JP5867373B2 - Battery system and method for estimating internal resistance of lithium ion secondary battery - Google Patents

Description

  The present invention relates to a technique for estimating internal resistance of a lithium ion secondary battery using a two-phase coexisting positive electrode active material.

  Patent Document 2 describes a lithium ion secondary battery using a two-phase coexisting positive electrode active material. Such a lithium ion secondary battery has a region in which insertion (charging) of lithium ions into the positive electrode active material and separation (discharge) of lithium ions from the positive electrode active material occur as a two-phase coexistence reaction.

JP 2011-043460 A International Publication No. 2010/125649 Pamphlet

When a compound in which a different metal element is added to LiNi _0.5 Mn _1.5 O ₄ is used as the positive electrode active material, the resistance value (internal resistance) of the lithium ion secondary battery is within the SOC range in which two phases coexist. ) Was affected by the past energization state. For this reason, the resistance value (internal resistance) of the lithium ion secondary battery cannot be accurately estimated unless the past energization state is taken into consideration.

  The battery system according to the first invention of the present application includes a lithium ion secondary battery using a two-phase coexisting positive electrode active material, and a controller that estimates the internal resistance of the lithium ion secondary battery. Here, the positive electrode active material is composed of a compound represented by the following general formula (I).

  In the above formula (I), M represents a trivalent or higher valent transition metal element. Further, a, b, and c shown in the above formula (I) are values arbitrarily set within the range shown in the above formula (I).

  When the SOC of the lithium ion secondary battery is included in the SOC range where the two-phase coexistence state is present, the controller determines the internal resistance when the current and immediately preceding energized state does not change, and the current and immediately energized state is the charged state and discharged. Estimate to a value higher than the internal resistance when changing between states.

  In the lithium ion secondary battery using the positive electrode active material of the two-phase coexistence type composed of the compound represented by the above formula (I), the internal resistance of the lithium ion secondary battery is not only the current energized state but also the immediately energized state. Will be affected. Specifically, the internal resistance when the current state immediately before and immediately before the current state does not change is higher than the internal resistance when the current state immediately before and immediately before the current state changes.

  Therefore, in the present invention, the internal resistance of the lithium ion secondary battery is estimated by grasping the current supply state immediately before and immediately before. Thereby, the precision which estimates the internal resistance of a lithium ion secondary battery can be improved.

  Here, when estimating the internal resistance of the lithium ion secondary battery when the current energized state is the discharged state, the immediately energized state is the charged state as the internal resistance when the immediately energized state is the discharged state. It can be estimated to be higher than the internal resistance when. Further, when the internal resistance of the lithium ion secondary battery is estimated when the current energization state is the charge state, the immediately previous energization state is the discharge state as the internal resistance when the immediately previous energization state is the charge state. It can be estimated to be higher than the internal resistance at a certain time.

  When estimating the internal resistance of the lithium ion secondary battery, information indicating the correspondence between the temperature and the internal resistance of the lithium ion secondary battery can be used. Specifically, the temperature of the lithium ion secondary battery is detected using a temperature sensor, and the internal resistance corresponding to the detected temperature can be specified using the correspondence relationship between the temperature and the internal resistance. Since the internal resistance of a lithium ion secondary battery tends to depend on the temperature of the lithium ion secondary battery, the internal resistance is estimated from the temperature of the lithium ion secondary battery by obtaining the correspondence relationship between the temperature and the internal resistance in advance. can do.

  When estimating the internal resistance of the lithium ion secondary battery, not only the temperature of the lithium ion secondary battery but also the current value and energization time can be taken into consideration. Specifically, if the correspondence relationship between temperature, current value and energization time and internal resistance is obtained in advance, the internal resistance can be specified by specifying the temperature, current value and energization time.

  When estimating internal resistance using information indicating the correspondence relationship between temperature and internal resistance, a correspondence relationship used when the energization state changes and a correspondence relationship used when the energization state does not change are prepared in advance. I can keep it. Since the internal resistance differs between when the energized state changes and when the energized state does not change, prepare a corresponding relationship between temperature and internal resistance when the energized state changes and when it does not change. Good.

  When the internal resistance of the lithium ion secondary battery is estimated, the overvoltage of the lithium ion secondary battery can be calculated (estimated) by multiplying the estimated internal resistance by the current value flowing through the lithium ion secondary battery. . In the present invention, since the estimation accuracy of the internal resistance can be improved, the estimation accuracy of the overvoltage can also be improved.

  When the overvoltage of the lithium ion secondary battery is estimated, the SOC of the lithium ion secondary battery can be estimated based on the overvoltage. Specifically, the open circuit voltage of the lithium ion secondary battery can be calculated by subtracting the overvoltage from the closed circuit voltage of the lithium ion secondary battery. The closed circuit voltage can be detected using a voltage sensor.

  Since the open circuit voltage and the SOC have a predetermined correspondence, the SOC can be specified from the open circuit voltage by using this correspondence. According to the present invention, since the overvoltage estimation accuracy can be improved, the open circuit voltage and SOC estimation accuracy can also be improved.

  The above-described SOC range can be expanded as the full charge capacity of the lithium ion secondary battery decreases. The decrease in the full charge capacity in the lithium ion secondary battery can be expressed by shifting the negative electrode potential to the high capacity side with respect to the positive electrode potential. Here, since the SOC range in which two phases coexist is dependent on the positive electrode potential, it is constant even if the negative electrode potential is shifted.

  On the other hand, when the negative electrode potential is shifted, the full charge capacity of the lithium ion secondary battery is reduced, so that the ratio of the SOC range depending on the positive electrode potential changes in the full charge capacity. That is, as the full charge capacity decreases, the proportion of the SOC range depending on the positive electrode potential increases. For this reason, the SOC range compared with the SOC of a lithium ion secondary battery can be expanded, so that the full charge capacity of a lithium ion secondary battery falls.

  By expanding the SOC range according to the decrease in the full charge capacity, it is possible to improve the estimation accuracy of the internal resistance. Here, if the SOC range is not expanded, the estimation process of the internal resistance based on the current state immediately before and immediately before the portion where the SOC range is expanded is not performed.

  In this case, the internal resistance estimated when the current state immediately before and immediately before is not changed easily deviates from the actual internal resistance, and the estimation accuracy of the internal resistance is lowered. Therefore, as in the present invention, by expanding the SOC range in response to a decrease in the full charge capacity, it is possible to perform the internal resistance estimation process based on the current state immediately before and at the portion where the SOC range is expanded. In addition, the estimation accuracy of the internal resistance can be improved.

  2nd invention of this application is an estimation method which estimates the internal resistance of the lithium ion secondary battery using the positive electrode active material of a two-phase coexistence type. Here, the positive electrode active material is composed of a compound represented by the above formula (I). When the SOC of the lithium ion secondary battery is included in the SOC range where the two-phase coexistence state is present, the internal resistance when the current and immediately before energization state does not change, and the current and immediately before energization state between the charge state and the discharge state Estimated to be higher than the internal resistance when changing at. Also in the second invention of the present application, the same effect as that of the first invention of the present application can be obtained.

  When it is predicted that the future energization state will not change with respect to the immediately previous energization state, the energization state can be changed in advance. As a result, it is possible to suppress an increase in internal resistance due to the current state immediately before and without change.

  Specifically, when the immediately energized state is a discharged state and the lithium ion secondary battery is to be discharged, the lithium ion secondary battery can be charged before discharging. As a result, when the lithium ion secondary battery is discharged, the immediately preceding energized state becomes a charged state, and an increase in internal resistance due to the current and immediately preceding energized state not changing in the discharged state can be suppressed.

  On the other hand, when the energized state immediately before is a charged state and the lithium ion secondary battery is to be charged, the lithium ion secondary battery can be discharged before charging. Thereby, when the lithium ion secondary battery is charged, the immediately preceding energized state becomes a discharged state, and an increase in internal resistance due to the current and immediately preceding energized states not changing in the charged state can be suppressed.

  As described above, if the increase in the internal resistance of the lithium ion secondary battery can be suppressed, the lithium ion secondary battery can be discharged and charged efficiently. Specifically, the discharge power and charge power of the lithium ion secondary battery can be increased.

It is a figure which shows the structure of a battery system. In Example 1, it is a flowchart which shows the process which estimates the overvoltage of a cell. It is a figure which shows the map which specifies the resistance value of a cell in normal mode. It is a figure which shows the relationship between OCV and SOC. In history mode, it is a figure which shows the map which specifies the resistance value of a cell when the last energization state is a charging state. In history mode, it is a figure which shows the map which specifies the resistance value of a cell when the last electricity supply state is a discharge state. It is a figure which shows the voltage value of a cell, the positive electrode potential, and the relationship of a negative electrode potential. It is a flowchart which shows the process which correct | amends an SOC range based on a capacity | capacitance fall amount. In Example 2, it is a flowchart which shows the process which suppresses the raise of the resistance value of a cell.

  Examples of the present invention will be described below.

  FIG. 1 is a diagram showing the configuration of the battery system of this example. The battery system shown in FIG. 1 can be mounted on a vehicle, for example. Such vehicles include hybrid vehicles and electric vehicles. The hybrid vehicle includes another power source such as an internal combustion engine or a fuel cell in addition to the assembled battery described later as a power source for running the vehicle. Moreover, the electric vehicle includes only an assembled battery described later as a power source for running the vehicle.

  In addition, this invention is not applied only to the battery system mounted in a vehicle. That is, the present invention can be applied to any system or apparatus that charges and discharges a single cell described later.

  The assembled battery 10 includes a plurality of unit cells 11 connected in series. A lithium ion secondary battery is used as the single battery 11. The unit cell 11 includes a battery case and a power generation element accommodated in the battery case. The power generation element is an element that performs charge and discharge, and includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. A solid electrolyte can be used instead of the separator.

  The positive electrode plate includes a current collector plate and a positive electrode active material layer formed on the surface of the current collector plate. The current collector plate can be formed of aluminum, for example. The positive electrode active material layer includes a positive electrode active material, a binder, and a conductive additive. As the binder, for example, polyvinylidene fluoride can be used, and as the conductive auxiliary agent, for example, acetylene black can be used.

  As the positive electrode active material, a compound represented by the following general formula (1) is used.

  In the above formula (1), M represents a trivalent or higher valent transition metal element. For example, as M, Al, Ti, Cr, Fe, Co, Zr, Nb, Mo, Ta, W, or the like can be used.

  Moreover, each value of a, b, and c shown in said Formula (1) becomes arbitrary values within said numerical range. B shown in the above formula (1) may be 0, and in this case, M is not included. When c shown in the above formula (1) is set to a value larger than 0, oxygen defects may be generated by re-baking or the like when the positive electrode active material is manufactured.

  The negative electrode plate has a current collector plate and a negative electrode active material layer formed on the surface of the current collector plate. The current collector plate can be formed of copper, for example. The negative electrode active material layer includes a negative electrode active material, a binder, and a thickener. As a material constituting the negative electrode active material layer, a known material can be appropriately selected. Here, as the negative electrode active material, for example, a natural graphite-based carbon material can be used.

  The number of the single cells 11 can be appropriately set based on the required output of the assembled battery 10 or the like. In the present embodiment, the assembled battery 10 is configured by connecting all the unit cells 11 in series, but is not limited thereto. That is, the assembled battery 10 can include a plurality of single cells 11 connected in parallel.

  The monitoring unit (corresponding to a voltage sensor) 21 detects a closed circuit voltage (CCV) of the assembled battery 10 or detects a closed circuit voltage (CCV) of each cell 11, and the detection result Is output to the controller 40. The current sensor 22 detects the current flowing through the assembled battery 10 and outputs the detection result to the controller 40. Here, when discharging the assembled battery 10, a positive value can be used as the current value (discharge current), and when charging the assembled battery 10, a negative value can be used as the current value (charging current).

  In the present embodiment, the current sensor 22 is provided on the positive electrode line PL connected to the positive terminal of the assembled battery 10, but the current sensor 22 only needs to be able to detect the current flowing through the assembled battery 10, and the position where the current sensor 22 is provided. Can be set as appropriate. For example, the current sensor 22 can be provided on the negative electrode line NL connected to the negative electrode terminal of the assembled battery 10. A plurality of current sensors 22 can also be provided.

  The temperature sensor 23 detects the temperature of the assembled battery 10 (unit cell 11) and outputs the detection result to the controller 40. When the temperature may be different depending on the position of the unit cell 11 included in the assembled battery 10, the temperature sensors 23 can be arranged at a plurality of locations in the assembled battery 10. Thereby, the temperature of each cell 11 can be detected with high accuracy.

  The controller 40 has a memory 41 and a timer 42. The memory 41 stores various types of information for the controller 40 to perform predetermined processing (for example, processing described in the present embodiment). The timer 42 is used to measure the energization time of the assembled battery 10 as will be described later. In this embodiment, the memory 41 and the timer 42 are built in the controller 40, but at least one of the memory 41 and the timer 42 may be provided outside the controller 40.

  A system main relay SMR-B is provided in the positive electrode line PL. System main relay SMR-B is switched between ON and OFF by receiving a control signal from controller 40. A system main relay SMR-G is provided in the negative electrode line NL. System main relay SMR-G is switched between on and off by receiving a control signal from controller 40.

  A system main relay SMR-P and a current limiting resistor R are connected in parallel to the system main relay SMR-G. System main relay SMR-P and current limiting resistor R are connected in series. System main relay SMR-P is switched between on and off by receiving a control signal from controller 40.

  The current limiting resistor R is used for suppressing an inrush current from flowing through the capacitor C when the battery pack 10 is connected to a load (specifically, the inverter 31). Capacitor C is connected to positive electrode line PL and negative electrode line NL, and is used to smooth voltage fluctuations between positive electrode line PL and negative electrode line NL.

  When connecting the assembled battery 10 to the inverter 31, the controller 40 first switches the system main relay SMR-B from off to on and switches the system main relay SMR-P from off to on. Thereby, the discharge current of the assembled battery 10 can be passed through the current limiting resistor R, and the inrush current can be suppressed from flowing into the capacitor C.

  Next, the controller 40 switches the system main relay SMR-G from off to on and switches the system main relay SMR-P from on to off. Thereby, the connection between the assembled battery 10 and the inverter 31 is completed, and the battery system shown in FIG. 1 is in an activated state (Ready-On). Information about on / off of the ignition switch of the vehicle is input to the controller 40, and the controller 40 activates the battery system shown in FIG. 1 in response to the ignition switch switching from off to on.

  On the other hand, when the ignition switch is switched from on to off, the controller 40 switches the system main relays SMR-B and SMR-G from on to off. Thereby, the connection between the assembled battery 10 and the inverter 31 is cut off, and the battery system shown in FIG. 1 enters a stopped state (Ready-Off).

  The inverter 31 converts the DC power output from the assembled battery 10 into AC power, and outputs the AC power to the motor / generator 32. As the motor generator 32, for example, a three-phase AC motor can be used. The motor / generator 32 receives the AC power output from the inverter 31 and generates kinetic energy for running the vehicle. The kinetic energy generated by the motor / generator 32 is transmitted to the wheels so that the vehicle can run.

  When the vehicle is decelerated or stopped, the motor / generator 32 converts kinetic energy generated during braking of the vehicle into electric energy (AC power). The inverter 31 converts the AC power generated by the motor / generator 32 into DC power and outputs the DC power to the assembled battery 10. Thereby, the assembled battery 10 can store regenerative electric power.

  In the present embodiment, the assembled battery 10 is connected to the inverter 31, but this is not a limitation. Specifically, a booster circuit can be provided in the current path between the assembled battery 10 and the inverter 31. The booster circuit can boost the output voltage of the assembled battery 10 and output the boosted power to the inverter 31. The booster circuit can step down the output voltage of the inverter 31 and output the stepped down power to the assembled battery 10.

  Next, a part of processing in the battery system of the present embodiment will be described with reference to the flowchart shown in FIG. The process shown in FIG. 2 is a process for switching the method for estimating the overvoltage of the unit cell 11, and is executed by the controller 40.

  In step S <b> 101, the controller 40 detects the voltage value of the unit cell 11 based on the output of the monitoring unit 21, and detects the temperature of the unit cell 11 based on the output of the temperature sensor 23. Further, the controller 40 detects the value of the current flowing through the single battery 11 based on the output of the current sensor 22, and measures the energization time while the current value is not changing, using the timer 42.

  In step S102, the controller 40 estimates the overvoltage of the unit cell 11 based on the information acquired in the process of step S101. When the unit cell 11 is in an energized state (charged state or discharged state), the closed circuit voltage value (CCV) of the unit cell 11 detected by the monitoring unit 21 due to the occurrence of polarization is the open circuit voltage value of the unit cell 11. Deviation from (OCV; Open Circuit Voltage). Here, the difference between the closed circuit voltage value and the open circuit voltage value corresponds to the overvoltage.

  Specifically, the controller 40 can estimate the overvoltage of the unit cell 11 using the map shown in FIG. The map shown in FIG. 3 shows the relationship between the current value flowing through the unit cell 11, the temperature of the unit cell 11, and the resistance value (internal resistance) R_nor of the unit cell 11 corresponding to the current value and temperature.

  The map shown in FIG. 3 can be created by conducting an experiment or the like in advance, and information regarding the map shown in FIG. 3 can be stored in the memory 41. Instead of the map, an arithmetic expression that can calculate the resistance value R_nor from the current value and the temperature can also be used.

  The maps shown in FIG. 3 include a map used when the current energized state is a charged state and a map used when the current energized state is a discharged state. That is, when the current energized state is the charged state, the map shown in FIG. 3 corresponding to the charged state is used, and when the current energized state is the discharged state, the map shown in FIG. 3 corresponding to the discharged state is used. It is done.

  Here, the controller 40 can determine whether the energized state is the charged state or the discharged state by checking the current value detected by the current sensor 22. That is, if the current value is a positive value, the controller 40 can determine that the energized state of the unit cell 11 is a discharged state. If the current value is a negative value, the controller 40 can determine that the energized state of the unit cell 11 is a charged state.

  Since the current value and the temperature are acquired by the processing in step S101, the resistance value R_nor corresponding to the current value and the temperature can be specified using the map shown in FIG. The map shown in FIG. 3 shows the relationship between the current value and temperature and the resistance value R_nor, but the resistance value R_nor may change depending on the energization time.

  For this reason, as the map shown in FIG. 3, a map showing a correspondence relationship between the current value, temperature, energization time, and resistance value R_nor can be used. Using this map, the resistance value R_nor can be specified based on the current value, temperature, and energization time.

  In the present embodiment, the resistance value R_nor is specified based on the current value, the temperature, and the energization time, but is not limited thereto. Specifically, the resistance value R_nor can be specified based on at least one of the parameters of current value, temperature, and energization time. In this case, a relationship between at least one parameter and the resistance value R_nor may be obtained in advance. Here, since the resistance value R_nor easily depends on the temperature of the unit cell 11, the resistance value R_nor can be specified based on the temperature of the unit cell 11.

  Since the resistance value R_nor is affected by the current value, the temperature, and the energization time, the estimation accuracy of the resistance value R_nor is improved by specifying (estimating) the resistance value R_nor based on the current value, the temperature, and the energization time. be able to.

  In step S102, the controller 40 can calculate the overvoltage of the unit cell 11 by multiplying the resistance value R_nor and the current value. The current value used here is the current value acquired in the process of step S101.

  In step S103, the controller 40 estimates the SOC (State of Charge) of the unit cell 11. The SOC indicates the ratio of the current charge capacity to the full charge capacity. Specifically, the controller 40 calculates the OCV of the single battery 11 by subtracting the overvoltage calculated in the process of step S102 from the voltage value (CCV) of the single battery 11 acquired in the process of step S101.

  Then, the controller 40 specifies the SOC corresponding to the OCV using the correspondence relationship between the SOC and the OCV shown in FIG. Since the SOC and the OCV have the correspondence shown in FIG. 4, the SOC corresponding to the OCV can be specified by specifying the OCV. The relationship shown in FIG. 4 can be specified in advance by an experiment or the like, and the information shown in FIG. 4 can be stored in the memory 41.

  In step S104, the controller 40 determines whether or not the SOC (estimated SOC) estimated in the process of step S103 is included in a predetermined SOC range. It has been found that when the compound represented by the above formula (1) is used as the positive electrode active material, two phases coexist in a predetermined SOC range. Here, the SOC range varies depending on the composition of the compound represented by the formula (1).

  The state in which lithium ions are inserted into the positive electrode active material is referred to as a first phase, and the state in which lithium ions are released (detached) from the positive electrode active material is referred to as a second phase. In the compound represented by the above formula (1), the first phase and the second phase may coexist in a stable state in one positive electrode active material. When a positive electrode active material that is a two-phase coexistence type positive electrode active material comprising the compound represented by the above formula (1) is used, the resistance of the single cell 11 is determined according to the past history when the single cell 11 is charged and discharged. It was found that the values (internal resistance) were different.

  When the SOC of the unit cell 11 is included in the SOC range in which the two-phase coexistence state is established, the resistance value (internal resistance) of the unit cell 11 changes. Therefore, in the process of step S104, it is determined whether or not the SOC of the single battery 11 is included in a predetermined SOC range.

  In step S104, when the estimated SOC is out of the predetermined SOC range, the controller 40 performs the process of step S105. On the other hand, when the estimated SOC is included in the predetermined SOC range, the controller 40 performs the process of step S106.

  In step S105, the controller 40 sets the normal mode as an overvoltage estimation method. In the normal mode, the overvoltage of the unit cell 11 is estimated based on the current energization state of the unit cell 11 as described in the process of step S102. Specifically, first, by using the map shown in FIG. 3 corresponding to the current energization state, the resistance value R_nor of the single battery 11 is specified, and the single battery 11 is multiplied by the resistance value R_nor and the current value. The overvoltage of is calculated.

  In step S106, the controller 40 sets the history mode as an overvoltage estimation method. In the history mode, the overvoltage of the unit cell 11 is estimated by a method different from that in the normal mode. Specifically, in the history mode, the overvoltage of the unit cell 11 is estimated based on the current state of the unit cell 11 at the present time and immediately before.

  The immediately preceding energized state is a past energized state and is the most recently energized state with respect to the present. When the process of step S101 is performed in a predetermined cycle, the immediately preceding energized state is an energized state specified in the immediately preceding cycle with respect to the current time. Further, if the current energization state is an energization state immediately after stopping the charging / discharging of the unit cell 11, the immediately preceding energization state becomes the energization state immediately before stopping the charging / discharging of the unit cell 11. Here, if the information regarding the current value detected by the current sensor 22 is stored in the memory 41, the controller 40 can determine whether the immediately previous energized state is the charged state or the discharged state.

  When estimating the resistance value (internal resistance) of the unit cell 11 in the history mode, the controller 40 uses the map shown in FIG. 5 or FIG. 6 in accordance with the energization state of the unit cell 11 immediately before. The maps shown in FIGS. 5 and 6 can be obtained in advance by experiments or the like, and information regarding the maps shown in FIGS. 5 and 6 can be stored in the memory 41.

  The maps shown in FIGS. 5 and 6 are respectively provided when the current energized state is in the discharged state and when the current energized state is in the charged state. That is, when the current energization state is the discharge state, the controller 40 specifies the maps shown in FIGS. 5 and 6 corresponding to the current discharge state, and the map shown in FIGS. A map corresponding to the energization state of the battery 11 is used. Further, when the current energized state is the charged state, the controller 40 identifies the maps shown in FIGS. 5 and 6 corresponding to the current charged state, and among the maps shown in FIGS. A map corresponding to the energization state of the battery 11 is used.

  The map shown in FIG. 5 is used to specify the resistance value (internal resistance) R_ch of the unit cell 11 when the immediately energized state is the charged state. The map shown in FIG. 5 corresponds to the map shown in FIG. 3, and shows the relationship between the current temperature and current value of the cell 11 and the resistance value (internal resistance) R_ch. In the map shown in FIG. 5, the energization time can be taken into consideration as in the map shown in FIG. Instead of the map, an arithmetic expression that can calculate the resistance value R_ch from the temperature and the current value can also be used.

  When the immediately previous energized state is the charged state, the controller 40 specifies the resistance value R_ch corresponding to the temperature, current value, and energized time acquired in the process of step S101 by using the map shown in FIG. After specifying the resistance value R_ch, the controller 40 can calculate the overvoltage of the unit cell 11 by multiplying the resistance value R_ch by the current current value of the unit cell 11.

  The map shown in FIG. 6 is used to specify the resistance value (internal resistance) R_dis of the unit cell 11 when the previous energization state is the discharge state. The map shown in FIG. 6 corresponds to the map shown in FIG. 3 and shows the relationship between the current temperature and current value of the cell 11 and the resistance value (internal resistance) R_dis. In the map shown in FIG. 6, the energization time can be taken into consideration as in the map shown in FIG. Instead of the map, an arithmetic expression that can calculate the resistance value R_dis from the temperature and the current value can also be used.

  When the previous energization state is the discharge state, the controller 40 specifies the resistance R_dis corresponding to the temperature, current value, and energization time acquired in the process of step S101, using the map shown in FIG. After specifying the resistance value R_dis, the controller 40 can calculate the overvoltage of the unit cell 11 by multiplying the resistance value R_dis by the current current value of the unit cell 11.

  When a two-phase coexisting positive electrode active material comprising the compound represented by the above formula (1) is used and the estimated SOC is included in a predetermined SOC range, the current energized state and the immediately preceding energized state According to the relationship, the resistance value (internal resistance) of the unit cell 11 changes. Here, it has been found that the change in the resistance value (internal resistance) depends only on the current state (current state or state of charge) immediately before and after.

  That is, it has been found that the change in the resistance value (internal resistance) is not affected by the energization time and current rate in the previous energization state, the time during which the energization of the unit cell 11 is stopped, and the like. For this reason, it is possible to estimate a change in resistance value (internal resistance) by checking only the current and previous energization states.

  For example, the resistance value (internal resistance) when the current and immediately energized state is a discharged state is the resistance value (internal resistance) when the immediately energized state is a charged state and the current energized state is a discharged state. Higher than. In addition, the resistance value (internal resistance) when the current and immediately preceding energized state is the charged state is the resistance value (internal resistance) when the immediately preceding energized state is the discharged state and the current energized state is the charged state. Higher than.

  That is, the resistance value (internal resistance) when the current and immediately before energization state does not change is higher than the resistance value (internal resistance) when the current and immediately before energization state changes between the discharge state and the energization state. Become. Thus, even if the current energized state is a discharged state or a charged state, the resistance value (internal resistance) changes depending on whether the immediately previous energized state is a discharged state or a charged state.

  According to the present embodiment, in the history mode, the resistance value (internal resistance) of the unit cell 11 can be accurately estimated by considering the immediately energized state. Moreover, the overvoltage of the unit cell 11 can be estimated with high accuracy by improving the estimation accuracy of the resistance value (internal resistance). If the overvoltage of the unit cell 11 can be estimated, the SOC of the unit cell 11 can be estimated after calculating the OCV of the unit cell 11 as described in the process of step S103.

  In this embodiment, when the normal mode and the history mode are determined, the processing from step S101 to step S103 shown in FIG. 2 is performed. However, the present invention is not limited to this. That is, before the discrimination between the normal mode and the history mode, the SOC of the unit cell 11 can be estimated by a process different from the processes in steps S101 to S103.

  For example, in a state where the assembled battery 10 is not connected to the load (inverter 31), the OCV of the cell 11 is detected, and the SOC corresponding to the detected OCV is specified using the correspondence relationship between the OCV and the SOC. it can. When the OCV of the unit cell 11 is detected, a weak current that is less likely to cause polarization is passed through the unit cell 11, and the voltage value (CCV) of the unit cell 11 at this time can be regarded as the OCV. On the other hand, the SOC of the single battery 11 can also be estimated by continuing to integrate the current values after the start of charging / discharging of the assembled battery 10 (single battery 11).

  Note that, after the discrimination between the normal mode and the history mode, the SOC of the unit cell 11 can be estimated based on the overvoltage of the unit cell 11 as described above.

  In the process shown in FIG. 2 described above, the overvoltage and SOC of the unit cell 11 are estimated, but the present invention is not limited to this. That is, if it is a battery system shown in FIG. 1, the overvoltage and SOC of the assembled battery 10 can also be estimated by performing the process similar to the process shown in FIG. In this case, as the maps shown in FIGS. 3, 4, and 5, a map that can specify the resistance value of the assembled battery 10 may be used.

  The full charge capacity of the unit cell 11 decreases according to the deterioration of the unit cell 11 or the like. In this case, as will be described below, the SOC range before the full charge capacity of the single battery 11 is lowered may be different from the SOC range after the full charge capacity of the single battery 11 is lowered. .

  Here, the decrease in the full charge capacity in the unit cell 11 can be expressed by shifting the negative electrode potential to the high capacity side with respect to the positive electrode potential as shown in FIG. In FIG. 7, a dotted line shows the voltage value and negative electrode potential of the cell 11 before the cell 11 deteriorates. On the other hand, the solid line shown in FIG. 7 indicates the positive electrode potential, the voltage value of the single cell 11 after the single cell 11 has deteriorated, or the negative electrode potential. The voltage value of the unit cell 11 is represented by the difference between the positive electrode potential and the negative electrode potential.

  When the unit cell 11 deteriorates, the negative electrode potential can be shifted in the direction of arrow D in FIG. 7 by the amount of deterioration. When the negative electrode potential is shifted in the direction of the arrow D in FIG. 7, the full charge capacity of the unit cell 11 is reduced. As shown in FIG. 7, when the single battery 11 deteriorates, the full charge capacity of the single battery 11 decreases from FCC1 to FCC2.

  FCC1 indicates a range in which the SOC of the unit cell 11 is 0 to 100 [%] before the unit cell 11 deteriorates. FCC2 indicates a range in which the SOC of the unit cell 11 is 0 to 100 [%] after the unit cell 11 has deteriorated.

  Range_soc shown in FIG. 7 indicates the SOC range used in the process of step S104 shown in FIG. As described above, since the two-phase coexistence state depends on the positive electrode active material, the SOC range Range_soc is determined by the positive electrode potential. Here, when the full charge capacity of the single battery 11 decreases, the range occupied by Range_soc in the range of the full charge capacity (SOC range of 0 to 100%) changes. Specifically, the range occupied by Range_soc for the full charge capacity FCC2 is wider than the range occupied by Range_soc for the full charge capacity FCC1.

  Thus, when the full charge capacity of the single battery 11 decreases, it is necessary to change the SOC range Range_soc. Therefore, in this embodiment, the SOC range used in the process of step S104 shown in FIG. 2 is corrected by the process shown in FIG. The process shown in FIG. 8 is executed by the controller 40.

  In step S201, the controller 40 estimates the capacity decrease amount ΔAh_c of the single battery 11. The capacity decrease amount ΔAh_c can be obtained by subtracting the current full charge capacity FCC_c from the full charge capacity FCC_ini before the single battery 11 deteriorates.

  Since the capacity reduction amount ΔAh_c can be obtained by comparing the full charge capacity before and after the deterioration of the single battery 11, it is only necessary to calculate the full charge capacity of the single battery 11 before and after the deterioration of the single battery 11. As a method for calculating the full charge capacity of the single battery 11, for example, a method described below can be used.

  Detecting the current value (charging current) until the SOC of the unit cell 11 changes from 0 [%] to 100 [%], and calculating the full charge capacity of the unit cell 11 by integrating the current value Can do. Note that the current value (discharge current) until the SOC of the unit cell 11 changes from 100 [%] to 0 [%] is detected, and this current value is integrated to calculate the full charge capacity of the unit cell 11. You can also

  On the other hand, the full charge capacity of the unit cell 11 can be calculated without changing the SOC of the unit cell 11 between 0 and 100 [%]. Specifically, the full charge capacity of the unit cell 11 can be calculated based on the following formula (2).

  In the above formula (2), FCC is the full charge capacity of the unit cell 11. I is a current value that flows through the cell 11 when the cell 11 is charged (or discharged), and ΣI is an integrated value (current) of the current value while the cell 11 is being charged (or discharged). Integrated value). When the cell 11 is charged (or discharged) with a constant current, the current integrated value ΣI can be easily calculated.

  In the above formula (2), SOC_s is the SOC of the single battery 11 when charging (or discharging) is started, and SOC_e is the SOC of the single battery 11 when charging (or discharging) is completed. When charging the cell 11, SOC_e becomes higher than SOC_s, and when discharging the cell 11, SOC_e becomes lower than SOC_s.

  As can be seen from the above formula (2), when calculating the full charge capacity FCC of the single battery 11, it is necessary to make SOC_s and SOC_e different from each other. Further, in order to improve the calculation accuracy of the full charge capacity FCC, it is preferable to widen the difference between SOC_s and SOC_e. According to the above formula (2), the full charge capacity FCC can be calculated only by changing the SOC of the unit cell 11 between SOC_s and SOC_e instead of 0 to 100 [%].

  In step S202, the controller 40 determines whether or not the capacity decrease amount ΔAh_c estimated in the process of step S201 is larger than the threshold value ΔAh_lim. The threshold value ΔAh_lim is used to determine whether or not to correct the SOC range used in the process of step S104 shown in FIG. Information regarding the threshold value ΔAh_lim can be stored in the memory 41.

  The value of the threshold value ΔAh_lim can be set as appropriate. Here, the threshold value ΔAh_lim can be set in consideration of the calculation error of the full charge capacity FCC. The smaller the threshold value ΔAh_lim, the easier it is to perform the SOC range correction process described later. When the capacity decrease amount ΔAh_c is larger than the threshold value ΔAh_lim, the controller 40 performs the process of step S203. On the other hand, when the capacity decrease amount ΔAh_c is smaller than the threshold value ΔAh_lim, the controller 40 ends the process shown in FIG.

  In step S203, the controller 40 corrects the SOC range used in the process of step S104 shown in FIG. Specifically, the controller 40 shifts the negative electrode potential in the direction of the arrow D shown in FIG. 7 by the amount of capacity decrease ΔAh_c estimated in the process of step S201. Here, the positive electrode potential and the negative electrode potential before the single cell 11 deteriorates can be obtained in advance.

  Then, the controller 40 calculates the full charge capacity FCC2 shown in FIG. 7 after shifting the negative electrode potential by the capacity decrease amount ΔAh_c. In addition, the controller 40 specifies a range occupied by Range_soc in the full charge capacity FCC2. This range is the SOC range used in the process of step S104 shown in FIG. After correcting the SOC range, the controller 40 stores information on the corrected SOC range in the memory 41, and uses the corrected SOC range when performing the processing shown in FIG.

  According to the process shown in FIG. 8, the SOC range is corrected according to the deterioration of the unit cell 11, in other words, according to the decrease in the full charge capacity of the unit cell 11. The overvoltage can be estimated with high accuracy. That is, by setting a range according to the deterioration of the unit cell 11 as the SOC range in which the two-phase coexistence state is established, the resistance value (internal resistance) using the normal mode or the history mode can be accurately estimated. .

  If the SOC range is not corrected, the resistance value (internal resistance) of the cell 11 should be estimated based on the history mode, but the resistance value of the cell 11 may be estimated based on the normal mode. is there. In this case, the estimation accuracy of the resistance value is lowered. According to the present embodiment, as described above, erroneous determination of the history mode and the normal mode can be suppressed, and the resistance value estimation accuracy can be improved. If the estimation accuracy of the resistance value can be improved, the accuracy of estimating the overvoltage and SOC of the single cell 11 can be improved.

  A battery system that is Embodiment 2 of the present invention will be described. In the present embodiment, the same members as those described in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Hereinafter, differences from the first embodiment will be mainly described.

  As described in Example 1, in the unit cell 11 using the two-phase coexisting positive electrode active material, the resistance value (internal resistance) of the unit cell 11 when the immediately preceding and current energized state is maintained in the discharged state. Is higher than the resistance value (internal resistance) of the unit cell 11 when the energized state immediately before and at the present time changes from the charged state to the discharged state.

  For this reason, when the last energization state is a discharge state when trying to discharge the unit cell 11, the resistance value of the unit cell 11 is likely to increase, and the output power (discharge power) of the unit cell 11 is increased. It tends to decrease. In other words, there is a possibility that the unit cell 11 cannot be discharged efficiently.

  On the other hand, in the unit cell 11 using the two-phase coexistence type positive electrode active material, the resistance value (internal resistance) of the unit cell 11 when the immediately previous and current energized state is maintained in the charged state is the energized immediately before and present. It becomes higher than the resistance value (internal resistance) of the unit cell 11 when the state changes from the discharged state to the charged state.

  For this reason, when it is going to charge the cell 11, if the energization state immediately before is a charge state, the resistance value of the cell 11 will become easy to rise, and the input electric power (charge power) of the cell 11 will be increased. It tends to decrease. In other words, the unit cell 11 may not be charged efficiently.

  Therefore, in this embodiment, the unit cell 11 can be discharged and charged efficiently. This process will be described with reference to the flowchart shown in FIG. The process shown in FIG. 9 is executed by the controller 40.

  In step S301, the controller 40 determines whether or not the usage state of the unit cell 11 is discharge priority. The discharge priority is to give priority to discharging the cell 11 over charging the cell 11. In the battery system shown in FIG. 1, the vehicle may be driven by giving priority to the discharge (output) of the assembled battery 10.

  Here, the setting of giving priority to the discharge of the assembled battery 10 can be performed by a user input or can be performed under the control of the controller 40. For example, in order to drive the vehicle using the output of the assembled battery 10, the user can make a setting for giving priority to the output of the assembled battery 10. Moreover, priority can be given to the output of the assembled battery 10 according to the operation of the accelerator pedal by the user. Specifically, when the accelerator pedal is operated, the output of the assembled battery 10 can be prioritized.

  Further, in controlling charging / discharging of the assembled battery 10, the controller 40 can prioritize the output of the assembled battery 10. For example, when the SOC of the assembled battery 10 is increasing, the controller 40 can prioritize the output of the assembled battery 10 in order to suppress overcharging of the assembled battery 10. Further, when driving the auxiliary equipment (such as air conditioning equipment) mounted on the vehicle using the output of the assembled battery 10, when the power consumption of the auxiliary equipment increases, the controller 40 outputs the output of the assembled battery 10. Can be prioritized.

  Furthermore, when controlling the charging / discharging of the assembled battery 10, when the temperature of the assembled battery 10 rises, the controller 40 can suppress the temperature rise of the assembled battery 10 by limiting the output of the assembled battery 10. it can. Here, if the temperature of the assembled battery 10 falls, the controller 40 can cancel the output restriction of the assembled battery 10. When the output restriction is released, the output of the assembled battery 10 can be prioritized.

  Thus, if priority is given to the output of the assembled battery 10, the controller 40 determines that the use state of the unit cell 11 is discharge priority. If the use state of the single battery 11 is discharge priority, the controller 40 performs the process of step S302. If the use state of the single battery 11 is not discharge priority, the controller 40 performs the process of step S306. In step S <b> 306, the controller 40 determines that the usage state of the unit cell 11 is charge priority. The charge priority is to give priority to charging the cell 11 over discharging the cell 11.

  Setting that prioritizes charging of the assembled battery 10 can be performed by user input or can be performed under the control of the controller 40. For example, in order to store the regenerative power in the assembled battery 10, the user can make a setting for giving priority to the input of the assembled battery 10. Moreover, the input of the assembled battery 10 can be prioritized according to the operation of the accelerator pedal or the brake pedal by the user. Specifically, when the accelerator pedal is not operated or the brake pedal is operated, the input of the assembled battery 10 can be prioritized.

  Further, in controlling charging / discharging of the assembled battery 10, the controller 40 can prioritize the input of the assembled battery 10. For example, when the SOC of the assembled battery 10 is decreasing, the controller 40 can prioritize the input of the assembled battery 10 in order to suppress overdischarge of the assembled battery 10.

  Furthermore, when controlling the charging / discharging of the assembled battery 10, when the temperature of the assembled battery 10 rises, the controller 40 can suppress the temperature rise of the assembled battery 10 by restricting the input of the assembled battery 10. it can. Here, if the temperature of the assembled battery 10 decreases, the controller 40 can release the input restriction of the assembled battery 10. When the input restriction is canceled, the input of the assembled battery 10 can be prioritized.

  In step S302, the controller 40 estimates the SOC of the single battery 11. Here, as a method for estimating the SOC, the method described in the first embodiment can be used. In step S303, the controller 40 determines whether or not the SOC (estimated SOC) estimated in the process of step S302 is included in a predetermined SOC range.

  Here, the SOC range is the same as the SOC range described in step S104 shown in FIG. Further, when the SOC range is corrected by the process shown in FIG. 8, the corrected SOC range is used in the process of step S302.

  When the estimated SOC is included in the predetermined SOC range, the controller 40 performs the process of step S304. On the other hand, when the estimated SOC is out of the predetermined SOC range, the controller 40 ends the process shown in FIG.

  In step S304, the controller 40 determines whether or not the energization state of the unit cell 11 immediately before is a discharge state. The immediately energized state is as described in the first embodiment. When the immediately energized state is the discharged state, the controller 40 performs the process of step S305. On the other hand, when the immediately energized state is the charged state, the controller 40 ends the process shown in FIG.

  In step S305, the controller 40 charges the single battery 11 before discharging the single battery 11 based on the discharge priority. That is, when the previous energization state is a discharge state and the unit cell 11 is to be discharged, the unit cell 11 is first charged. Thereby, when discharging the cell 11, the immediately energized state becomes the charged state. By charging the cell 11 before discharging the cell 11, it is possible to suppress an increase in resistance value (internal resistance) due to the continuous discharge of the cell 11.

  For example, before discharging the cell 11, the cell 11 can be charged at a predetermined rate for a predetermined time after discharging the cell 11 at a predetermined rate for a predetermined time. Here, the discharge rate and the charge rate of the cell 11 can be made the same. Moreover, the discharge time and charge time of the cell 11 can be made the same. Further, when charging is performed after the discharge of the unit cell 11, the SOC of the unit cell 11 can be changed by 1 [%] or more in each of discharge and charge.

  By making the discharge rate and the charge rate the same, and making the discharge time and the charge time the same, the SOC of the unit cell 11 is not changed even if the process of charging after the unit cell 11 is discharged is performed. Can do.

  When the process proceeds from step S306 to step S307, the controller 40 estimates the SOC of the unit cell 11. Here, the method for estimating the SOC is the same as the method described in the first embodiment. In step S308, the controller 40 determines whether or not the SOC (estimated SOC) estimated in the process of step S307 is included in a predetermined SOC range.

  The predetermined SOC range is the same as the SOC range described in step S303. In addition, when the SOC range is corrected by the process shown in FIG. 8, the corrected SOC range is used in the process of step S308. When the estimated SOC is included in the predetermined SOC range, the controller 40 performs the process of step S309. On the other hand, when the estimated SOC is out of the predetermined SOC range, the controller 40 ends the process shown in FIG.

  In step S309, the controller 40 determines whether or not the energization state of the unit cell 11 immediately before is a charging state. When the immediately energized state is the charged state, the controller 40 performs the process of step S310. On the other hand, when the immediately energized state is the discharged state, the controller 40 ends the process shown in FIG.

  In step S310, the controller 40 discharges the single battery 11 before charging the single battery 11 based on the charge priority. That is, when the previous energized state is a charged state and the unit cell 11 is to be charged, the unit cell 11 is first discharged. Thereby, when charging the cell 11, the immediately energized state becomes the discharged state. By discharging the cell 11 before charging the cell 11, it is possible to suppress an increase in resistance value (internal resistance) associated with the continued charging of the cell 11.

  For example, before charging the cell 11, the cell 11 can be discharged at a predetermined rate for a predetermined time after charging the cell 11 at a predetermined rate for a predetermined time. Here, the charge rate and the discharge rate of the unit cell 11 can be made the same. Moreover, the charging time and discharging time of the unit cell 11 can be made the same. Further, when discharging is performed after charging the cell 11, the SOC of the cell 11 can be changed by 1 [%] or more in each of charging and discharging.

  By making the charging rate and the discharging rate the same, and making the charging time and the discharging time the same, the SOC of the unit cell 11 is not changed even if the discharge process is performed after the unit cell 11 is charged. Can do.

10: assembled battery, 11: single cell, 21: monitoring unit (voltage sensor), 22: current sensor,
23: Temperature sensor, 31: Inverter, 32: Motor generator
40: Controller, 41: Memory, 42: Timer, PL: Positive line,
NL: negative line, SMR-B, SMR-G, SMR-P: system main relay,
R: current limiting resistor, C: capacitor

Claims (9)

A lithium ion secondary battery comprising a compound represented by the following general formula (I) and using a two-phase coexisting positive electrode active material;
A controller for estimating an internal resistance of the lithium ion secondary battery,

In the above formula (I), M represents a trivalent or higher transition metal element.
When the SOC of the lithium ion secondary battery is included in the SOC range in which the two-phase coexistence state is present, the controller charges the internal resistance when the current and immediately before energization state does not change, and the current and immediately before energization state is charged. The battery system is estimated to be higher than the internal resistance when changing between a state and a discharge state.   The controller estimates the internal resistance when the energized state does not change in the discharged state to a value higher than the internal resistance when the energized state changes from the charged state to the discharged state. The battery system described in 1.   The controller estimates the internal resistance when the energized state does not change in the charged state to a value higher than the internal resistance when the energized state changes from the discharged state to the charged state. The battery system described in 1. It has a temperature sensor that detects the temperature of the lithium ion secondary battery,
The controller determines the internal resistance corresponding to the temperature detected by the temperature sensor using information indicating a correspondence relationship between the temperature of the lithium ion secondary battery and the internal resistance. The battery system according to any one of 1 to 3.   5. The battery system according to claim 4, wherein the information indicating the correspondence relationship differs between when the energized state does not change and when the energized state changes.   6. The controller according to claim 1, wherein the controller calculates an overvoltage of the lithium ion secondary battery by multiplying the estimated internal resistance and a current value flowing through the lithium ion secondary battery. The battery system according to any one of the above. A voltage sensor for detecting a closed circuit voltage of the lithium ion secondary battery;
The controller is
By calculating the open circuit voltage of the lithium ion secondary battery by subtracting the calculated overvoltage from the closed circuit voltage detected by the voltage sensor,
The battery system according to claim 6, wherein the SOC corresponding to the calculated open circuit voltage is specified using information indicating a correspondence relationship between the open circuit voltage and the SOC.   The battery system according to any one of claims 1 to 7, wherein the controller widens the SOC range as the full charge capacity of the lithium ion secondary battery decreases. An estimation method for estimating the internal resistance of a lithium ion secondary battery comprising a compound represented by the following general formula (II) and using a two-phase coexisting positive electrode active material,

In the above formula (II), M represents a trivalent or higher transition metal element.
When the SOC of the lithium ion secondary battery is included in the SOC range in which the two-phase coexistence state is established, the internal resistance when the current and immediately before energization state does not change, and the current and immediately before energization state are the charged state and the discharge state An estimation method characterized by estimating to a value higher than the internal resistance when changing between.