JP6485708B2 - Battery system - Google Patents

Description

  The present invention relates to a battery system.

  In recent years, lithium ion secondary batteries, nickel metal hydride batteries, and other secondary batteries have become increasingly important as power sources for in-vehicle use. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source for mounting on a vehicle such as a plug-in hybrid (PHV) or an electric vehicle (EV).

  In this type of secondary battery, it is possible to improve the performance of the secondary battery by determining the deterioration state of the secondary battery and limiting the use when the deterioration occurs or by performing processing to eliminate the deterioration. Is planned. For example, in Patent Document 1, the deterioration due to wear of the secondary battery and the deterioration due to the salt concentration distribution inside the secondary battery (high rate deterioration) are distinguished, the deterioration state of the secondary battery is determined, and the salt concentration distribution is determined. A battery system is disclosed that performs processing to eliminate the salt concentration distribution when deterioration occurs.

International Publication No. 2013/121466

  By the way, in a secondary battery such as a lithium ion secondary battery, the main causes of deterioration are deterioration due to wear and salt concentration distribution, as well as charge carriers in the negative electrode (lithium in the case of a lithium ion secondary battery). There is precipitation. With the technique disclosed in Patent Document 1, even though deterioration due to wear and deterioration due to salt concentration distribution can be determined, it is difficult to determine deterioration due to precipitation of charge carriers.

  The present invention has been made in view of such points, and its main purpose is to provide a battery system capable of discriminating deterioration due to precipitation of charge carriers in addition to deterioration due to wear and deterioration due to salt concentration distribution. Is to provide.

The battery system proposed here includes a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, a battery capacity acquisition unit that acquires a chargeable / dischargeable battery capacity A of the secondary battery, and the secondary battery. Based on the acquired battery capacity A and the internal resistance B, using an internal resistance acquisition means for acquiring the internal resistance B and a map showing the correspondence between the battery capacity decrease amount, the internal resistance increase amount, and the deterioration mode The state of the secondary battery is the following (1) to (3):
(1) Deterioration due to wear of the secondary battery;
(2) deterioration due to deposition of charge carriers at the negative electrode inside the secondary battery; and
(3) A discriminating means for discriminating which degradation mode is the degradation mode due to the bias of the salt concentration distribution of the non-aqueous electrolyte in the secondary battery.
According to this configuration, in addition to deterioration due to wear and deterioration due to salt concentration distribution, deterioration due to precipitation of charge carriers can be determined. For this reason, it is possible to appropriately cope with the deterioration of the battery, and it is possible to perform optimal battery control in accordance with the battery state.

It is a block diagram which shows the structure of the battery system controlled by the control apparatus of the secondary battery which concerns on this embodiment. It is a graph which shows the relationship between a capacity | capacitance fall amount and resistance increase amount. It is a graph which shows the relationship between a capacity | capacitance fall amount and resistance increase amount. It is a graph which shows the relationship between a capacity | capacitance fall amount and resistance increase amount. It is the figure which illustrated the relationship between positive / negative electrode potential and battery capacity. It is the figure which illustrated the relationship between positive / negative electrode potential and battery capacity. It is the figure which illustrated the relationship between positive / negative electrode potential and battery capacity. It is the figure which illustrated the relationship between positive / negative electrode potential and battery capacity. It is an example of the map which shows the correspondence of battery capacity fall amount, internal resistance increase amount, and deterioration mode. It is a figure which shows the processing flow of a battery system.

  Hereinafter, preferred embodiments of the present invention will be specifically described, but the present invention is not intended to be limited to those shown in the specific examples. 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. Moreover, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted.

  The secondary battery to be processed by the battery system disclosed herein is not particularly limited as long as it is a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. For example, it is possible to target various types of secondary batteries in which charge and discharge are repeatedly realized by movement of charges accompanying movement of charge carriers between positive and negative electrodes. For example, a lithium ion secondary battery is a secondary battery that uses lithium ions as a charge carrier, and may be an example of a suitable secondary battery targeted by the present technology. Although not intended to be particularly limited, the present invention will be described in detail below by taking as an example a case where the present invention is mainly applied to a lithium ion secondary battery mounted on a vehicle.

  FIG. 1 is a block diagram showing a configuration of a battery system 1 according to the present embodiment. This battery system 1 is suitably used for a vehicle (typically, an automobile including an electric motor such as an automobile, particularly a hybrid automobile, an electric automobile, or a fuel cell automobile).

  The battery system 1 includes a lithium ion secondary battery 10, a load 20 connected to the lithium ion secondary battery 10, and an electronic control unit (ECU) 30 that adjusts the operation of the load 20 according to the state of the lithium ion secondary battery 10. It can be a configuration. The load 20 connected to the lithium ion secondary battery 10 may include a power consumer (for example, a motor) that consumes the power stored in the lithium ion secondary battery 10. The load 20 may include a power supply device (charger) that supplies power that can charge the battery 10.

  The lithium ion secondary battery 10 is composed of a positive electrode and a negative electrode facing each other, and a non-aqueous electrolyte solution (liquid electrolyte) containing lithium ions supplied between the positive and negative electrodes. The positive electrode and the negative electrode contain an active material capable of inserting and extracting lithium ions. When the battery is charged, lithium ions are released from the positive electrode active material, and the lithium ions are occluded in the negative electrode active material through the electrolyte. On the contrary, when the battery is discharged, the lithium ions stored in the negative electrode active material are released, and the lithium ions are again stored in the positive electrode active material through the non-aqueous electrolyte. As the lithium ions move between the positive electrode active material and the negative electrode active material, electrons flow from the active material to the external terminal. Thereby, the load 20 is discharged.

Here, it is known that lithium ion secondary batteries generally deteriorate (decrease in capacity and increase in internal resistance) with use. According to the inventor's knowledge, as a main cause of deterioration,
(1) Degradation due to wear of the secondary battery (hereinafter also referred to as “normal degradation”),
(2) Deterioration due to lithium deposition at the negative electrode inside the secondary battery, and (3) Degradation due to uneven distribution of salt concentration of the nonaqueous electrolyte inside the secondary battery (typically repeated high-rate charge / discharge) (Deterioration caused by unevenness (unevenness) depending on the location of the lithium salt concentration of the non-aqueous electrolyte permeating into the positive electrode and the negative electrode due to the above, also referred to as “high rate deterioration” hereinafter.)
Can be considered.

  As a result of various experiments, the present inventor has found that there is a certain correlation between the deterioration of the above (1) to (3), the amount of decrease in battery capacity, and the amount of increase in internal resistance. . Specifically, a cycle deterioration test with the deterioration (1) to (3) is performed on the lithium ion secondary battery, and the amount of change in the battery capacity and internal resistance of the secondary battery before and after the cycle deterioration test is measured. did. The results are shown in FIGS. 2 to 4 are graphs showing the relationship between the capacity reduction amount and the internal resistance increase amount before and after the cycle deterioration test.

  As shown in FIGS. 2 to 4, after the cycle deterioration test accompanied by the deterioration (normal deterioration) due to the wear of (1) above, the battery capacity decreased and the internal resistance tended to increase. On the other hand, in the cycle deterioration test with deterioration due to lithium deposition in (2) above, although the battery capacity decreased, the internal resistance did not increase so much, and the resistance against capacity deterioration increased compared to the normal deterioration in (1) above. It was small. Further, in the cycle deterioration test with deterioration due to the uneven distribution of salt concentration in (3) above, although the internal resistance increased, the battery capacity did not decrease so much, and compared with the normal deterioration in (1) above, The resistance increase was large.

  The reason why such a tendency can be obtained is not particularly limited, but is considered as follows, for example. Here, FIG. 5 is a diagram illustrating the relationship between the positive and negative electrode potentials of the secondary battery and the battery capacity before the cycle deterioration test (that is, the initial state), and FIG. 6 shows the normal deterioration due to the wear of (1) above. FIG. 7 is a diagram illustrating the relationship between the positive and negative electrode potentials of the secondary battery and the battery capacity after the accompanying cycle deterioration test, and FIG. 7 is a graph illustrating the positive and negative of the secondary battery after the cycle deterioration test involving deterioration due to lithium deposition in (2) above. FIG. 8 is a diagram illustrating the relationship between the negative electrode potential and the battery capacity, and FIG. 8 shows the relationship between the positive and negative electrode potentials of the secondary battery and the battery capacity after the cycle deterioration test with deterioration due to the deviation of the salt concentration distribution in (3) above. FIG.

  As described above, the positive electrode and the negative electrode are provided with an active material. The potential at which the active material occludes lithium ions is determined by the crystal structure, composition, etc., and the battery capacity (reversible capacity) that can be reversibly charged and discharged as a battery is the open circuit potential (OCV) between the positive electrode and the negative electrode. The positive electrode potential and the negative electrode potential are determined by the size of the overlapping region of the capacity operation area. In the initial state of the secondary battery shown in FIG. 5, in the open circuit potential of the positive electrode and the negative electrode, the region where the capacity operation region of the positive electrode potential and the negative electrode potential overlap is the initial capacity. Moreover, during charging, an overvoltage is added to the open circuit potential at each of the positive electrode and the negative electrode due to internal resistance (positive electrode charging potential and negative electrode charging potential), and the potential difference becomes a charging curve of the secondary battery.

  Here, in the cycle deterioration test with deterioration (normal deterioration) due to wear in (1) above, as shown in FIG. 6, lithium ions as charge carriers are consumed due to film formation on the positive electrode and the negative electrode, resulting in an irreversible capacity. Therefore, at the end of charging, a negative electrode capacity shift that does not return to the initial negative electrode potential occurs (that is, the negative open circuit potential shifts to the left). In addition, the positive electrode resistance and the negative electrode resistance increase due to the film formation on the positive electrode and the negative electrode, and the internal resistance (and thus overvoltage) increases. As a result, the potential at the time of positive electrode charging shifts upward and the potential at the time of negative electrode charging shifts downward It is done. That is, it is considered that after the cycle deterioration test with normal deterioration due to wear (1), the battery capacity decreases as compared with the initial capacity and the internal resistance tends to increase.

  On the other hand, as shown in FIG. 7, in the cycle deterioration test with deterioration due to lithium deposition in (2) above, the irreversible capacity increases because lithium ions are deposited on the negative electrode surface and deactivated. (The open circuit potential of the negative electrode shifts to the left), but the positive electrode resistance does not change, and the negative electrode resistance increases little compared to normal deterioration due to wear (during positive electrode charging) It is considered that the electric potential and the electric potential at the time of negative electrode charging do not change compared to normal deterioration). In other words, in the cycle deterioration test with deterioration due to lithium deposition described in (2) above, it is considered that the increase in resistance to capacity deterioration is smaller than the normal deterioration due to wear.

  Further, as shown in FIG. 8, in the cycle deterioration test involving deterioration due to the uneven distribution of salt concentration in (3) above, the amount of lithium ions in the electrolyte is insufficient at the portion where the lithium salt concentration is relatively low. As a result of increase in resistance and negative electrode resistance and increase in internal resistance (and overvoltage), the positive charge potential shifts upward and the negative charge potential shifts downward, but no irreversible capacity is generated. It is considered that the capacity shift of the negative electrode hardly occurs (the open circuit potential of the negative electrode hardly changes). That is, in the cycle deterioration test with deterioration due to the deviation of the salt concentration distribution of (3) above, it is considered that the increase in resistance to capacity deterioration is larger than normal deterioration due to wear.

  In the technology disclosed here, paying attention to the difference in resistance increase behavior with respect to capacity degradation due to each degradation mode, the degradation mode of the secondary battery is estimated by grasping the behavior of resistance increase with respect to capacity degradation. Like to do.

That is, the battery system 1 includes a battery capacity acquisition unit that acquires a chargeable / dischargeable battery capacity A of the secondary battery, an internal resistance acquisition unit that acquires the internal resistance B of the secondary battery, a battery capacity reduction amount, and an internal Based on the acquired battery capacity A and the internal resistance B, using the map showing the correspondence between the resistance increase amount and the deterioration mode, the state of the secondary battery,
The following (1) to (3):
(1) Deterioration due to wear of the secondary battery;
(2) deterioration due to deposition of charge carriers at the negative electrode inside the secondary battery; and
(3) A discriminating means for discriminating which degradation mode is the degradation mode due to the bias of the salt concentration distribution of the non-aqueous electrolyte in the secondary battery. 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. The ROM stores a map indicating a correspondence relationship between the battery capacity decrease amount, the internal resistance increase amount, and the deterioration mode. Various signals from a voltage sensor, a current sensor, a temperature sensor, and the like (not shown) are input to the ECU 30 via an input port. Further, the ECU 30 outputs a drive signal or the like to the load 20 (power consumption machine and / or power supply machine) via an output port. The ECU 30 constitutes battery capacity acquisition means, internal resistance acquisition means, and determination means of the present embodiment.

  The battery capacity acquisition means is configured to acquire (estimate) the battery capacity A of the secondary battery that can be charged and discharged. The method for obtaining the battery capacity A is not particularly limited, and a conventionally known method that is conventionally used in a general battery system can be employed. For example, based on various data detected by a current sensor, a current sensor, a temperature sensor, etc., a method for estimating the battery capacity of a secondary battery according to a battery model equation (for example, opening of positive and negative electrodes of a secondary battery obtained in advance). The circuit voltage characteristics are stored, the stored data and the data detected by the current sensor, current sensor, and temperature sensor are referred to, and the active material amount, capacity density, and resistance of the positive electrode and the negative electrode are extracted and extracted. A method for estimating the battery capacity of a secondary battery using parameters) is exemplified. This method can be performed with reference to, for example, Japanese Patent Application Laid-Open No. 2014-10003 as necessary.

  The internal resistance acquisition means is configured to acquire (estimate) the internal resistance B of the secondary battery. The method for obtaining the internal resistance B is not particularly limited, and a conventionally known method that is conventionally used in a general battery system can be adopted. For example, based on the current sensor and various data detected by the current sensor, a method of estimating the internal resistance by dividing the voltage change during charging / discharging by the current change at that time (for example, the current change amount) A method of linearly approximating a parameter and a parameter based on the amount of change in voltage and the amount of change in impedance and calculating the slope of the approximated straight line as the impedance of the battery is exemplified. This method can be implemented, for example, with reference to Japanese Patent Laid-Open No. 2006-250905 as necessary.

  The determination means uses a map showing a correspondence relationship between the battery capacity decrease amount, the internal resistance increase amount, and the deterioration mode, and based on the acquired battery capacity A and the internal resistance B, the state of the secondary battery is: Deterioration due to secondary battery wear, deterioration due to charge carrier deposition at the negative electrode inside the secondary battery, or deterioration due to bias in the non-aqueous electrolyte salt concentration distribution inside the secondary battery It is configured to determine whether or not there is. In this embodiment, the determination unit calculates the battery capacity decrease amount by subtracting the acquired battery capacity A from the initial capacity. Further, the determining means calculates an increase in internal resistance by subtracting the initial internal resistance from the acquired internal resistance B. The deterioration mode corresponding to the calculated battery capacity decrease amount and the internal resistance increase amount is described with reference to the map showing the correspondence relationship between the battery capacity decrease amount, the internal resistance increase amount, and the deterioration mode as shown in FIG. Is identified. This map can be created by conducting a preliminary experiment or the like in advance. Also, a plurality of maps showing the correspondence relationship may be prepared, and the plurality of maps may be switched according to battery usage conditions. The initial capacity and the initial internal resistance can also be obtained by conducting preliminary experiments and the like in advance.

  The battery system 1 may output the result determined by the determining means to a display device (not shown). In the display device, the deterioration mode determined by the determining means is displayed. Thereby, the deterioration state of a secondary battery can be grasped visually.

  The battery system 1 may include a control unit that performs battery control according to the deterioration mode determined by the determination unit. The control means drives and controls the load 20 (power consumption machine and / or power supply machine) so that the battery state is kept good based on the deterioration mode determined by the determination means. Based on the degradation mode determined by the means, the degradation eliminating means is driven and controlled so that the degradation is eliminated or alleviated.

  For example, when the deterioration mode is a deterioration mode due to lithium deposition on the negative electrode, the control unit can drive-control the load 20 so as to remove the lithium deposited on the negative electrode. This method can be implemented with reference to, for example, Japanese Patent Application Laid-Open No. 2013-11085 as necessary. The control means can drive the load 20 to increase the potential of the negative electrode so that lithium deposited on the negative electrode is dissolved and removed. This method can be carried out with reference to, for example, Japanese Patent Application Laid-Open No. 2009-199936 as necessary. Further, the control means can drive the battery so that the deterioration eliminating means (heating means) is driven and controlled to be equal to or higher than the battery temperature at which lithium deposited on the negative electrode is dissolved. This method can be carried out, for example, with reference to JP 2011-142016 A as necessary.

  Further, when the deterioration mode is a deterioration mode due to deterioration due to bias in the lithium salt concentration distribution (high-rate deterioration), the control means performs pulse control so that the load 20 is controlled to eliminate the unevenness in the lithium salt concentration distribution. Processing can be performed. This method can be performed with reference to, for example, Japanese Patent Application Laid-Open No. 2010-272470 as necessary. Further, the control means can set a maximum allowable output (discharge power value) of the battery to be small, and can drive and control the load 20 within the set maximum output range. This method can be performed with reference to, for example, Japanese Patent Application Laid-Open No. 2009-123435 as necessary. In addition, the control means can drive and control the deterioration elimination means (electrolyte vibration excitation means) to promote the flow of the electrolyte so that the uneven distribution of the lithium salt concentration is eliminated or alleviated. This method can be implemented, for example, with reference to Japanese Patent Application Laid-Open No. 2010-251025 as necessary. In addition, the control means can drive and control the deterioration elimination means (heating means) to heat the battery so that the unevenness of the lithium salt concentration distribution is eliminated or alleviated. This method can be performed with reference to, for example, Japanese Patent Application Laid-Open No. 2014-154399 as necessary.

  Further, the control means can stop the use of the battery when the deterioration of the battery is not eliminated or alleviated even when the deterioration elimination means is driven and controlled.

  The operation of the battery system 1 configured as described above will be described. FIG. 10 is a flowchart illustrating an example of a deterioration mode determination processing routine executed by the ECU 30 of the battery system 1 according to the present embodiment. This routine is repeatedly executed periodically every predetermined time immediately after being mounted on the vehicle, for example.

  When the deterioration mode determination processing routine shown in FIG. 10 is executed, the CPU of the ECU 30 first acquires the battery capacity A for the lithium ion secondary battery 10 to be processed in step S10. For example, the battery capacity A may be estimated according to the battery model formula based on data detected by a current sensor, a current sensor, and a temperature sensor. In step S20, the internal resistance B of the secondary battery is acquired. For example, based on the current sensor and the data detected by the current sensor, the internal resistance may be estimated by dividing the voltage change during charging / discharging by the current value change at that time.

  Next, in step S30, the battery capacity reduction amount (ΔAh) is calculated by subtracting the acquired battery capacity A from the initial capacity. Further, the amount of increase in internal resistance (ΔR) is calculated by subtracting the initial internal resistance from the acquired internal resistance B.

  Next, in step S40, the calculated battery capacity decrease amount (ΔAh) and the internal resistance increase are referred to with reference to a map showing the correspondence relationship between the battery capacity decrease amount, the internal resistance increase amount, and the deterioration mode stored in the ROM. The deterioration mode corresponding to the quantity (ΔR) is specified. Specifically, referring to the map shown in FIG. 9, the state of the secondary battery is due to deterioration due to wear of the secondary battery (normal deterioration), deterioration due to lithium deposition at the negative electrode, and bias in the salt concentration distribution. It is determined which degradation mode is degradation (high-rate degradation). When the deterioration mode of the secondary battery is deterioration due to wear (in the case of YES), it is determined that the secondary battery is normal, and this processing routine is ended. On the other hand, when the deterioration mode of the secondary battery is deterioration due to lithium deposition at the negative electrode or deterioration due to bias in the salt concentration distribution (in the case of NO), it is determined that the secondary battery is not normal, and the process proceeds to step S50.

  In step S50, battery control is performed according to the determined deterioration mode (that is, the deterioration mode due to lithium deposition at the negative electrode or the deterioration mode due to bias in the salt concentration distribution). Specifically, based on the determined deterioration mode, the load 20 is driven and controlled so that the battery state is kept good, or the deterioration eliminating means is driven and controlled so that the deterioration of each deterioration mode is eliminated. Or When the process of step S50 is not performed, the use of the battery may be stopped.

  According to the above embodiment, in addition to deterioration due to wear and deterioration due to salt concentration distribution, it is possible to determine deterioration due to lithium precipitation. For this reason, it is possible to appropriately cope with the deterioration of the battery, and it is possible to perform optimal battery control in accordance with the battery state.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

10 Secondary battery 20 Load 30 ECU

Claims (1)

A secondary battery comprising a positive electrode and a negative electrode and a non-aqueous electrolyte;
Battery capacity acquisition means for acquiring a chargeable / dischargeable battery capacity A of the secondary battery;
Internal resistance acquisition means for acquiring the internal resistance B of the secondary battery;
Based on the acquired battery capacity A and the internal resistance B, using the map showing the correspondence between the battery capacity decrease amount, the internal resistance increase amount, and the deterioration mode, the state of the secondary battery is:
The following (1) to (3):
(1) Deterioration due to wear of the secondary battery;
(2) deterioration due to deposition of charge carriers at the negative electrode inside the secondary battery; and
(3) A battery system comprising: discrimination means for discriminating which degradation mode is degradation due to bias in the salt concentration distribution of the non-aqueous electrolyte in the secondary battery.

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