JP6658340B2 - Battery system - Google Patents

Description

  The present invention relates to a battery system, and more particularly, to a battery system including a nickel hydrogen battery.

Japanese Patent Laying-Open No. 2011-233423 (Patent Document 1) discloses an alkaline storage battery (nickel-metal hydride battery) including a nickel positive electrode. When Ni ₂ O ₃ H is generated in the nickel positive electrode, the full charge capacity of the battery decreases. In this alkaline storage battery, by appropriately designing the length and height (width) of the nickel positive electrode, generation of Ni ₂ O ₃ H in the nickel positive electrode is suppressed. According to this alkaline storage battery, since the generation of Ni ₂ O ₃ H in the nickel positive electrode is suppressed, a decrease in the full charge capacity of the alkaline storage battery can be suppressed (see Patent Document 1).

JP 2011-233423 A

Patent Literature 1 discloses a structure of a nickel positive electrode for suppressing generation of Ni ₂ O ₃ H in a nickel positive electrode. However, an increase in Ni ₂ O ₃ H reduces a full charge capacity of a battery. No action has been taken in the event of a decline.

For example, if the full charge capacity is reduced more than expected due to an increase in Ni ₂ O ₃ H, the influence on various controls using the information on the full charge capacity becomes large, which is a problem. Therefore, it is necessary to appropriately protect the nickel-metal hydride battery so that Ni ₂ O ₃ H does not increase excessively. On the other hand, if the nickel-metal hydride battery is excessively protected, the performance of the nickel-metal hydride battery may not be sufficiently exhibited.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a battery system capable of sufficiently exhibiting the performance of a nickel-metal hydride battery while appropriately protecting the nickel-metal hydride battery. To provide.

A battery system according to an aspect of the present invention includes a nickel-metal hydride battery and a control device. The control device includes a memory and controls a charging voltage of the nickel-metal hydride battery. The memory stores data indicating the relationship between the voltage and temperature of the nickel-metal hydride battery and the amount of decrease in the full charge capacity of the nickel-metal hydride battery caused by Ni ₂ O ₃ H generated in the positive electrode of the nickel-metal hydride battery. The control device is configured to charge the battery when the decrease in the full charge capacity is equal to or more than a predetermined amount, which is derived from the voltage and temperature of the nickel-metal hydride battery and the above data, than when the decrease in the full charge capacity is less than the predetermined amount. Lower the upper voltage limit.

In this battery system, attention is paid to the relationship between the voltage and temperature of the nickel-metal hydride battery and the amount of reduction in the full charge capacity of the nickel-metal hydride battery caused by Ni ₂ O ₃ H generated in the positive electrode. In particular, where the voltage of the nickel-metal hydride battery increases during charging, when the charging voltage of the nickel-metal hydride battery is high, Ni ₂ O ₃ H is more easily generated in the nickel positive electrode than when the charging voltage is low. In this battery system, the upper limit of the charging voltage is lower when the amount of decrease in the full charge capacity of the nickel-metal hydride battery is equal to or more than a predetermined amount than when the amount of decrease in the full charge capacity is less than the predetermined amount. Therefore, according to this battery system, when the amount of decrease in the full charge capacity becomes equal to or more than the predetermined amount, the generation of Ni ₂ O ₃ H is suppressed, so that the nickel-metal hydride battery can be appropriately protected. Further, by appropriately lowering the upper limit of the charging voltage, the performance of the nickel-metal hydride battery can be sufficiently exhibited.

  According to the present invention, it is possible to provide a battery system capable of sufficiently exhibiting the performance of a nickel-metal hydride battery while appropriately protecting the nickel-metal hydride battery.

It is a figure showing roughly composition of a vehicle in which a battery system is carried. Is a diagram showing an example of experimental results on the relationship between the presence ratio and the full charge capacity of Ni 2 _O 3 _H in the positive electrode. 9 is a flowchart illustrating a processing procedure in a first experiment. Is a diagram illustrating an example of a deliberately NiMH batteries Ni 2 _O 3 _H analysis result by the number X-ray diffraction method of the positive electrode was produced (diffraction pattern). FIG. 4 is a diagram illustrating an example of a relationship between the ratio of Ni ₂ O ₃ H in a sample and a peak area ratio in an X-ray diffraction method, which is obtained by a first experiment. It is a flowchart which shows the processing procedure in a 2nd experiment. It is a figure showing an example of a map in which the result obtained by the 2nd experiment was put together. It is a flowchart which shows the processing procedure of charge control of an assembled battery.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

(Configuration of battery system)
FIG. 1 is a diagram schematically showing a configuration of a vehicle 1 on which a battery system 2 according to the present embodiment is mounted. Hereinafter, a case where vehicle 1 is a hybrid vehicle will be described. However, battery system 2 according to the present embodiment is not limited to a vehicle mounted on a hybrid vehicle, but is applicable to all vehicles equipped with nickel-metal hydride batteries, and further to vehicles It can be applied to other uses.

  Referring to FIG. 1, vehicle 1 includes a battery system 2, a power control unit (PCU) 30, motor generators (MG: Motor Generators) 41 and 42, an engine 50, and a power split device 60. , A drive shaft 70 and a drive wheel 80. The battery system 2 includes a battery pack 10, a monitoring unit 20, and an electronic control unit (ECU: Electronic Control Unit) 100.

  The engine 50 generates a driving force for rotating a crankshaft by combustion energy generated when combusting a mixture of air and fuel. MGs 41 and 42 function as both a generator and a motor.

  MG 41 mainly operates as a generator that generates electric power by using a part of the output of engine 50 transmitted through power split device 60. The power generated by MG 41 is supplied to MG 42 or battery pack 10 through PCU 30.

  MG 42 is driven by at least one of the power from battery pack 10 and the power generated by MG 41. The driving force of MG 42 is transmitted to drive shaft 70. When the vehicle 1 is braked, the MG 42 operates as a generator by being driven by the rotational force of the drive wheels 80. The power generated by MGs 41 and 42 is charged to battery pack 10 through PCU 30.

  Battery pack 10 stores electric power for driving MGs 41 and 42. The assembled battery 10 includes a plurality of nickel-metal hydride cells (single cells) connected in series. The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects a voltage between terminals of each cell (hereinafter, also referred to as “cell voltage”). The current sensor 22 detects a charge / discharge current of the battery pack 10. The temperature sensor 23 detects the temperature of each cell (hereinafter, also referred to as “cell temperature”). Each sensor outputs a signal indicating the detection result to ECU 100. Note that the output of the current sensor 22 indicates a negative value during charging and a positive value during discharging.

  PCU 30 is configured to execute bidirectional power conversion between battery pack 10 and MGs 41 and 42 in accordance with a switching command from ECU 100. PCU 30 is configured to be able to control the states of MGs 41 and 42 separately, and for example, can place MG 42 in a powering state while MG 41 is in a regenerative (power generation) state.

  The ECU 100 includes a CPU (Central Processing Unit), an input / output interface (both are not shown), and a memory 105. The ECU 100 controls charging and discharging of the battery pack 10 by controlling the engine 50 and the PCU 30 based on signals from the sensors and information stored in the memory 105.

  The ECU 100 calculates, for each cell of the battery pack 10, an SOC value indicating a state of charge (a value indicating a remaining capacity with respect to a full charge capacity of the secondary battery from 0 to 100%). As a method of calculating the SOC value, various known methods such as a method of calculating using the relationship between the voltage and the SOC value, and a method of calculating using the integrated value of the current can be used.

  ECU 100, for example, based on the SOC value, inputtable power Win indicating the upper limit of the input power to battery pack 10, and outputtable power Wout indicating the upper limit of the output power from battery pack 10 (both in watts) Set. For example, in a region where the SOC value is equal to or larger than the first predetermined value, ECU 100 limits inputtable electric power Win to a smaller value as the SOC value is larger (approaching 100% which is a value at the time of full charge), and the SOC value is smaller. In a region equal to or smaller than a second predetermined value (<first predetermined value), the available output power Wout is limited to a smaller value as the SOC value is smaller (approaching 0% which is the value at the time of depletion).

(Suppression of drop in full charge capacity)
In each unit cell included in the battery pack 10, when Ni ₂ O ₃ H is generated in the positive electrode, the full charge capacity decreases.

FIG. 2 is a diagram illustrating an example of an experimental result regarding the relationship between the abundance ratio of Ni ₂ O ₃ H in the positive electrode and the full charge capacity. Referring to FIG. 2, the abscissa indicates the abundance ratio of Ni ₂ O ₃ H in the positive electrode, and the ordinate indicates the full charge capacity. From this experimental result, it can be seen that the full charge capacity decreases as the proportion of Ni ₂ O ₃ H increases.

For example, when the full charge capacity is greatly reduced due to an increase in Ni ₂ O ₃ H, the influence on various controls using the information on the full charge capacity becomes large, which is a problem. Therefore, it is necessary to appropriately protect the battery pack 10 so that Ni ₂ O ₃ H does not excessively increase in the positive electrode. On the other hand, if the battery pack 10 is excessively protected, the performance of the battery pack 10 may not be able to be sufficiently exhibited.

The amount of Ni ₂ O ₃ H generated in the positive electrode depends on the voltage and temperature of the cell. In particular, when the charging voltage is high, Ni ₂ O ₃ H is more likely to be generated in the nickel positive electrode than when the charging voltage is low, which may cause a decrease in the full charge capacity.

Therefore, the following configuration is employed in battery system 2 according to the present embodiment. The memory 105 stores a map (data) indicating the relationship between the voltage and the temperature and the amount of decrease in the full charge capacity due to Ni ₂ O ₃ H generated in the positive electrode for the single cell included in the battery pack 10. I do. The ECU 100 sets the upper limit of the charging voltage when the amount of decrease in the full charge capacity derived from the voltage and temperature of the cell and the above map is equal to or more than a predetermined amount, than when the amount of decrease in the full charge capacity is less than the predetermined amount. Lower.

According to the battery system 2, when the amount of decrease in the full charge capacity is equal to or more than the predetermined amount, the generation of Ni ₂ O ₃ H is suppressed, so that the battery pack 10 can be appropriately protected. Further, by appropriately lowering the upper limit of the charging voltage, the performance of the battery pack 10 can be sufficiently exhibited.

The above-described map is created in advance through a plurality of experiments. Hereinafter, a method of creating a map will be described first, and thereafter, a charge control for preventing the full charge capacity from being significantly reduced due to Ni ₂ O ₃ H will be described.

(Map creation)
An experiment for creating a map is performed, for example, in the following order. First, an experiment (hereinafter also referred to as a “first experiment”) for examining the relationship between the amount of Ni ₂ O ₃ H mixed in the positive electrode and the peak area ratio when the positive electrode is analyzed using the X-ray diffraction method. ) Is performed. Then, an experiment for examining the relationship between the endurance conditions (voltage and temperature) and the amount of Ni ₂ O ₃ H generated in the positive electrode using the results of the single cell and the first experiment that have undergone an endurance test (described later). (Hereinafter, also referred to as “second experiment”). In the second experiment, finally, a map showing the relationship between the endurance conditions (voltage and temperature) and the decrease per unit time of the full charge capacity of the single cell due to Ni ₂ O ₃ H was created. You. Hereinafter, the first and second experiments will be described in order.

  FIG. 3 is a flowchart showing a processing procedure in the first experiment. Referring to FIG. 3, the processing shown in this flowchart is performed by an experimenter.

The experimenter prepares a sample in which a predetermined amount (for example, a predetermined amount Q1) of Ni ₂ O ₃ H powder is uniformly mixed with a new electrode (positive electrode) powder (step S100). Thereafter, the experimenter analyzes the sample by the X-ray diffraction method (Step S110). Specifically, the experimenter measures the peak area of the X-ray at a predetermined diffraction angle. Next, how to determine the X-ray diffraction angle will be described.

FIG. 4 shows an example of a result (diffraction pattern) of intentionally generating a large amount of Ni ₂ O ₃ H in the battery pack 10 and then analyzing the positive electrode by an X-ray diffraction method. Referring to FIG. 4, the horizontal axis indicates the diffraction angle (2θ), and the vertical axis indicates the diffraction intensity. During extremely full discharge of the positive electrode to produce a _{Ni 2 O 3 H, Ni 2} O 3 H, β-Ni (OH) 2, and the metal Ni (collector) it may include. If the battery is not completely discharged, β-NiOOH may be included.

The diffraction peak at the diffraction angle corresponding to the position of “◇” includes the influence of the diffraction by Ni ₂ O ₃ H. The diffraction peak at the diffraction angle corresponding to the position of “○” includes the influence of diffraction by β-Ni (OH) ₂ . The diffraction peak at the diffraction angle corresponding to the position of “x” includes the influence of diffraction by metal Ni.

For example, the diffraction peaks at the diffraction angles D1, D2, D3, and D4 are mainly affected by diffraction by Ni ₂ O ₃ H (“◇”), and are hardly affected by diffraction by other compounds. Therefore, the experimenter can measure the area of the diffraction peak caused by Ni ₂ O ₃ H by using X-rays having any of the diffraction angles D1, D2, D3, and D4. In the present embodiment, for example, the X-ray peak at the diffraction angle D1 is used for analysis by the X-ray diffraction method. Further, for example, the total area of the diffraction angles D1, D2, D3, and D4 may be used for analysis by the X-ray diffraction method.

Referring again to FIG. 3, when the sample is analyzed by the X-ray diffraction method in step S110, the experimenter records the peak area at diffraction angle D1 as the analysis result (step S120). As described above, the peak area at the diffraction angle D1 when a predetermined amount (for example, the predetermined amount Q1) of Ni ₂ O ₃ H is mixed in the sample is obtained through the processing of steps S100 to S120.

Next, as in the case of Ni ₂ O ₃ H, focusing on the diffraction peaks attributed to Ni (OH) ₂ (for example, D′ 1 and D′ 2 shown in FIG. 4), Ni ₂ O ₃ H Calculate the D'1 area when mixed in a fixed amount (Q1).

In the first experiment, the amount of Ni ₂ O ₃ H mixed into the sample is changed (for example, predetermined amounts Q2, Q3, etc.), and the processes of steps S100 to S120 are performed a plurality of times. As a result, the ratio of Ni ₂ O ₃ H in the sample (the amount of Ni ₂ O ₃ H / (the amount of Ni (OH) ₂ + the amount of Ni ₂ O ₃ H)) and the peak area ratio at the diffraction angle D1 (D1 / (D1 + D) '1)) can be obtained.

FIG. 5 is a diagram showing an example of the relationship between the ratio of Ni ₂ O ₃ H in the sample and the peak area ratio in the X-ray diffraction method, which was obtained through the first experiment. Referring to FIG. 5, the abscissa indicates the ratio of Ni ₂ O ₃ H in the sample (Ni ₂ O ₃ H amount / (Ni (OH) ₂ amount + Ni ₂ O ₃ H amount)), and the ordinate indicates X. The peak area ratio (D1 / (D1 + D'1)) in the line diffraction method is shown.

When predetermined amounts Q1, Q2, and Q3 of Ni ₂ O ₃ H were mixed in the sample, the peak area ratios at the diffraction angle D1 were S1, S2, and S3, respectively. From the above experimental results, for example, the relationship shown in FIG. 5 can be obtained as the relationship between the ratio of Ni ₂ O ₃ H in the sample and the peak area ratio at the diffraction angle D1. The first experiment is completed by determining the relationship between the ratio of Ni ₂ O ₃ H in the sample and the peak area ratio at the diffraction angle D1. Although the relationship in FIG. 5 is defined here based on the peak area ratio, the relationship in FIG. 5 may be defined based on the peak intensity, for example.

  FIG. 6 is a flowchart illustrating a processing procedure in the second experiment. Referring to FIG. 6, the processing shown in this flowchart is performed by an experimenter.

After setting the durability conditions (voltage and temperature), the experimenter performs a durability test on a single cell in the new assembled battery 10 (step S200). For example, in the durability test, the single cell is installed in a charging system provided in a thermostat. The temperature in the thermostat is maintained at the temperature set by the experimenter. Then, the single cell is charged with a constant voltage. It is considered that the voltage that increases due to the metal resistance does not contribute to the generation of Ni ₂ O ₃ H in the positive electrode.

  The durability test is performed, for example, by repeating charging for a predetermined time and discharging for a predetermined time so that the SOC value of a single cell falls within a predetermined range (for example, 50% to 80%). The predetermined range is, for example, a control range in which the SOC value is controlled in battery system 2. The durability test is performed over several days to several months as a whole, for example.

The reason why charging and discharging are repeated so that the SOC value falls within the predetermined range in the durability test will be described below. For example, when the SOC value exceeds the upper limit of the predetermined range, a part of β-NiOOH may be changed to γ-NiOOH in the positive electrode due to overcharging. When γ-NiOOH is generated in the positive electrode, the full charge capacity increases. In this case, even if the single cell after the durability test is analyzed, it is difficult to correctly estimate the amount of decrease in the full charge capacity due to Ni ₂ O ₃ H in the positive electrode. Therefore, in the endurance test of the present embodiment, in order to accurately examine the amount of decrease in the full charge capacity per unit time due to Ni ₂ O ₃ H, charge and discharge are performed so that the SOC value falls within a predetermined range. Repeated.

  The experimenter measures the full charge capacity of the single cell after the durability test (Step S210). For example, an experimenter puts a single cell into a fully charged state, discharges the cell until the voltage of the cell reaches the discharge end voltage, and measures the full charge capacity by integrating the current value at the time of discharge. Further, as described later, the electrode (positive electrode) may be disassembled and taken out from the single cell after the durability test, and the electrode capacity of the positive electrode alone may be measured.

  Thereafter, the experimenter calculates a decrease in the full charge capacity by subtracting the full charge capacity measured in step S210 from the full charge capacity (for example, the nominal capacity) of the new cell (step S220).

After confirming the decrease in the full charge capacity, the experimenter disassembles the cell, takes out the positive electrode, and performs analysis by the X-ray diffraction method (step S230). Thereafter, the experimenter determined the relationship between the ratio of Ni ₂ O ₃ H in the electrode and the peak area ratio in the X-ray diffraction method (derived in the first experiment (FIG. 5)), and the peak area ratio as the analysis result. Is used to calculate the generation ratio of Ni ₂ O ₃ H (step S240). For example, when the peak area ratio is S10, the generation ratio of Ni ₂ O ₃ H is estimated to be Q10 (FIG. 5).

After confirming that the decrease in the full charge capacity is caused by the generation of Ni ₂ O ₃ H, the experimenter calculates the decrease in the full charge capacity per unit time (step S250). Specifically, the experimenter divides the decrease amount of the full charge capacity calculated in step S220 by the total charge time in the durability test. Thereby, it is possible to calculate the amount of decrease in the full charge capacity of the nickel-metal hydride cell per unit charging time due to Ni ₂ O ₃ H. The reason why the division is performed not by the duration of the durability test but by the total charging time in the durability test is that Ni ₂ O ₃ H is not generated unless a certain voltage is applied to the cell, and is hardly generated during discharge. Because it is possible. In the present embodiment, the unit time is, for example, one second.

Thereafter, the experimenter records the amount of decrease in the full charge capacity per unit time calculated in step S250 as a result under the set endurance conditions (voltage and temperature) (step S260). As described above, through the processing of steps S200 to S260, the amount of decrease in the full charge capacity of the nickel-metal hydride unit cell per unit time due to Ni ₂ O ₃ H under the set endurance condition is determined.

In the second experiment, the processing of steps S200 to S260 is performed a plurality of times with the durability condition changed. As a result, the relationship between the voltage and temperature of the cell and the amount of decrease in the full charge capacity of the cell per unit time due to Ni ₂ O ₃ H can be obtained. This ends the second experiment.

  FIG. 7 is a diagram illustrating an example of a map in which results obtained through the second experiment are summarized. Referring to FIG. 7, the horizontal axis represents the temperature under the durability condition, and the vertical axis represents the voltage under the durability condition.

In the map 200, the full charge capacity of the single cell caused by Ni ₂ O ₃ H is determined for each combination of the cell temperature (T0, T1, T2...) And the cell voltage (V0, V1, V2...). (W00, W01, W10...) Are associated with each other. Note that the voltages (V0, V1, V2,...) Are values obtained by removing the voltage rise due to the metal resistance from the cell voltage. The amount of decrease in the full charge capacity per unit time (W00, W01, W10,...) Is a result obtained through the second experiment. In battery system 2 according to the present embodiment, map 200 is created in advance through the first and second experiments, and created map 200 is stored in memory 105. Hereinafter, the charge control in consideration of the decrease in the full charge capacity due to Ni ₂ O ₃ H will be described.

(Charge control)
FIG. 8 is a flowchart illustrating a procedure of the charging control of the battery pack 10. Referring to FIG. 8, the process shown in this flowchart is repeatedly executed by ECU 100 when battery pack 10 is charged, with the above-mentioned unit time as one cycle.

The ECU 100 acquires signals indicating the voltage, temperature, and current of each cell from the voltage sensor 21, the temperature sensor 23, and the current sensor 22 (step S300). The ECU 100 calculates, for each cell, a voltage obtained by subtracting the voltage rise due to the metal resistance from the cell voltage. The voltage corresponding to the voltage increase is calculated based on the metal resistance and the current that are recognized in advance. After that, the ECU 100 refers to the map 200 stored in the memory 105 and, for each cell, per unit time of the full charge capacity caused by Ni ₂ O ₃ H corresponding to the voltage and the cell temperature calculated above. The information indicating the amount of decrease (absolute value) of is obtained (step S310).

The ECU 100 adds the reduction amount of the full charge capacity calculated in step S310 to the total reduction amount (absolute value) of the full charge capacity due to Ni ₂ O ₃ H calculated one cycle before for each cell. Then, the total decrease amount of the current full charge capacity is calculated (step S320). The total reduction amount calculated one cycle before is stored in the memory 105.

  Thereafter, the ECU 100 determines whether or not there is a cell whose calculated total reduction amount is equal to or more than the predetermined amount Th1 (Step S330). As the predetermined amount Th1, for example, a value allowable as the total decrease amount of the full charge capacity is set.

  If it is determined that there is no cell whose total amount of decrease is equal to or greater than the predetermined amount Th1 (NO in step S330), a voltage obtained by subtracting the voltage increase due to the metal resistance from the applied voltage for charging (charging voltage) for each cell Is set to the predetermined voltage V10 (step S340). The predetermined voltage V10 is set in advance according to the characteristics of the cell.

On the other hand, if it is determined that there is a cell whose total reduction amount is equal to or greater than predetermined amount Th1 (YES in step S330), ECU 100 determines that the charging voltage of any of the cells whose total reduction amount is equal to or greater than predetermined amount Th1 is equal to the predetermined voltage. It is determined whether the voltage is equal to or higher than V20 (<predetermined voltage V10) (step S350). The predetermined voltage V20 is, for example, a value slightly lower than the above-described voltage at which Ni ₂ O ₃ H is generated in the positive electrode, and lower than the predetermined voltage V10 indicating the voltage upper limit when the total decrease is less than the predetermined amount Th1. .

If it is determined that the charging voltage of any of the cells is lower than predetermined voltage V20 (NO in step S350), the process proceeds to step S340 described above. On the other hand, if it is determined that the charging voltage of any of the cells is equal to or higher than predetermined voltage V20 (YES in step S350), ECU 100 sets charging voltage to predetermined voltage V20 in order to suppress further generation of Ni ₂ O ₃ H. The upper limit of the charging voltage of the cell is set to the predetermined voltage V20 (step S360). As a result, the charging voltage of at least the cell whose charging voltage has become equal to or higher than the predetermined voltage V20 is suppressed to less than the predetermined voltage V20. For example, ECU 100 decreases inputtable power Win regardless of the SOC value so that the charging voltage of a cell whose charging voltage is equal to or higher than predetermined voltage V20 is lower than predetermined voltage V20.

  As described above, in the battery system 2 according to the present embodiment, the ECU 100 sets the full charge capacity when the decrease in the full charge capacity derived from the battery voltage and temperature and the above-described map is equal to or greater than the predetermined amount Th1. The upper limit of the charging voltage is set lower than when the decrease amount of the charging voltage is less than the predetermined amount Th1.

According to the battery system 2, when the amount of decrease in the full charge capacity is equal to or more than the predetermined amount Th < _b > 1, generation of Ni ₂ O ₃ H is suppressed, so that the battery pack 10 can be appropriately protected. Further, by appropriately lowering the upper limit of the charging voltage, the performance of the battery pack 10 can be sufficiently exhibited.

[Other embodiments]
As described above, the above embodiment has been described as an embodiment of the present invention. However, the present invention is not necessarily limited to the above embodiment. Here, an example of another embodiment will be described.

In the above embodiment, the relationship between the voltage and temperature of the single cell and the amount of decrease in the full charge capacity of the single cell per unit time due to Ni ₂ O ₃ H was stored in the memory 105 as the map 200. . However, the above relationship does not necessarily need to be stored in the memory 105 as the map 200. For example, a result obtained through the first and second experiments may be expressed as a relational expression, and the relational expression (data) may be stored in the memory 105. In this case, the decrease amount of the full charge capacity of the single cell per unit time is obtained by using this relational expression.

Further, in the above-described embodiment, the map 200 holds the amount of decrease in the full charge capacity per unit time due to Ni ₂ O ₃ H. However, the target held by the map 200 is not limited to this. For example, the map 200 may hold the amount of Ni ₂ O ₃ H generated per unit time for each endurance condition.

In this case, the memory 105 needs to further store a conversion table for converting the amount of Ni ₂ O ₃ H generated per unit time into the amount of decrease in the full charge capacity per unit time. After estimating the amount of Ni ₂ O ₃ H generated per unit time using the map 200, the ECU 100 needs to determine the amount of decrease in the full charge capacity per unit time using the conversion table.

In the above embodiment, the amount of Ni ₂ O ₃ H generated in the positive electrode of the nickel-metal hydride single cell was analyzed by using the X-ray diffraction method. However, the method of analyzing the amount of generated Ni ₂ O ₃ H is not limited to this. For example, thermal analysis (DTA-TG (Differential Thermal Analysis-Thermo Gravimetric)) measurement may be used, or XAFS (X-ray Absorption Fine Structure) measurement may be used (note the change in average valence of Ni). .).

  In the above embodiment, the voltage (cell voltage) and the temperature (cell temperature) are monitored for each nickel-metal hydride unit cell. However, the monitoring unit of the voltage and the temperature is not limited to this. For example, a plurality of nickel-metal hydride cells may be used as one monitoring unit. In this case, for example, the map 200 may hold the amount of decrease in the full charge capacity per unit time in the monitoring unit (a plurality of cells).

  In the above-described embodiment, the durability test in the second experiment was performed by using a nickel-metal hydride single cell (single cell). However, the unit for performing the durability test is not limited to a single cell. For example, an endurance test may be performed on the assembled battery 10 or an endurance test may be performed on a plurality of nickel-metal hydride cells as one unit.

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  REFERENCE SIGNS LIST 1 vehicle, 2 battery system, 10 battery pack, 20 monitoring unit, 21 voltage sensor, 22 current sensor, 23 temperature sensor, 30 PCU, 41, 42 MG, 50 engine, 60 power split mechanism, 70 drive shaft, 80 drive wheels , 100 ECU, 105 memory, 200 maps.

Claims (1)

Nickel-metal hydride batteries,
Including a memory, a control device for controlling the charging voltage of the nickel-metal hydride battery,
The memory stores data indicating a relationship between a voltage and a temperature of the nickel-metal hydride battery and a decrease in a full charge capacity of the nickel-metal hydride battery caused by Ni ₂ O ₃ H generated in a positive electrode of the nickel-metal hydride battery. Remember
The control device sets the upper limit of the charging voltage when the reduction amount derived from the voltage and temperature of the nickel-metal hydride battery and the data is equal to or more than a predetermined amount, than when the reduction amount is less than a predetermined amount. Battery system to lower.

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