JP2016144367A - Control device for battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for a battery pack capable of keeping a restriction load constant.SOLUTION: A control device 1 comprises: temperature detection means for detecting average battery temperatures of groups of unit cells A and a unit cell B; SOC detection means for detecting SOC of the groups of unit cells A and SOC of the unit cell B; and storage means for storing data indicating a relation between the SOC and the average battery temperature of the groups of unit cells A and an SOC setting value of the unit cell B that should be set. If the detected SOC detection value of the unit cell B is greater than the SOC setting value of the unit cell B, the unit cell B is discharged and if the detected SOC detection value of the unit cell B is smaller than the SOC setting value of the unit cell B, the unit cell B is charged.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an assembled battery control device to which a plurality of chargeable / dischargeable cells are connected.

  In recent years, lithium ion secondary batteries, nickel metal hydride batteries, and other secondary batteries have become increasingly important as power sources for mounting on vehicles or as power sources for personal computers and portable terminals. Especially, the lithium ion secondary battery which is lightweight and can obtain a high energy density is preferably used as a high output power source for mounting on a vehicle. For example, as an example of an assembled battery for a vehicle, Patent Document 1 is configured by arranging a plurality of rectangular unit cells and connecting a positive electrode terminal and a negative electrode terminal provided in each unit cell in series. An assembled battery is disclosed.

  In addition, the assembled battery mounted on a vehicle such as an automobile is assumed to be used in a state in which vibration is generated in addition to limiting the mounting space, so that a number of single cells are arranged and restrained An assembled battery (that is, a state in which the individual cells are fixed to each other) is constructed. In such an assembled battery, for example, a pair of end plates are installed on the outermost side (both end faces) of the unit cell group arranged in the stacking direction of the unit cells, and the pair of end plates are tightened and fixed in the approaching direction. Yes.

JP 2010-009978 A

  By the way, in this type of assembled battery, expansion and contraction occur in the electrode plates (positive electrode and negative electrode) in the electrode body of each unit cell due to charging / discharging (that is, variation in SOC), temperature change, and the like. When expansion and contraction occur in the electrode plate, the thickness in the arrangement direction of each unit cell increases and decreases, so that the restraining load (and consequently the surface pressure applied to each unit cell) increases and decreases. Such increase / decrease of the restraining load may cause an uneven distribution of the electrolytic solution (salt concentration) in the electrode body, which may cause a decrease in charge carrier (for example, lithium in the case of a lithium ion secondary battery) deposition resistance. It is desirable to keep the restraining load as constant as possible so that an appropriate surface pressure can be applied to each unit cell. The present invention solves the above problems.

  The control device provided by the present invention is a control device for controlling charging / discharging of a battery pack configured by connecting a plurality of chargeable / dischargeable cells in series. The plurality of unit cells includes a unit cell A group and at least one unit cell B connected by a separate circuit from the unit cell A group. The unit cells A and the unit cells B are arranged in a predetermined direction and are restrained in a state where a load is applied in the arrangement direction. Here, the control device includes temperature detection means for detecting an average battery temperature of the unit cell A group and the unit cell B, and SOC detection unit for detecting the SOC of the unit cell A group and the SOC of the unit cell B. Storage means storing data indicating the SOC of the unit cell A group, the average cell temperature of the unit cell A group and the unit cell B, and the SOC set value of the unit cell B to be set. I have. Then, from the SOC detection value of the battery A group detected by the SOC detection means and the detection value of the average battery temperature of the battery A group and the battery B detected by the temperature detection means, the data When the SOC set value of the unit cell B is set and the SOC detection value of the unit cell B detected by the SOC detection means is larger than the set SOC set value of the unit cell B, The unit cell B is discharged, and the unit cell B is charged when the SOC detection value of the unit cell B detected by the SOC detection means is smaller than the set SOC set value of the unit cell B. It is configured as follows. According to such a configuration, the restraint load (surface pressure) applied to each unit cell can be kept constant by causing the unit cell B to function as a load adjusting mechanism.

  In this specification, the “unit cell” is a term indicating individual storage elements that can be connected in series to form an assembled battery, and includes batteries and capacitors having various compositions unless otherwise specified. . The “secondary battery” generally refers to a battery that can be repeatedly charged, and includes so-called storage batteries such as lithium ion secondary batteries and nickel metal hydride batteries. The electric storage element constituting the lithium ion secondary battery is a typical example included in the “unit cell” referred to herein, and a lithium ion secondary battery pack including a plurality of such unit cells is disclosed herein. This is a typical example of an “assembled battery”.

It is a block diagram which shows typically the structure of the control apparatus which concerns on one Embodiment. It is a perspective view which shows typically the structure of the assembled battery which concerns on one Embodiment. It is a figure which shows the SOC-temperature map which concerns on one Embodiment. It is a flowchart which shows an example of the processing routine performed by the control apparatus which concerns on one Embodiment. It is a graph which shows the relationship between the cell number of the single battery A, and a restraint load. It is a graph which shows the relationship between the cell number of the single battery A, and a restraint load.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, each drawing is drawn typically and does not necessarily reflect a real thing. Each drawing shows only an example, and each drawing does not limit the present invention unless otherwise specified.

  FIG. 1 is a block diagram illustrating a configuration of a control device 1 that controls charging / discharging of the assembled battery 10 according to the present embodiment. The control device 1 of the assembled battery 10 is suitably used as a vehicle-mounted high-output power source that is mounted on a vehicle (typically, an automobile equipped with an electric motor such as a hybrid automobile, an electric automobile, or a fuel cell automobile). It is done.

  The control device 1 may include a load 20 connected to the assembled battery 10 and an electronic control unit (ECU) 30 that adjusts the operation of the load 20 according to the state of the assembled battery 10. The load 20 connected to the assembled battery 10 may include a power consumer that consumes the electric power stored in the assembled battery 10. The load 20 may include a power supply machine that supplies power that can charge the battery pack 10. For example, the load 20 can be an electric motor with a regeneration function.

  FIG. 2 is a perspective view schematically showing the configuration of the assembled battery 10 controlled by the control device according to the present embodiment. The assembled battery 10 disclosed herein may be an assembled battery formed by arranging single cells (typically, single cells having a flat outer shape), and the configuration of the single cells is not particularly limited. Although not intended to be particularly limited, the present invention will be described in detail below using an example of an assembled battery in which a flat lithium ion secondary battery is a single battery and a plurality of the single batteries are connected in series. Explained.

  As shown in FIG. 2, the assembled battery 10 is configured by connecting a plurality of chargeable / dischargeable cells in series. The plurality of unit cells includes a unit cell A group and at least one unit cell B connected by a separate circuit from the unit cell A group. In the illustrated example, a unit cell A group of eight unit cells A having the same shape and one unit cell B are arranged in series at regular intervals. In this embodiment, the unit cell B is arranged at the center of the unit cell A group arranged in series.

  The unit cell A and the unit cell B each include an electrode body (not shown) provided with a positive electrode and a negative electrode, and a container for housing the electrode body and the electrolyte. The electrode body of the present embodiment is composed of predetermined battery constituent materials (active materials for positive and negative electrodes, current collectors for positive and negative electrodes, separators, etc.) as well as single cells equipped in typical assembled batteries. Yes.

As the positive electrode material (positive electrode active material) of the single battery A and the single battery B, one kind or two or more kinds of substances conventionally used in lithium ion secondary batteries can be used without particular limitation. Examples of the positive electrode active material used in the unit cell A and unit cell B, include lithium transition metal oxides such as LiNiCoMnO 2 _{(lithium-nickel-cobalt-manganese} composite oxide).

  As the negative electrode material (negative electrode active material) of the unit cell A, one or more kinds of substances conventionally used in lithium ion secondary batteries can be used without particular limitation. If the example of the negative electrode active material used for the cell A is given, carbon-type materials, such as graphite carbon and amorphous carbon, will be mentioned. On the other hand, as the negative electrode material (negative electrode active material) of the unit cell B, it is preferable to use a material that has a larger expansion and contraction due to charge / discharge than the negative electrode active material of the unit cell A. Examples of the negative electrode active material used for the unit cell B include silicon (Si), an alloy of silicon and another element X (Si-X), tin (Sn), an alloy of tin and another element X ( Sn-X) and the like. Here, the element X is at least one selected from the group consisting of alkali metal elements, alkaline earth metal elements, elements belonging to Groups 13 to 16 of the periodic table, transition metal elements, and rare earth elements. Preferably, X is nickel (Ni). Since these materials have a large expansion and contraction associated with occlusion and release of lithium ions, they can be suitably used as the negative electrode active material of the unit cell B suitable for the purpose of the present invention.

  On the upper surface of the container of the unit cell A, a positive electrode terminal 60A that is electrically connected to the positive electrode of the wound electrode body and a negative electrode terminal 62A that is electrically connected to the negative electrode are provided. In addition, the unit cell A group is arranged by being inverted one by one so that the positive terminals 60A and the negative terminals 62A are alternately arranged. In addition, between the adjacent unit cells A, one positive terminal 60 </ b> A and the other negative terminal 62 </ b> A are electrically connected by an inter-terminal connector 64. Thus, the assembled battery 10 of the desired voltage is constructed | assembled by connecting each cell A in series. The positive electrode terminal 60A and the negative electrode terminal 62A of the cell A are connected to the load 20 (FIG. 1) by a circuit (not shown) (for example, a power drive circuit).

  Further, a positive electrode terminal 60B that is electrically connected to the positive electrode of the wound electrode body and a negative electrode terminal 62B that is electrically connected to the negative electrode are provided on the upper surface of the container of the unit cell B. The positive terminal 60B and the negative terminal 62B of the unit cell B are connected to the load 20 (FIG. 1) by a circuit (not shown) separate from the unit cell A group.

  The unit cells A and the unit cells B of the present embodiment are arranged in a predetermined direction and are restrained in a state where a load is applied in the arrangement direction. Specifically, the unit cell A group and the unit cell B are in the direction in which the side walls of the respective containers (the wide surface of the container, that is, the surface corresponding to the flat surface of the wound electrode body housed in the container) face each other. Arranged. And around the arranged unit cell A group and unit cell B, a restraining member (not shown) is provided for constraining the plurality of unit cell A group and unit cell B together. That is, a pair of restraining plates (not shown) are arranged on the outer side of the unit cell A located on the outermost side in the unit cell arrangement direction. A tightening beam member (not shown) is attached so as to bridge the pair of restraining plates. The unit cell A and the unit cell B can be constrained so that a predetermined load is applied in the arrangement direction by fastening and fixing the end of the beam member to the constraining plate with screws. A restraining load (surface pressure) in the tightening direction (that is, the arrangement direction) is applied to the container side walls of each unit cell A and unit cell B at a level according to the tightening condition of the beam material.

  Here, in each single battery A constituting the assembled battery 10, expansion and contraction occur in the positive electrode and the negative electrode in the electrode body due to charging / discharging (that is, variation in SOC), temperature change, and the like. When expansion and contraction occur in the positive electrode and the negative electrode, the thickness in the arrangement direction of the single cells A increases and decreases, and the restraining load (and consequently the surface pressure applied to the single cells A) increases and decreases. Such an increase or decrease in the surface pressure can cause an uneven distribution of the electrolyte solution (salt concentration) in the electrode body, which can be a factor in reducing the resistance to lithium deposition. It is desirable to keep the restraining load as constant as possible so that an appropriate surface pressure can always be applied to each single cell A.

  In the control device 1 disclosed here, paying attention to the increase / decrease of the thickness in the arrangement direction due to the SOC variation or temperature change of the single battery A group, the increase / decrease in the arrangement direction of the thickness of the single battery A group is simply changed. By absorbing the change in the thickness of the battery B, a constant restraining load (surface pressure) is applied to each unit cell A.

  That is, the control device 1 includes temperature detection means (not shown), SOC detection means (not shown), and an electronic control unit (ECU) 30.

  The temperature detecting means is configured to detect the average battery temperature of the unit cell A group and the unit cell B. For example, the temperature detection means may be a temperature sensor attached to each of the unit cell A group and the unit cell B. An output signal of each temperature sensor is input to the ECU 30 via an input port. And ECU30 acquires the information of the average battery temperature of the cell A group and the cell B based on the output signal from each temperature sensor.

  The SOC detection means is configured to detect the SOC (average SOC) of the unit cell A group and the SOC of the unit cell B. Here, SOC (State Of Charge) is a ratio of the charge capacity to the battery capacity predicted from the positive electrode theoretical capacity. Specifically, the charge rate (%) = “charge capacity (mAh) / battery capacity ( mAh) ”× 100. For example, the SOC detection means may be voltage sensors attached to the unit cell A group and the unit cell B, respectively. The output signal of each voltage sensor is input to the ECU 30 via the input port. And ECU30 acquires the information of SOC of the cell A group and the cell B based on the output signal from each voltage sensor. For example, the ECU 30 may obtain information on the average SOC of the unit cell A group and the SOC of the unit cell B from the voltage between the terminals of each unit cell detected by each voltage sensor. Alternatively, the SOC detection means may be current sensors attached to the unit cell A group and the unit cell B, respectively. In this case, the ECU 30 can acquire the SOC information from the integrated values of the currents flowing into and out of the unit cell A group and the unit cell B.

  The electronic control unit (ECU) 30 is configured such that when the SOC detection value of the single battery B detected by the SOC detection means is larger than the SOC set value of the single battery B, the single battery B is discharged. The load 20 is controlled to operate. In addition, when the SOC detection value of the single battery B detected by the SOC detection means is smaller than the SOC set value of the single battery B, the operation of the load 20 is controlled so that the single battery B is charged. Here, the SOC set value of the single battery B is set to a value that decreases as the thickness of the single battery A group increases with the SOC fluctuation or temperature change of the single battery A group, and the SOC fluctuation or temperature change of the single battery A group. Accordingly, it may be set to a value that increases as the thickness of the unit cell A group decreases. For example, since the thickness of the single cell A group tends to increase as the SOC of the single cell A group increases, in this case, the SOC set value of the single cell B is set to a small value so that the thickness of the single cell B decreases. Good. Further, since the thickness of the single cell A group tends to increase as the battery temperature of the single cell A group increases, in this case, the SOC set value of the single cell B is set to a small value so that the thickness of the single cell B decreases. It is good to set. The typical configuration of the ECU 30 stores at least a ROM (Read Only Memory) storing a program for performing such control, a CPU (Central Processing Unit) capable of executing the program, and temporarily stores data. A random access memory (RAM) and an input / output port (not shown) are included.

In this embodiment, the average SOC of the single battery A group (“SOC _A ”), the average battery temperature of the single battery A group and the single battery B (“T _AVE ”), and the SOC set value of the single battery B to be set ("SOC _MAP ") is stored in a ROM (storage means) in the form of a map, and data of the unit cell A group detected by the SOC detection means is referenced with reference to this SOC-temperature map. The SOC set value of the unit cell B is set from the SOC detection value (average value) and the average battery temperature detection value detected by the temperature detection means. FIG. 3 shows an example of the SOC-temperature map. As shown in FIG. 3, the SOC _{MAP of the} single battery B to be set is uniquely determined from the SOC _A of the single battery A group and the average battery temperature T _AVE . Then, the set SOC set value is compared with the SOC detection value of the single battery B detected by the SOC detection means. If the SOC detection value is larger, the load 20 is set so that the single battery B is discharged. On the other hand, if the SOC detection value is smaller, the load 20 is controlled so that the cell B is charged. A plurality of SOC-temperature maps corresponding to the number of batteries constituting the single battery A group are prepared, and the plurality of SOC-temperature maps are appropriately switched according to the number of batteries constituting the single battery A group. May be.

  The operation of the control device 1 configured as described above will be described. FIG. 4 is a flowchart illustrating an example of a cell B charge / discharge processing routine executed by the ECU 30 of the control device 1 according to the present embodiment. This routine is repeatedly executed every predetermined time (for example, every second) immediately after the assembled battery is activated.

When the battery B charge / discharge processing routine shown in FIG. 4 is executed, the CPU of the ECU 30 first determines the average battery temperature of the battery A group and the battery B from the output of the temperature detection means for the battery 10 to be controlled. (" _TAVE "). Further, the average SOC (“SOC _A ”) of the single cell A group and the SOC of the single cell B (“SOC _B ”) are acquired from the output of the SOC detection means (step S10). Next, with reference to the SOC-temperature map (FIG. 3) stored in the ROM, the SOC detection value (“SOC _A ”) of the unit cell A detected by the SOC detection means and the temperature detection means are detected. The SOC set value (SOC _MAP ) of the unit cell B is set from the detected value (“T _AVE ”) of the average battery temperature. (Step S20).

Then, in step S30, this set SOC setpoint _{(SOC MAP),} by comparing the SOC detection value of the cell B ( "SOC _B"), SOC detection value ( "SOC _B") and SOC setting It is determined whether or not the value (SOC _MAP ) is equal. If the SOC detection value (“SOC _B ”) is equal to the SOC setting value (SOC _MAP ) (YES in step S30), this routine is completed. On the other hand, when the SOC detection value (“SOC _B ”) and the SOC set value (SOC _MAP ) are not equal (NO in step S30), the process proceeds to step S40.

In step S40, it is determined whether or not the SOC detection value (“SOC _B ”) is larger than the SOC setting value (SOC _MAP ). When the SOC detection value (“SOC _B ”) is larger than the SOC set value (SOC _MAP ) (YES in step S40), the load 20 is controlled to be discharged so that the unit cell B is discharged (step S50). . On the other hand, when the SOC detection value (“SOC _B ”) is equal to or lower than the SOC set value (SOC _MAP ) (NO in step S40), the operation of load 20 is controlled so that unit cell B is charged (step S60). ). Then, the current cell B charge / discharge processing routine is terminated.

  According to the said embodiment, the restraint load (surface pressure) added to each cell can be kept constant by functioning the cell B as a load adjustment mechanism. That is, even when the thickness in the arrangement direction of the unit cell A group increases or decreases due to the SOC variation or temperature change, the unit cell B is charged and / or charged so that the increase and decrease in thickness can be absorbed by the unit cell B thickness change. Or since discharge is performed, the restraint load (surface pressure) applied to each unit cell can be kept constant. Thereby, an appropriate surface pressure can be applied to each of the single cells A and B, and a decrease in resistance to lithium deposition can be suppressed. According to the above aspect, since it is only necessary to add the unit cell B as a load adjusting mechanism, it can be easily incorporated into a conventional assembled battery, and the cost can be reduced.

  In addition, you may utilize the cell B which functions as the said load adjustment mechanism as a backup power supply as needed. For example, the ECU 30 may control the operation of the display device using the electric power of the unit cell B when the SOC of the unit cell A group decreases and a system down is likely to occur in a low temperature environment. On the display device, for example, an alarm or the like indicating that the system is down is displayed. Further, for example, when it is desired to reduce or not charge the charging current to the unit cell A group during regeneration of the load 20 (for example, an electric motor with a regeneration function), the ECU 30 changes the charging current charging destination from the unit cell A group. Control to switch to the single battery B may be performed. Thereby, idling of the motor can be avoided.

  In order to confirm the application effect of the present invention, the following experiment was conducted. Here, an assembled battery was constructed by changing the number of cells of the single battery A group, and the number of cells of the single battery A group capable of suppressing a load change in one single battery B was evaluated.

That is, the positive and negative electrode sheets each holding the positive electrode active material and the negative electrode active material on the sheet-like positive electrode current collector and the negative electrode current collector are wound through the separator sheet and accommodated in the case together with the electrolyte. A plurality of prismatic lithium ion secondary batteries were prepared (single cell group A). The positive electrode current collector of the lithium ion secondary battery (unit cell A group) prepared here is an aluminum foil, the negative electrode current collector is a copper foil, the positive electrode active material is lithium nickelate (LiNiO ₂ ), and the negative electrode active material is Graphite. The electrolyte of the lithium ion battery has a composition containing LiPF ₆ at a concentration of 1 mol / L in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate and diethyl carbonate.

  Moreover, the square lithium ion secondary battery of the structure similar to the said lithium ion secondary battery (single battery A group) except having changed the negative electrode active material into the Sn-Ni alloy was prepared (single battery B).

  The unit cell A and the unit cell B having the above configuration are charged to the upper limit SOC (in this case, SOC 100%), and the unit cells A and B after charging are connected in series to form the assembled battery 10 having the configuration shown in FIG. . In this example, a plurality of assembled batteries were constructed by varying the number of cells of the unit cell A group in the range of 2 to 28 cells. Further, the restraining load was adjusted so that the surface pressure applied to each of the cells A and B was 910 kgf. This restraining load of 910 kgf is the maximum value of the restraining load assumed under the condition of “upper limit SOC, 60 ° C.” in which each cell expands most in the usage environment of the on-vehicle assembled battery. Next, the unit cell B was discharged to the lower limit SOC (here, SOC 0%), and the change in the restraining load applied to each unit cell was measured. Here, the case where the restraint load is 800 kgf or less is “◯”, and the case where the restraint load exceeds 800 kgf is “x”. The restraining load of 800 kgf is the upper limit value of the load variation allowable region where the Li precipitation resistance satisfies the allowable standard in the lithium ion secondary battery having the above configuration. The results are shown in FIG.

  As shown in FIG. 5, a single battery B is discharged to the lower limit SOC for an assembled battery having a maximum of 18 single batteries A, so that the Li deposition resistance is 800 kgf or less satisfying the acceptable standard. It has been confirmed that can be reduced.

  Further, the unit cell A and the unit cell B having the above-described configuration are discharged to the lower limit SOC (in this case, SOC 0%), and the discharged unit cells A and B are connected in series, and the assembled battery 10 having the configuration shown in FIG. It was. In this example, a plurality of assembled batteries were constructed by varying the number of cells of the unit cell A group in the range of 2 to 28 cells. Further, the restraining load was adjusted so that the surface pressure applied to each of the single cells A and B was 65 kgf. This 65 kgf restraint load is the minimum value of the restraint load assumed under the condition of “lower limit SOC, −35 ° C.” at which each single battery is most reduced under the usage environment of the on-vehicle assembled battery. Next, the unit cell B was charged to the upper limit SOC (here, SOC 100%), and the change in the restraining load applied to each unit cell was measured. Here, the case where the restraint load is 80 kgf or more is “◯”, and the case where the restraint load is less than 80 kgf is “x”. The restraining load of 80 kgf is the lower limit value of the load variation allowable region where the Li precipitation resistance satisfies the allowable standard in the lithium ion secondary battery having the above configuration. The results are shown in FIG.

  As shown in FIG. 6, for an assembled battery including a maximum of 12 single cells A, by charging one single cell B to the upper limit SOC, a restraint load up to 80 kgf or more satisfying an acceptable standard for Li deposition resistance. It was confirmed that it can be increased.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Control apparatus 10 Assembly battery 20 Load 60A, 60B Positive electrode terminal 62A, 62B Negative electrode terminal 64 Inter-terminal connector A Cell B Cell

Claims (1)

A control device for controlling charging / discharging of an assembled battery configured by connecting a plurality of chargeable / dischargeable cells in series,
The plurality of unit cells includes a unit cell A group and at least one unit cell B connected in a separate circuit from the unit cell A group,
The unit cell A group and the unit cell B are arranged in a predetermined direction and restrained in a state where a load is applied in the arrangement direction.
Here, the control device
Temperature detecting means for detecting an average battery temperature of the unit cell A group and the unit cell B;
SOC detecting means for detecting the SOC of the unit cell A and the SOC of the unit cell B;
Storage means storing data indicating the SOC of the unit cell A group, the average cell temperature of the unit cell A group and the unit cell B, and the SOC set value of the unit cell B to be set ,
The SOC setting of the unit cell B with reference to the data from the SOC detection value of the unit cell A detected by the SOC detection unit and the detection value of the average cell temperature detected by the temperature detection unit Set the value
When the SOC detection value of the single battery B detected by the SOC detection unit is larger than the set SOC setting value of the single battery B, the single battery B is discharged,
An assembled battery configured to charge the unit cell B when the SOC detection value of the unit cell B detected by the SOC detection unit is smaller than the set SOC set value of the unit cell B Control device.