the battery cell  14  flows into the vent path structure  26  through the communicating hole  30 . The vent gas that has flowed into the vent path structure  26  passes the vent gas path  33  which is an internal space of the case  27 , and flows in a direction orthogonal to the gravity direction. Then, as shown by an arrow in  FIG. 3 , via two communicating holes  31  of the upper side member  29 , the intermediate communicating holes  32  of the control substrate  17 , and the two vent gas release portions  25  of the upper case  12 , the vent gas sequentially flows to the outside of the battery case  11 . 
     The vent gas in the vent path structure  26  flows in a mist form (a steam-like state). At this time, the first heat sink portion  36  of the lower side member  28  and the second heat sink portion  38  of the upper side member  29  have large surface areas, and thus have a high heat transfer coefficient. Accordingly, in the present embodiment, by the vent gas coming in contact with the first heat sink portion  36  of the lower side member  28  and the second heat sink portion  38  of the upper side member  29 , in which fine successive convex and concave capillarity is generated, cooling of the vent gas is facilitated, which can make it easy to liquefy the vent gas. 
     Furthermore, the vent gas that was cooled and liquefied in the vent gas path  33  can be stored in each concave portion of the first heat sink portion  36  of the lower side member  28  and each concave portion of the upper side member  29  by capillarity. 
     At this time, an amount of liquid of the vent gas to be liquefied is small, and by overcoming the gravity and a flow rate of the vent gas, the vent gas can be trapped in each concave portion of the first heat sink portion  36  of the lower side member  28 , and each concave portion of the second heat sink portion  38  of the upper side member  29  by capillarity. 
     This can avoid improper flow of the vent gas that was liquefied in the inner portion of the battery case  11 , and blocks a narrow portion on the vent gas path  33 , for example, a surrounding portion of a slit of the thin-walled portion  16   a  of the battery cell  14  and a surrounding portion of the two communicating holes  31  of the upper side member  29 . 
     In addition, the communicating holes  30 , communicating with each pressure relief portion  16  of the five battery cells  14  of the battery module  15 , are formed in the lower side member  28  of the vent path structure  26 . Furthermore, the communicating holes  31 , communicating with the two vent gas release portions  25  of the upper case  12 , are formed in the upper side member  29  of the vent path structure  26 . Accordingly, the vent gas is first liquefied in the surroundings of the communicating hole  30  on the upstream side of the vent gas path  33  so that the volume of the vent gas flow can be reduced. Thereby, an internal pressure and a gas flow rate of the vent gas flowing in the inner portion of the vent gas path  33  can be lowered so as to make it easy to trap the liquefied vent gas. 
     Furthermore, the liquid trap portion  34  is provided in the upstream vent gas path  33  of a narrow location and a complex location (a bent location, a location where a cross-sectional area is not successive, and a location where a liquid pool is likely to be generated due to an effect of gravity) of the path through which the gas flows like the two vent gas release portions  25  of the upper case  12 . Thus, flowing of the vent gas that is liquefied into the two vent gas release portions  25  can be suppressed. 
     In addition, a plurality of convex portions  35  of the first heat sink portion  36  of the lower side member  28  consisting of the liquid trap portion  34 , and a plurality of convex portions  37  of the second heat sink portion  38  of the upper side member  29 , are configured into a shape protruding in a direction orthogonal to a direction in which the vent gas flowing in the inner portion of the vent gas path  33  flows. Accordingly, the liquid trapping power can be improved. Note that the liquid trapping power can also be improved by arranging the liquid trap portion  34  vertically to the gravity direction. Specifically, the plurality of convex portions  35  and the plurality of convex portions  37  protrude in a direction orthogonal to the gravity direction. An example is a configuration in which the case  27  shown in  FIG. 4  is rotated by 90 degrees. 
     The battery  11 A of the present embodiment with the above configuration brings about the following effects. By providing the first heat sink portion  36  of the lower side member  28  and the second heat sink portion  38  of the upper side member  29  in a large place of the vent gas path  33 , cooling of the vent gas can be facilitated when liquefying. 
     Furthermore, at the same time as liquefaction of the vent gas, the vent gas that is liquefied is stored among a plurality of convex portions  35  of the first heat sink portion  36  of the lower side member  28  and among a plurality of convex portions  37  of the second heat sink portion  38  of the upper side member  29  by capillarity. Thereby, improper flow of the vent gas that is liquefied in the inner portion of the vent gas path  33  and blocking a narrow portion on the vent gas path  33  can be avoided. 
     Thus, in the battery  11 A of the present embodiment, at the time of abnormality of the battery, in a case where a high temperature vent gas is expelled from the battery cell  14  of the battery  11 A, the vent gas can be safely and smoothly released to the outside of the battery case  11  of the battery  11 A. 
       FIG. 6  shows the lower side member  28  of the vent path structure  41 , which is a modification of the vent path structure  26  of the battery  11 A of the above embodiment. Note that in  FIG. 6 , the identical portions as those of  FIGS. 1-5  are denoted as the identical reference signs and explanation thereof will be omitted. The upper side member  29  may be the same as that explained with reference to  FIGS. 1-5 . 
     In the vent path structure  41  of the present modification, a first heat sink portion  43  is formed having a plurality of fine convex portions  42  that are formed into a pin-fin shape protruding upward on a lower surface (a bottom surface  27   a ) of the case  27  of the lower side member  28 . In other words, a plurality of convex portions  42  are formed instead of a plurality of convex portions  35 . In  FIG. 6 , the first heat sink portion  43  of the lower side member  28  is indicated, but a second heat sink portion having a plurality of fine convex portions  42  formed into a pin-fin shape may of course be formed instead of a plurality of convex portions  37 . In this case as well, the main path  33   a  is formed between the first heat sink portion and the second heat sink portion. 
     In the vent path structure  41  of the present modification, the liquid trap portion  34 , which facilitates liquefaction of the vent gas flowing in the vent gas path  33  by a plurality of fine convex portions  42  formed into a pin-fin shape and traps the vent gas which is liquefied, can be configured. Thus, in the present modification, the same effect as that of the vent path structure  26  of the battery  11 A of the above embodiment can be obtained. 
     Alternatively, the pin-fin shaped convex portion  42  may be formed only in the lower side member  28 , and the upper side member  29  may be formed into a plate-like shape. In this case, the convex portion  42  may have a height such that its upper end comes in contact with the upper side member  29 . In this case, a space between the convex portions  42  is set so that the vent gas can flow and capillarity is not generated. In this case, it is possible to facilitate the liquefaction of the vent gas, but is not possible to trap liquid between the convex portions  42 . 
     In the present embodiment, the vent path is configured by the case  27  and the control substrate  17 . However, the vent path may be configured only by the case  27 . In this case, the intermediate communicating hole  31  formed in the upper side member  29  of the case  27  communicates with the hole  25   b  of the vent gas release portion  25  not via the control substrate  17 . In this case, for example, a peripheral portion of the intermediate communicating hole  31  of the upper side member  29  is abutted to a peripheral portion of the hole  25   b  of the upper case  12 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.