Battery processing system and battery processing method

Abstract

To resolve the degradation arising from unevenness in electrical potential.SOLUTION: A control device executes a process that includes: a step (S106) in which a first resolution process is executed when an execution condition is met (Yes in S100), and when there is a history of integration in degradation index value ΣD (No in S102) and the degradation index value ΣD is larger than a first threshold TH1 (Yes in S104); a step (S108) in which the property value of a cell is measured; a step (S110) in which a second resolution process is executed; a step (S114) in which determination is made that reuse is possible when the property value is within a permissible range (Yes in S112); a step (S116) in which determination is made that reuse is impossible when being out of the permissible range (NO in S112); and a step (S118) in which a second resolution process is executed when the degradation index value ΣD is smaller than or equal to the first threshold TH1 (No in S104).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a battery processing system. [Background technology]

[0002] An electric vehicle may be equipped with, for example, a lithium-ion battery as a power storage device for driving. It is known that this lithium-ion battery may deteriorate due to charging and discharging at a large current (high rate). This deterioration is also called "high-rate deterioration." Various techniques have been proposed to suppress the high-rate deterioration of lithium-ion batteries.

[0003] For example, JP 2021-103646 A (Patent Document 1) discloses a technology for calculating a degradation index value ΣD indicating the degree of progression of high-rate degradation, and performing degradation mitigation processing when the calculated degradation index value ΣD exceeds a threshold value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-103646 A Summary of the Invention [Problem to be solved by the invention]

[0005] When a lithium-ion battery is charged and discharged at a high rate, degradation due to bias in potential (uneven potential) on the electrode surface may occur in addition to the high-rate degradation described above due to bias in salt concentration (lithium ion concentration) on the electrode surface (uneven salt concentration). Therefore, even if high-rate degradation can be mitigated by executing a degradation mitigation process on the lithium-ion battery as in the above-mentioned Patent Document 1, degradation due to uneven potential may remain. As a result, when the lithium-ion battery is subsequently replaced in another vehicle as a reused battery, the degree of degradation may be perceived as greater than it actually is, or the recoverable capacity may not be grasped and the battery life may be erroneously perceived as short.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has as its object to provide a battery processing system and a battery processing method that eliminate deterioration caused by uneven potential. [Means for solving the problem]

[0007] A battery processing system according to an aspect of the present disclosure includes a lithium ion battery having an electrode assembly, and a control device that controls charging and discharging of the lithium ion battery. The control device acquires an index value indicating a degree of deterioration of the lithium ion battery caused by a bias in the concentration distribution of lithium ions inside the electrode assembly. When the index value exceeds a first threshold value, the control device executes a first elimination process to eliminate the deterioration caused by the bias in the concentration distribution. When there is a period during which the index value is equal to or less than the first threshold value and exceeds a second threshold value that is smaller than the first threshold value, the control device executes a second elimination process to eliminate the deterioration caused by a bias in the potential on the electrode surface of the electrode assembly due to discharging of the lithium ion battery.

[0008] In this way, when there is a period in which the index value exceeds the second threshold value, the second resolution process is executed, so that the deterioration of the lithium ion battery caused by the bias of the potential on the electrode surface of the electrode body can be resolved. Furthermore, when the index value exceeds the first threshold value, the first resolution process is executed, so that the deterioration caused by the bias of the concentration distribution can be resolved.

[0009] In one embodiment, the second resolution process includes a process of over-discharging the lithium ion battery to a predetermined voltage.

[0010] In this way, by overdischarging the lithium ion battery to a predetermined voltage, it is possible to bring about a change that quickly eliminates the bias in potential on the electrode surface of the electrode assembly.

[0011] Furthermore, in one embodiment, the control device executes the second resolution process when the index value is equal to or less than the first threshold value and there is a history of the index value changing from the initial value to exceed the second threshold value.

[0012] In this way, if there is a history of the index value changing from the initial value to exceeding the second threshold value, there is a possibility that deterioration of the lithium ion battery due to biased potential on the electrode surface of the electrode body has occurred. Therefore, by executing the second elimination process, the deterioration can be eliminated.

[0013] In yet another embodiment, the control device is configured to: 1 After performing the resolution process, 2 Execute the cancellation process.

[0014] In this way, the deterioration of the lithium ion battery caused by the bias of the potential on the electrode surface of the electrode body can be eliminated by executing the second elimination process, and further, the deterioration caused by the bias of the concentration distribution can be eliminated by executing the first elimination process.

[0015] In yet another embodiment, the electrode assembly includes a positive electrode and a negative electrode, wherein at least one of the positive electrode active material and the negative electrode active material includes a material capable of inserting and desorbing lithium ions.

[0016] In this way, since the active material of the positive electrode or the active material of the negative electrode contains a material capable of inserting and detaching lithium ions, it is possible to eliminate deterioration of the lithium ion battery caused by the biased potential on the electrode surface of the electrode body by performing the second elimination process.

[0017] Battery according to another aspect of the present disclosure process The method is a battery treatment method for eliminating deterioration of a lithium ion battery having an electrode assembly, and includes the steps of acquiring an index value indicating a degree of deterioration of the lithium ion battery caused by a bias in the concentration distribution of lithium ions inside the electrode assembly, executing a first elimination process for eliminating the deterioration caused by the bias in the concentration distribution when the index value exceeds a first threshold value, and executing a second elimination process for eliminating the deterioration caused by a bias in the potential on the electrode surface of the electrode assembly due to discharging of the lithium ion battery when there is a period during which the index value is equal to or less than the first threshold value and exceeds a second threshold value that is smaller than the first threshold value. Effect of the Invention

[0018] According to the present disclosure, it is possible to provide a battery processing system and a battery processing method that eliminate deterioration caused by uneven potential. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing an example of a configuration of a battery processing system according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram for explaining an example of a cell configuration in more detail. [Diagram 3] FIG. 13 is a diagram illustrating an example of the relationship between the amount of unevenness and the number of days elapsed after high-rate degradation. [Figure 4] 4 is a flowchart illustrating an example of a process executed by a control device. [Diagram 5] FIG. 4 is a diagram showing an example of the relationship between SOC and negative electrode potential. [Figure 6] FIG. 13 is a diagram showing an example of a change in distribution of a negative electrode potential with respect to a position on an electrode surface. [Figure 7] 13 is a diagram showing an example of a distribution of a negative electrode potential with respect to a position on an electrode surface after a second cancellation process is executed. FIG. [Figure 8] 11A and 11B are diagrams showing an example of a change in the amount of unevenness due to potential unevenness before and after various discharges are performed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0021] 1 is a diagram showing an example of the configuration of a battery processing system 2 according to the present embodiment. As shown in FIG 1, the battery processing system 2 includes a charge / discharge device 10, a cell 31, a detection unit 40, and a control device 100.

[0022] 1 shows, as an example, a case where the battery 30 is removed from the vehicle 50, and one of the multiple cells 31 constituting the removed battery 30 is electrically connected to the charging / discharging device 10. The multiple cells 31 may be in a state of an assembled battery in which various terminals of each cell can be connected to the charging / discharging device 10, or the assembled battery state may be released and the cell may be movable individually.

[0023] Vehicle 50 is not particularly limited as long as it is a vehicle equipped with at least a lithium-ion battery, such as an electric vehicle or a hybrid vehicle.

[0024] The charging / discharging device 10 has a function of, for example, supplying charging power to the cell 31 to charge the cell 31, or discharging the power stored in the cell 31. The charging / discharging device 10 charges the cell 31 or discharges the cell 31 in response to a control signal from the control device 100.

[0025] The cell 31 is a lithium ion battery that has a voltage of about 3V to 4V when fully charged.

[0026] The detection unit 40 includes a voltage sensor, a current sensor, and a temperature sensor (none of which are shown). The voltage sensor detects the voltage V of the cell 31. The current sensor detects the current I input to or output from the cell 31. The temperature sensor detects the temperature T of the cell 31. Each sensor outputs a signal indicating the detection result to the control device 100.

[0027] The control device 100 includes a processor 101 such as a central processing unit (CPU), a memory 102 such as a read only memory (ROM) and a random access memory (RAM), and an input / output port (not shown) for inputting and outputting various signals. The control device 100 controls the charging / discharging device 10 based on the input of signals from each sensor and a map and a program stored in the memory. The control device 100 is configured to be able to communicate with the vehicle 50 on which the battery 30 was mounted. When the battery 30 is removed, an electronic control unit (ECU) of the vehicle 50 and the control device 100 are communicatively connected, and predetermined information is transmitted from the vehicle 50 to the control device 100. The control device 100 stores the received predetermined information in the memory 102 or a large-capacity storage device (not shown). In this embodiment, the main controls executed by the control device 100 include a resolution process (first resolution process and second resolution process) for resolving (which may also be expressed as recovery or mitigation) high-rate degradation of the cell 31. The resolution process will be described in detail later.

[0028] Fig. 2 is a diagram for explaining in more detail an example of the configuration of the cell 31. In Fig. 2, the cell 31 is shown in a see-through manner with its interior seen through.

[0029] The cell 31 has a battery case 32 having a substantially rectangular parallelepiped shape. The upper surface of the battery case 32 is sealed by a lid 33. One end of each of a positive electrode terminal 34 and a negative electrode terminal 35 protrudes from the lid 33 to the outside. The other ends of the positive electrode terminal 34 and the negative electrode terminal 35 are connected to an internal positive electrode terminal and an internal negative electrode terminal (neither of which are shown) inside the battery case 32, respectively.

[0030] An electrode body 36 is housed inside the battery case 32. The electrode body 36 is formed by stacking a positive electrode 37 and a negative electrode 38 with a separator 39 between them and winding the laminate. An electrolyte (not shown) is held in the positive electrode 37, the negative electrode 38, and the separator 39. It is also possible to adopt a laminate as the electrode body 36 instead of the wound body.

[0031] The positive electrode 37, the negative electrode 38, the separator 39, and the electrolyte may have a conventionally known configuration and material. At least one of the active material of the positive electrode 37 and the active material of the negative electrode 38 includes, for example, a material capable of inserting and removing lithium ions. Specifically, the active material of the positive electrode 37 may include a lithium composite oxide having a layered structure. Examples of the lithium composite oxide having a layered structure include a lithium cobalt-based composite oxide, a lithium nickel cobalt aluminum-based composite oxide, and a lithium nickel cobalt manganese-based composite oxide. Examples of the active material of the negative electrode 38 include a carbon-based negative electrode active material such as graphite.

[0032] For example, the separator may be made of polyolefin (e.g., polyethylene or polypropylene). The electrolyte includes an organic solvent (e.g., a mixed solvent of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), and EC (ethylene carbonate), a lithium salt (e.g., LiPF6), and an additive (e.g., LiBOB (lithium bis(oxalate)borate) or Li[PF2(C2O4)2]).

[0033] In the cell 31 configured as described above, various types of deterioration may occur due to the use of the vehicle 50 while the cell 31 is mounted on the vehicle 50. In particular, in the cell 31 which is a lithium ion battery, when the cell 31 is continuously charged and discharged with a relatively large current (high-rate current), "high-rate deterioration" may occur, which is a deterioration phenomenon in which the internal resistance of the cell 31 increases. High-rate deterioration is deterioration caused by a bias in the concentration distribution of lithium ions (salt concentration distribution) inside the electrode body 36.

[0034] High-rate degradation is a type of degradation that can be eliminated. In other words, if the internal resistance of the cell 31 increases due to high-rate degradation, the internal resistance of the cell 31 can be reduced (returned to the original state) by performing a process to eliminate the high-rate degradation.

[0035] In this embodiment, the extent to which high-rate degradation, which is recoverable degradation among various types of degradation, has progressed is quantitatively evaluated. Then, when the progress of the high-rate degradation reaches a predetermined degree, a resolution process for resolving the high-rate degradation is executed. More specifically, the control device 100 acquires a "degradation index value ΣD" which is an index value indicating the progress of the high-rate degradation. For example, the control device 100 may acquire information for calculating the degradation index value ΣD from the ECU 60 of the vehicle 50 in which the battery 30 was mounted, and calculate the degradation index value ΣD at the time of removal from the vehicle 50 using the acquired information. Alternatively, the ECU 60 and the control device 100 may perform the following operations. That is, the ECU 60 calculates the degradation index value ΣD at a predetermined control period and stores it in the memory of the ECU 60. When the battery 30 is removed from the vehicle 50, the control device 100 communicates with the ECU 60 to receive a history of the degradation index value ΣD, and stores the received history of the degradation index value ΣD in the memory 102. The control device 100 acquires the deterioration index value ΣD from the memory 102. Note that the communication between the control device 100 and the ECU 60 may be wireless communication or wired communication.

[0036] Hereinafter, assuming that the deterioration index value ΣD is calculated in the ECU 60, an example of a method for calculating the deterioration index value ΣD using the ECU 60 will be briefly described.

[0037] The ECU 60 calculates an index value D for calculating the deterioration index value ΣD at every predetermined control period Δt. The index value of the battery 30 calculated in the Nth (current) control period is represented as D(N), and the index value calculated in the (N-1)th (previous) control period is represented as D(N-1). N is a natural number. The index value D(N) is calculated according to the following recurrence formula, taking into account both increases and decreases in the bias of the salt concentration distribution that accompanies charging and discharging of the battery 30. The initial value D(0) of the index value is set to 0, for example.

[0038] D(N)=D(N-1)-D(-)+D(+) ···(1) In the above formula (1), the decrease amount D(-) of the index value represents the decrease amount of the bias of the salt concentration distribution caused by the diffusion of lithium ions from the time when the previous index value was calculated to the time when the current index value was calculated (during the control period Δt). The decrease amount D(-) can be calculated using the forgetting factor α as shown in the following formula (2). Note that 0<α×Δt<1.

[0039] D(-)=α×Δt×D(N-1) ···(2) The forgetting factor α is a coefficient corresponding to the diffusion speed of lithium ions in the electrolyte, and depends on the temperature T and SOC (State Of Charge) of the battery 30. Therefore, the correlation between the forgetting factor α and the temperature T and SOC is obtained in advance by a prior evaluation (experiment or simulation) and is stored in the ECU as a map or a conversion formula. 60 Note To Stored in the ECU 60 By referring to the map or conversion formula, the forgetting factor α can be calculated from the temperature T and the SOC. Similarly, for the current factor β and the limit threshold C, a map or conversion formula can be created from the results of prior evaluation.

[0040] Returning to formula (1), the increase in the index value D(+) represents the increase in the bias of the salt concentration distribution due to charging and discharging from the time when the index value was calculated last time to the time when the index value was calculated this time (during the control period Δt). The increase in the index value D(+) can be calculated using the current coefficient β, the limit threshold C, and the current I, as shown in formula (3) below.

[0041] D(+)=(β / C)×I×Δt (3) ECU 60 As shown in the following formula (4), the deterioration index value ΣD(N) is calculated by accumulating the index value D(N) for all N from the initial value (0) to the current value (N).

[0042] ΣD(N)=γ×ΣD(N-1)+η×D(N) ···(4) In the above formula (4), γ is a decay coefficient. Since the bias in salt concentration is alleviated by the diffusion of lithium ions over time, it is desirable to take into consideration that the previous index value ΣD(N-1) has decreased when calculating the current index value ΣD(N). Therefore, the decay coefficient γ, which is the coefficient of the previous index value ΣD(N-1), is set to a value smaller than 1. η is a correction coefficient, which is set appropriately. As the decay coefficient γ and the correction coefficient η, values ​​that are determined in advance and stored in the memory 102 are used.

[0043] In this way, by expressing the occurrence and alleviation of salt concentration bias using the above-mentioned increase D(+) and decrease D(-), respectively, and calculating the current degradation index value ΣD(N), it is possible to properly grasp changes (increases and decreases) in high-rate degradation.

[0044] In this embodiment, a value (first threshold value TH1) is set in advance for the degradation index value ΣD(N) indicating that the bias in salt concentration has increased to a certain extent and that it is desirable to prevent further progression of high-rate degradation. When the degradation index value ΣD(N) exceeds the first threshold value TH1, the control device 100 executes a first elimination process to eliminate the high-rate degradation of the cell 31. Execution of the first elimination process eliminates the degradation caused by the bias in salt concentration, and the charge capacity of the cell 31 can be increased compared to before execution of the first elimination process.

[0045] However, when charging and discharging at a high rate, deterioration of the battery 30 may occur due to bias in the concentration distribution of lithium ions, as well as deterioration due to bias in the potential (hereinafter also referred to as potential unevenness) on the electrode surface (hereinafter referred to as "deterioration due to potential unevenness"). Potential unevenness occurs due to uneven resistance on the electrode surface caused by bias in the concentration distribution, etc. Therefore, even if the deterioration due to bias in the salt concentration of the lithium ion battery can be eliminated by the first elimination process, deterioration due to potential unevenness may remain.

[0046] FIG. 3 is a diagram showing an example of the relationship between the amount of unevenness after high-rate degradation and the number of days that have passed. The vertical axis of FIG. 3 shows the amount of unevenness after high-rate degradation. The horizontal axis of FIG. 3 shows the number of days that have passed. The "amount of unevenness" corresponds to the amount of power that cannot be charged due to potential unevenness (or the magnitude of SOC). LN1 in FIG. 3 shows the change in the amount of unevenness caused by the bias in potential when the cell 31 is left alone after high-rate degradation occurs. LN2 in FIG. 3 shows the change in the amount of unevenness caused by the bias in salt concentration when the cell 31 is left alone after high-rate degradation occurs. As shown in LN2 in FIG. 3, the amount of unevenness caused by the bias in salt concentration decreases (deterioration is resolved) as the number of days that have passed increases even without the first resolution process. On the other hand, as shown in LN1 in FIG. 3, the amount of unevenness caused by potential unevenness decreases (deterioration is resolved) as the number of days that have passed increases, but the rate of decrease is smaller than the rate of decrease in the amount of unevenness caused by the bias in salt concentration, making it difficult to resolve the deterioration.

[0047] Therefore, when the battery 30 including the cell 31 is replaced in another vehicle as a reused battery, the degree of deterioration may be perceived as greater than it actually is, or the recoverable capacity may not be grasped and the lifespan of the battery 30 may be mistakenly perceived as short.

[0048] Therefore, in this embodiment, the control device 100 acquires the deterioration index value ΣD(N) of the cell 31, and when there is a period during which the acquired deterioration index value ΣD(N) is less than the first threshold value TH1 and exceeds a second threshold value TH2 that is smaller than the first threshold value TH1, the control device 100 executes a second elimination process to eliminate deterioration due to potential unevenness.

[0049] More specifically, the control device 100 executes the second resolution process when the deterioration index value ΣD(N) is equal to or smaller than the first threshold value TH1 and has a history of changing from the initial value (zero) to exceed the second threshold value TH2. On the other hand, when the deterioration index value ΣD(N) exceeds the first threshold value TH1, the control device 100 executes the second resolution process. 1 After performing the resolution process, 2 The cancellation process will be carried out.

[0050] In this way, when there is a period during which the degradation index value ΣD(N) exceeds the second threshold value TH2, there is a possibility that degradation due to potential unevenness has occurred, and therefore the second elimination process is executed to eliminate the degradation due to potential unevenness. In this embodiment, the second threshold value TH2 is set to, for example, the same value as the initial value (i.e., zero) of the degradation index value ΣD.

[0051] An example of the process executed by the control device 100 will be described below with reference to Fig. 4. Fig. 4 is a flow chart showing an example of the process executed by the control device 100.

[0052] In step (hereinafter, step will be abbreviated as S) 100, the control device 100 determines whether or not an execution condition for the resolution process is met. The execution condition includes, for example, a condition that a request to execute the resolution process has been received. The control device 100 determines that a request to execute the resolution process has been received, for example, when an operator connects the charging / discharging device 10 and the cell 31 and receives an operation to execute the resolution process on the control device 100. If it is determined that the execution condition is met (YES in S100), the process is S102 will be transferred to.

[0053] In S102, the control device 100 determines whether or not there is a history of accumulation of the deterioration index value ΣD. The control device 100 determines that there is a history of accumulation of the deterioration index value ΣD when, for example, there is a history in which the value of the deterioration index value ΣD is a value other than the initial value. The control device 100 determines whether or not there is a history of accumulation by using the history of the deterioration index value ΣD received from the ECU 60. If it is determined that there is a history of accumulation of the deterioration index value ΣD (YES in S102), the process proceeds to S104.

[0054] In S104, control device 100 determines whether deterioration index value ΣD is greater than first threshold value TH1 or not. If it is determined that deterioration index value ΣD is greater than first threshold value TH1 (YES in S104), the process proceeds to S106.

[0055] In S106, the control device 100 executes a first resolution process. The first resolution process includes, for example, a process of causing a volume change in each of the positive electrode 37 and the negative electrode 38 of the cell 31.

[0056] The control device 100 executes, as a first resolution process, control of the charging / discharging device 10 so that the voltage V of the cell 31 falls within a predetermined voltage range including the peak voltage Vc, for example, by increasing or decreasing the voltage V of the cell 31 around the peak voltage Vc or by maintaining the voltage V near the peak voltage Vc.

[0057] The peak voltage Vc is a voltage value indicating the position of the main peak of the dQ / dV voltage characteristic line of the cell 31. The dQ / dV voltage characteristic line is a line indicating the relationship between the ratio dQ / dV of the change amount dQ of the stored amount Q of the cell 31 to the change amount dV of the voltage V of the cell 31, and the voltage V of the cell 31. The memory 102 of the control device 100 stores the dQ / dV voltage characteristic line and the peak voltage Vc. The control device 100 may receive the dQ / dV voltage characteristic line and the peak voltage Vc from the ECU 60. Note that the first resolution process is not limited to the above-mentioned process, and may be any known technique for resolving deterioration caused by the bias in salt concentration. When the first resolution process is executed, a volume change occurs such that the positive electrode 37 temporarily shrinks. Since the positive electrode 37 and the negative electrode 38 are in contact with each other, a volume change occurs in which the negative electrode 38 expands as the positive electrode 37 shrinks. When the negative electrode 38 expands, at least a portion of the excess electrolyte in the battery case 32 flows into the electrode body 36. This reduces the concentration unevenness of the electrolyte, and can eliminate deterioration caused by the bias in the salt concentration. Then, the process proceeds to S108.

[0058] In S108, the control device 100 measures the characteristic value (resistance) of the cell 31. For example, the control device 100 measures the resistance value of the cell 31 using a detection result obtained by the detection unit 40. A known technique may be used to measure the resistance of the cell 31, and a detailed description thereof will not be given. Thereafter, the process proceeds to S110.

[0059] In S110, the control device 100 executes a second resolution process. The second resolution process includes a process of discharging the voltage of the cell 31 until the voltage reaches a predetermined voltage at which the power of change that resolves the unevenness in potential increases. The control device 100 executes, as the second resolution process, for example, control of the charging / discharging device 10 to over-discharge the voltage of the cell 31 until it reaches the predetermined voltage. For example, the control device 100 controls the charging / discharging device 10 to discharge at a constant current, and over-discharges the cell 31 until the voltage of the cell 31 detected by the detection unit 40 reaches a predetermined voltage (for example, about 1.5 V). The predetermined voltage is, for example, a voltage corresponding to an SOC lower than the range of SOC used in a vehicle described later, and is set by experiment or the like to a voltage at which irreversible changes do not occur in the cell 31. The process then proceeds to S112.

[0060] In S112, the control device 100 determines whether the characteristic value of the cell 31 is within an allowable range. The characteristic value includes, for example, the resistance value of the cell 31. The allowable range is a preset range that is adapted through experiments or the like. If the control device 100 determines that the characteristic value of the cell 31 is within the allowable range (YES in S112), the process proceeds to S114.

[0061] In S114, control device 100 determines that cell 31 can be reused. Then, the process ends. On the other hand, if it is determined that the characteristic value of cell 31 is outside the allowable range (NO in S112), the process proceeds to S116.

[0062] In S116, the control device 100 determines that the cell 31 cannot be reused. Then, the process ends. If it is determined that the deterioration index value ΣD is equal to or smaller than the first threshold value TH1 (NO in S104), the process proceeds to S118.

[0063] In S118, the control device 100 executes a second resolution process. The second resolution process is similar to the second resolution process described in the process of S110. Therefore, detailed description thereof will not be repeated. The process then ends. Also, if it is determined that the execution condition is not satisfied (NO in S100) or if it is determined that there is no change history in the degradation index value ΣD (NO in S102), the process then ends.

[0064] The operation of the control device 100 based on the above-described structure and flowchart will be described with reference to FIGS. 5, 6, 7 and 8. FIG.

[0065] For example, when the battery 30 is removed from the vehicle 50, one of the multiple cells 31 constituting the battery 30 is electrically connected to the charging / discharging device 10, and the control device 100 is requested to execute the cancellation process, it is determined that the execution condition is met (YES in S100). In this case, it is determined whether or not there is a history of accumulation of the deterioration index value ΣD (S102). When it is determined that there is a history of accumulation of the deterioration index value ΣD from the history of the deterioration index value ΣD received from the ECU 60 (YES in S102), the control device 100 determines whether or not the deterioration index value ΣD is greater than a first threshold value TH1.

[0066] When it is determined that the deterioration index value ΣD is equal to or less than the first threshold value TH1 (NO in S104), a second resolution process is executed (S118). When the second resolution process is executed, the charge / discharge device 10 controls the discharge control at a constant current until the voltage of the cell 31 reaches a predetermined voltage (approximately 1.5 V).

[0067] When the cell 31 is discharged to about 1.5 V (hereinafter also referred to as deep discharge), the relationship between the SOC of the cell 31 and the potential of the negative electrode 38 (hereinafter referred to as the negative electrode potential) becomes such that the negative electrode potential fluctuates greatly with changes in the SOC.

[0068] Fig. 5 is a diagram showing an example of the relationship between SOC and negative electrode potential. The vertical axis of Fig. 5 represents the negative electrode potential. The horizontal axis of Fig. 5 represents the SOC. LN3 in Fig. 5 represents the change in negative electrode potential with respect to the change in SOC.

[0069] As shown in LN3 of Fig. 5, the relationship between the SOC and the negative electrode potential in a lithium ion battery is such that the lower the SOC, the higher the negative electrode potential. In particular, in the range of use in which the cell 31 is mounted on the vehicle 50 as the battery 30, for example, the amount of change ΔV1 in the negative electrode potential relative to the amount of change ΔSOC in the SOC of the cell 31 is smaller than the amount of change ΔV2 in the negative electrode potential relative to the amount of change ΔSOC in the SOC in a range lower than the range of use. Such an amount of change in the negative electrode potential relative to the change in SOC affects the ability to eliminate potential unevenness occurring on the electrode surface.

[0070] Fig. 6 is a diagram showing an example of the change in distribution of the negative electrode potential with respect to the position on the electrode surface. Fig. 6(A) shows an example of the distribution of the negative electrode potential with respect to the position on the electrode surface in the initial state (LN4). Fig. 6(B) shows an example of the distribution of the negative electrode potential with respect to the position on the electrode surface after high-rate degradation (LN5).

[0071] As shown in LN4 of FIG. 6, in the initial state, the negative electrode potential of the cell 31 is a constant value regardless of the position of the electrode surface. After high-rate degradation, the negative electrode potential of the cell 31 generates potential unevenness, and as shown in LN5 of FIG. 6, the negative electrode potential near the center of the electrode surface is lower than the negative electrode potential in the initial state, and the negative electrode potential near the end is higher than the negative electrode potential in the initial state. At this time, as shown by the arrow in (B) of FIG. 6, a changing force occurs in the direction in which the negative electrode potential increases near the center of the electrode surface, and a changing force occurs in the direction in which the negative electrode potential decreases near the end of the electrode surface. However, this changing force is smaller than the changing force occurring after the execution of the second solving process described later, so it takes a long time to solve the potential unevenness as described with reference to FIG. 3.

[0072] Fig. 7 shows an example of the distribution of the negative electrode potential with respect to the position of the electrode surface after the second resolution process is executed. LN6 in Fig. 7 shows the change in the negative electrode potential with respect to the change in the position of the electrode surface after the second resolution process is executed.

[0073] As shown in LN6 of Fig. 7, after the second resolution process is performed, the negative electrode potential near the center of the electrode surface is significantly lower than that of LN5 of Fig. 6 described above, and the negative electrode potential near the end of the electrode surface is significantly higher than that of LN5 of Fig. 6 described above. At this time, as shown by the arrows in Fig. 7, the force of change in the direction of increasing the negative electrode potential acts more strongly near the center of the electrode surface than that of LN5 of Fig. 6 described above, and the force of change in the direction of decreasing the negative electrode potential acts more strongly near the end of the electrode surface than that of LN5 of Fig. 6 described above. The force of change generated by the second resolution process acts until the potential unevenness is resolved, so that the potential unevenness is resolved in a shorter time than before the second resolution process was performed.

[0074] FIG. 8 is a diagram showing an example of the change in the amount of unevenness due to potential unevenness before and after various discharges. As described above, the "amount of unevenness" corresponds to the amount of power (or the magnitude of SOC) that cannot be charged due to potential unevenness. In the following description, the "amount of unevenness" is also referred to as the "amount of potential unevenness." FIG. 8A shows an example of the amount of potential unevenness after high-rate degradation and before the second resolution process is performed. FIG. 8B shows an example of the amount of potential unevenness after the discharge control is performed up to 3.0V. Furthermore, FIG. 8C shows an example of the amount of potential unevenness after the second resolution process is performed (i.e., after the discharge control is performed up to 1.5V). LN7 in FIG. 8 shows an example of the amount of potential unevenness in the initial state of cell 31.

[0075] As shown in Fig. 8C, after the second resolution process is performed, the amount of potential unevenness is reduced compared to the amount of potential unevenness before the discharge control shown in Fig. 8A. The amount of reduction in the amount of potential unevenness in this case is smaller than the amount of reduction in the amount of potential unevenness after the discharge control is performed to 3.0V shown in Fig. 8B, and is a value that reduces the amount of potential unevenness to approximately the same amount as the amount of potential unevenness in the initial state shown in LN7 in Fig. 8. In this way, by performing the second resolution process, it is possible to resolve the deterioration caused by the potential unevenness to the amount of potential unevenness in the initial state.

[0076] On the other hand, when it is determined that the deterioration index value ΣD exceeds the first threshold value TH1 (YES in S104), a first resolution process is executed (S106). By executing the first resolution process, for example, discharging is performed at a voltage around the peak voltage Vc in the above-mentioned dQ / dV voltage characteristic line, causing a volume change at the positive and negative electrodes and causing the electrolyte to flow in, thereby resolving the deterioration caused by the unevenness in the salt concentration. Thereafter, the resistance value of the cell 31 is measured (S108), and a second resolution process is executed (S110), and the deterioration caused by the unevenness in the potential is resolved. If the resistance value of the cell 31 is within the allowable range after the execution of the second resolution process, it is determined that the cell 31 can be reused (S114). Note that, if the resistance value of the cell 31 is outside the allowable range, it is determined that the cell 31 cannot be reused (S116).

[0077] By performing the above-mentioned process on all the cells 31 constituting the battery 30, it is possible to distinguish between cells that can be reused and cells that cannot be reused.

[0078] As described above, according to the battery processing system 2 of the present embodiment, when there is a history of the deterioration index value ΣD changing from the initial value, there is a possibility that deterioration due to biased potential on the electrode surface of the electrode body 36 has occurred, and therefore the second resolution process is executed to resolve the deterioration. Furthermore, when the deterioration index value ΣD is greater than the first threshold value TH1, the first resolution process is executed, and therefore the deterioration due to biased lithium ion concentration distribution can be resolved. Therefore, it is possible to provide a battery processing system and a battery processing method that resolve deterioration due to uneven potential.

[0079] Furthermore, since the second resolution process includes a process of overdischarging the cells 31 to a predetermined voltage, it is possible to cause a change in the electrode surface of the electrode body 36 that quickly resolves the bias in potential.

[0080] Furthermore, when the deterioration index value ΣD exceeds the first threshold value TH1, 1 After performing the resolution process, 2 Therefore, the second elimination process is performed to eliminate the deterioration caused by the bias of the potential on the electrode surface of the electrode body 36, and the first elimination process is performed to eliminate the deterioration caused by the bias of the concentration distribution.

[0081] Furthermore, since at least one of the active material of the positive electrode and the active material of the negative electrode contains a material capable of inserting and detaching lithium ions, the deterioration caused by the biased potential on the electrode surface of the electrode body 36 can be eliminated by performing the second elimination process.

[0082] Modifications will be described below. In the above embodiment, the control device 100 acquires the deterioration index value ΣD of the cells 31 constituting the battery 30 from the ECU 60, and executes the first or second cancellation process using the charging / discharging device 10 based on the acquired deterioration index value ΣD, but instead of the control device 100, the ECU 60 may execute the first or second cancellation process using a power conversion device (not shown) mounted on the vehicle 50 based on the deterioration index value ΣD. In this case, the vehicle 50 may have a circuit that individually charges or discharges any of the multiple cells 31 constituting the battery 30, or separates them from the charge / discharge target.

[0083] Furthermore, in the above embodiment, it has been described that at least the second resolution process is executed when there is a history of accumulation of the deterioration index value ΣD. However, it is sufficient that the second resolution process is executed when there is a period during which the deterioration index value ΣD exceeds the second threshold value TH2. 2 If the state is such that the difference is greater than the first resolution process, at least the second resolution process may be executed.

[0084] Furthermore, in the above embodiment, the second threshold value TH2 has been described as being zero, but it is not limited to being zero.

[0085] The above-described modified examples may be implemented in whole or in part in appropriate combination. The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0086] 2 battery processing system, 10 charging / discharging device, 30 battery, 31 cell, 32 battery case, 33 lid, 34 positive terminal, 35 negative terminal, 36 electrode body, 37 positive electrode, 38 negative electrode, 39 separator, 40 detection unit, 50 vehicle, 60 ECU, 100 control device, 101 processor, 102 memory.

Claims

1. A lithium ion battery having an electrode body; A control device for controlling charging and discharging of the lithium ion battery, The control device includes: obtaining an index value indicating a degree of deterioration of the lithium ion battery caused by a bias in the concentration distribution of lithium ions inside the electrode body; executing a first resolution process for resolving deterioration caused by the bias in the concentration distribution when the index value exceeds a first threshold value; A battery processing system that executes a second elimination process to eliminate deterioration caused by a bias in potential on the electrode surface of the electrode body due to discharging of the lithium ion battery when the index value is equal to or less than the first threshold value and there is a history of the index value changing from an initial value to exceed a second threshold value that is smaller than the first threshold value.

2. 2. The battery processing system according to claim 1, wherein the second cancellation process includes a process of over-discharging the lithium ion battery so that the lithium ion battery reaches a predetermined voltage.

3. The battery processing system according to claim 1 , wherein the control device executes the second resolution process after executing the first resolution process when the index value exceeds the first threshold value.

4. The electrode assembly includes a positive electrode and a negative electrode, The battery processing system according to claim 1 , wherein at least one of the positive electrode active material and the negative electrode active material includes a material capable of inserting and desorbing lithium ions.

5. A battery treatment method for eliminating deterioration of a lithium ion battery having an electrode body, comprising: acquiring an index value indicating a degree of deterioration of the lithium ion battery caused by a bias in the concentration distribution of lithium ions inside the electrode assembly; executing a first resolution process for resolving deterioration caused by the bias in the concentration distribution when the index value exceeds a first threshold value; and performing a second elimination process to eliminate deterioration caused by a bias in potential on the electrode surface of the electrode body due to discharging of the lithium ion battery when the index value is equal to or less than the first threshold value and there is a history of the index value changing from an initial value to exceed a second threshold value that is smaller than the first threshold value.

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