JP2019091565A - Control arrangement of battery pack - Google Patents

Abstract

To allow for appropriate setting of battery use range in consideration of thickness change incident to deterioration, in a control arrangement of a battery pack for controlling the battery pack in a battery use range determined by a lower limit SOC and an upper limit SOC.SOLUTION: An ECU acquires the negative electrode potential of a battery pack, and the temperature of the battery pack (S11). The ECU estimates the cell thickness Th by using the negative electrode potential of the battery pack, and the temperature of the battery pack (S12). The ECU sets the lower limit SOC when the cell thickness Th is larger than a threshold level Lim, to a value lower than the lower limit SOC when the cell thickness Th is smaller than a threshold level Lim (S13, S14). The ECU controls the battery pack in a range determined by the lower limit SOC and the upper limit SOC.SELECTED DRAWING: Figure 10

Description

  The present disclosure relates to a control device for a battery pack, and more particularly to a control device for a battery pack that controls the battery pack within a range determined by a lower limit SOC and an upper limit SOC.

  The assembled battery is composed of a plurality of secondary batteries. A large capacity assembled battery can be obtained by combining a plurality of secondary batteries. However, the capacity of the assembled battery decreases with the deterioration of the secondary battery that constitutes the assembled battery. In the control device of the battery pack disclosed in Japanese Patent Laid-Open No. 2016-167368 (Patent Document 1), the battery pack is controlled in consideration of the deterioration of the secondary battery. Specifically, in view of the fact that the SOC (State Of Charge) of the battery pack affects the deterioration susceptibility of the secondary battery, the battery pack is controlled by the working potential width determined by the lower limit SOC and the upper limit SOC. There is.

  For example, when the battery pack is left in a state where the SOC is close to 100%, deterioration of the battery pack is likely to progress. In addition, when the battery pack is used (discharged) in a state where the SOC is close to 0%, the output characteristics of the battery pack tend to be degraded. For this reason, in Patent Document 1, the lower limit SOC is set to a value higher than 0%, and the upper limit SOC is set to a value lower than 100%. In the battery pack control device described in Patent Document 1, the lower limit of the use potential of the positive electrode of the secondary battery after deterioration obtained from usage history information (past temperature, SOC, etc.) of the secondary battery is used as the lower limit. I am changing the SOC.

  In addition, SOC shows the electrical storage residual amount of a cell, for example, represents the electrical storage amount with respect to a full charge state by 0 to 100%. Moreover, each secondary battery which comprises an assembled battery is also called a "cell", a "cell", etc. Below, each secondary battery is called a "cell." Further, the range determined by the lower limit SOC and the upper limit SOC is hereinafter referred to as a “battery use range”.

JP, 2016-167368, A

  As described above, by narrowing the battery use range of the assembled battery, the assembled battery is less likely to deteriorate and can maintain high performance. However, when the battery use range of the assembled battery is narrow, the high performance can not be sufficiently exhibited in control of the assembled battery. Specifically, in the control of the assembled battery, the battery use range of the assembled battery corresponds to the substantial discharge capacity of the assembled battery. Therefore, when the battery use range of the assembled battery is narrowed, the discharge capacity of the assembled battery decreases. For example, when the SOC of the battery pack reaches the lower limit SOC, it is not possible to use (discharge) the power (power corresponding to the lower limit SOC) even if the power stored in the battery pack remains.

  Therefore, in order to increase the discharge capacity of the assembled battery, it is desirable to widen the use range of the assembled battery. However, the lower the SOC of the assembled battery, the more the cell shrinks, and when the cell becomes thinner due to such shrinkage, the cell is easily detached from the assembled battery, and there is a limit to setting the lower limit SOC low.

  The present disclosure has been made to solve the above problems, and an object of the present disclosure is to provide a control device for an assembled battery that controls an assembled battery within a battery usage range determined by a lower limit SOC and an upper limit SOC. An appropriate battery use range can be set in consideration of changes.

  The battery pack control device of the present disclosure is a battery pack control device configured by stacking a plurality of cells, and includes a cell thickness estimation unit and a battery control unit. The cell thickness estimation unit is configured to estimate the thickness of the cell using the negative electrode potential of the assembled battery and the temperature of the assembled battery. The battery control unit is configured to control the assembled battery within a range determined by the lower limit SOC and the upper limit SOC. Further, the battery control unit sets the lower limit SOC when the cell thickness (Th) is larger than the threshold (Lim) to a value lower than the lower limit SOC when the cell thickness is smaller than the threshold. Configured as.

  The inventors of the present application have found through experiments and the like that as the deterioration of the assembled battery progresses, the cell gets thicker. When the deterioration of the assembled battery progresses, the cells become thick, so that problems (dropping of the cells, etc.) due to the cells becoming thin are less likely to occur.

  In addition, the inventor of the present application has found that the cell thickness, the negative electrode potential of the assembled battery, and the temperature of the assembled battery are correlated by an experiment or the like. Specifically, the lower the temperature of the battery pack, the thinner the cell tends to be. Further, the cell tends to be thicker as the amount of fluctuation of the negative electrode potential of the assembled battery (potential shift from the initial value) becomes larger.

  Based on the above findings, the battery pack control device of the present disclosure estimates the cell thickness using the battery pack negative electrode potential and the battery pack temperature, and the estimated cell thickness is greater than the threshold value. The lower limit SOC in the case of being large is set to a value lower than the lower limit SOC in the case where the estimated cell thickness is smaller than the threshold. By performing such control, it is possible to change the lower limit SOC so as to expand the battery use range according to the change in cell thickness caused by the deterioration of the assembled battery. That is, when the cell is sufficiently thick (thick enough to cause no problems), the lower limit SOC can be lowered to alleviate the power limitation. This makes it possible to use (discharge) more stored power in the battery pack in a degraded state. As a result, the reduction of the dischargeable power amount accompanying the deterioration of the assembled battery is suppressed, and the life of the assembled battery can be extended.

  Note that the battery assembly configured by stacking a plurality of cells also includes a battery assembly configured by alternately stacking a plurality of cells and a plurality of spacers.

  According to the present disclosure, in a control device for an assembled battery that controls a battery pack within a battery use range determined by the lower limit SOC and the upper limit SOC, setting an appropriate battery use range in consideration of a change in cell thickness due to deterioration. Can.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows roughly the whole structure of the vehicle by which the control apparatus of the assembled battery which concerns on embodiment of this indication was applied. It is the perspective view which showed schematic structure of the assembled battery shown in FIG. It is a side view of the assembled battery shown in FIG. It is sectional drawing which showed the internal structure of the cell of the assembled battery shown in FIG. It is a figure which shows the relationship between the cell thickness of a assembled battery, and battery discharge capacity for every battery deterioration degree (small, middle, large). It is a figure for demonstrating the setting method of the battery use range by the control apparatus of the assembled battery which concerns on embodiment of this indication. It is a graph which shows the relationship between the temperature of an assembled battery, and cell thickness variation. It is a graph which shows the relationship between SOC of an assembled battery, cell thickness, and negative electrode electric potential. It is a graph which shows the relationship between the negative electrode electric potential fluctuation amount of a assembled battery, and a cell thickness change amount. It is a flowchart explaining the procedure of the process performed by the control device of the battery module concerning an embodiment of this indication.

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

  FIG. 1 is a view showing a schematic configuration of a vehicle to which a control device of a battery pack according to an embodiment of the present disclosure is applied. Referring to FIG. 1, a vehicle 10 includes an assembled battery 100, a battery monitoring unit 11, a power control unit (PCU) 12, a motor generator (MG: Motor Generator) 13, and driving wheels 14. And an electronic control unit (ECU) 15, a storage unit 16 (for example, a non-volatile memory), a communication device 17, and a communication line 18. The ECU 15, the storage unit 16, and the communication device 17 are connected by a communication line 18, and are configured to be able to transmit and receive information to and from each other.

  Vehicle 10 is configured to travel using power stored in battery assembly 100. Vehicle 10 may be an electric vehicle that can travel using only the power stored in battery assembly 100, or a hybrid that can travel using both the power stored in battery assembly 100 and the output of the engine. It may be a vehicle. Vehicle 10 may be configured to be able to charge assembled battery 100 with the power of an external power supply outside the vehicle. The power supply method from the external power supply may be a method in which the external power supply supplies power to the vehicle 10 via a cable, and the external power supply supplies power to the vehicle 10 in a noncontact manner without the cable (( A wireless power supply method may be used.

  For example, the battery assembly 100 is configured by appropriately connecting a plurality of cells in series and / or in parallel. The battery assembly 100 supplies the PCU 12 with power for driving the drive wheels 14 by the MG 13.

  The battery monitoring unit 11 includes various sensors, and is configured to monitor the state of the battery assembly 100 having the above configuration. The battery monitoring unit 11 includes, for example, a voltage sensor, a current sensor, and a temperature sensor. The voltage sensor detects the voltage of the battery pack 100 and outputs it to the ECU 15. The current sensor detects the current of the battery pack 100 and outputs it to the ECU 15. The temperature sensor detects the temperature of the battery pack 100 and outputs it to the ECU 15.

  MG 13 is a rotating electrical machine, and is, for example, a three-phase AC motor generator. The MG 13 is driven by the PCU 12 to rotate the drive wheel 14. In addition, the MG 13 can also perform regenerative power generation at the time of braking of the vehicle 10 or the like. The electric power generated by the MG 13 is rectified by the PCU 12 and charged in the assembled battery 100.

  The PCU 12 is configured to include an inverter and a converter (both not shown), and drives the MG 13 in accordance with a drive signal from the ECU 15. The PCU 12 converts the power stored in the battery pack 100 into AC power and supplies it to the MG 13 during powering drive of the MG 13, and supplies power to the MG 13 during regenerative driving of the MG 13 (during braking of the vehicle 10, etc.) Are rectified and supplied to the battery pack 100.

  The ECU 15 includes a central processing unit (CPU), a memory (read only memory (ROM) and a random access memory (RAM)), an input / output port for inputting / outputting various signals, etc. ). The ECU 15 controls various devices in the vehicle 10. For example, the ECU 15 controls charging and discharging of the PCU 12 and the battery assembly 100 so that the vehicle 10 is in a desired state. The various controls are not limited to software processing, and may be processed by dedicated hardware (electronic circuits).

  The storage unit 16 includes initial information of the battery pack 100 (for example, traceability data stored at the time of shipment) and information of the battery pack 100 periodically stored by the ECU 15 (for example, usage history information of the battery pack 100). I remember. The traceability data of the assembled battery 100 includes information indicating the initial state of the assembled battery 100 (cell thickness, cell capacity, cell resistance, electrode thickness, electrode potential, electrode coverage, etc.). The storage unit 16 stores the potential for each SOC as the potential of the electrodes (positive electrode and negative electrode) in the battery pack 100 in the initial state.

  The initial information of the assembled battery 100 includes information indicating the relationship between the thickness of the cell, the negative electrode potential of the assembled battery 100, and the temperature of the assembled battery 100 (hereinafter referred to as “cell thickness corresponding information”). The cell thickness correspondence information makes it possible to obtain the thickness of the cell from the negative electrode potential of the assembled battery 100 and the temperature of the assembled battery 100.

  The storage unit 16 may further store correspondence information (such as a map) for measuring the negative electrode potential of the assembled battery 100. For example, information indicating the relationship between the negative electrode potential of the battery pack 100 and the SOC of the battery pack 100 (hereinafter, referred to as “f-SOC correspondence information”) may be stored in the storage unit 16.

  The respective correspondence information can be obtained in advance by experiment or the like. Each correspondence information obtained by an experiment or the like is stored, for example, in the storage unit 16 when the assembled battery 100 is shipped. Each of the correspondence information may be a map, a table, an equation, or a model. Further, each correspondence information may be configured by combining a plurality of maps and the like.

  The storage unit 16 further stores the battery use range. The ECU 15 controls the battery assembly 100 according to the battery use range. Specifically, when the SOC of the battery assembly 100 approaches the upper limit SOC, the ECU 15 limits the power supplied to the battery assembly 100 (that is, the charging power of the battery assembly 100), and the SOC of the battery assembly 100 reaches the upper limit SOC. Do not exceed. Further, when the SOC of the battery assembly 100 approaches the lower limit SOC, the ECU 15 limits the power released from the battery assembly 100 (that is, the discharge power of the battery assembly 100), and the SOC of the battery assembly 100 falls below the lower limit SOC. I will not. The numerical value of the lower limit SOC stored in the storage unit 16 can be changed by the ECU 15. The numerical value of the upper limit SOC stored in the storage unit 16 may be fixed or may be changed by the ECU 15. The SOC of the battery assembly 100 can be measured, for example, from the voltage value of the battery assembly 100 detected by the battery monitoring unit 11 or the like.

  2 to 4 are diagrams showing the configuration of the battery assembly 100 in detail. In FIGS. 2 to 4, the arrangement direction D1 indicates the direction in which the plurality of cells 110 constituting the battery pack 100 are arranged, and the width direction D2 indicates the direction orthogonal to the arrangement direction D1.

  Referring to FIG. 2, the battery assembly 100 is configured by alternately stacking a plurality of cells 110 and a plurality of spacers 120 in the arrangement direction D1. That is, the battery assembly 100 includes the plurality of cells 110 arranged in the arrangement direction D1, and the spacer 120 interposed between the cells 110. The number of cells 110 is, for example, 2 or more and 20 or less. However, the number of cells 110 can be appropriately changed according to the output and the like required for the battery pack 100.

  The cell 110 is a non-aqueous electrolyte secondary battery (for example, a lithium ion battery). The cell 110 includes a positive electrode terminal 131 and a negative electrode terminal 132. Further, a gas release valve 130 is provided between the positive electrode terminal 131 and the negative electrode terminal 132.

  The plurality of cells 110 shown in FIG. 2 are electrically connected in series. Specifically, the plurality of cells 110 constituting the battery assembly 100 are arranged while being reversed in direction. The positive electrode terminal 131 of one cell 110 and the negative electrode terminal 132 of another adjacent cell 110 are electrically connected by the connection member 140 (bus bar). The restraint plates 141 and 142 are disposed at both ends of the battery pack 100 in the arrangement direction D1. Further, the restraint plate 141 and the restraint plate 142 are connected to each other via the restraint band 151. The restraint band 151 and the restraint plates 141 and 142 are connected by a screw 152. The plurality of cells 110 and the spacer 120 can be fixed by the restraint band 151 and the restraint plates 141 and 142 by tightening the screw 152. In addition, by tightening the screw 152, pressure (restraint force) is applied to the cell 110 and the spacer 120.

  Referring to FIG. 3, the spacer 120 has a plate-like main body 122 and a projection 121 (for example, a rib) projecting from the main body 122 toward the cell 110. Although the example in which the projection part 121 is formed only in the one side of the main-body part 122 is shown in FIG. 3, the projection part 121 may be formed in the both sides of the main-body part 122. FIG. Body portion 122 and protrusion 121 are formed integrally, for example. However, the present invention is not limited to this, and the protrusion 121 and the main body 122 may be separate. Also, the protrusion 121 may be provided detachably to the main body 122.

  Of the two main surfaces F1 and F2 of the cell 110 (surfaces at both ends in the arrangement direction D1), the protrusion 121 is in contact with the main surface F1, and the main body 122 is in contact with the main surface F2. The substantially entire area of the main surface F2 of the cell 110 is in contact with the main body portion 122. Further, the main surface F1 of the cell 110 is in contact with the protrusion 121, and a refrigerant flow path is formed in the gap between the main surface F1 of the cell 110 and the main body portion 122. When a restraining force is applied from the restraining plates 141 and 142, the protrusion 121 of the spacer 120 presses the main surface F1 of the cell 110. Spacer 120 is made of, for example, a resin. However, the material of the spacer 120 is not limited to resin, and may be metal or the like. Moreover, it is not essential that the spacer 120 has the protrusion 121, and the shape of the spacer 120 may be flat.

  Referring to FIG. 4, cell 110 includes an electrode group 114 and a case 115 (battery case). The electrode group 114 is housed in the case 115. Further, although not shown, an electrolytic solution is also accommodated in the case 115. By immersing the electrode group 114 in the electrolytic solution, the electrolytic solution also enters the inside of the electrode group 114.

  The electrode group 114 is a wound electrode group configured by winding a laminate of the positive electrode plate 111, the separator 113, and the negative electrode plate 112. The positive electrode plate 111 and the negative electrode plate 112 are stacked with the separator 113 interposed therebetween. The electrode group 114 is not limited to the wound electrode group, and may be a stack electrode group.

  The positive electrode plate 111 includes a positive electrode current collector (for example, an aluminum foil) and a positive electrode active material layer. The positive electrode active material layer is formed on both sides of the positive electrode current collector, for example, by applying a positive electrode mixture containing the positive electrode active material on the surface of the positive electrode current collector. Negative electrode plate 112 includes a negative electrode current collector (for example, copper foil) and a negative electrode active material layer. The negative electrode active material layer is formed on both surfaces of the negative electrode current collector, for example, by applying a negative electrode mixture containing the negative electrode active material on the surface of the negative electrode current collector. Separator 113 is, for example, a microporous membrane. The presence of the pores in the separator 113 facilitates retention of the electrolytic solution in the pores.

  As an example of a positive electrode active material, lithium transition metal oxide (Specifically, lithium nickel cobalt manganese complex oxide etc.) can be mentioned. The positive electrode active material layer may contain, in addition to the positive electrode active material, a conductive material (for example, acetylene black) and a binder (for example, polyvinylidene fluoride). Examples of the negative electrode active material include carbon-based materials (specifically, graphite etc.). The negative electrode active material layer may contain, in addition to the negative electrode active material, a thickener (for example, carboxymethyl cellulose) and a binder (for example, styrene butadiene rubber). Examples of the material of the separator 113 include polyolefin resins (specifically, polyethylene, polypropylene, and the like).

The electrolytic solution includes a non-protic solvent, a lithium salt dissolved in the solvent (e.g., LiPF ₆₎ and. Examples of aprotic solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). Two or more solvents may be mixed and used.

  Case 115 is, for example, a square case. The outer shape of the rectangular case is a rectangular parallelepiped (for example, a flat rectangular parallelepiped). An example of the material of the case 115 is an aluminum alloy.

  Incidentally, the restraining force (restraint load) of the cell 110 by the restraining plates 141 and 142 is adjusted to an appropriate size in consideration of the expansion and contraction of the cell 110. The reason is described below.

  Referring to FIG. 4, electrode group 114 expands when charging of battery assembly 100. Then, when the electrode group 114 expands in the case 115, the electrode group 114 contacts the inner wall of the case 115 to press the case 115 outward. As a result, the thickness of the cell 110 (cell thickness Th) is increased. On the other hand, outside the case 115, the main surface F <b> 1 of the cell 110 is pressed toward the inside of the case 115 by the protrusion 121 of the spacer 120.

  At the time of discharge of the assembled battery 100, the electrode group 114 contracts conversely to the above, and the cell thickness Th becomes thin. Further, the cell 110 also expands or contracts due to a change in temperature of the battery assembly 100, and the cell thickness Th can be changed due to such expansion or contraction.

  If the restraint force of the cell 110 by the restraint plates 141 and 142 is too large or too small, the following problems may occur.

  If the restraining force of the cell 110 is too large, the electrode group 114 in the case 115 is heavily stressed by the pressing of the spacer 120 when the electrode group 114 expands, and the cell 110 is likely to be degraded. For example, in a non-aqueous electrolyte secondary battery, the positive electrode active material layer is composed of a relatively hard material (eg, metal oxide), and the negative electrode active material layer is composed of a relatively soft material (eg, carbon-based material) Often. For this reason, the negative electrode plate of the non-aqueous electrolyte secondary battery is often softer than the positive electrode plate. When stress is applied to the soft negative electrode plate 112, the electrolytic solution held in the negative electrode active material layer of the negative electrode plate 112 is pushed out, and the internal resistance of the cell 110 tends to increase.

  On the other hand, when the restraint force of the cell 110 is too small, the cell 110 is easily detached from the assembled battery 100 when the cell 110 contracts. In addition, when the cell 110 contracts, the ion concentration distribution in the electrolytic solution tends to be biased. Therefore, if the restraining force of the cell 110 is too small, the internal resistance of the cell 110 is increased and the performance of the assembled battery 100 is likely to be degraded.

  As described above, when the restraining force of the cell 110 is too large, problems (such as an increase in internal resistance) due to the expansion of the cell 110 may occur. In addition, when the restraining force of the cell 110 is too small, problems (dropping of the cell, increase in internal resistance, etc.) due to the contraction of the cell 110 may occur. Therefore, the restraining force of the cell 110 by the restraining plates 141 and 142 is adjusted to an appropriate size in consideration of the expansion and contraction of the cell 110. However, when the cell 110 is greatly expanded or greatly contracted, it is difficult to suppress the performance decrease of the battery assembly 100 only by adjusting the restraining force.

  On the other hand, in the control device (ECU 15) of the battery assembly 100 according to the present embodiment, the range determined by the lower limit SOC and the upper limit SOC (battery) in order to suppress the expansion and contraction of the cell 110 accompanying the SOC change of the assembled battery 100. The battery assembly 100 is controlled within the range of use.

  However, if the lower limit SOC is set high in order to suppress the contraction of the cell 110, the discharge capacity of the assembled battery 100 decreases. The reason for this is that when the SOC of the battery assembly 100 reaches the lower limit SOC, it becomes impossible to use (discharge) the electric power (power corresponding to the lower limit SOC) even if the power stored in the battery assembly 100 remains. It is. That is, by setting the lower limit SOC high (narrowing the battery use range), it becomes possible to suppress the problems caused by the contraction of the cells 110, but the discharge capacity of the assembled battery 100 becomes smaller. It is also conceivable to compensate for the discharge capacity of the battery pack 100 which is insufficient by narrowing the battery use range of the battery pack 100 by increasing the number of cells 110, but the increase of the cells 110 complicates the structure of the battery pack 100. , Leading to cost increase.

  Therefore, in the control device (ECU 15) of battery assembly 100 according to the present embodiment, battery assembly 100 sufficient for a long period of time while suppressing a defect (cell dropout, increase in internal resistance, etc.) caused by contraction of cell 110. In order to secure the discharge capacity of the above, while estimating the thickness of the cell 110 (cell thickness Th), the lower limit SOC that matches the cell thickness Th is set. As a result, when the cell 110 is sufficiently thick (thick enough to cause no problem), the lower limit SOC is set low. By setting the lower limit SOC low, the battery use range of the assembled battery 100 is expanded, and the discharge capacity of the assembled battery 100 is increased.

  The inventors of the present application have found through experiments that the cell 110 becomes thicker as the deterioration of the battery assembly 100 progresses. Based on such findings, in the control device (ECU 15) of the battery assembly 100 according to the present embodiment, the cell thickness Th is estimated in consideration of the battery deterioration degree in addition to the temperature of the battery assembly 100. The lower limit SOC is changed according to the accompanying thickness change of the cell. Hereinafter, the advantages of changing the lower limit SOC in this manner will be described in detail with reference to FIGS. 5 and 6.

  FIG. 5 is a view showing the relationship between the cell thickness of the assembled battery and the battery discharge capacity, for each degree of battery deterioration (small, medium, large). In FIG. 5, a solid line K11 indicates the characteristics of the battery pack in the initial state (hereinafter referred to as “state A”). The solid line K12 indicates the characteristics of the assembled battery in a state in which deterioration has progressed more than the state A (hereinafter, referred to as "state B"). A solid line K13 indicates the characteristics of the assembled battery in a state in which the deterioration has progressed more than the state B (hereinafter, referred to as "state C").

  Referring to FIG. 5, broken line L1 indicates the thickness of the cell necessary to prevent the cell from falling off. In order to prevent the detachment of the cell of the assembled battery in the state A (degree of battery deterioration: small), it is necessary to set the lower limit SOC corresponding to the broken line L1. Since the cell becomes thinner as the SOC decreases, if the lower limit SOC is set too low, the cell thickness may fall below the broken line L1 and cell detachment may occur.

  As indicated by solid lines K11 to K13 in FIG. 5, the discharge capacity of the assembled battery decreases as the deterioration of the assembled battery progresses. Also, as the deterioration of the battery pack progresses, the cell becomes thicker. However, if the battery use range of the assembled battery is not changed, the assembled batteries of state B (battery degradation degree: medium) and state C (battery degradation degree: large) are also controlled according to the same battery use range as the assembled battery of state A Be done. Then, the cell thickness and the battery discharge capacity when the SOC of the assembled battery reaches the lower limit SOC change as indicated by a broken line L2 with the deterioration of the assembled battery. That is, in state B, when the cell is thicker than in state A and the battery discharge capacity is small, the battery pack SOC reaches the lower limit SOC, and in state C, the cell is thicker than in state B and the battery discharge capacity is When small, the SOC of the battery pack reaches the lower limit SOC. When the SOC of the battery pack reaches the lower limit SOC, even if the power stored in the battery pack remains, the power (power corresponding to the lower limit SOC) can not be used (discharged). In the states B and C, the SOC of the assembled battery reaches the lower limit SOC with a cell thickness which still has room for the broken line L1.

  On the other hand, in the battery pack control device (ECU 15) according to the present embodiment, the lower limit SOC is determined according to the thickness change of the cell 110 caused by the deterioration of the battery pack 100 by estimating the cell thickness Th by a method described later. It is possible to change. For example, by changing lower limit SOC in accordance with broken line L1, in states B and C as well as in state A, the lower limit SOC corresponding to broken line L1 (and consequently battery use range) is set, and cell thickness Th is broken line Discharge of the assembled battery 100 is allowed until L1 is reached. FIG. 6 shows the battery use range set in this way. In FIG. 6, the horizontal axis indicates SOC (0% to 100%), and the vertical axis indicates the degree of battery deterioration. Further, ranges R1, R2, and R3 indicate the battery use ranges set in the states A, B, and C, respectively.

  Referring to FIG. 6, when the battery use ranges in states A, B and C are arranged in order from the narrow side, range R1, range R2 and range R3 are obtained. As indicated by the broken line L3, as the deterioration of the battery pack progresses, the lower limit SOC is set lower, and the battery use range becomes wider. As a result, in the battery pack in the deteriorated state (states B and C), the stored power can be used (discharged) more. Therefore, the reduction of the dischargeable power amount accompanying the deterioration of the assembled battery is suppressed, and the life of the assembled battery can be prolonged.

  As described above, the progress degree of the deterioration of the assembled battery 100 (the degree of deterioration of the battery) and the cell thickness Th are correlated. Further, the inventor of the present application has found that the negative electrode potential of the assembled battery 100 fluctuates according to the progress of the deterioration of the cell 110 by an experiment or the like. Further, as described above, the cell 110 can expand or contract due to a change in temperature of the battery assembly 100 as described above. The control device (ECU 15) of the battery assembly 100 according to the present embodiment estimates the cell thickness Th using the negative electrode potential of the battery assembly 100 and the temperature of the battery assembly 100 using such a relationship. ing.

  FIG. 7 is a graph showing the relationship between the temperature of the battery assembly and the amount of change in cell thickness. FIG. 8 is a graph showing the relationship between the SOC of the assembled battery, the cell thickness, and the negative electrode potential. FIG. 9 is a graph showing the relationship between the negative electrode potential fluctuation amount of the assembled battery and the cell thickness change amount.

  Referring to FIG. 7, as indicated by solid line K21, the temperature of the assembled battery and the amount of change in cell thickness have a substantially proportional relationship, and more specifically, the higher the temperature of the assembled battery, the thicker the cell. Have a relationship.

  Referring to FIG. 8, as shown by solid lines K22 and K23, in the region where the amount of change in cell thickness with respect to SOC change is large (the region with low SOC), the amount of change in negative electrode potential with respect to SOC change is also large. In a region where the amount of change in cell thickness relative to the change is small, the amount of change in the negative electrode potential relative to the change in SOC also becomes small. The negative electrode potential of the assembled battery is correlated with the cell thickness, and the cell tends to be thicker as the variation amount of the negative electrode potential of the assembled battery becomes larger. Specifically, as indicated by a solid line K24 in FIG. 9, the negative electrode potential fluctuation amount of the assembled battery and the cell thickness change amount have a substantially proportional relationship. The negative electrode potential fluctuation amount corresponds to the fluctuation amount (potential deviation) from the initial value of the negative electrode potential stored in the storage unit 16.

  When charge and discharge of the assembled battery are repeated, the surface state of the negative electrode of the assembled battery changes. Specifically, charge carriers (lithium in lithium ion batteries) are deposited on the negative electrode surface, or a film is formed. Thereby, the negative electrode potential fluctuates. In addition, when charge and discharge of the assembled battery are repeated, the amount by which the charge carrier can be released or stored at the negative electrode tends to decrease. Hereinafter, the change in the state and performance of the negative electrode due to the use of the assembled battery (charge and discharge) is referred to as "deterioration of the negative electrode". As the deterioration of the negative electrode progresses, the negative electrode potential fluctuation tends to increase. In addition, when the deterioration of the negative electrode progresses, the voltage and capacity of the battery pack tend to decrease.

  As described above, the cell thickness Th, the negative electrode potential of the assembled battery 100, and the temperature of the assembled battery 100 are correlated. Therefore, the cell thickness Th can be estimated from the negative electrode potential of the assembled battery 100 and the temperature of the assembled battery 100. In the present embodiment, the ECU 15 (battery control unit) controls the battery assembly 100 within a range determined by the lower limit SOC and the upper limit SOC. Further, the ECU 15 (cell thickness estimation unit) estimates the thickness (cell thickness Th) of the cell 110 using the negative electrode potential of the assembled battery 100 and the temperature of the assembled battery 100. Further, the ECU 15 (battery control unit) sets the lower limit SOC when the cell thickness Th is larger than the threshold to a value lower than the lower limit SOC when the cell thickness Th is smaller than the threshold. This makes it possible to set an appropriate battery use range in consideration of the thickness change of the cell 110. Hereinafter, the control method of the battery assembly 100 by the ECU 15 will be described in detail with reference to FIG.

  FIG. 10 is a flow chart for explaining the procedure of processing executed by the ECU 15. The process shown in this flowchart is called from the main routine and repeatedly executed every predetermined time or when the predetermined condition is satisfied.

  Referring to FIG. 10, ECU 15 acquires information of battery assembly 100 (hereinafter sometimes referred to as "battery information") and stores the information in storage unit 16 (step S11). The battery information includes the negative electrode potential of the battery pack 100, the temperature of the battery pack 100, and the current measured values.

  The negative electrode potential of the assembled battery 100 can be measured using a reference electrode. For example, metallic lithium can be used as the reference electrode. The negative electrode potential of the assembled battery 100 can be measured based on the potential difference between the negative electrode of the assembled battery 100 and the reference electrode. The method of measuring the negative electrode potential is not limited to the above actual measurement but is arbitrary. For example, the negative electrode potential of the assembled battery 100 may be estimated from the SOC of the assembled battery 100 by referring to the correspondence information (f-SOC correspondence information) in the storage unit 16.

  The temperature of the battery pack 100 can be obtained, for example, from the battery monitoring unit 11. The battery monitoring unit 11 can detect the temperature of the battery pack 100 by a temperature sensor.

  When the negative electrode potential of assembled battery 100 is estimated from the SOC of assembled battery 100, the SOC of assembled battery 100 can be estimated using the current value and the voltage value of assembled battery 100 acquired by battery monitoring unit 11, for example. . However, the method of measuring the SOC is arbitrary, and a method by current value integration (coulomb count) or a method by estimation of an open circuit voltage (OCV: Open Circuit Voltage) may be employed.

  Subsequently, the ECU 15 estimates the thickness (cell thickness Th) of the cell 110 using the negative electrode potential of the battery pack 100 acquired in step S11 and the temperature of the battery pack 100 (step S12).

  Assuming that the thickness of the cell 110 is Th, the negative electrode potential of the assembled battery 100 is f, and the temperature of the assembled battery 100 is T, the thickness of the cell 110 can be determined according to the following equation (1). In addition, "a" in Formula (1) is a constant previously calculated | required by experiment etc., for example, may be "1".

Th = a × f × T (1)
Formula (1) corresponds to the aforementioned cell thickness correspondence information, and defines the relationship between Th (cell thickness), f (negative electrode potential), and T (temperature). From the f (negative electrode potential) and T (temperature) obtained in step S11, Th (cell thickness) can be determined by the equation (1).

  Subsequently, the ECU 15 determines whether the cell thickness Th acquired in step S12 is larger than the threshold value Lim (step S13). The threshold Lim can be set arbitrarily. As the threshold value Lim, for example, the smallest value of the cell thickness (the smallest cell thickness that does not cause a defect) in which a defect (dropping of the cell 110, increase in internal resistance, etc.) due to thinning of the cell 110 does not occur Is preferably determined in advance by experiments or the like.

  If cell thickness Th is larger than threshold value Lim (YES in step S13), ECU 15 changes the lower limit SOC of the battery use range stored in storage unit 16 to a value lower than the current value (updated) (Step S14). The ECU 15 may set, as the lower limit SOC, an SOC with which the cell thickness Th matches the threshold value Lim, using, for example, the f-SOC correspondence information in the storage unit 16 and the above-mentioned equation (1). it can. The SOC in which the cell thickness Th matches the threshold value Lim is defined as “T” in the equation (1), and the temperature of the battery pack 100 acquired in step S11 is “Th” in the equation (1). It is SOC corresponding to "f (negative electrode electric potential)" which satisfies Formula (1), when threshold value Lim is each substituted. However, the set value of the lower limit SOC in step S14 is arbitrary as long as it is a value lower than the current value.

  By setting a value lower than the current value as the lower limit SOC, the battery use range is expanded. Then, the ECU 15 controls the battery assembly 100 according to the expanded battery use range. When the change of the lower limit SOC is completed in step S14, the process is returned to the main routine.

  If the cell thickness Th is less than or equal to the threshold value Lim (NO in step S13), the process is returned to the main routine without changing the lower limit SOC.

  According to the control method described above, the lower limit SOC when the cell thickness Th is larger than the threshold Lim is set to a value lower than the lower limit SOC when the cell thickness Th is smaller than the threshold Lim. Specifically, when the cell thickness Th is larger than the threshold value Lim (YES in step S13), the lower limit SOC is changed to a value lower than the current value in step S14. On the other hand, when cell thickness Th is smaller than threshold value Lim (NO in step S13), lower limit SOC is not changed, and lower limit SOC remains at the current value. By such control, it is possible to secure a sufficient discharge capacity of the assembled battery 100 for a long period of time while suppressing a failure due to the contraction of the cell 110 (dropping of the cell, increase in internal resistance, etc.).

  As described above, as the deterioration of the battery pack 100 progresses, the cell 110 becomes thicker. For this reason, when the deterioration of the battery assembly 100 progresses, it becomes difficult for the problem due to the thinning of the cell 110 to occur. According to the above control method, it is possible to change the lower limit SOC so as to expand the battery use range in accordance with the thickness change of the cell 110 caused by the deterioration of the assembled battery. That is, when the cell 110 is sufficiently thick (thick enough to cause no problem), the lower limit SOC can be lowered to alleviate the power limitation. This makes it possible to use (discharge) the stored power more in the deteriorated battery pack 100. As a result, the reduction of the dischargeable power amount accompanying the deterioration of the battery assembly 100 is suppressed, and the life of the battery assembly 100 can be extended.

  In step S13 of FIG. 10, when the cell thickness Th and the threshold value Lim are the same, it is determined as NO. However, the present invention is not limited to this, and step S13 may be changed so that YES is determined when the cell thickness Th and the threshold value Lim are the same, and the process proceeds to step S14.

  The cell thickness correspondence information is not limited to the above equation (1) but is arbitrary. For example, the cell thickness correspondence information may be a map defining the relationship as shown in FIGS. 7 and 9. With such a map, it is possible to estimate the current cell thickness from the initial value of the cell thickness and the total amount of the cell thickness change according to the temperature change and the negative electrode potential change.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention 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.

  Reference Signs List 10 vehicle 11 battery monitoring unit 12 PCU 13 MG 14 drive wheel 15 ECU 16 storage unit 17 communication device 18 communication line 100 assembled battery 110 cells 111 positive plate 112 negative plate 113 separator , 114 electrode group, 115 case, 120 spacer, 121 protrusion, 122 main body, 131 positive electrode terminal, 132 negative electrode terminal, 130 gas release valve, 140 connection member, 141, 142 restraint plate, 151 restraint band, 152 screw.

Claims (1)

A control device for an assembled battery configured by stacking a plurality of cells,
A cell thickness estimation unit that estimates the thickness of the cell using the negative electrode potential of the assembled battery and the temperature of the assembled battery;
A battery control unit configured to control the battery assembly within a range determined by the lower limit SOC and the upper limit SOC;
The battery control unit sets the lower limit SOC when the thickness of the cell is larger than a threshold to a value lower than the lower limit SOC when the thickness of the cell is smaller than the threshold. Battery control unit.

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