Patent Publication Number: US-2013252051-A1

Title: Battery system

Description:
TECHNICAL FIELD 
     The present invention relates to a battery system including an assembled battery. 
     BACKGROUND ART 
     Secondary batteries are typically classified into two types of a wound type and a stacked type. Each type of the secondary batteries has a configuration (hereinafter referred to as a stacked electrode body) in which electrode plates (a positive electrode plate and a negative electrode plate) are stacked through a separator serving as an insulator. The wound-type secondary battery has a configuration in which one sheet-like positive electrode plate and one sheet-like negative electrode plate are stacked through a separator and are rolled up and housed in a battery container. The stacked-type secondary battery has a configuration in which a plurality of sheet-like positive electrode plates and a plurality of sheet-like negative electrode plates are sequentially stacked through a separator and are housed in a battery container without being rolled up. The battery container includes members such as a container body having an opening, and a cover that covers the opening. After the stacked electrode body is housed in the container body, the opening is covered by the cover, thereby sealing the battery container. 
     The secondary battery is capable of repeatedly charging and discharging. However, when charging and discharging are repeatedly carried out, the battery container may expand due to the expansion of an internal electrode plate, decomposition of an electrolyte, or the like. The expansion of the battery container may lead to an occurrence of a failure of the secondary battery. For this reason, it is necessary to detect the expansion at an appropriate time to prevent occurrence of a failure of the secondary battery. 
     In this regard, a battery system and the like have been developed in which special equipment such as a press button switch or a strain detector is provided on the surface of a secondary battery and the special equipment is brought into press contact with adjacent secondary batteries, thereby detecting the expansion (see PTL 1 and PTL 2). 
     CITATION LIST 
     Patent Literature 
     {PTL 1} 
     
         
         Japanese Unexamined Patent Application, Publication No. Hei 06-52901 
       
    
     {PTL 2} 
     
         
         PCT International Publication No. WO 2002/099922 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, when special equipment such as a press button switch or a strain detector for detecting an expansion of a battery container as disclosed in PTL 1 and PTL 2 is newly provided in the battery container, a dedicated circuit or the like is required, which complicates the configuration and leads to an increase in cost. 
     The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a battery system capable of easily detecting an expansion of a battery container of a secondary battery that constitutes an assembled battery with a simple configuration without an increase in cost. 
     Solution to Problem 
     To solve the above-mentioned problem, a battery system according to a first aspect of the present invention includes: a first secondary battery including a stacked electrode body connected to a first electrode terminal and a second electrode terminal, the stacked electrode body being housed in a first battery can, the first electrode terminal and the first battery can being electrically connected through a first conductive path; a second secondary battery including a stacked electrode body connected to a third electrode terminal and a fourth electrode terminal, the stacked electrode body being housed in a second battery can, the third electrode terminal and the second battery can being electrically connected through a second conductive path; a first battery can voltage sensor that measures a first voltage of the first battery can; a second battery can voltage sensor that measures a second voltage of the second battery can; and a control device that receives information corresponding to the measured first and second voltages of the first and second battery can voltage sensors. The control device activates expansion detection information based on the information when the first voltage increases and the second voltage decreases substantially simultaneously with the increase. 
     According to the configuration described above, the control device can easily recognize a contact or the like between battery cans due to an expansion of a battery can, when the expansion detection information is active, by using the information corresponding to the voltage measured by the first and second battery can voltage sensors which are respectively arranged in the first and second battery cans. This eliminates the need to provide special equipment such as a press button switch or a strain detector to the battery can. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a battery system capable of easily detecting an expansion of a battery container of a secondary battery that constitutes an assembled battery with a simple configuration without an increase in cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration of a battery system according to an embodiment of the present invention. 
         FIG. 1  is a breakaway view of a secondary battery used for a battery system according to an embodiment of the present invention. 
         FIG. 3  is a diagram illustrating an array of each secondary battery in the battery system according to an embodiment of the present invention. 
         FIG. 4A  is a schematic view illustrating an electric circuit obtained after battery cans of adjacent two secondary batteries among a plurality of arrayed secondary batteries contact each other. 
         FIG. 4B  is an electric circuit diagram obtained after battery cans of adjacent two secondary batteries among a plurality of arrayed secondary batteries contact each other. 
         FIG. 5  is a schematic diagram illustrating an electric circuit obtained after battery cans of adjacent three secondary batteries among a plurality of arrayed secondary batteries contact each other. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of a battery system according to the present invention will be described below with reference to the drawings.  FIG. 1  is a block diagram illustrating a configuration of a battery system  100  according to this embodiment. 
     The battery system  100  according to this embodiment includes a higher-level control device  1 , a display device  2 , a power load  3 , and a battery module  4 . The battery module  4  is formed of an assembled battery  5  and a BMS (Battery Management System)  6 . The battery module  4  has a form of a module which is easily replaced from the outside of the battery system  100 . The higher-level control device  1 , the display device  2 , and the power load  3  are incorporated in the battery system  100  in advance. In this case, a combination of the higher-level control device  1  and a BMS  6  is also referred to simply as a control device. 
     The battery system  100  according to the present invention may be an industrial vehicle such as a forklift having wheels connected to an electric motor serving as the power load  3 , a moving body such as a electric car or an electric vehicle, or a moving body such as an airplane or a ship with a propeller or a screw connected to an electric motor serving as the power load  3 . Alternatively, the battery system  100  may be a power storage system for domestic use, a stationary system such as a power grid stabilization system in combination with power generation by natural energy such as a windmill or sunlight, for example. That is, the battery system  100  is a system that utilizes charging and discharging of power by a plurality of secondary batteries that constitute an assembled battery. 
     The assembled battery  5  within the battery module  4  supplies power to the power load  3  of the battery system  100 , and has a configuration in which an arm (first arm) composed of secondary batteries  7 A to  7 D, which are connected in series, and an arm (second arm) composed of secondary batteries  7 E to  7 H, which are connected in series, are connected in parallel. 
     In the secondary batteries  7 A to  7 H that constitute the assembled battery  5 , temperature sensors  8 A to  8 H that measure the container temperature (battery can temperature) of each secondary battery and cell voltage sensors  9 A to  9 H that measure the inter-terminal voltage (voltage between the positive electrode terminal and the negative electrode terminal of each secondary battery) are arranged so as to respectively correspond to the secondary batteries. Each arm includes a corresponding current sensor  10 - 1  and a corresponding current sensor  10 - 2 , thereby enabling measurement of a current flowing through each arm. 
     Further, in the battery system  100 , the battery container is a battery can made of conductive metal such as aluminium. Examples of the battery container that houses the stacked electrode body include a battery container made of plastic and a battery container made of metal. In the case of using a battery can, the electrolyte encapsulated in the battery can together with the stacked electrode body described above reacts with the inner wall of the battery can, which may modify the battery can or deteriorate the performance of the battery. For example, in the case of a lithium ion secondary battery using a battery can made of an aluminum-based material, pull-up resistors  12 A to  12 H having a high resistance (about 1 kΩ or more) and electrically connecting the positive electrode terminals, which are provided to secondary batteries  7 A to  7 H as described later, with battery cans  11 A to  11 H respectively corresponding to the positive electrode terminals, are provided to respective secondary batteries  7 A to  7 H, so as to avoid the failure occurring due to the reaction between the inner walls of the battery cans  11 A to  11 H and the electrolyte encapsulated in the battery cans. Since these pull-up resistors form a conductive path, the voltage of each battery can is substantially the same as the voltage of the positive electrode terminal. To check the connections of the pull-up resistors  12 A to  12 H, battery can voltage sensors  13 A to  13 H that measure the battery can voltage of each secondary battery (voltage between the negative electrode terminal and the battery can of each secondary battery) are arranged so as to respectively correspond to the secondary batteries. 
     Although not illustrated, in a similar manner, in the case of a lithium ion secondary battery using a battery can made of an iron-based material (including an iron alloy), for example, pull-down resistors having a high resistance (about lkQ or more) and electrically connecting negative electrode terminals, which are provided to secondary batteries, with battery cans respectively corresponding to the negative electrode terminals are arranged so as to respectively correspond to the secondary batteries. Since these pull-down resistors form a conductive path, the voltage of each battery can is substantially the same as the voltage of each negative electrode terminal. To check the connections of the pull-down resistors, battery can voltage sensors that measure the battery can voltage (voltage between the positive electrode terminal and the battery can of each secondary battery) of each secondary battery are arranged so as to respectively correspond to the secondary batteries. 
     The battery can voltage sensor may be a so-called voltmeter, a comparator indicating that the can voltage is equal to or higher than a reference voltage or equal to or lower than the reference voltage, or the like. 
     Since a battery can is used as the battery container, an insulating sheet made of plastic, for example, is disposed between the stacked electrode body and the inner wall of the battery can so as to prevent an electrical contact between the stacked electrode body and the inner wall of the battery can. 
     The measurement information (battery can temperature, current values of each arm, and values of inter-terminal voltages of each secondary battery (inter-terminal voltage value) and information corresponding to a value (battery can voltage value) of a battery can voltage), which are measured by various sensors and output, are input to the BMS  6 . 
     Specifically, the measurement information of each of the temperature sensors  8 A to  8 D, cell voltage sensors  9 A to  9 D, and battery can voltage sensors  13 A to  13 D, which are arranged so as to respectively correspond to the secondary batteries  7 A to  7 D constituting the first arm, and the current sensor  10 - 1  arranged to correspond to the first arm is input to a CMU  14 - 1  which is arranged in the BMS  6  so as to correspond to the first arm through a bus. Similarly, the measurement information of each of the temperature sensors  8 E to  8 H, cell voltage sensors  9 E to  9 H, and battery can voltage sensors  13 E to  13 H, which are arranged so as to respectively correspond to the secondary batteries  7 E to  7 H constituting the second arm, and the current sensor  10 - 2  arranged so as to correspond to the second arm is input to a CMU  14 - 2  which is arranged in the BMS  6  so as to correspond to the second arm through a bus. 
     The measurement information input to each of the CMU  14 - 1  and CMU  14 - 2  is output from these CMU at an appropriate time and input to the BMU  15 . 
     In the BMU  15  having received the measurement information described above, the related information such as the information corresponding to the measurement information, information on a charging rate (SOC) of each secondary battery, which is calculated within the BMU  15  by using the measurement information, or expansion detection information (described later) is transmitted to the higher-level control device  1  at an appropriate time. 
     The higher-level control device  1  controls the power load  3  according to an instruction of a user or an operator (for example, the amount by which an accelerator pedal is depressed by a user), receives the related information transmitted from the BMS  6 , and controls the display device  2  to cause the display device  2  to display the related information as needed. When determining that the related information indicates an abnormal value, the higher-level control device  1  causes an abnormality lamp incorporated in the display device  2  to light, for example, and activates an acoustic device such as a buzzer or the like incorporated in the display device  2  to issue an alarm, thereby stimulating a sense of vision and a sense of hearing by light and sound to attract attention of a user. 
     The display device  2  is a monitor, such as a liquid crystal panel, including the acoustic device, and is capable of displaying the related information of the secondary batteries  7 A to  7 H constituting the assembled battery  5  based on the control from the higher-level control device  1 , for example. 
     The power load  3  is an electric power converter such as an electric motor or an inverter connected to wheels of an electric vehicle, for example. The power load  3  may be an electric motor that drives a wiper or the like. 
     In this case, the assembled battery  5  has a configuration in which four secondary batteries are connected in series to form one arm, and two arms in total are connected in parallel. However, the number of secondary batteries to be connected to each arm and the number of arms are arbitrarily designed as long as at least two secondary batteries are provided. As described later, this is because at least two secondary batteries using a battery can are required to detect an expansion of the battery can in the battery system  100 . 
     Referring next to  FIG. 2 , the outline of the configuration of each of the secondary batteries  7 A to  7 H will be described. Since these secondary batteries have the same configuration, the secondary batteries are simply denoted by reference numeral “7”, and reference symbols “A” to “H” are omitted. Similarly, identical secondary batteries are used as the temperature sensors  8 A to  8 H, cell voltage sensors  9 A to  9 H, battery can voltage sensors  13 A to  13 H, and pull-up resistors  12 A to  12 H, which are arranged so as to correspond to the secondary batteries  7 A to  7 H, and the battery cans  11 A to  11 H of the secondary batteries  7 A to  7 H. Accordingly,  FIG. 2  illustrates that each battery can and each pull-up resistor are denoted by reference numerals “11” and “12”, respectively, and reference symbols “A” to “H” are omitted. 
     The secondary battery  7  is a secondary battery including a stacked electrode body in which electrode plates (a positive electrode plate and a negative electrode plate) are stacked through a separator serving as a porous insulator. In this case, a stacked type lithium ion secondary battery incorporating a battery can having a square shape (square-shaped) with dimension H×dimension L×dimension W and having sides on X, Y, and Z axes which are perpendicular to each other is illustrated (where H&gt;0, L&gt;0, W&gt;0). 
     In this case, a square battery can  11  is formed of an aluminium-based material (for example, A3000 system). On one surface (corresponding to a cover) of the battery can  11 , a positive electrode terminal  17  and a negative electrode terminal  18  are arranged in the state of penetrating through the corresponding battery can  11 . Note that an insulator  16  is arranged between the positive electrode terminal  17 , the negative electrode terminal  18 , and the battery can  11  such that the positive electrode terminal  17  and the negative electrode terminal  18  are not in electrically contact with the battery can  11 . Further, on the one surface of the battery can  11 , a safety valve  22  that is self-destroyed by a pressure having a certain value or greater in case the internal pressure (inner pressure) of the battery can  11  increases due to generation of a gas within the battery can  11 . Furthermore, a pull-up resistor  12  is connected between the positive electrode terminal  17  and the battery can  11 , and the voltage of the battery can  11  is substantially the same as the voltage of the positive electrode terminal  17 . 
     The battery can  11  houses a stacked electrode body in which a positive electrode plate  20  having lithium manganate (LiMn 2 O 4 ) as an active material, for example, and a negative electrode plate  21  having carbon as an active material, for example, are sequentially stacked through a separator  19 . An insulating sheet (not illustrated) is arranged between the stacked electrode body and the battery can  11  such that the stacked electrode body does not contact the wall surface of the battery can  11 . 
     A predetermined amount of electrolyte (not illustrated) is injected into the battery can  11 . The positive electrode plate  20  is connected to the positive electrode terminal  17  within the battery can  11 , and the negative electrode plate  21  is connected to the negative electrode terminal  18  is connected within the battery can  11 . 
     Note that the battery can  11  is hermetically and airtightly sealed in the state where the stacked electrode body and the electrolyte are contained therein. 
     Next,  FIG. 3  illustrates an array configuration of a plurality of secondary batteries constituting one arm. In this case, the configuration in which the secondary batteries  7 A to  7 D constitute the first arm is illustrated as a typical example. This is an arrangement on an XY-plane when viewed from one surface on which the electrode terminals (the positive electrode terminal  17  and the negative electrode terminal  18 ) of the secondary battery  7  illustrated in  FIG. 2  are formed. Note that in  FIG. 3 , the illustration of each of the pull-up resistor  12 , the temperature sensors  8 A to  8 D, the cell voltage sensors  9 A to  9 D, and the battery can voltage sensors  13 A to  13 D of each secondary battery is omitted. 
     If the battery can  11  expands, the degree of the deformation is largest in the vicinity of the center of one surface (a surface having a largest area among the surfaces of the battery can  11 , i.e., a surface having dimension L×dimension H) of the battery can  11  on the xz-plane of the secondary battery  7  arranged as illustrated in  FIG. 2 . Accordingly, the one surfaces are aligned and arranged at an interval by a width t (where t&gt;0) so as to face the adjacent secondary battery. 
     The electrode terminals of the secondary batteries  7 A to  7 D are physically connected as needed in series by a bus bar  23 . The bus bar  23  is fixed to the electrode terminal with a screw (not illustrated), so that the arranged relative positions of the secondary batteries  7 A to  7 D are fixed by the bus bar  23  and are housed in the container  24 . The dimension of the inner wall of the container  24  is substantially dimension L×(dimension 4 W+dimension 3 t)×dimension H. 
     As described above, the relative positions of the secondary batteries  7 A to  7 D are fixed by the bus bar  23 . However, when a gas is generated in the battery can  11  and the inner pressure increases, for example, the vicinity of the center expands and deforms to contact the adjacently arranged battery can  11  of the secondary battery. The detection of the expansion of the battery can in the battery system according to the present invention utilizes the contact. 
     Accordingly, the dimension of the width t is appropriately designed so that a width W of the battery can  11  can be deformed into a width (W+2 t) due to the expansion before the inner voltage at which the safety valve  22  is destroyed is reached. 
     Now, the detection of the expansion of the battery can  11  in the battery system  100  will be described in detail below.  FIG. 4  is a diagram illustrating the case where in the secondary batteries  7 A to  7 D arranged in the container  24  as illustrated in  FIG. 3 , the inner voltage of the battery can  11 A of the secondary battery  7 A increases, for example, so that the battery can  11 A expands and contacts the battery can  11 B of the adjacent secondary battery  7 B. When the secondary battery  7 A expands, one surface of the battery can  11 A along the XZ-plane can expand so as to contact the battery can  11 B of the secondary battery  7 B, but the expansion of the other surface is inhibited by the inner wall of the container  24 . That is,  FIG. 4  is a typical explanatory diagram in the case where the battery cans  11  of the two adjacent secondary batteries  7  contact each other (the case where the battery cans  11  of three secondary batteries  7  contact each other will be described later). 
     As illustrated in  FIG. 4A , when the battery can  11 A expands and contacts the battery can  11 B, a conductive path is generated between these two battery cans. In this configuration, as illustrated in an electric circuit diagram of  FIG. 4B , the pull-up resistor  12 A and the pull-up resistor  12 B are connected in series between the positive electrode terminal and the negative electrode terminal of the secondary battery  7 A and the positive electrode terminal of the secondary battery  7 B is connected to the negative electrode of the secondary battery  7 B. 
     Accordingly, assuming that the voltage value measured by the battery can voltage sensor  13 A prior to the contact is V A ; the voltage value measured by the battery can voltage sensor  13 B prior to the contact is V B ; the resistance value of the pull-up resistor  12 A is R A ; the resistance value of the pull-up resistor  12 B is R B ; the voltage value measured by the battery can voltage sensor  13 A after the contact is V A ′; and the voltage value measured by the battery can voltage sensor  13 B prior to the contact is V B ′, V A ′ and V B ′ are expressed by the following formulas (1) and (2). 
     
       
         
           
             
               
                 
                   
                     V 
                     A 
                     ′ 
                   
                   = 
                   
                     
                       
                         R 
                         B 
                       
                       
                         
                           R 
                           A 
                         
                         + 
                         
                           R 
                           B 
                         
                       
                     
                      
                     
                       V 
                       A 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     V 
                     B 
                     ′ 
                   
                   = 
                   
                     
                       
                         
                           R 
                           B 
                         
                         
                           
                             R 
                             A 
                           
                           + 
                           
                             R 
                             B 
                           
                         
                       
                        
                       
                         V 
                         A 
                       
                     
                     + 
                     
                       V 
                       B 
                     
                   
                 
               
               
                 
                   ( 
                   2 
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     where in consideration that V A  and V B  are substantially the same voltage value Vp, and R A  and R B  are substantially the same resistance value R, the voltage values V A =V B =Vp obtained prior to the contact change into V A =(½)Vp and V B =( 3/2)Vp after the contact. 
     Specifically, assuming that the inter-terminal voltage of the positive electrode terminal  17  and the negative electrode terminal  18  of the secondary battery  7  is 4 V, the battery can voltage of the secondary batteries whose battery cans  11  are not in contact with each other among the second batteries connected in series in a certain arm is 4 V. Meanwhile, the battery can voltage of one of the two secondary batteries whose battery cans  11  contact each other is 2 V, and the battery can voltage of the other secondary battery is 6 V. 
     Accordingly, in the BMU  15  that receives the measurement information, when one of the pieces of measurement information which are input from the CMU  14 - 1  corresponding to the first arm and correspond to the battery can voltage sensors  13 A to  13 D decreases to the corresponding value from Vp to (½)Vp and the other one increases simultaneously (substantially simultaneously) with the decrease to the corresponding value from Vp to ( 3/2)Vp, the battery cans  11  of the two secondary batteries  7  corresponding to the battery can voltage sensors within the first arm that output these values are determined to be in contact with each other. In the example of  FIG. 4 , a contact between the battery cans of the secondary batteries  7 A and  7 B within the first arm is specified. 
     Then, after the specification, the BMU  15  transmits expansion detection information as the related information to the higher-level control device  1 . Examples of the expansion detection information may include information indicating the presence or absence of expansion of a battery can (for example, active or “1” when an expansion is present, and inactive or “0” when an expansion is absent). 
     Having received expansion detection information (for example, when the expansion detection information indicates “1”) indicating that the battery can expands, the higher-level control device  1  controls display device  2  to cause the abnormality lamp described above to light, for example, and activates the acoustic device such as a buzzer incorporated in the display device  2  to issue an alarm, thereby allowing the user or operator to recognize the abnormality of the battery system  100  and to move the battery system  100  to a safe place, for example, to promote an inspection/repair. In this case, the display device  2  is allowed to display an abnormality by causing the abnormality lamp to light, for example, or activating the acoustic device. 
     As a matter of course, when a battery can expansion lamp is provided to the display device  2  separately from the abnormality lamp and the higher-level control device  1  receives the expansion detection information (for example, when the expansion detection information indicates “1”), the higher-level control device  1  may control the display device  2  to cause the battery can expansion lamp to light, for example, and may activate an acoustic device such as a buzzer incorporated in the display device  2  to issue an alarm. Further, the related information described above also includes information on the can voltage value of each secondary battery  7 . Accordingly, in the case where the higher-level control device  1  controls the display device  2 , it is also possible to allow the display device  2  to display which of the secondary batteries  7  is specified. 
     Note that in the determination, measurement information on voltage values which are input to the BMU  15  and measured by the cell voltage sensors  9  arranged respectively to correspond to the secondary batteries  7  may also be used. The example will be described in detail below. 
     The example illustrates the case where the battery cans  11 A and  11 B contact each other. The voltage values of the cell voltage sensors  9 A and  9 B prior to the contact are approximately Vp. Thus, at this time, each value obtained by subtracting a voltage measured by each battery can voltage sensor from a voltage measured by each cell voltage sensor is about 0. After these two battery cans contact each other, the values change into V A =(½)Vp and V B =( 3/2)Vp as described above. Accordingly, values obtained by subtracting voltages measured by each battery can voltage sensor from voltages measured by each cell voltage sensor are (½)Vp and (−½)Vp, respectively. That is, in the BMU  15 , differences between the pieces of measurement information of these two sensors arranged in the corresponding secondary battery are obtained using the measurement information which is input from the CMU  14 - 1  corresponding to the first arm and corresponds to the cell voltage sensors  9 A to  13 D and battery can voltage sensors  13 A to  13 D. When one of the differences decreases to the corresponding value from about 0 to (−½)Vp and when the other difference increases simultaneously (substantially simultaneously) with the decrease to the corresponding value from about 0 to (½)Vp, the battery cans  11  of the two secondary batteries  7  within the first arm corresponding to these values are determined to be in contact with each other. In the example of  FIG. 4 , it is specified that the battery cans of the second batteries  7 A and  7 B within the first arm contact each other. 
     As described above, the circuit diagram of  FIG. 4  illustrates the case where the battery can  11 A expands and contacts the battery can  11 B of the adjacent secondary battery  7 B. In the secondary battery on both sides of which the secondary batteries  7  are arranged, when the expansion of the battery can  11  is not uniform and only one of the two surfaces of the battery can  11  along the xz-plane first contacts the battery can  11  of the adjacent secondary battery  7 , the same circuit diagram may also be used. For example, in the case where the battery can  11 B of the secondary battery  7 B expands and, if the surface on the side of the secondary battery  7 A first contacts the battery can  11 A, rather than the surface on the side of the secondary battery  7 C of the two surfaces of the battery can  11 B along the xz-plane does, the same circuit as that illustrated in  FIG. 4  can be used. Also in this case, the operation of the BMS  6  including the BMU  15 , and the operation of the higher-level control device  1  are same as those described above. 
     Note that in the secondary battery on both sides of which the secondary batteries  7  are arranged within one arm, when the battery can  11  expands uniformly and two surfaces of the battery can  11  along the xz-plane contact substantially simultaneously with the battery cans  11  of the secondary batteries  7  on both sides, the circuit diagram illustrated in  FIG. 5  is obtained.  FIG. 5  is a diagram illustrating a circuit in which in the secondary batteries  7 A to  7 D arranged within the container  24  as illustrated in  FIG. 3 , the inner voltage of the battery can  11 B of the secondary battery  7 B increases, for example, so that the battery can  11 B expands and contacts the battery can  11 A of the secondary battery  7 A and the battery can  11 C of the secondary battery  7 C, which are adjacently arranged, simultaneously (substantially simultaneously). The pull-up resistor  12 A and the pull-up resistor  12 B are connected in series between the positive electrode terminal and the negative electrode terminal of the secondary battery  7 A; the pull-up resistor  12 B and the pull-up resistor  12 C are connected in series between the positive electrode terminal and the negative electrode terminal of the secondary battery  7 B; and the negative electrode terminal of the secondary battery  7 B is connected to the positive electrode terminal of the secondary battery  7 C. 
     Assuming herein that the voltage value measured by the battery can voltage sensor  13 C prior to the contact is V C ; the resistance value of the pull-up resistor  12 C is Rc; and the voltage value measured by the battery can voltage sensor  13 C after the contact is V C ′, V B ′ and V C ′ are expressed by the following formulas (3) and (4). V A ′ is the same as the formula (1) described above. 
     
       
         
           
             
               
                 
                   
                     V 
                     B 
                     ′ 
                   
                   = 
                   
                     
                       
                         R 
                         C 
                       
                       
                         
                           R 
                           B 
                         
                         + 
                         
                           R 
                           C 
                         
                       
                     
                      
                     
                       V 
                       B 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     V 
                     C 
                     ′ 
                   
                   = 
                   
                     
                       
                         
                           R 
                           C 
                         
                         
                           
                             R 
                             B 
                           
                           + 
                           
                             R 
                             C 
                           
                         
                       
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                         V 
                         B 
                       
                     
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                       V 
                       C 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     where in consideration that each of V A , V B , and V C  represents substantially the same voltage value Vp and each of R A , R B , and R C  represents substantially the resistance value R, the voltage values V A =V B =V C =Vp obtained prior to the contact simultaneously (substantially simultaneously) change into V A =(½) Vp, V B =(½) Vp, and V C =( 3/2) Vp after the contact. 
     Specifically, assuming that the inter-terminal voltage of the positive electrode terminal  17  and the negative electrode terminal  18  of the secondary battery  7  is 4 V, the battery can voltage of the secondary batteries whose battery cans  11  are not in contact with each other among the secondary batteries connected in series in a certain arm is 4 V. Meanwhile, the battery can voltages of three secondary batteries whose battery cans  11  contact each other are 2 V, 2 V, and 6 V, respectively. 
     Accordingly, in the BMU  15  that receives measurement information, when arbitrary two of the pieces of measurement information which are input from the CMU  14 - 1  corresponding to the first arm and correspond to the battery can voltage sensors  13 A to  13 D decrease to the corresponding value from Vp to (½)Vp and when any one of the information increases simultaneously (substantially simultaneously) with the decrease to the corresponding value from Vp to ( 3/2)Vp, it is determined that the battery cans  11  of the three secondary batteries  7  corresponding to the battery can voltage sensors within the first arm that output these values contact each other. In the example of  FIG. 4 , it is specified that the battery cans of the secondary batteries  7 A,  7 B, and  7 C within the first arm contact each other. 
     After the specification, the BMU  15  transmits expansion detection information as the related information to the higher-level control device  1 , as in the case where the battery cans  11  of the two secondary batteries  7  contact each other as described above. The subsequent operation in the higher-level control device  1  is similar to that described above. 
     In the control device of the battery system  100  described above, i.e., in the higher-level control device  1  and the BMS  6 , as described above, the secondary batteries  7  whose battery cans  11  contact each other can be specified based only on a change in the measurement information of the battery can voltage sensors  13 A to  13 H, or on a change in the difference between the two pieces of measurement information of the battery can voltage sensors  13 A to  13 H and the cell voltage sensors  9 A to  13 H. Further, the display device  2  is allowed to display which of the secondary batteries  7  within the battery system  100  are the secondary batteries  7  specified as being in contact with each other. Note that in the battery system  100 , the BMU  15  transmits the expansion detection information as the related information to the higher-level control device  1 . This expansion detection information is activated (or “1”) when a conductive path is generated between two battery cans due to short-circuiting or the like, for example. Accordingly, the expansion detection information is activated not only when each battery can expands, but also when the conductive path is generated due to adhesion of a conductor such as a metal scrap to the two battery cans, for example. In the case of adhesion of the conductor, for example, it is effective that the user or the like is notified of an abnormality, though it is not due to an expansion of a battery can, to thereby promote the inspection, repair, or the like. 
     However, when the measurement information on the battery can temperatures of the temperature sensors  8 A to  8 H is also taken into consideration, it is possible to specify the plurality of contacting secondary batteries  7 , and it is also possible to specify that the cause is an expansion involving heat generation and to specify the expanding secondary batteries  7 . 
     Specifically, in the case of an expansion involving heat generation of the battery can  11 , it can be specified that the secondary battery  7  corresponding to the temperature sensor that measures a high temperature that is greatly different from the temperature of another secondary battery  7  (for example, a high temperature with a temperature difference of 10° C. or more) among the contacting secondary batteries  7  surely expands. 
     Accordingly, the control device performs control such that the secondary battery  7 , which is specified as surely expanding, is displayed in a different manner (for example, the secondary battery  7  whose contact is specified are displayed with different display and color) upon display of the secondary battery  7  whose contact is specified, for example, thereby allowing the user or operator to recognize the secondary battery  7  that has surely expanded. This facilitates the inspection/repair. 
     Although the present invention has been described above with reference to the embodiments, the technical scope of the present invention is not limited to the scope of the embodiments. The embodiments described above can be changed or modified in various manners without departing from the gist of the invention. 
     For example, in the battery system of the embodiment described above, square battery cans are used in a plurality of secondary batteries  7 , but the battery cans may have any shape. For example, a cylindrical-shape battery can may also be used. The shape of each battery can is not limited to a can shape. As long as the battery can is a conductive battery container, the battery can may include a laminated battery container. 
     A stacked type has been described above as the stacked electrode body, but any type may be employed. That is, a wound type, a button type, or a coin type may be employed. 
     Furthermore, the battery can voltage sensor  13  measures the voltage of the battery can  11  with respect to the negative electrode terminal  16  of the corresponding secondary battery  7 , but may measure the voltage of the battery can  11  with respect to the positive electrode terminal  17  of the corresponding secondary battery  7 . 
     REFERENCE SIGNS LIST 
     
         
           1  HIGHER-LEVEL CONTROL DEVICE 
           2  DISPLAY DEVICE 
           3  POWER LOAD 
           4  BATTERY MODULE 
           5  ASSEMBLED BATTERY 
           6  BMS 
           7  SECONDARY BATTERY 
           8  TEMPERATURE SENSOR 
           9  CELL VOLTAGE SENSOR 
           10 - 1 ,  10 - 2  CURRENT SENSOR 
           11  BATTERY CAN 
           12  PULL-UP RESISTOR 
           13  BATTERY CAN VOLTAGE SENSOR 
           14 - 1 ,  14 - 2  CMU 
           15  BMU 
           16  INSULATOR 
           17  POSITIVE ELECTRODE TERMINAL 
           18  NEGATIVE ELECTRODE TERMINAL 
           19  SEPARATOR 
           20  POSITIVE ELECTRODE PLATE 
           21  NEGATIVE ELECTRODE PLATE 
           22  SAFETY VALVE 
           23  BUS BAR 
           24  CONTAINER