JP2013161543A - Secondary battery control device and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery control device and control method which, by controlling constraint forces applied to a secondary battery, can recover the battery capacity and also extend the battery life of a battery whose degradation due to charges and discharges has progressed to some extent.SOLUTION: The secondary battery control device includes: a constraint force generation unit which restrains the large side face of a case from the outside to press it in a direction in which the plate faces of electrode plates are brought close together; a battery capacity acquisition unit which acquires the battery capacity of the secondary battery; and a constraint force control unit which, on the basis of an integrated used capacity derived by integrating the used capacity of the secondary battery at charge and discharge time and the battery capacity acquired by the battery capacity acquisition unit, controls the magnitude of the constraint force generated by the constraint force generation unit. When the degree of reduction in the battery capacity acquired by the battery capacity acquisition unit against an increase in the integrated used capacity changes from a moderate first degree to a severer second degree, the constraint force control unit increases the constraint force generated by the constraint force generation unit.

Description

  The present invention relates to a control device and a control method for a secondary battery that is restrained by a restraining member from the outside. More specifically, the present invention relates to a secondary battery control device and control method for controlling the restraining force of the restraining member in accordance with the state of the secondary battery.

  For example, as a secondary battery for automobiles, a plurality of battery cells stacked and bundled and modularized are often used. When modularizing battery cells, a restraining member that restrains a plurality of stacked battery cells from the outside may be used. It is known that the restraining force applied to the battery cells in the module by this restraining member affects the characteristics of the battery cells. For example, Patent Document 1 discloses a restraining means for keeping the pressure applied to the battery by restraint within a predetermined pressure range.

JP 2009-238606 A

  In the case of a lithium ion secondary battery that is modularized, it is generally known that the battery capacity decreases as charging and discharging are repeated. It has also been found that the magnitude of the restraining force by the restraining means is also related to the deterioration and life of the secondary battery. Therefore, there has been a demand for a binding force that can maximize the battery life.

  The present invention has been made to solve the above-described problems of the prior art. In other words, the problem is that the secondary battery control device can control the binding force applied to the secondary battery to recover the battery capacity of the battery that has deteriorated to some extent due to charge / discharge and extend the battery life. And providing a control method.

  In order to solve this problem, the secondary battery control device according to the present invention is a rectangular case having a pair of large side surfaces each having a larger area than the other surfaces, with a wound or laminated electrode plate and electrolyte solution. A control device for a secondary battery for controlling a secondary battery enclosed in a container, comprising: a restraining force generator that restrains the plate surfaces of the electrode plates toward each other by restraining the large side surface of the case from the outside; The battery capacity acquisition unit for acquiring the battery capacity of the secondary battery, the accumulated usage capacity obtained by integrating the usage capacity during charging and discharging of the secondary battery, and the binding capacity based on the battery capacity acquired by the battery capacity acquisition unit A restraint force control unit that controls the magnitude of the restraint force generated by the generator, and the restraint force control unit gradually increases the degree of decrease in the battery capacity acquired by the battery capacity acquisition unit with respect to the increase in the accumulated use capacity. 1st degree to 2nd, more intense If there is a change to the extent, and increases the restraint force by the restraining force generating unit.

  According to the secondary battery control apparatus of the present invention, the restraint force control unit monitors the transition of the battery capacity with respect to the increase in the accumulated usage capacity, and when the degree of decrease becomes larger than before, the restraint force generator Increase power. In other words, when the battery deterioration progresses and the battery capacity decreases more rapidly than before, the binding force by the binding force generator is increased. Such a situation is likely to occur when the electrode active material layer is cracked, in which case the battery capacity of the secondary battery can be increased somewhat by increasing the binding force. . Therefore, the secondary battery control device can control the binding force applied to the secondary battery to recover the battery capacity of the battery that has been deteriorated to some extent by charge and discharge and extend the battery life.

Further, in the present invention, the restraint force control unit has a newly acquired battery capacity and a previously acquired battery on a graph having the square root of the accumulated used capacity as the horizontal axis and the battery capacity acquired by the battery capacity acquisition unit as the vertical axis. When the vertical axis intercept of the straight line drawn by the capacity increases by a predetermined percentage with respect to the initial value, it may be considered that the degree of decrease in battery capacity has changed. desirable.
In such a case, the binding force can be increased at an appropriate timing, so that the battery life can be appropriately extended.

Furthermore, in the present invention, the restraint force control unit increases the restraint force once and then temporarily increases it back to the original size, and then acquires the battery capacity again by the battery capacity acquisition unit. If the battery increases from before the temporary increase, the secondary battery is used as it is. If the battery capacity does not increase, the binding force is increased to maintain the increased state. desirable.
In this way, it is possible to effectively increase the binding force without increasing the load on the case.

Furthermore, in the present invention, it is desirable that the restraint force control unit increases the restraint force by the restraint force generation unit only within a predetermined upper limit value range of the restraint force.
In such a case, since the binding force is increased within an appropriate range, the battery capacity can be effectively increased.

  Furthermore, the present invention provides a secondary battery for controlling a secondary battery in which a wound or laminated electrode plate and an electrolyte are enclosed in a rectangular case having a pair of large side surfaces larger than the other surfaces. In the control method, the target secondary battery is pressed so that the plate surfaces of the electrode plates approach each other by restraining the large side surface of the case from the outside. Based on the accumulated used capacity obtained by integrating the used capacity at the time of discharge and the battery capacity history of the secondary battery, the degree of decrease in the battery capacity with respect to the increase in the accumulated used capacity is increased from a moderate first degree to a more severe one. This also extends to a secondary battery control method that increases the binding force when there is a change to a degree of 2.

  According to the control device and control method for a secondary battery of the present invention, the binding force applied to the secondary battery is controlled to recover the battery capacity of the battery that has been deteriorated to some extent by charge and discharge and to prolong the battery life. Can do.

It is a block diagram which shows the structure for the restraint force control which concerns on this form. It is explanatory drawing which shows the example of a binding force generation | occurrence | production part. It is a graph which shows the relationship between integrated use capacity | capacitance and a capacity | capacitance maintenance factor. It is a graph which shows the relationship between a restraint increase rate and a capacity | capacitance recovery rate. It is a flowchart which shows the control by a restraint force control part.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the present invention is applied to a control device and a control method for controlling a binding force for a lithium ion secondary battery.

  As shown in FIG. 1, the control configuration of this embodiment includes a battery 10, a binding force generation unit 13, a binding force control unit 15, and a battery capacity acquisition unit 17. The battery 10 according to this embodiment is a so-called square lithium ion secondary battery. The battery 10 is formed by flatly forming a rolled electrode plate, and sealing it together with an electrolytic solution in a flat rectangular metal case. In the metal case, the electrode plate is disposed substantially parallel to a surface having the largest area (hereinafter referred to as a large side surface) among the outer surfaces of the metal case.

  Note that the battery 10 of the present embodiment is not limited to the wound type but may be a stacked type. Even in the case of the laminated type, each electrode plate is arranged substantially parallel to the large side surface. Further, the battery 10 may be a single battery cell, or may be a battery cell included in a battery module or a battery pack in which a plurality of battery cells are stacked and integrated.

  The restraining force generator 13 applies restraining force to the battery 10. The restraining force by the restraining force generator 13 may be applied to each battery cell. That is, a binding force may be applied to each battery cell included by pressing the entire battery module or battery pack. The restraining force generated by the restraining force generator 13 is a force that presses the large side surfaces on both sides in a direction approaching each other from the outside of the metal case. When the large side surface is pressed from the outside, the electrode plate of the battery 10 receives an inward force substantially perpendicular to the surface inside the battery case. That is, when receiving the restraining force by the restraining force generator 13, the surface of the electrode plate of the battery 10 is pressed against the adjacent surface.

  The restraint force controller 15 is a control device that controls the magnitude of the restraint force generated by the restraint force generator 13. That is, the magnitude of the restraining force applied to the battery 10 by the restraining force generator 13 of this embodiment is controlled by the restraining force controller 15. This control may be performed, for example, by adjusting the pressing force as long as the restraining force generator 13 presses the plate member against the large side surface of the battery cell.

  An example of the restraining force generator 13 is shown in FIG. In the configuration of this figure, a plurality of batteries 10 are arranged with their large side surfaces 10a in contact with each other. End plates 110 are arranged on the outside of the battery 10 at both ends so as to be in contact with the large side surface 10a. Further, the end plates 110 on both sides are fastened to each other by bolts 111 and nuts 112. The battery 10 receives a binding force due to the tightening force. That is, in this example, a set of the end plate 110, the bolt 111, and the nut 112 corresponds to the restraining force generation unit 13.

  Furthermore, the binding force applied to each battery 10 can be changed by the tightening amount of the bolt 111 and the nut 112. That is, if the restraint force control unit 15 controls the nut 112, the restraint force control unit 15 can control the magnitude of the restraint force. In order to appropriately perform the control by the restraining force control unit 15, it is preferable to examine the relationship between the tightening amount and the restraining force in advance.

  The battery capacity acquisition unit 17 acquires the battery capacity of the battery 10. The battery capacity acquisition unit 17 includes a circuit and elements for charging and discharging the battery 10 and a measuring instrument for acquiring a voltage value and a current value at the time of discharging. Then, the battery capacity acquisition unit 17 acquires the battery capacity in the actual use area. That is, the battery capacity acquisition unit 17 charges the battery 10 to the upper limit voltage (for example, full charge) in the actual use region and then slowly discharges the battery 10 from the voltage value and current value at the time of discharge. Calculate battery capacity. Acquisition of the battery capacity by the battery capacity acquisition unit 17 is performed for each battery cell.

  The actual use area where the battery capacity acquisition unit 17 acquires the battery capacity is a voltage range mainly used in the environment where the battery 10 is used. Therefore, the actual use area varies depending on the type of vehicle on which the battery 10 is mounted. For example, in a PHV (plug-in hybrid vehicle), the battery capacity acquisition unit 17 acquires the capacity from full charge to change to the hybrid mode. In an EV (electric vehicle), the battery capacity acquisition unit 17 acquires a capacity from full charge to a predetermined minimum voltage. In the HV (hybrid vehicle), the battery capacity acquisition unit 17 acquires the capacity within a predetermined voltage range used during the hybrid travel. For example, it is within a range from an upper limit voltage that can be increased by HV traveling to a voltage for forcibly starting the engine.

  As described above, the voltage range for acquiring the battery capacity by the battery capacity acquisition unit 17 varies depending on the type of vehicle and the usage environment. However, the range is usually set in advance by the start of use of the battery 10 and stored in the battery capacity acquisition unit 17. The battery capacity acquisition unit 17 calculates, for example, a battery capacity by discharging from a battery voltage of 3.9 V to a battery voltage of 3.45 V and measuring a current value therebetween.

  The binding force control unit 15 of this embodiment accumulates and stores the used capacity of the battery 10 from when it is new. That is, every time the battery 10 is charged, the amount of charge is acquired and integrated. Alternatively, each time discharge is performed, the discharge amount may be acquired and integrated. Or both at the time of charge and at the time of discharge may be sufficient.

  Further, the restraint force control unit 15 causes the battery capacity acquisition unit 17 to acquire the battery capacity at an appropriate timing, including when the battery 10 is new, and stores the result. Then, the binding force control unit 15 calculates the capacity maintenance rate based on the battery capacity acquired by the battery capacity acquisition unit 17. The capacity maintenance rate is a percentage of the acquired battery capacity with respect to the battery capacity of the battery 10 when it is new.

  Further, the restraint force control unit 15 monitors the change state of the capacity maintenance rate with respect to the increase in the usage capacity, based on the usage capacity and the capacity maintenance rate calculated as described above. For example, FIG. 3 shows an example in which the capacity maintenance rate with respect to the square root of the accumulated usage capacity is graphed from the start of use of the battery 10. That is, as indicated by the black diamonds in the figure, the capacity retention rate gradually decreases as the use of the battery 10 proceeds from the new state. The plot interval Q on the horizontal axis of this graph is, for example, 950 times the battery capacity in the initial state.

  When graphed as shown in FIG. 3, in the battery 10 that has not deteriorated so much, the capacity retention rate decreases linearly on this graph as indicated by the solid line L1 in the figure. However, the degree of this decrease increases from a certain point, and the capacity maintenance rate drops sharply away from the previous straight line. That is, in the figure, the plot point D drops from the solid line L1 after dropping from the plot point A (initial state) to the plot points B and C along the solid line L1. A straight line connecting the plot point C and the plot point D is a broken line L2, and the downward slope of the broken line L2 is steeper than the solid line L1. In the example of this figure, the degree of decrease in the capacity maintenance rate with respect to the square root of the accumulated used capacity is larger than before at the plot point C.

  As described above, it has been found that one of the causes of the rapid increase in the battery capacity is a crack generated in the positive electrode active material layer in the positive electrode plate. Then, the present inventors have found that the gap between the cracked portions can be reduced by pressing the plate surface more strongly than before against the positive electrode plate in which the active material layer has cracked, and the battery capacity can be recovered to some extent. I found it. Therefore, it was found that when the battery 10 having a short life was restrained with a larger restraining force, the electrode plates were pressed against each other and the battery 10 could be extended in life.

  The timing of increasing the binding force is determined based on the change in the slope of the straight line connecting the plot points in the graph of FIG. That is, when the degree of the battery capacity decreasing tendency with respect to the increase in the accumulated usage capacity changes from the gentle first degree to the more severe second degree, the restraining force control unit 15 increases the restraining force. In this embodiment, the restraint force control unit 15 has a degree of decrease in the capacity maintenance rate with respect to the square root of the accumulated used capacity for each predetermined accumulated used capacity (the slope between plot points in the graph of FIG. 3) from the initial state. When it becomes larger than a predetermined level, the binding force on the battery 10 is increased.

  This timing is, for example, in the graph of FIG. 3 when the intersection (vertical intercept) between the extension line of the line connecting adjacent plot points and the vertical axis is greater than a predetermined ratio from the initial value. I can grasp it. Then, the restraint force control unit 15 of the present embodiment controls the restraint force generation unit 13 to control the restraint force on the battery 10 when the capacity retention rate in the initial state is 100% and the vertical axis intercept is 105% or more. Increase. As a result, the battery capacity increases as shown by the arrows in FIG. In the example of this figure, the capacity retention rate increases from the plot point D (black diamond) to the plot point E (black circle) by about 8%.

  Next, an example of the relationship between the constraint increase rate (%) and the capacity recovery rate (%) is shown in FIG. This figure shows the results of examining the degree of recovery of battery capacity when multiple types of batteries 10 of the same type with different binding forces in the initial state are prepared and the binding force is increased by changing the increasing rate of the binding force. is there. The restraining force by the initial state was made into four types, 0.5, 1.0, 1.5, and 2.0 (MPa). The horizontal axis in this figure represents the restraint force in the initial state as 100%, and the magnitude of the increased restraint force as a percentage of the restraint force in the initial state.

  From the graph of FIG. 4, it can be confirmed that there is an effect of capacity recovery if the restraining force is increased to 120% or more of the initial value regardless of the magnitude of the restraining force in the initial state. Furthermore, it was confirmed that the capacity could be recovered more greatly by increasing the binding force within the range of 170% to 330% of the initial value. In other words, the rate of increase is more important than the magnitude of the restraining force before and after the increase. In this embodiment, the capacity recovery rate is particularly effectively increased by setting the increase rate of the binding force to 170% to 330%.

  On the other hand, if the rate of increase exceeds 330% and is too large, the capacity recovery effect is small. Since the load on the battery case increases as the restraining force increases, it is not preferable to increase the restraining force at a restraint increase rate exceeding 330%. Therefore, when the restraint force control unit 15 determines the restraint force increase timing as described above, the restraint force control unit 15 increases the restraint force by the restraint force generating unit 13 within a range of 120% to 330%. Even within that range, it is more preferable if the increase rate of the binding force is within the range of 170 to 180%. In this way, the rate of increase is not so large, and the capacity recovery effect is particularly great.

  Furthermore, when increasing the binding force, the present inventors have not only a steady increase maintained in an increased state, but also a temporary increase that is once increased and then returned to the original size, so that the effect of increasing the capacity is effective. I found out. The temporary increase is preferable because the load on the battery case is smaller than the steady increase. Therefore, the restraint force control unit 15 of the present embodiment first temporarily increases when the restraint force is increased as described above. Thereafter, the battery capacity is acquired again, and if the battery capacity has not increased, the battery capacity is constantly increased.

  If the appropriate effect cannot be obtained even by steady increase, the restraint force control unit 15 further increases the increase amount and repeats from the temporary increase. However, as described above, the larger the amount of increase in the binding force, the more the capacity is not recovered. This is because a constraint increase rate exceeding 330% has a small capacity recovery effect. Therefore, for example, the restraint force control unit 15 may increase the restraint force at an increase rate of about 120% first, and may set the increase rate to about 170% when an appropriate effect is not obtained.

  Alternatively, even when an effect is obtained even with a small increase rate, as shown by the black circle plot points F to H in FIG. Decreases. Therefore, the time when the restraining force is increased is assumed to be 100%, and a new graph is generated therefrom. When the vertical axis intercept becomes 105% or more, the restraining force may be increased again. In the example of this figure, the binding force is increased again at the plot point H, and the capacity is restored to the plot point I (black triangle).

  There is also a physical upper limit for the binding force. The upper limit value of the binding force varies depending on the size of the battery 10 and the type of the battery case. Therefore, an upper limit value that can appropriately apply a binding force to the electrode plate without damaging or deforming the battery 10 is set in advance for each type of battery 10. This value is, for example, about 15 MPa. The restraint force control unit 15 does not increase the restraint force further when the restraint force generated by the restraint force generator 13 exceeds the predetermined upper limit value.

  Note that the plot point K indicated by a white diamond in FIG. 3 indicates the capacity retention rate in the conventional case where the vertical axis intercept is 105% or more and continues to be used as it is without performing the process of increasing the binding force. It is an example. Conventionally, the plot point D is followed by the plot point K, and after that, the battery capacity rapidly decreases, so it has been determined that the battery 10 has reached the end of its life.

  Next, the restraint force control process by the restraint force control unit 15 of this embodiment will be described based on the flowchart shown in FIG. First, as described above, the restraint force control unit 15 controls the battery capacity acquisition unit 17 and acquires the capacity maintenance rate at an appropriate interval determined in advance from the start of battery use (S101). In this embodiment, the battery capacity is acquired every time the integrated value of the usage amount from the initial state of the battery 10 reaches an integral multiple of 950 times the initial battery capacity, and the value is the ratio of the value to the initial battery capacity. The capacity maintenance rate is calculated.

  Then, the calculated capacity maintenance ratio is plotted on a graph as shown in FIG. 3, and the vertical axis intercept is obtained from the difference from the previous measurement value. It is determined from the obtained value of the intercept of the vertical axis whether or not the degree of change in the capacity maintenance rate has increased beyond a predetermined range (S102). If not increased (S102: No), the binding force is maintained as it is, and the process returns to S101 again to obtain the capacity maintenance rate.

  When the degree of change in the capacity maintenance ratio increases and the value of the vertical axis intercept becomes 105% or more (S102: Yes), first, the binding force is temporarily increased. In this case, the restraint force controller 15 controls the restraint force generator 13 to increase the restraint force until a predetermined rate (a value within the range of 120 to 330%) is reached (S103). Further, as soon as the restraining force reaches a predetermined rate, the restraining force is decreased and returned to the original restraining force (S104). That is, after the end of S104, the magnitude of the binding force is not changed before the execution of S103.

  Thereafter, the battery capacity of the battery 10 is measured again, and compared with the measured value before the execution of S103, it is confirmed whether the battery capacity has been recovered (S105). If the capacity has been recovered (S105: Yes), the process returns to S101 and enters the monitoring state again. On the other hand, if the capacity has not recovered (S105: No), the restraining force is increased again (S106). Furthermore, this time, the restraint force is not returned, but it is maintained in an increased state. The increase rate to be increased this time may be the same as or smaller than the increase rate temporarily increased in S103 within a range of 120 to 330%.

  Thereafter, the battery capacity of the battery 10 is measured again, and it is confirmed whether or not the battery capacity has been restored by comparison with the measured value before the execution of S103 (S107). If the capacity has increased (S107: Yes), the process returns to S101 as it is and enters the monitoring state again. On the other hand, if the capacity has not increased (S107: No), it is confirmed whether the binding force has reached a predetermined upper limit (S108).

  If the upper limit has not been reached (S108: No), there is still room for increasing the binding force, so the process returns to S103 to temporarily increase the binding force again. At this time, an increase rate larger than that employed in the previous S103 is employed. Further, the binding force is further increased while monitoring the battery capacity in the same manner as the previous time, and S103 to S108 are executed until the binding force reaches the upper limit value. When the binding force reaches the upper limit (S108: Yes), it is not preferable to increase it further. In this case, no further capacity recovery can be expected for the battery 10 due to an increase in binding force. This is the end of the description of this process.

  As described above in detail, the secondary battery control device of the present embodiment includes the binding force generation unit 13, the binding force control unit 15, and the battery capacity acquisition unit 17. The restraint force control unit 15 monitors the change state of the battery capacity with respect to the accumulated use capacity obtained by integrating the use capacity of the secondary battery, and when the degree of change becomes larger than before, the restraint force is increased. increase. Thereby, the battery capacity of the secondary battery can be recovered and the life of the secondary battery can be extended. Therefore, by controlling the binding force applied to the secondary battery, it is possible to recover the battery capacity of the battery that has been deteriorated to some extent by charging and discharging and to prolong the battery life.

  In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.

DESCRIPTION OF SYMBOLS 10 Battery 10a Large side surface 13 Restraint force generation part 15 Restraint force control part 17 Battery capacity acquisition part

Claims (5)

In a secondary battery control device for controlling a secondary battery in which a wound or laminated electrode plate and an electrolyte are enclosed in a square case having a pair of large side surfaces larger than the other surfaces,
A restraining force generating portion that compresses the plate surfaces of the electrode plates toward each other by restraining the large side surface of the case from the outside;
A battery capacity acquisition unit for acquiring a battery capacity of the secondary battery;
Restraint force for controlling the magnitude of the restraint force generated by the restraint force generation unit based on the accumulated use capacity obtained by integrating the use capacities during charging / discharging of the secondary battery and the battery capacity obtained by the battery capacity obtaining unit. A control unit,
The restraint force control unit
When the degree of decrease in the battery capacity acquired by the battery capacity acquisition unit with respect to the increase in the accumulated usage capacity has changed from a gradual first degree to a more severe second degree, the binding force A control device for a secondary battery, characterized in that the restraining force by the generator is increased. The control apparatus for a secondary battery according to claim 1,
The restraint force control unit includes a newly acquired battery capacity, a previously acquired battery capacity, and a previously acquired battery capacity on a graph having the horizontal axis of the square root of the accumulated used capacity and the vertical axis of the battery capacity acquired by the battery capacity acquisition unit. If the vertical axis intercept of the straight line drawn by is increased by a predetermined rate with respect to its initial value, it is considered that the degree of decrease in battery capacity has changed. Secondary battery control device. The control apparatus for a secondary battery according to claim 1 or 2,
The restraint force control unit
After temporarily increasing the binding force and then temporarily increasing it back to its original size, the battery capacity acquisition unit acquires the battery capacity again,
If the battery capacity has increased from before the temporary increase in binding force, use the secondary battery as it is,
When the battery capacity does not increase, the secondary battery control device performs a steady increase that maintains the increased state by increasing the binding force. In the control apparatus of the secondary battery as described in any one of Claim 1- Claim 3,
The control device for a secondary battery, wherein the restraint force control unit performs the increase of the restraint force by the restraint force generating unit only within a predetermined upper limit value range of the restraint force. In a secondary battery control method for controlling a secondary battery in which a wound or laminated electrode plate and an electrolyte are enclosed in a square case having a pair of large side surfaces larger than the other surfaces,
The target secondary battery is one in which the large side surfaces of the case are constrained from the outside so that the plate surfaces of the electrode plates are pressed toward each other.
Based on the accumulated used capacity obtained by integrating the used capacity at the time of charge and discharge of the secondary battery, and the battery capacity history of the secondary battery
The binding force is increased when there is a change from a gradual first degree to a more severe second degree in the degree of decrease in the battery capacity with respect to the increase in the accumulated usage capacity. Secondary battery control method.

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