JPH0689745A - Secondary battery system - Google Patents

Abstract

PURPOSE:To give information about the number of charging cycles admitted till the battery replacement or the date of it previously and prevent occurrence of accident by furnishing a current sensor, cumulator, counter, memory part, calculation part, and display part. CONSTITUTION:When operation of the system is started, the discharging capacity during discharging period is cumulated via a current sensor 11, counter 12, and cumulator 13 installed in series to a pack of batteries and is stored in a memory part 14. A calculation part 51 determines the factor while the discharge capacity per cycle is used as a function of the number of cycles, and the number of cycles until the minimum guaranteed discharge capacity of the secondary battery system as the object is attained, is calculated by means of extrapolation, and the anticipated lifetime is given on a display part 52. As this anticipation of the system lifetime allows knowing in advance the timing of battery replacement, it is practicable to operate the system with well-prepared schedule, and the coordination with the load side using secondary battery can be enhanced. It is also possible to prevent occurrence of accident by sensing failure in advance in the system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery system using an alkali metal as a negative electrode active material, and more particularly to a secondary battery system including a display device for the remaining charge / discharge cycle life of the secondary battery.

[0002]

2. Description of the Related Art In a secondary battery, the battery must be replaced when the life of the battery is exhausted by repeating charging and discharging. When the instruction of the replacement time appears without the notice period, the power supply to the load side is stopped when the replacement battery does not have a function such as automatic switching to the spare battery. If the battery becomes larger, a large load will be added to the auxiliary battery, and the effect of stopping the power supply to the load side will be great. For this reason, predicting the remaining cycle life, that is, knowing when to replace the battery with a certain notice period in advance can avoid the power supply to the load side and can systematically deal with the battery replacement. Has a big meaning. Conventionally, technological development has been advanced because it is necessary to know the time for battery replacement in a primary battery and the time for charging in a secondary battery to indicate the estimated remaining time and remaining capacity of a battery in use. Came. For example, the amount of electricity discharged up to that point is integrated to calculate the difference from the initial capacity, or as described in JP-A-59-75581, the battery voltage is measured and compared with a reference voltage. The remaining capacity can be displayed by a method or the like.

On the other hand, regarding the prediction of the remaining cycle life as to how many times the repeated charge / discharge can be performed,
Little done due to technical difficulties. For open type lead storage batteries, a method of detecting the specific gravity of the electrolytic solution or the position of the liquid surface of the electrolytic solution is well known as a method for instructing the battery replacement timing. This method is possible only in an open-type lead acid battery in which a large amount of free electrolyte is filled in the battery container. On the other hand, regarding the display of the life of a sealed lead-acid battery, a method of detecting expansion of a grid current collector has been proposed, as described in, for example, JP-A-60-30067. However, these methods are peculiar to lead-acid batteries.

Since it is difficult to predict the life of other battery systems, the number of times of charging is measured as described in, for example, JP-A-4-87159 or JP-A-4-98769, and the difference from the nominal cycle life is calculated. Has proposed a method for estimating the remaining cycle life.

[0005]

SUMMARY OF THE INVENTION In the present invention, in a secondary battery system, in order to predict the end of life and contribute to the planned operation of the secondary battery, in order to contribute to the planned operation of the secondary battery group, the operating data and the open data of the secondary battery group during use are displayed. An object of the present invention is to provide a battery system equipped with a display unit that collects circuit state data, estimates the remaining cycle life at that time, and notifies in advance of the number of times of charging until battery replacement or the date and time of battery replacement based on this. And At the same time, the aim was to provide a system for detecting battery abnormalities in advance and preventing accidents.

[0006]

[Means for Solving the Problems] In order to give advance notice of the life of a secondary battery with a certain grace period before it becomes unusable, the cause of battery life is quantified using a detectable index. Therefore, it is necessary to estimate the period until the life is deteriorated or the number of times of charge and discharge. The causes of the life of a secondary battery are broadly divided into two cases: when the charging or discharging reaction does not proceed due to the deterioration of the electrode active material, and when the electrolyte depletes, the internal resistance of the battery increases and the voltage drop due to the internal resistance is large. In some cases, charging / discharging becomes impossible.

Regarding the deterioration of the electrode active material, the change rate of the discharge capacity of the secondary battery and the change rate of the index obtained from the AC impedance of the battery can be used as the index. That is, the rate of change of discharge capacity is the discharge capacity obtained by integrating the amount of electricity discharged from one charge to the next, and the rate of change of this discharge capacity for each cycle is extrapolated to the lower limit of the discharge guaranteed by the battery system. Estimate the number of times the capacity is reduced and display it as the remaining cycle life. If the secondary battery system is operated under the condition that the discharge amount is constant, a change in the discharge capacity is not detected in principle, so as another index, it is particularly effective in the case of a lithium secondary battery. The remaining cycle life can be extrapolated using the voltage at the end of discharge or the open circuit voltage after the end of discharge. As the voltage at the end of discharge, it is desirable to use a value obtained by subtracting the voltage drop due to the internal resistance of the battery. Hereinafter, the method of predicting the remaining cycle life using the change in discharge capacity will be mainly described, but the method of predicting the discharge end voltage can also be implemented by the same method.

In order to improve the accuracy of life prediction, it is effective to measure the AC impedance of the battery in an open circuit state after charging or discharging, together with extrapolation of the discharge capacity, and add this as an index. . Among the causes of deterioration of the secondary battery described above, the measurement of AC impedance is
It is effective for evaluating both depletion of the electrolyte and deterioration of the electrode active material. An indicator of electrolyte depletion is obtained by measuring the AC impedance in the region of relatively high frequency. On the other hand, regarding the deterioration of the electrode active material, an index can be obtained by measuring the AC impedance in a relatively low frequency region and displaying the complex number to obtain the ratio of the imaginary part and the real part. Since the most suitable measurement frequency range differs depending on the type, size, shape, etc. of the battery, it is necessary to determine in advance two optimum measurement frequency ranges for the target battery system. As the low frequency region, for example, a frequency of 1 Hz or less can be used. The measured AC impedance is displayed as a complex number, the ratio of the imaginary number component (capacitance component) and the real number component (resistance component) is calculated, and this is used as one index. In the high frequency region, for example, the AC impedance is measured at a frequency of about 1 kHz, and the resistance component value is used as one index.

Usually, a small battery pack uses several batteries, and when a large battery is used, a larger number of batteries are connected in series to obtain a voltage of 100V or 200V. When the batteries are connected in series, the unevenness of the characteristics among the individual batteries forming the battery group may be expanded and the characteristics of the battery group may be deteriorated. For example, a battery having a low capacity completes the discharge first to lower the discharge voltage of the battery group, causing a decrease in the capacity. Further, in a battery using an alkali metal as a negative electrode active material, when a battery that has been completely discharged is dragged by another battery to continue discharging and overpolarization occurs, the negative electrode is activated on the positive electrode. Alkali metal, which is a substance, is deposited (reverse charging reaction), which may cause a serious accident. In order to avoid this, it is necessary to stop the use when the discharge voltage of the specific battery in the assembled battery drops to 0V.

In the case of a battery pack in which several batteries are connected in series, it is possible to measure the voltages of all the batteries.
However, in the case of a large battery that generates a voltage of about 100 V or 200 V, it is 30 in the case of a lithium secondary battery.
It is necessary to connect 70 to 70 batteries in series. In this case, it is possible in principle to measure the voltage for all the batteries, but it is easier to measure the voltage for each battery group (module) in which unit cells are connected in series in units of several batteries. In this case, if an abnormality occurs, the modules can be replaced, and the battery replacement work can be simplified.
When the voltage is measured for each module, for example, when the capacity of one of the five battery modules connected in series as shown in FIG. Occurs. This can be detected as an abnormality of the differential value of the module voltage with respect to the discharged electricity amount. In this detection method, it is desirable to reduce the number of batteries connected in series as a module in order to avoid an error due to a minute voltage change during discharging. For example, in the case of a lithium secondary battery, if a voltage change from near 2V to 0V corresponding to an overdischarge reaction occurs in one battery, 5
In this series, change of 2V / 15V = 0.133 is 1
The change of 2V / 30V = 0.0667 occurs in the case of 0 series, and the detection is easier in the case of 5 series.

In the case of a large battery group, the AC impedance of the battery is also measured for each module, and the abnormality alarm of the module detected by the change of the AC impedance and the discharge voltage is prioritized for the life prediction of the battery system, and the voltage and AC impedance Instruct to replace the module in which the error occurred. This makes it possible to deal with an abnormal situation that occurs suddenly other than the normal cause of deterioration in cycle life.

[0012]

When the operation of the secondary battery system which is the object of the present invention is started, the discharge capacities during the discharging period are integrated by the current detecting device installed in series with the battery group and stored in the storage device. The life prediction is basically done by determining the coefficient as a function of the discharge capacity for each cycle and calculating the number of cycles until reaching the minimum guaranteed discharge capacity of the target secondary battery system by extrapolation. To be done.

At this time, it should be noted that there are two patterns of changes in the discharge capacity of the secondary battery with each repeated charge / discharge cycle, as shown in FIG. The first pattern is a case where the discharge capacity rapidly decreases after a certain discharge capacity has passed until the end of the cycle (Type I). The second pattern is the case where the discharge capacity decreases almost linearly as the charge / discharge cycle progresses (Type II). The difference between the two is often a difference in battery system, for example, a nickel-cadmium battery behaves like type I and a lithium secondary battery behaves like type II in many cases. of course,
Even the same battery system behaves differently depending on the battery design and usage conditions. For example, if the discharge is repeated under a discharge condition shallow with respect to the design capacity, a type I lithium-ion battery that behaves originally as a type II under deep discharge conditions
In some cases, the behavior of

Based on this point, various studies are made on a method of predicting the remaining cycle life by combining numerical values of the nominal cycle life, discharge capacity, discharge voltage and AC impedance (two points of low frequency and high frequency) of the secondary battery. As a result, the accuracy of the remaining cycle life prediction is determined by prioritizing the above parameters according to the pattern of changes in the discharge capacity with progress of the charge / discharge cycle shown in FIG. 6 and the usage status until the life prediction time. Turned out to be able to raise. For type II batteries, the remaining cycle life can be predicted from the change in discharge capacity with each cycle. To more accurately predict the remaining cycle life, extrapolation and the coefficients of the underlying equation are updated at regular intervals, for example, using the last 100 cycles of discharge capacity data to correct the remaining cycle life prediction. Is desirable. In the former case, the life is rarely considered during the period when the discharge capacity is constant.

On the other hand, in the case of the type I battery, if it can be confirmed by comparing the discharge capacities for each cycle that it is in the phase I region at present, the number of charge / discharge cycles until then is subtracted from the nominal cycle life, Alternatively, in the lithium secondary battery, the F. O. M. Can be used to estimate the remaining cycle life, or the value of the voltage at the end of discharge can be extrapolated to predict the life. When the discharge capacity of each discharge cycle is compared and a decreasing tendency is detected in the discharge capacity, it is judged that the discharge capacity has shifted to the phase II area, and the change in discharge capacity for each cycle is extrapolated to estimate the remaining cycle life. To do. After the phase II of the type I battery, the life is predicted by the same method as the type II battery.
Along with correction of life prediction based on changes in discharge capacity at regular intervals, AC impedance of each battery module is measured at two frequencies during non-use, and voltage change of each module is measured during discharge. . Regarding the AC impedance, the deviation between the modules is taken for each value on the low frequency side and the high frequency side, and if a module with a large change in the AC impedance occurs, an alarm for inspection or module replacement is issued as Phase III. Regarding the voltage change at the time of discharge, the differential value with respect to the discharge amount is calculated for each module, and when the set value is exceeded, a module replacement alarm is issued.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 FIG. 1 shows an outline of a case where the secondary battery system according to the present invention is applied to power storage equipment. AC bus 1 to switch 4
And the load 2 and the assembled battery 3 via the inverter / rectifier 5.
Are connected in parallel. The voltage of the assembled battery 3 is measured by the voltage measuring device 7, and conditions are set so that the battery 3 is discharged to a certain lower limit voltage during discharging. A timer 6 is attached to the switch 4 to set the charging time. The charging time is set to, for example, 8 hours from 11:00 pm at night to 7:00 the next morning. A current detector 11 is connected to the assembled battery 3 in series. The current detector 11 is configured to be able to detect the direction of current as well. Thereby, the change in the direction of the current is detected to detect charging and discharging, and the current flowing in the discharging direction between charging and the next charging is integrated by the integrator 13. At the same time, a pulse is sent to the counter 12 when the direction of the current changes from the discharge state to the charge state, and integration is performed as an increase in the number of cycles. The accumulated amount of electricity and the number of cycles are stored in the storage unit 14, and the accumulated value of the amount of electricity discharged in the calculation unit 51 is determined as a function of the number of cycles, and a coefficient is determined until the lower limit discharge capacity determined by extrapolation is reached. , And the result is displayed on the display unit 52. The life is displayed as follows. 20 just before being stored in the storage unit 14
The discharge capacities are compared in the calculation unit 51, and the life is not displayed while no change is recognized. When the discharge capacity of the last 20 discharges starts to decrease, the calculation unit 5
The life value calculated in 1 is converted by the built-in calendar and displayed as the battery replacement time on a monthly basis. The estimation is repeated every 100 cycles using the latest discharge capacity data. When the remaining cycle life falls below 200 cycles, the battery replacement time is displayed in units of 10 days.

As shown in FIG. 2, the assembled battery 3 is a battery module 21 in which a number of unit cells required to obtain a predetermined voltage are first connected in series to form a battery module 21, which is further connected in series. Configure a battery group.

An AC power supply 17 having an oscillation frequency of 1 kHz and 0.05 Hz and a signal analysis unit 18 are provided, and are connected to a battery module 21 of an assembled battery via a wiring 24, a contact switching device 22 and a switch 25. After discharging and charging are completed, the load and the measuring unit are opened by the switch 23, and then the changeover switch 25 is connected to the AC power supply 17 and the signal analyzing unit 18 to measure the AC impedance at two frequencies. The measured AC impedances are sent to the storage unit / calculation unit 53, and the AC impedances of the modules are compared to calculate the deviation. If the deviation exceeds the set value, an alarm for replacing the corresponding module is issued to the alarm unit 55.

Similarly, the voltage measuring unit 16 is connected from the module via the wiring 24, the contact switching device 22 and the switch 25.
Connect to. The voltage of each module during the discharging operation is sequentially switched by the contact switching device 22 to change the input voltage.
Is sent to and the voltage of each module is measured. The module voltage is differentiated by the discharge electricity amount in the calculation unit 54, and if the differential value is larger than the set value, the alarm unit 55 issues an alarm for replacement of the corresponding module.

Example 2 FIG. 3 shows an outline of the case where the secondary battery system according to the present invention is applied to power storage equipment. AC bus 1 to switch 4
And the load 2 and the assembled battery 3 are connected in parallel via the inverter / rectifier 5. This battery pack is set to stop discharging when a certain amount of electricity is discharged by the integrator 13 during discharging. A timer 6 is attached to the switch 4 to set the charging time. The charging time is set to, for example, 8 hours from 11:00 pm at night to 7:00 the next morning. A current detector 11 is connected to the assembled battery 3 in series. The current detector 11 is configured to be able to detect the direction of current as well. As a result, changes in the direction of current are detected to detect charging, discharging, and open circuit conditions. The voltage immediately before the transition from the discharge to the open circuit state is measured by the voltage measuring device 7, the resistance loss is subtracted and stored in the storage unit 14, and the data is updated every time the transition from the discharge to the open circuit state is made. The data remaining in the storage unit 14 at the time of shifting from the open circuit state to the next charge is stored as the discharge end voltage. At the same time, when the direction of the current changes from the discharge state to the charge state, a pulse is sent to the counter 12 and integrated as an increase in the number of cycles and stored in the storage unit 14 as the number of cycles. The calculation unit 51 determines a coefficient by using the discharge end voltage as a function of the number of cycles, estimates the life until reaching a predetermined lower limit discharge end voltage by extrapolation, and displays the result on the display unit 52. The life is displayed as follows. The discharge end voltage for the last 20 times stored in the storage unit 14 is compared in the calculation unit 51 and is not displayed while no change is recognized. When a decrease in the discharge end voltage for the last 20 times is recognized, the life value calculated by the calculation unit 51 is converted by the built-in calendar and displayed as the battery replacement time on a monthly basis. The estimation is repeated every 100 cycles using the latest discharge end voltage capacity data. When the remaining cycle life falls below 200 cycles, the battery replacement time is displayed in units of 10 days. Example 1 for displaying an alarm when an abnormality occurs
It is carried out by the same method as shown in.

Example 3 FIG. 4 shows an outline of the case where the secondary battery system according to the present invention is applied to a lithium secondary battery pack. The current detection device 11 is connected in series to the battery group 15 in which five batteries are connected in series, and the wiring 26 for voltage detection is drawn out from the bipolar terminals of each battery. The current detection device 11 has a function of generating a pulse by reversing the direction of the current. The integration of the output from the current detection device 11 is started by the pulse when the current is reversed from the charging direction to the discharging direction, and the integration is continued by the integrator 13 until the current is reversed from the discharging direction to the charging direction. The integrated result is stored in the storage unit 14. At the same time, the counter 12 is advanced by one by the pulse when the current is reversed from the discharging direction to the charging direction, and is stored in the storage unit 14 as the number of cycles. A coefficient is determined as a function of the number of cycles of the discharge capacity accumulated for each cycle in the calculation unit 51, and the number of cycles until reaching a preset lower limit capacity is estimated and displayed as the number of cycles remaining on the display unit 52. .

The voltage of the five batteries is measured by the voltage detecting device 16. At this time, only one voltage detection device may be installed via the contact switching device 22 as shown in FIG. 4, or the voltage detection device may be installed in each battery. When one voltage detection device is used via the contact switching device, the input from the battery is switched at regular intervals. The voltage of each battery being discharged is sequentially measured, and the comparison circuit 15
In comparison with the set value at, if the set value is less than the set value, a warning of discontinuation of use is issued on the display unit 55.

[0024]

According to the present invention, the life of the secondary battery system can be predicted and the battery replacement timing can be known in advance, so that the secondary battery system can be systematically operated and the secondary battery is used. Cooperation with the load side can be enhanced. Further, according to the present invention, the abnormality in the secondary battery system can be detected in advance, and the occurrence of the accident in the secondary battery system can be prevented.

[Brief description of drawings]

FIG. 1 shows a configuration in which a secondary battery system according to the present invention is applied to power storage equipment.

FIG. 2 shows a configuration of a battery group in the secondary battery system according to the present invention.

FIG. 3 shows a configuration when the secondary battery system according to the present invention is applied to power storage equipment.

FIG. 4 shows a configuration when the secondary battery system according to the present invention is applied to a lithium secondary battery pack.

FIG. 5 shows how the discharge voltage changes in a 5-series lithium secondary battery.

FIG. 6 shows how the discharge capacity of the secondary battery changes in cycles.

[Explanation of symbols]

1 ... AC bus bar, 2 ... Load, 3 ... Assembly battery, 4, 23, 2
5 ... Switch, 5 ... Inverter / rectifier, 6 ... Timer,
7 ... Voltage measuring device, 11 ... Current detector, 12 ... Counter, 13 ... Accumulator, 14 ... Storage part, 15 ... Battery group, 16
… Voltage measuring unit, 17… AC power supply, 18… Signal analysis unit, 2
1 ... Battery module, 22 ... Contact switching device, 24 ...
Wiring, 51, 54 ... Calculation section, 52 ... Display section, 53 ... Storage section / calculation section, 55 ... Alarm section, 71 ... Voltage change when a normal battery is connected, 72 ... Half the capacity of one battery Voltage change when the voltage drops to 81, a change in discharge capacity of the type I battery due to repeated charge and discharge, and a change in discharge capacity of the type II battery due to repeated charge and discharge.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Nishimura 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Works, Ltd., Hitachi Research Laboratory (72) Inventor Tatsuo Horiba 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Nitate Works Co., Ltd. Hitachi Research Laboratory

Claims (5)

[Claims] 1. A collective type secondary battery group comprising a plurality of secondary batteries connected in series, which can be charged and discharged from that point to the end of its life in the process of repeatedly charging and discharging over time. A secondary battery system having a function of estimating the number of times and displaying this. 2. A collective type secondary battery group in which a plurality of secondary batteries are connected in series can be charged / discharged from that point to the end of its life in the process of repeatedly charging and discharging over time. A secondary battery system that has a function of estimating the number of times and displaying it as a battery replacement date and time. 3. An assembly type secondary battery group comprising a plurality of secondary batteries connected in series, wherein (2) the discharge capacity of each discharge cycle during the process of repeatedly charging and discharging over time. Alternatively, (2) the voltage at the end of discharge in each discharge cycle is extrapolated, the number of times that charging and discharging can be performed from that time to the end of the life is estimated, and the function to display this is provided. Secondary battery system. 4. An assembled secondary battery group comprising a plurality of secondary batteries connected in series, wherein the battery group is divided into a plurality of battery modules, and the AC impedance of the battery modules is in an open circuit state. The secondary battery system according to any one of claims 1 to 3, wherein the secondary battery system measures the measured values, compares the measured results between the battery modules, and issues an alarm for battery module replacement when the deviation exceeds a set value. 5. A collective type secondary battery group formed by connecting a plurality of secondary batteries in series, dividing the battery group into a plurality of battery modules, detecting the discharge voltage of the battery modules, and discharging. The secondary battery system according to any one of claims 1 to 3, wherein when the value obtained by differentiating the voltage with respect to the discharged electricity amount exceeds a set value, an alarm for replacement of the corresponding battery module is issued.