Abstract:
This invention concerns a secondary battery which ensures safety with a simple structure and promotes exaltation of the service life of battery. This secondary battery is formed by interposing a nonaqueous electrolyte between the positive pole and the negative pole and connecting a group of diodes between the positive pole terminal forming the positive pole and the negative pole terminal forming the negative pole in the direction in which the forward direction voltage is applied. Owing to this structure, the secondary battery is enabled to possess the function of protecting the battery from overcharging and overdischarging even when the voltage is abnormally lowered during the course of discharging.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a secondary battery which possesses the function of protecting itself from overcharging or overdischarging even when the voltage abnormally rises during the course of charging or when the voltage abnormally falls during the course of discharging.  
         [0003]     2. Description of Related Art  
         [0004]     In recent years, the hybrid electric vehicle (HEV) has begun undergoing reduction into practical use in response to the mounting public consciousness of the environmental problem. The secondary battery is used as the power source for the motor which is mounted on the HEV. In answer to the demand for decreasing size and weight, the thin battery of a high energy density has come to find popular acceptance. The thin battery is formed by laminating a plurality of battery cells each resulting from interposing a nonaqueous electrolyte between positive poles and negative poles each of the shape of a sheet.  
         [0005]     The individual battery cells which form the thin battery are so produced as to assume as uniform a volume as permissible. Since the positive poles, the negative poles, and the nonaqueous electrolyte layers nevertheless cannot be formed equally in thickness and surface area, however, the individual battery cells are suffered to have their volumes dispersed to a certain extent. When the battery cells have their volumes dispersed, those of smaller volumes are first charged fully to capacity during the course of charging and those of such small volumes tend to be rather overcharged.  
         [0006]     Meanwhile, during the course of discharging, the battery cells of smaller volumes first complete discharging, the battery cells having small volumes tend to be rather overdischarged. Since the overcharging and the overdischarging of a battery largely affect the service life of the battery, such controls as bypassing or blocking the battery cell depending on the voltage of the battery cell is resorted to with the object of eliminating this inconvenience as disclosed in the official gazette of JP-A 2002-369399, the official gazette of JP-A 2002-25628, and the specification of Patent No. 3331529.  
         [0007]     Incidentally, when the techniques disclosed in these patent documents are applied to the secondary battery, they possibly result in varying the impedance of the secondary battery as a whole and degrading the performance of the secondary battery under the influence of the separated battery cells and they also necessitate a complicated control circuit for keeping a constant watch on the voltages of the individual battery cells and effecting a control for separating or blocking the battery cells which have developed abnormal voltages.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     This invention has originated in the light of such problems of the prior art as mentioned above and is aimed at providing a secondary battery which, by having a group of diodes connected between a positive pole and a negative pole of a secondary batter, is enabled to secure safety and design exaltation of the service life of a battery with a simple structure.  
         [0009]     For the purpose of accomplishing this object, the secondary battery contemplated by this invention is a secondary battery of a construction having a nonaqueous electrolyte interposed between a positive pole and a negative pole and having the group of diodes connected between the positive pole terminals forming the positive pole and the negative pole terminals forming the negative pole in a direction in which the voltage of the forward direction is applied. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is an outline drawing of a secondary battery according to the present mode of embodiment.  
         [0011]      FIG. 2  is a cross section taken through the secondary battery illustrated in  FIG. 1  along the line A-A.  
         [0012]      FIG. 3  is a concrete schematic diagram of the secondary battery using a bipolar electrode illustrated in  FIG. 2 .  
         [0013]      FIG. 4  is a diagram schematically illustrating the construction of battery cells and a group of diodes.  
         [0014]      FIG. 5  is an electrically equivalent circuit diagram of the construction illustrated in  FIG. 4 .  
         [0015]      FIG. 6  is a voltage-amperage characteristic diagram of the group of diodes shown in  FIG. 5 .  
         [0016]      FIG. 7  is a diagram illustrating another mode of the group of diodes; A depicting a mode of six series of diodes, B a mode of 3 series of diodes, and C a mode of two parallel rows each of six series of diodes.  
         [0017]      FIG. 8  is a concrete schematic diagram of the secondary battery in a mode of having battery cells in parallel connection.  
         [0018]      FIG. 9  is a diagram schematically illustrating a structure of battery cells and a group of diodes.  
         [0019]      FIG. 10  is a diagram schematically illustrating a structure of battery cells and a group of diodes.  
         [0020]      FIG. 11  is an electrically equivalent circuit diagram of the structure shown in  FIG. 10 .  
         [0021]      FIG. 12A  (a) through (d) are diagrams schematically illustrating a process for the production of a group of diodes.  
         [0022]      FIG. 12B  (e) through (g) are diagrams schematically illustrating a process for the production of a group of diodes.  
         [0023]      FIG. 13A  (a) through (d) are diagrams schematically illustrating a process for the production of a group of diodes.  
         [0024]      FIG. 13B  (e) through (g) are diagrams schematically illustrating a process for the production of a group of diodes.  
         [0025]      FIG. 14A  (a) through (e) are diagrams schematically illustrating a process for the production of a group of diodes.  
         [0026]      FIG. 14B  (f) through (j) are diagrams schematically illustrating a process for the production of a group of diodes.  
         [0027]      FIG. 15  is a schematic diagram of a built-up battery; A depicting a top view of the built-in battery, B depicting a partially broken cross section of the built-in battery, and C depicting a partially broken front view of the built-in battery.  
         [0028]      FIG. 16  is a diagram illustrating the state of having the built-in battery mounted on a vehicle. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     Now, the structure of the secondary battery according to this invention will be described as divided into “mode 1 of embodiment” through “mode 3 of embodiment” and one example of the process for the production of a group of diodes in the secondary battery will be described in detail below with reference to the drawings attached hereto.  
         [0000]     Structure of Secondary Battery  
         [0030]     [Mode 1 of Embodiment] 
         [0031]      FIG. 1  is an outline drawing of the secondary battery according to the present mode of embodiment,  FIG. 2  is a cross section taken through the secondary battery shown in  FIG. 1  along the line A-A, and  FIG. 3  is a concrete schematic diagram of a bipolar electrode shown in  FIG. 2 . In the secondary battery of the present mode of embodiment, a group of diodes are connected between positive pole terminals forming a positive pole and negative pole terminals forming a negative pole in a direction in which the forward direction voltage is applied.  
         [0032]     A secondary battery  10  according to the present mode of embodiment is a thin battery in a rectangular shape as illustrated in  FIG. 1 , having a positive pole tab  12  and a negative pole tab  14  drawn out of the opposite short sides thereof. The positive pole tab  12  and the negative pole tab  14  are connected to a battery element  20  in a laminate film  16  which is a sheathing material for the secondary battery  10  as illustrated in  FIG. 2 . The battery element  20  is what is formed by laminating a plurality of bipolar electrodes each having a positive pole layer and a negative pole layer disposed on the opposite sides of a current collecting body, with a solid electrolyte interposed between the adjacent superposed bipolar electrodes. It consequently assumes a structure in which a plurality of battery cells each formed of a laminated body of a current collecting body (negative pole terminal)-a negative pole layer-a solid electrolyte-a positive pole layer-a current collecting body (positive pole terminal) are connected in series.  
         [0033]     A diode forming region  24  intended to form a group of diodes is disposed on one side of each of current collecting bodies  22  which form a bipolar electrode  30  as illustrated in  FIG. 3 . The group of diodes are formed on the current collecting body  22  by using the semiconductor forming technique. The group of diodes are connected in such a direction that the forward direction voltage may be applied between the positive pole terminals and the negative pole terminals. On one side of the current collecting body  22 , a negative pole layer  26  is formed so as to detour a sealing part  25  serving to secure insulation. On the other side of the current collecting body  22 , a positive pole layer (not shown) is formed so as to detour a sealing part (not shown) disposed on that side.  
         [0034]     While  FIG. 3  depicts the disposition of diode forming regions  24  one each on both sides of the bipolar electrode  30 , this disposition may be limited to either of the sides when the electric current flowing through the group of diodes is not very large. In the case of the bipolar electrode  30 , a current collecting body and a positive pole layer form a positive pole and a current collecting body and a negative pole layer form a negative pole. Further, the current collecting body of the positive pole serves as a positive pole terminal and the current collecting body of the negative pole serves as a negative pole terminal.  
         [0035]      FIG. 4  is a diagram schematically illustrating the structure of battery cells and the group of diodes. A battery cell  40  is formed by laminating a current collecting body  22 A destined to serve as a positive pole terminal, a positive pole layer  28 , a solid electrolyte (nonaqueous electrolyte)  27 , a negative pole layer  26 , and a current collecting body  22 B destined to serve as a negative pole terminal. The group of diodes  50  result from laminating stepwise five diode elements  35  each formed by laminating an N-type semiconductor layer  32 , a P-type semiconductor layer  33 , and a metal layer  34  on the diode forming region  24  of a current collecting body  22 B and connecting them to the current collecting body  22 A destined to serve as a positive pole terminal through the medium of an electrically conducting adhesive agent layer  36 . The group of diodes  50  are electrically insulated from the positive pole and the negative pole by the sealing part  25 . The battery cell  40  has a thickness in the approximate range of 50-100 μm and the five diode elements  35  excluding the electrically conducting adhesive agent layer  36  have a total thickness of about 20 μm.  
         [0036]     The structure shown in  FIG. 4  is fated to assume such an electrically equivalent circuit as illustrated in  FIG. 5 . To be specific, an anode of the group of diodes  50  is connected to the positive pole side of the battery cell  40  and the cathode of the group of diodes  50  is connected to the negative pole side thereof.  
         [0037]     The group of diodes  50  are connected in the forward direction to the battery cell  40 . Since the group of diodes  50  are adapted to be connected in series to the five diode elements  35 , the voltage at which a large electric current begins to flow to the group of diodes  50  is five times the voltage at which a large electric current begins to flow to the individual diode elements  35 . A general diode element  35  allows substantially no flow of electric current till the forward direction voltage reaches about 0.6 V (it may as well be regarded as a near equivalent to an insulator). Thus, the group of diodes  50  which is formed by serially connecting five diode elements  35  allow virtually no flow of electric current till the voltage reaches about 3.0 V as shown in  FIG. 6 .  
         [0038]     To be specific, when the voltage of the battery cell  40  exeeds 3 V and reaches a level of not lower than 3.5 V, the electric current begins to flow gradually to the group of diodes  50  (the insulator changes to a conductor) and the charging speed of the battery cell decreases gradually (the electric current is bypassed). When the voltage further increases and eventually exceeds 4 V, the electric current nearly wholly flows toward the diodes and the voltage of the battery cell  40  finally becomes restricted by the voltage which follows the voltage-amperage characteristic property of the group of diodes  50 .  
         [0039]     The conventional secondary battery possesses a structure in which a plurality of battery cells  40  are connected in series. The voltage applied to the individual battery cells  40  during the course of charging, therefore, is the voltage which results from dividing the charging voltage to the individual battery cells  40  proportionately to their capacities. Since the voltage applied during the course of charging varies between the battery cell having a large capacity and the battery cell having a small capacity, some of the battery cells expose themselves to application of unduly large voltages and eventually suffer from overcharging.  
         [0040]     Incidentally, the secondary battery conforming to the present mode of embodiment has the battery cells individually provided with the group of diodes  50 , the charging begins to be controlled after the battery voltage reaches about 3.5 V and eventually controlled to the voltage corresponding to the electric current shown in  FIG. 6  without reference to the magnitude of the electric current advanced to the individual battery cells during the course of charging. Even when the individual battery cells  40  have different capacities, all the battery cells are prevented from succumbing to overcharging unless the electric current exceeds the prescribed magnitude.  
         [0041]     If the electric current exceeds the prescribed magnitude, the excess will encounter extreme difficulty in growing into an overcharging hugely surpassing the safe region and inducing abnormality because the rise of the electric current in the diodes is steep. Particularly when the secondary battery is put to such use in a hybrid electric vehicle as to necessitate charging and discharging to be repeated in a brief period, since the electric current by-passing the diodes is not large up to the neighborhood of 4 V, the energy of the battery can never be consumed instantaneously in the diodes and the energy once stored in the battery can be effectively discharged at the timing of prompting the next cycle of discharging. The degree of the voltage to be used and the amount of the electric current to be passed in this case can be freely determined by the number of diodes connected in series, the number of diodes connected in parallel, and the surface area of the array of diodes.  
         [0042]     For the purpose of setting the optimum charging voltage of the battery cell  40  at a little short of 4 V, for example, it suffices to form the group of diodes  50  by having six diode elements  35  connected in series as shown in  FIG. 7A . Then, for the purpose of setting the optimum charging voltage of the battery cell  40  at a little short of 2 V, it suffices to form the group of diodes  50  by having three diode elements  35  connected in series as shown in  FIG. 7B . Further, when the large electric current is required to be by-passed while the optimum charging voltage of the battery cell  40  does not need to be varied, it suffices to cause two groups of diodes  50  each formed by having five diodes elements  35  connected in series to be connected in parallel as shown in  FIG. 7C .  
         [0043]     To be specific, it suffices to form a group of diodes  50  in each of the two diode forming regions  24  of the current collecting body  22 B and form two groups of diodes  50  for one battery cell  40  as shown in  FIG. 3  or double the surface area of the diode forming region  24  and form the group of diodes  50  in the resultant region. Further, the fine adjustment of the voltage-amperage characteristic property of the group of diodes  50  may be realized by diversifying the kind of diode elements  35  forming the group of diodes  50 .  
         [0044]     In the case of silicon diodes, the voltage at which the electric current begins to flow through the diodes connected in the forward direction is about 0.6 V. In the case of germanium diodes, this voltage is about 0.1 V. By forming the group of diodes  50  by mixing silicon diodes and germanium diodes, therefore, it is made possible to obtain an arbitrary voltage-amperage characteristic property.  
         [0045]     The battery of a bipolar structure is characterized by generating a high-voltage by one cell and entailing only a low resistance but encountering difficulty in effecting control of voltage by the battery cell unit. By incorporating a plurality of diode elements in a battery cell as contemplated by this invention, it is made possible to line up the charged state automatically in spite of more or less dispersion of capacity among the diode elements during the course of manufacture and consequently manufacture a battery of a bipolar structure of a high reliability at a very low cost.  
         [0046]     Incidentally, the diode element is only a component resulting from uniting an n-type semiconductor and a p-type semiconductor. When a plurality of such diode elements are to be used, therefore, it is commendable to have them integrated into a single element. The formation of diode elements on the current collecting body of the battery cell is at an advantage in giving rise to a very simple structure without requiring to provide the secondary battery in the outer part thereof with a protective circuit as a separate item. Further when the electric current of a large amount flows through the diode elements, abnormal generation of heat can be avoided because the current collecting body serves as a radiator plate.  
         [0047]     Though the foregoing present mode of embodiment has depicted a secondary battery using a bipolar electrode  30 , namely a bipolar secondary battery, this invention can be applied to a secondary battery of a pattern having battery cells connected in parallel as illustrated in  FIG. 8 .  
         [0048]     Negative pole layers  26 A,  26 B, and  26 C and diode forming regions  24 A,  24 C, and  24 E are respectively formed on one side each of negative pole current collecting bodies  23 A,  23 B, and  23 C as illustrated in  FIG. 8 . Then, positive pole layers  28 A,  28 B, and  28 C and  24 B,  24 D, and  24 F are respectively formed on one side each of positive pole current collecting bodies  21 A,  21 B, and  21 C. The group of diodes  50  are formed on these current collecting bodies by using the semiconductor forming technique and the group of diodes  50  are connected between the positive pole terminal and the negative pole terminal in the direction in which the forward direction voltage is applied. The negative pole current collecting bodies  23 A,  23 B, and  23 C and the positive pole current collecting bodies  21 A,  21 B, and  21 C are alternately laminated as illustrated in the diagram, with a nonaqueous electrolyte is interposed between each negative pole layer or each positive pole layer and each current collecting body. The negative pole current collecting bodes  23 A,  23 B, and  23 C are bundled collectively on the right side in the bearings of the diagram and have the negative pole tub  14  attached thereto as shown in  FIG. 1 .  
         [0049]     The positive pole current collecting bodies  21 A,  21 B, and  21 C are bundled collectively on the left side in the bearings of the diagram and have the positive pole tab  12  attached thereto as shown in  FIG. 1 . The secondary battery of this type, therefore, turns out to be a product which results from connecting battery cells (formed between the positive pole current collecting body and the negative pole current collecting body) in parallel. The group of diodes  50  are fated to control the voltage during the charging of the individual battery cells connected in parallel in accordance with the characteristic property of the group of diodes  50  and are enabled to control the voltage on the battery cell unit.  
         [0050]     The bipolar secondary battery mentioned above is a product which results from connecting a plurality of battery cells in series and, therefore, constitutes the most suitable battery for a load requiring a comparatively high voltage. The secondary battery of the type mentioned above is a product which results from connecting a plurality of battery cells in parallel and, therefore, constitutes the most suitable battery for a load requiring a comparatively large electric current.  
         [0051]     [Mode 2 of Embodiment] 
         [0052]     The mode 1 of embodiment has illustrated the formation of the group of diodes by laminating diode elements  35  in the same direction as the direction of lamination of battery cells. In the present mode of embodiment, the group of diodes  50  is formed by connecting diode elements  35  in series along the longitudinal direction of the surfaces of the current collecting bodies.  
         [0053]      FIG. 9  is a diagram schematically illustrating the structure of a battery cell and the group of diodes. The battery cell  40  is formed by laminating the current collecting body  22 A destined to serve as a positive pole terminal, the positive pole layer  28 , the solid electrolyte (nonaqueous electrolyte)  27 , the negative pole layer  26 , and the current collecting body  22 B destined to serve as a negative pole terminal. Then, the group of diodes  50  is formed by sequentially laminating the N-type semiconductor layer  32 , the P-type semiconductor layer  33 , the metal layer  34 , and the insulating layer  31  through the medium of the insulating layer  31  on the diode forming region  24  of the current collecting body  22 B as illustrated in the diagram and causing five serially connected diode elements  35  to the current collecting body  22 A destined to serve as the positive pole terminal through the medium of the metal layer  34  and the electrically conducting adhesive agent layer  36 . The group of diodes  50  are electrically insulated from the positive pole and the negative pole by means of the sealing part  25 .  
         [0054]     The structure shown in  FIG. 9  forms the same electrically equivalent circuit as in the mode 1 of embodiment which is shown in  FIG. 5 . That is, the anode of the group of diodes  50  is connected to the positive electrode side of the battery cell  40  and the cathode of the group of diodes  50  is connected to the negative pole side thereof.  
         [0055]     Since the function of the group of diodes  50  is the same as described in the mode 1 of embodiment, it will be omitted from the following description.  
         [0056]     [Mode 3 of Embodiment] 
         [0057]     The modes 1 and 2 of embodiment have illustrated a structure having all the diode elements  35  forming the group of diodes  50  connected in the forward direction. The present mode of embodiment, however, forms the group of diodes  50  which include diode elements  35  connected in the reverse direction.  
         [0058]      FIG. 10  is a diagram schematically illustrating the structure of a battery cell and the group of diodes. The battery cell  40  is formed by laminating the current collecting body  22 A designed to serve as a positive pole terminal, the positive pole layer  28 , the solid electrolyte (nonaqueous electrolyte)  27 , the negative pole layer  26 , and the current collecting body  22 B destined to serve as a negative pole terminal. Then, the group of diodes  50  is formed by causing five stages of diode elements  35  each resulting from laminating the N-type semiconductor layer  32 , the P-type semiconductor layer  33 , and the metal layer  34  on the diode forming region  24  of the current collecting body  22 B and just one stage of the P-type semiconductor layer  33  and the N-type semiconductor layer laminated parallelly thereto to be connected to the current collecting body  22 A designed to serve as the positive pole terminal through the medium of the electrically conducting adhesive agent layer  36 . The group of diodes  50  are electrically insulated from the positive pole and the negative pole by means of the sealing part  25 .  
         [0059]     The structure shown in  FIG. 10  assumes such an electrically equivalent circuit as shown in  FIG. 11 . That is, the anode of five serially connected diode elements  35  is connected to the positive pole side of the battery cell  40  and the cathode thereof to the negative pole side thereof and the cathode of one diode element  35  is connected parallelly thereto to the positive pole side of the battery cell  40  and the anode thereof to the negative pole side thereof.  
         [0060]     Of the diode elements  35  which form the group of diodes  50 , the five serially connected diode elements  35  are connected in the forward direction to the battery cell  40  during the course of charging. The voltage at which the electric current of a large amount begins to flow to the group of diodes  50 , therefore, is five times the voltage at which the electric current of a large amount begins to flow to the individual diode elements  35 . The general diode elements  35  allow flow of virtually no electric current therethrough till the voltage in the forward direction reaches about 0.6 V. In the group of diodes  50  formed by connecting five diode elements in series, therefore, allow flow of virtually no electric current therethrough till the voltage reaches about 3.0 V as shown in  FIG. 6 . Meanwhile, of the diode elements  35  which form the group of diodes  50 , one diode element  35  is connected in the reverse direction to the battery cell  40 . As a natural consequence, this diode element  35  allows flow of virtually no electric current at a voltage of about 3.0 V.  
         [0061]     That is, when the voltage of the battery cell  40  exceeds 3 V and reaches a level of not lower than 3.5 V during the course of charging, the electric current abruptly begins to flow to the group of diodes  50  and the electric current ceases to be supplied to that battery cell (because it is by-passed) and the voltage of the battery cell  40  is eventually controlled to the magnitude conforming to the voltage-amperage characteristic property of the group of diodes  50 .  
         [0062]     Since the conventional secondary battery possesses a structure of having a plurality of battery cells  40  connected in series, the voltages applied to the individual battery cells  40  during the course of charging assume the magnitudes resulting from dividing the charging voltage in accordance with the capacities of the individual battery cells  40 . Since the applied voltages during the course of charging are different between the battery cells having large capacities and the battery cells having small capacities, some of the battery cells are fated to be overcharged in consequence of the application of an unduly large voltage. The secondary battery conforming to the present mode of embodiment, however, has the battery cells individually provided with the group of diodes  50  including the serially connected diode elements  35 , the voltage is eventually controlled to the magnitude of about 3.5 V without reference to the magnitude of the voltage applied to the individual battery cells during the course of charging. Even when the individual battery cells  40  have different capacities, all the battery cells are prevented from succumbing to overcharging unless the electric current exceeds the prescribed magnitude.  
         [0063]     Conversely, during the course of discharging, since one diode element  35  of all the diode elements  35  forming the group of diodes  50  is connected in the reverse direction to the battery cell  40 , virtually no electric current flows till the voltage reaches about −0.6 V. When a negative voltage exceeding this level begins to be applied, the electric current of a large amount begins to flow. Meanwhile, of the diode elements  35  which form the group of diodes  50 , the five diode elements  35  which are connected in series are connected in the forward direction to the battery cell  40 , it naturally follows that virtually no electric current flows at the voltage of about −0.6 V.  
         [0064]     In other words, when the voltage of the battery cell  40  exceeds −0.6 V during the course of discharging, the electric current abruptly begins to flow to the group of diodes  50  and the electric current ceases to be supplied from that battery cell (the current is by-passed) and the voltage of the battery cell  40  is eventually controlled by the magnitude conforming to the voltage-amperage characteristic property of the group of diodes  50 . The secondary battery conforming to the present mode of embodiment, therefore, has the voltage thereof controlled to about −0.6 V during the course of discharge even in the worst case because it is provided with the group of diodes  50  including diode elements  35  connected in the reverse direction to the individual battery cells. Thus, all the battery cells are prevented from succumbing to overcharging even when the individual battery cells  40  have different capacities.  
         [0065]     When the diode elements are connected in the forward direction, the possibility that the battery cells having lost capacity balance will be overcharged during the course of charging ceases to exist. When the charging is completed and shifted to discharging, the batteries having small capacities fall in the state of overdischarging during the course of discharging. When the battery voltage continues the state of positive-negative reversal, the capacity is abruptly aggravated because the electrolyte of the battery continues decomposition and the current collecting body undergoes liquation. By having one diode element connected in the reverse direction to the battery cell, the battery is enabled to avoid sudden deterioration because the possibility that a potential of not more than −0.6 V will be applied to the battery ceases to exist. It is permissible to use a structure having a plurality of diode elements connected in series in conformity to the magnitude of the electric current to be passed.  
         [0000]     Process for Production of a Group of Diodes  
         [0066]     Now, the process for the production of the group of diodes  50  will be described below in an outlined form with reference to  FIG. 12A - FIG. 14B .  
         [0067]     The process of production illustrated in  FIG. 12A  and  FIG. 12B  is a procedure which is intended to form a group of diodes  50  by laminating diode elements  35  as described in the mode 1 of embodiment ( FIG. 4 ).  
         [0068]     For a start, the current collecting body  22 B which is shown in (a) is prepared and the insulating layers  31 A and  31 B which are shown in (b) are formed as parted by a prescribed distance on the diode forming region  24  of the current collecting body  22 B. Next, the N-type semiconductor layer  32  is formed so as to fill up the interval between the insulating layers  31 A and  31 B as shown in (c). Then, the P-type semiconductor layer  33  is formed so as to cover the N-type semiconductor layer  32  as shown in (d). Further, the metal layer  34  is formed so as to cover the P-type semiconductor layer  33  as shown in (e). Then, the insulating layers  31 C and  31 D are formed so as to cover the metal layer  34  except the part of a contact hole  37  with the overlain N-type semiconductor layer  32  as shown in (f).  
         [0069]     The steps described thus far will form one diode element  35 . The formation of another diode element  35  laminated on this diode element  35  is accomplished by repeating the steps of (a) through (f) mentioned above and finishing the lamination as shown in (g). In the case of the mode 1 of embodiment, since five diode elements  35  are laminated, the foregoing steps of (a) through (f) are carried out up to five repetitions.  
         [0070]     The process of production illustrated in  FIG. 13A  and  FIG. 13B  is a procedure which is intended to form a group of diodes  50  by lining diode elements  35  in the lateral direction of the current collecting body as described in the mode 2 of embodiment ( FIG. 9 ).  
         [0071]     For a start, the current collecting body  22 B which is shown in (a) is prepared and the insulating layer  31  which is shown in (b) is formed uniformly on the diode forming region  24  of the current collecting body  22 B. Next, the N-type semiconductor layers  32 A- 32 E are formed as spaced with prescribed distance. The N-type semiconductor layer  32 A is formed at such a position as to sit astraddle on the current collecting body  22 B and the insulating layer  31  and the remaining N-type semiconductor layers  32 B- 32 E are formed on the insulating layer  31 . Incidentally, the N-type semiconductor layers are formed at five positions because five diode elements  35  are formed. Then, the P-type semiconductor layers  33 A- 33 E are formed at such positions as to sit astraddle on the N-type semiconductor layers  32 A- 32 E and the insulating layer  31  as shown in (d).  
         [0072]     Next, the metal layers  34  are formed so as to connect electrically the adjacent P-type semiconductor layers and the N-type semiconductor layers as shown in (e). To be specific, the metal layers  34 A is formed so as to cover the P-type semiconductor layer  33 A and the N-type semiconductor layer  32 B, the metal layer  34 B is formed so as to cover the P-type semiconductor layer  33 B and the N-type semiconductor layer  32 C, the metal layer  34 C is formed so as to cover the P-type semiconductor layer  33 C and the N-type semiconductor layer  32 D, and the metal layer  34 D is formed so as to cover the P-type semiconductor layer  33 D and the N-type semiconductor layer  32 E. Then, the insulating layer  31  is formed so as to cover all the laminated bodies excepting part of the N-type semiconductor layer  32 E as shown in (f). Finally, the metal layer  34 E is formed so as to cover the insulating layer  31  with the object of forming connection with the N-type semiconductor layer  32 E as shown in (g).  
         [0073]     By performing the preceding steps, it is made possible to form one diode element  35  with the current collecting body  22 B, the N-type semiconductor layer  32 A, the P-type semiconductor layer  33 A, and the metal layer  34 A. In the case of this process of production, therefore, the five diode elements  35  are destined to be formed along the longitudinal direction of the current collecting body  22 B.  
         [0074]     The process of production illustrated in  FIG. 14A  and FIG.  14 B is a procedure which is intended to form a group of diodes  50  by lining diode elements  35  in the lateral direction of the current collecting body as described in the mode 2 of embodiment ( FIG. 9 ).  
         [0075]     For a start, the current collecting body  22 B which is shown in (a) is prepared and the insulating layers  31 A and  31 B which ae shown in (b) are formed on the diode forming region  24  of the current collecting body  22 B. Next, depressions are formed by etching one each at two positions of the insulating layer  31 B as shown in (c) and the metal layers  34 A and  34 B are formed above these depressions. Then, the N-type semiconductor layers  32 A- 32 C are formed between the insulating layers  31 A and  31 B and partly on the metal layers  34 A and  34 B as shown in (d). Next, the P-type semiconductor layers  33 A- 33 E are formed on the N-type semiconductor layers  32 A- 32 C and in the regions of the metal layers  34 A and  34 B in which the N-type semiconductor layer  32 B and  32 C are not formed as shown in (e). Next, the N-type semiconductor layers  32 D and  32 E are formed selectively on the P-type semiconductor layers  33 B and  33 D as shown in (f). Then, the depressed part of the laminated body  39  is filled up with an insulating material to give the laminated body a flat upper surface.  
         [0076]     Next, the metal layers  34  for connecting the adjacent P-type semiconductor layers and N-type semiconductor layers are formed as shown in (h). To be specific, the metal layer  34 C is formed so as to cover the P-type semiconductor layer  33 A and the N-type semiconductor layer  32 D, the metal layer  34 D is formed so as to cover the P-type semiconductor layer  33 C and the N-type semiconductor layer  32 E, and the metal layer  34 E is formed on the P-type semiconductor layer  33 E. Then, the depressed part of the laminated body  39  is filled up with an insulating material so as to give the laminated body with a plat upper surface as shown in (i). Then, the metal layer  34 F is formed so as to cover the insulating layer with the object of finally effecting connection with the metal layer  34 E as shown in (j).  
         [0077]     By carrying out the preceding steps, it is made possible to form one diode element  35  with the current collecting body  22 B, the N-type semiconductor layer  32 A, the P-type semiconductor layer  33 A, and the metal layer  34 C. Thus, in the case of the present process of production as well, the five diode elements  35  are formed along the longitudinal direction of the current collecting body  22 B.  
         [0078]     One example of the process for production of the group of diodes  50  has been illustrated. The group of diodes  50  can be formed by other process than the process of production described above. Further, instead of directly forming the group of diodes  50  on the current collecting body, the group of diodes  50  may be formed as a single semiconductor element and disposed within the battery cell (between the current collecting bodies).  
         [0079]     This invention embraces formation of a group battery by having at least two flat secondary batteries  10  mentioned above (refer to  FIG. 1 ) connected in series or in parallel. To be specific, a group battery  70  may be obtained, for example, by connecting four secondary batteries  10  in parallel as shown in  FIG. 15  (refer to  FIG. 15B ), arraying six rows each of four parallelly connected secondary batteries  10  in series, and stowing the resultant array in a group battery case  60  made of a metallic material (refer to FIGS.  15 A-C). The group battery  70  which can cope with any arbitrary amperage, voltage, and capacity can be provided by thus connecting a desired number of secondary batteries  10  in a serial-parallel pattern.  
         [0080]     Incidentally, a positive pole terminal  62  and a negative pole terminal  64  of the group battery  70  disposed on the lid in the upper part of the group battery case  60  and the positive pole tab  12  and the negative pole tab  14  of each of the secondary batteries  10  are electrically connected by the use of a positive pole terminal lead wire  66  and a negative pole terminal lead wire  68  of the group battery  70 . For the purpose of connecting four secondary batteries  10  in parallel, it suffices to connect electrically the electrode tabs  12  and  14  of each of the secondary batteries  10  to the repevant terminals by the use of proper connecting members such ass spacers. For the sake of connecting in series six sets each of four parallelly connected secondary batteries  10 , it suffices to cause the electrode tabs  12  and  14  of each of the secondary batteries  10  sequentially connected by the use of proper connecting members such as spacers  72  (refer to  FIG. 15C ).  
         [0081]     In the group battery, the application of this invention brings the effect of averaging the voltage during the course of charging and simplifies greatly the part using the conventional control circuit. In the case of the group battery using a plurality of batteries, when the individual batteries have dispersed capacities, this dispersion has a high possibility of inducing overcharging or overdischarging and consequently posing a serious problem of finding a way of uniformizing their capacities. The application of this invention can give a solution to this problem.  
         [0082]     Then, by causing at least two group batteries  70  mentioned above to be connected in series, in parallel, or in series-parallel thereby forming a group battery module, it is made possible to cope comparatively inexpensively with the demand for the capacity and output of a battery for a varying purpose of use without requiring new manufacture of a group battery. The group battery module which is formed by connecting a plurality of group batteries in series-parallel, when part of the batteries or the group batteries encounter an accident, can be repaired by simply replacing the batteries in trouble.  
         [0083]     In an electric vehicle  80 , the group battery  70  is mounted under the seat in the central part of the body thereof as shown in  FIG. 16 . The part below the seal is selected with the object of enabling the interior of the body and the trunk of the vehicle to occupy large spaces. The position for mounting the battery does not need to be limited to the part below the seat. The part below the trunk of the vehicle or the engine room in the front part of the vehicle may be used instead. This invention is particularly effective in an electric vehicle which repeats charging and discharging within a comparatively brief period of time and is effective for the purpose of manufacturing an electric vehicle using a multiplicity of batteries inexpensively while retaining high reliability.  
         [0084]     The secondary battery contemplated by this invention has the group of diodes connected between the positive pole terminal and the negative pole terminal in the direction in which the forward direction voltage is applied as described above. When the voltage between the positive pole terminal and the negative pole terminal rises above a certain level, the magnitude of the resistance offered by the group of diodes is lowered to give rise to a bypass circuit for the electric current, ensure the safety of the battery, and exalt the service life of the battery.  
       EXAMPLES  
       [0085]     The present example of the invention uses the secondary battery of the structure shown in  FIG. 1 , namely the second battery having a plurality of diode elements connected in series in the forward direction. The number of steps of series connection is increased or decreased in conformity with the operating voltage of the secondary battery. Though the number of steps of series connection depends on the kind of battery, particularly the lithium secondary battery is preferred to have such a number of steps of series connection which falls in the approximate range of 3-6 relative to the battery cell. Then, the number of diode elements connected in parallel is increased or decreased in conformity with the magnitude of the electric current flowing to the secondary battery. As a means to produce the same effect as increasing the number of steps of parallel connection, the method of giving the diode elements an increased cross section may be cited. Since the batteries having particularly high output and high input allow flow of a large amount of electric current thereto, the electric current of such a large amount can flow to the diode elements used for bypassing. More often than not, therefore, the diode elements are required to have a larger surface area than usual. The measure of having one diode element connected in the reverse direction in addition to having a plurality of diode elements connected in series in the forward direction to the battery cell is effective in the sense of preventing overdischarging.  
       Example 1  
       [0086]     A group of diodes was manufactured by connecting in series five 6A Diodes made by General Semiconductor Corp. When a voltage was applied gradually to the group of diodes and the electric current flowing out of them was measured, results similar to those shown in  FIG. 6  were obtained. Next, a 20-unit module battery was manufactured by preparing 20 such groups of diodes, connecting 20 separately prepared canned 1600 mAh lithium ion batteries (4.2 V during ordinary charging and 2.5V during discharging) one each in the forward direction to the 20 groups of diodes, and thereafter connecting the individual batteries in series. This module battery was not furnished particularly with a protective circuit. Further, 20 such module batteries were prepared and subjected to charging and discharging at 3200 mA and 50 V of lower limit and 80 V of upper limit respectively of cutoff voltage up to 100 repetitions. Thereafter, the module batteries were examined to find any sign of abnormality and were tested for 1 C discharge capacity from 72 V.  
         [0087]     As a result, none of the 20 module batteries was found to have induced any leakage and none of them was found to emit smoke. The module batteries had a capacity (average) of 752 mAh prior to the cycles and a capacity (average) of 665 mAh after the cycles. The ratio of the charging capacity to the discharging capacity in the final cycle was 96%.  
       Example 2  
       [0088]     To each of the module batteries of Example 1, one 6A diode produced by General Semiconductor Corp was connected in the reverse direction. Twenty (20) such module batteries were prepared and were subjected to charging and discharging at 3200 mA and 50 V of lower limit and 80 V of upper limit respectively of cutoff voltage up to 100 repetitions. Thereafter, the module batteries were examined to find any sign of abnormality and tested for 1 C discharge capacity from 72 V.  
         [0089]     As a result, none of the 20 module batteries was found to have induced any leakage and none of them was found to emit smoke. The module batteries had a capacity (average) of 748 mAh prior to the cycles and a capacity (average) of 681 mAh after the cycles. The ratio of the charging capacity to the discharging capacity in the final cycle was 95%.  
       Comparative Example 1  
       [0090]     Twenty (20) module batteries were prepared by following the procedure of Example 1 while omitting use of the group of diodes and were subjected to charging and discharging at 3200 mA and 50 V of lower limit and 80 V of upper limit respectively of cutoff voltage up to 100 repetitions. Thereafter, the module batteries were examined to find any sign of abnormality and tested for 1 C discharge capacity from 72 V.  
         [0091]     As a result, six of the twenty module batteries were found to induce leakage and one of them was found to emit smoke. The module batteries had a capacity (average) of 758 mAh prior to the cycles and a capacity (average) of 420 mAh after the cycles. The ratio of the charging capacity to the discharging capacity in the final cycle was 98%.  
         [0092]     When Comparative Example 1 is compared with Example 1 and Example 2, it is noted that Comparative Example 1 which was not provided with the group of diodes was suspected to entail leakage or emission of smoke and involve a large degree of reduction of capacity after repeated cycles of charging and discharging. The results indicate that the provision of the group of diodes results in elongating the service life of the battery. It is also noted that the consumption of energy by the addition of diodes is very small.  
       Example 3  
       [0093]     A SUS 316 stainless steel sheet measuring 20 μm in thickness and 20 cm×30 cm in surface area was prepared. A coating material produced by dissolving lithium manganese, LiMn 2 O 4 , having a diameter of 10 μm, acetylene black, and a PVDF binder at a composition of 90:5:5 in N-methyl pyrrolidone was applied to the central part, 18 cm×26 cm, on one side of this sheet, and dried to prepare a positive pole active substance layer 50 μm in thickness.  
         [0094]     Next, a coating material produced by dissolving hard carbon having a diameter of 10 μm in diameter and a PVDF binder in a composition of 90:10 in N-methyl pyrrolidone was applied to the central part, 18 cm×26 cm, on the rear side of the sheet and dried to prepare a negative pole active substance layer 50 μm in diameter.  
         [0095]     At the positions 10 mm from the opposite edges of the short side, 20 cm, on the positive electrode active substance layer side of the stainless steel sheet, silver, p-dope silicon, and n-dope silicon were each sputtered at the range of 20 cm×0.1 cm to a thickness of 1 μm up to five repetitions to form five layers each of a group of diodes.  
         [0096]     In each of the areas adjoining the groups of diodes, an insulating layer of aluminum oxide was formed by sputtering in a width of 0.2 cm. Silver was further sputtered in a thickness of 1 μm on the uppermost layer and the resultant silver coat was coated with silver paste. The application of the paste was carried out so as to prevent the paste from protruding out of the aluminum oxide insulating layer.  
         [0097]     To the exposed part of the stainless steel sheet on which no group of diode was formed and no electrode was formed, carboxylic acid-modified polypropylene was pasted.  
         [0098]     A microporous polypropylene film having a thickness of 20 μm and measuring 20.5 cm×30.5 cm in surface area was prepared as a separator. This film was impregnated with an ethylene carbonae:propylene carbonate (1:1 vol) solution of polyethylene oxide macromonomer, 2,2-azobisisobutyronitrile, and 1 mol/L hexafluorophosphoric acid LiPF 6  and subsequently subjected to ultraviolet irradiation to manufacture a gel electrolyte-containing separator composed of 90 wt % of an electrolyte component and 10 wt % of polyethylene oxide.  
         [0099]     The positive pole active substance on the stainless steel sheet was covered with this separator. Twenty (20) such stainless steel sheets were superposed to manufacture a 400 mAh bipolar secondary battery formed of 20 units of series connection.  
         [0100]     The diode forming part was so formed that the part coated with the silver paste might adhere fast to the electrode opposite thereto. At this time, the stainless steel sheets forming the uppermost and lowermost layers were each coated on one side only so that the outer sides thereof might expose stainless steel surfaces and these stainless steel sheets were each joined to a copper foil for the lead.  
         [0101]     This bipolar battery was finally finished as wrapped in a sheathing material of aluminum laminate film. Twenty (20) such bipolar batteries were prepared and subjected to charging and discharging at 800 mA and a lower limit of 50 V and an upper limit of 80 V respectively of a cutoff voltage up to 100 repetitions. Subsequently, they were examined to find any sign of abnormality of module battery and tested for 1 C discharge capacity from 72 V.  
         [0102]     As a result, none of the 20 module batteries was found to induce leakage and none of them was found to emit smoke. The capacity (average) of the module batteries prior to the cycles was 202 mAh and the capacity (average) thereof after the final cycle was 171 mAh. Then, the ratio of the charging capacity to the discharging capacity in the final cycle was found to be 96%.  
       Comparative Example 2  
       [0103]     A bipolar secondary battery was manufactured by following the procedure of Example 3 while omitting the formation of a group of diodes. Twenty (20) such bipolar secondary batteries were prepared and subjected to charging and discharging at 800 mA and a lower limit of 50 V and an upper limit of 80V respectively of cutoff voltage up to 100 repetitions. Thereafter, they were examined to find any sign of abnormality and tested for 1 C discharge capacity from 72 V.  
         [0104]     As a result, seven of the 20 module batteries were found to induce leakage and two of them were found to emit smoke. Then, as many as ten of them were found to be inflated with the gas generated inside the battery. The capacity (average) of the module batteries prior to the cycles was 202 mAh and the capacity (average) after the cycles was 89 mAh. The ratio of the charging capacity to the discharging capacity in the final cycle was found to be 98%.  
         [0105]     When Comparative Example 2 is compared with Example 3, it is noted that Comparative Example 2 which was not provided with the group of diodes was suspected to entail leakage or emission of smoke and involve a large degree of reduction of capacity after repeated cycles of charging and discharging. The results indicate that the provision of the group of diodes results in elongating the service life of the battery. It is also noted that the consumption of energy by the addition of diodes is very small.  
         [0106]     It is noted that when the group of diodes are connected to the battery cell, the secondary battery can be made to operate very safely. Further even when diodes are annexed, the decrease of capacity during the course of performing charging and discharging in a brief period and the effect exerted on the degradation of performance is extremely small.  
         [0107]     The entire disclosure of Japanese Patent Application No. 2004-074590 filed on Mar. 16, 2004 including specification, claims, drawings, and summary are incorporated herein by reference in its entirety.