JP2016101048A - Capacity estimation device of on-vehicle secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for estimating a full charge capacity of a secondary battery.SOLUTION: A capacity estimation device disclosed by the present specification includes: a pressure sensor which measures a pressure acting on a secondary battery case; an SOC sensor which measures the SOC of the secondary battery; and a control device which estimates the full charge capacity of the secondary battery on the basis of a measured value of the pressure sensor and the SOC sensor. The control device stores an initial inclination change SOC (C0) when there is a discrete change in the inclination of a pressure change in the relationship of pressure with the initial SOC of the secondary battery. Based on the measured values of the pressure sensor and the SOC sensor, the control device identifies an inclination change SOC (C1) when there is a discrete change in the inclination of the pressure change in the relationship of pressure with a charge residual amount of the secondary battery currently in use (S7). The control device then estimates a drop amount of the full charge capacity from a difference value D=C1-C0 (S10).SELECTED DRAWING: Figure 8

Description

  The technology disclosed in this specification relates to a capacity estimation device for an in-vehicle secondary battery.

  Secondary batteries that can be repeatedly charged and discharged have become widespread. The secondary battery is mounted on, for example, a hybrid vehicle or an electric vehicle. It is known that the use of a secondary battery, that is, repeated charge / discharge, reduces the available battery capacity (discharge capacity). Hereinafter, a decrease in available battery capacity will be described first.

  In general, it is difficult to directly measure battery capacity. The battery capacity is measured using the output voltage (open circuit voltage) of the secondary battery that has a unique relationship with the battery capacity. Hereinafter, in order to simplify the description, the open circuit voltage is abbreviated as OCV. The OCV can be measured with a voltage sensor. Alternatively, even when only a closed circuit voltage (CCV: Close Circuit Voltage) can be measured, the OCV can be estimated from the CCV. More generally, the battery capacity of a battery is represented by a unit system called SOC (State Of Charge). The battery capacity is expressed as a percentage of the current OCV, where a lower limit value of a predetermined available OCV range is SOC = 0% and an upper limit value of the OCV range is SOC = 100%. The difference between the battery capacity corresponding to SOC = 100% (OCV = upper limit value) and the battery capacity corresponding to SOC = 0% (OCV = lower limit value) is the usable battery capacity. As will be described later, the battery capacity corresponding to the SOC value changes with time. That is, the battery capacity indicated by the SOC value changes with time. In order to help understanding, the SOC is referred to as the remaining battery capacity and is distinguished from the original battery capacity of the secondary battery.

  In a normal use period, the secondary battery is not completely discharged, and charging and discharging are repeated within a predetermined SOC range (that is, a predetermined OCV range). It is known that the battery capacity corresponding to OCV = lower limit value increases as charging / discharging is repeated. That is, as the secondary battery is used, the battery capacity corresponding to SOC = 0% increases. As a result, the difference between the battery capacity corresponding to SOC = 100% and the battery capacity corresponding to SOC = 0%, that is, the available battery capacity is reduced. A decrease in available battery capacity due to use over time may be expressed as “battery deterioration”. Hereinafter, for easy understanding of the description, a difference between the battery capacity corresponding to SOC = 100% and the battery capacity corresponding to SOC = 0% is referred to as a full charge capacity. In other words, the full charge capacity is a battery capacity that can be used when SOC = 100% (full charge).

  Research has been conducted on a technique for estimating a full charge capacity that has decreased due to use by utilizing a phenomenon peculiar to an in-vehicle secondary battery. In an in-vehicle secondary battery, pressure resistance is applied to the case from the outside, and the electrode body is in contact with the inside of the case to improve vibration resistance. On the other hand, the electrode body repeatedly expands and contracts with charge and discharge, and the degree of expansion changes as it deteriorates. That is, there is a unique relationship between the pressure applied to the case and the full charge capacity. For example, Patent Document 1 discloses a determination system that calculates a full charge capacity that has decreased due to use from a change in pressure applied to a case. In the discrimination system disclosed in Patent Document 1, a map indicating a relationship between a pressure measured in advance from an initial state to a deteriorated state and a remaining charge amount in a reference terminal voltage is stored. With reference to the map, the current full charge capacity (decreased full charge capacity) is estimated from the pressure applied to the case of the secondary battery after change with time. In Patent Document 1, the pressure applied to the case of the secondary battery is measured by a pressure sensor attached to the case of the secondary battery.

JP2013-092398A

  In the technique of Patent Document 1, the absolute value of the pressure measured by the pressure sensor is used. However, in addition to the pressure received from the electrode body, pressure is also applied to the case from the outside of the case. For example, the pressure applied from other than the electrode body changes due to loosening of a binding band that bundles a plurality of batteries. In the estimation using the absolute value of the pressure, an estimation error occurs due to a change in pressure applied from other than the electrode body. In this specification, similar to Patent Document 1, a change in internal pressure of a secondary battery is used, but a technique for estimating a reduced full charge capacity with higher accuracy without using an absolute value of pressure is provided. .

  The inventor observes a graph showing the relationship between the remaining charge amount and the pressure acting on the case of the secondary battery, and the slope of the pressure change in the relationship of the pressure with respect to the remaining charge amount is the predetermined remaining charge value. I noticed that it changed discretely. The inventor has also noticed that when the graph showing the relationship of the pressure to the remaining charge is compared between the initial state and the deteriorated state, the value of the predetermined remaining charge changes with deterioration. Therefore, the inventor has devised a system for estimating the full charge capacity of the secondary battery by using the value of the remaining charge when the slope of the pressure change in the relationship of the pressure to the remaining charge changes discretely. did. The principle on which such a phenomenon occurs will be described in Examples.

  An in-vehicle secondary battery capacity estimation device disclosed in this specification includes a pressure sensor that measures a pressure acting on a case of the secondary battery, an SOC sensor that measures a remaining charge of the secondary battery, a pressure sensor, and an SOC. And a control device that estimates the full charge capacity of the secondary battery after a change over time based on the measured value of the sensor. The control device stores the remaining charge amount (initial inclination change charge remaining amount) when the slope of the pressure change in the relationship of the pressure to the remaining charge amount of the initial secondary battery changes discretely. Based on the measurement values of the pressure sensor and the SOC sensor, the control device determines the remaining charge amount (change with time) when the slope of the pressure change in the relationship between the pressure and the remaining charge amount of the secondary battery after the change changes discretely. Identify the remaining slope change charge remaining). Then, the control device estimates the current full charge capacity from the difference between the initial gradient change charge remaining amount and the gradient change charge remaining amount after aging. The electrode body is in contact with the inside of the secondary battery case. According to this configuration, the full charge capacity of the secondary battery can be estimated using the phenomenon described above.

  According to the technology disclosed in the present specification, it is possible to estimate the full charge capacity of the secondary battery that has decreased due to use. Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a block diagram of the electric power system of an electric vehicle provided with the control apparatus of an Example. It is side surface sectional drawing of a secondary battery module. It is a front view of a secondary battery. It is a graph which shows the relationship between SOC and a pressure measurement value. It is a graph which shows the relationship between SOC and inclination. It is a graph which shows the relationship between a difference value and a fall amount. It is a graph which shows the relationship between a positive electrode potential and a total charge amount, and the relationship between a negative electrode potential and a total charge amount. It is a flowchart figure which shows the process which the control apparatus of an Example performs. It is a graph which shows the relationship between SOC and a pressure measurement value when creep deformation or gas generation occurs.

  A capacity estimation apparatus according to an embodiment will be described with reference to the drawings. FIG. 1 is a block diagram of an electric power system of an electric vehicle 200 including the capacity estimation device according to the embodiment. The electric vehicle 200 includes a traveling motor 5 and a secondary battery module 2 that supplies electric power to the motor 5. The secondary battery module 2 is connected to the motor 5 via the inverter 3. The DC power output from the secondary battery module 2 is converted into AC power by the inverter 3 and supplied to the motor 5. A system main relay 7 is disposed between the secondary battery module 2 and the inverter 3.

  The secondary battery module 2 is a module configured by connecting a plurality of secondary batteries 20 in series. The secondary battery module 2 is charged by an external power source (not shown). The secondary battery module 2 is also charged by regenerative power from the motor 5 generated during braking. Each secondary battery 20 is provided with a pressure sensor 24 described later. In FIG. 1, some of the secondary batteries 20 are depicted. In FIG. 1, among the plurality of secondary batteries, one secondary battery is assigned a reference numeral, and the other secondary batteries are omitted. The reference numerals of the pressure sensors provided in each secondary battery 20 are also the same.

  In addition, the electric vehicle 200 includes an SOC sensor 9 that measures the remaining charge (SOC) of the secondary battery module 2. Strictly speaking, what is directly measured is the voltage between the terminals of each secondary battery 20 of the secondary battery module 2. The inter-terminal voltage is a closed circuit voltage (CCV: abbreviation of Close Circuit Voltage) when a load is connected to the secondary battery module 2. The SOC sensor 9 obtains the remaining charge from the CCV of the secondary battery module 2 using a predetermined algorithm or a correspondence map of the closed circuit voltage and SOC stored in advance. For example, the SOC sensor 9 measures the output current of the secondary battery module 2 together with the CCV, specifies the voltage drop due to the load drive from the output current, and outputs the value obtained by adding the voltage drop to the CCV as the OCV. To do. As described above, the remaining charge SOC is a percentage of the current OCV when the lower limit value of the predetermined OCV range is set to SOC = 0% and the upper limit value of the OCV range is set to SOC = 100%. It is a numerical value expressed by Therefore, the current remaining charge SOC can be obtained uniquely from the obtained OCV. In the technical field of electric vehicles, it is well known that a device that obtains the SOC of a battery from a sensor such as a voltage sensor (and current sensor) and a map stored in advance is referred to as an SOC sensor. As described above, the OCV and the battery capacity (electric capacity stored in the battery = discharge capacity) also have a unique relationship.

  The electric vehicle 200 includes a control device 8 that estimates the amount of decrease in the full charge capacity of the secondary battery 20 based on the measurement value of the pressure sensor 24 and the measurement value of the SOC sensor 9. The “full charge capacity” is the difference between the battery capacity corresponding to SOC = 100% and the battery capacity corresponding to SOC = 0%, as described above. As the secondary battery 20 is repeatedly charged and discharged, the full charge capacity decreases. The above-mentioned “decrease amount” is the difference between the full charge capacity in the initial state and the full charge capacity that has decreased due to repeated charge and discharge. The control device 8 includes a memory (not shown) for storing data necessary for estimating the amount of decrease in the full charge capacity of the secondary battery 20. The process executed by the control device 8 to estimate the amount of decrease in the full charge capacity of the secondary battery 20 will be described later. The amount of decrease in the full charge capacity estimated by the control device 8 is stored in the diagnosis memory 12. By reading the information stored in the diagnostic memory 12 during maintenance, the maintenance staff can know the amount of decrease in the full charge capacity of the secondary battery 20. Moreover, the control apparatus 8 transmits a warning signal when the estimated value of the full charge capacity falls below a predetermined threshold value. The warning signal is transmitted to the instrument panel 13. On the instrument panel 13, a warning lamp is turned on in response to the warning signal. This warning light allows the driver to know that the full charge capacity of the secondary battery 20 has decreased. Note that a decrease in the full charge capacity of the secondary battery may be expressed as “deteriorating”.

  The configuration of the secondary battery module 2 will be described with reference to FIGS. FIG. 2 shows a side sectional view of the secondary battery module 2. FIG. 3 shows a front view of the secondary battery 20 constituting the secondary battery module 2. The secondary battery 20 includes a flat rectangular parallelepiped case 22 and an electrode body 21 accommodated in the case 22 together with an electrolytic solution. Each secondary battery 20 is laminated so that the outer surfaces 22c having the largest area of the case 22 face each other. A cooling plate 23 is disposed between the adjacent secondary batteries 20. The secondary battery 20 is bundled by a binding band (not shown). Due to the binding force of the binding band, a load (hereinafter referred to as a stacking load) acts on the secondary battery module 2 in the stacking direction, and the secondary battery 20 and the cooling plate 23 are in contact with each other. It should be noted that a part of the secondary battery module 2 is drawn in FIG.

  The electrode body 21 is configured by flatly winding a laminated body in which a belt-like positive electrode sheet and a belt-like negative electrode sheet are laminated with a belt-like separator interposed therebetween. The flat electrode body 21 is accommodated in the case 22 so that the relatively wide side surface of the electrode body 21 faces the inner surface having the largest area of the flat case 22. An insulating sheet 25 is disposed between the electrode body 21 and the case 22. Due to the stacking load acting on the secondary battery module 2, the electrode body 21 is in contact with the inner surface of the case 22 via the insulating sheet 25.

  A pressure sensor 24 is provided on the outer surface 22 c having the largest area of the case 22 of the secondary battery 20. As shown in FIG. 3, the pressure sensor 24 is disposed at the center of the outer surface 22c. The pressure sensor 24 is disposed so as to be sandwiched between the outer surface 22 c of the case 22 and the cooling plate 23.

  A positive electrode terminal 22 a and a negative electrode terminal 22 b are provided on one side surface of the secondary battery 20. The positive terminal 22a and the negative terminal 22b of each secondary battery 20 are connected in series by a bus bar (not shown).

  The secondary battery 20 is a lithium ion secondary battery. The positive electrode sheet of the electrode body 21 is obtained by applying a positive electrode active material to a conductive current collector. As the positive electrode active material, a lithium transition metal oxide is used. For example, the lithium transition metal oxide is a lithium nickel oxide (LiNiO 2 or the like), a lithium cobalt oxide (LiCoO 2 or the like), and a lithium manganese oxide (LiMn 2 O 4 or the like). The negative electrode sheet of the electrode body 21 is obtained by applying a negative electrode active material to a conductive current collector. As the negative electrode active material, for example, a carbon material having a layered structure is used. For example, the carbon material is graphite (graphite), hard carbon, soft carbon, or the like.

  As the charging of the secondary battery 20 proceeds, that is, as the battery capacity increases, lithium ions gather on the negative electrode sheet. Lithium ions enter between the layers of the negative electrode active material as the battery capacity increases. The phenomenon in which lithium ions enter between the layers of the negative electrode active material by charging is called an intercalation reaction. As lithium ions increase due to the intercalation reaction, the interlayer distance of the negative electrode active material increases, and the negative electrode sheet expands. As the battery capacity increases, the negative electrode sheet expands, so that the electrode body 21 also expands. As the electrode body 21 expands, pressure acts on the case 22 from the electrode body 21. As the secondary battery 20 deteriorates, the manner in which the negative electrode sheet expands also changes. That is, the deterioration of the secondary battery 20 affects the measurement value of the pressure sensor 24. However, the measurement value of the pressure sensor 24 is affected by the stacking load, and the stacking load may change over time. Therefore, if the deterioration of the secondary battery 20, that is, the amount of decrease in the full charge capacity is estimated from the absolute value of the pressure measured by the pressure sensor 24, the error increases. The control device 8 estimates the amount of decrease in the full charge capacity based on not the magnitude of the pressure measured by the pressure sensor 24 but the slope of the pressure change with respect to the SOC change. First, the principle will be described, and then the processing executed by the control device 8 for estimating the amount of decrease will be described.

  The relationship between the pressure applied to the case 22 and the deterioration will be described with reference to the graphs of FIGS. FIG. 4 is a graph showing the relationship of the pressure measurement value [Pa] measured by the pressure sensor 24 to the SOC of the secondary battery 20. As described above, there is a unique relationship between SOC and OCV, and there is also a unique relationship between OCV and battery capacity. As the SOC increases, that is, as the battery capacity increases, the negative electrode sheet expands and the pressure increases. In FIG. 4, a graph indicated by a solid line is a graph showing the relationship of the pressure measurement value to the SOC of the secondary battery 20 in the initial state. On the other hand, the graph shown with a dashed-dotted line is a graph which shows the relationship of the pressure measurement value with respect to SOC of the secondary battery 20 deteriorated by repeating charging / discharging. In the graph of FIG. 4, factors other than the expansion of the negative electrode sheet such as the lamination load are ignored. FIG. 5 is a graph showing the slope K of the change in the pressure measurement value in the relationship of the pressure measurement value to the SOC. The slope K is a value obtained by dividing the change amount dP of the pressure measurement value by the change amount dC of the SOC. In FIG. 5, as in FIG. 4, the graph indicated by the solid line indicates the initial state, and the graph indicated by the alternate long and short dash line indicates the deteriorated state.

  As shown in FIGS. 4 and 5, in the secondary battery 20 in the initial state, the slope K changes discretely when the initial slope change SOC (C0). As well represented in FIG. 5, the slope K is constant before the initial slope change SOC (C0). Even after the initial inclination change SOC (C0), the inclination K is constant. The slope K changes discretely before and after the initial slope change SOC (C0). Here, “discretely” means “stepwise” in other words. As described above, the slope K changes discretely because the carbon material having a layered structure is used as the negative electrode active material of the secondary battery 20. As described above, the interlayer distance of the negative electrode active material increases with the number of lithium ions that increase due to the intercalation reaction. An increase in the interlayer distance of the negative electrode active material means that the negative electrode sheet, that is, the electrode body expands. The slope of the change in the interlayer distance in the relationship between the interlayer distance and the number of lithium ions is substantially constant until the number of lithium ions reaches a predetermined number. In the intercalation reaction, it is known that the slope K changes discretely when the number of lithium ions exceeds a predetermined number. Specifically, when the number of lithium ions exceeds a predetermined number, the slope K decreases. This is presumed to be because the stage structure of lithium taken into the negative electrode sheet changes. Then, as charge and discharge are repeated, the amount of lithium left in the negative electrode sheet after discharge increases, and as the remaining amount of lithium increases, the SOC value (inclination change SOC) at the stage change shifts to the high voltage side. .

  As shown in FIG. 4, the graph showing the relationship between the SOC of the secondary battery 20 in the deteriorated state and the pressure measurement value (the dashed-dotted line graph) is compared with the graph in the initial state (solid line graph) as the slope change SOC. Changes to the right in the figure. As shown in FIG. 5, the value of the slope K does not change much between the initial state and the deteriorated state. The inventor examined the relationship between the difference value D between the slope change SOC (C1) and the initial slope change SOC (C0) in the deteriorated secondary battery 20 and the amount of decrease in the full charge capacity. As a result, it was found that there is a correlation between the difference value D and the amount of decrease in the full charge capacity. FIG. 6 is a graph showing the relationship between the difference value D and the reduction amount of the full charge capacity. As shown in FIG. 6, as the difference value D increases, the amount of decrease in the full charge capacity of the secondary battery 20 increases. The amount of decrease in the full charge capacity of the secondary battery can be accurately estimated by utilizing the slope K of the pressure change with respect to the change in SOC and the relationship between the difference value D and the amount of decrease shown in FIG.

  With reference to FIG. 7, it supplements about the phenomenon in which the full charge capacity of the secondary battery 20 falls. FIG. 7 is a graph showing the relationship between the total charge amount of the secondary battery 20, the potential of the positive electrode sheet (hereinafter, positive electrode potential) and the potential of the negative electrode sheet (hereinafter, negative electrode potential). The graph shown on the upper side in the figure having a tendency that the potential increases with the increase in the total charge amount is a graph showing the relationship between the total charge amount and the positive electrode potential. On the other hand, a graph shown on the lower side in the figure having a tendency that the potential decreases as the total charge amount increases is a graph showing the relationship between the total charge amount and the negative electrode potential. In the range where the total charge amount is high, the negative electrode potential is substantially constant. In FIG. 7, the difference between the positive electrode potential and the negative electrode potential is the output of the secondary battery 20, that is, OCV. The total charge amount when the positive electrode potential graph and the negative electrode potential graph intersect is the total charge amount when the OCV is 0V. The total charge amount is the total amount of charge stored in the secondary battery 20, and is expressed in units of ampere hours [Ah]. The total charge amount corresponds to the total amount of lithium ions that have moved from the positive electrode to the negative electrode in the secondary battery 20.

  In the relationship between the total charge amount and the negative electrode potential in FIG. 7, a graph indicated by a solid line is a graph in an initial state, and a graph indicated by a one-dot chain line is a state after repeated charge / discharge (hereinafter referred to as a state after change over time). It is a graph in. As shown in FIG. 7, the relationship between the total charge amount and the negative electrode potential changes between an initial state and a state after change with time. On the other hand, the relationship between the total charge amount and the positive electrode potential does not change much in the initial state and the state after change with time. As shown in FIG. 7, the relationship between the negative electrode potential and the total charge amount shifts to the right side in the figure in the state after change with time. This is because, when charging / discharging of the secondary battery 20 is repeated, a phenomenon occurs in which lithium ions that have entered the layer of the negative electrode active material by the intercalation reaction remain irreversibly after the discharge.

  In the secondary battery 20, the state where the OCV is 3.0 V in the initial state is defined as SOC 0% (that is, the complete discharge state). A state where the OCV is 4.1 V is defined as SOC 100% (that is, a fully charged state). Therefore, the full charge capacity of the secondary battery 20 is the difference between the total charge amount with an OCV of 4.1V and the total charge amount with an OCV of 3.0V. As shown in FIG. 7, the total charge amount at which the OCV becomes 3.0 V in the state after change with time is higher than that in the initial state. That is, the full charge capacity of the secondary battery 20 in the state after change with time is smaller than that in the initial state. That is, the secondary battery 20 has a full charge capacity that is reduced by repeating charge and discharge. As shown in FIG. 7, the full charge capacity decreases as the graph indicating the negative electrode potential shifts to the right side in the drawing, indicating that the deterioration of the secondary battery 20 is progressing. The difference between the full charge capacity in the initial state shown in FIG. 7 and the full charge capacity in the state after change with time corresponds to the amount of decrease shown in FIG.

  The relationship between the graph of FIG. 7 and the graph of FIG. 4 (that is, the SOC when the gradient K of the change in the pressure measurement value in the relationship between the pressure measurement value and the SOC changes discretely) will be described. As described with reference to FIG. 4, the inclination K changes discretely with a predetermined SOC (inclination change SOC). The inclination change SOC shifts to the right side of FIG. 4 as it is used. That is, the slope change SOC increases as it is used. Referring to FIG. 7, the graph of the negative electrode potential is bent halfway. The point Pa in the graph (solid line) in the initial state, and the point Pb in the graph (one-dot chain line) after the change with time. The point Pa and the point Pb are correlated with the change point of the stage structure described above. Then, the distance Qb from the SOC = 0% line to the point Pb in the graph after change is larger than the distance Qa from the SOC = 0% line to the point Pa in the graph in the initial state. This distance Qa corresponds to the initial inclination change SOC (C0), and the distance Qb corresponds to the inclination change SOC (C1) after the change with time. Due to the relationship between the slope of the negative potential graph and the OCV value that determines SOC = 0%, the slope change SOC increases as the deterioration progresses, as shown in FIG.

  FIG. 8 shows a flowchart of the full charge amount estimation process using the above principle. The control device 8 executes the flowchart of FIG. A series of processes shown in FIG. 8 is appropriately executed while the electric vehicle 200 is traveling. The series of processes in FIG. 8 can be performed on all the secondary batteries 20 constituting the secondary battery module 2. Below, it demonstrates paying attention to one secondary battery 20. FIG.

  First, the control device 8 acquires the current SOC and pressure from the SOC sensor 9 and the pressure sensor 24, respectively (S2). The memory of the control device 8 includes a matrix storage area for storing pressure measurement values. In the first column of the matrix storage area, SOCs arranged at predetermined intervals (for example, several sequences arranged at a constant interval between 20% and 80%) are preset, and in the second column of the matrix storage area, A pressure storage area for storing a pressure measurement value corresponding to each SOC in the first column is set. When the measured value is not stored in the pressure storage area corresponding to the SOC obtained in step S2 (in the case of YES in S3), the control device 8 stores the pressure acquired in step S1 in the pressure storage area corresponding to this SOC. The measured value is stored (S4). On the other hand, when the measured value is stored in the pressure storage area corresponding to the SOC obtained in step S2 (NO in S3), the control device 8 returns to step S2. If pressure measurement values are stored in all pressure storage areas (YES in S5), the control device 8 proceeds to step S6. On the other hand, when the pressure measurement values are not stored in all the pressure storage areas (NO in S5), the control device 8 returns to Step S2. That is, until the pressure measurement values are stored in all the pressure storage areas, the control device 8 repeatedly executes the processing from steps S2 to S4.

  In step S6, the control device 8 calculates, for each SOC value, the slope K of the change in the pressure measurement value in the relationship between the pressure measurement value and the SOC from the pressure measurement value stored in the matrix storage area. For example, it is calculated by the following method by the control device 8. First, the control device 8 specifies the SOC for which the slope K is to be obtained. Then, the control device 8 reads out the pressure measurement values corresponding to the specified SOC and the nearby SOC from the pressure storage area. Then, the control device 8 calculates the slope K by the least square method from the SOC and the read pressure measurement value. This is performed for all SOCs.

  Next, the control device 8 calculates SOC (C1) (gradient change SOC (C1) after time change) when the slope K changes discretely from the relationship of the slope K to the SOC calculated in step S6 ( S7). Next, the control device 8 reads the initial inclination change SOC (C0) from the memory (S8). The initial inclination change SOC (C0) is an inclination change SOC measured in the secondary battery 20 in the initial state. The initial inclination change SOC (C0) is calculated in advance from the relationship of the pressure measurement value to the SOC of the secondary battery 20 in the initial state, and the initial inclination change SOC (C0) is stored in the memory of the control device 8 in advance. Yes.

  Next, the control device 8 calculates a difference value D, which is the difference between the slope change SOC (C1) after the change with time and the initial slope change SOC (C0) (S9). And the control apparatus 8 estimates the fall amount of the full charge capacity of the secondary battery 20 from the difference value D (S10). The relationship between the difference value D and the decrease amount is obtained in advance by experiments, and a map indicating the relationship between the difference value D and the decrease amount is stored in the memory of the control device 8. The control device 8 estimates the reduction amount based on the map. FIG. 6 described above is an example of the map.

  Next, the control device 8 transmits a warning signal to the instrument panel 13 when the amount of decrease estimated in step S10 is equal to or greater than a predetermined threshold (YES in S11) (S12). On the other hand, when the amount of decrease is less than the predetermined threshold (NO in S11), no warning signal is transmitted. And the control apparatus 8 memorize | stores the estimated fall amount in the memory 12 for a diagnosis (S13). Then, the control device 8 clears all pressure storage areas (S14).

  By executing the above-described processing, it is possible to estimate the amount of decrease in the full charge capacity of the secondary battery 20 from the initial state.

  As described above, there is a correlation between the measured pressure value and the SOC, which is caused by an increase in the number of lithium ions that enter the negative electrode active material as the SOC increases. The slope K of the change in the pressure measurement value with respect to the change in the SOC changes discretely with a predetermined SOC. This is presumed to be caused by a change in the stage structure of lithium ions captured by the negative electrode active material. Further, as described above, the decrease in the full charge capacity is caused by the residual lithium ion of the negative electrode active material. Therefore, when lithium ions remain in the negative electrode sheet, a difference value D is generated in the relationship between the pressure measurement value and the SOC in the initial state, and the relationship between the pressure measurement value after the change with time and the SOC. The technology of the embodiment pays attention to the difference value D and estimates the amount of decrease in the full charge capacity.

  With reference to FIG. 9, the advantage of using the slope K will be described. FIG. 9 is a graph showing the relationship of the pressure measurement value to the SOC similar to FIG. The graph shown by the solid line in FIG. 9 is the same as the graph shown by the solid line in FIG. 4 (that is, the graph showing the initial state). The graph shown by the alternate long and short dash line in FIG. 9 is also the same as the graph shown by the alternate long and short dash line in FIG. 4 (that is, a graph showing a state after aging). Here, the graph shown with a dashed-dotted line is a graph which shows the state which the secondary battery 20 deteriorated in the state (henceforth an ideal state) where an external pressure does not fluctuate. As described above, the measured value of the pressure sensor 24 is the sum of the internal pressure and the external pressure. Therefore, an error occurs in the measured value of the pressure sensor 24 due to the fluctuation of the external pressure. For example, when the case 22 of the secondary battery 20 is creep-deformed or the stacking load is reduced (for example, when the binding band is loosened), the external pressure varies in a decreasing direction. Creep deformation is a phenomenon in which the case 22 undergoes irreversible compressive deformation when a laminated load acts on the case 22 for a long time. Due to the creep deformation, the width of the case 22 in the stacking direction is reduced, so that a gap is generated between the case 22 and the cooling plate 23, and the external pressure is reduced. In this case, the graph indicating the relationship between the SOC and the pressure measurement value is a graph shifted downward from the one-dot chain line graph indicating the ideal state (the graph indicated by the chain line in FIG. 9 and below the graph indicated by the one-dot chain line). Chart located at). Further, when the case 22 expands and deforms due to a factor different from the expansion of the electrode body 21, the external pressure varies in the increasing direction. For example, when gas is generated inside the secondary battery 20, the case 22 expands. In this case, the graph showing the relationship between the SOC and the pressure measurement value is a graph shifted upward from the one-dot chain line graph indicating the ideal state (the graph indicated by the chain line in FIG. 9 and above the graph indicated by the one-dot chain line). Chart located at).

  As shown in FIG. 9, an error occurs in the measured value of the pressure sensor 24 due to fluctuations in external pressure. Therefore, when the amount of decrease is estimated using the absolute value of the measurement value of the pressure sensor 24, the amount of decrease is estimated due to the influence of fluctuations in external pressure. On the other hand, the SOC (inclination change SOC) when the inclination K changes discretely does not depend on the absolute value of the measured pressure value, and is hardly affected by fluctuations in the external pressure. Therefore, the technique of the present embodiment using the slope change SOC can estimate the amount of decrease with higher accuracy than the case of using the absolute value.

  Hereinafter, points to be noted regarding the technology shown in the embodiments will be described. “Initial inclination change SOC (C0)” is an example of “initial inclination change charge remaining amount”, and “Inclination change SOC (C1) after time change” is an example of “Inclination change charge remaining amount after time change”. is there.

  The control device 8 of the example estimated the amount of decrease in the full charge capacity after change with time. The amount of decrease in the full charge capacity after change with time is substantially equivalent to the full charge capacity after change with time. This is because the value obtained by subtracting the amount of decrease after aging from the full charge capacity in the initial state is the full charge capacity after aging.

  In the flowchart of FIG. 8, the initial inclination change SOC (C0) is stored in the control device 8 in advance. While the integrated distance is short, steps S2 to S7 in the flowchart of FIG. 8 may be executed, and the result may be stored as the initial inclination change SOC (C0). Then, the estimation accuracy of the full charge capacity after the change with time estimated after the accumulated distance increases is further increased.

  As shown in FIGS. 4 and 5, the slope K changes discretely not only with the slope change SOC (C1) after the change with time but also with an SOC higher than the SOC (C1) (hereinafter, the second slope change SOC). To do. The difference value D described above may be calculated using the second slope change SOC, and the amount of decrease may be estimated from the difference value D. Further, the amount of decrease may be estimated using both the difference value using the slope change SOC (C1) after the change with time and the difference value using the second slope change SOC. By using a plurality of slope change SOCs, it can be expected that the amount of decrease is estimated with higher accuracy.

  The capacity estimation apparatus of the present embodiment may be provided in a hybrid vehicle. The secondary battery is not limited to a lithium ion secondary battery. If the secondary battery uses a negative electrode sheet coated with a negative electrode active material having a layer structure capable of causing the same phenomenon as the change in the stage structure, the same effect as in the example is expected.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: secondary battery module 3: inverter 5: motor 7: system main relay 8: control device 9: voltage sensor 12: diagnostic memory 13: instrument panel 20: secondary battery 21: electrode body 22: case 22a: positive electrode Terminal 22b: Negative electrode terminal 22c: Outer surface 23: Cooling plate 24: Pressure sensor 25: Insulation sheet 200: Electric vehicle C0: Initial inclination change SOC
C1: slope change SOC after change with time
D: difference value K: slope

Claims (1)

A device for estimating the full charge capacity of an in-vehicle secondary battery in which an electrode body is in contact with the inside of a case,
A pressure sensor for measuring the pressure acting on the case;
An SOC sensor for measuring the remaining charge of the secondary battery;
A control device that estimates a full charge capacity of the in-vehicle secondary battery after a change over time based on measurement values of the pressure sensor and the SOC sensor;
The control device comprises:
Storing the charge remaining amount (initial inclination change charge remaining amount) when the slope of the pressure change in the relationship of the pressure with respect to the charge remaining amount of the initial vehicle-mounted secondary battery changes discretely,
Based on the measured values of the pressure sensor and the SOC sensor, the remaining charge amount (time elapsed) when the slope of the pressure change in the relationship of the pressure to the remaining charge amount of the in-vehicle secondary battery after the change with time changes discretely. Identify the slope change charge remaining after the change)
From the difference between the “initial inclination change charge remaining amount” and the “gradient change charge remaining amount after time change”, the current full charge capacity is estimated.
The capacity estimation apparatus characterized by the above-mentioned.

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