JP7174327B2 - Method for determining state of secondary battery - Google Patents

Description

The present invention relates to a secondary battery state determination method.

Secondary batteries such as lithium-ion secondary batteries are widely used as portable power sources for personal computers and mobile terminals, or as power sources for driving vehicles such as EVs (electric vehicles), HVs (hybrid vehicles), and PHVs (plug-in hybrid vehicles). It is Since the state of the secondary battery changes depending on whether or not there is an abnormality in the secondary battery, it is desirable to be able to appropriately determine the state of the secondary battery. For example, Patent Literature 1 discloses a battery management device that manages a lithium ion secondary battery. A battery management device described in Patent Document 1 estimates the SOC (State of Charge) of a lithium ion secondary battery. In addition, the battery management device compares the estimated differential coefficient of battery voltage with respect to SOC and the differential coefficient of battery voltage with respect to SOC, which is a reference for determining lithium deposition. The battery management device determines that a lithium deposition abnormality has occurred in the lithium ion secondary battery when a difference is recognized between these differential coefficients.

Republished patent WO2016/147572

In the battery management device described in Patent Literature 1, the SOC and battery voltage measured for the secondary battery in the initial state serve as references for comparing the estimated SOC and battery voltage. In this case, the difference between the standard value and the estimated value is not only due to the presence or absence of an abnormality in the secondary battery (e.g., deposition of lithium), but also the influence of aging deterioration of the secondary battery that occurs regardless of the presence or absence of an abnormality. can be. Therefore, it has been difficult with the conventional method to accurately determine the abnormality of the secondary battery while considering the influence of deterioration over time.

SUMMARY OF THE INVENTION A typical object of the present invention is to provide a method for determining the state of a secondary battery that can more accurately determine an abnormality of the secondary battery while also considering the effects of deterioration over time.

In order to achieve such an object, a method for determining the state of a secondary battery according to one aspect disclosed herein is a secondary battery to be determined, based on at least one of the capacity and the internal resistance of a target battery. a first determination step for determining whether the state of the battery is good or bad; and a normal state in which, if the state of the subject battery is determined to be good in the first determination step, the state of deterioration over time matches the state of deterioration over time of the subject battery. a reference correspondence information obtaining step of obtaining information indicating a correspondence relationship between the SOC and the battery voltage of the secondary battery as reference correspondence information; and a second determination step of determining whether or not the target battery has an abnormality by comparing with the relationship.

According to this method, first, in the first determination step, it is mainly determined whether the state of deterioration over time of the target battery is good or bad. If it is determined in the first determination step that the state of the target battery is good, the second determination step is executed. In the second determination step, it is determined whether or not the target battery has an abnormality by comparing the correspondence between the SOC during charging and the battery voltage of the target battery with the correspondence indicated by the reference correspondence information. The reference correspondence information indicates the correspondence relationship between the SOC and the battery voltage of a normal secondary battery whose state of deterioration over time matches the state of deterioration over time of the subject battery (that is, no abnormality other than deterioration over time). Therefore, in the second determination step, the determination is made in a state where the influence of deterioration over time is excluded, so whether or not there is an abnormality in the target battery can be determined with high accuracy. Therefore, according to the above method, the abnormality of the secondary battery can be determined more accurately while also considering the influence of deterioration over time.

2 is a schematic diagram showing an example of a circuit configuration for acquiring battery information of a target battery 1; FIG. 4 is a flowchart of state determination processing executed by the control unit 2; FIG. 10 is a diagram showing an example of an SOC-OCV curve when there is no abnormality and an example of an SOC-OCV curve when there is an abnormality in secondary batteries of the same type and deterioration state over time.

One typical embodiment of the present disclosure will be described in detail below with reference to the drawings. Matters other than those specifically referred to in this specification that are necessary for implementation can be grasped as design matters for those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. In the drawings below, members and portions having the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

As used herein, the term “battery” is a general term for power storage devices from which electrical energy can be extracted, and is a concept that includes primary batteries and secondary batteries. "Secondary battery" refers to a general electricity storage device that can be repeatedly charged and discharged, and in addition to so-called storage batteries (that is, chemical batteries) such as lithium ion secondary batteries, nickel hydrogen batteries, and nickel cadmium batteries, electric double layer capacitors, etc. It contains a capacitor (ie a physical battery). Hereinafter, the state determination method according to the present disclosure will be described in detail by exemplifying the state determination method of a lithium-ion secondary battery, which is a type of secondary battery. However, the secondary battery state determination method according to the present disclosure is not intended to be limited to those described in the following embodiments. For example, at least part of the techniques exemplified in the present disclosure can be applied when determining the state of secondary batteries other than lithium-ion secondary batteries (for example, nickel-metal hydride batteries, etc.).

With reference to FIG. 1, an example of a circuit configuration for acquiring battery information of a secondary battery whose state is to be determined (hereinafter referred to as "target battery") will be schematically described. As described above, the target battery 1 of this embodiment is a lithium ion secondary battery. In the present embodiment, the target battery 1 is an assembled battery in which a plurality of secondary batteries are connected. However, one battery may be the target battery. Moreover, when a plurality of batteries are used, each of the plurality of batteries may be the target battery.

An input device (for example, a generator) 3 and an output device 4 (for example, an external device as an output destination) are connected in parallel to the positive terminal and the negative terminal of the target battery 1, respectively. A wire connecting the input device 3 and the target battery 1 is provided with a switch 6 . By turning on the switch 6 , the target battery 1 is charged with the power output from the input device 3 . Moreover, a switch 7 is provided in the wiring that connects the output device 4 and the target battery 1 . Power is supplied from the target battery 1 to the output device 4 by turning on the switch 7 .

A voltmeter 9 is connected in parallel to the target battery 1 . A voltmeter 9 measures the voltage between the positive and negative electrodes of the target battery 1 . An ammeter 10 is connected in series to the target battery 1 . The ammeter 10 measures the current flowing through the target battery 1 . Also, the target battery 1 is provided with a temperature sensor 11 . A temperature sensor 11 detects the temperature of the target battery 1 .

Input device 3 , output device 4 , switch 6 , switch 7 , voltmeter 9 , ammeter 10 , and temperature sensor 11 are connected to controller 2 . The control unit 2 includes a controller that determines the state of the target battery 1 and a storage device. Various devices (for example, an electronic control system (ECU) mounted on a vehicle) can be used for the control unit 2 . The control unit 2 controls the ON/OFF driving of the switches 6 and 7 . Also, the control unit determines the state of the target battery 1 based on information input from the voltmeter 9 , the ammeter 10 , and the temperature sensor 11 .

A secondary battery state determination method according to the present embodiment will be described with reference to FIG. Upon receiving an instruction to start determining the state of the target battery 1, the control unit 2 executes the state determination process illustrated in FIG. 2 according to the program stored in the storage device.

First, the control unit 2 acquires the voltage and current of the target battery 1 (S1). Specifically, in S1 of the present embodiment, the voltage and Current is obtained via voltmeter 9 and ammeter 10 . The control unit 2 acquires a plurality of sets of voltage values measured by the voltmeter 9 and current values measured by the ammeter 10 while the target battery 1 is being charged. Note that SOC (State of Charge) means the ratio of the remaining charge amount to the full charge capacity of the secondary battery. Also, OCV (Open Circuit Voltage) means the voltage of a secondary battery when not energized, and is also called open circuit voltage.

The control unit 2 acquires the capacity and internal resistance of the target battery 1 (S2). Specifically, in S2 of the present embodiment, the capacity retention rate and the internal resistance increase rate of the target battery 1 are acquired. The control unit 2 determines whether or not the target battery 1 is in good condition based on the capacity retention rate and the internal resistance increase rate acquired in S2 (S3).

The capacity retention rate will be explained. The capacity retention rate is the ratio of the battery capacity of the target battery 1 at the time of determination to the battery capacity of the target battery 1 in the initial state. The battery capacity of a secondary battery decreases with use. Therefore, in S3, the deterioration state over time of the target battery 1 is appropriately determined mainly by using the capacity retention rate.

A specific method for obtaining the capacity retention rate can be selected as appropriate. An example of a method for obtaining the capacity retention rate will be described below. The control unit 2 of the present embodiment uses a pre-charge voltage (open circuit voltage) V0 measured by the voltmeter 9 before charging the target battery 1 and a post-charge voltage V1 (open circuit voltage) measured by the voltmeter 9 after charging. circuit voltage). Further, the control unit 2 calculates the charge amount P by integrating the current values detected by the ammeter 10 from the start to the end of charging. The control unit 2 calculates the SOC of the target battery 1 before charging based on the pre-charging voltage V0. The control unit 2 calculates the SOC of the subject battery 1 after charging based on the post-charging voltage V1. The control unit 2 subtracts the SOC before charging from the SOC after charging to calculate ΔSOC increased by charging. Since the charge amount P calculated by integrating the current values corresponds to ΔSOC, the battery capacity W corresponding to the current SOC 100% of the target battery 1 is calculated from the charge amount P and the value of ΔSOC. The control unit 2 calculates the capacity maintenance rate by calculating the ratio of the current battery capacity W to the battery capacity of the target battery 1 in the initial state. Note that, in the present embodiment, the battery capacity of the target battery 1 in the initial state is stored in advance in the storage device within the control unit 2 . The battery capacity in the initial state may be the battery capacity calculated for the target battery 1 itself in the initial state, or may be the initial battery capacity for a secondary battery of the same type as the target battery 1 .

The internal resistance increase rate will be explained. The internal resistance increase rate is the ratio (increase rate) of the internal resistance of the subject battery 1 at the time of determination to the internal resistance of the subject battery 1 in the initial state. The internal resistance of secondary batteries increases with use. Therefore, in S3, the deterioration state over time of the target battery 1 is appropriately determined mainly by using the internal resistance increase rate.

A specific acquisition method of the internal resistance increase rate can also be selected as appropriate. As an example, the control unit of the present embodiment determines the current target battery 1 based on the voltage value measured by the voltmeter 9 during charging and the current value measured by the ammeter 10 at the timing of measuring the voltage value. Calculate the internal resistance of according to Ohm's law. Note that the temperature detected by the temperature sensor 11 may be taken into account in calculating the internal resistance. Also, the internal resistance may be calculated based on the amount of variation in the voltage value and the current value. The control unit 2 calculates the internal resistance increase rate by calculating the ratio of the current internal resistance of the target battery 1 to the internal resistance of the target battery 1 in the initial state. Note that in the present embodiment, the internal resistance of the target battery 1 in the initial state is stored in advance in the storage device within the control unit 2 . The internal resistance in the initial state may be the internal resistance calculated for the target battery 1 itself in the initial state, or may be the internal resistance in the initial state for a secondary battery of the same type as the target battery 1 .

As an example, in S3 of the present embodiment, when the capacity maintenance rate of the target battery 1 is greater than the threshold and the resistance increase rate is less than the threshold, it is determined that the state of the target battery 1 is good ( S3: YES). On the other hand, when at least one of the condition that the capacity retention rate is equal to or less than the threshold and the condition that the resistance increase rate is equal to or more than the threshold is satisfied, the state of the target battery 1 is not good (that is, deterioration over time progresses). (S3: NO). If it is determined that the condition is not good (S3: NO), the target battery 1 is disabled (S10) and the process ends.

However, it is also possible to change the specific determination method in S3. For example, the control unit 2 may make the determination in S3 based on one of the capacity retention rate and the resistance increase rate. Alternatively, the control unit 2 may perform the determination in S2 based on the current battery capacity and internal resistance values of the target battery 1 without acquiring the capacity maintenance rate and the resistance increase rate.

Here, when there is no abnormality in the secondary battery (for example, deposition of lithium in the lithium ion secondary battery, short circuit due to foreign matter, etc.), the capacity maintenance rate and resistance increase rate of the secondary battery, and the secondary battery The relationship between the frequency of use and the frequency of use is a fixed relationship to some extent. In other words, when there is no abnormality in the secondary battery, the capacity retention rate and resistance increase rate of the secondary battery can be estimated to some extent based on the frequency of use. If there is a large difference between the value estimated based on the usage frequency and the actually obtained value, there is a possibility that the secondary battery is abnormal. Therefore, in the determination of S3, the control unit 2 considers information indicating the frequency of use of the target battery 1 (for example, at least one of the number of days elapsed since the start of use and the number of times of charging and discharging). , there is a possibility that the presence or absence of an abnormality in the target battery 1 can be determined to some extent. However, with only this determination method, there is a possibility that the presence or absence of abnormality may not be accurately determined when the degree of abnormality in the secondary battery is small (for example, when the amount of lithium deposited is small). Further, depending on the type of abnormality, there may be cases where the secondary battery abnormality does not greatly affect the capacity and internal resistance. In addition, since the capacity of a secondary battery with an abnormality may decrease over time due to self-discharge, it may be possible to determine the presence or absence of an abnormality based on the capacity of the target battery 1 after being left unattended. However, the method of leaving the target battery 1 alone takes time. Therefore, in the state determination method of the present embodiment, the presence or absence of an abnormality in the target battery 1 is further determined in steps S5 to S8 described below.

If the state of the target battery 1 is determined to be good in the determination of S3 (S3: YES), the control unit 2 acquires the time-dependent deterioration state of the target battery 1 (S5). A method for acquiring the deterioration state over time can be selected as appropriate. Degradation of the secondary battery over time progresses according to the frequency of use (for example, at least one of the number of days elapsed since the start of use and the number of charge/discharge cycles). Further, as the secondary battery deteriorates over time, the temperature and current value of the secondary battery change. Therefore, in the present embodiment, the control unit 2 controls at least one of the information indicating the usage frequency of the target battery 1, the temperature of the target battery 1 detected by the temperature sensor 11, and the current measured by the ammeter 10. Based on this, the state of deterioration over time of the target battery 1 is acquired. As an example, in this embodiment, a table or formula is provided in advance for determining the state of deterioration over time based on at least one of usage frequency information, temperature, and current. The control unit 2 applies at least one of the usage frequency information, the temperature, and the current to a table or a calculation formula to acquire the deterioration state over time. In addition, as described above, as the secondary battery deteriorates over time, the capacity of the secondary battery decreases and the internal resistance increases. Therefore, the control unit 2 may acquire the time-dependent deterioration state of the target battery 1 based on at least one of the capacity retention rate and the resistance increase rate described above.

Next, the control unit 2 acquires reference correspondence information corresponding to the deterioration state over time acquired in S5 (S6). The reference correspondence information is information indicating the correspondence relationship between the SOC and the battery voltage in a secondary battery whose deterioration state over time matches the deterioration state over time of the target battery 1 and is normal (that is, there is no abnormality). In the present embodiment, for each of a plurality of normal secondary batteries of the same type as the target battery 1 and having different aging states, the correspondence information indicating the correspondence between the SOC and the battery voltage is sent to the control unit 2. Pre-stored in the storage device. In S6, correspondence information corresponding to the deterioration state with time acquired in S5 is acquired as reference correspondence information among the plurality of correspondence information stored in the storage device.

As an example, in the present embodiment, correspondence information indicating an SOC-OCV curve is stored for each of a plurality of aging deterioration states as correspondence information indicating the correspondence relationship between SOC and battery voltage. However, the correspondence information is not limited to information indicating the SOC-OCV curve. For example, table data or the like in which SOC and battery voltage values are associated with each other for each of a plurality of secondary batteries having different deterioration states over time may be stored in the storage device as correspondence information.

Next, the control unit 2 acquires the correspondence relationship (that is, voltage behavior) between the SOC and the battery voltage in the target battery 1 (S7). Various methods are known for acquiring the correspondence relationship between the SOC and the battery voltage (for example, information indicating the SOC-OCV curve) in the target battery 1, and any method may be employed. For example, the control unit 2 measures the charging/discharging current for the target battery 1, multiplies the measured current value by a predetermined charging efficiency, and integrates the multiplied value over a certain time interval. The control unit 2 may acquire (estimate) the SOC based on the integrated capacity obtained by the integration. The control unit 2 may acquire the correspondence relationship between the SOC and the battery voltage by associating the acquired SOC with the battery voltage (OCV).

The control unit 2 determines whether the target battery 1 has an abnormality by comparing the correspondence between the SOC and the battery voltage of the target battery 1 with the correspondence indicated by the reference correspondence information acquired in S6 ( S8). FIG. 3 is a diagram showing an example of an SOC-OCV curve when there is no abnormality and an example of an SOC-OCV curve when there is an abnormality in secondary batteries of the same type and deterioration state over time. As shown in FIG. 3, even if the type and deterioration state over time are the same, there is a difference between the correspondence between the SOC and the battery voltage when there is no abnormality, and the correspondence between the SOC and the battery voltage when there is an abnormality. occur. Therefore, by comparing the correspondence relationship between the SOC and the battery voltage of the target battery 1 with the correspondence relationship indicated by the reference correspondence information, it is possible to determine whether or not the target battery 1 has an abnormality in a state in which the influence of deterioration over time is excluded. determined with good accuracy. If it is determined in S8 that there is no abnormality (S8: NO), the target battery 1 is made usable (S9), and the process ends. If it is determined that there is an abnormality in S8 (S8: YES), the target battery 1 is disabled (S10), and the process ends.

A specific determination method in S8 can be selected as appropriate. For example, the control unit 2 may determine the presence or absence of an abnormality by comparing the differential coefficient of the battery voltage with respect to the SOC between each corresponding relationship. In this case, the control unit 2 may determine that the target battery 1 is abnormal when the differential coefficient difference is equal to or greater than the threshold. In addition, the control unit 2 specifies at least one SOC value with which the battery voltage is compared, and compares the battery voltage of the target battery 1 and the battery voltage in the reference correspondence information when the SOC is the specified value. may In this case, the control unit 2 may determine that the target battery 1 is abnormal when the difference in battery voltage is equal to or greater than the threshold.

The technology disclosed in the above embodiment is merely an example. Therefore, it is also possible to modify the techniques exemplified in the above embodiments. For example, in the above-described embodiment, first, in S3, mainly the deterioration state over time of the target battery 1 is determined (S3). In other words, the process of S3 is an example of a first determination step for determining whether the state of the target battery is good or bad based on at least one of the capacity and internal resistance of the target battery. If it is determined in S3 that the condition is good, in S8 it is determined whether or not the target battery 1 is abnormal. In other words, the process of S8 is an example of a second determination step for determining whether or not the target battery 1 has an abnormality. However, it is also possible to omit the first determination step and execute only the second determination step. Even in this case, it is possible to accurately determine whether or not the target battery 1 has an abnormality while excluding the effects of deterioration over time.

1 target battery 2 control unit 9 voltmeter 10 ammeter 11 temperature sensor

Claims (1)

a first determination step of determining whether the state of the target battery is good or bad based on at least one of the capacity and the internal resistance of the target battery, which is a secondary battery to be determined;
Shows the correspondence relationship between the SOC and the battery voltage of a normal secondary battery whose state of deterioration over time matches the state of deterioration over time of the subject battery when the state of the subject battery is determined to be good in the first determination step. a reference correspondence information obtaining step of obtaining information as reference correspondence information;
By comparing the correspondence relationship between the SOC and the battery voltage in the target battery with the correspondence relationship indicated by the reference correspondence information , deposition of lithium on the target battery in a state where the influence of deterioration over time is excluded, or short circuit due to foreign matter a second determination step of determining whether there is
A method for determining the state of a secondary battery, comprising:

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