JP6620689B2 - Battery system - Google Patents

Description

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

Japanese Unexamined Patent Publication No. 2011-233423 (Patent Document 1) discloses an alkaline storage battery including a nickel positive electrode. In an alkaline storage battery including a nickel positive electrode, when Ni ₂ O ₃ H is generated in the nickel positive electrode, the internal resistance increases and the battery capacity (full charge capacity) decreases. In this alkaline storage battery, the generation and generation of Ni ₂ O ₃ H are suppressed by appropriately designing the length and height (width) of the nickel positive electrode, and the decrease in battery capacity is suppressed (see Patent Document 1).

JP 2011-233423 A

As described above, Ni ₂ O ₃ H is generated in the nickel positive electrode. Depending on the size, physical property value (resistance value), etc. of the electrode sheet (current collector foil) constituting the positive electrode, Ni ₂ There may be a bias in the generation of O ₃ H (hereinafter referred to as “generation unevenness”). When the generation unevenness of Ni ₂ O ₃ H occurs, the current concentrates on a site where the amount of Ni ₂ O ₃ H generated is small (good active site), and the generation of Ni ₂ O ₃ H accelerates at that site, thereby the battery. There is concern that the deterioration of Such problems and countermeasures are not particularly discussed in Patent Document 1.

The present invention has been made to solve such problems, and its object is, in the battery system including a nickel hydride battery, together with the amount of Ni 2 _O 3 _H in the positive electrode of the Ni 2 _O 3 _H in the positive electrode In consideration of the generation unevenness, it is to suppress the deterioration of the battery due to the generation of Ni ₂ O ₃ H.

The battery system includes a nickel metal hydride battery and a control device that controls charging of the nickel metal hydride battery. The control device includes a memory, and the memory stores first to third data. The first data is data indicating a correspondence relationship between the voltage and temperature of the nickel metal hydride battery and the amount of Ni ₂ O ₃ H produced in the positive electrode of the nickel metal hydride battery. The second data is data indicating a correspondence relationship between the charging current and temperature of the nickel metal hydride battery and the magnitude of Ni ₂ O ₃ H generation unevenness in the positive electrode of the nickel metal hydride battery. The third data is data indicating a correspondence relationship between the amount of Ni ₂ O ₃ H generated and the size of the generation unevenness and the restriction region that limits the charging of the nickel metal hydride battery. The control device refers to the first data, calculates the amount of Ni ₂ O ₃ H generated from the voltage and temperature of the nickel metal hydride battery, and refers to the second data to charge current and temperature of the nickel metal hydride battery. From this, the size of Ni ₂ O ₃ H generation unevenness is calculated. The control device refers to the third data, and determines that the nickel hydride battery is charged when it is determined that the calculated generation amount of Ni ₂ O ₃ H and the generation unevenness are included in the restricted region. Predetermined control for restricting is executed.

  The predetermined control refers to, for example, suppressing the upper limit voltage of the nickel metal hydride battery as the temperature of the nickel metal hydride battery increases, lowering the upper limit temperature of use of the nickel metal hydride battery when charging the nickel metal hydride battery, Control for limiting the charging current (charging power).

When the generation unevenness of Ni ₂ O ₃ H occurs in the positive electrode, the deterioration of the battery is accelerated. In the battery system described above, not only the generation amount (F value) of Ni ₂ O ₃ H in the positive electrode but also in the positive electrode The size (G value) of the generation unevenness of Ni ₂ O ₃ H is also calculated, and predetermined control for limiting the charging of the nickel-metal hydride battery according to the amount of Ni ₂ O ₃ H generation and the size of the generation unevenness Is executed. Thereby, for example, even when the amount of Ni ₂ O ₃ H generated is not so large, even when the generation unevenness of Ni ₂ O ₃ H is large, charging is limited to suppress the generation of Ni ₂ O ₃ H, Battery deterioration can be suppressed.

According to this battery system, in consideration of the generation amount of Ni ₂ O ₃ H in the positive electrode of the nickel-metal hydride battery and the generation unevenness of Ni ₂ O ₃ H in the positive electrode, the deterioration of the battery due to the generation of Ni ₂ O ₃ H is prevented. Can be suppressed.

It is the figure which showed roughly the structure of the vehicle carrying the battery system according to embodiment of this invention. Is a diagram showing an example of the experimental results showing the relationship between the presence ratio and the full charge capacity of Ni 2 _O 3 _H in the positive electrode. It is a flowchart which shows the process sequence in 1st experiment. Intentionally nickel-hydrogen battery to Ni 2 _O 3 _H many analysis generated X-ray diffraction of the positive electrode was the result illustrates an example of a (diffraction patterns). Obtained by the first experiment, the ratio of Ni 2 _O 3 _H in the electrode is a diagram showing an example of the relationship between the peak area ratio in X-ray diffraction method. It is a flowchart which shows the process sequence in 2nd experiment. It is a figure which shows an example of the 1st map on which the result obtained by 2nd experiment was put together. It is a top view of the electrode sheet which comprises a positive electrode in each cell of an assembled battery. Ni 2 _O 3 _H degradation by the generation of a graph showing the measurement results in the initial battery. Ni 2 _O 3 _H measurement results in the battery was allowed to proceed for degradation by the generation of a diagram showing a. It is a flowchart which shows the procedure of the experiment for producing a 2nd map (2nd data). It is a figure which shows an example of the 2nd map where the result obtained by experiment was put together. And F value and the G value is a diagram showing an example of a correspondence relationship between the restricted area to limit the charge in order to suppress the formation of Ni 2 _O 3 _H. It is a flowchart explaining the process sequence of the battery deterioration suppression control based on F value and G value. It is a flowchart explaining the modification of the battery deterioration suppression control based on F value and G value. It is a flowchart explaining the other modification of the battery deterioration suppression control based on F value and G value.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Battery system configuration)
FIG. 1 schematically shows a configuration of a vehicle 1 on which a battery system according to an embodiment of the present invention is mounted. In the following, the case where the vehicle 1 is a hybrid vehicle will be described as a representative example. However, the battery system according to the present invention is not limited to the one mounted on the hybrid vehicle. Is applicable to uses other than vehicles.

  Referring to FIG. 1, vehicle 1 is referred to as a battery system 2, a power control unit (hereinafter referred to as “PCU (Power Control Unit)”) 30, and a motor generator (hereinafter referred to as “MG (Motor Generator)”). ) 41, 42, engine 50, power split device 60, drive shaft 70, and drive wheel 80. The battery system 2 includes an assembled battery 10, a monitoring unit 20, and an electronic control device (hereinafter referred to as “ECU (Electronic Control Unit)”) 100.

  The engine 50 is an internal combustion engine that outputs motive power by converting combustion energy generated when an air-fuel mixture is burned into kinetic energy of a moving element such as a piston or a rotor. Power split device 60 includes, for example, a planetary gear mechanism having three rotation shafts of a sun gear, a carrier, and a ring gear. Power split device 60 splits the power output from engine 50 into power for driving MG 41 and power for driving drive wheels 80.

  MGs 41 and 42 are AC rotating electric machines, for example, three-phase AC synchronous motors in which permanent magnets are embedded in a rotor. The MG 41 is mainly used as a generator driven by the engine 50 via the power split device 60. The electric power generated by the MG 41 is supplied to the MG 42 or the assembled battery 10 via the PCU 30.

  The MG 42 mainly operates as an electric motor and drives the drive wheels 80. The MG 42 is driven by receiving at least one of the electric power from the assembled battery 10 and the electric power generated by the MG 41, and the driving force of the MG 42 is transmitted to the driving shaft 70. On the other hand, when the vehicle is braked or when acceleration is reduced on a downward slope, the MG 42 operates as a generator and performs regenerative power generation. The electric power generated by the MG 42 is supplied to the assembled battery 10 via the PCU 30.

  The assembled battery 10 includes a plurality of nickel metal hydride cells (single cells) connected in series, and stores electric power for driving the MGs 41 and 42. That is, the assembled battery 10 can supply power to the MGs 41 and 42 through the PCU 50. The assembled battery 10 is charged by receiving generated power through the PCU 30 when the MGs 41 and 42 generate power.

  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 (hereinafter also referred to as “cell voltage”) VBi for each cell of the assembled battery 10. The current sensor 22 detects the charge / discharge current IB of the assembled battery 10. In this embodiment, the current sensor 22 detects the charging current as a positive value and the discharging current as a negative value for the assembled battery 10. The temperature sensor 23 detects the temperature (hereinafter also referred to as “cell temperature”) TBi for each cell. Each sensor outputs a signal indicating the detection result to ECU 100.

  Note that the voltage sensor 21 and the temperature sensor 23 may detect the voltage and temperature using a plurality of (for example, several) cells as monitoring units. In this case, for the voltage, the voltage (average value) for each cell can be calculated by dividing the detection values for a plurality of cells by the number of cells.

  The PCU 30 performs bidirectional power conversion between the assembled battery 10 and the MGs 41 and 42 in accordance with a control signal from the ECU 100. The PCU 30 is configured to be able to control the states of the MGs 41 and 42 separately. For example, the PCU 30 can place the MG 42 in a power running state while the MG 41 is in a regenerative (power generation) state. PCU 30 includes, for example, two inverters provided corresponding to MGs 41 and 42 and a converter that boosts a DC voltage supplied to each inverter to an output voltage of assembled battery 10 or higher.

  The ECU 100 includes a CPU (Central Processing Unit) 102, a memory (ROM (Read Only Memory) and RAM (Random Access Memory)) 105, and an input / output port (not shown) for inputting / outputting various signals. Consists of. The ECU 100 controls charging / discharging of the assembled battery 10 by controlling the engine 50 and the PCU 30 based on the signals received from the sensors and the program and map stored in the memory 105.

  For example, when it is necessary to charge the assembled battery 10, the ECU 100 causes the MG 41 to generate power using a part of the power of the engine 50, and charges the assembled battery 10 with the electric power generated by the MG 41. (MG41, MG42) is controlled.

(Battery deterioration suppression)
For nickel metal hydride cells, Ni ₂ O ₃ H is generated at the positive electrode under conditions of high temperature and high voltage (for example, when charging with a large current such that the cell voltage is 1.5 V or more). Is done. Since this Ni ₂ O ₃ H does not contribute to the battery reaction, when the amount of Ni ₂ O ₃ H generated in the positive electrode increases, the full charge capacity decreases (battery deterioration).

FIG. 2 is a diagram showing an example of an experimental result showing a correspondence 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 horizontal axis represents the abundance ratio of Ni ₂ O ₃ H in the positive electrode, and the vertical axis represents the full charge capacity. From this experimental result, it can be seen that when the abundance ratio of Ni ₂ O ₃ H increases, the full charge capacity decreases (the battery deteriorates).

Therefore, the amount of Ni ₂ O ₃ H produced is accurately estimated based on the temperature and voltage of the cell, and the battery voltage and the upper limit temperature of use are suppressed under circumstances where the amount of Ni ₂ O ₃ H produced increases. Thus, it is useful to perform control for suppressing the formation of Ni ₂ O ₃ H.

Here, FIG. 2 shows a correspondence relationship between the abundance ratio of Ni ₂ O ₃ H in the positive electrode, that is, the total generation amount, and the full charge capacity. In the positive electrode, the electrode sheet (current collector foil) Depending on the size, physical property value (resistance value), etc., uneven reaction occurs depending on the part, and as a result, uneven generation of Ni ₂ O ₃ H corresponding to the part may occur. When uneven production of Ni ₂ O ₃ H occurs, current (charging current) concentrates on a part (good active part) where the amount of Ni ₂ O ₃ H produced is small in the positive electrode, and reaction concentrates on that part. This accelerates the generation of Ni ₂ O ₃ H. That is, if the generation unevenness of Ni ₂ O ₃ H corresponding to the site in the positive electrode occurs, there is a concern that the generation of Ni ₂ O ₃ H is accelerated and the deterioration of the battery is accelerated.

Therefore, in battery system 2 according to this embodiment, the amount of Ni ₂ O ₃ H produced in the positive electrode (the total amount produced regardless of the site in the positive electrode, hereinafter referred to as “F value”) is estimated. In addition, the size of Ni ₂ O ₃ H generation unevenness in the positive electrode (hereinafter referred to as “G value”) is also estimated. As will be described later, the G value is a parameter indicating the relative size of the generation unevenness of Ni ₂ O ₃ H in the positive electrode, and is a dimensionless amount.

And when it determines with said F value and G value being contained in the predetermined | prescribed restriction | limiting area | region which restrict | limits charge of a battery, control (after-mentioned) for restrict | limiting charge is performed. Thus, generation of _Ni 2 _{O 3} H is suppressed, deterioration of the battery is suppressed.

In illustrates the method of calculating the F value that indicates the production amount of Ni 2 _O 3 _H in the positive electrode (the total generation amount does not depend on the site of the positive electrode), and the magnitude of the generated unevenness of Ni 2 _O 3 _H in the positive electrode below A method for calculating the G value will be described first, and then control based on the calculated F value and G value will be described.

(Calculation method of F value)
The amount of Ni ₂ O ₃ H produced at the positive electrode depends on the cell voltage and temperature. In particular, the amount of Ni ₂ O ₃ H produced increases under conditions of high temperature and high voltage (when charging with a large current such that the cell voltage is 1.5 V or higher). In this embodiment, for a nickel-metal hydride battery (single cell), a first map (first data) indicating the correspondence between voltage and temperature and the amount of Ni ₂ O ₃ H produced in the positive electrode is obtained in advance by experiments. Created and stored in the memory 105 of the ECU 100. Then, the ECU 100 refers to the first map during use of the assembled battery 10 (for example, when the system of the vehicle 1 is operating), based on the cell voltage and cell temperature detected by the monitoring unit 20. The production amount (F value) of Ni ₂ O ₃ H is calculated.

The experiment for creating the first map is performed, for example, in the following order. First, an 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 (hereinafter referred to as “first experiment”). ) Is performed. Thereafter, an experiment for investigating the relationship between the durability condition (voltage and temperature) and the amount of Ni ₂ O ₃ H produced in the positive electrode using the cell through the durability test (described later) and the result of the first experiment (hereinafter referred to as “the test result”) (Referred to as “second experiment”). In the second experiment, finally, a map (first map) showing the relationship between the durability condition (voltage and temperature) and the amount of Ni ₂ O ₃ H produced per unit time in a single cell is created. . 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 process shown in this flowchart is performed by an experimenter.

The experimenter creates a sample in which a predetermined amount (for example, a predetermined amount Q1) of Ni ₂ O ₃ H powder is uniformly mixed with 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 having a predetermined diffraction angle.

FIG. 4 is a diagram illustrating an example of an analysis result (diffraction pattern) of the positive electrode in which a large amount of Ni ₂ O ₃ H is intentionally generated in a nickel metal hydride battery 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. In addition, when not completely discharged, β-NiOOH may also be included.

The diffraction peak at the diffraction angle corresponding to the position of “◇” includes the influence of 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 to D4 are mainly affected by diffraction due to Ni ₂ O ₃ H (“）”) and hardly affected by diffraction due to other compounds. Therefore, the experimenter can measure the area of the diffraction peak due to Ni ₂ O ₃ H by using X-rays having a diffraction angle of any of D1 to 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 to D4 may be used for analysis in the X-ray diffraction method.

Referring to FIG. 3 again, when the sample is analyzed by the X-ray diffraction method in step S110, the experimenter records the peak area at the 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 electrode is obtained by the processing of steps S100 to S120.

Next, as with 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 is The D′ 1 area when a predetermined amount (Q1) is mixed is calculated.

In the first experiment, the amount of Ni ₂ O ₃ H mixed in the sample is changed (for example, a predetermined amount 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 (Ni ₂ O ₃ H amount / (Ni (OH) ₂ amount + Ni ₂ O ₃ H amount)) and the peak area ratio (D1 / (D1 + D) at the diffraction angle D1. The relationship with '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, obtained by the first experiment. Referring to FIG. 5, the horizontal axis 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 vertical axis indicates X The peak area ratio (D1 / (D1 + D′ 1)) in the line diffraction method is shown.

When a predetermined amount of Q1, Q2, and Q3 of Ni ₂ O ₃ H was 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. Here, the relationship of FIG. 5 is defined based on the peak area, but the relationship of FIG. 5 may be defined based on the peak intensity, for example.

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

The experimenter sets an endurance condition (voltage and temperature), and then performs an endurance test on the single cell in the new assembled battery 10 (step S200). For example, in this durability test, the single cell is installed in a charging system provided in a thermostat. The temperature in the thermostat is maintained at a temperature set by the experimenter. The single cell is charged with a constant voltage. The voltage that rises due to the metal resistance among the constant voltage is considered not to 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 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 the battery system 2. The durability test is performed, for example, over several days to several months as a whole.

When the endurance test is completed in step S200, the experimenter disassembles the cell subjected to the endurance test, takes out the positive electrode, and performs analysis by the X-ray diffraction method (step S210). Thereafter, the experimenter determined that 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 production amount of Ni ₂ O ₃ H per unit time (step S220).

For example, when the peak area is S10, the production ratio of Ni ₂ O ₃ H is estimated to be Q10 (FIG. 5). The unit charge time of Ni ₂ O ₃ H is obtained by dividing the amount of Ni ₂ O ₃ H that can be calculated from the estimated production ratio of Ni ₂ O ₃ H (Q10) by the total charge time in the durability test. The generation amount per hit can be calculated. The reason why division is performed not by the time of the endurance test but by the total charge time in the endurance test is that Ni ₂ O ₃ H is not generated unless a certain voltage (for example, 1.5 V or more) is applied, and at the time of discharging It is because it is thought that it is hard to be generated. In the present embodiment, the unit time is 1 second, for example.

Thereafter, the experimenter records the amount of Ni ₂ O ₃ H generated per unit time estimated in step S220 as a result of the voltage and temperature under the set durability conditions (step S230). As described above, the amount of Ni ₂ O ₃ H generated per unit time (per unit cell) under the set endurance conditions is determined by the processes in steps S200 to S230.

And about this 2nd experiment, durability conditions (voltage and temperature) are changed and the process of step S200-S230 is performed in multiple times. As a result, the relationship between the voltage and temperature and the amount of Ni ₂ O ₃ H produced per unit time for a single cell can be determined. This completes the second experiment.

  FIG. 7 is a diagram illustrating an example of the first map 200 in which the results obtained by the second experiment are summarized. Referring to FIG. 7, the horizontal axis indicates the temperature under the durability condition, and the vertical axis indicates the voltage under the durability condition.

In the first map 200, per unit time of Ni ₂ O ₃ H in a single cell for each combination of cell temperature (T0, T1, T2...) And cell voltage (V0, V1, V2...). Are associated with each other (f00, f01, f10...). Note that the voltages (V0, V1, V2,...) Are values obtained by removing the voltage increase derived from the metal resistance from the cell voltage. The amount of Ni ₂ O ₃ H produced per unit time (f00, f01, f10...) Is a result obtained by the second experiment. In the battery system 2 according to this embodiment, the first map 200 is created in advance by the first and second experiments, and the created first map 200 is stored in the memory 105.

Then, when the assembled battery 10 is in use (for example, when the system of the vehicle 1 is operating), the first map 200 is referred to, and the cell voltage and the cell temperature detected by the monitoring unit 20 for each cell of the assembled battery 10 are referred to. Based on this, the production amount (F value) of Ni ₂ O ₃ H is calculated.

(G value calculation method)
FIG. 8 is a plan view of an electrode sheet constituting a positive electrode in each cell of the assembled battery 10. The electrode body of the cell is formed by laminating a plurality of electrode sheets constituting the positive electrode (hereinafter also referred to as “positive electrode sheet”) and a plurality of electrode sheets constituting the negative electrode through a separator. . In FIG. 8, one positive electrode sheet 11 is shown.

  Referring to FIG. 8, positive electrode sheet 11 includes a metal current collector foil 12 and a positive electrode active material 13 formed on the surface of current collector foil 12. An electrochemical reaction occurs at a site where the positive electrode active material 13 is formed, and a current collecting terminal (not shown) is connected at a site where the positive electrode active material 13 is not formed (left end in the figure).

In the positive electrode sheet 11, the positive electrode active material 13 of the positive electrode sheet 11 according to the size (particularly the length in the x direction) of the sheet (current collector foil 12), the physical property value (metal resistance value of the current collector foil 12), and the like. In the site where is formed, uneven reaction occurs depending on the site, and as a result, uneven production of Ni ₂ O ₃ H depending on the site can occur. In this embodiment, the part where the positive electrode active material 13 is formed is divided into, for example, nine parts as shown, and the amount of Ni ₂ O ₃ H produced in each part after the durability test is measured by X-ray diffraction. The

9 and 10 are diagrams showing an example of the result of measuring the amount of Ni ₂ O ₃ H produced in each region A to D of the positive electrode sheet 11 shown in FIG. 8 by X-ray diffraction. 9 and 10, two types of batteries having different degrees of deterioration are selected from the batteries that have been subjected to various durability tests, and the analysis results are shown as representative diagrams. FIG. 9 shows a measurement result in the battery in which the deterioration due to the generation of Ni ₂ O ₃ H is early, and FIG. 10 shows a measurement result in the battery in which the deterioration due to the generation of Ni ₂ O ₃ H proceeds.

9 and 10, the horizontal axis represents the diffraction angle (2θ), and the vertical axis represents the diffraction intensity. The diffraction peaks at diffraction angles d1 and d2 in FIG. 9 and diffraction angles d1 to d3 in FIG. 10 are attributed to Ni ₂ O ₃ H. The diffraction peak at the diffraction angle d0 is attributed to a new phase (β-Ni (OH) ₂ / β-NiOOH).

From the measurement results of FIG. 9, it can be seen that in the battery in the initial stage of deterioration, the generation of Ni ₂ O ₃ H occurs preferentially in the regions C and D shown in FIG. From the measurement results of FIG. 10, in the battery having deteriorated, the generation of Ni ₂ O ₃ H occurs in the entire area of the positive electrode sheet 11, and the generation amount is uneven as in FIG. It can also be confirmed.

Therefore, based on the above-described knowledge, in this embodiment, a durability test is performed on a single cell in a new assembled battery 10, and the amount of Ni ₂ O ₃ H produced in each part of the positive electrode sheet 11 after the durability test. Is measured by X-ray diffraction, and the generation unevenness of Ni ₂ O ₃ H in the positive electrode is measured. The generation unevenness of Ni ₂ O ₃ H is, for example, a value (dimensionalless amount) obtained by normalizing the generation amount of the region where the generation amount of Ni ₂ O ₃ H is the largest with the average value of all parts. it can.

The size of the generation unevenness of Ni ₂ O ₃ H depends on the current (charging current) flowing through the cell and the temperature. In particular, the generation unevenness of Ni ₂ O ₃ H increases under conditions where the temperature is high and the charging current is large. In this embodiment, for a nickel metal hydride battery (single cell), a second map (second data) showing a correspondence relationship between the charging current and temperature and the magnitude of Ni ₂ O ₃ H generation unevenness in the positive electrode. Is created in advance by experiments and stored in the memory 105 of the ECU 100. Then, the ECU 100 refers to the second map during use of the assembled battery 10 (for example, during system operation of the vehicle 1), based on the charging current and the cell temperature detected by the monitoring unit 20, respectively. The size (G value) of the generation unevenness of Ni ₂ O ₃ H in

  FIG. 11 is a flowchart showing the procedure of an experiment for creating the second map (second data). Referring to FIG. 11, the process shown in this flowchart is performed by an experimenter.

  The experimenter sets an endurance condition (charging current and temperature), and then performs an endurance test on the single cell in the new assembled battery 10 (step S300). For example, in this durability test, the single cell is installed in a charging system provided in a thermostat. The temperature in the thermostat is maintained at a temperature set by the experimenter. The single cell is charged with a constant current. For example, the durability test is performed over several days to several months as a whole.

When the durability test is completed in step S300, the experimenter disassembles the cell subjected to the durability test, takes out the positive electrode, and analyzes the generation unevenness of Ni ₂ O ₃ H in the positive electrode (step S310). Specifically, for example, as shown in FIG. 8, the amount of Ni ₂ O ₃ H produced in each region obtained by dividing the positive electrode sheet into nine equal parts is measured by the X-ray diffraction method.

Thereafter, the experimenter calculates the size of the generation unevenness of Ni ₂ O ₃ H generated per unit time in the positive electrode of the cell from the analysis result of the Ni ₂ O ₃ H generation amount in each region of the positive electrode sheet (step S320). ). Specifically, based on the amount of Ni ₂ O ₃ H produced in each region, the magnitude of Ni ₂ O ₃ H production unevenness generated in the durability test is calculated, and the calculated value is used as the total charge time in the durability test. By dividing by, it is possible to calculate the size of the Ni ₂ O ₃ H generation unevenness that occurs in unit time.

As described above, the generation unevenness of Ni ₂ O ₃ H is, for example, a value obtained by normalizing the generation amount of the region with the largest Ni ₂ O ₃ H generation amount with the average value of all parts (none Dimension quantity). In addition, in the above, the reason why the division is performed not by the time of the durability test but by the total charging time in the durability test is that unevenness in the generation of Ni ₂ O ₃ H occurs during charging (particularly during charging with a large current). is there. The unit time is, for example, 1 second as in the case of calculating the F value.

Thereafter, the experimenter records the magnitude of the generation unevenness of Ni ₂ O ₃ H generated in unit time calculated in step S320 as a result of the charging current and temperature under the set endurance conditions (step S330). As described above, the size of Ni ₂ O ₃ H generation irregularity (per unit cell) generated per unit time under the set endurance conditions is determined by the processing in steps S300 to S330.

Then, the durability conditions (charging current and temperature) are changed, and the processes of steps S300 to S330 are performed a plurality of times. As a result, the relationship between the charging current and temperature and the generation unevenness of Ni ₂ O ₃ H generated per unit time for a single cell can be obtained.

  FIG. 12 is a diagram illustrating an example of the second map 300 in which the results obtained by the above-described experiment are summarized. Referring to FIG. 12, the horizontal axis indicates the temperature under the durability condition, and the vertical axis indicates the current under the durability condition (charging current).

In the second map 300, Ni ₂ O ₃ H generated per unit time in a single cell for each combination of cell temperature (T0, T1, T2...) And charging current (I0, I1, I2...). Are associated with each other (g00, g01, g10...). In battery system 2 according to this embodiment, this second map 300 is created in advance by the above-described experiment (endurance test), and the created second map 300 is stored in memory 105.

Then, when the battery pack 10 is in use (for example, when the system of the vehicle 1 is in operation), the second map 300 is referred to, and the current IB (charging current) detected by the monitoring unit 20 for each cell of the battery pack 10. Ni 2 _O 3 _H magnitude of generating unevenness of (G value) is calculated and based on the cell temperature.

  In the above description, the G value is calculated using the second map 300 created by an experiment (endurance test), but may be calculated as follows. That is, for the positive electrode sheet 11 constituting the positive electrode in each cell of the assembled battery 10, for example, the metal resistance and reaction resistance (with temperature dependence) in each region as shown in FIG. 8 are modeled by a ladder circuit. The G value may be calculated based on the current IB (charging current) detected by the monitoring unit 20 and the cell temperature.

(Battery deterioration suppression control based on F value and G value)
In the battery system 2 according to this embodiment, as described above, together with the F value that indicates the production amount of Ni 2 _O 3 _H in the positive electrode (the total generation amount does not depend on the site of the positive electrode), Ni ₂ O ₃ in the positive electrode A G value indicating the size of the generation unevenness of H is estimated. Then, the deterioration state of the assembled battery 10 is accurately determined in consideration of the G value as well as the F value, and control for suppressing the deterioration of the battery by suppressing the generation of Ni ₂ O ₃ H is executed.

FIG. 13 is a diagram illustrating an example of a correspondence relationship between the F value and the G value and a restriction region where charging is restricted in order to suppress the generation of Ni ₂ O ₃ H. Referring to FIG. 13, a region S indicated by diagonal lines is a region where charging of the assembled battery 10 is restricted in order to suppress generation of Ni ₂ O ₃ H and suppress deterioration of the battery. For example, when the F value and the G value are included in the region S for any of the cells of the assembled battery 10, control (described later) for restricting charging is executed.

In the battery system 2 according to the present embodiment, a third map (third data) indicating a correspondence relationship between the F value and the G value and the region S in which charging of the assembled battery 10 is restricted is prepared in advance, and the memory of the ECU 100 105 is stored. In the example shown in FIG. 13, as the F value increases (the amount of Ni ₂ O ₃ H generated increases), charging is limited, and as the G value increases (Ni ₂ O ₃ H in the positive electrode). Charging is limited as the generation unevenness increases. Thereby, for example, when the F value has not increased so much but the G value has increased, the deterioration of the battery can be accelerated by the uneven generation of Ni ₂ O ₃ H in the positive electrode. Deterioration can be suppressed.

  FIG. 14 is a flowchart illustrating a processing procedure for battery deterioration suppression control based on the F value and the G value. The processing shown in this flowchart is repeatedly executed by the ECU 100 while the battery pack 10 is being charged with the unit time as one cycle.

  Referring to FIG. 14, ECU 100 acquires signals indicating cell voltage VBi, current IB, and cell temperature TBi of assembled battery 10 from voltage sensor 21, current sensor 22, and temperature sensor 23 of monitoring unit 20 (step). S400).

Next, the ECU 100 refers to the first map 200 stored in the memory 105, and for each cell, the Ni ₂ O ₃ H per unit time corresponding to the cell voltage VBi and the cell temperature TBi acquired in step S400. Get the amount of generated. Then, ECU 100, for each cell, the production amount of _Ni 2 _{O 3} H per unit obtained by referring to the first map 200 times, the amount of the calculated _Ni 2 _{O 3} H in one cycle before ( By adding to the (F value), the current generation amount (F value) of Ni ₂ O ₃ H is calculated (step S410). Note that the calculated generation amount (F value) of Ni ₂ O ₃ H is stored in the memory 105. That is, the Ni ₂ O ₃ H generation amount (F value) calculated one cycle before is stored in the memory 105.

Subsequently, the ECU 100 refers to the second map 300 stored in the memory 105, and for each cell, Ni generated in unit time corresponding to the current IB (charging current) and the cell temperature TBi acquired in step S400. The size of the generation unevenness of ₂ O ₃ H is acquired. Then, the ECU 100 calculates, for each cell, the size of the Ni ₂ O ₃ H generation unevenness generated per unit time acquired with reference to the first map 200 and calculated for Ni ₂ O ₃ H one cycle before. Is added to the generation irregularity size (G value) of the current Ni ₂ O ₃ H to calculate the generation irregularity size (G value) (step S420). Note that the calculated generation unevenness (G value) of Ni ₂ O ₃ H is also stored in the memory 105. That is, the magnitude (G value) of Ni ₂ O ₃ H generation unevenness calculated one cycle before is stored in the memory 105.

  When the F value and the G value for each cell are calculated, the ECU 100 refers to the third map stored in the memory 105, and for each cell, the F value and the G value calculated in steps S410 and 420, respectively. Is included in the restriction region (region S) for restricting charging of the assembled battery 10 (step S430).

If it is determined in step S430 that there is a cell whose F value and G value are included in the restriction region (region S) (YES in step S430), ECU 100 restricts the upper limit Win of the charging power of battery pack 10 or the like. Then, in the cell in which the F value and the G value are included in the restricted region, the upper limit voltage is suppressed as the temperature is higher (step S440). Accordingly, the voltage of the cell is the charging of the assembled battery 10 so as not to exceed the upper limit voltage is limited, Ni 2 _O 3 _H generation of is suppressed. In addition, suppression of the upper limit voltage accompanying temperature may be continuous or discrete.

  On the other hand, when it is determined in step S430 that there is no cell in which the F value and G value are included in the restricted region (region S) (NO in step S430), ECU 100 returns to step without executing step S440. And migrate the process.

As described above, in this embodiment, the amount of _Ni 2 _{O 3} H in the positive electrode together with (F value) is calculated, the magnitude of the generated unevenness of _Ni 2 _{O 3} H in the positive electrode (G value) Is also calculated. And according to this embodiment, considering the G value as well as the F value, it is possible to suppress the deterioration of the assembled battery 10 due to the generation of Ni ₂ O ₃ H.

[Modification]
In the above embodiment, when there is a cell whose F value and G value are included in the restricted region (region S), the upper limit voltage of the cell is suppressed in order to suppress the generation of Ni ₂ O ₃ H in the cell. However, the method for suppressing the formation of Ni ₂ O ₃ H is not limited to this.

  FIG. 15 is a flowchart for explaining a modification of the battery deterioration suppression control based on the F value and the G value. The processing shown in this flowchart is also repeatedly executed by the ECU 100 while the battery pack 10 is being charged with the unit time as one cycle.

Referring to FIG. 15, this flowchart includes step S442 instead of step S440 in the flowchart shown in FIG. That is, when it is determined in step S430 that there is a cell in which the F value and G value are included in the restricted region (region S) (YES in step S430), ECU 100 includes the F value and G value in the restricted region. The use upper limit temperature of the cell is lowered (step S442). Thus, charging of the assembled battery 10 so that the temperature of the cell does not exceed the upper limit use temperature is limited, the generation of Ni 2 _O 3 _H is suppressed.

  FIG. 16 is a flowchart for explaining another modified example of the battery deterioration suppression control based on the F value and the G value. The processing shown in this flowchart is also repeatedly executed by the ECU 100 while the battery pack 10 is being charged with the unit time as one cycle.

Referring to FIG. 16, this flowchart includes step S444 instead of step S440 in the flowchart shown in FIG. That is, when it is determined in step S430 that there is a cell in which the F value and the G value are included in the restriction region (region S) (YES in step S430), ECU 100 restricts upper limit Win of the charging power of battery pack 10. Then, the charging current is limited (step S444). As a result, generation unevenness of Ni ₂ O ₃ H is suppressed, and deterioration of the assembled battery 10 is suppressed. That is, this modification is considered to be a useful control method when the G value is relatively large. Furthermore, by limiting the upper limit Win of the charging power of the assembled battery 10, the current flowing through the assembled battery 10 is limited while limiting the voltage of the cells included in the region S (FIG. 13) as in the above embodiment. There may be some restrictions.

In the above-described embodiment and its modification, the correspondence between the cell voltage and temperature and the amount of Ni ₂ O ₃ H produced in the positive electrode is stored in the memory 105 as the first map 200 (FIG. 7). However, the correspondence relationship may be expressed as a relational expression, and the relational expression (data) may be stored in the memory 105. Similarly, in the above description, it is assumed that the correspondence relationship between the charging current and the cell temperature and the generation unevenness of Ni ₂ O ₃ H in the positive electrode is stored in the memory 105 as the second map 300 (FIG. 12). However, the above correspondence relationship may be expressed as a relational expression, and the relational expression (data) may be stored in the memory 105. Further, the third map (FIG. 13) showing the correspondence between the F value and the G value and the restriction region for restricting charging of the assembled battery 10 may also be stored in the memory 105 as a relational expression. Good.

  In the above description, the voltage and temperature are monitored for each cell of the assembled battery 10. However, the voltage and temperature may be detected using a plurality of (for example, several) cells as monitoring units. In this case, for the voltage, the voltage (average value) for each cell can be calculated by dividing the detected value by the number of cells in the monitoring unit.

  In the above description, the durability test is performed on a single cell in the assembled battery 10. However, the durability test may be performed using a plurality of cells as one unit, or the durability test is performed on the assembled battery 10. May be.

In the above description, the X-ray diffraction method is used for the measurement of the amount of Ni ₂ O ₃ H produced. However, other measurement methods such as thermal analysis (DTA-TG (Differential Thermal Analysis-Thermo Gravimetric)) are used. ) Measurement or XAFS (X-ray Absorption Fine Structure) measurement may be used (focus on the change in the average valence of Ni).

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  DESCRIPTION OF SYMBOLS 1 Vehicle, 2 Battery system, 10 Assembly battery, 11 Positive electrode sheet, 12 Current collecting foil, 13 Positive electrode active material, 20 Monitoring unit, 21 Voltage sensor, 22 Current sensor, 23 Temperature sensor, 30 PCU, 41, 42 MG, 50 Engine, 60 power split device, 70 drive shaft, 80 drive wheel, 100 ECU, 102 CPU, 105 memory, 200 first map, 300 second map.

Claims (1)

A nickel metal hydride battery,
A control device including a memory and controlling charging of the nickel metal hydride battery,
The memory is
First data indicating a correspondence relationship between the voltage and temperature of the nickel metal hydride battery and the amount of Ni ₂ O ₃ H produced in the positive electrode of the nickel metal hydride battery;
Second data indicating a correspondence relationship between the charging current and temperature of the nickel-metal hydride battery and the magnitude of Ni ₂ O ₃ H generation unevenness in the positive electrode of the nickel-metal hydride battery;
Storing the generation amount and the size of the generation unevenness, and third data indicating a correspondence relationship between a restriction region for restricting charging of the nickel metal hydride battery,
The controller is
Referring to the first data, the amount of production is calculated from the voltage and temperature of the nickel metal hydride battery,
Referring to the second data, the size of the generation unevenness is calculated from the charging current and temperature of the nickel metal hydride battery,
Referring to the third data, when it is determined that the calculated generation amount and the generation unevenness size are included in the restriction region, a predetermined value for restricting charging of the nickel-metal hydride battery A battery system that executes control.

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