JP2007178333A - Method for estimating degradation state of secondary battery, and device for estimating deterioration state of on-vehicle secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for estimating the deterioration state, from the change in the battery voltage of a secondary battery making an open state, and also to provide an estimation device making the method feasible. <P>SOLUTION: The method for estimating the deterioration state comprises processes of: (S2) charging the secondary battery at a constant current; (S4) opening the secondary battery after charging; (S5) storing to correspond to an elapsed time, by measuring the battery voltage of the secondary battery during opening; calculating a deterioration index from the change with respect to the elapsed time of the stored battery voltage; and (S7) estimating the deterioration state of the secondary battery from the deterioration index. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for estimating a deterioration state of a secondary battery. The present invention also relates to a technique for classifying secondary batteries according to the degree of deterioration based on an index for estimating a deterioration state. Further, the present invention relates to an apparatus for estimating a deterioration state of a secondary battery mounted on a vehicle.

  In secondary batteries, deterioration phenomena such as an increase in internal resistance and a decrease in full charge capacity occur due to repeated charge and discharge cycles. When an overcharge or overdischarge phenomenon occurs in the secondary battery, the deterioration phenomenon is promoted. The degree of progress of the deterioration phenomenon is not uniform, and differs for each secondary battery.

  In order to estimate the deterioration state of a secondary battery mounted on a vehicle, the technique of Patent Document 1 has been developed. With the technology of Patent Document 1, the capacity of a secondary battery in an unused state (not deteriorated) can be charged and discharged, and the secondary battery that has started use (a state in which deterioration has progressed) can be charged and discharged. From the capacity, the degree of deterioration of the secondary battery that has started to be used is calculated.

JP 2004-354050 A

It has been found by the inventors' research that the technique described in Patent Document 1 has a low correlation between the estimated deterioration state and the actual deterioration state. The cause is presumed as follows. The progress of the charge / discharge phenomenon and the change in battery voltage are not always linear. In general, the battery voltage changes rapidly at the initial stage of charging / discharging, but gradually changes thereafter. The change in the battery voltage at the initial stage of charge / discharge is strongly influenced by the polarization of the secondary battery. In order to estimate the deterioration state of the secondary battery, it is necessary to distinguish in what state the polarization state of the secondary battery is. However, the technique of Patent Literature 1 does not consider what state the polarization of the secondary battery being charged is in. In order to estimate the deterioration state without distinguishing between the measurement result during the period when the battery voltage changes rapidly and the measurement result during the period when the battery voltage changes stably at a constant speed, the reliability of the estimation result is Presumed to be low.
The present invention provides a technique for accurately estimating the deterioration state of a secondary battery.

The inventors have studied a technique for more accurately estimating the deterioration state of the secondary battery. As a result, we focused on the polarization phenomenon of the secondary battery. The polarization phenomenon of the secondary battery includes concentration polarization and activation polarization. Concentration polarization is a polarization phenomenon derived from uneven electrolyte concentration in the secondary battery. Activation polarization is a polarization phenomenon derived from activation energy of electrode reaction.
In an open state where no current flows between the terminals of the secondary battery, the battery voltage decreases due to the effect of activation polarization. According to the inventors' research, if the level of activation polarization of the secondary battery before opening is leveled, the rate of change with respect to the elapsed time of the battery voltage that appears due to the effect of activation polarization after opening and the deterioration state of the secondary battery Has been found to correlate well.

  In the present invention, the deterioration state is estimated using the above correlation. The degradation state estimation method of the present invention includes a step of charging a secondary battery at a constant current, a step of opening the secondary battery after charging, and measuring a battery voltage of the opened secondary battery to cope with an elapsed time. And a step of storing the data, a step of calculating a deterioration index from the stored change in battery voltage with respect to the elapsed time, and a step of estimating the deterioration state of the secondary battery from the deterioration index.

In the estimation method of the present invention, the secondary battery is first charged with a constant current. By charging at a constant current, the activation polarization and concentration polarization in the secondary battery are leveled.
In this method, the secondary battery is opened in a state where the activation polarization and concentration polarization in the secondary battery are leveled. As described above, the voltage of the secondary battery after being opened gradually decreases due to the effect of activation polarization. In this method, the degree of the influence of activation polarization is measured by measuring the battery voltage of the opened secondary battery and storing it in association with the elapsed time.
As described above, when the degree of activation polarization of the secondary battery before opening is leveled, the rate of change of the battery voltage that appears after opening with respect to the elapsed time correlates well with the deterioration state of the secondary battery. According to this method, a deterioration index that correlates well with the deterioration state of the secondary battery can be calculated, and the deterioration state of the secondary battery can be accurately estimated by using the index.

The deterioration index may be an index that directly or indirectly indicates the change rate of the battery voltage of the secondary battery after being opened. For example, it may be calculated from the difference between the battery voltage at the time of opening and the battery voltage at the time when a predetermined time has passed since opening. The battery voltage change rate after opening may be directly calculated.
In particular, it is preferable to calculate a cumulative value of the difference between the stored battery voltage at each time point and the battery voltage at a predetermined measurement time.
Moreover, the process of measuring and storing the battery voltage until the predetermined measurement time has elapsed from the opening time is performed, and the battery voltage at each time point obtained during that time and the battery voltage at the time when the predetermined measurement time has elapsed. It is preferable to calculate the cumulative value of the differences.
In this case, it has been confirmed that the accumulated value correlates well with the deterioration state of the secondary battery.

The battery temperature affects the cumulative value. Even if the deterioration state of the secondary battery is about the same, if the battery temperature is different, the accumulated value is also different. In order to compensate for this influence, it is preferable to correct the accumulated value by the battery temperature.
It has been confirmed that the cumulative value corrected by the battery temperature correlates well with the deterioration state of the secondary battery.

The charging process is performed over a predetermined charging time, and the maximum battery voltage generated during the charging process is stored, and the stored maximum battery voltage and the accumulated value are plotted on a two-dimensional map. It is preferable to include a step of classifying the secondary battery according to the degree of deterioration according to the position of time. When the cumulative value is corrected by the battery temperature, it is preferable to use the corrected cumulative value.
The predetermined charging time used here refers to a time during which the degree of activation polarization of the secondary battery can be leveled. When the maximum battery voltage generated during the charging process and the cumulative value are plotted on a two-dimensional map, it is confirmed that the position when the secondary battery is plotted according to the degree of deterioration changes. It has been confirmed that secondary batteries can be classified according to the degree of deterioration.

The charging process is performed until the battery voltage reaches a predetermined charging voltage, and the charging capacity energized during the charging process is measured and stored, and the stored charging capacity and the accumulated value are 2 It is preferable to include a step of classifying the secondary battery according to the degree of deterioration according to the position when plotted on the dimension map. When the cumulative value is corrected by the battery temperature, it is preferable to use the corrected cumulative value.
The predetermined charging voltage used here refers to a voltage that can level the degree of activation polarization of the secondary battery. When the charge capacity required for charging and the accumulated value are plotted on a two-dimensional map, it is confirmed that the position when the secondary battery is plotted according to the degree of deterioration changes. It has been confirmed that it can be classified according to the degree of deterioration.

It is divided into a first charging step for charging until the battery voltage reaches a predetermined charging voltage, and a subsequent charging step for charging again for a predetermined recharging time after a certain charging stop period is provided. Also good. Subsequent charging steps may be repeated.
In this case, the secondary battery is determined according to the step of measuring and storing the charged capacity energized during the first charging process, and the position when the stored charge capacity and the accumulated value are plotted on a two-dimensional map. It is preferable to provide classification according to the degree of deterioration. When the cumulative value is corrected by the battery temperature, it is preferable to use the corrected cumulative value. When the subsequent charging process is repeatedly performed, the cumulative value is calculated from the battery voltage measured and stored after the last charging.
When the charge capacity required for charging and the accumulated value are plotted on a two-dimensional map, it is confirmed that the position when the secondary battery is plotted according to the degree of deterioration changes. It has been confirmed that it can be classified according to the degree of deterioration.

  The technology of the present invention is suitable for estimating the deterioration state of a secondary battery mounted on a vehicle, and provides an estimation device therefor. This estimation device is used by being connected to a vehicle that is not traveling, and determines the deterioration state of a secondary battery mounted on the vehicle. The estimation device includes means for waiting for a predetermined standby time to elapse after connection, means for charging the in-vehicle secondary battery with a constant current after the predetermined standby time has elapsed, and means for opening the in-vehicle secondary battery after charging. Means for measuring the battery voltage of the opened vehicle-mounted secondary battery and storing it in association with the elapsed time; means for calculating a deterioration index from the change of the stored battery voltage with respect to the elapsed time; and Means for estimating a deterioration state of the in-vehicle secondary battery from the deterioration index.

This estimation device is installed in a place where the vehicle is parked for a long time, such as a garage or an inspection factory, and is used by being connected to a non-traveling vehicle. The estimation device charges the in-vehicle secondary battery with a constant current after connecting to a non-running vehicle, that is, after waiting for a predetermined waiting time after the vehicle stops. By waiting for the waiting time, the degree of activation polarization of the in-vehicle secondary battery is leveled. In order to charge at a constant current from this state, the degree of activation polarization of the in-vehicle secondary battery is surely leveled.
This estimation device opens the in-vehicle secondary battery in a state in which the degree of activation polarization is leveled reliably, and calculates a deterioration index from the subsequent change in battery voltage with respect to elapsed time. The deterioration index obtained in this way correlates well with the deterioration state of the in-vehicle secondary battery. According to this estimation device, it is possible to accurately estimate the deterioration state of the in-vehicle secondary battery.
This estimation device is normally used by being connected to a non-running vehicle, but can also be used to estimate the deterioration state by connecting to a secondary battery removed from the vehicle.
It is preferable that the estimation apparatus is programmed so as to perform any one of the methods according to claims 1 to 6.

The main forms of the embodiments described in detail below are listed first.
(Embodiment 1) The secondary battery is a vehicle-mounted secondary battery.
(Mode 2) The secondary battery is a secondary battery that drives an electric motor of a hybrid vehicle.
(Mode 3) The secondary battery is a nickel metal hydride battery.
(Embodiment 4) The estimation apparatus includes a temperature sensor that measures the temperature of the secondary battery, and a unit that corrects a threshold value to be compared with the voltage change rate based on the detection result of the temperature sensor.
(Mode 5) The estimation device starts charging after a predetermined time has elapsed after the operation of the estimation device has started. The time is adjusted to a time when the activation polarization of the electrode is eliminated.
(Mode 6) The estimation apparatus includes a storage unit that stores a plurality of control programs. By providing a plurality of control programs, the processing method can be changed according to the situation.
(Embodiment 7) The estimation device includes means for storing areas corresponding to non-deteriorated batteries, deteriorated batteries, and deteriorated batteries in a two-dimensional map of maximum battery voltage / deterioration index or charge capacity / degradation index. I have.

FIG. 1 shows a secondary battery 30 mounted on the hybrid vehicle 1 and an estimation device 10 that determines a deterioration state of the secondary battery 30. The hybrid vehicle 1 includes an engine 2 and a motor 3 that is a second drive source. The motor 3 is a generator motor that operates as an electric motor that generates driving force using the electric power of the secondary battery 30 and also operates as a generator that generates electric power using the rotational force and charges the secondary battery 30. is there. The output of the engine 2 and the output of the motor 3 are transmitted to the wheels 6 through the power distributor 4 and the drive shaft 5.
When the hybrid vehicle 1 is traveling, the motor 3 is connected to the secondary battery 30 via the inverter 7 and the wiring switching means 32.
When the hybrid vehicle 1 is stopped and the driving of the engine 2 and the motor 3 is stopped, the secondary battery 30 and the estimation device 10 are connected via the wiring switching means 32. The wiring switching means 32 is provided with a socket. The secondary battery 30 is also provided with a socket. The estimation device 10 includes two cables each having a plug at the tip. One plug extending from the estimation device 10 is inserted into the socket on the wiring switching means 32 side. Thereby, the determination apparatus 10 and the wiring switching means 32 are connected. The other plug extending from the estimation device 10 is inserted into a socket on the secondary battery 30 side. Thereby, the secondary battery 30 and the estimation apparatus 10 are connected. And the secondary battery 30 and the discrimination | determination apparatus 10 are connected by switching the switch incorporated in the wiring switching means 32 to the estimation apparatus 10 side. The secondary battery 30 and the estimation device 10 are connected when the hybrid vehicle 1 is put in the garage or when the hybrid vehicle 1 is inspected.
The estimation device 10 has a built-in constant current power supply 16. The constant current power supply 16 need only be connectable to the control unit 20 (see FIG. 2) of the estimation device 10 described in detail later, and need not be built in the estimation device 10. Moreover, the structure which removes the secondary battery 30 from the hybrid vehicle 1, and connects the removed secondary battery 30 with the estimation apparatus 10 may be sufficient. In a state where the secondary battery 30 and the estimation device 10 are connected, the secondary battery 30 is charged using the constant current power supply 16, and the deterioration state of the secondary battery is determined from the change in the battery voltage after charging.

  The configuration of the estimation device 10 is shown in FIG. The estimation device 10 includes a voltage sensor 14 that measures a voltage between terminals of the secondary battery 30, a temperature sensor 12 that measures the temperature of the secondary battery 30, a constant current power supply 16 that charges the secondary battery 30, and a control. The unit 20 is configured.

The control unit 20 is composed of a microprocessor centered on the CPU 22. In addition to the CPU 22, the control unit 20 includes a ROM 24 that stores a control program, a RAM 26 that temporarily stores measurement data of the voltage sensor 13 and the temperature sensor 12, and a timer 28. These are connected by a bus 23.
The control unit 20 controls the constant current power supply 16 according to the control program stored in the ROM 24, and charges the secondary battery 30 in a state where the charging current is kept constant.
The estimation device 10 operates according to an operation instruction based on a control program stored in the ROM 24 of the control unit 20. The control unit 20 measures the battery voltage being charged by the voltage sensor 14, samples the battery voltage continuously measured by the voltage sensor 14 at fine time intervals, and stores the sampled voltage in the RAM 26. Similarly, the control unit 20 measures the battery temperature during charging by the temperature sensor 12, samples the battery temperature continuously measured by the temperature sensor 12 at fine time intervals, and stores the sampled temperature in the RAM 26. Data on the voltage value of the secondary battery 30 and temperature data from the temperature sensor 12 are input. The input data is stored in the RAM 26.

The control program stored in the ROM 24 is not limited to one. For example, a plurality of control programs may be stored, and the programs may be changed according to the situation. The control unit 20 also includes a timer 28 that counts the time of each processing step stored in the ROM 24. In the control unit 20, the CPU 22 performs an operation for estimating the deterioration state of the secondary battery 30 from the voltage value and temperature data stored in the RAM 26. The indicator indicating the deterioration state is output to a display device (not shown).
The estimation apparatus 10 of the present embodiment can change the method for estimating the deterioration state of the secondary battery by the control program stored in the ROM 24. Hereinafter, several estimation methods that can be realized using the estimation device 10 will be described.

<Method 1>
FIG. 3 is a flowchart showing the processing contents executed by the estimation apparatus 10. The determination procedure will be described with reference to FIG.
When the engine 2 and the motor 3 of the hybrid vehicle 1 are stopped, the wiring switching means 32 is switched, and the secondary battery 30 is connected to the estimation device 10. Next, a space between the positive terminal and the negative terminal of the secondary battery 30 is opened for a predetermined waiting time, and is maintained in a state in which neither charging nor discharging is performed (S1). If the secondary battery 30 is kept open for a certain period of time without being charged or discharged, the activated polarization of the electrode disappears. In step 1, the secondary battery 30 is kept open for a time (1 to 6 hours) when the activation polarization of the electrode disappears. Instead, the battery voltage is measured while maintaining the secondary battery 30 in a state of neither charging nor discharging, the rate of change of the battery voltage with respect to time is obtained, and the time until the rate of change becomes a certain value or less. May be a predetermined waiting time. When the activation polarization of the electrode disappears, the rate of change decreases to near zero.

After the process for opening the secondary battery 30 is completed, the CPU 22 controls the constant current power supply 16 and starts the charging process for the secondary battery 30 (S2). The charging process for the secondary battery 30 is performed at a constant current (for example, 1 A). The charging process to the secondary battery 30 is performed for a predetermined charging time (S3). The charging process time is measured by the timer 28 of the control unit 20. If the answer is yes in step S3, the secondary battery 30 is opened (S4).
After the secondary battery 30 is opened, the CPU 22 samples the battery voltage continuously measured by the voltage sensor 14 at fine time intervals and stores it in the RAM 26. Similarly, the battery temperature continuously measured by the temperature sensor 12 is sampled at fine time intervals and stored in the RAM 26 (S5). Sampling is performed for a predetermined measurement time (S6). If yes in step 6, the deterioration state is estimated from the stored data (S7).

The predetermined measurement time in step S6 for sampling and storing the battery voltage in the RAM 26 may be set between the time when the charging process is stopped and the time when the electrolyte of the secondary battery 30 starts natural convection. When the natural convection of the electrolyte starts, the influence of concentration polarization becomes stronger in the secondary battery. Therefore, the polarization voltage of the secondary battery 30 varies. When affected by concentration polarization, it is not preferable because it is not a change due to only the polarization voltage indicating the state of deterioration. When a nickel metal hydride battery is used as the secondary battery 30, the electrolyte is an aqueous solution of sodium hydroxide or potassium hydroxide. For nickel metal hydride batteries, the natural convection of the electrolyte begins in approximately 1 minute. Therefore, the predetermined measurement time may be set within 1 minute. The time at which the natural convection of the electrolyte begins to occur varies depending on properties such as the type of electrolyte, salt concentration, and viscosity. The predetermined measurement time may be appropriately set depending on the type of the secondary battery and the electrolyte contained in the secondary battery.
When the predetermined measurement time has elapsed, the CPU 22 calculates the deterioration index P of the secondary battery 30 from the battery voltage data and the temperature data stored in the RAM 26 (S7).

The deterioration index P of the secondary battery 30 calculated in step S7 will be described with reference to the graph of FIG. FIG. 4 shows the change over time of the battery voltage of the secondary battery 30. In the graph of FIG. 4, the horizontal axis indicates the open time, and the vertical axis indicates the value of the battery voltage. The indicator of the deterioration state of the secondary battery 30 is calculated according to Equation 1 from the battery voltage data and the temperature data stored in the RAM 26.

In the above formula 1, V (t) is a battery voltage stored in the RAM 26. t represents the sampled time (seconds), and V (t) represents the battery voltage at the sampled time. In Equation 1, the data sampling interval is 1 second, and the predetermined measurement time is 1 minute (60 seconds). The deterioration index P calculated by Equation 1 indicates the area of the colored display portion in FIG. The deterioration index P is calculated from the cumulative value of the change in battery voltage measured at 1 second intervals over 1 minute. Since the battery voltage varies depending on the temperature of the secondary battery 30, it is preferable to correct the battery voltage according to the temperature of the secondary battery 30 recorded simultaneously with the battery voltage. The maximum battery voltage during charging and the degradation index P are plotted on a two-dimensional map. Then, the deterioration state of the secondary battery 30 is determined according to which area of the two-dimensional map the plot position is located.

<Test 1>
The deterioration state of the secondary battery 30 mounted on the hybrid vehicle 1 was examined using the estimation device 10 to which the above method was applied. In this test, a two-dimensional map of the maximum battery voltage and the charging index P when charging for a predetermined time was actually created. As a test sample, an unused nickel-metal hydride battery (that is, a nickel-metal hydride battery in an undegraded state; hereinafter referred to as “unused battery”) and a full charge capacity are reduced by 7% or more than an unused product. 5 samples of nickel-metal hydride batteries (that is, nickel-metal hydride batteries in which deterioration has progressed, hereinafter referred to as “deteriorated batteries”) were prepared. Each sample battery is an assembled battery in which six nickel metal hydride batteries are connected in series. The internal resistance of the deteriorated battery used in this test was prepared to be equivalent to the internal resistance of the unused battery. FIG. 5 shows the results of a nickel-metal hydride battery having SOC (state of charge: charge capacity) at the start of the test of 40%, 50%, 60%, 70%, and 80%. This test was conducted in a constant temperature atmosphere at 25 ° C.

Briefly explain the test procedure.
First, each sample secondary battery was left open for 1 hour. Next, constant current charging at 1 A was performed for 10 minutes. After the charging was stopped, the secondary battery was opened, and the data of the open circuit voltage every 1 second was sampled at 1 second intervals for 1 minute. Thereafter, the voltage index P was calculated based on the above formula 1. A two-dimensional map of the test results of each sample secondary battery is shown in FIG. In the two-dimensional map of FIG. 5, the horizontal axis indicates the maximum voltage value during charging, and the vertical axis indicates the voltage index P. In FIG. 5, those indicated by white display are unused batteries, and those indicated by solid display are deteriorated batteries.
As shown in FIG. 5, it was found that the deterioration state of the secondary battery is clearly distinguished by a straight line h1 (solid line) in the two-dimensional map. By utilizing such a phenomenon, it is possible to set a predetermined threshold in the two-dimensional map and determine the deterioration state of the secondary battery. For example, in the two-dimensional map, when the plot position of the degradation index P is smaller than the straight line h1 (solid line), the state of the secondary battery is “good”, and the plot position of the degradation index P is the straight line h1 to the straight line h2 (broken line). The deterioration state may be determined by dividing the state of the secondary battery when the area is in the area of “2” into “capacity reduction” and the area where the plot position of the deterioration index P is larger than the straight line h2 as “replacement required”. The “threshold straight line” can be set based on a database created for the temperature condition and the full charge capacity of the secondary battery. By measuring secondary batteries in a predetermined deterioration state and storing the results as threshold straight lines h1 and h2, the deterioration state of the secondary batteries can be classified.
From the test results, it can be seen that the degradation state of the secondary battery can be clearly estimated according to the estimation device employing the method. This method can determine the deterioration state in a relatively short time.

<Method 2>
FIG. 6 is a flowchart showing the processing contents executed by the estimation apparatus 10. The determination procedure will be described with reference to FIG. The description overlapping with the process 1 will be omitted.
When the engine 2 and the motor 3 of the hybrid vehicle 1 are stopped, the secondary battery 30 is connected to the estimation device 10 by switching the wiring switching means 32. Next, a predetermined standby time is maintained in a state where neither charging nor discharging is performed between the plus terminal and the minus terminal of the secondary battery 30 (S11).

  After the predetermined standby time has elapsed, the CPU 22 controls the constant current power supply 16 and starts a charging process for the secondary battery 30 (S12). The charging process for the secondary battery 30 is performed at a constant current (for example, 1 A). The charging process to the secondary battery 30 is performed until the battery voltage of the secondary battery 30 reaches a predetermined charging voltage value (S13). If the answer is yes in step S13, the secondary battery 30 is opened.

  The setting of the “predetermined charging voltage value” when charging is stopped will be described with reference to the graph of FIG. FIG. 7 shows the relationship of the voltage value with respect to the charging time when the nickel hydride batteries of different SOCs in the same deterioration state are charged with a constant current of 1A. The charge start SOC of the nickel metal hydride battery is set to 40%, 50%, 60%, 70%, and 80%. The nickel metal hydride batteries shown in the graph have substantially the same internal resistance. As is apparent from the graph of FIG. 7, when the consumption of the charging power due to the polarization of the secondary battery is completed, the voltage value with respect to the charging time changes linearly. If the influence by polarization is removed, the change of the voltage value with respect to the charging time shows the same behavior. That is, if the change in the voltage value with respect to the charging time becomes constant, the polarization state in the secondary battery becomes constant.

  This phenomenon will be described in detail with reference to FIG. FIG. 8 is a graph showing a change in battery voltage (V) when a nickel hydride battery is charged with a constant current at 1A. In the graph of FIG. 8, the vertical axis represents the battery voltage (V), and the horizontal axis represents the SOC. The SOC at the start of charging of the secondary battery is 40%. The battery voltage (V) of the secondary battery includes the electromotive voltage (Vsoc) depending on the SOC of the secondary battery, the product (IR) of the charging current (I) and the internal resistance (R) of the secondary battery, and the secondary battery. It is the sum of polarization voltage (Vp) related to polarization in the battery. In the case of a nickel metal hydride battery, the internal resistance value (R) when the SOC is 40 to 80% is substantially constant. If the charging current (I) is a constant current, the (IR) at an SOC of 40 to 80% is substantially constant.

In the graph of FIG. 8, the portion indicated by A indicates the battery voltage at the start of charging. At the start of charging, there is no consumption of charging current for polarization. At the start of charging, the influence of the polarization voltage Vp does not occur. Therefore, the battery voltage V is the sum of Vsoc and IR.
In the graph of FIG. 8, a portion indicated by B indicates a voltage change at the initial stage of charging. In the initial stage of charging, the polarization voltage (Vp) gradually increases. At the beginning of charging, the battery voltage V increases in a curve.
A portion indicated by C in the graph of FIG. 8 indicates a voltage change during a period in which the polarization voltage Vp is saturated. When the polarization voltage Vp related to the initial charging is saturated, the battery voltage (V) with respect to the SOC is determined according to the electromotive voltage (Vsoc) depending on the SOC of the secondary battery. If the polarization voltage (Vp) is saturated, the change in the battery voltage V with respect to the SOC follows the same trajectory even when the SOC at the start of charging is different.

  The charging process of the secondary battery 30 is performed until a predetermined charging voltage is reached. The predetermined charging voltage may be set to a voltage value between the upper limit of the SOC range in which the secondary battery is normally used and the SOC at which the overcharge phenomenon starts. For example, in the case of a nickel metal hydride battery, the SOC range during normal use is 40 to 80%. In the case of a nickel metal hydride battery, the SOC at which an overcharge phenomenon occurs is 95% or more. Therefore, in the case of a nickel metal hydride battery, the predetermined voltage may be set to a voltage value between 80% and 95% SOC. For example, when 1 A constant current charging is performed in the state of an assembled battery in which six nickel metal hydride batteries are connected in series, the predetermined charging voltage can be 8.371 V, which is a voltage value equivalent to SOC of 80%.

After reaching a predetermined voltage value, the secondary battery 30 is opened. After opening the secondary battery 30, the CPU 24 measures the open time for the timer 28, measures the open circuit voltage for the voltage sensor 14, and measures the temperature of the secondary battery 30 for the temperature sensor 12. Instruct (S14). Next, the RAM 26 is instructed to record the open circuit voltage and temperature (S15). The predetermined measurement time of the RAM 26 is preferably set between the time when the charging process is stopped and the time when the electrolyte of the secondary battery 30 starts natural convection.
When the predetermined measurement time has elapsed (when YES in S16), the CPU 22 obtains an accumulated value of the difference between the open circuit voltages from the open circuit voltage and the open time data stored in the RAM 26. The cumulative value may be calculated by the same calculation method as that of Equation 1 shown in Method 1. The accumulated value of the difference between the open circuit voltages is corrected based on the temperature data, and the deterioration index P of the deterioration state of the secondary battery 30 is calculated (S17). The charge capacity and the deterioration index P are plotted on a two-dimensional map. Then, the deterioration state of the secondary battery 30 is determined according to which area of the two-dimensional map the plot position is located.

<Test 2>
Using the estimation device 10 to which the above method 2 was applied, the deterioration state of the secondary battery mounted on the hybrid vehicle was examined. In this test, a two-dimensional map of the charging capacity and the charging index P required to reach a predetermined charging voltage (8.371 V) was actually created. As a test sample, a nickel metal hydride battery was used as in Test 1 of Method 1. The test was carried out by preparing 4 samples of unused batteries and 5 samples of deteriorated batteries whose charging capacity was 7% or more lower than that of unused products. Each sample battery is an assembled battery in which six nickel metal hydride batteries are connected in series. In addition, the deterioration battery used by this test prepared the internal resistance equivalent to the internal resistance of an unused battery. Each sample was carried out by setting the SOC at the start of the test to 40%, 50%, 60%, 70%, and 80%. This test was conducted in a constant temperature atmosphere at 25 ° C.

Briefly explain the test procedure.
First, each sample secondary battery in a state where 6-cell nickel-metal hydride batteries were connected in series was waited for 1 hour in an open state. Next, the sample secondary battery was charged with a constant current of 1A. The constant current charging was performed until the charging voltage reached 8.371 V (voltage value when the 6-cell nickel-metal hydride battery in series connection was SOC 80%). After the charging was stopped, the secondary battery was opened, and battery voltage data every second was collected for 1 minute. Thereafter, the deterioration index P was calculated based on the above formula 1. The test result of each sample secondary battery is shown in the graph of FIG. FIG. 9 is a graph showing the estimation result. In FIG. 9, those indicated by white display are unused batteries, and those indicated by solid display are degraded batteries. In the graph of FIG. 9, the horizontal axis indicates the charging capacity, and the vertical axis indicates the deterioration index P.

As shown in FIG. 9, it was found that the deterioration state of the secondary battery can be distinguished by the straight line 11 (solid line). Using such a phenomenon, a predetermined threshold line can be set in the two-dimensional map of the charging capacity and the deterioration index P. For example, in the two-dimensional map, the state of the secondary battery when the plot position of the degradation index P is smaller than the straight line 11 (solid line) is “good”, and the plot position of the degradation index P is the straight line 11 to the straight line 12 (broken line). The secondary battery state when the battery is in the area of () is divided into “reduced capacity”, and when the deterioration index P is in the area from the straight line l2, “replacement is required”. Good. The “threshold straight line” can be set based on a database created for the temperature condition and the full charge capacity of the secondary battery.
This method is effective when the SOC of the secondary battery when starting the determination of the deterioration state is relatively low (for example, 40 to 60%). When the SOC of the secondary battery when starting the discrimination is high (for example, 70% or more), it is preferable to carry out the discharge process before the discrimination and lower the SOC.

<Method 3>
FIG. 10 is a flowchart showing the processing content executed by the estimation apparatus 10. The estimation method will be described with reference to FIG. The description overlapping with the processes 1 and 2 will be omitted.
When the engine 2 and the motor 3 of the hybrid vehicle 1 are stopped, the secondary battery 30 of the wiring switching unit 32 is connected to 10 by switching the wiring switching unit 32. Next, the space between the positive terminal and the negative terminal of the secondary battery 30 is opened for a predetermined standby time, and is maintained in an open state in which neither charging nor discharging is performed (S101).

After releasing the secondary battery 30 for a predetermined standby time, the CPU 22 controls the constant current power supply 16 and starts a constant current charging process for the secondary battery 30 (S102). The constant current charging to the secondary battery 30 is performed at a constant current (for example, 1 A). The constant current charging to the secondary battery 30 is performed until the battery voltage of the secondary battery 10 reaches a predetermined charging voltage value.
The setting of the “predetermined charging voltage value” is the same as the method 2 described above. After reaching the predetermined voltage value, the secondary battery 30 is opened. After the secondary battery 30 is opened, the CPU 22 instructs the timer 28 to measure the opening time, and is left in the opened state for a predetermined time.

  If the secondary battery is allowed to stand in an open state after being charged, the effects of activation polarization and concentration polarization of the secondary battery can be further reduced. With reference to the graph of FIG. 11, the effect of repeating constant current charge and an open process is demonstrated. FIG. 11 is a graph showing changes in battery voltage when charging and opening are repeated for a deteriorated state of the nickel metal hydride battery. In the graph of FIG. 11, the horizontal axis represents the charging time, and the vertical axis represents the voltage value. In the graph of FIG. 11, the voltage change of the deteriorated battery is indicated by a broken line, and the voltage change of the unused battery is indicated by a solid line. In the figure, t1 is a first constant current charging period up to 8.371 V (battery voltage value corresponding to SOC of 80% when charging with 1 A constant current in a state where 6 nickel-metal hydride batteries are connected in series). , T2 is a rest period (here 1 hour) resting in an open state, t3 is a second recharge period (here 10 seconds), and t4 is a predetermined measurement period.

  In the t1 period in FIG. 11, the unused battery and the deteriorated battery are charged up to 8.371V by constant current charging of 1A. Thereafter, by maintaining the predetermined rest time (t2) in the open state, the polarization voltage is eliminated, and the battery voltage decreases. By performing this operation, the voltage value of the polarization voltage occupied by the activation polarization and the concentration polarization of the secondary battery is determined. When constant current charging is performed again for a predetermined recharging time (t3), a voltage difference indicated by V1 is generated between the unused battery and the deteriorated battery. This voltage difference V1 reflects polarization due to deterioration of the secondary battery. The deterioration state of the secondary battery estimated from the change in the voltage value reflecting the deterioration of the secondary battery is highly reliable.

After being left for a predetermined time, reconstant current charging is started (S106). The charging process to the secondary battery 30 is performed for a predetermined recharging time (S107). The charging / recharging time is measured by the timer 28 of the control unit 20. After the charging process for a predetermined recharging time is completed, the secondary battery 30 is opened. Next, the RAM 26 is instructed to record the open circuit voltage, the predetermined measurement time, and the temperature (S108 to 110). The predetermined measurement time is preferably set between the time when the charging process is stopped and the time when the electrolyte of the secondary battery 30 starts natural convection.
When the predetermined measurement time has elapsed (when the determination is YES in step S110), the CPU 22 calculates the cumulative value of the difference between the open circuit voltages stored in the RAM 26. The cumulative value may be calculated by the same calculation method as that of Equation 1 shown in Method 1. The accumulated value is corrected based on the temperature data, and the deterioration index P of the deterioration state of the secondary battery 30 is calculated (S111). The charge capacity and the deterioration index P are plotted on a two-dimensional map. Then, the deterioration state of the secondary battery 30 is determined according to which area of the two-dimensional map the plot position is located.

<Test 3>
Using the estimation device 10 to which the above method 3 was applied, the deterioration state of the secondary battery mounted on the hybrid vehicle was examined. In this test, a two-dimensional map of the charging capacity and the charging index P required until the predetermined voltage (8.371 V) was obtained in the first constant current charging was actually created. In this test, a nickel metal hydride battery was used as in Tests 1 and 2. The test was carried out by preparing 4 samples of unused batteries and 5 samples of deteriorated batteries whose charging capacity was 7% or more lower than that of unused products. Each sample battery is an assembled battery in which six nickel metal hydride batteries are connected in series. In addition, the deterioration battery used by this test prepared the internal resistance equivalent to the internal resistance of an unused battery. Each sample was carried out by setting the SOC at the start of the test to 40%, 50%, 60%, 70%, and 80%. The test was conducted in a constant temperature atmosphere at 25 ° C.

Briefly explain the test procedure.
First, each sample secondary battery was left open for 1 hour. Next, constant current charging of 1 A was performed until it reached 8.371 V (voltage value when the 6-cell nickel metal hydride battery in series connection was SOC 80%). The charge capacity required for constant current charging of each sample battery was measured. After stopping charging, the secondary battery was kept open for 1 hour. Thereafter, constant current charging at 1 A was performed again for 10 seconds. After stopping the charging, the secondary battery was opened and the battery voltage data every 1 second was sampled for 1 minute. Thereafter, the deterioration index P was calculated based on the above formula 1. The test results of each sample secondary battery are shown in the two-dimensional map of FIG. FIG. 12 is a graph showing the estimation result. In FIG. 12, those indicated by white display are unused batteries, and those indicated by solid display are deteriorated batteries. In the two-dimensional map of FIG. 12, the horizontal axis indicates the charging capacity during the charging process, and the vertical axis indicates the deterioration index P.

As shown in FIG. 12, the deterioration state of the secondary battery is clearly distinguished by a straight line k <b> 1 (solid line) marked in the two-dimensional map for a sample whose SOC at the start of charging is 40 to 60%. all right. Also by this method, a predetermined threshold straight line can be set in the two-dimensional map. For example, the state of the secondary battery when the plot position of the degradation index P is smaller than the straight line k1 (solid line) is “good”, and the plot position of the degradation index P is in the range of the straight line k1 to the straight line k2 (broken line). The deterioration state of the secondary battery may be determined by dividing the state of the secondary battery as “decrease in capacity” and dividing the time when the plot position of the deterioration index P is larger than the straight line k2 as “replacement required”. As in the other methods, the “threshold straight line” can be set based on a database that creates a database relating to temperature conditions and the full charge capacity of the secondary battery.
Similar to Method 2, this method is effective when the SOC of the secondary battery when starting the determination of the deterioration state is relatively low (for example, 40 to 60%). When the SOC of the secondary battery when starting the discrimination is high (for example, 70% or more), it is preferable to carry out the discharge process before the discrimination and lower the SOC.

  The embodiment described above can be variously changed, modified, modified, and / or improved. Various changes can be made without departing from the spirit and scope of the invention. Accordingly, the methods and apparatus according to the present invention are intended to include all known or later developed changes, modifications, variations and / or improvements.

For example, although the said Example described the method of detecting the deterioration state of the secondary battery mounted in the hybrid vehicle, it is not restricted to this. For example, the present invention may be applied to a secondary battery for an electric vehicle or a secondary battery for an auxiliary battery.
Further, the present invention is not limited to a secondary battery mounted on a vehicle, and may be applied to a small secondary battery used for a power source of a portable device.
Of course, the type of secondary battery is not limited. In the said Example, although the nickel hydride battery was illustrated mainly, a lithium ion battery, a nickel cadmium battery, and a lead acid battery may be sufficient.

  The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

It is a schematic diagram which shows the structure of a hybrid vehicle It is a schematic diagram which shows the structure of an estimation apparatus. It is a flowchart which shows the method 2 concerning an Example. It is a graph which shows the voltage change which concerns on the constant current charge of a nickel metal hydride battery. 6 is a graph showing the results of Test 1. It is a flowchart which shows the method 2 concerning an Example. It is a graph which shows the relationship of the voltage value with respect to charge time when the nickel hydride battery of SOC is constant-current charged. It is a graph which shows the change of battery voltage (V) when a nickel hydride battery with 40% of SOC is charged with constant current. 6 is a graph showing the results of Test 2. It is a flowchart which shows one method concerning an Example. It is a graph which shows a time-dependent change of the open circuit voltage of a secondary battery. 10 is a graph showing the result of Test 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hybrid vehicle 2 Engine 3 Motor 4 Power distribution mechanism 5 Wheel shaft 6 Wheel 7 Inverter 10 Estimation apparatus 12 Temperature sensor 14 Voltage sensor 16 Constant current power supply 20 Control unit 22 CPU
24 ROM
26 RAM
28 Timer

Claims (8)

A method for estimating the deterioration state of a secondary battery,
Charging the secondary battery at a constant current;
Opening the secondary battery after charging;
Measuring the battery voltage of the opened secondary battery and storing it in association with the elapsed time;
Calculating a deterioration index from the stored battery voltage with respect to the elapsed time;
A step of estimating the deterioration state of the secondary battery from the deterioration index;
A method for estimating the deterioration state of a secondary battery. In the measurement storage step, the process of measuring and storing the battery voltage at a predetermined time interval is performed until a predetermined measurement time elapses from the opening time point,
2. The estimation method according to claim 1, wherein, in the deterioration index calculating step, a cumulative value of a difference between the stored battery voltage at each time point and a battery voltage at a predetermined measurement time has been calculated.   The estimation method according to claim 2, wherein in the deterioration index calculation step, the accumulated value is corrected based on a battery temperature. While carrying out the charging step over a predetermined charging time,
Storing the maximum battery voltage generated during the charging process;
Classifying the secondary battery according to the degree of deterioration according to the position when the stored maximum battery voltage and the cumulative value are plotted on a two-dimensional map;
The estimation method according to claim 2 or 3, further comprising: While carrying out the charging step until the battery voltage reaches a predetermined charging voltage,
Measuring and storing the charged capacity energized during the charging process;
Classifying the secondary battery according to the degree of deterioration according to the position when the stored charge capacity and the accumulated value are plotted on a two-dimensional map;
The estimation method according to claim 2 or 3, further comprising: The charging process is divided into an initial charging process that is performed until the battery voltage reaches a predetermined charging voltage, and a subsequent charging process that is performed over a predetermined recharging time after a certain charging stop period is provided thereafter. As well as
Measuring and storing the charged capacity energized during the first charging process;
Classifying the secondary battery according to the degree of deterioration according to the position when the stored charge capacity and the accumulated value are plotted on a two-dimensional map;
The estimation method according to claim 2 or 3, further comprising: It is a device that estimates the deterioration state of a secondary battery that is mounted on a vehicle connected to a non-traveling vehicle,
Means for waiting for a predetermined waiting time to elapse after connection;
Means for charging the in-vehicle secondary battery with a constant current after elapse of a predetermined standby time;
Means for opening the in-vehicle secondary battery after charging;
Means for measuring the battery voltage of the in-vehicle secondary battery being opened and storing it in association with the elapsed time;
Means for calculating a deterioration index from a stored change in battery voltage with respect to elapsed time;
Means for estimating the deterioration state of the in-vehicle secondary battery from the deterioration index;
An in-vehicle secondary battery deterioration state estimating device.   8. The degradation state estimation device of claim 7 programmed to perform the method of any of claims 1-6.

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