JP2018022650A - Method for controlling secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize a recovery process.SOLUTION: A method for controlling a secondary battery comprises: a step A for preparing a map showing the relation among a capacity contraction of the secondary battery and an amount of capacity deviation, a temperature and a voltage at the start of discharge, and an IV resistance when a predetermined discharge is performed; a step B for sensing the temperature and voltage of the secondary battery; a step C for measuring the IV resistance; a step D for deriving the capacity contraction and the amount of capacity deviation of the secondary battery based on the measurement in the step C and the map prepared in the step A; a step E for performing a predetermined first recovery process when capacity contraction derived in the step D is over a predetermined threshold; and a step F for performing a predetermined second recovery process when the amount of capacity deviation derived in the step D is over a predetermined threshold.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a method for controlling a secondary battery.

  As a secondary battery control method, for example, JP 2013-89424 A discloses a method for predicting battery deterioration. In the prediction method disclosed in the publication, a data table is prepared for predicting how much the battery deteriorates when staying at a certain temperature and SOC for a predetermined time. And actually, the deterioration degree of a battery is estimated based on the history about temperature and SOC.

  Japanese Patent Application Laid-Open No. 2014-32825 discloses a method for estimating a deterioration state by considering a relative capacity shift between a positive electrode and a negative electrode and a lithium deposition amount from a battery voltage when the battery is used.

JP2013-89424A JP 2014-32825 A

  By the way, the present inventor believes that it is desirable to estimate the deterioration degree of the secondary battery by a simple method. Further, it is desirable that the recovery process of the secondary battery is performed at an appropriate timing.

The proposed secondary battery control method includes the following steps A to F.
Step A provides a map showing the relationship between secondary battery capacity shrinkage, secondary battery capacity deviation, temperature and voltage at the start of discharge, and IV resistance when a predetermined discharge is performed. It is a process to do.
Step B is a step of detecting the temperature and voltage of the secondary battery.
Step C is a step of measuring IV resistance by performing a predetermined discharge when the voltage detected in step B is within a predetermined range.
Step D is based on the temperature and voltage at the start of discharge when discharged in Step C, the IV resistance measured in Step C, and the map prepared in Step A. And a step of deriving the amount of displacement.
Step E is a step of performing a predetermined first recovery process when the capacity shrinkage derived in step D exceeds a predetermined threshold.
Step F is a step of performing a predetermined second recovery process when the amount of capacity deviation derived in step D exceeds a predetermined threshold.
According to this method, the recovery process of the secondary battery is performed at an appropriate timing.

FIG. 1 is a graph showing a typical example of the relationship between the charging current amount of the secondary battery and the open circuit voltage (OCV). FIG. 2 is a graph showing an example of changes in the potential of the positive electrode single electrode and the potential of the negative electrode single electrode with respect to the charging current amount of the secondary battery. FIG. 3 is a graph showing a tendency of IV resistance. FIG. 4 is a schematic map prepared in step A. FIG. 5 is a schematic map prepared in step A. FIG. 6 is a schematic map prepared in step A. FIG. 7 is a schematic map prepared in step A. FIG. 8 is a flowchart showing an example of the secondary battery control method proposed here.

  Hereinafter, an embodiment of the secondary battery control method proposed here will be described. The embodiments described herein are, of course, not intended to limit the present invention in particular.

<Deterioration of secondary battery>
The deterioration of the secondary battery in this specification means the capacity deterioration of the secondary battery. For example, a lithium ion secondary battery has a tendency that the battery capacity is reduced from the initial state by use. The degree of deterioration of the lithium ion secondary battery is expressed as a ratio of the current battery capacity to the battery capacity in the initial state. That is, the degree of deterioration of the lithium ion secondary battery is represented by the following formula (A), and is a ratio of the current battery capacity when the battery capacity in the initial state is 100, and may also be referred to as a capacity maintenance ratio. .
Degree of deterioration of lithium ion secondary battery = (current battery capacity) / (initial battery capacity) × 100 (%) (A)

  Regarding the lithium ion secondary battery, the “initial state” can be arbitrarily determined in a state after the lithium ion secondary battery is assembled. For example, a state in which a lithium ion secondary battery is assembled, a predetermined conditioning process has passed, and can be normally used as a lithium ion secondary battery may be referred to as an “initial state”. The initial state of the lithium ion secondary battery may be a state when the lithium ion secondary battery is shipped.

<Battery capacity of lithium ion secondary battery>
Here, regarding the battery capacity of the lithium ion secondary battery, the upper limit voltage and the lower limit voltage of the lithium ion secondary battery are set in advance based on the open circuit voltage. Then, the lithium ion secondary battery is charged to the upper limit voltage by CCCV charging, and then the lithium ion secondary battery is discharged to the lower limit voltage by CCCV discharge. At this time, for the lithium ion secondary battery in the initial state, the discharge capacity when discharged from the upper limit voltage to the lower limit voltage is defined as the battery capacity in the initial state of the lithium ion secondary battery.

  In this embodiment, the lower limit voltage of the lithium ion secondary battery is set to 3.0 V and the upper limit voltage is set to 4.1 V based on the open circuit voltage for the target lithium ion secondary battery. In this case, the state where the open circuit voltage is 3.0 V is SOC 0%, and the state where the open circuit voltage is 4.1 V is SOC 100% (fully charged state). The battery capacity corresponds to the discharge capacity when charging until the open circuit voltage reaches 4.1 V by CCCV charging and discharging until the open circuit voltage reaches 3.0 V by CCCV discharge. Here, “SOC” is an abbreviation for “State Of Charge” and indicates the state of charge of the battery. Here, “SOC” is determined by the charging rate with respect to the fully charged state.

  The SOC of the lithium ion secondary battery is correlated with the voltage of the lithium ion secondary battery, and the SOC of the lithium ion secondary battery can be estimated based on the voltage of the lithium ion secondary battery. The capacity of a lithium ion secondary battery is reduced due to an event that lithium ions are unevenly distributed or a part of lithium does not contribute to the battery reaction. Further, when the degree of capacity deterioration of the lithium ion secondary battery is small, if the lithium ion secondary battery is left unattended, the uneven distribution of lithium ions is improved, and a part of the reduced capacity is recovered. For this reason, when the degree of deterioration of the lithium ion secondary battery is detected and the lithium ion secondary battery has deteriorated more than a predetermined level, the proper length of the lithium ion secondary battery can be obtained by taking appropriate recovery measures. Life can be extended.

  Here, FIG. 1 is a graph showing a typical example of the relationship between the charging current amount of the secondary battery and the open circuit voltage (OCV). FIG. 2 is a graph showing an example of changes in the potential of the positive electrode single electrode and the potential of the negative electrode single electrode with respect to the charging current amount of the secondary battery.

  1 and 2 are schematically shown and do not strictly show the measurement results. Here, the solid line S in FIG. 1 is a graph for the lithium ion secondary battery in the initial state, and the broken line S1 indicates a graph for the lithium ion secondary battery after deterioration. In FIG. 1, the horizontal axis indicates the SOC of the lithium ion secondary battery, and the vertical axis indicates the open circuit voltage (OCV). Moreover, as shown by a broken line, the positive electrode and the negative electrode are deteriorated by use (the capacity of the single electrode is reduced), and as a result, the battery capacity of the lithium ion secondary battery is reduced.

  A solid line P in FIG. 2 is a graph showing the relationship between the capacity of the lithium ion secondary battery in the initial state and the potential of the positive electrode (OCP +). The broken line P1 is a graph showing the relationship between the capacity of the deteriorated lithium ion secondary battery and the potential of the positive electrode single electrode. The solid line Q is a graph showing the relationship between the capacity of the lithium ion secondary battery in the initial state and the potential of the negative electrode single electrode (OCP−). The broken line Q1 is a graph showing the relationship between the capacity of the deteriorated lithium ion secondary battery and the potential of the negative electrode single electrode. A difference S between the potential of the single positive electrode and the potential of the single negative electrode corresponds to the battery voltage.

  A graph P1 showing the relationship between the capacity of the lithium ion secondary battery after deterioration and the potential of the positive electrode single electrode (hereinafter referred to as a graph P1 after deterioration) is the capacity of the lithium ion secondary battery in the initial state and the single positive electrode. When the graph P showing the relationship with the potential of the pole (hereinafter referred to as the graph P in the initial state) is used as a reference, the charging current amount is generally reduced. The shrinkage amount Px of the graph P1 after the deterioration with respect to the graph P in the initial state increases as the deterioration of the lithium ion secondary battery increases.

  Here, the degree of the shrinkage amount Px of the graph P1 after deterioration is referred to as “secondary battery capacity shrinkage”. Specifically, “secondary battery capacity shrinkage” is defined as a ratio (%) of the charge current amount of the single electrode after the deterioration, with the charge current amount from SOC 0% to SOC 100% in the initial state being 100. The Here, the amount of charge current of the positive electrode after the deterioration is, for example, from the potential corresponding to the potential of the positive electrode at the SOC of 0% in the initial state from the potential in the initial state based on the potential of the positive electrode after the deterioration. It is defined by the amount of charge current when the secondary battery is charged up to a potential corresponding to the potential of the positive electrode single electrode when the SOC is 100%. The “secondary battery capacity shrinkage” is not necessarily limited to the above definition. An appropriate amount for evaluating the degree of deterioration of the positive electrode single electrode of the lithium ion secondary battery may be adopted as the “secondary battery capacity shrinkage”.

  The graph Q1 showing the relationship between the capacity of the lithium ion secondary battery after deterioration and the potential of the single electrode of the negative electrode shows a high SOC with respect to the charge current amount when the potential P of the single electrode of the positive electrode of the lithium ion secondary battery is used as a reference. It seems to have shifted to the side. The deviation Qx of the potential Q1 of the negative electrode single electrode of the lithium ion secondary battery after the deterioration with respect to the potential Q of the negative electrode single electrode of the lithium ion secondary battery in the initial state increases as the deterioration of the lithium ion secondary battery increases. Become.

  Here, the degree of deviation Qx of the potential Q1 of the single negative electrode is referred to as “secondary battery capacity deviation”. Specifically, the “secondary battery capacity deviation amount” is defined as a ratio (%) of the charge current amount of the negative electrode single electrode after deterioration, with the charge current amount from SOC 0% to SOC 100% in the initial state being 100. Is done. Here, the charging current amount of the negative electrode single electrode after deterioration is, for example, from the potential corresponding to the potential of the negative electrode single electrode at SOC 0% in the initial state to the initial state based on the potential of the negative electrode single electrode after deterioration. It is defined by the amount of charging current when the secondary battery is charged to a potential corresponding to the potential of the negative electrode single electrode when the SOC is 100%. The “secondary battery capacity deviation” is not necessarily limited to the above definition. An appropriate amount for evaluating the degree of deterioration of the negative electrode single electrode of the lithium ion secondary battery may be adopted as the “secondary battery capacity shift amount”.

  Here, the use range of the positive electrode and the use region of the negative electrode are determined by the battery voltage (difference S between the potential of the single positive electrode and the potential of the single negative electrode). For example, when a lithium ion secondary battery is used between 3.0 V and 4.1 V, the use range of the positive electrode and the negative electrode is defined by the region where the battery voltage S indicates 3.0 V to 4.1 V. . As shown in FIG. 2, as the lithium ion secondary battery deteriorates, the positive electrode single electrode potential P1 and the negative electrode single electrode potential Q1 change, and the positive electrode single electrode potential P and the negative electrode single electrode potential Q1 change. The relationship is off. Accordingly, the positive electrode usage range and the negative electrode usage range change, and the relationship between the positive electrode usage range and the negative electrode usage range also shifts.

  The present inventor determined the capacity shrinkage and capacity deviation of a lithium ion secondary battery from the IV resistance when a predetermined discharge was performed in a low SOC range corresponding to about 0% to SOC 50% of the initial capacity SOC. We found new knowledge to estimate.

  FIG. 3 is a graph showing a tendency of IV resistance. In FIG. 3, there are five graphs G1 to G5. G1 is a graph of a lithium ion secondary battery that has not deteriorated most among G1 to G5. G1 to G5 are graphs of lithium ion secondary batteries that have deteriorated in order. G5 is a graph of a lithium ion secondary battery that is most deteriorated among G1 to G5. In the graph of FIG. 3, the horizontal axis represents the voltage of the lithium ion secondary battery when starting the measurement of the IV resistance (starting voltage: here also referred to as “start OCV”).

  As can be seen from the graph of FIG. 3, when the starting voltage of the lithium ion secondary battery at the time of starting the measurement of the IV resistance is low, the IV resistance increases as the lithium ion secondary battery deteriorates due to capacity shrinkage or capacity deviation. Tend to be higher. This tendency appears particularly when the starting voltage of the lithium ion secondary battery at the time of measuring the IV resistance is equal to or lower than a voltage corresponding to about 50% SOC (more significantly, equal to or lower than a voltage corresponding to about 40% SOC). .

  In FIG. 3, the graphs G1 to G5 are measured at the same temperature. Even at different temperatures, in a low SOC range of SOC 0% to SOC 50%, the IV resistance tends to increase as the deterioration of the lithium ion secondary battery progresses. The present inventor believes that this tendency is caused by capacity shrinkage or a capacity shift in which the relationship between the positive electrode use area and the negative electrode use area shifts as the deterioration of the lithium ion secondary battery progresses. That is, the use range of the positive and negative electrodes changes as the deterioration of the lithium ion secondary battery proceeds.

  In particular, as the deterioration of the lithium ion secondary battery progresses, the negative electrode is used on the side that exhibits a higher potential (the side that was used at a lower SOC in the initial state) (see FIG. 2). For this reason, when the IV resistance is measured in the low SOC region of the secondary battery, the IV resistance with respect to the starting voltage of the lithium ion secondary battery when measuring the IV resistance as the deterioration of the lithium ion secondary battery progresses. There is a tendency that the timing when becomes higher. From this tendency, the present inventor has found a method for estimating the capacity shrinkage and the capacity shift amount by observing the IV resistance in the low SOC region of the secondary battery.

The method proposed here includes the following steps A to D.
Step A is a map showing the relationship between the capacity shrinkage of the secondary battery, the capacity deviation of the secondary battery, the temperature and voltage at the start of discharge, and the IV resistance when a predetermined discharge is performed. It is a process to prepare.
Step B is a step of detecting the temperature and voltage of the secondary battery.
Step C is a step of measuring IV resistance by performing a predetermined discharge when the voltage detected in step B is within a predetermined range.
Step D is based on the temperature and voltage at the start of discharge when discharged in Step C, the IV resistance measured in Step C, and the map prepared in Step A. And a step of deriving the amount of displacement.

Further, when the capacity shrinkage derived in the process D exceeds a predetermined threshold, a process E for performing a predetermined first recovery process is added, and according to the capacity shrinkage derived in the process D. An appropriate recovery process may be performed on the secondary battery at an appropriate timing.
Further, when the amount of capacity deviation derived in step D exceeds a predetermined threshold value, a step F for performing a predetermined second recovery process is added to the amount of capacity deviation derived in step D. Accordingly, an appropriate recovery process may be performed on the secondary battery at an appropriate timing. Hereinafter, the steps A to F will be described in order.

  The map prepared in step A is, for example, a lithium ion secondary battery of the same type as the lithium ion secondary battery to be measured, and a lithium ion secondary battery with a known degree of deterioration (capacity shrinkage and capacity deviation). Prepared on the basis.

  Based on a lithium ion secondary battery with a known degree of deterioration (capacity shrinkage and capacity shift amount), for example, each lithium ion secondary battery in a predetermined range corresponding to a low SOC range (SOC 0% to SOC 50%). The relationship between the voltage of the secondary battery and the IV resistance is obtained by performing a test in advance. The relationship between the voltage and the IV resistance may be obtained by changing the temperature to, for example, -30 ° C, -10 ° C, 0 ° C, 25 ° C, 40 ° C. Such a preliminary test provides a map for estimating the capacity deviation. 4 to 7 schematically show maps prepared in step A, respectively.

  Here, FIG. 4 shows the capacity shift amount of the secondary battery in the temperature environment of 25% at a capacity shrinkage, the starting voltage (OCV) when starting the measurement of the IV resistance, and the IV resistance. It is a map which shows the relationship. FIG. 5 shows the relationship between the capacity shift amount of the secondary battery in the temperature environment of 0 ° C. and the start voltage (OCV) when starting the measurement of the IV resistance, and the IV resistance. It is a map to show. FIG. 6 shows the relationship between the capacity shift amount of the secondary battery in the temperature environment of 25 ° C., the starting voltage (OCV) when starting the measurement of the IV resistance, and the IV resistance. It is a map to show. FIG. 7 shows the relationship between the capacity shift amount of the secondary battery in a temperature environment of 0 ° C., the starting voltage (OCV) when starting the measurement of the IV resistance, and the IV resistance. It is a map to show.

  Here, the map of FIG. 4 shows, for example, when preparing a lithium ion secondary battery with a capacity shrinkage of 0% and a known capacity deviation and starting measurement of IV resistance in a temperature environment of 25 ° C. It can be obtained by examining the relationship between the starting voltage (OCV) and the IV resistance. Similarly, the map of FIG. 5 shows a case where a lithium ion secondary battery having a capacity shrinkage of 0% and a known capacity deviation is prepared and IV resistance measurement is started in a temperature environment of 0 ° C. It is obtained by examining the relationship between the onset voltage (OCV) and the IV resistance. The map of FIG. 6 shows, for example, the start when IV resistance measurement is started in a temperature environment of 25 ° C. by preparing a lithium ion secondary battery with a capacity shrinkage of 5% and a known capacity deviation. It is obtained by examining the relationship between voltage (OCV) and IV resistance. The map in FIG. 7 shows that the start voltage (when starting the measurement of IV resistance in a temperature environment of 0 ° C. with a lithium ion secondary battery having a capacity shrinkage of 5% and a known capacity deviation amount. It is obtained by examining the relationship between OCV) and IV resistance.

  Here, for the lithium ion secondary battery whose capacity shrinkage and capacity deviation amount are known, for example, a plurality of the same type lithium ion secondary batteries are prepared, and each is subjected to storage deterioration under predetermined conditions, and the capacity shrinkage and the capacity deviation amount are measured. . Such a measurement provides a map of storage deterioration, capacity shrinkage and capacity deviation of the lithium ion secondary battery. It is preferable to obtain a lithium ion secondary battery with known capacity shrinkage and capacity deviation by performing storage degradation under predetermined conditions based on the map.

  The relationship between the start voltage (OCV) and the IV resistance when starting the measurement of the IV resistance may be obtained by adjusting the voltage to a predetermined voltage (OCV: open circuit voltage) and measuring the IV resistance. 4 to 7, the IV resistance is arranged in a matrix in which the vertical axis indicates the capacity shift amount of the lithium ion secondary battery and the horizontal axis indicates the start voltage (OCV) when starting the measurement of the IV resistance. Is recorded. Here, the relationship between the starting voltage (OCV) and the IV resistance when starting the measurement of the IV resistance is shown for lithium ion secondary batteries having a capacity deviation of 0%, 5%, 10%, and 15%. Yes.

  In the measurement of IV resistance, for the lithium ion secondary battery with the known capacity deviation, the battery is adjusted to a predetermined SOC by constant current and constant voltage (CC-CV) charging under a predetermined temperature condition. To do. Next, a predetermined discharge is performed and the IV resistance is calculated from the voltage drop. As the discharge condition, for example, discharge is performed for 10 seconds at a current value of 100 A. In this case, the slope R was calculated from a current-voltage line in which the voltage drop amount (ΔV) for 10 seconds was plotted against the current, and the slope R was defined as IV resistance. In FIGS. 4 to 7, the unit of IV resistance is indicated by mΩ.

  The horizontal axis in FIGS. 4 to 7 is the OCV at the start of discharge when measuring the IV resistance, and is specifically set in increments of 3.05 V to 0.05 V. Furthermore, the largest voltage is set to 3.67V. 3.05 V corresponds to an OCV that is slightly larger than SOC 0% in the initial state of the prepared evaluation battery. 3.67 V corresponds to an OCV of 50% SOC in the initial state of the prepared evaluation battery. Here, an evaluation battery whose capacity deviation is known is adjusted to the open circuit voltage (OCV) on the horizontal axis, and IV resistance is measured for each. As a result, a map indicating the relationship between the start voltage (OCV) and the IV resistance value when starting the measurement of the capacitance deviation amount and the IV resistance is obtained.

  4 to 7 schematically show maps prepared in step A, and the configuration of the map prepared in step A is not limited to FIGS. 4 to 7. For example, the horizontal axis of the maps shown in FIGS. 4 to 7 is set in increments of 3.05 V to 0.05 V, but the relationship between the initial state SOC and the open circuit voltage depends on the battery design. change. For this reason, the starting voltage set in the map can be changed as appropriate according to the design of the battery. Further, a more detailed map may be prepared by narrowing the interval of the start voltage (OCV) when starting the measurement of the IV resistance.

  Further, the map prepared in step A may be prepared based on the IV resistance measured by performing a test in advance or may be created by simulation. Further, in step A, the relationship between the voltage and the IV resistance is represented by a map, but a map may be prepared based on the relationship between the SOC (for example, the SOC in the initial state) and the IV resistance instead of the voltage. That is, there is a certain correlation between the voltage of the secondary battery and the SOC, and the relationship between the voltage and the IV resistance can be appropriately replaced with the relationship between the SOC and the IV resistance. In addition, when it is considered that the correlation between the voltage of the secondary battery and the SOC changes due to deterioration, the map may be corrected accordingly.

  In step B, the temperature and voltage of the lithium ion secondary battery to be measured are detected. Here, when the map prepared in the process A records the relationship between the SOC and the IV resistance, the SOC may be detected instead of the voltage. In this case, the SOC may be obtained by, for example, obtaining a relationship between the voltage and the SOC for the lithium ion secondary battery to be measured and estimating the SOC from the voltage. The temperature should just be grasped | ascertained based on the temperature sensor attached to the battery case, for example, if the temperature of the use environment of the lithium ion secondary battery used as a measuring object is measured.

  In step C, the IV resistance is measured by performing a predetermined discharge for the lithium ion secondary battery to be measured. The discharge conditions in step C may be the same as the IV resistance measurement conditions in the map prepared in step A. Here, the IV resistance measured in step C is stored.

  In the process D, based on the temperature and voltage (or SOC) at the start of discharge when discharged in the process C, the IV resistance measured in the process C, and the map prepared in the process A, the two Deriving the capacity shrinkage and capacity deviation of the secondary battery. Here, referring to the map prepared in step A based on the measurement information of at least two IV resistances measured at different times in step C, the capacity shrinkage and capacity deviation amount of the secondary battery Is good to estimate. At this time, between the conditions defined by the map prepared in step A, the map may be interpolated to derive the capacity deviation amount of the secondary battery. Then, it is preferable to search for a condition where the temperature, voltage (or SOC), and IV resistance at the start of discharge are close to each other, and estimate the capacity shrinkage and the capacity deviation amount of the secondary battery based on the searched condition. Thereby, the amount of capacity deviation of the secondary battery can be estimated.

  In step E, when the capacity shrinkage derived in step D exceeds a predetermined threshold, a predetermined first recovery process is performed. Here, the threshold for capacity shrinkage can be set as appropriate. As the first recovery process, for example, the upper limit value of the current value in charging and discharging of the secondary battery may be kept low. Specifically, the upper limit value of the secondary battery charge and discharge calculated according to the capacity shrinkage of the secondary battery estimated in step D is set as a new upper limit value by a predetermined function equation. It is good to comprise so that. Thereby, charging and discharging at an excessively high rate are suppressed. The new upper limit value set here is temporary for a predetermined period, and the upper limit of charging and discharging of the secondary battery is appropriately determined according to the capacity reduction of the secondary battery estimated in the step D. The value may be updated. The first recovery process is not limited to the above-described process as long as it is a process that suppresses or recovers the capacity shrinkage of the secondary battery.

  In step F, when the amount of capacity deviation derived in step D exceeds a predetermined threshold, a predetermined second recovery process is performed. Here, the threshold for the amount of displacement can be set as appropriate. As the second recovery process, for example, charging and discharging of the secondary battery may be stopped for a certain period. Specifically, the time for stopping charging and discharging of the secondary battery is calculated based on the stop time calculated according to the capacity deviation amount of the secondary battery estimated in step D by a predetermined function equation. It may be set. As a result, the secondary battery is prevented from being excessively stopped or the stop time is insufficient, and the secondary battery is appropriately stopped. Note that the second recovery process is not limited to the above-described process, as long as it is a process that suppresses or recovers the capacity shift amount of the secondary battery.

  In this case, the map prepared in step A may be stored in advance in the control device or the like. In the operation of actually estimating the capacity deviation amount of the secondary battery, when the SOC of the target secondary battery is 0% to 50% (or a voltage corresponding thereto), for example, a current value of 100 A And discharged for 10 seconds under a predetermined condition, and the IV resistance is measured. Based on the measured IV resistance and the temperature and voltage (or SOC) at the start of discharge, the map prepared in step A is referred to, and the capacity shrinkage and the capacity deviation amount of the lithium ion secondary battery are obtained. Presumed. According to this method, the capacity shrinkage and the capacity shift amount can be estimated by discharging the lithium ion secondary battery for a predetermined short time. For example, in the above-described embodiment, since it is preferable to discharge twice for about 10 seconds, the capacity shrinkage and the capacity deviation amount can be estimated by a relatively simple calculation process. For this reason, in the control of the secondary battery mounted on the vehicle, the capacity shrinkage and the capacity deviation amount can be estimated by the control device mounted on the vehicle. In other words, the control device monitors the increase in IV resistance for the discharge behavior of about 10 seconds in a relatively low SOC region of 0% or more and 50% or less, thereby reducing the capacity shrinkage and the capacity deviation of the battery. Can be estimated. Hereinafter, a flowchart for estimating the capacity shrinkage and the capacity shift amount and appropriately recovering the secondary battery will be described.

  FIG. 8 is a flowchart showing an example of the secondary battery control method proposed here. The control device that executes the flowchart may store a map prepared in step A described above in advance. Such a process corresponds to Step B described above. According to the flowchart, first, the voltage, current, and temperature of the secondary battery are detected (S101). The SOC is detected based on the voltage detected in the process S101. Next, it is determined whether the SOC is 0% or more and 50% or less (S102). When the SOC is not 0% or more and 50% or less (N), the capacity deviation amount estimation process proposed here ends.

  If the SOC is not less than 0% and not more than 50% (Y), it is determined whether the engine is immediately after starting or immediately after stopping (S103). If it is immediately after the engine is started or immediately after the engine is stopped (Y), it is determined whether or not the required discharge with the capacity deviation amount can be confirmed (S104). That is, it is determined whether or not a predetermined discharge required for measuring the IV resistance is possible. For example, even when the SOC is 0% or more and 50% or less, when the secondary battery that is the control target does not have sufficient capacity to perform the discharge (N), the estimation of the capacity deviation amount is applied. Not. In this case, for example, processing may be performed so as to return to processing S101. When the required discharge with the capacity deviation amount can be confirmed (Y), the predetermined discharge is forcibly performed (S105). This process S105 corresponds to the above-described process C. Then, the IV resistance measured based on the forced discharge is stored (S106).

  In the determination process S103 for determining whether the engine has just been started or just stopped, if it is not immediately after the engine is started or just stopped (N), a predetermined time (for example, 1) is calculated after the previous displacement amount is calculated. It is determined whether or not (time) has elapsed (S121). When a predetermined time or more has elapsed since the previous capacity deviation amount was calculated (Y), it is determined whether or not the required discharge with which the capacity deviation amount can be confirmed is possible (S104). When the required discharge with the capacity deviation amount can be confirmed (Y), the predetermined discharge is forcibly performed (S105), the IV resistance is measured, and based on the discharge The measured IV resistance is stored (S106). Here, the predetermined time in the determination process S121 is not limited to one hour, and is arbitrarily determined.

  Further, in the process S121 for determining whether or not a predetermined time or more has elapsed since the previous capacity deviation amount was calculated, if the predetermined time or more has not elapsed (N), it is necessary to confirm the capacity deviation amount. It is determined whether or not there has been a discharge (S122). That is, in this flowchart, when there is a required discharge in which the capacity deviation amount can be confirmed in SOC 0% or more and 50% or less (Y), the IV resistance is measured based on the discharge, and the measured IV resistance is measured. Is stored (S106). That is, such discharge also corresponds to the above-described process C. Further, in the determination process S122, when there is no required discharge in which the capacity deviation amount can be confirmed (N), the capacity deviation amount estimation process proposed here ends.

  Next, it is determined whether or not the number m of stored IV resistances is the number n (for example, two) necessary for calculating the capacity shrinkage and the capacity shift amount (S107). If the necessary number n of IV resistances is not stored (N), the process returns to step S101, and when discharge is performed again in step S105, the IV resistance measured based on the discharge is stored. (S106). When the necessary number n of IV resistances is stored (Y), the capacity shrinkage J and the capacity shift amount K are calculated in accordance with a predetermined program (S108). The process S108 corresponds to the above-described process D, and the map prepared in the above-described process A is referred to. For example, the map prepared in step A is referred to from the two stored IV resistances, and the estimated values of the capacity shrinkage J and the capacity shift amount K of the lithium ion secondary battery to be measured are obtained. Here, the necessary number n of IV resistances set in step S107 is taken into consideration by a method for obtaining an estimated value of the capacity shrinkage J and the capacity shift amount K of the lithium ion secondary battery from the map prepared in step A. To be determined.

  Next, it is determined whether or not the calculated capacity shrinkage J (estimated value) is larger than a predetermined threshold value Jt (S109). In the determination process S109, when the capacity shrinkage J (estimated value) is larger than a predetermined threshold value Jt (Y), a first recovery process is performed (S110). Here, the first recovery process is, for example, to keep the upper limit value of the current value in charging and discharging of the secondary battery to be controlled low. For example, the upper limit value of charging and discharging of the secondary battery is calculated according to the capacity shrinkage J (estimated value) by a predetermined function formula, and the calculated upper limit value is set as a new upper limit value. Good. The process S110 corresponds to the process E described above. After the first recovery process is performed and when the capacity shrinkage J (estimated value) is not greater than a predetermined threshold value Jt (N), the next determination process S111 is performed.

  Next, it is determined whether or not the calculated capacity deviation amount K is larger than a predetermined threshold value Kt (S111). In the determination process S111, when the capacity shift amount K is larger than a predetermined threshold value Kt (Y), a second recovery process is performed (S112). That is, when the capacity deviation amount K of the secondary battery to be controlled is larger than a predetermined capacity deviation amount Kt (threshold), charging and discharging of the secondary battery are stopped, Restore deterioration. At this time, the time for stopping the charging and discharging of the secondary battery may be programmed so that the required time is calculated based on the measured capacity deviation K. This process S112 corresponds to the process F described above. If the capacity deviation amount K is not larger than the predetermined threshold value Kt (N), normal processing is performed (S113). That is, charging and discharging of the secondary battery are allowed. In addition, when the upper limit value of the current value in charging and discharging of the secondary battery to be controlled is kept low by the first recovery process described above, the secondary to be controlled in the normal process S113. The upper limit value of the current value in charging and discharging the battery can be kept low. Such a series of controls may be repeated, for example, from the start to the end of the control by the battery control unit. Thereby, deterioration of the secondary battery can be suppressed. The example of the flowchart embodying the control method of the secondary battery proposed here has been exemplified, but the control method of the secondary battery is performed according to the processing according to the flowchart illustrated here unless otherwise specified. It is not limited.

  The various secondary battery control methods proposed here have been described above. The secondary battery control method proposed here is not limited to the above-described embodiment, and various modifications are possible unless otherwise specified.

  For example, in the process A, the IV resistance may further prepare a map in which the current conditions (current value and energization time) at the time of measurement are changed. That is, the secondary battery mounted on the vehicle is discharged under various conditions while being energized during normal control. For this reason, it is good to prepare the map which changed various electric current conditions at the time of measuring IV resistance. By preparing a map in which various current conditions for measuring the IV resistance are prepared, for example, in the determination process of S122 shown in FIG. 8, it is determined that there is a required discharge whose capacity deviation amount can be confirmed. More cases. This increases the chance that the capacity deviation amount is measured based on the IV resistance measured at the time of discharge when discharged during normal control.

Moreover, the control method of the secondary battery proposed here is applicable to various lithium ion secondary batteries, for example.
Examples of the positive electrode active material of the lithium ion secondary battery to be controlled include a lithium transition metal composite oxide.
Examples of the lithium transition metal composite oxide include, for example, a cobalt-rich (cobalt) material as a transition metal, a nickel-rich (nickel) material as a transition metal, and nickel, cobalt, and manganese as transition metals (so-called three Original materials), manganese spinel materials, so-called olivine materials, and the like.
Examples of the negative electrode active material of the lithium ion secondary battery to be controlled include carbon-based negative electrode materials such as amorphous natural graphite and graphite, and lithium titanate.

Claims (1)

Step A for preparing a map showing the relationship between the capacity reduction of the secondary battery, the capacity deviation of the secondary battery, the temperature and voltage at the start of discharge, and the IV resistance when a predetermined discharge is performed, ,
Step B for detecting the temperature and voltage of the secondary battery;
Measuring the IV resistance by performing a predetermined discharge when the voltage detected in the step B is within a predetermined range; and
Based on the temperature and voltage at the start of discharge when discharged in Step C, the IV resistance measured in Step C, and the map prepared in Step A, the capacity shrinkage and capacity of the secondary battery Step D for deriving the deviation amount;
Step E for performing a predetermined first recovery process when the capacity shrinkage derived in Step D exceeds a predetermined threshold;
A control method of a secondary battery, comprising: a step F of performing a predetermined second recovery process when the capacity deviation amount derived in the step D exceeds a predetermined threshold value.

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