JP2018137165A - Battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery system capable of carrying out self-diagnosis for detecting loose connection between terminals in a secondary battery having a connection structure between terminals by caulking process.SOLUTION: When the battery temperature is measured (S100), a controller detects a voltage difference between terminals electrically connected to each other by means of caulking to calculate the contact resistance value between the terminals (S110). The controller sets a reference resistance value Rr from the measured battery temperature. When the calculated contact resistance value Ra is higher than the reference resistance value Rr, the controller detects loosen caulking, and outputs a diagnostic code (S150) and determines that a vehicle cannot travel by using the electric power of a secondary battery (S160). The higher battery temperature, the lower value is set to the reference resistance value Rr.SELECTED DRAWING: Figure 5

Description

  The present disclosure relates to a battery system, and more particularly to a diagnostic technique for a secondary battery having a connection structure by caulking.

  In the secondary battery, a structure for electrically connecting an external terminal for electrical contact with an element outside the battery and a current collecting terminal corresponding to the positive electrode and the negative electrode of the battery is required. Japanese Patent Laying-Open No. 2005-072746 (Patent Document 1) describes a manufacturing method that secures electrical connection between external monitoring and current collecting terminals by caulking with metal plastic deformation.

  According to Patent Document 1, since the variation in the shape of the external terminal is suppressed by electrically connecting the terminals without using welding, the effect of suppressing the variation in the contact resistance of the probe with respect to the external terminal is obtained. It is done.

JP 2005-072746 A

  However, the connection by caulking may be loosened due to expansion and contraction of the terminal due to a temperature change accompanying charging and discharging. Furthermore, when the secondary battery is mounted on a vehicle or the like, there is a concern that the connection between the terminals may be loosened due to vibration during traveling. If the connection between the terminals is loosened, the electrical resistance (contact resistance) between the terminals increases, so that heat generation increases. On the other hand, since it is difficult to directly detect the loosening of the caulking process, it becomes a problem how to detect the occurrence of the loosening of the caulking process associated with the use of the secondary battery.

  The present disclosure has been made to solve such a problem, and the purpose thereof is to perform self-diagnosis to detect loose connection between terminals in a secondary battery having a connection structure between terminals by caulking. Is to do.

  In one aspect of the present disclosure, a battery system includes a secondary battery, a voltage detector, a current detector, a temperature detector, and a control device. The secondary battery is configured such that a charge / discharge current passes between the first and second terminals connected by caulking. A potential difference between the voltage detector and the first and second terminals is detected. The current detector detects a charge / discharge current of the secondary battery. The temperature detector detects the temperature of the secondary battery. The control device makes a self-diagnosis based on the detected values of the voltage detector, the current detector, and the current detector to determine whether the contact area is reduced due to caulking between the first and second terminals. The control device is configured such that the contact resistance value between the first and second terminals calculated from the detection values by the voltage detector and the current detector is higher than the reference resistance value set based on the temperature detection value by the temperature detector. When it rises, it detects that loosening has occurred in the caulking process. The reference resistance value is set to a lower value as the temperature detected by the temperature detector is higher in accordance with a predetermined correspondence relationship indicating a change in the contact resistance value with respect to a temperature change of the secondary battery in the same contact area.

  According to the present disclosure, it is possible to perform self-diagnosis that detects loose connection between terminals in a secondary battery having a connection structure between terminals by caulking.

It is a schematic block diagram of the electric vehicle shown as an application example of the battery system according to the present embodiment. FIG. 2 is a schematic cross-sectional view for explaining the structure of the battery cell shown in FIG. 1. It is III-III sectional drawing of FIG. It is sectional drawing before the crimping process of the site | part shown by FIG. It is a flowchart for demonstrating the control process of the self-diagnosis by the battery system according to this Embodiment. It is a conceptual graph for demonstrating the setting of the reference | standard resistance value according to battery temperature.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

  FIG. 1 is a schematic configuration diagram of an electric vehicle shown as an application example of the battery system according to the present embodiment.

  Referring to FIG. 1, electrically powered vehicle 100 travels using a vehicle-mounted secondary battery as a vehicle drive power source. For example, the electric vehicle 100 is configured by a hybrid vehicle or an electric vehicle. A hybrid vehicle is a vehicle that includes a fuel cell, an engine, and the like in addition to a battery as a power source for running the vehicle. An electric vehicle is a vehicle that includes only a battery as a power source for the vehicle.

  Electric vehicle 100 includes a secondary battery 10, a boost converter 22, an inverter 23, a motor generator 25, a transmission gear 26, drive wheels 27, a charger 28, and a controller 30.

  The secondary battery 10 is constituted by an assembled battery having a plurality of battery cells 11 electrically connected in series. Each battery cell 11 can be composed of a lithium ion secondary battery, a nickel hydride secondary battery, or the like.

  Secondary battery 10 is connected to boost converter 22 via system main relays 21 a and 21 b, and boost converter 22 boosts the output voltage of secondary battery 10. Boost converter 22 is connected to inverter 23, and inverter 23 converts DC power from boost converter 22 into AC power.

  The motor generator (three-phase AC motor) 25 receives the AC power from the inverter 23 to generate kinetic energy for running the vehicle. The kinetic energy generated by the motor generator 25 is transmitted to the wheels. On the other hand, when the vehicle is decelerated or the vehicle is stopped, the motor generator 25 converts kinetic energy generated during braking of the vehicle into electrical energy. The AC power generated by the motor generator 25 is converted into DC power by the inverter 23. Boost converter 22 steps down the output voltage of inverter 23 and then supplies it to secondary battery 10. Thereby, regenerative electric power can be stored in the secondary battery 10. As described above, the motor generator 25 is configured to generate a driving force or a braking force of the vehicle with transmission / reception of electric power to / from the secondary battery 10 (that is, charging / discharging of the secondary battery 10). The The boost converter 22 can be omitted. Further, when a DC motor is used as the motor generator 25, the inverter 23 can be omitted.

  In the case where electric vehicle 100 is configured by a hybrid vehicle in which an engine (not shown) is further mounted as a power source, in addition to the output of motor generator 25, the output of the engine is driven for vehicle travel. Can be used for power. Alternatively, it is possible to further mount a motor generator (not shown) that generates electric power based on the engine output and generate charging power for the secondary battery 10 based on the engine output.

  The secondary battery 10 is provided with a current sensor 15, a temperature sensor 16, and a voltage sensor 17. The current sensor 15 detects a current (charge / discharge current I) flowing through the secondary battery 10 and outputs a detection value to the controller 30.

  The temperature sensor 16 detects the temperature of the secondary battery 10 and outputs the detected value to the controller 30. The number of temperature sensors 16 can be set as appropriate. When using the plurality of temperature sensors 16, the average value of the temperatures detected by the plurality of temperature sensors 16 is used as the temperature of the secondary battery 10, or the temperature detected by the specific temperature sensor 16 is used as the temperature of the secondary battery 10. Or can be used as Hereinafter, the temperature of the secondary battery 10 detected by the output of the temperature sensor 16 is referred to as a battery temperature Tb.

  The voltage sensor 17 detects the output voltage V across the secondary battery 10 and outputs the detected value to the controller 30. In this embodiment, the voltage of the secondary battery 10 is detected, but the present invention is not limited to this. For example, the voltage of the battery cell 11 constituting the secondary battery 10 can be detected. Moreover, it is also possible to divide the plurality of battery cells 11 constituting the secondary battery 10 into a plurality of blocks and detect the voltage of each block.

  The controller 30 is configured by, for example, an electronic control unit (ECU), and controls the operations of the system main relays 21a and 21b, the boost converter 22 and the inverter 23. The controller 30 includes a memory 31 that stores various types of information and a CPU (Central Processing Unit) 32. The memory 31 also stores a program for operating the controller 30. Each control function by the controller 30 in the present embodiment can be executed by the CPU 32 by software processing for executing a program stored in the memory 31 and / or hardware processing by a dedicated electronic circuit. In this embodiment, the controller 30 includes the memory 31, but the memory 31 can be provided outside the controller 30.

  When the ignition switch of the vehicle is switched from OFF to ON, the controller 30 switches the system main relays 21a and 21b from OFF to ON, or operates the boost converter 22 and the inverter 23. In addition, when the ignition switch is switched from on to off, the controller 30 switches the system main relays 21a and 21b from on to off, or stops the operation of the boost converter 22 and the inverter 23.

  The charger 28 supplies power from the external power supply 40 to the secondary battery 10. The charger 28 is connected to the secondary battery 10 through charging relays 29a and 29b. When the charging relays 29a and 29b are on, the power from the external power source can be supplied to the secondary battery 10.

  The external power source 40 is a power source provided outside the vehicle. As the external power source 40, for example, a commercial AC power source can be applied. The external power supply 40 and the charger 28 can be connected by a charging cable 45, for example. That is, when the charging cable 45 is attached, the external power source 40 and the charger 28 are electrically connected, so that the secondary battery 10 can be externally charged.

  When the ignition switch is turned on from an operation stop state (IG on), the electric vehicle 100 is in a state where it can travel using the power of the secondary battery 10 by turning on the system main relays 21a and 21b. Transition to the vehicle driving state.

  In the vehicle driving state, the output of the motor generator 25 is controlled with the charging / discharging of the secondary battery 10 so that the driving force or braking force of the vehicle is generated according to the operation of the accelerator pedal and the brake pedal by the driver. The That is, in the vehicle driving state (IG on state), the secondary battery 10 is charged or discharged according to the traveling state of the electric vehicle 100.

  When the ignition switch is turned off (IG off) in the vehicle driving state (IG on state), electrically powered vehicle 100 transitions to a driving stop state by turning off system main relays 21a and 21b.

  Electric vehicle 100 transitions to an external charging state when charging relays 29a and 29b are turned on and external charging of secondary battery 10 by external power supply 40 is started in the operation stop state. For example, in a state where power can be supplied from the external power supply 40 to the electric vehicle 100 by the charging cable 45 or the like, the external charging is triggered by the charging start operation by the user or the arrival of the charging start time according to the time schedule Is started.

Next, the structure and self-diagnosis of the secondary battery will be described in detail.
FIG. 2 is a schematic cross-sectional view for explaining the structure of the battery cell shown in FIG.

  Referring to FIG. 2, the battery cell 11 includes an electrode body 112, a negative electrode current collector terminal 114, an anode current collector terminal 116, a cover 118, and a case 120. By sealing the case 120 to the cover 118, a sealed space is formed in the case 120.

  In the case 120, an electrode body 112, a negative electrode current collector terminal 114, and an anode current collector terminal 116 are accommodated. The electrode body 112 is formed by laminating a large number of anode plates and negative electrode plates while being insulated from each other, and winding the laminate.

  A core body exposed portion 112a configured by bundling the negative electrode plates is formed at one end of the electrode body 112 (left side in FIG. 2). Similarly, a core body exposed portion 112b configured by bundling anode plates is formed at the other end (right side in FIG. 2) of the electrode body 112.

  The negative electrode current collecting terminal 114 is welded to the core exposed portion 112a in the vicinity of the lower end thereof. The upper end of the negative electrode current collecting terminal 114 is connected to an external terminal 122 provided on the cover 118. As a result, the potential of the core body exposed portion 112 a is output to the external terminal 122. The anode current collecting terminal 116 is welded to the core exposed portion 112b in the vicinity of the lower end thereof. The upper end of the anode current collecting terminal 116 is connected to an external terminal 124 provided on the cover 118. As a result, the potential of the core body exposed portion 112 b is output to the external terminal 124. The case 20 is filled with an electrolytic solution.

  3 is an enlarged cross-sectional view of an inter-terminal connection portion (III-III line in FIG. 2) between the negative electrode current collecting terminal 114 and the external terminal 122. A caulking portion 115 is formed at the upper end portion of the negative electrode current collecting terminal 114.

  The caulking portion 115 has a base portion 114a extending substantially parallel to the cover 118, a columnar portion 114b extending upward from the base portion 114a, and a caulking head portion 114c extending in an umbrella shape from the tip of the columnar portion 114b. On the base 114a, a gasket 132, a cover 118, an insulator 134, and an external terminal 122 are sequentially stacked.

  Each of the gasket 132, the cover 118, the insulator 134, and the external terminal 122 is formed with a through hole. The columnar portion 114b of the negative electrode current collecting terminal 114 is inserted through these through holes. The gasket 132, the cover 118, the insulator 134, and the external terminal 122 are sandwiched and fixed from both sides by a caulking head portion 114c and a base portion 114a with plastic deformation.

  Thus, the negative electrode current collecting terminal 114, the gasket 132, the cover 118, the insulator 134, and the external terminal 122 are fixed to each other by caulking. The gasket 132 is made of an elastic member such as rubber, and ensures the airtightness of the caulking portion 115. The insulator 134 insulates between the external terminal 122 and the cover 118. The caulking head 114 c is in close contact with the external terminal 122.

  For this reason, the external terminal 122 and the negative electrode current collection terminal 114 are electrically connected by the contact part 115x. Two concave portions 122a and 122b are formed on the upper surface of the external terminal 122 on both sides of the caulking head portion 114c. The recesses 122a and 122b are slightly recessed from the surface of the surrounding external terminal 122. Although not shown, the anode current collecting terminal 116 and the external terminal 124 are also connected by the same structure as in FIG.

  Further, the battery cell 11 is further provided with a voltage sensor 19 for detecting a potential difference (hereinafter also referred to as “inter-terminal voltage”) between the negative electrode current collecting terminal 114 and the external terminal 122. The value detected by the voltage sensor 19 is sent to the controller 30. In FIG. 3, the voltage sensor 19 does not show an actual arrangement example, but is schematically described in order to explain the measurement target part.

FIG. 4 shows a cross-sectional view of the portion shown in FIG. 3 before caulking.
Referring to FIG. 4, before caulking, a base 114a and a columnar portion 114b (rivet) are formed at the upper end of negative electrode current collecting terminal 114. The caulking head 114c is not formed at the tip of the columnar portion 114b, and the tip of the columnar portion 114b is cylindrical. In the caulking process, as shown in FIG. 3, the gasket 132, the cover 118, the insulator 134, and the external terminal 122 are laminated. Moreover, the negative electrode current collection terminal 114 is arrange | positioned so that the columnar part 114b of the negative electrode current collection terminal 114 may be inserted in each through-hole formed in these members.

  In a state where the respective members are arranged in this manner, a compression load indicated by a dotted arrow in the drawing is applied to the upper surface of the external terminal 122 by a compression tool (not shown). This compressive load is adjusted so that the external terminal 122 is plastically deformed. By compressing the external terminal 122 at the position where the pressing load is applied, the concave portions 122 a and 122 b shown in FIG. 3 are formed on the upper surface of the external terminal 122.

  Further, the caulking head portion 114c is formed by plastically deforming the cylindrical portion of the columnar portion 114b while maintaining the state where the compressive load is applied. That is, the gasket 132, the cover 118, the insulator 134, and the external terminal 122 are caulked by the negative electrode current collecting terminal 114. At this time, since the negative electrode current collecting terminal 114, the gasket 132, the cover 118, the insulator 134, and the external terminal 122 are fixed by the compressive load, it is possible to easily perform caulking. The caulking process may be performed by a press method or a rotary method. Thereby, the inter-terminal connection structure by caulking shown in FIG. 3 can be obtained.

  In the inter-terminal connection structure shown in FIG. 3, the conductive path between the external terminal 122 and the negative electrode current collecting terminal 114 is secured by the contact portion 115x obtained by caulking. Therefore, there is a concern that the connection between the terminals due to the caulking process is loosened due to the stress caused by the expansion and contraction of the terminals due to the temperature change accompanying charging and discharging, and the contact area of both terminals at the contact portion 115x is reduced. . Alternatively, the connection between terminals by caulking may be loosened due to the influence of vibration during vehicle travel.

  Due to these factors, when the contact area of both terminals at the contact portion 115x decreases, the contact resistance between the external terminal 122 and the negative electrode current collecting terminal 114 (hereinafter also referred to as “terminal contact resistance”) increases. Increases electrical resistance. As a result, since heat generation accompanying charging / discharging of the secondary battery (battery cell 11) increases, there is a concern about the occurrence of energy loss and the progress of battery deterioration due to temperature rise.

  Therefore, in the battery system according to the present embodiment, a self-diagnosis is performed to detect loose connection between terminals in the connection structure between terminals by caulking of the secondary battery.

  FIG. 5 is a flowchart for illustrating self-diagnosis control processing by the battery system according to the present embodiment. The control process according to the flowchart shown in FIG. 5 can be repeatedly activated by the controller 30.

  For example, the controller 30 can start the control process for the self-diagnosis according to FIG. 5 when the ignition switch of the electric vehicle 100 is turned on. Furthermore, the controller 30 can start the control process of FIG. 3 at any timing when the secondary battery 10 is charged or discharged during operation of the electric vehicle 100 (including when the electric vehicle 100 is stopped). Further, the control process shown in FIG. 5 may be repeatedly activated before a predetermined time elapses in the above-described vehicle operating state (the on period of the system main relays 21a and 21b).

  With reference to FIG. 5, the controller 30 measures the temperature of the battery cell 11 based on the detected value by the temperature sensor 16 by step S100. Furthermore, the controller 30 calculates the contact resistance value Ra between the terminals crimped in each battery cell 11 based on the detected value by the current sensor 15 and the detected value by the voltage sensor 19 in step S110.

  Here, since the charge / discharge current is common between the battery cells 11 connected in series, the voltage between the terminals detected by the voltage sensor 19 in each battery cell 11 is divided by the detection value of the current sensor 15. The inter-terminal contact resistance value Ra in each battery cell 11 can be calculated.

  Further, in step S120, the controller 30 sets the reference resistance value Rr in each battery cell 11 based on the temperature measured in step S100.

  FIG. 6 shows a conceptual graph for explaining the setting of the reference resistance value Rr according to the cell temperature.

  Referring to FIG. 6, the contact resistance increases as the contact area decreases at a constant temperature, and the resistance value increases as the temperature increases for the same contact area.

  Therefore, when the reference value St is determined as the contact area to be secured at the contact site 115x by caulking, the electrical resistance value when the contact area is St can be defined at each battery temperature.

  For example, as shown in FIG. 6, when the battery temperature Tb = T1, and the reference resistance value Rr = R1, when the contact resistance Ra is higher than Rr (R1), the contact area becomes St due to the loosening of the caulking process. Can be detected. That is, by setting Rr = R1, it is possible to self-diagnose the loosening of the caulking process.

  Since the contact resistance value decreases at a high temperature, if the determination is made with the reference resistance value Rr = R1 at the battery temperature T2 (T2> T1), the contact resistance must be reduced to Sx (Sx <St). Cannot detect the decrease in That is, the reference resistance value Rr is set to a lower value as the temperature of the battery cell 11 (battery temperature Tb) is higher in order to execute the determination based on the contact resistance with the same contact area St as a reference. For example, when the battery temperature is Tb = T2, it is possible to detect that the contact area is narrower than St due to the loosening of the caulking process by making the determination as the reference resistance value Rr = R2 (R2 <R1).

  A reference resistance value Rr corresponding to the contact resistance value when the contact area is St can be determined in advance corresponding to each battery temperature in accordance with the actual machine experimental results and the like. As a result, even if the battery temperature changes, a region where the contact area is smaller than St (slack detection region) is extracted by comparing the contact resistance value Ra with the reference resistance value Rr (that is, by determining Ra> Rr). can do. Note that the correspondence relationship indicating the change in the reference resistance value Rr corresponding to the change in the battery temperature can be stored in advance in the memory 31 as a map for setting the reference resistance value Rr for each battery temperature.

  Referring to FIG. 5 again, in step S120, the reference resistance value Rr can be set by referring to the map using the measured temperature (battery temperature) in step S100.

  When one temperature sensor 16 is disposed in the entire secondary battery 10, the reference resistance value Rr is set in common for all the battery cells 11. On the other hand, when the temperature sensor 16 is arranged for each battery cell 11, the reference resistance value Rr can be set separately for each battery cell 11. Further, when the temperature sensor 16 is arranged for each block obtained by dividing the entire battery cell 11 as appropriate, a reference resistance value Rr is set for each block, and a common reference resistance is shared between the battery cells 11 in the same block. The value Rr can be used. In this manner, the cell temperature can be detected for each battery cell 11 using the detection value obtained by the temperature sensor 16 in an arbitrary arrangement mode.

  In step S130, the controller 30 compares the contact resistance value Ra calculated in step S110 with the reference resistance value Rr set in step S120. When Ra ≦ Rr (NO in S130), the controller 30 advances the process to step S140, determines that the vehicle can be driven, and turns on the system main relays 21a and 21b. Allow. That is, the loosening of the caulking process in the secondary battery 10 is not detected.

  On the other hand, when Ra> Rr is detected (at the time of YES determination in S130), the controller 30 detects that an increase in electrical resistance due to loosening of the caulking process has occurred in the secondary battery 10, In step S150, a warning by a predetermined diagnosis code is generated for the user. Thereby, for example, a warning lamp is turned on.

  Furthermore, controller 30 determines that the vehicle is inoperable in step S160, and does not allow system main relays 21a and 21b to be turned on. For example, in the self-diagnosis when the ignition switch is turned on, the transition to the vehicle operating state is prohibited by step S160. Further, in the vehicle operating state, the system main relays 21a and 21b are turned off in step S160, so that traveling using the power of the secondary battery 10 is disabled. At this time, in the case where the electric vehicle 100 is a hybrid vehicle equipped with an engine, the retreat travel (battery-less travel) using only the engine output can be started.

  In order to prevent misdiagnosis, it is preferable that step S130 is determined as YES only in the case where Ra> Rr is detected a certain number of times or more or continuously for a certain time.

  Thus, according to the battery system according to the present embodiment, in a secondary battery having a connection structure between terminals by caulking, the connection between the terminals is loosened online when the secondary battery is used (charge / discharge). Self-diagnosis can be performed. In particular, the self-diagnosis can be performed with high accuracy in consideration of the change characteristic of the contact resistance value with respect to the temperature change. As a result, it is possible to prevent battery deterioration from progressing by continuing the high temperature state due to the increase in inter-terminal resistance (contact resistance) without noticing the loosening of the caulking process.

  In the present embodiment described above, the negative electrode current collecting terminal 114 and the external terminal 122 correspond to an example of “first and second terminals”, and the controller 30 corresponds to an example of a “control device”. Correspond. Further, the voltage sensor 19 corresponds to an embodiment of “voltage detector”, the current sensor 15 corresponds to an embodiment of “current detector”, and the temperature sensor 16 corresponds to an embodiment of “temperature detector”. Correspond.

  Further, in the present embodiment, the battery system mounted on the electric vehicle is illustrated, but the same self-diagnosis is possible to detect loosening of the caulking process even in the battery system applied to applications other than the vehicle mounting. It is.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10 Secondary battery, 11 Battery cell, 15 Current sensor, 16 Temperature sensor, 17, 19 Voltage sensor, 21a, 21b System main relay, 22 Boost converter, 23 Inverter, 25 Motor generator, 26 Transmission gear, 27 Drive wheel, 28 Charger, 29a, 29b Charging relay, 30 Controller, 31 Memory, 40 External power supply, 45 Charging cable, 100 Electric vehicle, 112 Electrode body, 112a, 112b Core body exposed part, 114 Negative current collecting terminal, 114a Base part, 114b Columnar shape Part, 114c, caulking head, 115 caulking part, 115x contact part, 116 anode current collecting terminal, 118 cover, 120 case, 122, 124 external terminal, 122a, 122b recess, 132 gasket, 134 insulator, Ra contact resistance value, r reference resistance value, St reference value (contact area), Tb battery temperature, V output voltage.

Claims (1)

A secondary battery in which a charge / discharge current passes between the first and second terminals connected by caulking,
A voltage detector for detecting a potential difference between the first and second terminals;
A current detector for detecting a charge / discharge current of the secondary battery;
A temperature detector for detecting the temperature of the secondary battery;
And a control device for self-diagnosis of a decrease in contact area due to caulking between the first and second terminals based on the voltage detector, the current detector, and a value detected by the current detector. ,
The controller is
When the contact resistance value between the first and second terminals calculated from the detection value by the voltage detector and the current detector is higher than the reference resistance value set from the temperature detection value by the temperature detector Detecting that loosening has occurred in the caulking process,
The reference resistance value is set to a lower value as the temperature detected by the temperature detector is higher in accordance with a predetermined correspondence relationship indicating a change in the contact resistance value with respect to a temperature change of the secondary battery in the same contact area. The battery system.

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