JP2021089140A - Deterioration degree measuring device for secondary batteries - Google Patents

Abstract

To provide a secondary battery deterioration degree measuring device that easily and accurately estimates the deterioration index of a secondary battery unit composed of a plurality of single batteries.SOLUTION: A secondary battery system 1 that measures the degree of deterioration of an assembled battery 4 configured by connecting a plurality of cells 4n in series, includes: a voltage sensor 7 that measures the voltage of each of multiple cells 4n; a discharge completion detection unit 19 that detects the existence of a cell battery that has dropped below a predetermined specified voltage Va among multiple cells 4n; a cell identification unit 14 that identifies a specific cell that first drops below the specified voltage Va among multiple cells 4n, when the discharge completion detection unit 19 detects that one of multiple cells 4n has dropped to the specified voltage Va or less; and an SOH estimation unit 16 that, after charging the assembled battery 4, estimates an SOH of the specific cell specified by the cell identification unit 14, and calculates the SOH of the specified cell as the SOH of the assembled battery 4 as a whole.SELECTED DRAWING: Figure 4

Description

The present invention relates to a deterioration degree measuring device for a secondary battery, and more particularly to a technique for estimating a deterioration index of a secondary battery unit composed of a plurality of single batteries.

SOH (State Of Health), which is the ratio of the current full charge capacity to the full charge capacity of a new battery, is widely known as a deterioration index indicating the degree of deterioration of the secondary battery.
This deterioration index SOH can be obtained, for example, by charging the secondary battery from a state where the remaining battery capacity is 0 to full charge, measuring the actual full charge capacity, and dividing by the full charge capacity at the time of new product. However, in order to estimate the deterioration index, it is necessary to charge the battery from the state where the remaining battery capacity is 0 to the full charge, and there is a problem that the time required for the estimation becomes significantly long.

Therefore, various methods have been proposed for estimating the deterioration index of the secondary battery while suppressing the time required for estimation. For example, from the voltage value of the feature point appearing on the differential curve V-dQ / dV within the range of the predetermined battery voltage V, specifically, the voltage value of the maximum point which is the apex part of the peak shape, the capacity which is the deterioration index of the secondary battery. The rate of decrease is sought (Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-19709

However, in the technique disclosed in Patent Document 1, since the voltage of a secondary battery unit including a plurality of secondary batteries (hereinafter referred to as a cell) is measured, the battery capacity of each cell is increased. Variations are not taken into account. That is, the fully charged capacity of the entire secondary battery unit having a plurality of single batteries after deterioration is such that one of the plurality of single batteries starts charging from the state where the remaining battery capacity is 0, and among the plurality of single batteries. Since it is the amount of charge when any one of them is charged until it is fully charged, it is difficult to easily and accurately estimate the SOH of the entire secondary battery unit.

The present invention has been made in view of such a problem, and an object of the present invention is to easily and accurately estimate the deterioration index of a secondary battery unit composed of a plurality of single batteries. The purpose of the present invention is to provide a battery deterioration degree measuring device.

In order to achieve the above object, the secondary battery deterioration degree measuring device of the present invention is a secondary battery deterioration degree measuring device for measuring the deterioration degree of a secondary battery unit configured by connecting a plurality of single batteries. Of the voltage sensor that measures the voltage of each of the plurality of cells and the plurality of cells measured by the voltage sensor when the secondary battery unit is discharged, the voltage falls below a predetermined specified voltage. When the discharge completion detection unit that detects the presence of a lowered cell and the discharge completion detection unit detects that one of the plurality of cells has reached the specified voltage, the plurality of units are said to be present. The deterioration index of the specific cell is estimated by first estimating the cell specific part that identifies the specific cell that has dropped below the specified voltage and the deterioration index of the specific cell specified by the cell specific part. Is provided with a deterioration index estimation unit that calculates the deterioration index of the secondary battery unit.

As a result, among the plurality of cells, the specific cell that first drops below the specified voltage when the secondary battery unit is discharged is identified, and the deterioration index estimation unit estimates the deterioration index of the specific cell. Since the deterioration index of the specific cell is calculated as the deterioration index of the secondary battery unit, it is not necessary to estimate the SOH of all the cells, and the SOH of the entire secondary battery unit can be estimated.

Moreover, it is preferable that the designated voltage is the discharge completion voltage of the cell.
As a result, when the deterioration index estimation unit estimates the deterioration index of the specific cell, the specific cell can be specified by discharging to the discharge completion voltage.
Further, preferably, the specified voltage is such that when the secondary battery unit is further discharged than when the specific cell has reached the specified voltage, the specific cell among the plurality of cell cells is completely discharged. It is preferable to set the value higher than the discharge completion voltage in the range where the voltage drops earliest.

As a result, when the deterioration index estimation unit estimates the deterioration index of the specific cell, the specific cell can be specified by discharging to a designated voltage higher than the discharge completion voltage. This makes it possible to estimate the deterioration index of the secondary battery unit in a short time by estimating the deterioration index of the specific cell.
Further, preferably, the present sensor for measuring the input / output current of each of the plurality of single batteries is provided, and the deterioration index estimation unit charges the voltage sensor and the secondary battery unit detected by the current sensor. It is advisable to estimate the deterioration index of the specific cell based on the changes in the voltage and the input / output current of the specific cell.

As a result, it is not necessary to charge the specific cell from the fully discharged state to the fully charged state, and the deterioration index of the specific cell can be easily estimated in a short time.
Further, preferably, the deterioration index estimation unit is a ratio of the voltage V of the specific cell and the change dV of the voltage V of the specific cell to the change dQ of the battery capacity Q of the specific cell. The deterioration index of the specific cell may be estimated based on the voltage V of the feature point on the differential curve V-dV / dQ showing the relationship with / dQ.

This makes it possible to estimate the deterioration index of the specific cell at an early stage based on the changes in the voltage and the input / output current.
Further, preferably, the deterioration index estimation unit is a ratio of the voltage V of the specific cell and the change dQ of the battery capacity Q of the specific cell to the change dV of the voltage V of the specific cell. The deterioration index of the specific cell may be estimated based on the voltage V of the feature point on the differential curve V-dQ / dV showing the relationship with / dV.

This makes it possible to estimate the deterioration index of the specific cell at an early stage based on the changes in the voltage and the input / output current.

According to the deterioration degree measuring device of the secondary battery of the present invention, when the secondary battery unit is discharged, the specific cell that first drops below the specified voltage is identified, and the deterioration index estimation unit deteriorates the specific cell. Since the index is estimated and the deterioration index of the specific cell is calculated as the deterioration index of the secondary battery unit, it is not necessary to measure the deterioration index of all the batteries, and the deterioration index varies among a plurality of batteries. Even if there is, the deterioration index of the entire secondary battery unit, that is, the degree of deterioration of the entire secondary battery unit can be easily and accurately estimated.

It is a schematic block diagram which shows the secondary battery system of this embodiment. It is a graph which shows an example of the charge capacity at the time of completion of discharge of each cell. It is a graph which shows an example of the charge capacity at the time of completion of charging of each cell. It is a characteristic figure which shows an example of the differential curve V−dV / dQ. It is a flowchart which showed the deterioration index estimation control procedure which concerns on this embodiment. It is a graph which shows an example of the relationship between the measurement result of SOH of a cell and the SOH of an assembled battery.

Hereinafter, an embodiment of a secondary battery system that embodies the present invention will be described.
FIG. 1 is a schematic configuration diagram showing a secondary battery system of the present embodiment.
The secondary battery system 1 of the present embodiment is mounted on an electric vehicle and supplies electric power to a traveling motor which is a traveling power source. As a whole, the secondary battery system 1 is composed of a main controller 2 for integrated control of the entire secondary battery system 1 and a battery pack 20 (secondary battery unit). The battery pack 20 is composed of a plurality of secondary battery modules 3 connected in parallel to the main controller 2.

The secondary battery module 3 is composed of an assembled battery 4, a sub controller 5, and a charge / discharge control unit 6.
The assembled battery 4 is configured by combining a plurality of cell cells 4n in parallel and in series in order to achieve the desired battery capacity and output voltage. The assembled battery 4 of the present embodiment contains LiMn2O4 and LiMO2 (M is a transition metal element containing at least one of Co, Ni, Al, Mn, and Fe) in its positive electrode plate.

A voltage sensor 7, a current sensor 8, and a temperature sensor 9 are connected to the assembled battery 4. The voltage sensor 7 detects the battery voltage V of each of the cell 4n constituting the assembled battery 4, the current sensor 8 detects the input / output current I of each of the cell 4n, and the temperature sensor 9 detects the temperature T of each cell 4n. Are detected, and the detection information thereof is input to the sub-controller 5.
The sub-controller 5 is composed of an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs, control maps, etc., a central processing unit (CPU), a timer counter, and the like. The sub-controller 5 has a function of driving the charge / discharge control unit 6 to control the charge / discharge of the assembled battery 4, and in the charge / discharge control, the maximum allowable current according to the deterioration index (degree of deterioration) of the assembled battery 4. And adjust the maximum permissible voltage. In this embodiment, SOH (State Of Health), which is the ratio of the current full charge capacity to the full charge capacity at the time of a new product, is used as the deterioration index of the assembled battery 4.

The charge / discharge command unit 11 outputs a charge / discharge control command to the sub-controller 5 of each secondary battery module 3 via the input / output unit 12 based on the SOH estimated by the SOH estimation unit 16 described later. For example, for the secondary battery module 3 in which the SOH estimated to be less than a predetermined value is estimated, a command for limiting the maximum allowable current and the maximum allowable voltage during charging / discharging is output. Charge / discharge control by the sub-controller 5 based on this command protects the assembled battery 4 that has deteriorated.

Further, the charge / discharge command unit 11 displays the vehicle on the display unit 18 provided in the driver's seat when it is estimated that the SOH of any of the unit batteries 4n in the assembled battery 4 is less than the life limit. Display a message prompting for inspection. As a result, the vehicle is inspected at the sales company or the like, and the assembled battery 4 is replaced if necessary.
On the other hand, like the sub controller 5, the main controller 2 has an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs, control maps, etc., a central processing unit (CPU), a timer counter, and the like. It is composed of.

The main controller 2 includes an input / output unit 12, a data storage unit 13, and a SOH estimation unit 16 (deterioration index estimation unit).
The data storage unit 13 stores the actually measured data input from the sub-controller 5 of each secondary battery module 3 via the input / output unit 12. Further, in the data storage unit 13, data showing the correlation between the specific feature points on the differential curve V−dV / dQ and the SOH of the assembled battery 4 (hereinafter referred to as reference data) is stored in advance for each temperature range. ing.

The process of creating the reference data is as follows.
First, a deterioration test of a cell battery of the same standard as the cell battery 4n of the present embodiment is carried out, and charging and discharging of an unused cell cell are repeated to gradually deteriorate the battery until the life limit is reached. At each SOH in the deterioration process, the cell is charged and discharged under a plurality of different temperature ranges.
Then, when the cell is charged or discharged, the battery capacity Q of the cell is sequentially calculated at predetermined time intervals, and the battery voltage V is acquired in synchronization with this. In this way, the differential value dV / dQ is calculated based on the battery voltage V and the battery capacity Q obtained by charging / discharging, and the differential curve V−dV / dQ showing the relationship between the battery voltage V and the differential value dV / dQ is obtained. After calculation, the positions (V, dV / dQ) of specific feature points appearing on the differential curve V−dV / dQ are obtained. The feature point may be, for example, the midpoint of two peaks appearing on the differential curve V−dV / dQ within a predetermined range of the battery voltage V. As a result, the correlation between the specific feature points and the SOH of the assembled battery 4 is determined for each temperature range, and is stored in advance in the data storage unit 13 as common reference data for each secondary battery module 3.

The SOH estimation unit 16 includes a differential curve calculation unit 10, a cell identification unit 14, and a discharge completion detection unit 19.
The unit cell specifying unit 14 specifies a specific cell battery 4m that estimates SOH from all the cell cells 4n.
2 and 3 are explanatory views of a method for specifying a specific cell. For example, when the assembled battery 4 is configured by connecting three cells 4a, 4b, and 4c in series, FIG. 2 shows the charge capacity (battery capacity Q) at the completion of discharging each of the cells 4a, 4b, and 4c. ), And FIG. 3 is a graph showing the charging capacities of the cells 4a, 4b, and 4c when charging is completed. In FIGS. 2 and 3, the shaded areas indicate the charging capacities of the cells 4a, 4b, and 4c, and the height of the entire bar graph indicates the full charging capacity of the cells 4a, 4b, and 4c. Further, the upward-sloping shaded portion is the charge capacity when the voltage of any one cell 4n becomes the discharge completion voltage V1 or less, and the voltage of any one cell 4n becomes the full charge voltage from that point. The charge capacity increased by the time it is reached is indicated by the downward-sloping shaded area. The charging capacity Q1 shown in FIGS. 2 and 3 corresponds to the charging capacity when the voltage of the cell 4n reaches the discharge completion voltage V1.

The cells 4n may have different degrees of deterioration SOH, and therefore the full charge capacities of the cells 4n may differ from each other. FIGS. 2 and 3 show cell batteries 4a, 4b, and 4c having different full charge capacities.
As shown in FIG. 2, when the voltage of any one of the cells 4n becomes the discharge completion voltage V1 or less, the discharge of the assembled battery 4 is completed. In FIG. 2, the cell 4a has a discharge completion voltage V1. At this time, the voltage of another cell, for example, the cell 4b or 4c, becomes a value higher than the discharge completion voltage V1. Then, when charging of the assembled batteries 4, that is, charging of all the cells 4a to 4c is started from such a discharge completed state, each of the cells 4a, 4b, and 4c connected in series are charged evenly, that is, all of them. The capacity increases by the same amount. Then, when any one of the cells reaches the full charge voltage, charging is completed. In FIG. 3, the cell 4a has a full charge capacity, that is, the cell 4a has reached the full charge voltage.

In this way, when any one of the plurality of cells 4n becomes the discharge completion voltage V1 or less, the charging of all the cells 4n is completed by the discharge completion voltage V1 of all the cells 4n. This is to prevent the generation of a cell that is less than, that is, over-discharged. Further, when any one of the plurality of cells 4n exceeds the full charge voltage, the charging of all the cells 4n is completed at the voltage exceeding the full charge voltage of all the cells 4n. That is, it is for preventing the generation of a single battery that becomes overcharged.

In the present embodiment, among the plurality of cell batteries 4n at the time of discharging, the cell battery that first reaches the discharge completion voltage V1, for example, the assembled battery 4 composed of the cell batteries 4a, 4b, and 4c shown in FIGS. In, the cell 4a is a specific cell 4m.
The differential curve calculation unit 10 sequentially calculates the battery capacity Q of the specific cell 4 m at predetermined time intervals when charging or discharging the specific cell 4 m, and acquires the battery voltage V in synchronization with this to obtain the specific cell voltage V. The differential value dV / dQ, which is the ratio of the change amount dV of the battery voltage V to the change amount dQ of the battery capacity Q of 4 m, is calculated. Then, the differential curve V−dV / dQ is calculated as a curve showing the relationship between the obtained differential value dV / dQ and the battery voltage V.

FIG. 4 is a characteristic diagram showing an example of the differential curve V−dV / dQ. In FIG. 4, the differential curve V−dV / dQ is represented with the differential value dV / dQ as the vertical axis and the battery voltage V as the horizontal axis. As the specific cell 4 m is charged or discharged, the battery voltage V increases or decreases with the charge rate (SOC) of the specific cell 4 m, and the differential value dV / dQ changes accordingly, for example, the differential curve V. Inflection points P1 and P2 appear on −dV / dQ.

The differential curve calculation unit 10 outputs the calculated differential curve V−dV / dQ to the SOH estimation unit 16. At this time, the sub-controller 5 outputs the temperature T (hereinafter, these are referred to as actual measurement data) detected by the temperature sensor 9 to the SOH estimation unit 16.
The SOH estimation unit 16 estimates the SOH of the specific cell 4 m using the differential curve V−dV / dQ, the reference data, and the actual measurement data output from the differential curve calculation unit 10. For example, among the reference data, the data that matches or approximates the measured data is compared with the inflection points P1 and P2 that appear on the differential curve V−dV / dQ output from the differential curve calculation unit 10, and the data matches or approximates. The SOH is estimated from the reference data to be used. The SOH estimation method may be another method. For example, in the differential curve calculation unit 10, the differential curve V-showing the relationship with dQ / dV, which is the ratio of the change amount dQ of the battery capacity Q of the specific cell 4 m to the change amount dV of the battery voltage V of the specific cell 4 m. The dQ / dV may be calculated, the feature points may be specified from the differential curve V-dQ / dV, and the SOH of the specific cell battery 4 m may be estimated. In this case, for example, in a predetermined range of the battery voltage V, the point where the slope of the differential curve V-dQ / dV is maximized is set as a feature point, or the midpoint of two points crossing one peak at a predetermined dQ / dV. May be used as a feature point.

FIG. 5 is a flowchart showing a deterioration index estimation control procedure of the assembled battery 4 according to the present embodiment, which is executed by the main controller 2.
Hereinafter, the deterioration index estimation control of the assembled battery 4, that is, the control of estimating the SOH of the assembled battery 4 will be described with reference to FIG.
This routine is executed by a predetermined operation of an operator at the time of vehicle maintenance carried out, for example, in a vehicle maintenance shop or the like. The start condition of this routine is that the voltages of all the cell cells 4n are higher than the specified voltage Va. This designated voltage Va is the minimum voltage in use of the cell 4n, and corresponds to the above-mentioned discharge completion voltage V1. The designated voltage Va may be set to a value higher than the discharge completion voltage V1. However, when any of the cells 4n of all the cells 4n reaches the specified voltage Va due to the discharge, even if the cells are further discharged, the cells 4a will always be the first discharge completion voltage of all the cells 4n. When it is known by experiments or the like that V1 is reached, the specified voltage Va may be set to a value higher than the discharge completion voltage V1.

First, in step S10, the assembled battery 4 is started to be discharged. Therefore, the voltage of all the cell batteries 4n connected in series with the assembled battery 4 drops. Then, the process proceeds to step S20.
In step S20, the voltage sensor 7 detects the voltage of each cell 4n. Then, the process proceeds to step S30.
In step S30, it is determined whether or not any of the plurality of cell cells 4n of the assembled battery 4 has a specified voltage Va or less. When any of the cells becomes the specified voltage Va or less, the process proceeds to step S40. If any of the cells is higher than the designated voltage Va, the process returns to step S20.

In step S40, the discharge from the assembled battery 4 is terminated. Then, the process proceeds to step S50.
In step S50, the cell cell determined to be equal to or less than the designated voltage Va in step S30, that is, the cell cell 4n determined to be equal to or less than the designated voltage Va first after being discharged is stored as the specific cell battery 4m. Then, the process proceeds to step S60.

In step S60, charging of the assembled battery 4 is started. Then, the process proceeds to step S70.
In step S70, the voltage sensor 7, the current sensor 8, and the temperature sensor 9 measure the voltage, current, and temperature of the specific cell 4 m stored in step S50. Then, the process proceeds to step S80.
In step S80, it is determined whether or not the specific cell battery 4 m stored in step S50 has reached the estimation index Vp. The estimation index Vp may be set so that the SOH is equal to or higher than the voltage of the cell cell that can be estimated. As shown in FIG. 4, the estimation index Vp is obtained from the voltage of the inflection point P2 on the high voltage side when the SOH of the cell is estimated from the inflection points P1 and P2 on the differential curve V−dV / dQ. The value should be high. Then, the process proceeds to step S90.

In step S90, the SOH estimation unit 16 estimates the SOH of the specific cell battery 4 m stored in step S50. Then, the process proceeds to step S100.
In step S100, the SOH of the entire assembled battery 4 is estimated. The SOH of the entire assembled battery 4 is the SOH of the specific cell battery 4 m estimated in step S90. Then, this routine is terminated.

By controlling as described above, in the secondary battery system 1 of the present embodiment, the assembled battery 4 provided with the plurality of cell cells 4n is first discharged and designated first among the plurality of cell cells 4n. A single battery whose voltage has dropped to Va is specified as a specific single battery 4 m. Then, the battery is charged, and the SOH, which is a deterioration index of the specified cell, is estimated and used as the SOH of the entire assembled battery 4.
FIG. 6 shows the estimation results of the SOH of each battery 4n and the SOH of the entire battery 4 for the assembled battery 4 configured by connecting 80 batteries 4n having cell numbers 1 to 80 in series. It is a graph which shows an example of a relationship.

The inventor charges the assembled battery 4 configured by connecting 80 cells 4n having cell numbers 1 to 80 in series, and performs deterioration index estimation control shown in FIG. 5 to specify the specific cell 4m. Further, the SOH was estimated by the SOH estimation unit 16 for all the cells 4n. Further, the voltage difference of the assembled battery 4 from the state where any of the single batteries 4n reaches the discharge completion voltage until the assembled battery 4 is charged and one of the single batteries reaches the full charge voltage. Based on the above, the actual SOH of the assembled battery 4 was measured. In FIG. 6, the actual SOH of the assembled battery 4 is shown by a broken line as SOHp.

As shown in FIG. 6, when the SOH of the assembled batteries 4 configured by connecting 80 cells 4n in series was measured for each SOH, each cell 4n showed different SOH. However, it was confirmed that the SOH of the specific cell battery 4 m specified by performing the deterioration index estimation control as described above matches the SOHp which is the actual SOH of the assembled battery 4 as a whole.
This is because the most deteriorated cell (specific cell 4 m) among the assembled batteries 4 has the lowest full charge capacity and the earliest voltage drop when discharged. Therefore, when charging / discharging the assembled battery 4, charging and discharging are restricted by the most deteriorated cell (4 m), and the SOH of the most deteriorated cell (4 m) becomes the SOH of the assembled battery 4.

As described above, in the present embodiment, when estimating the SOH of the assembled battery 4, the specific cell 4m that has reached the discharge completion voltage V1 or the designated voltage Va due to discharge is specified, and the SOH of the specific cell 4m is assembled. Since the SOH of the entire battery 4 is used, it is not necessary to measure the SOH of all the cell 4n, and the SOH of the entire assembled battery 4 can be easily estimated. Further, even if the SOH of the cell 4n varies, the SOH of the assembled battery 4 can be estimated accurately. Further, since the estimation of the SOH of the entire assembled battery 4 is completed when the estimation of the SOH of the specific cell 4 m is completed, the estimated time of the SOH of the entire assembled battery 4 can be shortened.

Further, in the present embodiment, in the SOH estimation unit 16, the ratio of the voltage V of the specific cell 4m and the change dV of the voltage V of the specific cell 4m to the change dQ of the battery capacity Q of the specific cell 4m. The voltage V of the feature point on the differential curve V-dV / dQ showing the relationship with dV / dQ, or the voltage V of the specific cell 4 m and the battery of the specific cell 4 m with respect to the change amount dV of the voltage V of the specific cell 4 m. The SOH of the specific cell 4 m is estimated based on the voltage V of the feature point on the differential curve V−dQ / dV showing the relationship with dQ / dV, which is the ratio of the amount of change in the capacity Q, dQ.

Therefore, the SOH of the specific cell 4m can be estimated at an early stage based on the changes in the voltage and the input / output current without charging the specific cell 4m until it is fully charged.
Further, in the present embodiment, when the specific cell 4m is specified, the designated voltage Va is set to a value higher than the discharge completion voltage V1, so that the discharge is performed when any cell 4n reaches the designated voltage Va. Can be completed. As a result, the estimation of the SOH of the assembled battery 4 can be further accelerated. In this way, the SOH of the specific cell 4 m can be estimated based on the feature points on the differential curve V−dV / dQ without discharging to the discharge completion voltage V1.

This completes the description of the secondary battery deterioration degree measuring device according to the present invention, but the present invention is not limited to the above embodiment and can be changed without departing from the gist of the present invention.
For example, in the present embodiment, the SOH of the assembled battery 4 is estimated, but the SOH of the entire battery pack 20 may be estimated for the battery pack 20 composed of the plurality of assembled batteries 4.

Further, in the present embodiment, the main controller 2 is mounted on the vehicle, but the main controller 2 may be separated from the vehicle and connected only when the SOH is estimated.

4 sets of batteries (secondary battery unit)
4m specific cell 4n cell 7 voltage sensor 8 current sensor 14 cell specific part 16 SOH estimation part (deterioration index estimation part)
19 Discharge completion detector 20 Battery pack (secondary battery unit)

Claims (6)

It is a secondary battery deterioration degree measuring device that measures the deterioration degree of a secondary battery unit configured by connecting a plurality of single batteries.
A voltage sensor that measures the voltage of each of the plurality of cells and
When the secondary battery unit is discharged, a discharge completion detection unit that detects that, among the plurality of cells measured by the voltage sensor, a cell whose voltage has dropped below a predetermined specified voltage is present,
When the discharge completion detection unit detects that one of the plurality of cells has dropped to the specified voltage or less, the specific cell that first drops to the specified voltage or less among the plurality of cells is selected. The cell identification part to be identified and
A deterioration index estimation unit that estimates the deterioration index of the specific cell specified by the cell specific unit and calculates the deterioration index of the specific cell as a deterioration index of the secondary battery unit.
A secondary battery deterioration degree measuring device characterized by being equipped with. The device for measuring the degree of deterioration of a secondary battery according to claim 1, wherein the designated voltage is the discharge completion voltage of the single battery. When the secondary battery unit is further discharged than the state in which the specified cell reaches the specified voltage, the specified voltage drops to the discharge completion voltage earliest among the plurality of cells. The degree of deterioration measuring device for a secondary battery according to claim 1, wherein the value is set higher than the discharge completion voltage within the range of the voltage. It has a current sensor that measures the input / output current of each of the plurality of cells.
The deterioration index estimation unit is a deterioration index of the specific cell based on changes in the voltage and input / output current of the specific cell when the secondary battery unit detected by the voltage sensor and the current sensor is charged. The degree of deterioration measuring device for a secondary battery according to any one of claims 1 to 3, wherein the degree of deterioration of the secondary battery is estimated. The deterioration index estimation unit has a relationship between the voltage V of the specific cell and dV / dQ, which is the ratio of the change dV of the voltage V of the specific cell to the change dQ of the battery capacity Q of the specific cell. The degree of deterioration measuring apparatus for a secondary battery according to claim 4, wherein the deterioration index of the specific cell is estimated based on the voltage V of the feature point on the differential curve V-dV / dQ showing the above. The deterioration index estimation unit has a relationship between the voltage V of the specific cell and dQ / dV, which is the ratio of the change dQ of the battery capacity Q of the specific cell to the change dV of the voltage V of the specific cell. The degree of deterioration measuring device for a secondary battery according to claim 4, wherein the deterioration index of the specific cell is estimated based on the voltage V of the feature point on the differential curve V-dQ / dV showing the above.

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