Patent Publication Number: US-2011070476-A1

Title: Power storage apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a power storage apparatus in which a plurality of power storage components are arranged side by side in one direction with a spacer interposed between the power storage components. 
     BACKGROUND ART 
     In using a secondary battery as the power source of a vehicle, a battery module formed of a plurality of secondary batteries (cells) is mounted on the vehicle. Specifically, the plurality of cells constituting the battery module are connected electrically in series to allow output of energy necessary for the running of the vehicle. An exemplary battery module includes a plurality of cells arranged side by side in one direction. Specifically, the plurality of cells having square shape are arranged side by side with a spacer interposed between the adjacent ones of them, and the plurality of cells and the spacers are sandwiched between end plates placed at both ends in the arrangement direction. The spacers are provided for preventing the two cells adjacent in the arrangement direction from coming into contact with each other. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     [Patent Document 1] Japanese Patent Laid-Open No. 2002-042753 
     [Patent Document 2] Japanese Patent Laid-Open No. 2002-134078 
     [Patent Document 3] Japanese Patent Laid-Open No. 2004-362879 
     [Patent Document 4] Japanese Patent Laid-Open No. 2000-323187 
     [Patent Document 5] Japanese Patent Laid-Open No. 2007-048750 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the configuration in which the plurality of cells are arranged side by side in one direction, for example when a particular one of the cells generates heat due to overcharge or the like, the heat may be transferred to the other cells placed adjacently to that particular cell. Since the spacer is placed between the two cells adjacent in the arrangement direction, the heat generated in the particular cell is transferred to the other cells through the spacers. In addition, the spacer is typically made of thermoplastic resin and may be melted by the heat from the cell. 
     It is thus an object of the present invention to provide a power storage apparatus having a configuration including a plurality of power storage components arranged side by side, wherein, even when the temperature suddenly rises in any of the power storage components, the transfer of the heat to the other power storage components placed adjacently to that power storage component can be suppressed. 
     Means for Solving the Problems 
     According to a first aspect, the present invention provides a power storage apparatus including a plurality of power storage components arranged side by side in a predetermined direction, and a spacer located between the power storage components adjacent in the predetermined direction and in contact with the power storage components. The spacer has a base material formed of resin and a blowing agent held by the base material and thermally decomposed in response to a temperature rise associated with heat generation of the power storage component. 
     The decomposition temperature of the blowing agent is lower than a temperature when the power storage component is in an abnormal state. This can achieve the thermal decomposition of the blowing agent when the power storage component approaches the abnormal state. 
     According to a second aspect, the present invention provides a power storage apparatus including a plurality of power storage components arranged side by side in a predetermined direction, a spacer located between the power storage components adjacent in the predetermined direction, and an insulating layer provided between the power storage component and the spacer and in contact with the power storage component and the spacer. The insulating layer has a base material formed of thermosetting resin and a blowing agent held by the base material and thermally decomposed in response to a temperature rise associated with heat generation of the power storage component. 
     The insulating layer can be a member in sheet form, or the insulating layer can be a film formed by coating to a surface of at least one of the power storage component and the spacer. The spacer can be formed of thermoplastic resin. In this case, the melting of the spacer can be suppressed even when the power storage component extremely generates heat. Even when the spacer is melted, the base material of the insulating layer is formed of thermosetting resin and thus the insulating layer is arranged between the power storage components adjacent in the predetermined direction to allow the prevention of contact of these power storage components. 
     In the present invention, the spacer can be provided with a protruding portion extending in the predetermined direction and configured to form a path within a plane orthogonal to the predetermined direction, the path where a heat exchange medium performing heat exchange with the power storage component is moved. This enables efficient temperature adjustment of the power storage components. A blowing agent of endothermic decomposition type can be used as the blowing agent. This can absorb heat transferred from the power storage component when the blowing agent is thermally decomposed. 
     In addition, a support structure can be provided. The support structure supports the power storage components and the spacers by using a force bringing the plurality of power storage components closer to each other in the predetermined direction. This can suppress thermal expansion of the power storage components. 
     EFFECT OF THE INVENTION 
     According to the first aspect of the present invention, when the temperature of the power storage component rises and the heat is transferred to the spacer, the blowing agent can be thermally decomposed to form a space portion in the spacer. This space portion can suppress the transfer of the heat in the spacer to reduce the transfer of the heat to the other power storage components. In addition, since the blowing agent is present in the spacer when the temperature of the power storage components does not rise suddenly, the mechanical strength of the spacer can be ensured. 
     According to the second aspect of the present invention, when the temperature of the power storage component rises and the heat is transferred to the insulating layer, the blowing agent can be thermally decomposed to form a space portion in the insulating layer. This space portion can suppress the transfer of the heat in the insulating layer to reduce the transfer of the heat to the spacers or the other power storage components. In addition, since the base material of the insulating layer is formed of thermosetting resin, it is possible to prevent contact of the two power storage components between which the insulating layer is sandwiched. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A side view showing a battery module which is Embodiment 1 of the present invention. 
         FIG. 2  A front view of a spacer in Embodiment 1. 
         FIG. 3  A side view showing the configuration of part of the battery module of Embodiment 1. 
         FIG. 4  A side view showing the configuration of part of a battery module which is Embodiment 2 of the present invention. 
         FIG. 5  A schematic diagram showing the configuration of an insulating sheet in Embodiment 2. 
         FIG. 6  A side view showing the configuration of part of a battery module which is a modification of Embodiment 2. 
         FIG. 7  A diagram showing the outer appearance of a cell surrounded by an insulating film in the modification of Embodiment 2. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Embodiments of the present invention will hereinafter be described. 
     Embodiment 1 
     A battery module (power storage apparatus) which is Embodiment 1 of the present invention will be described with reference to  FIG. 1 .  FIG. 1  is a side view showing the configuration of the battery module of the present embodiment. In  FIG. 1 , an X axis, a Y axis, and a Z axis represent axes orthogonal to each other, and the Z axis is defined as an axis corresponding to a vertical direction in the present embodiment. This applies to the figures other than  FIG. 1 . 
     The battery module  1  has a plurality of cells (power storage components)  10 . The plurality of cells  10  are arranged side by side in the X direction. A spacer  20  is placed between the two cells  10  adjacent to each other in the X direction. In the present embodiment, as shown in  FIG. 1 , the spacer  20  is also placed between the cell  10  located at one end of the battery module  1  (the right end in  FIG. 1 ) and an end plate  40 , later described. 
     A secondary battery such as a lithium-ion battery or a nickel metal hydride battery can be used as the cell  10 . Alternatively, an electric double layer capacitor (condenser) can be used instead of the secondary battery. 
     Each of the cells  10  is formed of a cell case and a power generating element (not shown) accommodated by the cell case. The cell case is made of metal. The power generating element is an element which can perform charge and discharge, and a known configuration can be used as appropriate therefor. Specifically, the power generating element can be provided by laminating a positive electrode component, a separator containing a liquid electrolyte, and a negative electrode component in this order. Each of the positive electrode component and the negative electrode component is formed of a collector plate and an active material layer formed on the surface of the collector plate. The active material is provided by using a material suitable for the positive electrode or the negative electrode. 
     A positive electrode terminal (electrode terminal)  11  and a negative electrode terminal (electrode terminal)  12  are provided on the top of each of the cells  10 . The positive electrode terminal  11  and the negative electrode terminal  12  are placed side by side in the Y direction in each of the cells  11 , and  FIG. 1  shows only one of the electrode terminals in each of the cells  10 . The positive electrode terminal  11  is electrically and mechanically connected to the positive electrode component of the power generating element described above. The negative electrode terminal  12  is electrically and mechanically connected to the negative electrode component of the power generating element described above. 
     The positive electrode terminal  11  in the cell  10  is electrically connected to the negative electrode terminal  12  in the cell  10  placed adjacently to the former cell  10  through a bus bar  30 . Similarly, the negative electrode terminal  12  in the cell  10  is electrically connected to the positive electrode terminal  11  in the cell  10  placed adjacently to the former cell  10  through the bus bar  30 . The plurality of cells  10  constituting the battery module  1  are connected electrically in series. 
     The positive electrode terminal  11  of one of the plurality of cells  10  serves as a general positive terminal of the battery module  1 . The negative electrode terminal  12  of another one of the cells  10  serves as a general negative terminal of the battery module  1 . The general positive terminal and the general negative terminal are connected to a general positive cable and a general negative cable for performing charge and discharge of the battery module  1 , respectively. 
     The number of the cells  10  can be set as appropriate. Specifically, for providing desired output from the battery module  1 , the number of the cells  10  can be set on the basis of the output value (voltage value) of the battery module  1 . 
     A safety valve can be provided on the top of each of the cells  10 , although not shown. The safety valve is used for discharging gas generated inside the cell  10  (generated from the power generating element) to the outside of the cell  10 . For example, if the cell  10  is overcharged, high-temperature gas may be generated from the power generating element of the cell  10 . Thus, the gas can be discharged to the outside of the cell  10  through the safety valve in order to suppress expansion or the like of the cell  10  (the cell case) due to the gas. 
     The cell  10  is formed in square shape and has six faces. Specifically, the cell  10  has an upper face, a lower face, two first side faces, and two second side faces. The first side faces refer to the side faces of the cell  10  that constitute Y-Z planes. The second side faces refer to the side faces of the cell  10  that constitute X-Z planes. The first side faces of the cell  10  are in contact with the spacers  20 . 
     Out of the plurality of cells  10  constituting the battery module  10 , the cell  10  located at the other end in the X direction (the left end in  FIG. 1 ) has the two first side faces, only one of which is in contact with the spacer  20 . The other first side face is in contact with the end plate  40 , later described. 
     The spacer  20  has a plurality of protruding portions  21 . As shown in  FIG. 2 , each of the protruding portions  21  extends in the Y direction from one end to the other end of the spacer  20 . The plurality of protruding portions  21  are provided at predetermined intervals in the Z direction.  FIG. 2  is a front view of the spacer  20  when it is viewed from the X direction. 
     The spacer  20  is sandwiched between two cells  10 , and the tips of the protruding portions  21  are in contact with the first side face of one of those cells  10 . The surface of the spacer  20  that is opposite in the X direction to the surface having the protruding portions  21  formed thereon is formed of a planar surface and is in contact with the first side face of the other cell  10 . The spacer  20  located at the one end of the battery module  1  (the right end in  FIG. 1 ) is sandwiched between the cell  10  and the end plate  40  and is in contact with the cell  10  and the end plate  40 . 
     The contact of the protruding portions  21  with the first side face of the cell  10  forms space S between the first side face of the cell  10  and the spacer  20 . The space S serves as a flow path for passing a heat exchange medium (gas) supplied to the battery module  1 . Arrows indicated by dotted lines in  FIG. 2  represent the moving directions of the heat exchange medium. 
     While the protruding portions  21  extending in the Y direction are used in the present embodiment, the present invention is not limited thereto. The shape and the number of the protruding portions  21  can be set as appropriate. It is essential only that the protruding portions  21  can form the space through which the heat exchange medium can be moved as described above. 
     The cell  10  may generate heat due to charge and discharge or the like. The cell  10  shows desired battery characteristics (characteristics about charge and discharge) within a predetermined temperature range, and if the temperature of the cell  10  falls outside the predetermined temperature range, the battery characteristics may be deteriorated. For this reason, the cell  10  needs to be heated or cooled depending on the temperature of the cell  10 . Specifically, the temperature of the cell  10  can be adjusted by supplying the heat exchange medium (gas) such as air to the battery module  1 . 
     When the heat exchange medium is introduced into the abovementioned space S, the heat exchange medium comes into contact with the cell  10  to perform heat exchange with the cell  10 . This can adjust the temperature of the cell  10 . Specifically, when the cell  10  generates heat, the cooled heat exchange medium is brought into contact with the cell  10  to allow suppression of a temperature rise in the cell  10 . On the other hand, when the cell is cooled, the heated heat exchange medium is brought into contact with the cell  10  to allow suppression of a temperature drop in the cell  10 . 
     In the present embodiment, the spacer  20  has a base material  22  made of resin and a blowing agent  23  embedded in the base material  22  as shown in  FIG. 3 . A thermosetting resin or a thermoplastic resin can be used as the resin forming the base material  22 . Examples of the thermosetting resin include phenol resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, polyurethane, and thermosetting polyimide. Examples of the thermoplastic resin include polyethylene, polypropylene, polychlorinated vinyl, and polystyrene. 
     The blowing agent  23  is fixed, in an unfoamed state, to the interior or the surface of the base material  22 . In other words, the base material  22  holds the blowing agent  23 . The blowing agent  23  can be provided only on the surface of the base material or can be provided only inside the base material  22 . The unfoamed state refers to the state in which the blowing agent  23  is not completely decomposed thermally, and in other words, to the state in which a space portion (recessed portion or hole portion) can be formed in the base material  22  by generation of gas associated with thermal decomposition. 
     Any material that is thermally decomposed at a predetermined temperature can be used for the blowing agent  23  as described later, and it is possible to use an organic blowing agent, an inorganic blowing agent, or a mixture thereof. Examples of the organic blowing agent include dinitrosopentamethylenetetramine, azodicarbonamide, p,p′-oxybis(benzenesulfonylhydrazide), and hydrazodicarbonamide. Examples of the inorganic blowing agent include sodium hydrogen carbonate and ammonium carbonate. 
     When the thermoplastic resin is used as the material of the base material  22 , the blowing agent  23  can be previously mixed into the thermoplastic resin before the spacer  20  is shaped into the predetermined form (the form shown in  FIGS. 1 and 2 ) or the blowing agent  23  can be mixed into the thermoplastic resin in the course of shaping of the spacer  20 . When the blowing agent  23  is previously mixed into the thermoplastic resin, the decomposition temperature of the blowing agent  23  is preferably higher than the shaping temperature of the thermoplastic resin. On the other hand, if the decomposition temperature of the blowing agent  23  is lower than the shaping temperature of the thermoplastic resin, the blowing agent  23  can be mixed during the course of cooling of the thermoplastic resin formed in the predetermined shape. 
     On the other hand, when the thermosetting resin is used as the material of the base material  22 , the blowing agent  23  can be previously mixed into the thermosetting resin before the spacer  20  is shaped into the predetermined form, and the thermosetting resin containing the blowing agent  23  can be shaped into the form of the spacer  20 . 
     The volume ratio of the base material  22  and the blowing agent  23  can be set as appropriate. If the volume of the blowing agent  23  occupying in the spacer  20  is significantly larger than the volume of the base material  22  occupying in the spacer  20 , the base material  22  may not hold the blowing agent  23 . 
     In  FIG. 1 , a pair of end plates (part of a support structure)  40  are placed at both ends of the battery module  1  in the X direction. The end plate  40  is formed of resin. One of the pair of end plates  40  is in contact with the cell  10 , and the other end plate  40  is in contact with the spacer  20 . Restraint members (part of the support structure)  41  extending in the X direction are fixed to the pair of end plates  40 . Specifically, one end of each of the restraint members  41  is fixed to the one of the end plates  40  through a bolt  42 , and the other end of each of the restraint members  41  is fixed to the other end plate  40  through a bolt  42 . 
     In the present embodiment, the two restraint members  41  are placed on an upper surface of the battery module  1  and the two restraint members  41  are placed on a lower surface of the battery module  1 .  FIG. 1  shows one of the restraint members  41  that is placed on each of the upper surface and the lower surface of the battery module  1 . The restraint member  41  can be formed of metal or resin. When the restraint member  41  formed of metal is used, the restraint member  41  is preferably placed separately from the cells  10 . 
     With the abovementioned configuration, forces (restraint forces) indicated by arrows F in  FIG. 1  are applied from the pair of end plates  40  to the plurality of cells  10  and the spacers  20  arranged side by side in the X direction. The forces F serve as the forces which allow the pair of end plates  40  to support the plurality of cells  10  and the spacers  20  sandwiched between the end plates  40 . Each of the cells  10  is subjected to the forces F to come into close contact with the spacers  20  or the end plate  40 . 
     The structure for supporting the plurality of cells  10  and the spacers  20  is not limited to the structure shown in  FIG. 1 . Any structure can be used as long as the forces indicated by the arrows F in  FIG. 1  are applied to the plurality of cells  10  and the spacers  20 . Specifically, the shape and the number of the restraint members  41 , and the position where the restraint members  41  are placed can be set as appropriate. 
     The battery module  1  described above is accommodated by a pack case (not shown), so that a battery pack is provided. The battery module  1  is fixed to the pack case. A plurality of battery modules  1  can be placed side by side within the pack case. The battery pack can be mounted on a vehicle. Examples of the vehicle include a hybrid vehicle and an electric vehicle. The hybrid vehicle refers to a vehicle which is provided not only with the battery pack as a power source but also with another power source such as an internal combustion engine or a fuel battery. The electric vehicle refers to a vehicle which runs only with the output from the battery pack. The battery pack in the present embodiment is discharged to output energy for use in running of the vehicle or is charged with kinetic energy generated in braking of the vehicle as regenerative power. The battery pack can be charged with power supplied from the outside of the vehicle. 
     Next, description will be made of the case where one of the plurality of cells  10  excessively generates heat (abnormal heat generation) in the battery module  1  of the present embodiment. The abnormal heat generation refers to a sudden rise in temperature of the cell  10  due to overcharge or the like. When gas is generated from the power generating element within the cell  10 , the temperature of the cell  10  may rise suddenly. 
     When one of the plurality of cells  10  constituting the battery module  1  abnormally generates heat, the temperature of the spacer  20  in contact with that cell  10  also rises. Since the blowing agent  23  is contained in the spacer  20 , the blowing agent  23  is thermally decomposed when the temperature of the spacer  20  becomes higher than the decomposition temperature of the blowing agent  23 . 
     When the thermal decomposition of the blowing agent  23  generates gas, a space portion (recessed portion or hole portion) is formed at the point where the blowing agent  23  was located. Air or the like is present in the space portion of the spacer  20 . Since the air has a thermal conductivity lower than the thermal conductivity of the resin forming the base material  22  of the spacer  20 , it is possible to suppress the transfer of the heat of the cell  10  abnormally generating heat to the other cells  10  through the spacer  20 . 
     It is conceivable that the abovementioned space portion may be previously formed in the spacer  20  in order to suppress the transfer of the heat of the cell  10  to the other cells  10  through the spacer  20 . In this case, however, the space  20  cannot have sufficient mechanical strength. 
     For example, when the restraint forces F (see  FIG. 1 ) are applied to the cells  10  and the spacers  20  as in the battery module  1  of the present embodiment, the spacers  20  need to perform their functions even when the spacers  20  are subjected to the restraint forces F. The functions of the spacer  20  include the formation of the space S for moving the heat exchange medium to the surface of the cell  10  and the holding of the insulating state of the two cells  10  between which the spacer  20  is sandwiched. Even in a structure in which the restraint forces F are not applied to the cells  10  and the spacers  20 , the mechanical strength of the spacers  20  is preferably ensured. 
     Since the blowing agent  23  is present in the spacer  20  in the state where the cell  10  does not generate heat abnormally in the present embodiment, the mechanical strength of the spacer  20  can be ensured. In this manner, in the battery module  1  of the present embodiment, while the mechanical strength of the spacer  20  is ensured, the space portion can be formed in the spacer  20  to suppress the transfer of the heat only when the cell  10  generates heat abnormally. 
     To hold the mechanical strength of the spacer  20  after the blowing agent  23  is thermally decomposed, inorganic particles can be contained in the base material  22  of the spacer  20 . For example, ceramics such as silica, alumina, and zirconia can be used as the inorganic particles. 
     When a blowing agent of endothermic decomposition type is used as the blowing agent  23 , that blowing agent  23  can absorb heat from the cell  10  abnormally generating heat during the thermal decomposition of the blowing agent  23 . This not only can suppress the transfer of the heat of the cell  10  abnormally generating heat to the other cells  10  but also can reduce the amount of heat transferred to the other cells  10 . Examples of the blowing agent of endothermic decomposition type include hydrazodicarbonamide and sodium hydrogen carbonate. 
     When a thermosetting resin is used as the base material  22  of the spacer  20 , the spacer  20  can be prevented from being melted even when the spacer  20  is subjected to the heat from the cell  10 . Thus, the two cells between which the spacer  20  is sandwiched can be prevented from coming into contact with each other. 
     In the present embodiment, the temperature of the cell  10  when it is determined that the cell  10  generates heat abnormally can be previously determined, and the material of the blowing agent  23  can be selected on the basis of that temperature. For example, when the temperature of the cell  10  at the time of abnormal heat generation is 300° C., hydrazodicarbonamide can be used as the blowing agent which is thermally decomposed at 245° C. lower than that temperature of the cell  10 . When the thermosetting resin is used as the base material  22  of the spacer  20 , phenol resin or epoxy resin can be used as the resin, for example. 
     While the blowing agent  23  is contained in each of the spacers  20  forming the battery module  1  in the present embodiment, the present invention is not limited thereto. Specifically, it is essential only that at least one of the plurality of spacers  20  forming the battery module  1  should contain the blowing agent  23 . In this case, the abovementioned effects can be achieved in the spacer  20  containing the blowing agent  23 . If one of the cells  10  that is likely to generate heat abnormally can be identified, the spacer  20  containing the blowing agent  23  can be placed in contact with that cell  10 . 
     Embodiment 2 
     Next, a battery module which is Embodiment 2 of the present invention will be described with reference to  FIG. 4 .  FIG. 4  is a side view showing the configuration of part of the battery module of the present embodiment. Members having the same functions as those of the members described in Embodiment 1 are designated with the same reference numerals and detailed description thereof is omitted. In the following, different points from those in Embodiment 1 will be described mainly. 
     In the present embodiment, an insulating sheet  60  is placed between a spacer  20  and a cell  10 , in other words, between cells  10  adjacent to each other in an X direction. The insulating sheet  60  is in contact with the spacer  20  and the cell  10  and is formed to have substantially the same size as that of the spacer  20  when the insulating sheet  60  is viewed from the X direction. As shown in  FIG. 5 , the insulating sheet  60  has a base material  61  formed of thermosetting resin and a blowing agent  62  embedded in the base material  61 . 
     The blowing agent  62  is unfoamed similarly to the case described in Embodiment 1. The blowing agent  62  can be provided in at least one of the surface and the interior of the base material  61 . The materials described in Embodiment 1 can be used as the thermosetting resin and the blowing agent  62 . In the present embodiment, the spacer  20  contains no blowing agent and is made of resin. 
     When any of the cells  10  generates heat abnormally in the battery module of the present embodiment, the heat of the cell  10  is transferred to the insulating sheet  60 . When the temperature of the insulating sheet  60  becomes higher than the decomposition temperature of the blowing agent  62 , the blowing agent  62  is thermally decomposed to form a space portion (recessed portion or hole portion) in the insulating sheet  60 . The formation of the space portion can suppress the transfer of the heat of the cell  10  abnormally generating heat to the spacers  20  or the other cells  10 . 
     Since the heat of the cell  10  abnormally generating heat is not easily transferred to the spacer  20 , it is possible to suppress melting of the spacer  20  due to the heat of the cell  10  even when the spacer  20  is made of thermoplastic resin. In other words, the functions of the spacer  20  can be maintained. On the other hand, even when the spacer  20  is melted, the base material  61  of the insulating sheet  60  is formed of thermosetting resin and thus the insulating sheet  60  is present between the two cells  10  between which the spacer  20  is sandwiched. Thus, the insulating sheet  60  can prevent the two cells  10  from coming into contact with each other. Even when the spacer  20  is melted, the heat from the cell  10  abnormally generating heat can be absorbed during the melting of the spacer  20 . 
     When a blowing agent of endothermic decomposition type is used as the blowing agent  62  of the insulating sheet  60 , that blowing agent  62  can absorb heat from the cell  10  abnormally generating heat during the thermal decomposition of the blowing agent  62 . This not only can suppress the transfer of the heat of the cell  10  abnormally generating heat to the other cells  10  but also can reduce the amount of heat transferred to the other cells  10 . 
     The insulating sheet  60  is placed at each of the positions sandwiched between the cell  10  and the spacer  20  in the present embodiment, the present invention is not limited thereto. In other words, the insulating sheet  60  can be placed only between a particular cell  10  and an associated spacer  20 . The thickness (the length in the X direction) of the insulating sheet  60  and the shape of the insulating sheet  60  when it is viewed from the X direction can be set as appropriate. 
     Next, a modification of the present embodiment will be described with reference to  FIGS. 6 and 7 .  FIG. 6  is a side view showing the configuration of part of a battery module which is the present modification, and  FIG. 7  is a perspective view of the outer appearance of a cell used in the present modification. Members having the same functions as those of the members described in Embodiment 1 are designated with the same reference numerals and detailed description thereof is omitted. In the following, different points from those in the present embodiment will be described. 
     In the present modification, an insulating film  70  containing dispersed blowing agent and made of thermosetting resin is formed by performing coating to outer surfaces of a cell  10 . The blowing agent contained in the insulating film  70  is unfoamed similarly to the present embodiment. As shown in  FIG. 7 , the insulating film  70  is formed on the outer surfaces of the cell  10  other than the outer surface on which the positive electrode terminal  11  and the negative electrode terminal  12  are provided. Alternatively, the insulating film  70  can also be formed on the outer surface on which the positive electrode terminal  11  or the like is provided. 
     Since the insulating film  70  also contains the blowing agent in the present modification, the blowing agent can be thermally decomposed to form a space portion in the insulating film  70  when the cell  10  generates heat abnormally. Such formation of the space portion can suppress the transfer of the heat of the cell abnormally generating heat to the spacers  20  and the other cells  10 . 
     While the insulating film  70  is formed on the outer surfaces of the cell  10  except for the upper surface in the present modification, the present invention is not limited thereto. Specifically, it is essential only that the transfer of the heat of the cell  10  abnormally generating heat to the other cells  10  should be suppressed and that the insulating film  70  should be located on the path where the heat moves. For example, the insulating film  70  can be formed on the surface (part or all thereof) of the cell  10  opposite to the spacer  20 . 
     The insulating film  70  is formed on the outer surfaces of the cell  10  in the present modification. Alternatively or additionally to the configuration, the insulating film  70  containing the blowing agent can be formed on outer surfaces of the spacer  20 . In this case, the insulating film  70  can be formed in all surfaces or part of the area of the spacer  20 . Specifically, the insulating film  70  can be formed in the tip area of protruding portions  21  of the spacer  20  or the insulating film  70  can be formed on the surface of the spacer  20  opposite to the surface on which the protruding portions  21  are formed. In other words, it is essential only that the insulating film  70  should be formed on the heat transfer path between two cells  10  placed such that the spacer  20  is sandwiched between them. 
     In the present embodiment or the present modification, the spacer  20  can be formed to have the configuration described in Embodiment 1. In addition, the thickness of the insulating film  70  can be set as appropriate based on the size of the blowing agent or the like.