Patent Publication Number: US-2021194263-A1

Title: Energy storage apparatus, external discharge device, and discharge method of energy storage device

Description:
TECHNICAL FIELD 
     The technology disclosed in the present specification relates to an energy storage apparatus, an external discharge device, and a discharge method for an energy storage device. 
     BACKGROUND ART 
     In an energy storage apparatus including an energy storage device such as a lithium-ion battery, it is known that a circuit breaker is provided in a current path in which the energy storage device is provided, and if over discharge of the energy storage device is predicted, the circuit breaker is opened to prevent the energy storage device from overdischarging (see Patent Document 1, for example). A storage battery pack  100  disclosed in Patent Document 1 includes a main body unit  120 , a secondary battery  101  (corresponding to an energy storage device), and a switch  104  (corresponding to a circuit breaker) connected in series with the secondary battery  101 . The storage battery pack  100  opens the switch  104  when the voltage of the secondary battery  101  reaches a standard value (end-of-discharge voltage) at which discharge of the secondary battery  101  is stopped. 
     Generally, an energy storage apparatus is disassembled when it is discarded. When disassembling the energy storage apparatus, it is desirable to discharge remaining electric power of the energy storage device for safety of work. The storage battery pack  100  disclosed in Patent Document 1 includes a power consumption unit  105  housed in the main body unit  120 , and a reception unit  114  (for example, a mechanical switch or communication unit) that receives an instruction to operate a circuit including the power consumption unit  105  from the outside. When the reception unit  114  receives the instruction, the storage battery pack  100  operates the circuit including the power consumption unit  105  to discharge the secondary battery  101 . 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Republished WO 2016/006152 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The storage battery pack  100  in Patent Document 1 described above must include the power consumption unit  105  for each storage battery pack  100 , which complicates the configuration of the storage battery pack  100 . 
     The present specification discloses a technique capable of discharging remaining electric power of an energy storage device to the end with a simple configuration while protecting the energy storage device from overdischarging. 
     Means for Solving the Problems 
     An energy storage apparatus, including: an energy storage device; a circuit breaker connected in series with the energy storage device; a reception unit that receives a discharge instruction to discharge remaining electric power of the energy storage device; and a management unit, in which the management unit executes protection processing of opening, when a state of charge of the energy storage device drops below a predetermined threshold value, the circuit breaker to protect the energy storage device from overdischarging, and protection release processing of releasing protection of the energy storage device when the discharge instruction is received by the reception unit. 
     Advantages of the Invention 
     It is possible to discharge remaining electric power of the energy storage device to the end with a simple configuration while protecting the energy storage device from overdischarging. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an energy storage apparatus according to a first embodiment and a vehicle equipped with the energy storage apparatus. 
         FIG. 2  is an exploded perspective view of the energy storage apparatus. 
         FIG. 3A  is a plan view of an energy storage device shown in  FIG. 2 . 
         FIG. 3B  is a sectional view taken along a line A-A shown in  FIG. 3A . 
         FIG. 4  is a perspective view showing a state in which the energy storage device is housed in a main body of  FIG. 1 . 
         FIG. 5  is a perspective view showing a state in which a bus bar is attached to the energy storage device of  FIG. 4 . 
         FIG. 6  is a schematic diagram showing an electrical configuration of the energy storage apparatus and a configuration of an external discharge device. 
         FIG. 7  is a schematic diagram showing an electrical configuration of an energy storage apparatus according to a second embodiment and a configuration of an external discharge device. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Overview of the Present Embodiment 
     An energy storage apparatus, including: an energy storage device; a circuit breaker connected in series with the energy storage device; a reception unit that receives a discharge instruction to discharge remaining electric power of the energy storage device; and a management unit, in which the management unit executes protection processing of opening, when a state of charge of the energy storage device drops below a predetermined threshold value, the circuit breaker to protect the energy storage device from overdischarging, and protection release processing of releasing protection of the energy storage device when the discharge instruction is received by the reception unit. 
     Without provision of a discharge resistance inside the energy storage apparatus, the remaining electric power of the energy storage device is discharged using an external discharge resistance. Since the remaining electric power of the plurality of energy storage apparatuses can be discharged using one external discharge resistance, the configuration of the energy storage apparatus can be simplified as compared with the case where each energy storage apparatus is provided with a discharge resistance. 
     However, if the energy storage device is protected from overdischarging, the circuit breaker opens when the state of charge of the energy storage device drops below a predetermined threshold value, so that, if an external discharge resistance is used, the remaining electric power of the energy storage device cannot be discharged to the end. Therefore, unless the worker disassembles the energy storage apparatus and exposes the internal energy storage device, the remaining electric power cannot be discharged to the end, which may cause a short circuit. Alternatively, when the circuit breaker opens, the terminal voltage becomes 0 V, so the worker may disassemble the apparatus thinking that it has completely discharged, and there is a possibility of a short circuit. 
     According to the above energy storage apparatus, the protection of the energy storage device is released when the discharge instruction is received, so that the remaining electric power of the energy storage device can be discharged to the end also by using an external discharge resistance. Therefore, it is possible to discharge the remaining electric power of the energy storage device to the end with a simple configuration while protecting the energy storage device from overdischarging. 
     The management unit, in the protection release processing, if the circuit breaker is closed when receiving the discharge instruction, may set operation thereof so as not to execute the protection processing even if the state of charge of the energy storage device subsequently drops below the threshold value. 
     When an external discharge resistance is attached to the energy storage apparatus and the state of charge of the energy storage device has not yet dropped below a predetermined threshold value, the protection processing of the energy storage device has not been executed, and thus the circuit breaker is closed. If the circuit breaker is closed and an external discharge resistance is attached, the external discharge resistance discharges the remaining electric power of the energy storage device, but when the state of charge of the energy storage device subsequently drops below the threshold value, the protection processing is executed and the circuit breaker opens. Therefore, the remaining electric power of the energy storage device is not discharged to the end. 
     According to the above energy storage apparatus, if the circuit breaker is closed when receiving the discharge instruction, the apparatus sets the operation of the management unit so as not to execute the protection processing even if the state of charge of the energy storage device subsequently drops below a predetermined threshold value, so that it is possible to prevent the circuit breaker from opening to stop discharging during the discharge of the remaining electric power. Therefore, it is possible to discharge the remaining electric power of the energy storage device to the end also by using an external discharge resistance. 
     The management unit, in the protection release processing, if the protection processing has already been executed and the circuit breaker is open when the discharge instruction is received, may close the circuit breaker. 
     When the external discharge resistance is attached and the state of charge of the energy storage device has already dropped below a predetermined threshold value, the protection processing is executed and the circuit breaker is open. Therefore, in this case, even if an external discharge resistance is attached to the energy storage apparatus, the remaining electric power of the energy storage device is not discharged. 
     According to the above energy storage apparatus, if the circuit breaker is open when the discharge instruction is received, the circuit breaker is closed, so that the remaining electric power of the energy storage device can be discharged to the end also by using an external discharge resistance. 
     A housing in which the energy storage device is housed is provided, and the reception unit may receive the discharge instruction from outside the housing in a non-contact manner. 
     As a configuration for receiving the discharge instruction of the energy storage device, a configuration using a mechanical switch operated by a worker from the outside of the housing can be considered. However, the mechanical switch is not preferable from the viewpoint of waterproof/dustproofness of the energy storage apparatus. According to the above energy storage apparatus, since the discharge instruction is received in a non-contact manner, the waterproof/dustproofness of the energy storage apparatus can be improved as compared with the case of using a mechanical switch. Therefore, it is possible to reduce the risk that the discharge of the remaining electric power of the energy storage device is hindered by the intrusion of water or dust. 
     The reception unit may include a magnetic switch that is provided inside the housing and that is turned on when driven by a magnetic force from the outside of the housing, and output an electric signal to the management unit when the magnetic switch is turned on. 
     According to the above energy storage apparatus, a discharge instruction from the outside can be received in a non-contact manner. This can improve the waterproof/dustproofness of the energy storage apparatus, and reduce the risk that the discharge of the remaining electric power of the energy storage device is hindered by the intrusion of water or dust. 
     The reception unit is provided in the housing, and may include a transmission part that transmits light outside the housing to the inside of the housing, a detachable shield member that covers the transmission part from the outside of the housing, and a photoelectric switch which is provided inside the housing and turned on by receiving the light transmitted through the transmission part, and output an electric signal to the management unit when the photoelectric switch is turned on. 
     According to the above energy storage apparatus, a discharge instruction from the outside can be received in a non-contact manner. This can improve the waterproof/dustproofness of the energy storage apparatus, and reduce the risk that the discharge of the remaining electric power of the energy storage device is hindered by the intrusion of water or dust. According to the above energy storage apparatus, it is possible to visually judge whether or not the remaining electric power is discharged by the presence or absence of the shielding member, so that the safety during work is improved. 
     The energy storage device may be a lithium-ion battery. 
     For example, if the energy storage device is a lead-acid battery, it can be disassembled by disconnecting the lead-acid battery, but if it is a lithium-ion battery, disassembling in this way is dangerous if there is electric power remaining in the energy storage device. According to the above energy storage apparatus, the remaining electric power of the lithium-ion battery can be discharged to the end, so the safety when disassembling the lithium-ion battery is improved. 
     The energy storage apparatus is mounted on a vehicle, and the management unit may execute the protection release processing only when the energy storage apparatus is removed from the vehicle. 
     According to the above energy storage apparatus, when the energy storage apparatus is mounted on the vehicle, the protection release processing is not executed even if the discharge instruction is received. Therefore, it is possible to prevent the case in which the discharge instruction is issued in a state where the energy storage apparatus is mounted on the vehicle, and the remaining electric power of the energy storage device is discharged to the end. As a result, it is possible to reduce the possibility that the energy storage device cannot be used due to overdischarge. 
     The external discharge device includes a first contact connected to one of a positive electrode external terminal and a negative electrode external terminal of the energy storage apparatus, a second contact connected to the other, a discharge resistance provided in a current path connecting the first contact and the second contact, and an instruction unit for instructing the energy storage apparatus to discharge. 
     According to the above external discharge device, since the external discharge device instructs the energy storage apparatus to discharge, it is not necessary to perform a work for instructing discharge separately from a work of attaching the external discharge device to the energy storage apparatus during work. Therefore, the convenience during work is improved. 
     The technology disclosed in this specification can be realized in various modes such as an apparatus, a method, a computer program for realizing the functions of the apparatus or method, and a recording medium recording the computer program. 
     First Embodiment 
     An embodiment will be described with reference to  FIGS. 1 to 6 . 
     (1) Configuration of Energy Storage Apparatus 
     An energy storage apparatus  1  according to the first embodiment will be described with reference to  FIG. 1 . The energy storage apparatus  1  is mounted on a vehicle  2 , and supplies electric power to a starter for starting an engine (an example of an internal combustion engine) of the vehicle  2  and auxiliary machineries (ECU, headlight, air conditioner, audio, etc.) mounted on the vehicle  2 . 
     As shown in  FIG. 2 , the energy storage apparatus  1  includes an outer case  10  (an example of a housing), and a plurality of energy storage devices  12  housed inside the outer case  10 . The outer case  10  is composed of a main body  13  and a lid body  14  made of a synthetic resin material. The main body  13  has a bottomed tubular shape, and is composed of a bottom surface portion  15  having a rectangular shape in plan view and four side surface portions  16  rising from four sides thereof to form a tubular shape. An upper opening  17  is formed in an upper end portion by the four side surface portions  16 . 
     The lid body  14  has a rectangular shape in plan view, and a frame body  18  extends downward from four sides thereof. The lid body  14  closes the upper opening  17  of the main body  13 . On the upper surface of the lid body  14 , a protruding portion  19  having a substantially T-shape in plan view is formed. A positive electrode external terminal  20  is fixed to one corner portion of the two locations where the protruding portion  19  is not formed on the upper surface of the lid body  14 , and a negative electrode external terminal  21  is fixed to the other corner portion. 
     The energy storage device  12  is a repeatedly chargeable secondary battery, and is specifically, for example, a lithium-ion battery. As shown in  FIGS. 3( a ) and 3( b ) , the energy storage device  12  has an electrode assembly  23  housed in a rectangular parallelepiped case  22  together with a non-aqueous electrolyte. The case  22  is composed of a case body  24  and a cover  25  that closes an opening above the case body  24 . 
     The electrode assembly  23 , although not shown in detail, has a separator made of a porous resin film arranged between a negative electrode element formed by applying an active material to a substrate made of copper foil and a positive electrode element formed by applying an active material to a substrate made of aluminum foil. These are all belt-shaped, and are wound in a flat shape so that they can be housed in the case body  24  in a state where the negative electrode element and the positive electrode element are displaced from each other on the opposite sides in the width direction with respect to the separator. 
     A positive electrode terminal  27  is connected to the positive electrode element via a positive electrode current collector  26 . A negative electrode terminal  29  is connected to the negative electrode element via a negative electrode current collector  28 . Each of the positive electrode current collector  26  and the negative electrode current collector  28  has a plate-shaped pedestal portion  30  and a leg portion  31  extending from the pedestal portion  30 . Through holes are formed in the pedestal portion  30 . The leg portion  31  is connected to the positive electrode element or the negative electrode element. Each of the positive electrode terminal  27  and the negative electrode terminal  29  has a terminal main body portion  32  and a shaft portion  33  protruding downward from the center portion of the lower surface thereof. The terminal main body portion  32  and the shaft portion  33  of the positive electrode terminal  27  are integrally formed of aluminum (single material). In the negative electrode terminal  29 , the terminal main body portion  32  is made of aluminum, the shaft portion  33  is made of copper, and these are assembled. The terminal main body portions  32  of the positive electrode terminal  27  and the negative electrode terminal  29  are arranged at both ends of the cover  25  via gaskets  34  made of an insulating material, and are exposed to the outside from the gaskets  34 . 
     As shown in  FIG. 4 , a plurality of (for example, twelve) energy storage devices  12  are housed in the main body  13  in a state of being arranged in the width direction. Here, the plurality of energy storage devices  12  are arranged from one end side to the other end side of the main body  13  (direction of arrow Y1 to Y2) with three energy storage devices  12  as one set so that in the same set, the terminal polarities of adjacent energy storage devices  12  are the same, and between adjacent sets, the terminal polarities of adjacent energy storage devices  12  are opposite to each other. In the three energy storage devices  12  (first set) located closest to the arrow Y1 side, the arrow X1 side is the negative electrode and the arrow X2 side is the positive electrode. In the three energy storage devices  12  (second set) adjacent to the first set, the arrow X1 side is the positive electrode and the arrow X2 side is the negative electrode. Furthermore, the third set adjacent to the second set has the same arrangement as the first set, and the fourth set adjacent to the third set has the same arrangement as the second set. 
     As shown in  FIG. 5 , terminal bus bars (connecting members)  36  to  40  as conductive members are connected to the positive electrode terminal  27  and the negative electrode terminal  29  by welding. On the arrow X2 side of the first set, the positive electrode terminals  27  are connected by the first bus bar  36 . Between the first set and the second set, the negative electrode terminals  29  of the first set and the positive electrode terminals  27  of the second set are connected by the second bus bar  37  on the arrow X1 side. Between the second set and the third set, the negative electrode terminals  29  of the second set and the positive electrode terminals  27  of the third set are connected by the third bus bar  38  on the arrow X2 side. Between the third set and the fourth set, the negative electrode terminals  29  of the third set and the positive electrode terminals  27  of the fourth set are connected by the fourth bus bar  39  on the arrow X1 side. On the arrow X2 side of the fourth set, the negative electrode terminals  29  are connected by the fifth bus bar  40 . 
     Referring also to  FIG. 2 , the first bus bar  36  located at one end of the flow of electricity is connected to the positive electrode external terminal  20  via a first electronic device  42 A (for example, fuse), a second electronic device  42 B (for example, relay), a bus bar  43  and a bus bar terminal (not shown). The fifth bus bar  40  located at the other end of the flow of electricity is connected to the negative electrode external terminal  21  via bus bars  44 A and  44 B and a negative electrode bus bar terminal (not shown). As a result, each energy storage device  12  can be charged and discharged via the positive electrode external terminal  20  and the negative electrode external terminal  21 . The electronic devices  42 A and  42 B and the electric component connecting bus bars  43 ,  43 A, and  44 B are attached to a circuit board unit  41  arranged above the plurality of energy storage devices  12  that are stacked. The bus bar terminal is arranged on the lid body  14 . 
     (2) Electrical Configuration of Energy Storage Apparatus 
     The electrical configuration of the energy storage apparatus  1  will be described with reference to  FIG. 6 . As shown in  FIG. 6 , the energy storage apparatus  1  includes a plurality of energy storage devices  12  described above and a battery management system  50  (BMS) that manages these energy storage devices  12 . 
     The BMS  50  is mounted on the circuit board unit  41  shown in  FIG. 2 . The BMS  50  includes a current sensor  51 , a relay  53  (an example of a circuit breaker), a reception unit  54 , and a management unit  55 . 
     The current sensor  51  is connected in series with the energy storage device  12 , and measures the current value I[A] of the current flowing through the energy storage device  12  and outputs it to the management unit  55 . The relay  53  is connected in series with the energy storage device  12 . The relay  53  is for protecting the energy storage device  12  from overcharging and overdischarging, and is opened and closed by the management unit  55 . 
     The reception unit  54  is for receiving a discharge instruction from the outside of the outer case  10 . The reception unit  54  includes a current path  57  that branches from a current path  56  to which the energy storage device  12  is connected and is connected to the management unit  55 , and a normally open relay  58  (an example of a magnetic switch) provided in the current path  57 . 
     When a magnet is brought close to the outer case  10  from outside the outer case  10 , the relay  58  is closed (that is, the relay  58  is turned on) by the magnetic force (an example of a discharge instruction) of the magnet. The end of the current path  57  on the side of the management unit  55  is connected to a predetermined input port of the management unit  55 , and when the relay  58  is turned on, a voltage (an example of an electric signal) is applied to the input port of the management unit  55 . 
     The management unit  55  operates with electric power supplied from the energy storage device  12 , and includes a CPU, ROM, RAM, a communication unit, and the like. The CPU manages each unit of the energy storage apparatus  1  by executing various programs stored in the ROM. 
     The management unit  55  may include an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or the like instead of the CPU or in addition to the CPU. 
     (3) Configuration of External Discharge Device 
     The configuration of an external discharge device  3  will be described with reference to  FIG. 6 . The external discharge device  3  discharges the remaining electric power of the energy storage device  12  when the energy storage apparatus  1  is disassembled. The external discharge device  3  includes a first contact  60 , a second contact  61 , a current path  62 , a discharge resistance  63 , and a magnet  64  (an example of an instruction unit). The first contact  60  is connected to one of the positive electrode external terminal  20  and negative electrode external terminal  21  of the energy storage apparatus  1 , and the second contact  61  is connected to the other one. The current path  62  connects the first contact  60  and the second contact  61 . The discharge resistance  63  is provided in the current path  62 . The magnet  64  is for closing the relay  58  of the energy storage device  12 , and is arranged at a position near the relay  58  when the external discharge device  3  is attached to the energy storage apparatus  1 . 
     (4) Processing Executed by Management Unit 
     As the processing executed by the management unit  55 , the protection processing for protecting the energy storage device  12  from overdischarging and the protection release processing for releasing the protection of the energy storage device  12  will be described. 
     (4-1) Protection Processing 
     The management unit  55  estimates the state of charge (SOC) of the energy storage device  12  at predetermined time intervals, and opens the relay  53  when the SOC drops below a predetermined threshold value (an example of protection processing). As a result, the current path  56  is cut off, and the energy storage device  12  is protected from overdischarging. 
     A current integration method, for example, is known as a method for estimating SOC. The current integration method is a method in which the charge/discharge current of the energy storage device  12  is constantly measured by the current sensor  51  to measure the amount of electric power flowing in and out of the energy storage device  12 , and this is adjusted from the initial capacity to estimate the SOC. 
     The SOC and the open circuit voltage (OCV) of the energy storage device  12  have a relatively accurate correlation. Therefore, instead of directly determining from the SOC whether the SOC has dropped below a predetermined threshold value, it may be determined that the SOC has dropped below a predetermined threshold value when the OCV drops below a predetermined reference value. The OCV is not necessarily a voltage when the circuit is open, but may be a voltage when the current flowing through the energy storage device  12  is below a predetermined reference value. 
     (4-2) Protection Release Processing 
     When disassembling the energy storage apparatus  1 , the worker attaches the external discharge device  3  to the energy storage apparatus  1  before disassembling the energy storage apparatus  1  in order to discharge the remaining electric power of the energy storage device  12 . When the external discharge device  3  is attached, the first contact  60  of the external discharge device  3  contacts the positive electrode external terminal  20  (or the negative electrode external terminal  21 ), and the second contact  61  contacts the negative electrode external terminal  21  (or the positive electrode external terminal  20 ). 
     When the external discharge device  3  is attached and the SOC of the energy storage device  12  has not yet dropped below the predetermined threshold value described above, the protection processing for the energy storage device  12  has not been executed, so the relay  53  is closed. When the relay  53  is closed and the external discharge device  3  is attached, the external discharge device  3  discharges the remaining electric power of the energy storage device  12 . When the external discharge device  3  is attached and the remaining electric power of the energy storage device  12  is discharged, the SOC of the energy storage device  12  subsequently drops below a threshold value, and thus, the protection processing is executed during discharge of the remaining electric power, and the relay  53  opens. Therefore, the remaining electric power of the energy storage device  12  is not discharged to the end as it is. 
     On the other hand, when the external discharge device  3  is attached and the SOC of the energy storage device  12  has already dropped below a predetermined threshold value, the protection processing has already been executed and the relay  53  is open, so even if the external discharge device  3  is attached to the energy storage apparatus  1 , the remaining electric power of the energy storage device  12  is not discharged. 
     Therefore, upon receiving the discharge instruction, the management unit  55  releases the protection of the energy storage device  12 , so that the remaining electric power of the energy storage device  12  is discharged to the end. Specifically, when the external discharge device  3  is attached to the energy storage apparatus  1 , the relay  58  is turned on by the magnetic force of the magnet  64  (the reception unit  54  receives the discharge instruction). When the relay  58  is turned on, a voltage is applied to the input port of the management unit  55 . When the voltage is applied to the input port, the management unit  55  determines whether or not the relay  53  is closed. 
     When the relay  53  is closed, the management unit  55  sets its operation so as not to execute the protection processing even if the SOC subsequently drops below a predetermined threshold value. Therefore, even if the SOC of the energy storage device  12  drops below the threshold value after the external discharge device  3  is attached, the relay  53  is not opened, and the remaining electric power of the energy storage device  12  is discharged to the end. 
     On the other hand, when the relay  53  is open, the management unit  55  closes the relay  53 . Therefore, even if the protection processing has been already executed and the relay  53  is open, the remaining electric power of the energy storage device  12  is discharged to the end. 
     (6) Effects of the Embodiment 
     According to the energy storage apparatus  1 , without provision of the discharge resistance inside the energy storage apparatus  1 , the remaining electric power of the energy storage device  12  is discharged by using the external discharge resistance  63 . Thus, the remaining electric power of the plurality of energy storage apparatuses  1  can be discharged by using one discharge resistance  63 . Therefore, the configuration of the energy storage apparatus  1  can be simplified as compared with the case where the discharge resistance  63  is provided for each energy storage apparatus  1 . Then, according to the energy storage apparatus  1 , when the discharge instruction is received, the protection of the energy storage device  12  is released, so that the remaining electric power of the energy storage device  12  can be discharged to the end also by using the external discharge resistance  63 . Therefore, according to the energy storage apparatus  1 , it is possible to discharge the remaining electric power of the energy storage device  12  to the end with a simple configuration while protecting the energy storage device  12  from overdischarging. 
     According to the energy storage apparatus  1 , if the relay  53  is closed when the discharge instruction is received, the apparatus sets its operation so as not to execute the protection processing even if the SOC of the energy storage device  12  subsequently drops below a predetermined threshold value. Therefore, it is possible to prevent the case in which the relay  53  opens during discharge of the remaining electric power to stop the discharge. Therefore, the remaining electric power of the energy storage device  12  can be discharged to the end also by using the external discharge resistance  63 . 
     According to the energy storage apparatus  1 , when the discharge instruction is received, the relay  53  is closed when the protection processing has been already executed and the relay  53  is open, so that the remaining electric power of the energy storage device  12  can be discharged to the end also by using the external discharge resistance  63 . 
     According to the energy storage apparatus  1 , since the discharge instruction from the outside of the outer case  10  is received in a non-contact manner, the waterproof/dustproofness of the energy storage apparatus  1  can be improved as compared with the case of using a mechanical switch. Accordingly, it is possible to reduce the risk that the discharge of the remaining electric power of the energy storage device  12  is hindered by the intrusion of water or dust. 
     According to the energy storage apparatus  1 , since it includes the relay  58  that is closed when driven by the magnetic force from the outside of the outer case  10 , the discharge instruction from the outside of the outer case  10  can be received in a non-contact manner. As a result, the waterproof/dustproofness of the energy storage apparatus  1  can be improved, and the risk that the discharge of the remaining electric power of the energy storage device  12  is hindered by the intrusion of water or dust can be reduced. 
     According to the energy storage apparatus  1 , the remaining electric power of the lithium-ion battery can be discharged to the end, and therefore the safety when disassembling the lithium-ion battery is improved. 
     According to the external discharge device  3 , since the external discharge device  3  instructs the energy storage apparatus  1  to discharge, it is not necessary to perform the work of instructing discharge separately from the work of attaching the external discharge device  3  to the energy storage apparatus  1  during work. Therefore, the convenience during work is improved. 
     Second Embodiment 
     The second embodiment will be described with reference to  FIG. 7 . An energy storage apparatus  201  according to the second embodiment is different from the energy storage apparatus  1  according to the first embodiment in the configuration of a reception unit  254  and the configuration of an external discharge device  203 . 
     (2-1) Electrical Configuration of Energy Storage Apparatus 
     The electrical configuration of the energy storage apparatus  201  will be described with reference to  FIG. 7 . The outer case  10  of the energy storage apparatus  201  is formed with an opening for allowing light to enter the inside of the outer case  10 . The reception unit  254  receives the discharge instruction by receiving light incident from the opening, not by the magnetic force from the outside. 
     Specifically, the reception unit  254  includes a transmission part  210 , a shielding member  211 , a current path  214 , and a phototransistor  215  (an example of a photoelectric switch). 
     The transmission part  210  closes the above-mentioned opening and transmits light to the inside of the outer case  10 , and is specifically transparent glass or plastic. The shielding member  211  is, for example, a seal (hereinafter referred to as a seal  211 ) that does not transmit light, and is detachably attached to the transmission part  210  from the outside of the outer case  10 . 
     The current path  214  is branched from the current path  56  to which the energy storage device  12  is connected and is connected to the management unit  55 . The phototransistor  215  is provided in the current path  214 . The phototransistor  215  closes when it receives light. When the phototransistor  215  is closed, a voltage (an example of an electric signal) is applied to the input port of the management unit  55 . 
     (2-2) Configuration of External Discharge Device 
     The configuration of the external discharge device  203  will be described with reference to  FIG. 7 . The external discharge device  203  is substantially the same as the external discharge device  3  according to the first embodiment except that the magnet  64  is not provided. 
     (2-3) Protection Release Processing 
     When disassembling the energy storage apparatus  201 , the worker peels off the seal  211  before (or after) attaching the external discharge device  203  to the energy storage apparatus  201 . When the seal  211  is peeled off, external light is received by the phototransistor  215 , and a voltage is applied to the input port of the management unit  55 . When the voltage is applied to the input port, the management unit  55  executes the protection release processing described in the first embodiment. 
     (2-4) Effect of Embodiment 
     According to the energy storage apparatus  201 , since it includes the phototransistor  215  that receives light from the outside of the outer case  10 , a discharge instruction from the outside of the outer case  10  can be received in a non-contact manner. Accordingly, the waterproof/dustproofness of the energy storage apparatus  201  can be improved, and the risk that the discharge of the remaining electric power of the energy storage device  12  is hindered by the intrusion of water or dust can be reduced. 
     According to the energy storage apparatus  201 , whether or not the remaining electric power is discharged can be visually determined by the presence or absence of the seal  211 , so that the safety during work is improved. 
     Other Embodiments 
     The technology disclosed in the present specification is not limited to the embodiments described by the above description and the drawings, and, for example, the following embodiments are also included in the technical scope disclosed in the present specification. 
     (1) In the first embodiment, the case where the external discharge device  3  is provided with the magnet  64  has been described as an example, but the external discharge device  3  may not include the magnet  64  as in the second embodiment. In that case, the worker may manually bring the magnet  64  close to the outer case  10  to turn on the relay  58 . In that case, the worker may leave the magnet  64  brought close to the outer case  10  as it is. By doing so, it is possible to visually judge whether or not the remaining electric power is discharged by the presence or absence of the magnet  64 , so that the safety during work is improved. 
     (2) In the above-described first embodiment, the case where the protection release processing is executed when the external discharge device  3  is attached regardless of whether or not the energy storage apparatus  1  is mounted on the vehicle  2  has been described as an example. On the other hand, the management unit  55  may execute the protection release processing only when the energy storage apparatus  1  is removed from the vehicle  2 . With this configuration, when the energy storage apparatus  1  is mounted on the vehicle  2 , the protection release processing is not executed even if the discharge instruction is received, so that it is possible to prevent the case in which the discharge instruction is issued in a state where the energy storage apparatus  1  is mounted on the vehicle  2 , and the remaining electric power of the energy storage device  12  is discharged to the end. As a result, it is possible to reduce the possibility that the energy storage device  12  cannot be used due to overdischarge. 
     Whether or not the energy storage apparatus  1  is mounted on the vehicle  2  can be determined, for example, from a signal transmitted from the vehicle  2  to the energy storage apparatus  1 . Specifically, in general, the energy storage apparatus  1  receives a signal that represents the state of an engine from the vehicle  2  at regular time intervals. Therefore, the management unit  55  may determine that it is mounted on the vehicle  2  when the signal is received from the vehicle  2  at regular time intervals, and may determine that it is not mounted on the vehicle  2  when the signal is not received even after the constant time elapses. 
     (3) Although the relay  53  is described as an example of the circuit breaker in the above embodiment, the circuit breaker is not limited to this. For example, the circuit breaker may be an FET (Field effect transistor). 
     (4) In the above embodiment, the case where the discharge instruction is received in a non-contact manner by the magnetic force or light from the outside has been described as an example, but the discharge instruction may be received by the mechanical switch, or the discharge instruction may be received via the communication unit included in the management unit  55 . 
     (5) In the above embodiment, as the configuration for receiving the discharge instruction in a non-contact manner, the case where it is received by magnetic force or light has been described as an example. However, the configuration in which the discharge instruction is received in a non-contact manner is not limited to this. For example, the discharge instruction may be received by wireless communication. 
     (6) In the above second embodiment, a seal is described as an example of the shielding member  211 , but the shielding member  211  is not limited to a seal as long as it is detachable and covers the transmission part  210  from the outside of the outer case  10 . For example, a plate material made of plastic and having a light shielding property may be detachably fixed with a screw or the like. A light-shielding cloth material may be attached with an adhesive or the like. 
     (7) In the above first embodiment, the case where the external discharge device  3  includes the magnet  64  as the instruction unit has been described as an example, but the instruction unit is not limited to the magnet  64 . For example, when the energy storage apparatus  1  receives a discharge instruction by wireless communication, the instruction unit may be a transmission unit that transmits a discharge instruction to the energy storage apparatus  1 . When the energy storage apparatus  1  receives a discharge instruction with a push button switch (mechanical switch), it may be a protruding portion that is protruding from the external discharge device so that the push button switch is pressed when the external discharge device is attached to the energy storage apparatus. 
     (8) In the above first embodiment, the case where the energy storage apparatus  1  is mounted on the vehicle  2  has been described as an example, but the energy storage apparatus  1  is not limited to being mounted on the vehicle  2 . For example, the energy storage apparatus  1  may be used in an energy storage system installed in a business office or the like and storing electric power. It may be mounted on an aircraft or a ship and used for driving. It may be an uninterruptible power supply (UPS) that supplies electric power to electrical equipment when the system loses power. 
     (9) In the above embodiment, the case where the management unit  55 , in the protection release processing, executes both of a process of setting its operation so as not to execute the protection processing if the relay  53  is closed when the discharge instruction is received, even if the SOC subsequently drops below the threshold value, and a process of closing the relay  53  when the discharge instruction is received and the protection processing has already been executed and the relay  53  is open, has been described as an example. On the other hand, only one of these processes may be executed. 
     (10) In the above embodiment, the lithium-ion battery is described as an example of the energy storage device  12 , but the energy storage device  12  may be, for example, a lead storage battery or a capacitor that causes an electrochemical reaction. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
         
           
               1 : energy storage apparatus 
               2 : vehicle 
               3 : external discharge device 
               10 : outer case (an example of housing) 
               12 : energy storage device 
               20 : positive electrode external terminal 
               21 : negative electrode external terminal 
               53 : relay (an example of circuit breaker) 
               54 : reception unit 
               55 : management unit 
               58 : relay (an example of magnetic switch) 
               60 : first contact 
               61 : second contact 
               62 : current path 
               63 : discharge resistance 
               64 : magnet (an example of instruction unit) 
               201 : energy storage apparatus 
               203 : external discharge device 
               210 : transmission part 
               211 : seal (an example of shielding member) 
               215 : phototransistor (an example of photoelectric switch) 
               254 : reception unit