JP2018133295A - Secondary battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery system, structured to be installed on a vehicle, capable of achieving highly precise estimation of a full charge capacity even if high-rate deterioration of a lithium ion secondary battery occurs.SOLUTION: An ECU 100 is configured to execute external charging control and calculate a section capacity of a battery 50 including a lithium ion secondary battery for estimation of a full charge capacity from the section capacity. The ECU 100 acquires an integrated evaluation value ΣD showing a progress degree of a high-rate deterioration caused by unbalancing of a concentration distribution of lithium ions in an electrode body. The ECU 100 corrects the full charge capacity using the integrated evaluation value ΣD in estimating the full charge capacity from the section capacity.SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to a secondary battery system, and more particularly, to a secondary battery system configured to be mountable on a vehicle and including a lithium ion secondary battery.

  In recent years, vehicles such as hybrid vehicles and electric vehicles have been widely used. In these vehicles, a lithium ion secondary battery is mounted as a traveling battery.

  It is known that the deterioration of the lithium ion secondary battery progresses as time elapses or charging and discharging are repeated, and the full charge capacity is reduced. For this reason, a technique for estimating the full charge capacity with high accuracy is desired.

  For example, in the controller disclosed in Japanese Patent Application Laid-Open No. 2013-053943 (Patent Document 1), the voltage of the lithium ion secondary battery (more specifically, OCV: Open Circuit Voltage) changes from the first voltage to the second voltage. The “interval capacity” that is the battery capacity at the time of the calculation is calculated. Then, the controller calculates a full charge capacity corresponding to the section capacity using information indicating a correspondence relationship between the section capacity and the full charge capacity.

JP2013-054343A Japanese Patent Laying-Open No. 2015-106482

  In general, in a lithium ion secondary battery, the concentration distribution of lithium ions in the electrode body can be biased by continuous charging and discharging with a large current. As a result, the internal resistance of the lithium ion secondary battery can be increased. This deterioration is also referred to as “high-rate deterioration”. The full charge capacity can also be reduced when high rate degradation occurs. Therefore, a technique for accurately estimating the full charge capacity of the lithium ion secondary battery after high rate deterioration is required.

  The present inventors improve the estimation accuracy of the full charge capacity by using an index value indicating the degree of progress of high-rate deterioration when executing “external charge control” for charging a secondary battery with electric power supplied from the outside of the vehicle. It was found that it can be improved.

  The present disclosure has been made in order to solve the above-described problems, and the purpose of the present disclosure is to fully charge a lithium-ion secondary battery in a secondary battery system that can be mounted on a vehicle when high-rate deterioration of the lithium-ion secondary battery occurs. It is to estimate the capacity with high accuracy.

  A secondary battery system according to an aspect of the present disclosure is configured to be mountable on a vehicle. The secondary battery system includes a secondary battery having an electrode body impregnated with an electrolytic solution containing lithium ions, and a control device. The control device performs external charging control for charging the secondary battery with electric power supplied from the outside of the vehicle, calculates the “section capacity” of the secondary battery, and calculates the full charge capacity of the secondary battery from the section capacity. It is configured to be able to be estimated. The section capacity is the capacity of the secondary battery corresponding to the first voltage and the second voltage corresponding to the second voltage when the voltage of the secondary battery is increased from the first voltage to the second voltage by the external charging control. This is the difference from the capacity of the secondary battery. The control device acquires an index value indicating the degree of progress of “high-rate degradation”, which is degradation caused by uneven concentration distribution of lithium ions in the electrode body. The control device corrects the full charge capacity using the index value when estimating the full charge capacity from the section capacity.

  According to the above configuration, when the full charge capacity is estimated from the section capacity calculated at the time of external charge control, correction using an index value indicating a high rate deterioration degree (an integrated index value ΣD described later) is performed. As a result, the capacity decrease due to the high rate deterioration can be appropriately reflected in the full charge capacity. Therefore, the full charge capacity can be estimated with high accuracy.

  According to the present disclosure, in a secondary battery system configured to be mountable in a vehicle, the full charge capacity can be estimated with high accuracy when high-rate deterioration of the lithium ion secondary battery occurs.

It is a block diagram which shows roughly the whole structure of the vehicle by which the secondary battery system which concerns on this Embodiment is mounted. It is a figure which shows an example of a structure of each cell. It is a flowchart for demonstrating the external charge control in this Embodiment. 4 is a flowchart for explaining in more detail the capacity calculation process (the process of S80) shown in FIG. It is a figure for demonstrating an example of the calculation method of a correction coefficient. It is a figure showing an example of relation between section capacity and full charge capacity.

  Hereinafter, embodiments of the present disclosure 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.

[Embodiment]
<Configuration of secondary battery system>
FIG. 1 is a block diagram schematically showing an overall configuration of a vehicle equipped with a secondary battery system according to the present embodiment. The vehicle 1 includes a secondary battery system 1A, a motor generator 10, drive wheels 20, a power control unit (PCU: Power Control Unit) 30, and a system main relay (SMR) 40. The secondary battery system 1A includes a battery 50, a monitoring unit 60, a charge relay (CHR) 70, a power converter 80, an inlet 90, and an electronic control unit (ECU) 100. Prepare.

  Motor generator 10 is a three-phase AC rotating electric machine in which permanent magnets are embedded in a rotor (not shown), for example. The motor generator 10 rotates the drive shaft with the electric power supplied from the battery 50. The motor generator 10 can also generate power by regenerative braking. The AC power generated by the motor generator 10 is converted into DC power by the PCU 30 and charged to the battery 50.

  The PCU 30 converts the DC power stored in the battery 50 into AC power in accordance with a control signal from the ECU 100 and supplies the AC power to the motor generator 10. Further, the PCU 30 converts the AC power generated by the motor generator 10 into DC power and supplies it to the battery 50.

  In FIG. 1, the configuration in which the vehicle 1 is an electric vehicle will be described as an example, but the vehicle 1 may be a plug-in hybrid vehicle. In that case, the vehicle 1 may include a plurality (for example, two) of motor generators.

  The SMR 40 is electrically connected to a power line that connects the PCU 30 and the battery 50. The SMR 40 switches between power supply and interruption between the PCU 30 and the battery 50 in accordance with a control signal from the ECU 100.

  The battery 50 is an assembled battery, and includes a plurality of cells 51 (see FIG. 2), each of which is a lithium ion secondary battery. The battery 50 supplies power for generating the driving force of the vehicle 1 to the PCU 30. Battery 50 stores the electric power generated by motor generator 10.

  Monitoring unit 60 includes a voltage sensor, a current sensor, and a temperature sensor (all not shown). The voltage sensor detects the voltage VB of the battery 50. The current sensor detects a current IB input / output to / from the battery 50. The temperature sensor detects the temperature TB of the battery 50. Each sensor outputs the detection result to ECU 100. ECU 100 estimates the SOC (State Of Charge) of battery 50 based on voltage VB, current IB, and temperature TB. Since a known method can be used for this estimation method, detailed description will not be repeated.

  Charging relay 70 is electrically connected to a power line connecting battery 50 and power conversion device 80. Charging relay 70 switches between power supply and interruption between battery 50 and power conversion device 80 in accordance with a control signal from ECU 100.

  The power conversion device 80 includes, for example, an AC / DC converter (not shown), converts AC power supplied from the charging device 2 outside the vehicle into DC power, and supplies the DC power to the battery 50.

  The inlet 90 is configured to be able to connect one end of the connector of the charging cable 3. The charging device 2 supplies AC power from the system power source 200 to the vehicle 1 via the charging cable 3.

  The ECU 100 includes a CPU (Central Processing Unit) 101, a memory 102, and a buffer (none of which are shown). The ECU 100 outputs a control signal based on input of signals from each sensor and a map and program stored in the memory 102 and controls each device so that the vehicle 1 is in a desired state. The main control executed by the ECU 100 includes external charging control of the vehicle 1, and this control will be described in detail with reference to FIG.

  In addition, although the example in which external charging is performed using the charging cable 3 is shown in FIG. 1, for example, power is transmitted in a non-contact manner from a power transmitting device embedded in the ground to an in-vehicle power receiving device (both not shown). External charge control described later can also be applied to “contactless charging”.

  FIG. 2 is a diagram illustrating an example of the configuration of each cell 51. The upper surface of the case 511 of the cell 51 is sealed with a lid 512. The lid 512 is provided with a positive terminal 513 and a negative terminal 514. One end of each of the positive terminal 513 and the negative terminal 514 protrudes from the lid 512 to the outside. The other end of each of the positive electrode terminal 513 and the negative electrode terminal 514 is electrically connected to an internal positive electrode terminal and an internal negative electrode terminal (both not shown) inside the case 511.

  An electrode body 515 is accommodated inside the case 511 (in FIG. 2, the case 511 is seen through and indicated by a broken line). The electrode body 515 is formed, for example, by winding a positive electrode sheet 516 and a negative electrode sheet 517 stacked via a separator 518 into a cylindrical shape.

  The positive electrode sheet 516 includes a current collector foil and a positive electrode active material layer (a layer including a positive electrode active material, a conductive material, and a binder) formed on the surface of the current collector foil. Similarly, the negative electrode sheet 517 includes a current collector foil and a negative electrode active material layer (a layer including a negative electrode active material, a conductive material, and a binder) formed on the surface of the current collector foil. The separator 518 is provided in contact with both the positive electrode active material layer and the negative electrode active material layer. The electrode body 515 (positive electrode active material layer, negative electrode active material layer, and separator 518) is impregnated with an electrolytic solution.

  As materials for the positive electrode sheet 516, the negative electrode sheet 517, the separator 518, and the electrolytic solution, various conventionally known materials can be used. As an example, for the positive electrode sheet 516, lithium cobalt oxide or lithium manganate is used. Carbon is used for the negative electrode sheet 517. Polyolefin is used for the separator 518. The electrolytic solution includes an organic solvent, lithium ions, and an additive. In addition, it is not essential that the electrode body 515 is a wound body, and the electrode body 515 may be a laminated body that is not wound.

<High rate degradation>
In the secondary battery system 1A configured as described above, when the battery 50 is continuously charged and discharged with a large current, the internal resistance of each cell 51 increases and the output voltage from the cell 51 decreases. It is known. Such deterioration is called “high-rate deterioration”. A factor that causes high-rate degradation is a bias in lithium ion concentration distribution (hereinafter abbreviated as “salt concentration distribution”) in the electrode body 515.

  The ECU 100 estimates the progress state of the high rate deterioration based on the charge / discharge history of the battery 50. More specifically, ECU 100 considers both the increase and decrease in the bias of the salt concentration distribution that accompanies charging / discharging of battery 50, and an evaluation value for evaluating the progress of high-rate deterioration (in other words, the amount of damage). D is calculated every predetermined control period ΔT. Hereinafter, a method for calculating the evaluation value D will be described in detail.

  The evaluation value D of the battery 50 calculated in the current (Nth) control cycle is represented as D (N), where N is an integer equal to or greater than 1, and was calculated in the previous ((N-1) th) control cycle. When the evaluation value D is represented as D (N-1), the evaluation value D (N) is calculated according to the following formula (1). The initial value D (0) of the evaluation value D is set to 0, for example.

D (N) = D (N−1) −D (−) + D (+) (1)
In the above equation (1), the amount of decrease D (−) of the evaluation value D is due to the diffusion of lithium ions from the previous evaluation value calculation to the current evaluation value calculation (during the control period ΔT). Represents a decrease in bias in salt concentration distribution. More specifically, the decrease amount D (−) is calculated using the forgetting factor α as shown in the following formula (2), for example. Note that 0 <α × ΔT <1.

D (−) = α × ΔT × D (N−1) (2)
The forgetting factor α is a factor corresponding to the diffusion rate of lithium ions in the electrolytic solution, and depends on the temperature TB and the SOC. More specifically, if the temperature TB is the same, the forgetting factor α increases as the SOC increases. If the SOC is the same, the forgetting factor α increases as the temperature TB increases. That is, the forgetting factor α increases as the diffusion of lithium ions easily occurs. Such a correlation between the forgetting factor α and the temperature TB and SOC is acquired in advance by experiment or simulation. Then, the forgetting factor α can be calculated from the temperature TB and the SOC by storing this correlation in the memory 102 of the ECU 100 as a map or conversion formula.

  Returning to the above equation (1), the increase amount D (+) of the evaluation value D is the distribution of salt concentration due to charge / discharge during the period from the previous evaluation value calculation to the current evaluation value calculation (during the control period ΔT). Represents an increase in the bias. More specifically, the increase amount D (+) is calculated using a current coefficient β, a limit threshold value γ, and a current IB, for example, as in the following formula (3).

D (+) = (β / γ) × IB × ΔT (3)
Although the detailed description will not be repeated, the correlation between the temperature TB and the SOC is acquired in advance by experiment or simulation in the same manner as the forgetting factor α for the current coefficient β and the threshold threshold γ, and the memory 102 is used as a map or conversion formula. Is remembered. Therefore, current coefficient β and limit threshold value γ can be calculated from temperatures TB and SOC. In this way, by calculating the evaluation value D (N) in consideration of both increase and decrease in the bias of the salt concentration distribution, the change in the bias of the salt concentration distribution is appropriately reflected in the evaluation value D (N). be able to.

  ECU 100 calculates integrated evaluation value ΣD (N) by integrating evaluation values D (N) for all integers N in order to estimate the progress of high-rate deterioration of battery 50. More specifically, as shown in the following formula (4), the integrated evaluation value from the initial value D (0) of the evaluation value D to the evaluation value D (N-1) in the (N-1) th control cycle. ΣD (N−1) is multiplied by the attenuation coefficient δ, and the evaluation value D (N) in the Nth control cycle is added.

ΣD (N) = δ × ΣD (N−1) + D (N) (4)
The attenuation coefficient δ is a coefficient determined in consideration of the decrease in the bias of the salt concentration distribution due to the diffusion of lithium ions over time. The attenuation coefficient δ is acquired in advance by experiment or simulation and stored in the memory 102.

  Although not shown in the flowchart, the ECU 100 calculates the integrated evaluation value ΣD of the battery 50 by appropriately executing the above-described processing. The calculated integrated evaluation value ΣD is stored in the memory 102 and read out as necessary.

<External charging control>
FIG. 3 is a flowchart for explaining external charging control in the present embodiment. This flowchart is called from the main routine and executed when a predetermined charge start condition is satisfied (for example, when the charge cable 3 is connected to the inlet 90 and a charge start command is output by a user operation). Each step (hereinafter abbreviated as S) is basically realized by software processing by the ECU 100, but may be realized by hardware processing by an electronic circuit fabricated in the ECU 100.

  In S10, ECU 100 controls power conversion device 80 to start charging of battery 50 (or to continue charging when charging is already in progress).

  In S20, ECU 100 determines whether or not voltage VB (more specifically, OCV) of battery 50 is equal to or higher than reference voltage V1 (first voltage). When voltage VB is less than reference voltage V1 (NO in S20), ECU 100 returns the process to S10. Thereby, charging of the battery 50 is continued.

  When voltage VB reaches reference voltage V1 (YES in S20), ECU 100 advances the process to S30, and integrates current IB acquired by a current sensor (not shown) in monitoring unit 60. This current integration is continued until the voltage VB reaches a reference voltage V2 (second voltage) higher than the reference voltage V1 (NO in S40).

  When voltage VB reaches reference voltage V2 (YES in S40), ECU 100 continues charging until a predetermined charging end condition is satisfied (S50). For example, when the voltage VB reaches the charge end voltage (voltage to end the charge) or when the charge end time comes, it is determined that the charge end condition is satisfied. When the charging end condition is satisfied (YES in S6), ECU 100 controls power conversion device 80 to end charging (S70). Then, the ECU 100 executes a capacity calculation process described below (S80).

<Capacity calculation process>
FIG. 4 is a flowchart for explaining in more detail the capacity calculation process (the process of S80) shown in FIG. In S81, the ECU 100 calculates the interval capacity until the voltage VB reaches the reference voltage V2 from the reference voltage V1 based on the integrated current value calculated in S30 of FIG. 3 (see, for example, Patent Document 1). The section capacity corresponds to the difference between the capacity of the battery 50 corresponding to the reference voltage V1 and the capacity of the battery 50 corresponding to the reference voltage V2.

  In S82, the ECU 100 acquires the integrated evaluation value ΣD of the battery 50 at the end of charging (at the end of the process of S70). Since this process has already been described in detail, the description will not be repeated, but the integrated evaluation value ΣD can be calculated by another flow (not shown). The integrated evaluation value ΣD is desirably calculated as a value up to the end of charging, but is not limited to this, and may be a value up to the end of the previous travel of the vehicle 1, for example. It may be a value until the start of execution of external charging control.

  In S83, the ECU 100 calculates a correction coefficient K for correcting the section capacity calculated in S81.

  FIG. 5 is a diagram for explaining an example of a method of calculating the correction coefficient K. In FIG. 5, the horizontal axis indicates the integrated evaluation value ΣD. The vertical axis represents the section capacity (value calculated in S81). On the vertical axis, a section capacity (for example, a section capacity when the reference voltages V1 and V2 are fixed) calculated under the same conditions for the amount of power charged to the battery 50 is shown.

  As shown in FIG. 5, when the battery 50 is in a new state (for example, a state immediately after manufacture), the integrated evaluation value ΣD is 0 and the section capacity is ΔC0. As time elapses or the battery 50 is charged / discharged, the integrated evaluation value ΔD increases, and the section capacity decreases accordingly. For example, when the integrated evaluation value ΣD = D1, the section capacity decreases to ΔC1, and when the integrated evaluation value ΣD = D2, the section capacity decreases to ΔC2.

  The correction coefficient K can be calculated, for example, from the amount of decrease in the section capacity with reference to the section capacity ΔC0 at the integrated evaluation value ΣD = 0. As an example, the ratio of the current section capacity (value calculated in S81) to the section capacity ΔC0 can be used as the correction coefficient K.

  Returning to FIG. 4, in S84, the ECU 100 estimates the full charge capacity from the section capacity calculated in S81. At this time, the ECU 100 corrects the full charge capacity using the correction coefficient K. More specifically, the ECU 100 stores a map (not shown) indicating the correspondence relationship between the section capacity and the full charge capacity in the memory 102. The ECU 100 can estimate the full charge capacity from the section capacity using this map. The ECU 100 may have a correspondence relationship between the section capacity and the full charge capacity in the form of a table or a relational expression instead of the map.

  FIG. 6 is a diagram illustrating an example of a correspondence relationship between the section capacity and the full charge capacity. In FIG. 6, the abscissa indicates the section capacity (value calculated in S81), and the ordinate indicates the full charge capacity. Note that it is desirable to prepare a plurality of correspondence relationships as shown in FIG. 6 for each temperature TB when the external charging control is executed.

  As shown in FIG. 6, when the section capacity is ΔC, when the integrated evaluation value ΣD of the battery 50 is 0, the full charge capacity is calculated as C0. On the other hand, when the integrated evaluation value ΣD is D1, the full charge capacity is calculated as C1 by the correction using the correction coefficient K. When the integrated evaluation value ΣD is D2, the full charge capacity is calculated as C2 by the correction using the correction coefficient K. This correction can be performed, for example, by multiplying the full charge capacity when the integrated evaluation value ΣD is 0 (in other words, the full charge capacity when high-rate deterioration is not considered) by the reciprocal of the correction coefficient K.

  As described above, according to the present embodiment, when the full charge capacity is estimated from the section capacity calculated at the time of external charge control, the correction using the integrated evaluation value ΣD indicating the progress degree of the high rate deterioration of the battery 50 is performed. Is done. As a result, the capacity decrease due to the high rate deterioration can be appropriately reflected in the full charge capacity. Therefore, the full charge capacity can be estimated with high accuracy.

  In addition, when the vehicle 1 is configured to limit the charging power (charging power control upper limit value Win) to the battery 50 in accordance with the full charging capacity of the battery 50, the estimation accuracy of the full charging capacity is low. Then, there is a possibility that the charging power is unnecessarily limited. According to the present embodiment, it is possible to suppress such excessive limitation of charging power by improving the estimation accuracy of the full charge capacity.

  Further, the reference voltages V1 and V2 (or a voltage width between the reference voltage V1 and the reference voltage V2) may be a predetermined value, or a plurality of combinations of the reference voltages V1 and V2 are prepared. Corresponding relationships as shown in FIG. 6 may be obtained for each combination.

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

  1 vehicle, 1A secondary battery system, 2 charging device, 3 charging cable, 10 motor generator, 20 driving wheel, 30 PCU, 40 SMR, 50 battery, 51 cell, 60 monitoring unit, 70 charging relay (CHR), 80 power Conversion device, 90 inlet, 100 ECU, 101 CPU, 102 memory, 200 system power supply, 511 case, 512 lid, 513 positive electrode terminal, 514 negative electrode terminal, 515 electrode body, 516 positive electrode sheet, 517 negative electrode sheet, 518 separator.

Claims (1)

A secondary battery system configured to be mountable on a vehicle,
A secondary battery having an electrode body impregnated with an electrolyte containing lithium ions;
External charge control for charging the secondary battery with electric power supplied from the outside of the vehicle is executed, and a section capacity of the secondary battery is calculated to estimate a full charge capacity of the secondary battery from the section capacity And a control device configured to be able to
The section capacity includes the capacity of the secondary battery corresponding to the first voltage and the second voltage when the voltage of the secondary battery rises from the first voltage to the second voltage by the external charging control. Is a difference from the capacity of the secondary battery corresponding to the voltage of
The controller is
Obtaining an index value indicating the degree of progress of high-rate deterioration, which is deterioration caused by uneven concentration distribution of the lithium ions in the electrode body;
A secondary battery system that corrects the full charge capacity using the index value when the full charge capacity is estimated from the section capacity.

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