Battery unit

Abstract

To eliminate a bias in salt concentration distribution within a cell.SOLUTION: A battery unit can also comprise: a battery pack in which a plurality of secondary battery cells are stacked and each provided with a cathode, an anode and an electrolyte; a load application device which applies a load to the battery pack in a lamination direction and which can adjust the load; and a control device which executes damage alleviation processing for the battery pack by controlling the load application device. The damage alleviation processing can also be processing for repeatedly increasing / decreasing the load applied to the battery pack by the load application device.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The technology disclosed in this specification relates to a battery unit, and particularly to a battery unit mounted on a vehicle.

Background Art

[0002] Patent Document 1 describes a battery unit. The battery unit includes a assembled battery having a plurality of secondary battery cells, a load applying device capable of adjusting the load applied to the assembled battery, and a control device for controlling the load applying device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described battery unit, when high-rate charging (hereinafter referred to as high-rate charge) is performed on the assembled battery, a bias may occur in the salt concentration distribution of the electrolyte in the assembled battery. This bias in the salt concentration distribution increases the internal resistance of the assembled battery and causes deterioration of battery characteristics (hereinafter referred to as high-rate deterioration). This specification provides a technology that can eliminate or mitigate the above-described problems.

Means for Solving the Problems

[0005] The technology disclosed in this specification is embodied in a battery unit mounted on a vehicle. In a first aspect, the battery unit may include an assembled battery in which a plurality of secondary battery cells are stacked, and each of the plurality of secondary battery cells has a positive electrode, a negative electrode, and an electrolytic solution; a load applying device that applies a load in a stacking direction to the assembled battery and is capable of adjusting the load; and a control device that executes a damage mitigation process on the assembled battery by controlling the load applying device. The damage mitigation process may be a process of repeatedly increasing and decreasing the load applied to the assembled battery by the load applying device.

[0006] In the above-described battery unit, the load applied to the assembled battery can be repeatedly increased and decreased by the load applying device. In response to the increase and decrease of the load, the volume of the assembled battery repeatedly contracts and expands. As a result, within each cell of the assembled battery, the flow of the electrolytic solution between the positive electrode and the negative electrode is promoted. Thereby, salts generated between the positive electrode and the negative electrode are dispersed, and the deviation in the salt concentration distribution can be eliminated.

[0007] In a second aspect, in the first aspect described above, the control device may execute the damage mitigation process while the cumulative damage amount accumulated in the assembled battery has reached a predetermined value and the main switch of the vehicle is turned off. According to such a configuration, the control device can execute the damage mitigation process at a frequency without excess or deficiency and at an appropriate timing. Note that the main switch in the vehicle is conventionally also referred to as an ignition switch.

[0008] In a third aspect, in the second aspect described above, when executing the damage mitigation process, the control device may determine the number of times of repeatedly increasing and decreasing the load according to the magnitude of the cumulative damage amount. According to such a configuration, the control device can change the degree of the damage mitigation process according to the amount of damage accumulated in the assembled battery.

[0009] In the fourth aspect, in the above-described third aspect, after executing the damage mitigation process, the control device may update the cumulative damage amount according to the number of times the load is repeatedly increased and decreased. According to such a configuration, the control device can continuously grasp the amount of damage accumulated in the battery pack. Therefore, the control device can execute the damage mitigation process at an appropriate timing according to the amount of damage accumulated in the battery pack.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

Examples

[0011] With reference to the drawings, the battery unit 10 of the example will be described. The battery unit 10 is mounted on a vehicle. The vehicle drives a driving motor with the power from the battery unit 10. As shown in FIG. 1, the battery unit 10 includes a battery stack 12, a battery ECU (Electronic Control Unit) 20, a load application device 22, and a control device 24. Here, the battery stack 12 is an example of the "battery pack" in the technology disclosed in this specification.

[0012] The battery stack 12 has a plurality of battery cells 14, a plurality of spacers 16, and a pair of end plates 18. Each battery cell 14 is a rechargeable secondary battery cell such as, for example, a lithium-ion battery cell. The battery cell 14 generally has a rectangular parallelepiped shape. In the battery stack 12, the battery cells 14 and the spacers 16 are alternately laminated. The spacer 16 generally has a flat plate shape and is an insulating member called an inter-cell spacer. The pair of end plates 18 are generally flat plate members. The pair of end plates 18 face each other with the plurality of battery cells 14 interposed therebetween. The pair of end plates 18 are connected to each other via a band material (not shown) extending in the stacking direction. Thereby, the battery stack 12 is constrained by a predetermined load by restraining members such as the pair of end plates 18 and the band material.

[0013] As shown in FIG. 2, the battery cell 14 has an electrode body 14a, an electrolytic solution 14b, and a casing 14c that houses them therein. The electrode body 14a is formed by laminating a positive electrode sheet, a negative electrode sheet, and a separator positioned between the positive electrode sheet and the negative electrode sheet.

[0014] The battery ECU 20 is communicably connected to the battery stack 12 and monitors the state (such as current, voltage, temperature data, etc.) of the battery stack 12. The battery ECU 20 calculates the cumulative damage amount ΣD due to high-rate deterioration of the battery stack 12 from each measurement data such as that of the battery stack 12. Here, high-rate deterioration is deterioration caused by charging or discharging the battery stack 12 with a large current (i.e., high-rate charging or discharging). When high-rate charging or discharging is performed, a bias occurs in the salt concentration distribution of the electrolytic solution 14b inside the battery cell 14. As a result, the internal resistance of the battery cell 14 increases, and the battery characteristics of the battery stack 12 deteriorate accordingly. The cumulative damage amount ΣD due to high-rate deterioration is an index that accumulates such high-rate deterioration over time.

[0015] There are no particular limitations on the specific calculation methods for high-rate degradation and the cumulative damage amount ΣD. High-rate degradation can be appropriately calculated based on the state of the battery stack 12 (such as current, voltage, temperature data, etc.) and a calculation formula based on experiments or simulations. Further, in the calculation of the cumulative damage amount ΣD, it is preferable that the high-rate degradation caused by high-rate charging is accumulated as a negative value, and the high-rate degradation caused by high-rate discharging is accumulated as a positive value. Although it is an example, the high-rate degradation and the cumulative damage amount ΣD can be calculated by the method described in Japanese Patent Laid-Open No. 2017-091602.

[0016] The load applying device 22 applies a load to the battery stack 12 in the stacking direction. Further, the load applying device 22 can adjust the load applied to the battery stack 12 (i.e., the load that restrains the battery stack 12) by adjusting the interval between the pair of end plates 18. Note that the specific configuration of the load applying device 22 is not particularly limited. The load applying device 22 may apply a load to the battery stack 12 with both of the pair of end plates 18 being movable, or may apply a load to the battery stack 12 with only one of the pair of end plates 18 being movable.

[0017] The control device 24 is communicably connected to the load applying device 22 and controls the load applying device 22. The control device 24 is communicably connected to the battery ECU 20 and receives the state data of the battery stack 12 from the battery ECU 20. The control device 24 has a processor and a memory. The control device 24 executes various processes using the load applying device 22 based on a program stored in advance in the memory, data received from the battery ECU 20, and the like. Among the various processes described above, the control device 24 can control the load applying device 22 to execute a damage mitigation process on the battery stack 12. The damage mitigation process is a process of repeatedly increasing and decreasing the load applied to the battery stack 12 by the load applying device 22.

[0018] Here, with reference to FIGS. 2-5, an example of a series of processes including the damage mitigation process executed by the control device 24 will be described. The control device 24 executes a process of controlling the load applying device 22 according to the flow shown in FIG. 3.

[0019] In step S12, the control device 24 receives the cumulative damage amount ΣD of high-rate degradation. The control device 24 receives the cumulative damage amount ΣD from, for example, the battery ECU 20. However, it is not limited to this, and the control device 24 may calculate the cumulative damage amount ΣD by itself based on the state of the battery stack 12 received from the battery ECU 20.

[0020] In step S14, the control device 24 determines whether the magnitude (i.e., absolute value) of the cumulative damage amount ΣD acquired in step S12 is greater than a predetermined value ΣDt. That is, it is determined whether the acquired cumulative damage amount ΣD is outside the range of -ΣDt or more and ΣDt or less shown in FIG. 4. When the magnitude of the cumulative damage amount ΣD is greater than the predetermined value ΣDt (YES in S14), the control device 24 proceeds to the process of step S16. Otherwise (NO in S14), the control device 24 remains in the process of step S14. When the cumulative damage amount ΣD is less than or equal to the predetermined value ΣDt, the damage mitigation process is not necessarily required. Until the cumulative damage amount ΣD reaches the predetermined value ΣDt, by prohibiting the execution of the damage mitigation process, negative effects (e.g., deterioration of the spacer 16) caused by the damage mitigation process can be avoided.

[0021] In step S16, the control device 24 determines whether the main switch of the vehicle (also referred to as the ignition switch) is in the off state. For example, the control device 24 can grasp the state of the main switch based on the ignition signal output from the battery ECU 20 or other ECUs. When the main switch is in the off state (YES in S16), the control device 24 proceeds to the process of step S18. Otherwise (NO in step S16), the control device 24 returns to the process of step S14.

[0022] In step S18, the control device 24 defines the number of repetitions in the damage mitigation process according to the magnitude of the cumulative damage amount ΣD acquired in step S12. Note that the number of repetitions is the number of times the load applied to the battery stack 12 is increased or decreased in the damage mitigation process. According to such a configuration, the control device 24 can change the degree of the damage mitigation process according to the cumulative damage amount ΣD accumulated in the battery stack 12. As shown in FIG. 4, the number of repetitions increases as the magnitude of the cumulative damage amount ΣD increases.

[0023] In step S20, the control device 24 controls the load application device 22 to execute the damage mitigation process. Specifically, the control device 24 repeatedly increases and decreases the load applied to the battery stack 12 by the load application device 22. As a result, as shown in FIG. 2, the volume of the battery stack 12 repeatedly contracts and expands. As a result, within each battery cell 14 of the battery stack 12, the flow of the electrolytic solution 14b is promoted within the electrode body 14a (between the positive electrode sheet and the negative electrode sheet). The salts generated within the electrode body 14a are dispersed, and the bias in the salt concentration distribution is eliminated.

[0024] Although it is an example, during the execution of the damage mitigation process, the control device 24 adjusts the load applied to the battery stack 12 according to the load pattern Lx shown in FIG. 5. The load pattern Lx varies between the lower limit load L1 and the upper limit load L2 along the time (t) axis. The lower limit load L1 is the minimum load required to hold the electrode body 14a. The lower limit load L1 may be, for example, in the range of about 2 to 6 kN. The upper limit load L2 is the maximum possible load that can prevent the battery stack 12 from being excessively compressed. The upper limit load L2 may be, for example, in the range of about 10 to 60 kN.

[0025] In step S22, the control device 24 determines whether or not the main switch of the vehicle is turned on. If the main switch is turned on (YES in S22), the control device 24 aborts the damage mitigation process and proceeds to the process of step S26. Otherwise (NO in S22), the control device 24 proceeds to the process of step S24.

[0026] In step S24, the control device 24 determines whether the damage mitigation process has been completed up to the number of repetitions specified in step S18. If the damage mitigation process has been completed up to the specified number of repetitions (YES in S24), the control device 24 ends the damage mitigation process and proceeds to the process of step S26. Otherwise (NO in S24), the control device 24 continues the damage mitigation process and returns to the process of step S22.

[0027] In step S26, the control device 24 updates the cumulative damage amount ΣD according to the number of repetitions executed in the damage mitigation process. Specifically, a new cumulative damage amount ΣD is calculated by subtracting the damage mitigation amount corresponding to the number of repetitions executed in the damage mitigation process from the cumulative damage amount ΣD stored so far. According to such a configuration, the control device 24 can continuously grasp the cumulative damage amount ΣD of the battery stack 12. Therefore, the control device 24 can execute the damage mitigation process at an appropriate timing according to the cumulative damage amount ΣD of the battery stack 12.

[0028] In step S28, the control device 24 restrains the battery stack 12 with a predetermined load by the load applying device 22. Thereby, the battery unit 10 returns to the normal state. By repeatedly executing the above-described series of processes, the control device 24 can suppress the accumulation of damage caused by high-rate deterioration of the battery stack 12 and maintain the battery characteristics of the battery stack 12.

[0029] As described above, specific examples of the technology disclosed in this specification have been described in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. The technology illustrated in this specification or the drawings can achieve multiple objectives simultaneously, and achieving one of these objectives itself has technical utility.

Description of Reference Numerals

[0030] 10: Battery unit, 12: Battery stack, 14: Battery cell, 14a: Electrode body, 14b: Electrolyte, 14c: Casing, 16: Spacer, 18: End plate, 20: Battery ECU, 22: Load applying device, 24: Control device, ΣD: Cumulative damage amount, ΣDt: Predetermined value

Claims

1. A battery unit mounted on a vehicle, in which a plurality of secondary battery cells are stacked, and each of the plurality of secondary battery cells is a battery pack having a positive electrode, a negative electrode, and an electrolytic solution; a load applying device that applies a load in the stacking direction to the battery pack and is capable of adjusting the load; a control device that executes a damage mitigation process on the battery pack by controlling the load applying device; comprising: the damage mitigation process is a process of repeatedly increasing and decreasing the load applied to the battery pack by the load applying device; the control device executes the damage mitigation process while the cumulative damage amount accumulated in the battery pack has reached a predetermined value and the main switch of the vehicle is turned off; a battery unit.

2. The battery unit according to claim 1, wherein the control device determines the number of times of repeatedly increasing and decreasing the load according to the magnitude of the cumulative damage amount when executing the damage mitigation process.

3. The battery unit according to claim 2, wherein the control device updates the cumulative damage amount according to the number of times of repeatedly increasing and decreasing the load after executing the damage mitigation process.

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