Abstract:
To provide a battery pack that is less likely to be affected by vibrations, shocks and the like and has a stable characteristic, and an electric bicycle that uses the battery pack. 
     A battery pack includes: a battery protective member having a first plate section and a second plate section which is integrally connected to both edge portions of a width direction of the first plate section and extends substantially in a direction perpendicular to both surfaces of the first plate section, wherein the flat batteries are placed on the first plate section; and a protective circuit board. A moistureproof film for the protective circuit board is formed using a plurality of film forming materials different in viscosity, hardness, and thixotropic properties.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a battery pack, which is formed by connecting a plurality of secondary batteries, and an electric bicycle in which the battery pack is installed. 
         [0003]    2. Description of Related Art 
         [0004]    In electric bicycles, various kinds of secondary batteries are used as power sources for drive or auxiliary drive. Among the above secondary batteries, a lithium ion secondary battery, in which charge and discharge take place as lithium ions move between positive and negative electrodes, is preferably used as a battery for a drive power source because the lithium ion secondary battery has the following battery characteristics: high energy density and high output power. 
         [0005]    The following lithium ion batteries are known: a lithium ion battery that is in the shape of a cylinder around which positive and negative electrodes are stacked and wound via separators; and a flat lithium ion battery in which positive and negative electrodes are stacked via separators. 
         [0006]    Among the above lithium ion batteries, the flat lithium ion battery is preferably used as a battery for a power source of a device driving motor or the like because it is easy to increase capacity per unit battery by increasing the number of positive and negative electrodes stacked or by increasing the areas of positive and negative electrodes. 
         [0007]    As for a unit battery of the flat lithium ion battery, it is possible to make effective use of the high energy density that the lithium ion battery has by covering battery elements with a film casing material. 
         [0008]    The film-covered battery is used in various ways. For example, what is proposed in Patent Document 1 (JP-A-2007-257901) is a battery pack for an electric bicycle that uses a film-covered battery. 
       SUMMARY OF THE INVENTION 
       [0009]    The following electric bicycles are known: an electric bicycle that is designed to reduce burden on a rider when the bicycle is running with the help of an operation of an attached motor; and an electric bicycle that can be self-propelled even when a rider is not pedaling. A motor, a driving device, and a motor-driving battery add to the mass of an electric bicycle. Therefore, such devices are required to be smaller in mass. The electric bicycles require a large-capacity battery when running a long distance or for a long time in order to make use of an operation of a motor. 
         [0010]    Among the various kinds of batteries, a lithium ion battery that is large in gravimetric energy density and volumetric energy density is preferably used for an electric bicycle. Among the above batteries, a film-covered battery, which is covered with a film casing material, is characterized by high energy efficiency compared with a battery for which a metal can is used as a casing material. 
         [0011]    When the electric bicycle is used in rainy conditions, water could get into the battery pack. Further, water condensation or the like could occur inside the battery pack due to temperature change. 
         [0012]    Although the battery is covered by a material having high sealing properties, a protective circuit board used in the battery pack is likely to malfunction or deteriorate due to presence of liquid. 
         [0013]    There are mounted, on the protective circuit board, comparatively small-sized electronic parts for handling a signal and large-sized electronic parts for controlling main current. Conventionally, to cover all these electronic parts with a moistureproof film, a dam member having a height exceeding a height of tall electronic parts is formed, and then a film forming material is poured inside the dam member. This involves an additional process of forming the dam member and unnecessary use of the film forming material. 
         [0014]    There is an electric bicycle whose wheel is mounted on a bearing that is attached to the body of the bicycle via a suspension. However, the impact imposed on the bicycle body is significantly different from that on an automobile. Therefore, a battery pack attached to the body of the bicycle is greatly affected by shocks and vibrations from a road surface, and measures are required to be taken in this regard. 
         [0015]    To solve the above problem, according to an aspect of the present invention, there is provided a battery pack including: a battery connecting structure in which a plurality of flat batteries are placed; and a protective circuit board that protects the flat batteries during charging and discharging of the flat batteries, and film formation for the protective circuit board being made using a plurality of film forming materials different in viscosity, hardness, and thixotropic properties. 
         [0016]    In the battery pack, film formation for circuit components having a large length from a surface of the board is made using a film formation material having high before curing viscosity. 
         [0017]    In the battery pack, film formation for the circuit components having a large length from the board surface is made using a film formation material having high viscosity, high hardness, and high thixotropic properties. 
         [0018]    In the battery pack, the battery connecting structure includes a battery protective member having a first plate section and a second plate section which is integrally connected to both edge portions of a width direction of the first plate section and extends substantially in a direction perpendicular to both surfaces of the first plate section, and the flat batteries are placed on the first plate section. 
         [0019]    In the present invention, “substantially perpendicular” includes a situation where it is effectively possible to obtain perpendicular and desired operations and effects, for example, including an angle of 80 to 100 degrees. 
         [0020]    In the battery pack, a surface on which the flat batteries are placed is formed on both surfaces of the first plate section. 
         [0021]    In the battery pack, a flat-plate surface of the flat battery is put on the first plate section. 
         [0022]    In the battery pack, the flat batteries are film-covered batteries. 
         [0023]    In the battery pack, pull-out tabs of the flat batteries are taken out in the longer direction of the first plate section of the protective member. 
         [0024]    In the battery pack, one adhesive side of a two-sided adhesive tape is attached to the flat battery, which then adheres to the first plate section or an adjoining flat battery surface. 
         [0025]    According to another aspect of the present invention, there is provided an electric bicycle including the above-described battery pack. 
       Advantages of the Invention 
       [0026]    According to the battery pack of the present invention, only application of film forming materials having different physical properties allows components mounted on the protective circuit board to be coated with a moistureproof film, thereby ensuring excellent productivity. 
         [0027]    Energy-efficient lithium ion batteries or the like covered with the film casing material can definitely be protected from shocks and the like by the lightweight battery protective member of the present invention, so that even if the battery pack is constantly affected by vibrations and shocks when being used as in a battery pack of an electric bicycle, it is possible to expect that stable operation is maintained for a long time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIGS. 1A and 1B  are diagrams showing a unit battery  100  that makes up a battery pack according to an embodiment of the present invention.  FIG. 1A  is a diagram showing the unit battery  100  whose opening is sealed with heat-sealing sections formed on four sides.  FIG. 1B  is a diagram showing the unit battery  100  whose opening is sealed with heat-sealing sections formed on three sides. 
           [0029]      FIG. 2  is a diagram showing how to connect a connection tab  125  to a positive-electrode pull-out tab  120  of the unit battery  100 . 
           [0030]      FIG. 3  is a diagram showing the situation where holes are made on a positive pull-out tab and negative pull-out tab for connecting unit batteries  100  in series. 
           [0031]      FIGS. 4A-4D  are diagrams illustrating a holder member  200  that makes up the battery pack according to the embodiment of the present invention. 
           [0032]      FIG. 5  is a perspective view of a board  300  that is used in connecting unit batteries  100  in series in the battery pack according to the embodiment of the present invention. 
           [0033]      FIGS. 6A and 6B  are diagrams illustrating a battery protective member  400  that makes up the battery pack according to the embodiment of the present invention. 
           [0034]      FIG. 7  is a diagram illustrating a process of producing a battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0035]      FIG. 8  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0036]      FIG. 9  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0037]      FIG. 10  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0038]      FIG. 11  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0039]      FIG. 12  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0040]      FIG. 13  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0041]      FIG. 14  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0042]      FIG. 15  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0043]      FIGS. 16A and 16B  are diagrams illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0044]      FIG. 17  is a diagram illustrating a process of producing the battery connecting structure  500  that makes up the battery pack according to the embodiment of the present invention. 
           [0045]      FIG. 18  is a diagram illustrating a process of producing a battery pack according to the embodiment of the present invention. 
           [0046]      FIG. 19  is a diagram illustrating a process of producing the battery pack according to the embodiment of the present invention. 
           [0047]      FIG. 20  is a diagram illustrating a process of producing the battery pack according to the embodiment of the present invention. 
           [0048]      FIG. 21  is a diagram illustrating a process of producing the battery pack according to the embodiment of the present invention. 
           [0049]      FIG. 22  is a diagram illustrating a process of producing the battery pack according to the embodiment of the present invention. 
           [0050]      FIG. 23  is a diagram illustrating a process of producing the battery pack according to the embodiment of the present invention. 
           [0051]      FIG. 24  is a diagram illustrating a process of producing the battery pack according to the embodiment of the present invention. 
           [0052]      FIG. 25  is a diagram illustrating a process of producing the battery pack according to the embodiment of the present invention. 
           [0053]      FIG. 26  is a diagram illustrating an electric bicycle according to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0054]    The following describes an embodiment of the present invention with reference to the accompanying drawings.  FIG. 1  is a diagram showing a unit battery  100  that makes up a battery pack according to an embodiment of the present invention. What is used for the unit battery  100  is a lithium ion secondary battery in which charge and discharge take place as lithium ions move between positive and negative electrodes. 
         [0055]    The unit battery  100  of the present invention has a flat shape and therefore is also referred to as a flat battery. 
         [0056]    A main unit  110  of the unit battery has a structure in which the following components are stored in a film casing material, which is in the shape of a rectangle in planar view: a laminated electrode assembly, in which a plurality of sheet positive electrodes and a plurality of sheet negative electrodes are stacked via separators, and an electrolytic solution (both not shown). From an upper end portion  111  of the unit battery main unit  110 , a positive-electrode pull-out tab  120  and a negative-electrode pull-out tab  130  are pulled out. 
         [0057]    The positive-electrode pull-out tab  120  and the negative-electrode pull-out tab  130  are both in the shape of a plate, and are each connected directly, or via a lead body or the like, to the sheet positive electrodes and the sheet negative electrodes in the film casing material. The film casing material includes a heat-sealing resin layer on a plane facing the inside of the battery. Moreover, a film casing material is used for a plane facing the outside of the battery: the film casing material is made by stacking protective films on laminated metallic foil made of aluminum foil or the like. 
         [0058]    More specifically, on a plane that is positioned on the outer-surface side of the aluminum foil, a member that has strength and heat resistance, such as nylon or polyethylene terephthalate, is stacked; on the inner-surface side, a material that is excellent in heat-sealing performance, such as polypropylene or polyethylene, is stacked. 
         [0059]    With a battery element, in which positive and negative electrodes are stacked via separators, and an electrolytic solution stored in the film casing material, the periphery of the film casing material, i.e. the upper end portion  111 , lower end portion  112  and two side end portions  113 , is heat-sealed. Therefore, the inside thereof is hermetically sealed. 
         [0060]    In the above unit battery  100 , aluminum or aluminum alloy is used as a material of the positive-electrode pull-out tab  120 ; nickel, nickel-plated copper, or nickel-copper clad is generally used as a material of the negative-electrode pull-out tab  130 . According to the present embodiment, the positive-electrode pull-out tab  120  made of aluminum and the negative-electrode pull-out tab  130  made of nickel are used. 
         [0061]    In order to make the battery pack of the present invention, a positive pull-out tab of a unit battery  100  and a negative pull-out tab of a unit battery  100 , which is adjacent to the above unit battery  100 , are mechanically bound together with bolts and nuts and therefore connected together electrically. In this case, the structure in which the aluminum positive-electrode pull-out tab  120  of the unit battery  100  and the nickel negative-electrode pull-out tab are mechanically bound together could lead to a decline in conductivity after a predetermined period of time has passed due to problems pertaining to differences in potential. Accordingly, in the battery pack of the present invention, at a point where a positive pull-out tab of a unit battery  100  and a negative pull-out tab, which is adjacent to the above unit battery  100 , are mechanically bound together, the pull-out tabs are connected in such a way that the members made of nickel come in contact with each other. 
         [0062]    The configuration to achieve the above will be described. As shown in  FIG. 1 , in a process of making the battery pack, suppose that the aluminum positive-electrode pull-out tab  120  of the unit battery  100  has a length of a from the upper end portion  111 , and the nickel negative-electrode pull-out tab  130  a length of b (b&gt;a) from the upper end portion  111 . Then, to the aluminum positive-electrode pull-out tab  120  having a length of a, a tab member  125  made of nickel is connected and added by means of ultrasonic waves so that the length from the upper end portion  111  comes to b (see  FIGS. 2 and 3 ). In order to allow unit batteries  100  to be connected in series, a hole  127  is made on the tab member  125 , which serves as a positive pull-out tab; a hole  137  is made on the negative-electrode pull-out tab  130 . Incidentally, hereinafter, the entire pull-out tab, which is formed by connecting the tab member  125 , is also referred to as a positive-electrode pull-out tab  120 . 
         [0063]    As described below, in the battery pack of the present invention, in a process of electrically connecting a plurality of unit batteries  100 , the pull-out tabs having different polarities are connected together in such a way that the nickel members (the tab members  125  and the negative-electrode pull-out tabs  130 ) come in contact with each other. Accordingly, the electrically connected portions of the adjoining unit batteries turn out to be the portions that are made of the same type of metallic material and are connected electrically. Therefore, the problems pertaining to differences in potential do not arise, and it is substantially possible to prevent a decline over time in conductivity from occurring. 
         [0064]    The following describes a holder member  200 , which is used in electrically connecting the positive pull-out tabs and negative pull-out tabs of a plurality of unit batteries  100  in the battery pack of the embodiment of the present invention.  FIG. 4  is a diagram illustrating the holder member  200 .  FIG. 4A  is a diagram showing the holder member  200  seen from a first main surface side.  FIG. 4B  is a diagram showing the holder member  200  seen from a second main surface side.  FIG. 4C  is a cross-sectional view of  FIG. 4A  taken along X-X′.  FIG. 4D  is a side view of the holder member  200 . 
         [0065]    On the holder member  200 , a first surface  210  and a second surface  250 , which is on the opposite side of the holder member  200  from the first surface  210 , are formed; the holder member  200  is a member made of synthetic resin such as ABS resin. In a first row  211  of the first surface  210  of the holder member  200 , pull-out tab insertion holes  215  are formed side by side from top to bottom as shown in  FIG. 4A . Similarly, in a second row  212  of the first surface  210 , pull-out tab insertion holes  215  are formed side by side from top to bottom. When a unit battery  100  is attached to the holder member  200 , the pull-out tab insertion holes  215  provided on the first surface  210  are used. The pull-out tab insertion holes  215  are holes passing therethrough from the first surface  210  to the second surface  250 ; and holes into which the pull-out tabs of the unit battery  100  can be inserted. 
         [0066]    As shown in  FIG. 4A , on the upper and lower sides of the first and second rows  211  and  212 , pull-out tab guide ribs  203  are provided. A pull-out tab guidance section  213  is provided in such a way that the pull-out tab guidance section  213  is sandwiched between the pull-out tab guide ribs  203  of the first row  211 . Moreover, a pull-out tab guidance concave section  214  is provided in such a way that the pull-out tab guidance concave section  214  is sandwiched between the pull-out tab guide ribs  203  of the second row  212 . 
         [0067]    In the first row  211 , based on regulations by the pull-out tab guide ribs  203 , a pull-out tab of an edge-side unit battery  100 , out of a plurality of unit batteries  100  connected in series, is guided to the second surface  250  from the first surface  210  via the pull-out tab guidance section  213 . 
         [0068]    In the second row  212 , based on regulations by the pull-out tab guide ribs  203 , a pull-out tab of an edge-side unit battery  100 , out of a plurality of unit batteries  100  connected in series, is guided to the second surface  250  from the first surface  210  via the pull-out tab guidance concave section  214 . 
         [0069]    Among a plurality of unit batteries  100  connected in series, a pull-out tab of a unit batter  100  that is not on the edge side passes through the pull-out tab insertion hole  215  and is attached to the holder member  200 . In the upper and lower areas of the pull-out tab insertion hole  215  (as shown in  FIG. 4A ), pull-out tab guide projecting sections  220  are provided in such a way that the pull-out tab insertion hole  215  is sandwiched between the pull-out tab guide projecting sections  220 , which are positioned on the upper and lower sides of the pull-out tab insertion hole  215 . The pull-out tab guide projecting sections  220  are generally made up of a top section  221  and two tapered sides  222 , which are seamlessly connected to the top section  221 . When a pull-out tab of a unit battery  100  is inserted into a pull-out tab insertion hole  215 , a space between the two tapered sides  222  becomes gradually narrower, making it easy to attach the unit battery  100  to the holder member  200 . Therefore, it is possible to improve efficiency in connecting a plurality of unit batteries  100  in series and increase productivity. 
         [0070]    To the second surface  250  of the holder member  200 , a board  300  can be attached. On the board  300 , the pull-out tabs of the adjacent unit batteries  100  are bent, put on each other and connected, resulting in an electrical connection. When the pull-out tabs of the adjacent unit batteries  100  are connected, the pull-out tabs are mechanically bound together with bolts and nuts. Accordingly, six nut housing sections  255  for housing nuts  256  are provided in the first row  211  of the second surface  250 , and five in the second row  212 . Moreover, on the second surface  250 , divider pieces  260 , which are designed to ensure insulation between the pull-out tab connection sections of a unit battery  100  that are formed on the board  300  or between pull-out tab connection sections and pull-out tabs, are provided at three locations in the first row  211  and at two locations in the second row  212 . 
         [0071]    Positioning projecting sections  263  are projections that help position the board  300  when the board  300  is attached to the holder member  200 ; one positioning projection section  263  is positioned in the first row  211 , and the other in the second row  212 . Moreover, one screw hole  270 , which is used to bind the board  300  and the holder member  200  together after the board  300  is attached to the holder member  200  with the use of the above positioning projecting sections  263 , is provided in the first row  211 , and the other in the second row  212 . 
         [0072]    The following describes the configuration of the board  300  on which connection sections for the pull-out tabs of a plurality of unit batteries  100  are formed in the battery pack of the embodiment of the present invention. 
         [0073]      FIG. 5  is a perspective view of the board  300  that is used in connecting unit batteries  100  in series in the battery pack of the embodiment of the present invention. 
         [0074]    The board  300 , which is made by mainly using glass epoxy or the like as base material, is attached to the second surface  250  of the holder member  200  before being used. The peripheral shape of the board  300  substantially matches the peripheral shape of the second surface  250  of the holder member  200 . At two locations on the periphery of the board  300 , pull-out tab guidance notch sections  314  are formed so as to correspond to the pull-out tab guidance concave sections  214  of the holder member  200 . 
         [0075]    Moreover, on the board  300 , pull-out tab extraction holes  315  are provided so as to correspond to the pull-out tab insertion holes  215  of the holder member  200 . Moreover, on the board  300 , divider piece extraction holes  317  are provided so as to correspond to the divider pieces  260  of the holder member  200 . Furthermore, on the board  300 , pull-out tab/divider piece extraction holes  316  are provided to support both the pull-out tab insertion holes  215  and divider pieces  260  of the holder member  200 . The above holes are all through-holes that pass through the board  300  from one main surface to the other main surface; and are so formed that the pull-out tabs of unit batteries  100 , the divider pieces  260  and the like can be inserted therein. 
         [0076]    In areas where the pull-out tabs of unit batteries  100  are fixed to the board  300  with bolts and nuts, the following sections are provided: thin-film electrode sections  320   a,    320   b  and  320   c.    
         [0077]    There is an electrical connection between a thin-film electrode sections  320   a  and a metallic positive terminal electrode washer  321 , which is fixed to the board  300 . There is an electrical connection between a thin-film electrode section  320   c  and a metallic negative terminal electrode washer  322 , which is fixed to the board  300 . To the positive terminal electrode washer  321  and the negative terminal electrode washer  322 , the pull-out tabs of an edge portion of a unit battery  100  that is connected in series are connected. Therefore, the positive terminal electrode washer  321  and the negative terminal electrode washer  322  are used as terminals for charge and discharge of power for the battery pack. 
         [0078]    Moreover, there is an electrical connection between a thin-film electrode section  320   b  and a terminal section, not shown, of a connector  340 , allowing the potential for monitoring each unit battery  100  to be measured through the connector  340 . Incidentally, the connector  340  may be formed so that a signal from a temperature measurement sensor (not shown) that measures temperatures of unit batteries  100  can be taken out. 
         [0079]    For each of the thin-film electrode sections  320   a,    320   b  and  320   c,  pull-out tab connection screw holes  325  are provided: pull-out tab connection bolts  257 , which are used to fix the pull-out tabs of unit batteries  100 , are inserted into the pull-out tab connection screw holes  325 . To the thin-film electrode section  320   a  and the thin-film electrode section  320   c,  one pull-out tab of an edge-portion unit battery  100 , out of the unit batteries  100  connected in series, is fixed. Meanwhile, two thin-film electrode sections  320   b  are fixed in such a way that the pull-out tabs of the adjoining unit batteries  100  are bent and put on each other. 
         [0080]    On the board  300 , two positioning holes  328  are formed so as to correspond to the positioning projecting sections  263  provided on the second surface  250  of the holder member  200 . As the two positioning projecting sections  263  pass through the positioning holes  328 , the holder member  200  and the board  300  can be easily positioned when being bound together, contributing to an improvement in productivity. Moreover, board fixing screw holes  329 , which are formed on the board  300 , are holes into which board fixing screws  271 , which are used to fix the holder member  200  to the board  300 , are inserted. 
         [0081]    The following describes a battery protective member  400 , which protects a plurality of unit batteries  100  at a time when the unit batteries  100  are connected in series and turned into a battery connecting structure  500  in the battery pack of the embodiment of the present invention. 
         [0082]      FIG. 6  is a diagram illustrating the battery protective member  400 , which makes up the battery pack of the embodiment of the present invention.  FIG. 6A  is a diagram showing the battery protective member  400  in a way that faces a first plate section  410  to which a main surface of a unit battery  100  is bonded.  FIG. 6B  is a diagram showing the battery protective member  400  seen from an upper end of  FIG. 6A . 
         [0083]    When unit batteries  100  are placed, the battery protective member  400  of the present invention is inserted between the unit batteries  100  placed before being used. 
         [0084]    The battery protective member  400  may be made of synthetic resin, such as ABS resin, polyethylene terephthalate resin or polycarbonate resin. The use of such a material enables a lightweight and inexpensive battery protective member  400  to be realized. 
         [0085]    Moreover, the battery protective member  400  may also be made of a metallic member and a member made of synthetic resin with dispersed, highly heat-conductive material particles. The use of such a material enables a highly heat-conductive and lightweight battery protective member  400  to be realized. 
         [0086]    More specifically, the metallic member is aluminum, aluminum alloy, or copper. The highly heat-conductive material particles are aluminum nitride, silicon nitride or alumina. 
         [0087]    For the synthetic resin material, the following can be listed: ABS resin, polyethylene terephthalate resin, or polycarbonate resin. A material with highly heat-conductive material particles dispersed in the above resin can be listed. 
         [0088]    Among the above substances, aluminum or aluminum alloy is suitable. 
         [0089]    In the case of aluminum, aluminum alloy or the like, an alumite treatment film or insulating film is preferably formed on the surface. The above film prevents troubles from occurring even when a voltage applying section comes in contact with the protective member. 
         [0090]    The first plate section  410  of the battery protective member  400  is a member that is sandwiched between a unit battery  100  and a unit battery  100  that is connected in series to the above unit battery  100 . Meanwhile, second plate sections  440  are so provided as to extend in a direction perpendicular to the first plate section  410  from both edge portions of the first plate section  410 . Therefore, as shown in  FIG. 6B , the cross-sectional surface of the battery protective member  400  is in the shape of “H.” 
         [0091]    Moreover, a notch section  420 , which are made up of the following, is formed on the first plate section  410 : a first notch section  421 , which is the deepest notch section; second notch sections  422 , which are disposed on both sides of the first notch section  421  and are the second deepest notch sections after the first notch section  421 ; and third notch sections  423 , which are disposed on both sides of the second notch sections  422  and are the shallowest notch sections. 
         [0092]    The following describes processes of producing, from each of the above members, a battery connecting structure  500  in which unit batteries  100  are connected, with reference to  FIGS. 7 to 17 .  FIGS. 7 to 17  are diagrams illustrating the processes of producing the battery connecting structure  500 , which makes up the battery pack of the embodiment of the present invention. 
         [0093]    First, in a process shown in  FIG. 7 , nuts  256  are mounted in all the nut housing sections  255 , which are provided on the second surface  250  of the holder member  200 . The dimensions of the inner periphery of the nut housing sections  255  are so set that the nuts  256  cannot be easily removed once the nuts  256  are placed into the nut housing sections  255 . 
         [0094]    In a subsequent process shown in  FIG. 8 , the positioning projecting sections  263  of the holder member  200  are inserted into the positioning holes  328  of the board  300  so that the holder member  200  and the board  300  are positioned. Subsequently, two board fixing screws  271  are inserted into the board fixing screw holes  329  and screwed into screw holes  270 . As a result, the holder member  200  is fixed to the board  300 . Incidentally, for the board fixing screw holes  329 , various kinds of screw can be used. However, the use of self-tapping screws helps improve work efficiency during the production process. 
         [0095]    In a subsequent process shown in  FIG. 9 , a unit battery  100  is disposed on the first surface  210  of the holder member  200 . The negative-electrode pull-out tab  130  of the unit battery  100  is bent so as to come in contact with the thin-film electrode section  320   b  of the board  300  with the help of the pull-out tab guidance concave section  214 . Moreover, the positive-electrode pull-out tab  120  of the unit battery  100  is bent so as to come in contact with the thin-film electrode section  320   a  of the board  300  with the help of the pull-out tab guidance section  213 . The pull-out tab connection bolts  257  are inserted into the holes  127  of the positive-electrode pull-out tab  120  and the pull-out tab connection screw holes  325 ; the pull-out tab connection bolts  257  are screwed into the nuts  256  housed in the nut housing sections  255 . In this manner, the process of mounting the first unit battery  100  is completed. 
         [0096]    A subsequent process shown in  FIG. 10  takes place on the first surface  210  of the holder member  200 . In the process, as shown in the diagram, two strips of two-sided adhesive tape  460  are attached to an upper main surface of the unit battery  100 . The two-sided adhesive tapes  460  are used to fix the first unit battery  100 , which is attached to the holder member  200 , to a second unit battery  100 , which is to be attached to the holder member  200 . The reason the two strips of two-sided adhesive tape  460  are provided on the main surface of the unit battery  100  as shown in the diagram is to allow a spacer, described later, to be disposed between the two strips of two-sided adhesive tape  460  in order to improve productivity. 
         [0097]    In a subsequent process shown in  FIG. 11 , a spacer (not shown) that is thicker than the two-sided adhesive tapes  460  is placed on the first unit battery  100  attached. Furthermore, two pull-out tabs of the second unit battery  100  slide on the spacer and are inserted into the pull-out tab insertion holes  215 . As described above, the pull-out tab guide projecting sections  220  are disposed on the upper and lower sides of the two pull-out tab insertion holes  215 . Furthermore, the tapered sides  222  are provided on the pull-out tab guide projecting sections  220 . Therefore, a space between the upper and lower pull-out tab guide projecting sections  220  becomes gradually narrower, enabling the pull-out tabs of a unit battery to be easily guided to the pull-out tab insertion holes  215  of the holder member  200 . 
         [0098]    In this case, the positive-electrode pull-out tab  120  of the first unit battery  100  attached to the holder member  200  is disposed in the first row  211 , and the negative-electrode pull-out tab  130  in the second row  212 . On the other hand, the positive-electrode pull-out tab  120  of the second unit battery  100  attached to the holder member  200  is disposed in the second row  212 , and the negative-electrode pull-out tab  130  in the first row  211 . Hereinafter, in a process of sequentially placing unit batteries  100 , the positive-electrode pull-out tabs  120  of the odd unit batteries  100  attached are disposed in the first row  211 , and the negative-electrode pull-out tabs  130  in the second row  212 . The positive-electrode pull-out tabs  120  of the even unit batteries  100  attached are disposed in the second row  212 , and the negative-electrode pull-out tabs  130  in the first row  211 . In this manner, in a direction in which the unit batteries  100  are placed or stacked, the unit batteries  100  are so disposed that the pull-out tabs of the adjacent unit batteries  100  face different directions. Accordingly, on the board  300 , connection does not have to take place diagonally with respect to the placing or stacking direction. 
         [0099]    After it is confirmed that the upper end portion  111  of the second unit battery  100  is pushed into until the upper end portion  111  hits the first surface  210  of the holder member  200 , a subsequent task starts on the board  300 . 
         [0100]    In a subsequent process shown in  FIG. 12 , the positive-electrode pull-out tab  120  of the second unit battery  100  attached is bent downward as shown in the diagram, and is put on the negative electrode  130  of the first unit battery  100  attached. After that, a pull-out tab connection bolt  257  is inserted into a hole of each pull-out tab, or pull-out tab connection screw hole  325 , and is screwed into a nut  256 , forming a connection portion for the negative-electrode pull-out tab  130  of the first unit battery  100  attached on the thin-film electrode section  320   b  and the positive-electrode pull-out tab  120  of the second unit battery  100  attached. In this manner, an electrical connection is completed. 
         [0101]    Meanwhile, the negative-electrode pull-out tab  130  of the second unit battery  100  attached is bent upward as shown in the diagram, thereby making preparations for the positive-electrode pull-out tab  120  of the third unit battery  100  attached to be connected. 
         [0102]    In a subsequent process shown in  FIG. 13 , in a similar way to the case where the second unit battery  100  is attached, a battery protective member  400  is attached with the use of a spacer. The upper surface of the second unit battery  100  and the lower surface of the battery protective member  400  are bonded together with two strips of two-sided adhesive tape  460 . Furthermore, as shown in the diagram, two strips of two-sided adhesive tape  460  are attached to the upper surface of the battery protective member  400 . With the use of the two-sided adhesive tapes  460 , the battery protective member  400  is fixed to the third unit battery  100  attached to the holder member  200 . 
         [0103]      FIG. 14  shows the situation where the third to eighth unit batteries  100  are sequentially attached to the holder member  200  and the board  300  in a similar way to that described above. On the board  300 , each time one unit battery  100  is attached, the pull-out tabs are bent and put on each other, and the pull-out tabs of the adjacent unit batteries  100  are connected by means of the pull-out tab connection bolts  257 . In this manner, an electrical connection is realized. 
         [0104]    In a subsequent process shown in  FIG. 15 , what is shown is the situation where, after the eighth unit battery  100  is attached, still another battery protective member  400  is attached. In this manner, in the battery connecting structure  500  of the present embodiment, two battery protective members  400  are disposed so as to form two battery protective member blocks  450 , which are protected by the battery protective members. In this manner, each unit battery  100  is protected against external shocks and the like. 
         [0105]    Moreover, the unit batteries  100  are so placed as to rise above an upper end portion of a direction of the height between the first plate section  420  and the second plate section  440 . In this manner, since the unit batteries are so placed as to rise above the upper end portion of the second plate section  440 , there is an improvement in heat-release performance from the peripheries of the unit batteries. 
         [0106]    Batteries that are placed so as to rise above the upper end portion of the above second plate section may be placed on an upper or lower battery protective member  400 , or both, in the case of the diagram. 
         [0107]      FIG. 16  shows the situation where, on the first plate section  420  of the battery protective member  400 , the ninth and tenth unit batteries  100  are further attached to the holder member  200  and the board  300 . 
         [0108]    The negative-electrode pull-out tab  130  of the tenth unit battery  100  is fixed to a thin-film electrode section (not shown) of the board  300  with the use of the pull-out tab guidance section  213 . As a result, the pull-out tabs of the first to tenth unit batteries  100  are each connected on the board  300 , and a process of connecting ten unit batteries  100  in series is completed. In this manner, the battery connecting structure  500  including two battery protective member blocks  450  is completed. 
         [0109]    Moreover, in the battery connecting structure  500  shown in the diagram, the unit batteries  100  are so placed as to rise above the upper end portion, in the direction of the height from a surface of the first plate section  420 , of the second plate section  440  of a side of a battery protective member. The sides of some of the unit batteries are not covered with the second plate section  440 [ 400 → 440 ]. 
         [0110]    Therefore, the air in the surrounding area flows into the unit batteries  100  from a space between the second plate sections  440  of the upper and lower battery protective members  400 , contributing to an improvement in heat-release performance of the unit batteries  100 . 
         [0111]    A unit battery  100  covered with a film casing material has a heat-sealing section on the periphery. A side edge portion  113  is not bent; the side edge portion  113  is so large in size that the side edge portion  113  comes in contact with an inner surface of the second plate section  440  of the battery protective member  400 . Therefore, the unit battery  100  can be precisely positioned on the battery protective member  400  and smoothly placed on the first plate section. 
         [0112]    The film casing material is flexible. However, on the heat-sealing section, there is a portion that is higher in rigidity than other portions. Therefore, the heat-sealing section can sufficiently resist a force applied from the side edge portion  113 , and therefore can withstand vibrations, shocks and other forces. 
         [0113]      FIG. 17  is a diagram showing the battery connecting structure shown in  FIG. 16  when seen from the board. 
         [0114]    The battery connecting structure includes two battery protective member blocks  450 . A process of charging and discharging ten unit batteries  100  connected in series takes place with the use of the positive terminal electrode washer  321  and negative terminal electrode washer  322  attached to the board  300 . A terminal member  331  is attached to the positive terminal electrode washer  321 , and a terminal member  332  to the negative terminal electrode washer  322 . 
         [0115]    As described above, the battery pack of the present invention is made in the following manner: the positive and negative pull-out tabs of a plurality of unit batteries  100  are inserted into the pull-out tab insertion holes  215  of the holder member  200 , and the pull-out tabs having different polarities of a plurality of the unit batteries  100  are connected together on the board  300 . Therefore, the production of battery packs is highly efficient, resulting in an improvement in productivity. 
         [0116]    Moreover, the pull-out tabs having different polarities of a plurality of the unit batteries  100  are connected together on the board  300  with pull-out tab connection bolts  257  and nuts  256 . Therefore, it is easy to connect a plurality of unit batteries  100  electrically. Thus, the production of battery packs is highly efficient, resulting in an improvement in productivity. 
         [0117]    The following describes processes of making a battery pack of the present invention using the battery connecting structure  500 , which is formed as described above, with reference to  FIGS. 18 to 25 . 
         [0118]    In a process shown in  FIG. 18 , to a first case body  600  that houses the battery connecting structure  500 , a discharge terminal  613  and a charge terminal  614  are fixed with screws with the help of a discharge terminal attachment concave section  611  and a charge terminal attachment concave section  612 , which are provided on the first case body  600 . 
         [0119]    In a process shown in  FIG. 19 , a first cushioning member  621  is attached to a second housing section  602  of the first case body  600  with an adhesive or the like, and a second cushioning member  622  to a circuit housing section  603 . 
         [0120]    In the battery pack of the present invention, as shown in  FIGS. 18 and 19 , a drain hole  682  is provided on a bottom portion of the battery pack, and a drain hole  681  on an upper compartment section  680 . 
         [0121]    The battery pack is used outdoors. Therefore, rainwater or the like could get into the battery pack. Water condensation or the like could occur as unit batteries and protective circuit board sections in the battery pack heat up and cool down after the liquid gets in from the outside. 
         [0122]    According to the present invention, in addition to the drain hole  682  on the bottom portion, another drain hole is provided on the upper compartment section  680 , a compartment in which a protective circuit board, which could be affected by the liquid, is installed, whereby liquid can be quickly discharged from inside of the battery pack. Therefore, it is possible to prevent an adverse effect associated with the liquid. 
         [0123]    In a process shown in  FIG. 20 , to a second housing section  662  of a second case body  660 , a third cushioning member  663  is attached with an adhesive or the like. 
         [0124]    In processes shown in  FIGS. 21 and 22 , to the battery connecting structure  500 , cushioning materials are attached. In the battery pack of the present invention, two structures, i.e. a first battery connecting structure  500  and a second battery connecting structure  500 , are stored in the battery pack. 
         [0125]    In a process shown in  FIG. 21 , as for the first battery connecting structure  500 , fourth cushioning members  504 , which are thick, are attached to an edge-portion unit battery  100 ; to the second plate sections of all the battery protective members, fifth cushioning members  505 , which are thinner than the fourth cushioning members  504 , are attached. An adhesive or the like is used in attaching the fourth cushioning members  504  and the fifth cushioning members  505  to parts. 
         [0126]    Meanwhile, in a process shown in  FIG. 22 , as for the second battery connecting structure  500 , fourth cushioning members  504  are attached to an edge-portion unit batter  100 ; only to the second plate sections of a one-side battery protective member, fifth cushioning members  505  are attached. As in the case described above, an adhesive or the like is used in attaching the fourth cushioning members  504  and the fifth cushioning members  505  to parts. 
         [0127]    In a process shown in  FIG. 23 , a discharge terminal  613 , a charge terminal  614  and a protective circuit board  700  are connected with wires. Moreover, the protective circuit board  700  is fixed to the circuit housing section  603  of the first case body  600  with screws. 
         [0128]    In a process shown in  FIG. 24 , the first battery connecting structure  500 A is stored in the first housing section  601  of the first case body  600 , and the second battery connecting structure  500 B in the second housing section  602 . 
         [0129]    In the protective circuit board  700 , for tall circuit components such as FETs, a coating material having high viscosity, high hardness, and high thixotropic properties and thus not running down on a surface of the protective circuit board but forming a film having a predetermined thickness is used. 
         [0130]    On the other hand, for short circuit components, a coating material having low viscosity, low hardness, and low thixotropy is used to form a film. 
         [0131]    As the coating materials for both tall and short circuit components, a silicone-based adhesive material can be used. The use of the silicone-based material as the coating materials for both tall and short circuit components allows formation of a film having a tight interface between the materials having different physical properties. For example, for the tall circuit components, Cemedine SX720W (viscosity: 45 Pa·s 23° C.) consisting primarily of acrylic modified silicone resin can be used; for the short circuit components, SINWE 500 (viscosity: 0.6 Pa·s 25° C.) made by Hong Kong Xinwei Chemical Co., Ltd can be used. 
         [0132]    In the protective circuit board  700  of the present invention, of all the portions on the circuit board for which coating is necessary, curable resin having high before curing viscosity may be used to coat a portion at which the tall circuit components such as FETs and curable resin having low before curing viscosity may be used to coat the remaining portion. This can reduce unnecessary use of the film forming material positioned at a portion for which the coating is unnecessary. The portion at which the curable resin having high before curing viscosity is used may be set to a portion including the tallest circuit component on the circuit board surface. 
         [0133]    The curable resin to be used for the protective circuit board  700  to be used, particularly, in the electric bicycle, is preferably a silicone-based adhesive material that reacts with two types of water having before curing viscosities at room temperature (e.g., about 25° C.) of 20 Pa·s to 90 Pa·s and 0.3 Pa·s to 1.0 Pa·s, respectively to cure. The use of such an adhesive material allows the circuit board to be used in the protective circuit board  700  of the battery pack for electric bicycle to be coated satisfactorily. 
         [0134]    The first battery connecting structure  500 A, to which cushioning members have been attached, is stored in the first housing section  601  in such a way that a direction CP in which clearance is positive is parallel to the bottom face of the first housing section  601 , and a direction CM in which clearance is negative is perpendicular to the bottom face of the first housing section  601 . 
         [0135]    Furthermore, the second battery connecting structure  500 B, to which cushioning members have been attached, is also stored in the second housing section  602  in such a way that a direction CP in which clearance is positive is parallel to the bottom face  601 U of the first housing section  601 , and a direction CM in which clearance is negative is perpendicular to the bottom face  602 U of the second housing section  602 . 
         [0136]    Incidentally, the positive clearance means that a distance of an outer surface between cushioning members is 1.5 mm to 2 mm smaller than the size of a housing section. The negative clearance means that a distance of an outer surface between cushioning members is 3 mm to 4 mm larger than the size of a housing section. 
         [0137]    The first battery connecting structure  500 A, to which cushioning members have been attached, and the second battery connecting structure  500 B, to which cushioning members have been attached, are each connected to the protective circuit board  700  with lead wires, which are substantially the same in length. Therefore, it is possible to shorten the wires, as well as to make the impedance between the protective circuit board and one battery connecting structure equal to the impedance between the protective circuit board and the other battery connecting structure. 
         [0138]    As a result, when the two battery connecting structures are connected in parallel, it is possible to draw energy from batteries in an efficient manner. 
         [0139]    Moreover, a surface of the first battery connecting structure to be housed in the first housing section  601 , on which the flat batteries are placed is parallel to the bottom face  601 U of the first housing section. Meanwhile, a surface of the second battery connecting structure on which the flat batteries are placed is perpendicular to the bottom face  602 U of the second housing section. Since the bottom face  601 U of the first housing section and bottom face  602 U of the second housing section are parallel to each other, the surface of the first battery connecting structure, on which the flat batteries are placed is perpendicular to the surface of the second battery connecting structure, on which the flat batteries are placed. 
         [0140]    That is, when the battery pack is mounted on a bicycle, in the second housing section  602  that is positioned in a lower area, a surface of the shortest interval of an portion that is formed by a visible outline of a battery connecting structure and is substantially in the shape of a rectangular parallelepiped, i.e. a surface that is at right angles to a surface of a battery connecting structure on which the flat batteries are placed in the case of the diagram, is placed so as to run parallel to the bottom face of the second housing section  602 . 
         [0141]    On the bottom face of the first housing section  601 , a surface a battery connecting structure, on which the flat batteries are placed is placed so as to be parallel to the bottom face. The surface of the first battery connecting structure, on which the flat batteries are placed and the surface of the second battery connecting structure, on which the flat batteries are placed are disposed so as to cross each other at right angles. In this manner, the battery connecting structures, which are the same in shape and structure, are mounted in the first thick housing section  601  and in the second thin housing section  602 . 
         [0142]    In a process shown in  FIG. 25 , the first case body  600  is fixed to the second case body  660  with screws. 
         [0143]    In the process, the second case body is placed on the first case body  600 . The second case body is fixed to the first case body  600  with screws as the second case body is pushed in a direction in which the clearance of the battery connecting structure to which cushioning members have been attached is negative. As a result, the battery pack of the present invention is completed; in the battery pack, the battery connecting structure does not move even when vibrations or shocks are applied. 
         [0144]      FIG. 26  is a diagram illustrating an electric bicycle on which the battery pack of the present invention is mounted. 
         [0145]    An electric bicycle  1  has a frame  2  on which a battery pack  4  of the present invention is mounted. The battery pack  4  supplies power to a driving mechanism  3  of the electric bicycle. 
         [0146]    As described above with reference to  FIG. 24 , the battery pack  4  includes two housing sections that are different in structure but accommodate the battery connecting structures that are the same in shape. A battery pack upper section  41 , which is thick and corresponds to the first housing section  601  shown in  FIG. 24 , is positioned in a space between a saddle  5  and a rear wheel. Therefore, the battery pack upper section  41  does not come in contact with a leg or the like when a rider rides the bicycle. 
         [0147]    Moreover, a battery pack lower section  42 , which is thin and corresponds to the second housing section  602 [first→second] shown in  FIG. 24 , is positioned in a space between a seat post  6  and the rear wheel. However, since the second hosing section, the battery connecting structure  500  is thin even, the second hosing section does not come in contact with a pedal or leg even when a rider rotates the pedal  7 . 
         [0148]    The battery pack  4  of the present invention is mounted directly on the frame  2  that is subject to vibrations and shocks from a road surface. In the battery pack  4 , measures have been taken against vibrations and shocks. Therefore, the battery pack  4  operates in a stable manner. 
       INDUSTRIAL APPLICABILITY 
       [0149]    According to the battery pack of the present invention, energy-efficient lithium ion batteries or the like covered with the film casing material are definitely protected from shocks and the like by the light weight battery protective member. Moreover, a plurality of coating materials having different physical properties are applied to the protective circuit board inside the battery pack depending on the height of the circuit component, so that it is possible to form a reliable protective film on both the tall circuit components and short circuit components, thereby providing a battery pack provided with a high-reliable protective circuit board not adversely affected by liquid. 
       EXPLANATION OF SYMBOLS 
       [0150]      1 : Electric bicycle 
         [0151]      2 : Frame 
         [0152]      3 : Driving mechanism 
         [0153]      4 : Battery pack 
         [0154]      41 : Battery pack upper section 
         [0155]      42 : Battery pack lower section 
         [0156]      5 : Saddle 
         [0157]      6 : Seat post 
         [0158]      7 : Pedal 
         [0159]      100 : Unit battery 
         [0160]      110 : Unit battery main unit 
         [0161]      111 : Upper end portion 
         [0162]      112 : Lower end portion 
         [0163]      120 : Positive-electrode pull-out tab 
         [0164]      125 : Tab member 
         [0165]      127 : Hole 
         [0166]      130 : Negative-electrode pull-out tab 
         [0167]      137 : Hole 
         [0168]      200 : Holder member 
         [0169]      203 : Pull-out tab guide rib 
         [0170]      210 : First surface 
         [0171]      211 : First row 
         [0172]      212 : Second row 
         [0173]      213 : Pull-out tab guidance section 
         [0174]      214 : Pull-out tab guidance concave section 
         [0175]      215 : Pull-out tab insertion hole 
         [0176]      220 : Pull-out tab guide projecting section 
         [0177]      221 : Top section 
         [0178]      222 : Tapered side 
         [0179]      250 : Second surface 
         [0180]      255 : Nut housing section 
         [0181]      256 : Nut 
         [0182]      257 : Pull-out tab connection bolt 
         [0183]      260 : Divider piece 
         [0184]      263 : Positioning projecting section 
         [0185]      270 : Screw hole 
         [0186]      271 : Board fixing screw 
         [0187]      300 : Board 
         [0188]      314 : Pull-out tab guidance notch section 
         [0189]      315 : Pull-out tab extraction hole 
         [0190]      316 : Pull-out tab/divider piece extraction hole 
         [0191]      317 : Divider piece extraction hole 
         [0192]      320   a,    320   b,    320   c:  Thin-film electrode section 
         [0193]      321 : Metallic positive terminal electrode washer 
         [0194]      322 : Metallic negative terminal electrode washer 
         [0195]      325 : Pull-out tab connection screw hole 
         [0196]      328 : Positioning hole 
         [0197]      329 : Board fixing screw hole 
         [0198]      331 ,  332 : Terminal member 
         [0199]      340 : Connector 
         [0200]      400 : Battery protective member 
         [0201]      410 : First plate section 
         [0202]      420 : Notch section 
         [0203]      421 : First notch section 
         [0204]      422 : Second notch section 
         [0205]      423 : Third notch section 
         [0206]      440 : Second plate section 
         [0207]      450 : Battery protective member block 
         [0208]      460 : Two-sided adhesive tape 
         [0209]      500 : Battery connecting structure 
         [0210]      504 : Fourth cushioning member (thick) 
         [0211]      505 : Fifth cushioning member (thin) 
         [0212]      600 : First case body 
         [0213]      601 : First housing section 
         [0214]      601 U: Bottom face 
         [0215]      602 : Second housing section 
         [0216]      602 U: Bottom face 
         [0217]      603 : Circuit housing section 
         [0218]      611 : Discharge terminal attachment concave section 
         [0219]      612 : Charge terminal attachment concave section 
         [0220]      613 : Discharge terminal 
         [0221]      614 : Charge terminal 
         [0222]      621 : First cushioning member 
         [0223]      622 : Second cushioning member 
         [0224]      660 : Second case body 
         [0225]      661 : First housing section 
         [0226]      662 : Second housing section 
         [0227]      663 : Third cushioning section 
         [0228]      673 : Circuit housing section 
         [0229]      680 : Upper compartment section 
         [0230]      681 ,  682 : Drain hole 
         [0231]      700 : Protective circuit board