JP6824614B2 - Deterioration judgment device and deterioration judgment method - Google Patents

Description

The present invention relates to a deterioration determination device for determining a deterioration state of an olivine-based (iron phosphate) lithium ion secondary battery.

Lithium-ion secondary batteries are generally controlled by storage life and cycle life, and when used for about 10 years, the capacity is reduced by about 20 to 30% from the initial capacity. If the use is continued in this state, the battery deterioration (dendride) accelerates at 60% or less of the initial value, and the battery system becomes dangerous.

In particular, the olivine-based lithium-ion secondary battery has different charging characteristics from the widely used manganese-based lithium-ion secondary battery, and as shown in FIG. 6, the remaining battery level (SOC) In the region where State Of Charge) is 20% to 80%, the battery voltage is almost constant with respect to the change in SOC, and there is a problem that it is difficult to grasp the state of the secondary battery at the time of charging. ..

As a technique for determining deterioration of a lithium ion secondary battery, for example, the techniques shown in Patent Documents 1 to 3 are disclosed. In the technique shown in Patent Document 1, when a secondary battery 12 such as a lithium ion battery, a nickel cadmium battery, or a nickel hydrogen battery is connected to the charging device 1, the type is detected by the identification element 20, and the control unit 18 detects the type. The constant current charging process is started according to the battery voltage, and when the battery voltage reaches the reference voltage value according to the type of battery during this charging process, the timer provided in the control unit 18 measures the constant current charging time. The time is started when the battery is switched to constant voltage charging or when −ΔV is detected by the charge control method according to the type of battery, and the control unit 18 ends the time counting based on the constant current charging time obtained by this time measurement. , How much the charging capacity of this battery is compared with the constant current charging time for a new battery is determined according to the type of battery, and when the degree of cycle deterioration of the battery is determined, the notification unit 26 informs. An alarm is output to inform the user of the degree of cycle deterioration such as cycle life.

In the technique shown in Patent Document 2, the microcomputer 50 uses the battery voltage discrimination value V2 before the start of constant voltage charging and the constant current charging time required for charging the secondary battery as a reference in accordance with the battery voltage value V2. The relationship with the discriminant value t2 is stored in advance in the storage device (ROM) 55, and the microcomputer 50 starts charging the secondary battery to be charged with the actual measurement time (t) of constant current charging and constant voltage charging. When the previous measured battery voltage (Vo) is detected and the measured time (t) corresponding to the measured battery voltage (Vo) is equal to or less than the discriminant value (V2, t2) stored in the storage device 55 in advance. When it is determined, the display means 121 of the display circuit 120 indicates that the charged secondary battery 2 is nearing the end of its life.

The technique shown in Patent Document 3 is a deterioration state detection device 100 that detects a deterioration state of the power storage element 200, and determines the magnitude of a change in the energization capacity with respect to the voltage of the power storage element 200 when the power storage element 200 is charged or discharged. The acquisition unit 110 that acquires the second capacitance change amount, which is the magnitude of the change in the energized capacity with respect to the first capacitance change amount, is compared with the acquired second capacitance change amount and a predetermined threshold value. By doing so, the detection unit 120 for detecting the deteriorated state of the power storage element 200 is provided.

Japanese Unexamined Patent Publication No. 11-329512 Japanese Unexamined Patent Publication No. 2008-193797 Japanese Unexamined Patent Publication No. 2014-109477

However, although the techniques according to the above patent documents determine the deterioration of the secondary battery, they cannot sufficiently solve the problems peculiar to the olivine-based lithium ion secondary battery shown above.

The present invention provides a deterioration determination device and the like for appropriately determining the degree of deterioration of a secondary battery in consideration of charging characteristics peculiar to an olivine-based lithium ion secondary battery.

The deterioration determination device according to the present invention uses an arbitrary voltage value indicated by the charging characteristic in a change region other than the flat region where the voltage value of the charging characteristic of each cell in the olivine lithium ion secondary battery becomes flat as a reference voltage. A reference voltage value storage means for storing as a value, a change calculation means for calculating a change in the voltage value with respect to a predetermined time set in advance, triggered by the fact that the voltage value of each cell reaches the reference voltage value. It is provided with a deterioration determining means for determining that the cell is deteriorated when the calculated change amount exceeds a predetermined preset threshold value.

As described above, in the deterioration determination device according to the present invention, any of the above-mentioned charging characteristics shown in the change region other than the flat region where the voltage value of the charging characteristics of each cell in the olivine lithium ion secondary battery becomes flat. The voltage value is stored as a reference voltage value, and when the voltage value of each cell reaches the reference voltage value as a trigger, the change in the voltage value with respect to a preset predetermined time is calculated, and the calculated change is calculated. In order to determine that the cell has deteriorated when the amount exceeds a predetermined threshold set in advance, an appropriate deterioration determination is made in consideration of the flat region in the charging characteristics peculiar to the olivine lithium ion secondary battery. It has the effect of being able to do it.

The deterioration determination device according to the present invention is provided with a correction means for correcting a preset reference current value and converting the amount of change in the voltage value when the charging current at the time of charging is not constant.

As described above, in the deterioration determination device according to the present invention, when the charging current at the time of charging is not constant, the charging current is corrected to a preset reference current value and the change amount of the voltage value is converted. Even when the current is not always constant, the state of the secondary battery can be accurately grasped, and the deterioration can be appropriately determined.

The deterioration determination device according to the present invention is a temperature measuring means for measuring temperature information during charging, and a correction for correcting the measured temperature information to a preset reference temperature and converting the amount of change in the voltage value. It is provided with means.

As described above, in the deterioration determination device according to the present invention, the temperature measuring means for measuring the temperature information during charging and the change in the voltage value by correcting the measured temperature information to a preset reference temperature. Since the amount is converted, there is an effect that accurate deterioration judgment can be performed without being affected by the temperature environment at the time of judgment.

In the deterioration determination device according to the present invention, the temperature measuring means samples the temperature information in the environment where the olivine lithium ion secondary battery is placed, and the deterioration determining means samples the sampled temperature information. As a parameter, the deterioration of the cell is determined.

As described above, in the deterioration determination device according to the present invention, the temperature information in the environment where the olivine-based lithium ion secondary battery is placed is sampled, and the sampled temperature information is used as a parameter to determine the deterioration of the cell. Therefore, it is possible to make an accurate deterioration judgment in consideration of what kind of temperature environment the secondary battery is usually used in.

It is a system block diagram of the olivine lithium ion secondary battery which concerns on 1st Embodiment. It is a functional block diagram which shows the structure of the BMS (Battery Management System) in the deterioration determination apparatus which concerns on 1st Embodiment. It is a figure which shows the deterioration state of a secondary battery. It is a flowchart which shows the operation of the deterioration determination apparatus which concerns on 1st Embodiment. It is a functional block diagram which shows the structure of the deterioration determination apparatus which concerns on 2nd Embodiment. It is a figure which shows the charge / discharge characteristic of an olivine lithium ion secondary battery.

Hereinafter, embodiments of the present invention will be described. In addition, the same elements are designated by the same reference numerals throughout the present embodiment.

(First Embodiment of the present invention)
The deterioration determination device according to the present embodiment will be described with reference to FIGS. 1 to 4. The deterioration determination device according to the present embodiment is a predetermined time in a change region other than the flat region where the voltage value of the charging characteristic of each cell in the olivine lithium ion secondary battery (hereinafter, simply referred to as the secondary battery) becomes flat. By confirming the change in the voltage value with respect to the above, the degree of battery deterioration of the secondary battery is determined.

As described above, the olivine-based lithium-ion secondary battery has the charging characteristics as shown in FIG. 6, unlike the manganese-based lithium-ion secondary battery which is widely used in general. As shown in FIG. 6, in the case of the olivine-based lithium ion secondary battery, the battery voltage changes according to the change in SOC in the regions where the SOC is 0% to 20% and 80% to 100%. In the region where the SOC is 20% to 80%, the battery voltage is almost constant with respect to the change in SOC, and it is difficult to measure the degree of deterioration of the secondary battery in the region where the SOC is 20% to 80%. .. The region where the battery voltage changes with respect to the change in SOC of 0% to 20% and 80% to 100% of SOC is the change region, and the battery voltage with respect to the change of SOC with SOC of 20% to 80%. The area where does not change is defined as a flat area.

In the present embodiment, the degree of deterioration of the secondary battery is determined by observing the change in the charging voltage value with respect to a predetermined time in the change region in consideration of the charging characteristics peculiar to the olivine lithium ion secondary battery. Further, since the deterioration of the secondary battery is greatly affected by the temperature, the degree of deterioration is determined in consideration of the temperature at the time of deterioration determination and / or the temperature environment under normal operating conditions.

FIG. 1 is a system configuration diagram of an olivine-based lithium ion secondary battery according to the present embodiment. The secondary battery system 1 includes a BMS 2 that monitors and controls the entire system, a secondary battery module 4 formed by connecting a plurality of cells 3 in series, and an ECU that monitors the state of each secondary battery module 4. It consists of an Electronic Control Unit) 5, a charge / discharge changeover switch 6 that switches charging / discharging of the secondary battery system 1, a discharge control unit 7 that is connected to the load during discharging, and a charging control unit 8 that is connected to the power supply during charging. It includes a charge / discharge control unit 9.

At the time of charging, the charge / discharge changeover switch 6 is connected to the charge control unit 8 under the control of the BMS 2, and the secondary battery module 4 is charged. At the time of discharging, the charge / discharge changeover switch 6 is connected to the discharge control unit 7, and the power of the secondary battery module 4 is supplied to the load. Further, the BMS 2 receives information from the ECU 5 that monitors each secondary battery module 4, detects an abnormality in the secondary battery module 4, and manages the safety of the entire secondary battery system 1. The deterioration determination process of the secondary battery is performed by the CPU of the BMS 2 executing the deterioration determination program based on the information collected by the BMS 2.

FIG. 2 is a functional block diagram showing a configuration of BMS in the deterioration determination device according to the present embodiment. The BMS 2 has a receiving unit 21 that receives information about the state of the secondary battery module 4 transmitted from the ECU 5, and an area determination that determines whether the received state of the secondary battery module 4 is a state in a flat region or a state in a changing region. Based on the unit 22, the memory unit 23 that stores the reference time for calculating the change in the voltage value, the threshold value of the change in the voltage value for performing the deterioration determination, and the like, and the reference time stored in the memory unit 23. The voltage change calculation unit 24 that calculates the change in the voltage value during charging, and the deterioration determination unit that determines the deterioration of the secondary battery based on the calculated change in the voltage value and the threshold value stored in the memory unit 23. 25 and an output control unit 26 that outputs the result of deterioration determination as output information 27 to a display or paper.

Here, the deterioration determination process will be described with reference to FIG. FIG. 3 is a diagram showing a deteriorated state of the secondary battery. As shown in the graph of FIG. 3, in the initial state where there is no battery deterioration, the battery capacity with respect to the charging time becomes a graph as shown in (1), whereas in the battery deteriorated state, it becomes a graph as shown in (2). .. That is, when the battery deteriorates, the maximum capacity is reached in a short time, so that the capacity of the battery (corresponding to the area of the graph) becomes very small. As shown in the graph of FIG. 3, the slope of the graph increases as the deterioration of the battery progresses. That is, it is possible to estimate the degree of deterioration of the battery from the degree of inclination of the graph.

In the present embodiment, the SOC linearity calculated based on the current value and the voltage value cannot be obtained from the charging characteristics peculiar to the olivine-based lithium ion secondary battery as shown in FIG. 6, and the degree of deterioration of the battery is not obtained. Is difficult to calculate accurately. Therefore, in the deterioration determination process, the degree of deterioration of the battery is calculated from the magnitude of the voltage change with respect to the time change in the change region. Specifically, using an arbitrary potential set in advance in a change region other than the flat region as a trigger, the slope is obtained by φ = tan (voltage change ΔV / time change Δt), and the obtained slope and the slope in the initial state are obtained. The degree of deterioration of the battery is determined by comparing.

Next, the operation of the deterioration determination device according to the present embodiment will be described. FIG. 4 is a flowchart showing the operation of the deterioration determination device according to the present embodiment. First, the BMS 2 receives the battery voltage measured by the ECU 6 at the receiving unit 21 (S1), and the area determination unit 22 determines whether or not the measured voltage value has reached the reference voltage value (S2). .. The reference voltage value is a preset voltage value, and an arbitrary voltage value in the change region is set. That is, when the reference voltage value is reached, it can be determined as a state in the change region, and when it has not reached the reference voltage value, it can be determined as a state in the flat region. If the reference voltage value has not been reached, the process returns to step S1 and the voltage value measurement is continued. When the reference voltage value has been reached, the voltage change calculation unit 24 calculates φ = tan (ΔV / Δt) from the time change Δt and the voltage change ΔV after reaching the reference voltage value (S3).

The deterioration determination unit 25 compares φ ₀ calculated in advance in the initial operation of the operation and stored in the memory unit 23 with φ calculated in step S3 (S4). As a result of comparison, when the difference between φ and φ ₀ is less than a predetermined threshold value (S5), it is determined that the secondary battery has not deteriorated, and normal operation is continued and the process returns to step S1. When the difference between φ and φ ₀ is equal to or greater than a predetermined threshold value (S5), it is determined that the secondary battery is deteriorated, and the output control unit 46 determines that the secondary battery is deteriorated. Is output (S6), and the deterioration determination process is terminated.

The deterioration determination unit 25 determines the degree of deterioration of the secondary battery from the difference between φ and φ ₀ (the larger the difference, the greater the degree of deterioration), and the secondary battery is not completely deteriorated, that is, to some extent. Although it is deteriorated, the degree of deterioration of the secondary battery may be output as necessary even if the operation can be continued within the allowable range.

Further, the above assumes that the charging current is constant. That is, for example, assuming that the battery is charged with a constant current of 10 A during the initial operation of operation, it is assumed that the battery is charged with a constant current of 10 A even during the deterioration determination process. However, when charging electric power generated by natural energy such as sunlight, the charging current is not always constant. In such a case, the measured current value may be corrected to the current value at the time of initial operation, and then the calculation of φ may be performed. Specifically, it is based on the time change Δts obtained by multiplying the measured time change Δt by the ratio (I / I ₀ ) of the current value I at the time of measurement and the current value I ₀ at the time of initial operation. By obtaining φ, deterioration can be properly determined even when charging with a current value different from that at the time of initial operation.

As described above, in the deterioration determination device according to the present embodiment, the voltage value in the change region in the olivine lithium ion secondary battery is stored as the reference voltage value, and the voltage value of each cell reaches the reference voltage value. Is used as a trigger to calculate the change in voltage value with respect to a preset predetermined time, and when the calculated change amount exceeds a preset predetermined threshold, it is determined that the cell has deteriorated. Appropriate deterioration determination can be performed in consideration of the flat region in the charging characteristics peculiar to the olivine lithium ion secondary battery.

In addition, when the charging current during charging is not constant, it is corrected to a preset reference current value and the amount of change in the voltage value is converted. Therefore, even if the charging current is not always constant, it is secondary. It becomes possible to accurately grasp the state of the battery, and it is possible to properly determine the deterioration.

(Second Embodiment of the present invention)
The deterioration determination device according to the present embodiment will be described with reference to FIG. The deterioration determination device according to the present embodiment makes a more accurate deterioration determination by considering the temperature during the deterioration determination process. In this embodiment, the description overlapping with the first embodiment will be omitted.

The temperature environment is a very important factor in the use of secondary batteries. For example, when it is used for a long time in a high temperature or low temperature environment, it deteriorates faster than when it is used at room temperature. Further, the battery is easily activated and the output is easy to be output at a relatively high temperature, but the output is not so much because the battery is difficult to be activated at a low temperature. In this way, the deterioration and output of the secondary battery differ depending on the temperature environment. Therefore, in the present embodiment, the deterioration is determined more accurately by storing the reference φ at high temperature, normal temperature, and low temperature in advance and making corrections in consideration of the normal operating temperature, the temperature at the time of deterioration determination processing, and the like. I do.

FIG. 5 is a functional block diagram showing the configuration of the deterioration determination device according to the present embodiment. The configuration of FIG. 2 in the first embodiment is different from that of the temperature information acquisition unit 51 that acquires the temperature information measured by the temperature sensor of the ECU 6, and the acquired temperature information is periodically stored in the memory unit 23. When the deterioration determination process is executed, the temperature information at that time is passed to the deterioration determination unit 25. Further, in the memory unit 23, for example, φ _{H as} a reference in a high temperature state of 60 ° C., φ _{M as} a reference in a normal temperature state of 25 ° C., and φ _{L as a} reference in a low temperature state of −20 ° C. are stored in advance. There is. Further, the memory unit 23 has reference information (for example, in the case of 60 ° C., deterioration in 7 years, 25) which is a guideline for deterioration when used in each temperature environment of 60 ° C., 20 ° C. and -20 ° C. Information such as deterioration in 10 years at ℃ and deterioration in 8 years at -20 ℃) is stored in advance.

The deterioration determination unit 25 comprehensively determines the deterioration of the secondary battery based on the temperature information acquired by the temperature information acquisition unit 51 and the information stored in the memory unit 23. Specifically, the current temperature information is acquired, the appropriate reference φ that best matches the current temperature is selected from φ _H , φ _M , or φ _L, and the deterioration judgment is made using the selected reference φ. I do. By doing so, it becomes possible to perform a more accurate deterioration determination in consideration of the temperature parameter.

Further, the deterioration determination unit 25 calculates from the measured temperature information stored in the memory unit 23 under what temperature environment the secondary battery to be determined for deterioration has been used, and has used it so far. Deterioration judgment is performed in consideration of the environment. That is, for example, for a secondary battery that does not deteriorate for 10 years under normal conditions (under normal temperature environment), if a tendency for deterioration occurs in about 7 years, the operating temperature environment for these 7 years is calculated. When it is determined that the product is used in a high temperature or low temperature environment, it can be determined that the deterioration determination process is accurate. On the contrary, if the product deteriorates in about 7 years even though it is used in a normal temperature environment, which is normally not deteriorated for 10 years, there may be some problem in the usage environment other than the temperature. It has the property and can be maintained at an early stage.

By using the temperature information as a parameter for battery deterioration judgment as described above, accurate deterioration judgment can be performed. However, selection of the reference φ in consideration of the current temperature information and the operating temperature environment so far In the deterioration determination in consideration of, the deterioration determination process may be performed in consideration of both, or only one of the temperature information may be used as a parameter.

(Other Embodiments of the present invention)
The deterioration determination device according to the present embodiment determines the degree of deterioration based on the temperature rise change of the secondary battery. That is, in each of the above embodiments, it is determined whether or not the secondary battery is deteriorated by observing the change in φ when the deterioration of the secondary battery progresses, but in the present embodiment, the temperature change ΔT with respect to the predetermined time Δt Deterioration is determined by calculating.

As the deterioration of the secondary battery progresses, the resistance value increases due to the inhibitors deposited in the battery. That is, the temperature rises as the resistance value increases. This is because the temperature rise increases as the deterioration of the secondary battery progresses, so that it is possible to determine the degree of deterioration of the secondary battery by observing the change in the temperature rise. Specifically, the deterioration is determined by measuring the time Δt from the start of charging until the secondary battery reaches a predetermined reference temperature T and comparing it with the pre-stored Δt at the time of initial startup. Can be done. As the deterioration of the secondary battery progresses, the value of Δt becomes smaller (the temperature reaches a high temperature sooner).

In this way, when determining the deterioration of the secondary battery, it is possible to accurately determine the deterioration of any secondary battery regardless of the charging characteristics by observing the temperature rise rather than the change in the voltage value. It will be possible.

1 Rechargeable battery system 2 BMS
3 cell 4 rechargeable battery module 5 ECU
6 Charge / discharge changeover switch 7 Discharge control unit 8 Charge control unit 9 Charge / discharge control unit 21 Reception unit 22 Area determination unit 23 Memory unit 24 Voltage change calculation unit 25 Deterioration judgment unit 26 Output control unit 27 Output information 51 Temperature information acquisition unit

Claims (3)

Reference voltage value storage means for storing an arbitrary voltage value indicated by the charging characteristics in a change region other than the flat region where the voltage value of the charging characteristics of each cell in the olivine lithium ion secondary battery becomes flat as a reference voltage value. When,
A change calculation means for calculating the amount of change in the voltage value with respect to a predetermined time set in advance, triggered by the fact that the voltage value of each cell reaches the reference voltage value.
Deterioration determination means for determining that the cell has deteriorated when the calculated amount of change exceeds a predetermined threshold value set in advance.
It is provided with a correction means for correcting the amount of change in the voltage value when the charging current at the time of charging is not constant.
Based on the predetermined time obtained by the correction means by multiplying the ratio (I / I ₀ ) of the current value (I) at the time of measurement and the current value (I ₀ ) at the time of initial operation by the predetermined time. , A deterioration determination device characterized in that the amount of change in the voltage value is corrected. In the deterioration determination device according to claim 1,
Temperature measuring means for measuring temperature information during charging,
It is equipped with a memory unit that stores reference information that is the amount of change in the voltage value with respect to a predetermined time when used in a plurality of temperature environments and is a guideline for deterioration for each temperature environment.
The deterioration determination means acquires the measured temperature information, selects the reference information in the temperature zone that best matches the temperature information, and compares the amount of change in the voltage value with the reference information to determine deterioration. Deterioration determination device characterized by performing. Any said voltage value indicated by the charging characteristic in a change region other than the flat region where the voltage value of the charging characteristic of each cell in the olivine lithium ion secondary battery becomes flat is stored in the reference voltage value storage means as a reference voltage value. Has been
The change calculation step in which the CPU calculates the amount of change in the voltage value with respect to a preset predetermined time triggered by the fact that the voltage value of each cell reaches the reference voltage value, and the charging current at the time of charging are constant. If not, a correction step for correcting the amount of change in the voltage value, and a deterioration determination for determining that the cell has deteriorated when the corrected amount of change exceeds a predetermined threshold set in advance. Step and perform,
The correction step is based on the predetermined time obtained by multiplying the predetermined time by the ratio (I / I ₀ ) of the current value (I) at the time of measurement and the current value (I ₀ ) at the time of initial operation. , A deterioration determination method characterized by correcting the amount of change in the voltage value.

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