JP2017220329A - Secondary battery system - Google Patents

Abstract

In a secondary battery system including a nickel metal hydride secondary battery, calculation accuracy of a voltage drop amount due to a memory effect is improved. A secondary battery system includes a battery (a nickel hydride secondary battery) having a positive electrode plate (141) impregnated with an electrolyte containing potassium ions, and an ECU (300). ECU 300 calculates the insertion amount Xtime, Xoc of potassium ions into the active material of positive electrode plate 141 from the battery standing time Δt and the SOC, and calculates the voltage drop amount ΔV due to the memory effect of battery 100 from the calculated insertion amount Xtotal. To do. [Selection] Figure 4

Description

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

  2. Description of the Related Art In recent years, secondary battery systems including nickel metal hydride secondary batteries have become widespread and are also installed in electric vehicles such as hybrid vehicles. In nickel-metal hydride secondary batteries, the so-called “memory effect”, a phenomenon in which the voltage drops while charging and discharging are repeated without using up the capacity, is known, and various technologies to reduce errors due to the memory effect Has been proposed. For example, Japanese Patent Laid-Open No. 2000-212249 (Patent Document 1) discloses a technique for correcting SOC based on the detection result of voltage and current in order to eliminate a shift in SOC (State Of Charge) -voltage characteristics due to the memory effect. Disclose.

JP 2000-212249 A

  In various charge / discharge control of a secondary battery system including a nickel hydride secondary battery, the voltage of the nickel hydride secondary battery is one of the main control parameters (control factors). In order to control the voltage of the nickel metal hydride secondary battery with high accuracy, it is desirable to calculate the amount of voltage drop due to the memory effect with high accuracy.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a technique for improving the calculation accuracy of the amount of voltage drop due to the memory effect in a secondary battery system including a nickel-hydrogen secondary battery. Is to provide.

  A secondary battery system according to an aspect of the present invention includes a nickel hydride secondary battery having a positive electrode impregnated with an electrolytic solution containing alkali metal ions (for example, potassium ions), and a control device. The control device calculates the insertion amount of alkali metal ions into the active material of the positive electrode from the standing time and the state of charge (SOC) of the nickel hydrogen secondary battery, and the memory effect of the nickel metal hydride secondary battery from the calculated insertion amount. The amount of voltage drop due to is calculated.

  The present inventors have found that the amount of voltage drop due to the memory effect increases as the amount of alkali metal ions inserted into the positive electrode increases. According to the above configuration, the amount of insertion of alkali metal ions is calculated from the charge / discharge history and state of charge (SOC) of the nickel metal hydride secondary battery using, for example, a predetermined map or relational expression, and the calculated amount of insertion is further calculated. From this, the voltage drop due to the memory effect is calculated. Thus, by considering the insertion amount of alkali metal ions, it is possible to improve the calculation accuracy of the voltage drop amount due to the memory effect.

It is a block diagram which shows roughly the whole structure of the hybrid vehicle by which the secondary battery system which concerns on this Embodiment is mounted. It is a figure which shows the structure of a battery cell roughly. It is a schematic diagram for demonstrating insertion of the potassium ion to a positive electrode active material. It is a flowchart which shows the calculation process of the voltage drop amount by the memory effect in this Embodiment. It is a figure which shows an example of the map for calculating the amount of ion insertion by leaving from the leaving time of a battery. It is a figure which shows an example of the map for calculating the ion insertion amount by overcharge from SOC of a battery. It is a figure which shows an example of the map for calculating the voltage fall amount by a memory effect from total ion insertion amount.

  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.

  In the embodiments described below, a configuration in which the secondary battery system according to the present invention is mounted on a hybrid vehicle will be described as an example. However, the vehicle on which the secondary battery system according to the present invention can be mounted is not limited to a hybrid vehicle, and may be an electric vehicle or a fuel vehicle. Moreover, the use of the secondary battery system according to the present invention is not limited to vehicles, and may be, for example, stationary.

<Configuration of secondary battery system>
FIG. 1 is a block diagram schematically showing an overall configuration of a hybrid vehicle equipped with a secondary battery system according to the present embodiment. The vehicle 1 includes a secondary battery system 2, motor generators (MG) 10 and 20, a power split mechanism 30, an engine 40, and drive wheels 50. The secondary battery system 2 includes a battery 100, a system main relay (SMR) 150, a power control unit (PCU) 200, and an electronic control unit (ECU) 300. Prepare.

  Each of motor generators 10 and 20 is a three-phase AC rotating electric machine. Motor generator 10 is coupled to the crankshaft of engine 40 via power split mechanism 30. The motor generator 10 rotates the crankshaft of the engine 40 using the power of the battery 100 when starting the engine 40. The motor generator 10 can also generate power using the power of the engine 40. The AC power generated by the motor generator 10 is converted into DC power by the PCU 200 and the battery 100 is charged. Further, the AC power generated by the motor generator 10 may be supplied to the motor generator 20.

  Motor generator 20 rotates the drive shaft using at least one of the electric power from battery 100 and the electric power generated by motor generator 10. The motor generator 20 can also generate power by regenerative braking. The AC power generated by the motor generator 20 is converted into DC power by the PCU 200 and the battery 100 is charged.

  Power split device 30 is, for example, a planetary gear mechanism, and mechanically connects the three elements of the crank shaft of engine 40, the rotation shaft of motor generator 10, and the drive shaft. The engine 40 is an internal combustion engine such as a gasoline engine, and generates a driving force for the vehicle 1 to travel in response to a control signal from the ECU 300.

  Although not shown, PCU 200 includes an inverter and a converter. The inverter is a general three-phase inverter. During the boosting operation, the converter boosts the voltage supplied from the battery 100 and supplies the boosted voltage to the inverter. During the step-down operation, the converter steps down the voltage supplied from the inverter and charges battery 100. SMR 150 is electrically connected to a current path connecting battery 100 and PCU 200. When SMR 150 is closed in response to a control signal from ECU 300, power can be exchanged between battery 100 and PCU 200.

  The battery 100 is a direct current power source including a nickel metal hydride secondary battery and configured to be rechargeable. The battery 100 includes a plurality of battery cells 110. The detailed configuration of each battery cell 110 will be described with reference to FIG.

  The battery 100 is provided with a voltage sensor 101, a current sensor 102, and a temperature sensor 103. The voltage sensor 101 detects the voltage VB of the battery 100. Current sensor 102 detects current IB input / output to / from battery 100. The temperature sensor 103 detects the temperature of the battery 100. Each sensor outputs the detection result to ECU 300. ECU 300 calculates the SOC (State Of Charge) of battery 100 based on the detection results of the sensors.

  The ECU 300 includes a CPU (Central Processing Unit) 301, a memory 302, a timer 303, an input / output buffer (not shown), and the like. ECU 300 controls each device so that vehicle 1 is in a desired state based on a signal received from each sensor and a map and a program stored in memory 302. The main control executed by the ECU 300 includes charge / discharge control of the battery 100, which will be described later.

  FIG. 2 is a diagram schematically showing the configuration of the battery cell 110. Since the configuration of each battery cell 110 included in the battery 100 is common, only one battery cell 110 is representatively shown in FIG. The battery cell 110 is, for example, a square sealed cell, and includes a case 120, a safety valve 130 provided in the case 120, an electrode body 140 accommodated in the case 120, and an electrolytic solution (not shown). In FIG. 2, the electrode body 140 is shown through a part of the case 120.

  Case 120 includes a case main body 121 and a lid body 122 each made of metal (for example, nickel-plated steel plate). The case 120 is sealed by the cover body 122 being welded all around the opening of the case body 121. When the pressure inside the case 120 exceeds a predetermined value, the safety valve 130 discharges a part of the gas (hydrogen gas or the like) inside the case 120 to the outside.

  The electrode body 140 includes a positive electrode plate 141, a negative electrode plate 142, and a separator 143. The positive electrode plate 141 is inserted into a bag-like separator 143, and the positive electrode plate 141 and the negative electrode plate 142 inserted into the separator 143 are alternately stacked. The positive electrode plate 141 and the negative electrode plate 142 are electrically connected to a positive electrode terminal and a negative electrode terminal (not shown), respectively.

Various conventionally known materials can be used as the material of the electrode body 140 and the electrolytic solution. In this embodiment, although not shown, the positive electrode plate 141 includes a positive electrode active material layer containing nickel hydroxide (nickel hydroxide (Ni (OH) ₂ ) or nickel oxyhydroxide (NiOOH)); An electrode plate including an active material support such as foamed nickel is used. An electrode plate containing a hydrogen storage alloy is used for the negative electrode plate 142. For the separator 143, a nonwoven fabric made of a synthetic fiber subjected to a hydrophilic treatment is used. An alkaline aqueous solution containing potassium hydroxide (KOH) is used as the electrolytic solution. However, the electrolytic solution is not particularly limited as long as it is an alkaline aqueous solution, and may contain, for example, sodium hydroxide (NaOH) instead of or in addition to potassium hydroxide.

<Voltage drop due to memory effect>
In the charge / discharge control of the secondary battery system 2 configured as described above, the voltage VB of the battery 100 is one of the main control parameters (control factors). In order to control the voltage VB of the battery 100 with high accuracy, it is desirable to calculate the voltage drop amount ΔV due to the memory effect with high accuracy.

  Here, as one of the factors causing the memory effect, the present inventors inserted alkali metal ions (potassium ions in the present embodiment) in the electrolyte into the positive electrode active material layer formed on the positive electrode plate 141. We focused on the points. As described below, insertion of potassium ions mainly occurs when the battery 100 is left or overcharged.

FIG. 3 is a schematic diagram for explaining insertion of potassium ions into the positive electrode active material. As shown in FIG. 3A, in an initial state of the battery 100 (for example, a state immediately after manufacture or a state immediately after refresh), hydrogen ions are mainly present between the NiO ₂ layers 141A constituting the positive electrode active material layer of the positive electrode plate 141. Exists. On the other hand, if the battery 100 is left without being charged / discharged, as shown in FIG. 3B, potassium ions are inserted between the NiO ₂ layers 141A as time passes, and some of the hydrogen ions are converted into potassium ions. Replaced. This reaction is a reversible reaction, and once inserted potassium ions may be eliminated and replaced with hydrogen ions.

Further, as shown in FIG. 3 (C), even when the battery 100 is overcharged, hydrogen ions between the NiO ₂ layers can be desorbed and replaced with potassium ions. This reaction is also a reversible reaction. In general, when the battery is overcharged, the decomposition reaction of the electrolyte proceeds as a side reaction, and the pressure and temperature inside the battery may increase excessively. Therefore, since the battery 100 is controlled to be charged and discharged so as not to reach an overcharge state as much as possible, it seems that insertion of potassium ions due to overcharge hardly occurs. However, even when the battery 100 as a whole is not in an overcharged state, there is uneven charging / discharging due to, for example, the conductive material not being uniformly dispersed in the positive electrode plate 141, and local An overcharge condition can occur. Therefore, insertion of potassium ions can occur even within the normal SOC range.

  Thus, the insertion amount of potassium ions in the positive electrode active material can change according to the usage history of the battery 100 (the history of neglect or overcharge), and the present inventors have found that the insertion amount of potassium ions increases. The present inventors have found that the voltage drop amount Δ due to the memory effect increases. Therefore, in this embodiment, a configuration is employed in which the amount of potassium ions inserted into the positive electrode active material is calculated, and the voltage drop amount ΔV of battery 100 is calculated from the calculated amount of insertion.

  Hereinafter, the amount of potassium ions inserted into the positive electrode active material when the battery 100 is left is described as “Xtime”, and the amount of potassium ions inserted into the positive electrode active material when the battery 100 is overcharged is “Xoc”. It describes. Then, the total ion insertion amount Xtotal, which is the total insertion amount of potassium ions, is expressed by the following formula (1).

Xtotal = Xtime + Xoc (1)
A correlation existing between the total ion insertion amount Xtotal and the voltage drop amount ΔV due to the memory effect is acquired in advance by experiment or simulation, and the acquisition result is stored in the memory 302 of the ECU 300, whereby the total ion insertion amount is stored. The voltage drop amount ΔV can be calculated from Xtotal. By adopting such a calculation method, the calculation accuracy of the voltage drop amount ΔV can be improved. Hereinafter, this calculation method will be described in more detail with reference to a flowchart.

<Calculation flow of voltage drop>
FIG. 4 is a flowchart showing a calculation process of the voltage drop amount ΔV due to the memory effect in the present embodiment. This flowchart is called from the main routine and executed every predetermined period or whenever a predetermined condition is satisfied. Each step (abbreviated as “S”) included in this flowchart is basically realized by software processing by the ECU 300, but part or all of it is realized by hardware (electric circuit) produced in the ECU 300. May be.

  In S10, ECU 300 acquires voltage VB, current IB, and temperature TB of battery 100 from voltage sensor 101, current sensor 102, and temperature sensor 103, respectively.

  In S <b> 20, ECU 300 uses battery 303 to obtain battery 100 leaving time Δt. The neglected time Δt is the time that has elapsed without charging since the battery 100 is refreshed (when the voltage of each battery cell 110 is discharged to the end voltage of about 0.8 V), or the manufacture of the battery 100. It means the time elapsed without charging / discharging from time.

  In S30, the ECU 300 calculates the ion insertion amount Xtime due to leaving using the function f or map (see FIG. 5) shown below from the leaving time T acquired in S20. When the battery 100 is left, the ion insertion speed (ion insertion amount per unit time) into the positive electrode active material is affected by the battery 100 leaving time Δt, voltage VB, and temperature TB. Therefore, the ion insertion amount Xtime due to leaving can be calculated using a function f having the leaving time Δt, voltage VB, and temperature TB as variables, as shown in the following formula (2).

Xtime = f (Δt, VB, TB) (2)
FIG. 5 is a diagram showing an example of a map for calculating the ion insertion amount Xtime due to leaving from the leaving time Δt of the battery 100. In FIG. 5, the horizontal axis represents the standing time Δt, and the vertical axis represents the ion insertion amount Xtime due to the standing. The ion insertion amount Xtime can be defined as, for example, an increase amount (unit: mol) of the potassium ion substance amount per unit substance amount (unit: mol) of nickel in the positive electrode active material.

  As shown in FIG. 5, the ion insertion speed due to leaving is greatest immediately after the start of leaving, and decreases as the leaving time Δt increases. Then, the ion insertion amount Xtime due to neglecting finally converges to a certain value Xmax. From the correlation shown in FIG. 5, the above formula (2) can be more specifically expressed as the following formula (3). The coefficient α in the equation (3) is determined by experiment or simulation according to the voltage VB and temperature TB of the battery 100.

L1: Xtime = Xmax [1-exp (α × Δt)] (3)
A correlation as shown in Expression (3) or FIG. 5 is acquired in advance by experiment or simulation for each voltage VB and temperature TB of the battery 100 and stored in the memory 302 of the ECU 300. Therefore, by referring to this correlation, the ion insertion amount Xoc due to leaving can be calculated from the leaving time Δt of the battery 100.

  Returning to FIG. 4, in S40, ECU 300 calculates the SOC of battery 100 using voltage VB, current IB, and temperature TB of battery 100 acquired in S10. Since this calculation method is known, detailed description will not be repeated.

  In S50, the ECU 300 calculates the ion insertion amount Xoc due to overcharge from the SOC calculated in S40 using the function g or map (see FIG. 6) shown below. The ion insertion amount Xoc due to overcharging of the battery 100 is affected by the SOC and charging / discharging history (voltage VB, current IB, temperature TB history) of the battery 100. Therefore, the ion insertion amount Xoc due to overcharge is calculated using a function g having SOC, voltage VB, current IB, and temperature TB as variables (see the following formula (4)).

Xoc = g (SOC, VB, IB, TB) (4)
FIG. 6 is a diagram illustrating an example of a map for calculating the ion insertion amount Xoc due to overcharge from the SOC of the battery 100. In FIG. 6, the horizontal axis indicates the SOC, and the vertical axis indicates the ion insertion amount Xoc due to overcharge.

  As shown in FIG. 6, as the SOC increases, the ion insertion amount Xoc due to overcharging increases monotonously (in a straight line in the example shown in L2). Therefore, from the correlation shown in FIG. 6, the above equation (4) can be more specifically described as, for example, the following equation (5). Note that the slope β of the straight line L2 in Expression (5) is determined by experiment or simulation according to the voltage VB, current IB, and temperature TB of the battery 100.

L2: Xoc = β × SOC (5)
A correlation as shown in Expression (5) or FIG. 6 is acquired in advance for each charge / discharge history of the battery 100 and the battery 100 and stored in the memory 302. Therefore, by referring to this correlation, the ion insertion amount Xoc due to overcharge can be calculated from the SOC of the battery 100.

  In S60, the ECU 300 calculates the total ion insertion amount Xtotal by adding the ion insertion amount Xtime due to neglect calculated in S30 and the ion insertion amount Xoc due to overcharge calculated in S50 (the above formula ( 1)).

  In S70, the ECU 300 calculates the voltage drop amount ΔV due to the memory effect from the total ion insertion amount Xtotal calculated in S60, for example, using the map shown below.

  FIG. 7 is a diagram showing an example of a map for calculating the voltage drop amount ΔV due to the memory effect from the total ion insertion amount Xtotal. In FIG. 7, the horizontal axis represents the total ion insertion amount Xtotal, and the vertical axis represents the voltage drop amount ΔV.

  As shown in FIG. 7, as the total ion insertion amount Xtotal increases, the voltage drop amount ΔV due to the memory effect also increases monotonously. In the example shown in FIG. 7, the voltage drop amount ΔV increases linearly (see the straight line L3). Therefore, the correlation shown in the following formula (6) is established between the total ion insertion amount Xtotal and the voltage drop amount ΔV. The slope γ of the straight line L3 in Expression (6) is determined according to, for example, the material or shape of the positive electrode active material. By using such a correlation, the voltage drop amount ΔV can be calculated from the total ion insertion amount Xtotal.

L3: ΔV = γ × Xoc (6)
In the correlation shown in FIGS. 6 and 7, the example in which the ion insertion amount Xoc and the voltage drop amount ΔV increase linearly has been described. However, the increase mode is not limited to this as long as it is monotonously increased. It may be increased in a curved line or stepwise.

  As described above, according to the present embodiment, a predetermined map (see, for example, FIG. 5 to FIG. 7) or a relational expression (from FIG. For example, by using formulas (3), (5), and (6)), the insertion amount (Xtime, Xoc) of potassium ions is calculated, and further, the memory effect is calculated from the calculated insertion amount (Xtotal = Xtime + Xoc). A voltage drop amount ΔV is calculated. Thus, the calculation accuracy of the voltage drop amount ΔV due to the memory effect can be improved by considering the total ion insertion amount Xtotal into the positive electrode active material.

  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 embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Vehicle, 2 Secondary battery system 10,20 Motor generator, 30 Power split mechanism, 40 Engine, 50 Driving wheel, 100 Battery, 101 Voltage sensor, 102 Current sensor, 103 Temperature sensor, 110 Battery cell, 120 Case, 121 Case body, 122 lid, 130 safety valve, 140 electrode body, 141 positive electrode plate, 141A NiO ₂ layer, 142 negative electrode plate, 143 separator, 300 ECU, 301 CPU, 302 memory, 303 timer.

Claims (1)

A nickel metal hydride secondary battery having a positive electrode impregnated with an electrolyte containing alkali metal ions;
The insertion amount of the alkali metal ions into the active material of the positive electrode is calculated from the standing time and the charged state of the nickel metal hydride secondary battery, and the voltage drop due to the memory effect of the nickel metal hydride secondary battery is calculated from the calculated insertion amount A secondary battery system comprising a control device for calculating the amount.

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