JP2021175340A - Status determination method and status determination device of secondary battery - Google Patents

Abstract

To provide a status determination method and a status determination device of a secondary battery to solve a problem that determination accuracy of remaining capacity difference of a battery module is insufficient in the conventional status determination method.SOLUTION: A status determination method according to the present invention includes: a discharging step (S2) for discharging a battery module to a determination charge rate range that fulfills a condition where a slope of changing in battery voltage with respect to an average charge rate becomes an average charge rate that is larger than the slope of the battery voltage with respect to the average charge rate in a range where the average charge rate is estimated to be 45% to 55%, and the average charge rate is not to be the average charge rate 0%; a relaxation speed calculation step (S3) for calculating a relaxation speed which is a speed of increase of the battery voltage when electrodes of the battery module are opened, in the battery module after completing the discharge step; and a determination step (S4) for determining that one or more of the plurality of cells are ;;defective when the relaxation speed measured in the relaxation speed calculation step is smaller than a preset determination threshold value.SELECTED DRAWING: Figure 3

Description

The present invention relates to, for example, a method for determining the state of a secondary battery and a state determining device for an assembled battery including a battery module to which a plurality of secondary batteries are connected.

In a vehicle battery pack in which a battery module in which a plurality of secondary battery cells are connected in series and further stacked and connected in series, the positive electrode capacity varies between the cells in the pack or the module due to the temperature variation. When such a variation occurs between cells, some cells are over-discharged during traveling, and the battery voltage output by the module decreases. Battery packs with such defects are recovered from the market, but such battery packs have only some defects in the cells and most of them can be reused. Therefore, Patent Document 1 proposes a method of selecting a defective battery module from a battery pack having variations between cells.

The deterioration determination device for a secondary battery described in Patent Document 1 determines the state of a battery module in which a plurality of single batteries are connected in series. The deterioration determination device of Patent Document 1 is a discharge circuit that discharges a battery module to a predetermined capacity, and a battery module having a predetermined capacity at a speed at which the voltage between the terminals rises after the terminals are opened. Based on the relaxation speed calculation unit that acquires a certain relaxation speed and the relaxation speed corresponding to the diffusion resistance portion from the acquired relaxation speeds, the specified relaxation speed is smaller than the preset determination threshold value. It is provided with a determination unit for determining that the remaining capacity varies among a plurality of single batteries as a deteriorated state of the battery module.

JP-A-2018-156759

In the deterioration determination device described in Patent Document 1, the battery module is discharged to a predetermined battery capacity, and it is determined whether or not there is a variation in the remaining amount among a plurality of single batteries based on the relaxation speed of the battery after discharge. However, the battery is characterized in that the relaxation speed differs depending on the discharge condition, but Patent Document 1 does not clarify the discharge condition. Due to such a difference in discharge conditions, in the deterioration determination device described in Patent Document 1, the range in which a battery module having a variation in remaining capacity between cells determined to be a non-defective product is determined to be a defective product becomes large. There's a problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the determination accuracy of the residual capacity difference determination of a battery module configured so that a plurality of secondary batteries are connected in series.

One aspect of the secondary battery status determination method of the present invention is a secondary battery status determination method for determining the status of a battery module configured by connecting a plurality of cells in series, and is determined to be a non-defective product. In the graph showing the relationship between the average charge rate of the battery module and the battery voltage, the average charge in the range in which the slope of the change in the battery voltage with respect to the average charge rate is estimated to be 45% to 55%. A discharge step of discharging the battery module to a determination charge rate range that satisfies a condition that the average charge rate is larger than the gradient of the battery voltage with respect to the rate and the average charge rate is not 0%, and the discharge. With respect to the battery module for which the process has been completed, the relaxation speed calculation step for calculating the relaxation speed, which is the rising speed of the battery voltage when the electrode of the battery module is opened, and the relaxation speed calculation step measured in the relaxation speed calculation step. It has a determination step of determining that one of the plurality of cells is defective when the relaxation speed is smaller than a preset determination threshold.

Further, one aspect of the secondary battery state determination method of the present invention is a secondary battery state determination method for determining the state of a battery module in which a plurality of cells are connected in series, and is an average of the battery modules. In the battery module whose charging rate is such that the variation in the remaining capacity of the plurality of cells is within the good product range, the recovery speed of the battery voltage within a preset determination period during the relaxation phenomenon of the battery voltage after the discharge is stopped. The electrodes of the battery module are opened for the discharge step of discharging the battery module until the relaxation speed is equal to or higher than the preset relaxation speed threshold and within the determination charge rate range, and for the battery module for which the discharge step has been completed. When the relaxation speed calculation step for measuring the relaxation speed and the relaxation speed measured in the relaxation speed calculation step are smaller than the preset determination threshold value, one of the plurality of cells is defective. It has a judgment process for judging.

Further, one aspect of the secondary battery status determination device of the present invention is a secondary battery status determination device for determining the status of a battery module configured by connecting a plurality of cells in series, and determining that the product is non-defective. In the graph showing the relationship between the average charge rate of the battery module and the battery voltage, the slope of the change in the battery voltage with respect to the average charge rate is in the range in which the average charge rate is estimated to be 45% to 55%. A discharge control unit that discharges the battery module to a determination charge rate range that is a condition that the average charge rate is larger than the gradient of the battery voltage with respect to the average charge rate and the average charge rate is not 0%. With respect to the battery module that has been discharged by the discharge control unit, a relaxation speed calculation unit that calculates the relaxation speed, which is the rate of increase of the battery voltage when the electrodes of the battery module are opened, and the relaxation speed calculation unit. It has a determination unit for determining that one of the plurality of cells is defective when the relaxation speed measured by the unit is smaller than a preset determination threshold value.

In the state determination method and the state determination device of the secondary battery of the present invention, the detection accuracy of the residual capacity variation among the cells of a plurality of cells is improved by setting the discharge conditions more strictly.

According to the state determination method and the state determination device for the secondary battery of the present invention, the defect determination accuracy of the battery module can be improved.

It is a block diagram of the state determination system which concerns on Embodiment 1. FIG. It is a figure explaining the variation of the remaining capacity in a battery module. It is a flowchart explaining the flow of the state determination method which concerns on Embodiment 1. FIG. It is a graph explaining the relationship between the battery capacity of a battery module, and a battery voltage. It is a graph explaining the voltage change during the voltage relaxation phenomenon in a battery module. It is a graph explaining the voltage at the time of polarization relaxation in a battery module. It is a figure explaining the relaxation rate constant in the state determination method which concerns on Embodiment 1. FIG. It is a graph explaining the relationship between the charge rate difference in a module, and the relaxation rate constant. It is a figure explaining the difference of the erroneous determination range between the state determination method which concerns on a reference example, and the state determination method which concerns on Embodiment 1. FIG. It is a figure explaining the determination charge rate range in the state determination method which concerns on Embodiment 1. FIG. It is a figure explaining the difference in the average remaining capacity at the time of discharge stop due to the difference in the discharge rate with respect to a battery module. It is a figure explaining the flow of the discharge process of the state determination method which concerns on Embodiment 2. FIG.

In order to clarify the explanation, the following description and drawings have been omitted or simplified as appropriate. In addition, each element described in the drawing as a functional block that performs various processes can be composed of a CPU, a memory, and other circuits in terms of hardware, and a program loaded in the memory in terms of software. It is realized by such as. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof, and is not limited to any of them. In each drawing, the same elements are designated by the same reference numerals, and duplicate explanations are omitted as necessary.

In addition, the programs described above can be stored and supplied to a computer using various types of non-transitory computer readable medium. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-temporary computer-readable media include magnetic recording media (eg, flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (eg, magneto-optical disks), CD-ROMs (Read Only Memory) CD-Rs, CDs. -R / W, including semiconductor memory (for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory)). The program may also be supplied to the computer by various types of transient computer readable medium. Examples of temporary computer-readable media include electrical, optical, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or a wireless communication path.

Embodiment 1
The state determination system 1 according to the first embodiment determines the state of the battery module included in the vehicle battery pack collected from the market, and determines whether or not the battery module is a non-defective product. More specifically, the battery module is one in which a plurality of single batteries are connected in series. Then, in the state determination system 1 according to the first embodiment, the battery module in which the variation in the remaining capacity among the plurality of cells included in the battery module is determined to be a certain amount or more is determined as a defective product.

FIG. 1 shows a block diagram of the state determination system according to the first embodiment. In the example shown in FIG. 1, the battery module 30 is shown as an inspection target. In the example shown in FIG. 1, the battery module 30 is formed by connecting six cells of the cells 30a to 30f in series. The number of single batteries included in the battery module 30 may be set as long as it is two or more.

In the state determination system 1 according to the first embodiment, the battery module 30 in which the remaining capacity difference between the cells included in the battery module 30 is a certain amount or more is detected as a defective product. Therefore, in the state determination system 1, the state determination device 10 is used. Further, the state determination device 10 uses a discharge circuit 20, an ammeter 21, and a voltmeter 22 for controlling and monitoring the charge state of the battery module 30. That is, the discharge circuit 20, the ammeter 21, and the voltmeter 22 can be regarded as a part of the state determination device 10.

The discharge circuit 20 discharges by drawing a current from the battery module 30. The magnitude and discharge time of the discharge current drawn by the discharge circuit 20 during discharge are controlled by the discharge control unit 12 in the state determination device 10. The ammeter 21 measures the measured value of the discharge current drawn from the battery module 30 by the discharge circuit 20 and gives it to the discharge control unit 12. The voltmeter 22 measures the voltage value of the battery voltage of the battery module 30 and gives it to the discharge control unit 12 and the relaxation speed calculation unit 13 of the state determination device 10.

The state determination device 10 includes a storage unit 11, a discharge control unit 12, a relaxation speed calculation unit 13, and a determination unit 14. The state determination device 10 is a device having an arithmetic processing unit capable of executing a program such as a computer. The discharge control unit 12, the relaxation speed calculation unit 13, and the determination unit 14 can also be implemented by a program. Further, the storage unit 11 is, for example, a non-volatile storage device such as a hard disk, and stores the values of the determination threshold value Sth and the discharge end voltage DS, which are determined in advance.

The discharge control unit 12 performs processing in the discharge process described later. In the graph showing the relationship between the average charge rate and the battery voltage of the battery module 30 determined to be a non-defective product (FIG. 4 described later), the discharge control unit 12 determines that the slope of the change in the battery voltage with respect to the average charge rate is the average charge rate. Judgment charge rate range that is a condition that the average charge rate is larger than the slope of the battery voltage with respect to the average charge rate in the range estimated to be 45% to 55%, and the average charge rate is not 0%. The battery module is discharged using the discharge circuit 20 until. From another viewpoint, the discharge control unit 12 determines that the average charge rate of the battery module 30 is the battery voltage after the discharge is stopped in the battery module 30 in which the variation in the remaining capacity of the plurality of single batteries is within the good product range. The value increases as the rate of battery voltage change within the preset determination period during the relaxation phenomenon increases. The relaxation rate constant is within the determination charge rate range that is equal to or greater than the preset relaxation rate threshold (for example, constant threshold). Discharge the battery module until. The details of the operation of the discharge control unit 12, the relaxation rate constant, the determination charge rate range, the determination threshold value, and the constant threshold value will be described later.

The relaxation speed calculation unit 13 performs processing in the relaxation speed calculation step. The relaxation rate calculation unit 13 calculates a relaxation rate constant whose value increases as the relaxation rate, which is the rate of increase of the battery voltage when the electrodes of the battery module are opened, increases for the battery module 30 for which the discharge process has been completed. .. As will be described in detail later, the relaxation rate constant is a value proportional to the relaxation rate.

The determination unit 14 determines that one of the plurality of cells is defective when the relaxation rate constant measured by the relaxation rate calculation unit 13 is smaller than the preset determination threshold value. Here, the defect of the battery module 30 is a state in which the difference in the remaining capacity between the plurality of cell cells included in the battery module 30 is a certain amount or more in the present embodiment, and the defect of the battery module 30 is a state of the plurality of cell cells. The difference in the remaining capacity between them is referred to as the difference in the charge rate in the module below.

Here, the charge rate difference in the module will be described in detail. Therefore, FIG. 2 shows a diagram for explaining the variation in the remaining capacity of the battery module. FIG. 2 shows a battery module 30 determined to be a non-defective product (upper figure of FIG. 2) and a battery module 30 determined to be a defective product (lower figure of FIG. 2). Further, in FIG. 2, the amount of electric power left as the remaining capacity is shown as a hatching region.

As shown in FIG. 2, in the battery module 30 determined to be a non-defective product, there is no large difference in the remaining capacities of the cells 30a to 30f, and even if the discharge progresses, no over-discharge state occurs in any of the cells. .. On the other hand, in the battery module 30 determined to be a defective product, the cell 30e has a smaller remaining capacity than the other cells. When the difference in charge rate in the module becomes large in this way, the cell 30e having a smaller remaining capacity than the other cell is emptied before the other cell, resulting in an over-discharged state.

When such over-discharging of some of the cells occurs, the battery voltage output by the battery module 30 decreases, which causes a problem. In the state determination system 1 according to the first embodiment, such a battery module 30 in which the remaining capacity of some cells is smaller than that of other cells is determined as a defective product. ..

In the battery module 30 having a large difference in the charging rate in the module and the battery module 30 having a small difference in the charging rate in the module, the voltage change during the voltage relaxation phenomenon that occurs after discharging when the average charging rate of the plurality of single batteries is low. There is a difference. Then, in the state determination system 1 according to the first embodiment, the average charge rate during the relaxation phenomenon between the battery module 30 having a large difference in the charge rate in the module and the battery module 30 having a small difference in the charge rate in the module becomes large. By measuring the voltage during the relaxation phenomenon within the range of, the defective battery module can be determined with higher accuracy. Hereinafter, the processing in the state determination system 1 according to the first embodiment will be described in detail.

Subsequently, the flow of the state determination method according to the first embodiment will be described in detail. FIG. 3 shows a flowchart for explaining the flow of the state determination method according to the first embodiment. As shown in FIG. 3, in the state determination method according to the first embodiment, the battery module 30 is taken out from the vehicle battery pack collected from the market, and the battery module 30 is inspected (step S1).

Next, a discharge step of performing a discharge process on the battery module 30 is performed (step S2). In this discharge step, the discharge control unit 12 performs discharge control, and details of this discharge control will be described later. Next, a relaxation rate calculation step of calculating the relaxation rate constant from the change in the battery voltage during the voltage relaxation phenomenon that occurs immediately after the end of the discharge process is performed (step S3). In this relaxation rate calculation step, the relaxation rate calculation unit 13 calculates the relaxation rate constant, and how to calculate the relaxation rate constant will be described later.

Next, the determination unit 14 performs a non-defective product determination step of comparing the relaxation rate constant calculated in the relaxation speed calculation step with a preset determination threshold value to determine whether or not the battery module 30 to be inspected is a non-defective product (step S4). ). In this non-defective product determination step, if the relaxation rate constant is equal to or greater than the determination threshold value, the battery module 30 is determined to be a non-defective product, and if the relaxation rate constant is smaller than the determination threshold value, the battery module 30 is determined to be a defective product. Then, the battery module 30 determined to be a non-defective product is determined to be reusable (step S5), and the battery module 30 determined to be a defective product is determined to be non-reusable (step S6).

Here, the discharge process will be described in more detail. First, FIG. 4 shows a graph for explaining the relationship between the battery capacity of the battery module and the battery voltage. In the graph shown in FIG. 4, the horizontal axis represents the average remaining capacity of the battery module 30, and the vertical axis represents the battery voltage of the battery module 30. As shown in FIG. 4, in the battery module 30, there is a plateau region in which the change in the battery voltage with respect to the average charge rate is small. Then, on each of the side where the average charge rate is higher and the side where the average charge rate is lower than the plateau region, there is a non-plateau region in which the voltage change with respect to the average charge rate is larger than that in the plateau region. In the state determination system 1 according to the first embodiment, the discharge is performed focusing on the non-plateau region on the side where the average charge rate is lower than the plateau region among the non-plateau regions.

The average remaining capacity in the present specification is the average remaining capacity measured in the battery module 30 determined to be a non-defective product. Even in the battery module 30 determined to be a defective product, discharge control is performed based on the average remaining capacity obtained in advance from this non-defective product.

Subsequently, the voltage relaxation phenomenon in the battery module 30 will be described. FIG. 5 shows a graph for explaining the voltage change during the voltage relaxation phenomenon in the battery module 30. As shown in FIG. 5, in the battery module 30, a voltage relaxation phenomenon occurs in which the battery voltage recovers after the discharge is stopped. This voltage relaxation phenomenon occurs due to the internal resistance of the cell and the parasitic capacitance of the positive electrode. Then, in the battery module 30, the rate at which the battery voltage recovers after the discharge is stopped due to the voltage relaxation phenomenon and the voltage after the recovery (for example, the voltage at the timing t3, which is the voltage at the timing t3, are as follows, due to the difference in the average remaining capacity when the discharge is stopped. , The voltage at the time of polarization relaxation is referred to as OCV.)

More specifically, when the average remaining capacity when the discharge is stopped is larger than the average remaining capacity (for example, the determination charge rate range) targeted in the first embodiment described below, the polarization relaxation voltage OCV becomes high. When it is reduced, the voltage OCV at the time of polarization relaxation becomes low (timing t3). Further, assuming that the timing t0 is the discharge stop time, the change in the battery voltage from the timing t1 in which the first time elapses from the timing t0 to the timing t2 in which the second time longer than the first time elapses from the timing t0. There is a difference in tilt. More specifically, when the average remaining capacity at the time of discharge stop is larger or smaller than the judgment charge rate range, the slope of the change in the battery voltage during the period t1 to t2 (hereinafter referred to as the judgment period). Is smaller than when the average remaining capacity is set as the determination charge rate range. The relaxation rate constant, which will be described later, has a feature that the larger the slope of the battery voltage during the determination period, the smaller the relaxation rate constant.

Moreover, the voltage relaxation phenomenon will be described from another viewpoint. FIG. 6 shows a graph for explaining the voltage during polarization relaxation in the battery module. In the graph shown in FIG. 6, the horizontal axis represents the average remaining capacity of the battery module 30 after discharge, and the vertical axis represents the battery voltage of the battery module 30. As shown in FIG. 6, the difference voltage between the battery voltage after the end of discharge and the polarization relaxation voltage OCV differs depending on the average remaining capacity. Further, FIG. 6 also shows the battery voltages at the timings t1 and t2 shown in FIG. Looking at the difference voltage between the timings t1 and t2, there is also a difference depending on the average remaining capacity, and the voltage difference between the timings t1 and t2 is the largest under the condition near the center of FIG. The place where the voltage difference between the timings t1 and t2 is the largest is the condition within the range of the determination charge rate range targeted by the first embodiment described with reference to FIG.

Next, the relaxation rate constant will be described. Therefore, FIG. 7 shows a diagram for explaining the relaxation rate constant in the state determination method according to the first embodiment. FIG. 7 shows a graph of the battery voltage change from the discharged state to the state where the discharge is stopped, an enlarged view of the battery voltage change graph of the region A, and a graph of the relaxation rate constant.

Looking at the voltage change graph from the discharged state to the state after the discharge is stopped, the battery voltage drops due to the discharge, and the voltage relaxation phenomenon occurs immediately after the discharge is stopped and the battery voltage rises. Then, in FIG. 7, a graph is shown for both a non-defective product and a defective product. Looking at the voltage change graph from the discharged state to the state after discharge suspension, the voltage OCV at the time of relaxation is almost the same between the non-defective product and the defective product because of the good culture after the voltage relaxation phenomenon.

On the other hand, the period in which the battery voltage rises from the time when the discharge is stopped is defined as the region A, and an enlarged view of the portion of the region A is shown as an enlarged view of the battery voltage change graph of the region A. With reference to the battery voltage change graph in this region A, it can be seen that there is a difference in the voltage change up to the polarization relaxation voltage OCV between the non-defective product and the defective product. Specifically, the defective battery module 30 has a faster voltage rise rate during the voltage relaxation phenomenon than the non-defective battery module 30. Then, the inclination of the battery voltage of the non-defective battery module 30 is larger than that of the defective battery module 30 between the non-defective product and the defective product in the determination period between the timings t1 and t2.

Then, the graph of the relaxation rate constant a for this region A is referred to. In the graph of the relaxation rate constant, the horizontal axis is 1 / square root (1 / √ hours) of the elapsed time from the time when the discharge is stopped, and the vertical axis is the battery voltage. The relaxation rate constant a is smaller for defective products in which the slope of the change in battery voltage with time is steep. In the example shown in FIG. 7, the slope α of the non-defective product is larger than the slope β of the defective product. Then, the relaxation rate constant is calculated from this inclination. In the first embodiment, the relaxation rate constant is calculated based on the relaxation rate between the timings t1 to t2. Therefore, in the first embodiment, the relaxation rate constant is proportional to the magnitude of the relaxation rate.

A method for calculating the relaxation rate constant will be described more specifically. The relaxation speed calculation unit 13 first calculates the amount of change in the battery voltage per hour within the determination period set after the discharge is stopped as the relaxation speed [V / s]. Then, the relaxation rate calculation unit 13 calculates the relaxation rate constant a based on the relationship between the battery voltage and 1 / square root (1 / √t) of the length of the determination time. The relaxation rate constant a is a constant derived from Eq. (1) when the length of the determination period is t and the voltage change is ΔE (t _2- t _1).

Here, I is the discharge current, τ is the current application time, n is the number of electrons involved in the reaction, Vm is the molar volume, F is the Faraday constant, A is the reaction surface area, and dE / dy is the slope of the battery voltage during the determination period. D is the diffusion coefficient.

Subsequently, the relaxation rate constant a and the difference in the charge rate in the module will be described. FIG. 8 shows a graph for explaining the relationship between the charge rate difference in the module and the relaxation rate constant. In FIG. 8, in addition to the relaxation rate constant a calculated in the state determination method according to the first embodiment, a graph of the relaxation rate constant a according to the comparative example is also shown. As described in Patent Document 1, the reference example is calculated from the voltage change measured after discharging until the average charge rate becomes close to 0%.

As shown in FIG. 8, the relaxation rate constant a becomes larger as the difference in charge rate in the module is smaller. Then, in the state determination method according to the first embodiment, the slope of the relaxation rate constant a with respect to the difference in the charge rate in the module becomes large. By increasing the slope of the relaxation rate constant a with respect to the difference in charge rate in the module in this way, the range in which erroneous determination occurs can be reduced.

Therefore, FIG. 9 shows a diagram for explaining the difference in the erroneous determination range between the state determination method according to the reference example and the state determination method according to the first embodiment. Also in FIG. 9, the reference example described in FIG. 8 is shown as a comparative example of the state determination method according to the first embodiment. As shown in FIG. 9, when the state is determined, the confidence interval upper limit value and the confidence interval lower limit value are set with respect to the median value which is the ideal curve of the relaxation rate constant a in consideration of the measurement error. Then, the determination threshold value Sth for the relaxation rate constant a is set so that the defective product is not overlooked with respect to the confidence interval upper limit value, which is the worst condition. The determination unit 14 determines that the product is defective if the relaxation rate constant a is smaller than the determination threshold value Sth, and determines that the product is good if the relaxation rate constant a is equal to or greater than the determination threshold value Sth.

Then, referring to FIG. 9, even when the margin of the reliability section having the same width is secured by increasing the slope of the relaxation rate constant a with respect to the difference in the charge rate in the module, the first embodiment is more than the comparative example. However, the erroneous judgment range becomes smaller. Here, in order to increase the difference in the charge rate in the module of the relaxation rate constant a, the charge rate at which the discharge is stopped and the discharge condition have a great influence. Therefore, the charging rate and the discharging conditions for suspending the discharging will be described in detail below.

FIG. 10 shows a diagram illustrating a determination charge rate range in the state determination method according to the first embodiment. The graph shown in FIG. 10 is a plot of the relaxation rate constant a with respect to the average remaining capacity of the battery module 30 for the battery module 30 determined to be a non-defective product. As shown in FIG. 10, the relaxation rate constant a is higher than the case where the average remaining capacity is in the range of 1% to 3% and becomes another average remaining capacity. Therefore, when increasing the slope of the relaxation rate constant a with respect to the difference in the charging rate in the module, it is preferable to set the discharge end voltage DS in which the average remaining capacity is about 1% to 3%. In the following description, the range in which the average remaining capacity shown in FIG. 10 is 1% to 3% is referred to as a determination charge rate range. Regarding the range of the average remaining capacity for stopping the discharge, the relaxation speed threshold value (for example, the constant threshold value) shown in the graph shown in FIG. 10 is determined in the stage before the actual state determination process and set based on the constant threshold value. do.

Subsequently, the discharge rate in the discharge step and the temperature of the battery module 30 to be subjected to the state determination process will be described. Therefore, FIG. 11 shows a diagram for explaining the difference in the average remaining capacity when the discharge is stopped due to the difference in the discharge rate with respect to the battery module. As shown in FIG. 11, when the discharge rate is set low (when the discharge current is reduced), the average remaining capacity of the battery module 30 determines the lower limit of the determined charge rate range when the battery voltage reaches the discharge end voltage DS. Below. This tendency becomes even more remarkable when the discharge rate is low and the temperature of the battery module 30 at the start of discharge is set to a high temperature. On the other hand, when the discharge rate is set high (when the discharge current is increased), the average remaining capacity of the battery module 30 exceeds the upper limit of the determined charge rate range when the battery voltage reaches the discharge end voltage DS. This tendency becomes even more remarkable when the discharge rate is high and the temperature of the battery module 30 at the start of discharge is set to a low temperature. For this reason, it is important to appropriately set the discharge rate and the temperature of the battery module 30 at the start of discharge.

Here, the appropriate discharge conditions are such that the discharge rate is C / 3 to 7C, the temperature of the battery module 30 at the start of discharge is about 10 ° C to 60 ° C, and more preferably the discharge rate is C / 2 to 5C. The temperature of the battery module 30 at the start of discharge is about 20 ° C to 50 ° C. It can be seen that the relaxation rate constant a having a good inclination can be obtained by setting such a discharge condition.

From the above description, in the state determination method according to the first embodiment, the average remaining capacity at the time of discharge stop is the average charge rate in the graph showing the relationship between the average charge rate of the battery module 30 determined to be a non-defective product and the battery voltage. The determined charge rate range is such that the gradient of the change in the battery voltage with respect to the relative is larger than the gradient of the battery voltage with respect to the average charge rate in the range in which the average charge rate is estimated to be 45% to 55%. From another point of view, in the state determination method according to the first embodiment, the average remaining capacity at the time of stopping the discharge, the average charge rate of the battery module 30, and the variation in the remaining capacity of the plurality of single batteries are within the good product range. In the battery module to be used, the relaxation rate constant (for example, the relaxation rate constant) in which the value becomes smaller as the rate of change in the battery voltage within the preset determination period during the relaxation phenomenon of the battery voltage after the discharge is stopped increases (for example). , Constant threshold) or more. As a result, in the state determination method according to the first embodiment, the inclination of the relaxation rate constant a with respect to the difference in the charge rate in the module can be increased, and the erroneous determination range can be reduced. Then, by setting the determination charge rate range to a range in which the average remaining capacity is 1% to 3%, the slope of the relaxation rate constant a can be further increased.

Further, in the state determination method according to the first embodiment, the average remaining capacity at the time of stopping the discharge is more reliably set to the average remaining capacity by appropriately setting the discharge rate and the temperature of the battery module 30 at the start of the discharge. be able to. That is, by appropriately setting the discharge rate and the temperature of the battery module 30 at the start of discharge, the accuracy of the inclination of the relaxation rate constant a with respect to the difference in the charge rate in the module can be further improved.

Embodiment 2
In the second embodiment, another embodiment of the discharge process will be described. Therefore, FIG. 12 shows a diagram for explaining the flow of the discharge process of the state determination method according to the second embodiment. As shown in FIG. 12, in the second embodiment, the average remaining capacity of the battery module 30 is set as the determination charge rate range through the two-step discharge process.

More specifically, in the discharge process according to the second embodiment, the discharge is performed by three steps of a first discharge step, a voltage relaxation step, and a second discharge step. In the first discharge step, the battery module 30 is discharged with a predetermined amount of fast discharge current up to an average charge rate higher than the determined charge rate range. In the voltage relaxation step, after the first discharge step is stopped, the discharge to the battery module is stopped to relax the battery voltage of the battery module 30. In the second discharge step, after the voltage relaxation step, the battery module is discharged to the determination charge rate range with a discharge current smaller than the rapid discharge current in the first discharge step. The discharge current in this second discharge step is preferably within the appropriate range shown in FIG. 11 (discharge rate is C / 2 to 5C, discharge start temperature is 20 ° C to 50 ° C).

In the discharge method according to the second embodiment, the time required for the state determination process can be shortened by increasing the discharge rate by the first discharge process.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit. For example, in the above embodiment, the relaxation rate is converted into the relaxation rate constant, and the defect of the battery module is determined, but it is not necessary to convert the relaxation rate into the relaxation rate constant.

1 Status judgment system 10 Status judgment device 11 Storage unit 12 Discharge control unit 13 Relaxation speed calculation unit 14 Judgment unit 20 Discharge circuit 21 Ammeter 22 Voltmeter 30 Battery module 30a Single battery Sth Judgment threshold DS Discharge end voltage

Claims (8)

This is a method for determining the status of a secondary battery, which determines the status of a battery module composed of a plurality of cells connected in series.
In the graph showing the relationship between the average charge rate and the battery voltage of the battery module determined to be a non-defective product, the slope of the change in the battery voltage with respect to the average charge rate is estimated to be 45% to 55% for the average charge rate. Discharge that discharges the battery module to a determination charge rate range that satisfies the condition that the average charge rate is larger than the gradient of the battery voltage with respect to the average charge rate in the range and the average charge rate is not 0%. Process and
With respect to the battery module for which the discharge step has been completed, a relaxation rate calculation step for calculating a relaxation rate, which is an increase rate of the battery voltage when the electrodes of the battery module are opened, and a relaxation rate calculation step.
A determination step of determining that one of the plurality of cells is defective when the relaxation rate measured in the relaxation rate calculation step is smaller than a preset determination threshold value.
A method for determining the state of a secondary battery having. In the relaxation speed calculation step, based on the relaxation speed, it is determined in advance during the measurement time in a graph in which 1 / square root of the measurement time of the relaxation speed is on the horizontal axis and the battery voltage during the measurement time is on the vertical axis. The relaxation speed constant, which is the slope of the battery voltage between the first time and the second time, is calculated.
The method for determining the state of a secondary battery according to claim 1, wherein in the determination step, the quality of the plurality of single batteries is determined using the relaxation rate constant. The secondary according to claim 2, wherein the first time and the second time are set between the time after the discharge treatment for the battery module and the time until the polarization relaxation phenomenon generated after the discharge treatment converges. Battery status determination method. The method for determining the state of a secondary battery according to any one of claims 1 to 3, wherein the discharging step is performed in a state where the average charge rate of the battery module determined to be a non-defective product is between 1% and 3%. .. The discharge step is
A first discharge step of discharging the battery module with a predetermined amount of fast discharge current up to an average charge rate higher than the determined charge rate range.
A voltage relaxation step of stopping the discharge to the battery module after the first discharge step is stopped to relax the battery voltage of the battery module.
A second discharge step of discharging the battery module to the determined charge rate range with a discharge current amount smaller than the rapid discharge current amount after the voltage relaxation step.
The method for determining the state of a secondary battery according to any one of claims 1 to 4. It is a method of determining the state of a secondary battery that determines the state of a battery module in which a plurality of cells are connected in series.
The average charge rate of the battery module is within a preset determination period during the relaxation phenomenon of the battery voltage after the discharge is stopped in the battery module in which the variation in the remaining capacity of the plurality of cells is within the non-defective range. A discharge step of discharging the battery module until the relaxation speed, which is the recovery speed of the battery voltage, reaches the determination charge rate range in which the relaxation speed is equal to or higher than the preset relaxation speed threshold.
With respect to the battery module for which the discharge step has been completed, a relaxation speed calculation step of measuring the relaxation speed with the electrodes of the battery module open, and a relaxation speed calculation step.
A determination step of determining that one of the plurality of cells is defective when the relaxation rate measured in the relaxation rate calculation step is smaller than a preset determination threshold value.
A method for determining the state of a secondary battery having. The method for determining a state of a secondary battery according to claim 6, wherein the determination period is set between the time after the discharge process for the battery module and the time until the polarization relaxation phenomenon generated after the discharge process converges. A secondary battery status determination device that determines the status of a battery module configured by connecting multiple cells in series.
In the graph showing the relationship between the average charge rate and the battery voltage of the battery module determined to be a non-defective product, the slope of the change in the battery voltage with respect to the average charge rate is estimated to be 45% to 55% for the average charge rate. Discharge that discharges the battery module to the determination charge rate range, which is a condition that the average charge rate is larger than the gradient of the battery voltage with respect to the average charge rate in the range and the average charge rate is not 0%. Control unit and
With respect to the battery module that has been discharged by the discharge control unit, a relaxation speed calculation unit that calculates a relaxation speed that is an increase speed of the battery voltage when the electrodes of the battery module are opened, and a relaxation speed calculation unit.
When the relaxation speed measured by the relaxation speed calculation unit is smaller than the preset determination threshold value, the determination unit determines that one of the plurality of cells is defective.
Secondary battery status determination device having.

Images