JP2013247054A - Battery system and deterioration state determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate determination that the deterioration component occurring due to deviation of the salt concentration has been eliminated.SOLUTION: The battery system includes a secondary battery (10) performing charge and discharge, and a controller (30). The controller determines that a first deterioration component (high rate deterioration) generated due to deviation of the salt concentration in a secondary battery has been eliminated, if the time (τ) when the secondary battery is not charging nor discharging is equal to or longer than a predetermined time (τlim). Furthermore, the controller calculates a resistance increase amount (ΔRa) of a second deterioration component (abrasive deterioration) generated due to abrasion of the secondary battery, and shortens the predetermined time depending on the increase in resistance increase amount.

Description

  The present invention relates to a technology for specifying a deterioration state of a secondary battery, specifically, a deterioration state caused by wear of the secondary battery.

  The deterioration of the secondary battery includes deterioration caused by wear of the secondary battery (referred to as wear deterioration) and deterioration caused by uneven salt concentration inside the secondary battery (referred to as high-rate deterioration). Since the resistance increase of secondary batteries is a mixture of resistance increase due to wear deterioration and resistance increase due to high rate deterioration, in order to specify the resistance increase due to high rate deterioration, the resistance increase due to wear deterioration The amount needs to be specified. That is, by subtracting the amount of increase in resistance associated with wear deterioration from the resistance of the secondary battery, the amount of increase in resistance associated with high rate deterioration can be specified.

  High-rate degradation occurs with an uneven salt concentration, so if the uneven salt concentration is eliminated, the high-rate degradation is eliminated. Here, if the secondary battery is left without being charged / discharged, it is possible to eliminate the uneven salt concentration. If the high-rate deterioration is eliminated, the resistance of the secondary battery corresponds to the resistance increase amount due to wear deterioration, and the resistance increase amount due to wear deterioration can be specified.

JP 2010-060406 A

  The determination of whether or not the high-rate deterioration has been eliminated can take into account the time (referred to as the elimination time) during which the salt concentration unevenness is eliminated. That is, if the time for leaving the secondary battery exceeds the elimination time, it can be determined that the high-rate deterioration has been eliminated. Here, if the maximum time for eliminating the high rate degradation is set as the elimination time by conducting an experiment or the like in advance, by determining that the time for leaving the secondary battery exceeds the elimination time, It can be determined that the degradation has been eliminated.

  However, in order to determine that the high-rate degradation has been eliminated, it is necessary to wait until the time for leaving the secondary battery exceeds the elimination time. As described above, if the maximum time during which high-rate degradation is resolved is set as the resolution time, the opportunity to determine that high-rate degradation has been eliminated decreases. In particular, when the secondary battery is left for a relatively short period of time, when the charge / discharge of the secondary battery is resumed frequently, the time for leaving the secondary battery is less likely to exceed the elimination time, and high-rate deterioration is eliminated. Cannot be determined.

  If it is not possible to determine that high-rate deterioration has been eliminated, the amount of increase in resistance accompanying wear deterioration cannot be calculated, and the amount of increase in resistance accompanying high-rate deterioration is calculated based on the amount of increase in resistance accompanying wear deterioration. Accuracy will be reduced.

  The battery system according to the first invention of the present application includes a secondary battery that performs charging and discharging, and a controller. When the time during which the secondary battery is not charged / discharged is equal to or longer than a predetermined time, the controller determines that the first deterioration component generated due to the uneven salt concentration in the secondary battery is eliminated. In addition, the controller calculates the amount of increase in resistance of the second deterioration component that occurs due to wear of the secondary battery, and shortens the predetermined time according to the increase in the amount of increase in resistance.

  Since the first deterioration component is generated due to the salt concentration unevenness, the first deterioration component can be eliminated if the salt concentration unevenness is alleviated. If the secondary battery is not charged / discharged, the uneven concentration of the salt is alleviated. Therefore, by determining that the time during which the secondary battery is not charged / discharged is a predetermined time or more, the first deterioration component Can be determined.

  In order to suppress an increase in resistance of the secondary battery (including the first deterioration component and the second deterioration component) when the second deterioration component is included in the resistance of the secondary battery, the resistance increase of the second deterioration component is suppressed. It is preferable to suppress the resistance increase amount of the first deterioration component according to the amount. If the resistance increase amount of the first deteriorated component is suppressed, the time until the first deteriorated component is eliminated is shortened, so that the predetermined time used when determining the elimination of the first deteriorated component can be shortened. .

  Therefore, according to the first invention of the present application, in accordance with the increase in the resistance increase amount of the second deterioration component, the opportunity to determine that the first deterioration component has been eliminated is increased by shortening the predetermined time. be able to. If the opportunity to determine that the first deterioration component has been eliminated is increased, the deterioration state of the secondary battery in the state in which the first deterioration component has been eliminated, in other words, the resistance increase amount of the second deterioration component can be easily obtained. Become. If it becomes easy to acquire the resistance increase amount of the second deterioration component, it is possible to acquire the resistance increase amount of the first deterioration component using the most recent resistance increase amount of the second deterioration component, and the resistance of the first deterioration component A highly accurate value can be obtained as the amount of increase.

  By removing the resistance increase amount of the second deterioration component from the upper limit value that allows the resistance increase of the secondary battery, the allowable amount allowing the resistance increase of the first deterioration component can be calculated. Since the resistance increase of the first deterioration component changes within the allowable range, the predetermined time described above may be set based on the allowable amount. For this reason, if the allowable amount decreases, the predetermined time can be shortened.

  When the first deterioration component is eliminated, only the second deterioration component is included in the deterioration state of the secondary battery. Therefore, if the resistance of the secondary battery is calculated, the resistance increase amount of the second deterioration component can be specified. Here, when the secondary battery is not deteriorated, the secondary battery has an initial resistance. For this reason, if the initial resistance is subtracted from the resistance of the current secondary battery, the resistance increase amount of the second deterioration component can be obtained.

  If the resistance change rate of the secondary battery is calculated when the first deterioration component is eliminated, the resistance change rate is a value reflecting only the second deterioration component. Here, the resistance change rate represents the ratio of the resistance of the current secondary battery to the initial resistance of the secondary battery, and the initial resistance is the resistance when the secondary battery is not deteriorated. The resistance change rate increases as the deterioration of the secondary battery progresses. As the resistance change rate when the first deterioration component is eliminated increases, the resistance increase amount of the second deterioration component increases. Therefore, the predetermined time can be shortened as the resistance change rate increases. The opportunity for determining that the first deterioration component has been eliminated can be increased.

  When setting the predetermined time described above, it is possible to consider the capacity retention rate in at least one of the positive electrode and the negative electrode of the secondary battery. The capacity maintenance ratio represents the ratio of the capacity when the second deterioration component is generated to the initial capacity. The initial capacity is a unipolar capacity when the secondary battery is not deteriorated. Since the capacity maintenance ratio depends only on the second deterioration component, even when the first deterioration component is not eliminated, the amount of increase in resistance of the second deterioration component can be grasped by calculating the capacity maintenance ratio. . As the capacity maintenance ratio decreases, the amount of increase in resistance of the second deterioration component increases. Therefore, as the capacity maintenance ratio decreases, the predetermined time described above can be shortened, and the first deterioration component is eliminated. Opportunities that can be identified can be increased.

  A second invention of the present application is a determination method for determining a deterioration state of a secondary battery that performs charge and discharge, and when the time during which the secondary battery is not charged and discharged is a predetermined time or more, It is determined that the first deterioration component generated due to the uneven concentration of salt is eliminated. Here, the amount of increase in the resistance of the second deterioration component generated by the wear of the secondary battery is calculated, and the predetermined time is shortened according to the increase in the amount of increase in resistance. 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.

It is a figure explaining the time which high rate degradation is canceled. It is a figure which shows the relationship between high rate deterioration allowance and leaving time. It is a figure which shows the structure of a battery system. It is a flowchart which shows the process which calculates the elimination time of high rate degradation. It is a flowchart which shows the process which discriminate | determines cancellation | release of high-rate degradation. It is the schematic which shows the structure of a secondary battery. It is a figure explaining the salt concentration distribution of the electrolyte solution in a secondary battery. It is a figure which shows the relationship between the salt concentration of electrolyte solution, and reaction resistance. It is a figure explaining the fall of the salt concentration of the electrolyte solution in an electrode. It is a figure explaining the fall of the salt concentration of the electrolyte solution in an electrode. It is a figure which shows the list of variables etc. which are used with a battery model type | formula. It is a conceptual diagram explaining a battery model. It is a conceptual diagram which shows the active material model shown by the polar coordinate. It is a figure which shows the relationship between the terminal voltage of a secondary battery, and various average electric potential. It is a figure explaining the temperature dependence of a diffusion coefficient. It is a figure which shows the relationship between an open circuit voltage (positive electrode) and local SOC. It is a figure which shows the relationship between an open circuit voltage (negative electrode) and local SOC. It is the schematic which shows the internal structure of a controller. It is a correlation diagram between the salt concentration of the electrolyte solution between electrodes, and an electric current estimation error. It is a flowchart explaining the process of a battery state estimation part. It is a flowchart which shows the process which specifies resistance change rate when the high-rate degradation is eliminated. It is a figure which shows the change of the open circuit potential of a single pole accompanying the reduction | decrease of a single pole capacity. It is a figure explaining the shift | offset | difference of composition correspondence between a positive electrode and a negative electrode. It is a figure explaining the shift | offset | difference of composition correspondence by deterioration. It is a figure explaining the relational expression formed between the average charging rate inside a positive electrode active material, and the average charging rate inside a negative electrode active material. It is a flowchart which shows the search process of a degradation parameter.

  Examples of the present invention will be described below.

  The secondary battery may be deteriorated due to various factors. The deterioration of the secondary battery includes wear deterioration (corresponding to the second deterioration component of the present invention) and high rate deterioration (corresponding to the first deterioration component of the present invention). Included). Examples of the secondary battery include a nickel metal hydride battery and a lithium ion battery. Abrasion degradation is degradation that increases the resistance (internal resistance) of the secondary battery as the material constituting the secondary battery wears over time. High-rate deterioration is deterioration in which the resistance (internal resistance) of the secondary battery is increased due to an uneven salt concentration inside the secondary battery. An uneven salt concentration is likely to occur when, for example, a secondary battery is charged or discharged at a rate equal to or higher than a predetermined value.

  Wear deterioration and high-rate deterioration can be expressed as an increase in resistance of the secondary battery. Here, the amount of increase in resistance associated with wear deterioration is referred to as wear deterioration amount, and the amount of increase in resistance associated with high rate deterioration is referred to as high rate resistance increase amount. The amount of wear deterioration increases with time.

  Since the high rate deterioration occurs due to the salt concentration unevenness, the high rate deterioration can be eliminated if the salt concentration unevenness is alleviated. Here, if the secondary battery is left without being charged / discharged, the reactant (for example, lithium ion in the case of a lithium ion secondary battery) can be diffused to alleviate the uneven concentration of the salt. In the present specification, leaving the secondary battery refers to a state in which the secondary battery is not charged or discharged.

  If the resistance of the secondary battery is calculated in a state where the high-rate deterioration is eliminated, the wear deterioration amount can be acquired (learned). Specifically, the resistance of the secondary battery can be calculated from the current and voltage of the secondary battery. The resistance of the secondary battery is a value obtained by adding the amount of increase in resistance (amount of wear deterioration or amount of increase in high-rate resistance) to the initial resistance of the secondary battery. The amount of wear deterioration can be calculated by subtracting the initial resistance from the amount.

  The initial resistance is the resistance of the secondary battery when no high-rate deterioration or wear deterioration occurs. As the initial resistance, the resistance immediately after manufacturing the secondary battery can be used, and the initial resistance can be obtained in advance. If the wear deterioration amount is learned, the high rate resistance increase amount can be calculated every time the resistance of the secondary battery is calculated. Since the amount of increase in resistance of the secondary battery is the sum of the amount of wear deterioration and the amount of increase in high-rate resistance, if the amount of increase in resistance and wear deterioration of the secondary battery is calculated, the amount of increase in high-rate resistance can be calculated. it can. The amount of increase in resistance of the secondary battery is obtained by subtracting the initial resistance from the current resistance of the secondary battery.

  When learning the amount of wear deterioration, it is only necessary to calculate the amount of increase in resistance of the secondary battery after confirming that high-rate deterioration has been eliminated. Whether or not the high rate deterioration has been eliminated can be determined based on the time during which the secondary battery is left unattended. Specifically, first, a time until the high rate resistance increase amount can be regarded as eliminated (referred to as elimination time) is obtained in advance by an experiment or the like. Then, the time from when the secondary battery starts to be left is measured, and when the measurement time (leaving time) exceeds the elimination time, it can be determined that the high rate deterioration has been eliminated.

  The elimination time can be specified based on an amount that allows an increase in the high-rate resistance (referred to as a high-rate degradation allowable amount). This point will be described with reference to FIG. In FIG. 1, the vertical axis indicates battery resistance, and the horizontal axis indicates time. FIG. 1 shows a state in which the secondary battery is left after charging and discharging of the secondary battery.

  The battery deterioration allowable amount ΔRlim is an upper limit value that can allow the secondary battery to increase in resistance, and is set in advance in consideration of the input / output performance of the secondary battery, the target usage period of the secondary battery, and the like. The battery deterioration allowable amount ΔRlim can be changed according to time. FIG. 1 shows the allowable battery deterioration amount ΔRlim at a specific time.

  Here, when the amount of increase in the resistance of the secondary battery reaches the battery deterioration allowable amount ΔRlim, by restricting the input / output (charge / discharge) of the secondary battery, the amount of increase in the resistance of the secondary battery becomes the battery deterioration allowable amount ΔRlim. Can not be exceeded. By controlling charging / discharging of the secondary battery in this way, the amount of increase in resistance of the secondary battery can be changed within the range of the allowable battery deterioration amount ΔRlim.

  Here, when wear deterioration progresses, the wear deterioration amount only increases. On the other hand, since the high rate deterioration depends on the bias of the salt concentration, the amount of increase in the high rate resistance can be reduced by limiting the input / output of the secondary battery. For this reason, by controlling charging / discharging of the secondary battery, the resistance increase amount of the secondary battery can be changed within the range of the allowable battery deterioration amount ΔRlim.

  When the secondary battery has no wear deterioration, the battery deterioration allowable amount ΔRlim can be used as the high rate deterioration allowable amount. The allowable high rate deterioration amount at this time is ΔRhlim (ini).

  Since the actual increase amount of the high-rate resistance in the secondary battery cannot be accurately grasped, the elimination time is the time τlim (ini) until the high-rate resistance increase amount changes from the battery deterioration allowable amount ΔRlim to 0. be able to. If the elimination time τlim (ini) is set in this way, as long as the actual high-rate resistance increase amount is suppressed within the range of the battery deterioration tolerance ΔRlim, the secondary battery leaving time τlim (ini) It is possible to confirm that the high rate resistance increase amount has been eliminated, in other words, that the high rate deterioration has been eliminated.

  When the wear deterioration does not occur, the high rate deterioration allowable amount may be considered as the battery deterioration allowable amount ΔRlim. However, when the wear deterioration occurs, the high rate deterioration allowable amount ΔRhlim (t0) is greater than the battery deterioration allowable amount ΔRlim. Becomes smaller. As described above, since the battery deterioration allowable amount ΔRlim is set to the upper limit value, when the wear deterioration amount is larger than 0, the high rate deterioration allowable amount ΔRhlim (t0) is limited by the wear deterioration amount ΔRa (t0). Is done. That is, the value obtained by subtracting the wear deterioration amount ΔRa (t0) from the battery deterioration allowance amount ΔRlim becomes the high rate deterioration allowance amount ΔRhlim (t0).

  In FIG. 1, when the wear deterioration amount is ΔRa (t0), the high-rate deterioration allowance amount ΔRhlim (t0) is a value obtained by subtracting the wear deterioration amount ΔRa (t0) from the battery deterioration allowance amount ΔRlim. It is assumed that t0 is the latest timing when the wear deterioration amount is learned, and the wear deterioration amount ΔRa (t0) is learned in advance.

  When the allowable high-rate deterioration amount is ΔRhlim (t0), the high-rate deterioration can be eliminated without leaving the secondary battery for the elimination time τlim (ini) or longer. That is, if the increase rate of the high-rate resistance is reduced from the battery deterioration allowable amount ΔRlim to the wear deterioration amount ΔRa (t0), the high-rate deterioration is eliminated.

  Since the secondary battery resistance increase amount (the sum of the wear deterioration amount and the high rate resistance increase amount) is limited within the range of the battery deterioration allowable amount ΔRlim, when the wear deterioration amount ΔRa (t0) occurs, the high rate is increased. The amount of increase in resistance changes within the range of the high rate deterioration allowable amount ΔRhlim (t0). Therefore, if the high-rate resistance increase amount decreases from the battery deterioration allowable amount ΔRlim to the wear deterioration amount ΔRa (t0), it can be determined that the high-rate deterioration has been eliminated. The time until the high rate resistance increase amount decreases from the battery deterioration allowable amount ΔRlim to the wear deterioration amount ΔRa (t0) is τlim (t0). The elimination time τlim (t0) is shorter than the elimination time τlim (ini).

  Therefore, in this embodiment, the elimination time is changed based on the wear deterioration amount ΔRa (t0). If the elimination time is fixed at τlim (ini), it can be confirmed that the high-rate deterioration has been eliminated by confirming that the leaving time exceeds the elimination time τlim (ini). However, in other words, it cannot be determined that the high-rate deterioration has been eliminated unless the elimination time τlim (ini) has elapsed.

  For example, when charging / discharging of the secondary battery is started between time t11 and time t12 shown in FIG. 1, if τlim (ini) is set as the elimination time, the high rate deterioration is not eliminated. It will be discriminated. If it is determined that the high-rate deterioration has not been eliminated, the wear deterioration amount cannot be learned. In particular, in a situation where charging / discharging of the secondary battery is frequently resumed and it is difficult to secure a time for leaving the secondary battery, it becomes difficult to learn the wear deterioration amount.

  On the other hand, when the elimination time is set to τlim (t0), it can be determined that the high-rate deterioration has been eliminated even when charging / discharging of the secondary battery is started between time t11 and time t12. That is, after the time t11, since the leaving time has already exceeded the elimination time τlim (t0), it is determined that the high rate deterioration has been eliminated. If it can be determined that high-rate deterioration has been eliminated, the amount of wear deterioration can be learned. Thus, when the wear deterioration amount is generated, it is not necessary to leave the secondary battery for the elimination time τlim (ini) or more, and the elimination time τlim (t0) or more corresponding to the wear degradation amount ΔRa (t0), It is only necessary to leave the secondary battery.

  If the wear deterioration amount ΔRa increases, the high rate deterioration allowable amount ΔRhlim decreases. Therefore, the elimination time τlim can be shortened as the allowable high-rate deterioration amount ΔRhlim decreases. FIG. 2 shows the relationship between the high rate deterioration allowable amount ΔRhlim and the standing time.

  When the high-rate degradation allowable amount ΔRhlim is ΔRhlim (ini), the time until the high-rate degradation is eliminated is τlim (ini). As the high rate deterioration allowable amount ΔRhlim decreases, the time until the high rate deterioration is eliminated becomes shorter. When the allowable high-rate deterioration amount ΔRhlim is ΔRhlim (t0), the time until the high-rate deterioration is eliminated is τlim (t0) shorter than τlim (ini).

  If an experiment or the like is performed in advance, as shown in FIG. 2, a correspondence relationship (one example) between the high rate deterioration allowable amount ΔRhlim and the elimination time τlim can be acquired. Since the high-rate deterioration allowable amount ΔRhlim depends on the wear deterioration amount ΔRa, if the wear deterioration amount ΔRa is learned, the elimination time τlim can be specified using the map shown in FIG. According to the map shown in FIG. 2, the elimination time τlim becomes shorter as the high-rate degradation allowable amount ΔRhlim decreases, in other words, as the wear degradation amount ΔRa increases.

  Here, since the resistance of the secondary battery depends on the temperature of the secondary battery and the state of charge (SOC), the high-rate degradation allowable amount ΔRhlim calculated from the resistance of the secondary battery is also equal to the temperature of the secondary battery and the SOC. Depends on. The SOC is a ratio of the current charge capacity to the full charge capacity of the secondary battery. In order to consider the dependency of temperature and SOC, it is preferable to provide the map shown in FIG. 2 for each temperature of the secondary battery and each SOC of the secondary battery.

  As described above, by reducing the elimination time τlim in accordance with the increase in the wear degradation amount ΔRa, it is possible to increase the chance of determining that the high-rate degradation has been eliminated. If the chance of determining that the high-rate deterioration has been eliminated is increased, the chance of learning the wear deterioration amount ΔRa can be increased.

  In order to grasp the current high rate resistance increase amount, it is preferable to grasp the latest wear deterioration amount ΔRa. Since the wear deterioration amount ΔRa increases with the passage of time, if the high rate deterioration allowance is calculated based on the past wear deterioration amount ΔRa, the past wear deterioration amount ΔRa is small, and thus the high rate deterioration allowance amount increases. Further, the secondary battery is used more than the original high rate deterioration allowable amount (high rate deterioration allowable amount corresponding to the latest wear deterioration amount ΔRa).

  If the frequency of learning the wear deterioration amount ΔRa can be increased as in the present embodiment, the latest wear deterioration amount ΔRa can be easily obtained, and the calculation accuracy of the high-rate deterioration allowance amount can be improved.

  Hereinafter, a process for determining whether or not the high rate deterioration has been eliminated will be described. First, the configuration of the battery system that performs this determination processing will be described with reference to FIG. In the battery system of the present embodiment, the secondary battery is mounted on the vehicle, but the present invention is not limited to this. That is, the present invention can be applied to a device using a secondary battery.

  Vehicles on which the battery system of this embodiment is mounted include HV (Hybrid Vehicle), PHV (Plug-in Hybrid Vehicle), and EV (Electric Vehicle). The HV includes other power sources such as an internal combustion engine and a fuel cell in addition to a battery pack described later as a power source for running the vehicle. The PHV is a vehicle that can charge a battery pack using electric power from an external power source in HV. The EV includes only a battery pack as a power source for the vehicle.

  The battery pack 100 includes a plurality of secondary batteries 10 that are electrically connected in series. The number of secondary batteries 10 constituting the battery pack 100 can be appropriately set based on the required output. The monitoring unit 21 detects the voltage between the terminals of the battery pack 100 or detects the voltage Vb between the terminals of the secondary battery 10, and outputs the detection result to the controller 30. The battery pack 100 may include a plurality of secondary batteries 10 electrically connected in parallel.

  The current sensor 22 detects the charge / discharge current Ib flowing through the battery pack 100 and outputs the detection result to the controller 30. Here, the discharge current Ib is a positive value, and the charging current Ib is a negative value. The temperature sensor 23 detects the temperature Tb of the battery pack 100 and outputs the detection result to the controller 30.

  The controller 30 includes a memory 30a, and the memory 30a stores various information for the controller 30 to perform predetermined processing (for example, processing described in the present embodiment). In the present embodiment, the memory 30 a is built in the controller 30, but the memory 30 a may be provided outside the controller 30. Information relating to the ignition switch of the vehicle (on / off information) is input to the controller 30.

  System main relay SMR-B is connected to the positive terminal of battery pack 100. System main relay SMR-B is switched between on and off by receiving a control signal from controller 30. System main relay SMR-G is connected to the negative terminal of battery pack 100. System main relay SMR-G is switched between on and off by receiving a control signal from controller 30.

  A system main relay SMR-P and a limiting resistor 24 are connected in parallel to the system main relay SMR-G. System main relay SMR-P is switched between on and off by receiving a control signal from controller 30. The limiting resistor 24 is used to suppress the inrush current from flowing when the battery pack 100 is connected to a load (specifically, the inverter 31).

  When battery pack 100 is connected to inverter 31, controller 30 first switches system main relay SMR-B from off to on and system main relay SMR-P from off to on. As a result, a current flows through the limiting resistor 24.

  Next, the controller 30 switches the system main relay SMR-P from on to off after switching the system main relay SMR-G from off to on. As a result, the connection between the battery pack 100 and the inverter 31 is completed, and the battery system is activated (Ready-ON). The controller 30 activates the battery system 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 30 switches the system main relays SMR-B and SMR-G from on to off. As a result, the connection between the battery pack 100 and the inverter 31 is cut off, and the battery system enters a stopped state (Ready-OFF).

  The inverter 31 converts DC power from the battery pack 100 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 AC power from the inverter 31 and generates kinetic energy for driving the vehicle. The kinetic energy generated by the motor generator 32 is transmitted to the wheels.

  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 battery pack 100. Thereby, the battery pack 100 can store regenerative electric power.

  In the present embodiment, the battery pack 100 is connected to the inverter 31, but the present invention is not limited to this. Specifically, the battery pack 100 can be connected to the booster circuit, and the booster circuit can be connected to the inverter 31. By using the booster circuit, the output voltage of the battery pack 100 can be boosted. Further, the booster circuit can step down the output voltage from the inverter 31 to the battery pack 100.

  Next, processing for calculating the elimination time τlim will be described with reference to the flowchart shown in FIG. The process shown in FIG. 4 is executed by the controller 30.

  In step S101, the controller 30 acquires the resistance change rate gr when only wear deterioration has occurred. The resistance change rate gr is expressed by the following formula (1).

  In the above formula (1), Ran is the initial resistance of the secondary battery 10, and Ra is the resistance of the secondary battery 10 after use (after charge / discharge). Since the initial resistance Ran can be obtained in advance, the resistance change rate gr can be obtained by calculating the current resistance Ra of the secondary battery 10. Since the resistance changes according to the deterioration over time associated with the use of the secondary battery 10, the resistance Ra becomes higher than the initial resistance Ran. Therefore, the resistance change rate gr is a value larger than 1.

  Here, the resistance change rate gr is a resistance change rate when only wear deterioration occurs, and a method of obtaining the resistance change rate gr will be described later. In step S102, the controller 30 calculates the wear deterioration amount ΔRa based on the resistance change rate gr acquired in the process of step S101. A method for calculating the wear deterioration amount ΔRa will be described later.

  In step S103, the controller 30 calculates a high rate deterioration allowable amount ΔRhlim based on the wear deterioration amount ΔRa calculated in the process of step S102. Specifically, the high rate deterioration allowable amount ΔRhlim can be calculated based on the following equation (2).

  In the above equation (2), ΔRlim indicates the battery deterioration tolerance, and ΔRa indicates the wear deterioration amount. As described above, the allowable battery deterioration amount ΔRlim is the sum of the high rate deterioration allowable amount ΔRhlim and the wear deterioration amount ΔRa, and therefore the high rate deterioration allowable amount ΔRhlim can be calculated by using the above equation (2).

  In step S104, the controller 30 calculates the elimination time τlim based on the high rate deterioration allowance ΔRhlim calculated in the process of step S103. Specifically, by using the map shown in FIG. 2, the elimination time τlim corresponding to the high rate deterioration allowable amount ΔRhlim is calculated. Here, as the resistance change rate gr increases, the wear deterioration amount ΔRa increases and the elimination time τlim decreases.

  Next, processing for determining whether or not high-rate deterioration has been eliminated will be described using the flowchart shown in FIG. The process shown in FIG. 5 is executed by the controller 30 at a predetermined cycle.

  In step S201, the controller 30 determines whether or not the secondary battery 10 is being left. If the secondary battery 10 is left unattended, the controller 30 counts the time τ in step S202. Here, the controller 30 can count the time τ using a timer. When the secondary battery 10 is switched from the energized state (charge / discharge state) to the neglected state, the counting of the time τ is started, and the elapsed time (leaving time τ) when the secondary battery 10 is neglected is measured. be able to. On the other hand, if the secondary battery 10 is not left, the controller 30 performs the process of step S203.

  In step S203, the controller 30 determines whether or not it is immediately after the battery system is activated. Immediately after the battery system is activated is the time until the predetermined time elapses from the timing when the battery system is activated, in other words, from the timing when the ignition switch is switched from OFF to ON. The predetermined time can be set as appropriate.

  Here, when the battery system is started after the standing time τ exceeds the elimination time, only the wear deterioration occurs in the secondary battery 10 immediately after the start, and the high rate deterioration does not occur. Become. On the other hand, the longer the time since startup, the greater the effect of high rate degradation. For this reason, in order to learn the wear deterioration amount ΔRa after determining that the high-rate deterioration has been eliminated, it is preferable to perform it immediately after starting the battery system. In consideration of this point, the predetermined time described above can be determined in advance.

  If the battery system has just started, the controller 30 calculates the elimination time τlim in step S204. The elimination time τlim can be calculated based on the processing shown in FIG. If it is not immediately after the battery system is activated, the controller 30 ends the processing shown in FIG.

  In step S205, the controller 30 determines whether or not the leaving time τ obtained in the process of step S202 is equal to or longer than the elimination time τlim calculated in the process of step S204. When the leaving time τ is equal to or longer than the elimination time τlim, the controller 30 determines in step S206 that the high rate deterioration has been eliminated. On the other hand, when the leaving time τ is shorter than the elimination time τlim, the controller 30 determines that the high-rate deterioration has not been eliminated, and ends the processing shown in FIG. When it is determined that the high-rate deterioration has been eliminated, only the wear deterioration has occurred in the secondary battery 10, and therefore the wear deterioration amount ΔRa is specified by calculating the resistance of the secondary battery 10. can do.

  Next, a method of calculating the high rate resistance increase amount will be described. The amount of increase in the high-rate resistance can be calculated using a battery model described below. First, the battery model will be described.

  FIG. 6 is a schematic diagram showing the configuration of the secondary battery. The secondary battery 10 includes a negative electrode (also referred to as an electrode) 12, a separator 14, and a positive electrode (also referred to as an electrode) 15. The separator 14 is located between the negative electrode 12 and the positive electrode 15 and contains an electrolytic solution. A coordinate axis x shown in FIG. 6 indicates a position in the thickness direction of the electrode.

Each of the negative electrode 12 and the positive electrode 15 is composed of an aggregate of spherical active materials 18. When the secondary battery 10 is discharged, a chemical reaction that releases lithium ions Li ⁺ and electrons e ⁻ is performed on the interface of the active material 18 of the negative electrode 12. Further, a chemical reaction that absorbs lithium ions Li ⁺ and electrons e ⁻ is performed on the interface of the active material 18 of the positive electrode 15.

The negative electrode 12 has a current collector plate 13 made of copper or the like, and the current collector plate 13 is electrically connected to the negative electrode terminal 11 n of the secondary battery 10. The positive electrode 15 has a current collector plate 16 made of aluminum or the like, and the current collector plate 16 is electrically connected to the positive electrode terminal 11 p of the secondary battery 10. The secondary battery 10 is charged and discharged by the exchange of lithium ions Li ⁺ between the negative electrode 12 and the positive electrode 15, and a discharge current Ib (> 0) or a charge current Ib (<0) is generated.

At the time of discharging the secondary battery 10, lithium ions Li ⁺ released from the negative electrode 12 move to the positive electrode 15 by diffusion and migration and are absorbed by the positive electrode 15. At this time, if a delay occurs in the diffusion of lithium ions Li ⁺ in the electrolytic solution, the lithium ion Li ⁺ concentration (that is, the salt concentration of the electrolytic solution) increases in the electrolytic solution in the negative electrode 12. On the other hand, in the electrolytic solution in the positive electrode 15, the lithium ion Li ⁺ concentration decreases. This is shown in FIG. The average salt concentration shown in FIG. 7 is a value when the salt concentration of the electrolytic solution becomes uniform in the entire secondary battery 10. For example, the salt concentration of the electrolytic solution can be made uniform by leaving the secondary battery 10 for a long time.

FIG. 8 shows the relationship between electrolyte salt concentration and reaction resistance. The reaction resistance is a resistance that acts as an electrical resistance equivalently when a reaction current is generated at the interface of the active material 18, in other words, a resistance component related to the entry and exit of lithium ions Li ^{+ on} the electrode surface. Reaction resistance is also called charge transfer resistance.

  According to the characteristic diagram shown in FIG. 8, it can be seen that the reaction resistance is a function of the electrolyte salt concentration. In particular, in the region where the electrolyte salt concentration is higher than the threshold value Cth, the change in the reaction resistance is moderate with respect to the change in the electrolyte salt concentration. Further, in the region where the electrolyte salt concentration is lower than the threshold value Cth, the reaction resistance changes rapidly with respect to the electrolyte salt concentration change. That is, in the region where the electrolyte salt concentration is lower than the threshold value Cth, the rate of change of the reaction resistance value with respect to the electrolyte salt concentration is larger than in the region where the electrolyte salt concentration is higher than the threshold value Cth.

  Considering FIGS. 7 and 8, even when the electrolyte salt concentration in the positive electrode 15 decreases during discharge, when the electrolyte salt concentration in the positive electrode 15 is higher than the threshold value Cth, the reaction resistance decreases. It turns out that it hardly occurs. On the other hand, when the electrolyte salt concentration in the positive electrode 15 is lower than the threshold value Cth, it can be seen that a decrease in the electrolyte salt concentration in the positive electrode 15 causes an increase in reaction resistance.

  As a cause of such an increase in reaction resistance, for example, as shown in FIG. 9A, it is conceivable that the electrolyte salt concentration in the positive electrode becomes lower than the threshold value Cth as the average salt concentration of the electrolyte decreases. . Further, for example, as shown in FIG. 9B, it is conceivable that the electrolyte salt concentration in the positive electrode becomes lower than the threshold value Cth due to the repeated discharge and the cumulative decrease in the electrolyte salt concentration in the positive electrode. . The case where an increase in the reaction resistance occurs due to a decrease in the electrolyte salt concentration in the positive electrode 15 at the time of discharging is illustrated. However, even during charging, a decrease in the electrolyte salt concentration in the negative electrode 12 causes a decrease in the reaction resistance. An increase appears.

The combination of the reaction resistance and the pure electrical resistance (pure resistance) against the movement of electrons e ⁻ at the electrodes 12 and 15 is the battery resistance (internal resistance) when the secondary battery 10 is viewed macroscopically. Corresponds to DC resistance component.

  The basic battery model formula used in the present embodiment is represented by a basic equation consisting of the following formulas (3) to (13). FIG. 10 shows a list of variables and constants used in the battery model formula.

  Regarding the variables and constants in the model formula described below, the subscript e indicates a value in the electrolytic solution, and s indicates a value in the active material. The subscript j distinguishes between the positive electrode and the negative electrode. When j is 1, the value at the positive electrode is indicated. When j is 2, the value at the negative electrode is indicated. When the variables or constants in the positive electrode and the negative electrode are described comprehensively, the suffix j is omitted. In addition, the notation (t) indicating that it is a function of time, the notation (T) indicating the dependency of the battery temperature, the (θ) indicating the dependency of the local SOC θ, and the like are indicated in the specification. Sometimes omitted. The symbol # attached to a variable or constant represents an average value.

  The above formulas (3) and (4) are formulas showing the electrochemical reaction in the electrode (active material), and are called Butler-Volmer formulas.

  The following formula (5) is established as a formula for the conservation law of lithium ion concentration in the electrolytic solution. As an equation relating to the law of conservation of lithium concentration in the active material, the diffusion equation of the following equation (6) and the boundary condition equations shown in the following equations (7) and (8) are applied. The following formula (7) represents the boundary condition at the center of the active material, and the following formula (8) represents the boundary condition at the interface between the active material and the electrolyte (hereinafter also simply referred to as “interface”).

Local SOC θ _j that is a local lithium concentration distribution at the active material interface is defined by the following formula (9). Csej in the following formula (9) indicates the lithium concentration at the active material interface between the positive electrode and the negative electrode, as shown in the following formula (10). Csj, max indicates the limit lithium concentration in the active material.

The following equation (11) is established as an equation relating to the charge conservation law in the electrolytic solution, and the following equation (12) is established as an equation relating to the charge conservation law in the active material. As an electrochemical reaction formula at the active material interface, the following formula (13) showing the relationship between the current density I (t) and the reaction current density j _j ^Li is established.

  The battery model formula represented by the basic equations of the above formulas (3) to (13) can be simplified as described below. The simplification of the battery model formula can reduce the calculation load and the calculation time.

  It is assumed that the electrochemical reaction in each of the negative electrode 12 and the positive electrode 15 is uniform. That is, it is assumed that the reaction in the x direction occurs uniformly in each of the electrodes 12 and 15. In addition, since it is assumed that the reactions in the plurality of active materials contained in the electrodes 12 and 15 are uniform, the active materials of the electrodes 12 and 15 are treated as one active material model. Thereby, the structure of the secondary battery shown in FIG. 6 can be modeled into the structure shown in FIG.

  In the battery model shown in FIG. 11, it is possible to model electrode reactions on the surfaces of the active material model 18p (j = 1) and the active material model 18n (j = 2) during charging and discharging. Further, in the battery model shown in FIG. 11, it is possible to model lithium diffusion (radial direction) in the active material models 18p and 18n and lithium ion diffusion (concentration distribution) in the electrolytic solution. Furthermore, potential distribution and temperature distribution can be modeled in each part of the battery model shown in FIG.

  As shown in FIG. 12, the lithium concentration Cs in each of the active material models 18p and 18n is expressed by the coordinate r in the radial direction of the active material models 18p and 18n (r: the distance from the center of each point, rs: the active material model (Radius) as a function on Here, it is assumed that there is no position dependency in the circumferential direction of the active material models 18p and 18n. The active material model shown in FIG. 12 is used to estimate the lithium diffusion phenomenon inside the active material due to the electrochemical reaction at the interface. For each region (k = 1 to N) divided into N (N: natural number of 2 or more) in the radial direction of the active material models 18p, 18n, the lithium concentration Cs, k (t) is estimated according to the diffusion equation described later. The

  According to the battery model shown in FIG. 11, the basic equations (3) to (8) and (10) can be expressed by the following equations (3 ') to (8') and (10 ').

  In the above formula (5 '), it is assumed that Cej (t) is a constant value by assuming that the concentration of the electrolytic solution is invariable with respect to time. For the active material models 18n and 18p, the diffusion equations (6) to (8) are transformed into the diffusion equations (6 ') to (8') in consideration of only the distribution in the polar coordinate direction. In the above formula (10 '), the lithium concentration Csej at the active material interface corresponds to the lithium concentration Csi (t) in the outermost region of the N-divided region shown in FIG.

  The above equation (11) relating to the law of conservation of electric charge in the electrolysis solution is simplified to the following equation (14) using the above equation (5 ′). That is, the potential φej of the electrolytic solution is approximated as a quadratic function of x. The average potential φej # in the electrolytic solution used for calculation of the overvoltage ηj # is obtained by the following equation (15) obtained by integrating the following equation (14) with the electrode thickness Lj.

  For the negative electrode 12, the following formula (16) is established based on the following formula (14). Therefore, the potential difference between the electrolyte average potential φe2 # and the electrolyte potential at the boundary between the negative electrode 12 and the separator 14 is expressed by the following formula (17). For the positive electrode 15, the potential difference between the electrolyte average potential φe1 # and the electrolyte potential at the boundary between the positive electrode 15 and the separator 14 is expressed by the following formula (18).

  The above formula (12) relating to the law of conservation of charge in the active material can also be simplified to the following formula (19). That is, the potential φsj of the active material is also approximated as a quadratic function of x. The average potential φsj # in the active material used for calculation of the overvoltage ηj # is obtained by the following equation (20) obtained by integrating the following equation (19) with the electrode thickness Lj. Therefore, with respect to the positive electrode 15, the potential difference between the active material average potential φs1 # and the active material potential at the boundary between the active material 18p and the current collector plate 16 is represented by the following formula (21). Similarly, the following formula (22) is established for the negative electrode 12.

FIG. 13 shows the relationship between the terminal voltage V (t) of the secondary battery and each average potential obtained as described above. In FIG. 13, since the reaction current density j _j ^Li is 0 in the separator 14, the voltage drop at the separator 14 is proportional to the current density I (t), and L _s / κ _s ^eff · I (t) Become.

In addition, by assuming that the electrochemical reaction in each electrode is uniform, the current density I (t) per unit area of the electrode plate and the reaction current density (lithium generation amount) j _j ^Li are as follows. Formula (23) is materialized.

  Based on the potential relationship shown in FIG. 13 and the above equation (23), the following equation (24) is established for the battery voltage V (t). The following formula (24) is based on the potential relational formula of the following formula (25) shown in FIG.

Next, an average overvoltage η # (t) is calculated. Assuming that j _j ^Li is constant and the charge / discharge efficiency is the same in the Butler-Bolmer relational expression and αaj and αej are 0.5, the following expression (26) is established. The average overvoltage η # (t) is obtained by the following equation (27) by inversely transforming the following equation (26).

  The average potentials φs1 and φs2 are obtained using FIG. 13, and the obtained values are substituted into the above equation (24). Further, the average overvoltages η1 # (t) and η2 # (t) obtained from the equation (27) are substituted into the equation (25). As a result, a voltage-current relationship model formula (M1a) according to the electrochemical reaction model formula is derived based on the formulas (3 ′), (23) and the formula (4 ′).

  The active material diffusion model equation (M2a) for the active material models 18p and 18n is obtained by the above equation (6 ′) and boundary condition equations (7 ′) and (8 ′) which are the lithium concentration conservation law (diffusion equation). .

  The first term on the right side of the model formula (M1a) represents an open circuit voltage (OCV) determined by the concentration of the reactant (lithium) on the active material surface, and the second term on the right side represents an overvoltage (η1 # − η2 #), and the third term on the right side represents a voltage drop due to the battery current. That is, the DC pure resistance of the secondary battery 10 is represented by Rd (T) in the formula (M1a).

  In the formula (M2a), diffusion coefficients Ds1 and Ds2 used as parameters for defining the diffusion rate of lithium as a reactant have temperature dependence. Therefore, the diffusion coefficients Ds1 and Ds2 can be set using, for example, the map shown in FIG. The map shown in FIG. 14 can be acquired in advance. In FIG. 14, the battery temperature T on the horizontal axis is the temperature acquired using the temperature sensor 23. As shown in FIG. 14, the diffusion coefficients Ds1 and Ds2 decrease as the battery temperature decreases. In other words, the diffusion coefficients Ds1, Ds2 increase as the battery temperature increases.

  Regarding the diffusion coefficients Ds1 and Ds2, not only the temperature dependency but also the local SOC θ dependency may be considered. In this case, a map indicating the relationship between the battery temperature T, the local SOC θ, and the diffusion coefficients Ds1 and Ds2 may be prepared in advance.

  The open circuit voltage U1 included in the above formula (M1a) decreases as the local SOC θ1 increases, as shown in FIG. 15A. Further, as shown in FIG. 15B, open circuit voltage U2 rises as local SOC θ2 rises. If the maps shown in FIGS. 15A and 15B are prepared in advance, the open-circuit voltages U1 and U2 corresponding to the local SOCs θ1 and θ2 can be specified.

  Exchange current densities i01 and i02 included in the above formula (M1a) have dependence on local SOC θ and battery temperature T. Therefore, if a map showing the relationship between exchange current density i01, i02, local SOCθ and battery temperature T is prepared in advance, exchange current density i01, i02 can be specified from local SOCθ and battery temperature T.

  The DC pure resistance Rd has temperature dependence. Therefore, if a map showing the relationship between the DC pure resistance Rd and the battery temperature T is prepared in advance, the DC pure resistance Rd can be specified from the battery temperature T. In addition, about the map mentioned above, it can create based on experimental results, such as the well-known alternating current impedance measurement regarding the secondary battery 10. FIG.

  The battery model shown in FIG. 11 can be further simplified. Specifically, a common active material model can be used as the active material of the electrodes 12 and 15. By treating the active material models 18n and 18p shown in FIG. 11 as one active material model, the following equation (28) can be replaced. In the following formula (28), the suffix j indicating the distinction between the positive electrode 15 and the negative electrode 12 is omitted.

The model formulas (M1a) and (M2a) can be expressed by the following formulas (M1b) and (M2b). In the battery model using one active material model, the following formula (23 ′) is applied instead of the above formula (23) as the relational expression of the current density I (t) and the reaction current density j _j ^Li. The

  The following equation (M1c) is obtained by first-order approximation (linear approximation) of the arcsinh term in the above equation (M1a). By performing linear approximation in this way, it is possible to reduce the calculation load and the calculation time.

  In the above formula (M1c), as a result of the linear approximation, the second term on the right side is also represented by the product of the current density I (t) and the reaction resistance Rr. The reaction resistance Rr is calculated from the exchange current densities i01 and i02 depending on the local SOC θ and the battery temperature T as shown in the above equation (29). Therefore, when the above formula (M1c) is used, a map showing the relationship between the local SOC θ, the battery temperature T, and the exchange current densities i01 and i02 may be prepared in advance. According to the above formula (M1c) and the above formula (29), the above formula (30) is obtained.

  If the arcsinh term of the second term on the right side in the above equation (M1b) is linearly approximated, the following equation (M1d) is obtained.

  Considering the resistance change rate gr shown in the above formula (1), the above formula (M1b) can be expressed as the following formula (M1e).

  The above formula (M1e) is expressed by the following formula (M1f) by performing linear approximation.

  FIG. 16 is a schematic diagram showing the internal configuration of the controller 30. The battery state estimation unit 300 includes a diffusion estimation unit 310, an open-circuit voltage estimation unit 320, a current estimation unit 330, a parameter setting unit 340, and a boundary condition setting unit 350. In the configuration shown in FIG. 16, the battery state estimation unit 300 calculates the current density I (t) by using the above formula (M1f) and the above formula (M2b), and the calculation result is sent to the resistance change rate calculation unit 360. Output.

  In this embodiment, the current density I (t) is calculated using the above formula (M1f), but the present invention is not limited to this. Specifically, the current density I (t) can be calculated based on any combination of the above formulas (M1a) to (M1e) and the above formula (M2a) or (M2b). In this embodiment, since the resistance change rate gr is used, when using the above equations (M1a) to (M1d), the arcsinh term or the term obtained by linear approximation of the arcsinh term in these equations is used. The current density I (t) is multiplied by the resistance change rate gr.

  Diffusion estimation unit 310 calculates the lithium concentration distribution inside the active material based on the boundary condition set by boundary condition setting unit 350 using equation (M2b). The boundary condition is set based on the above formula (7 ') or (8'). Diffusion estimation unit 310 calculates local SOC θ based on the calculated lithium concentration distribution using equation (9). Diffusion estimation unit 310 outputs information on local SOC θ to open-circuit voltage estimation unit 320.

  The open-circuit voltage estimation unit 320 identifies the open-circuit voltages U1 and U2 of the electrodes 12 and 15 based on the local SOC θ calculated by the diffusion estimation unit 310. Specifically, the open-circuit voltage estimation unit 320 can specify the open-circuit voltages U1 and U2 by using the maps shown in FIGS. 15A and 15B. The open-circuit voltage estimation unit 320 can calculate the open-circuit voltage of the secondary battery 10 based on the open-circuit voltages U1 and U2. The open circuit voltage of the secondary battery 10 is obtained by subtracting the open circuit voltage U2 from the open circuit voltage U1.

  Parameter setting unit 340 sets parameters used in the battery model equation according to battery temperature T and local SOC θ. As the battery temperature T, the temperature Tb detected by the temperature sensor 23 is used. The local SOC θ is acquired from the diffusion estimation unit 310. Parameters set by the parameter setting unit 340 include the diffusion constant Ds in the above formula (M2b), the current density i0 in the above formula (M1f), and the DC resistance Rd.

  The current estimation unit 330 calculates (estimates) the current density I (t) using the following formula (M3a). The following formula (M3a) is a formula obtained by modifying the above formula (M1f). In the following formula (M3a), the open circuit voltage U (θ, t) is the open circuit voltage U (θ) estimated by the open circuit voltage estimation unit 320. The voltage V (t) is the battery voltage Vb acquired using the monitoring unit 21. Rd (t) and i0 (θ, T, t) are values set by the parameter setting unit 340. In the following formula (M3a), gr is the resistance change rate gr calculated by the resistance change rate calculation unit 360.

  Note that even when any one of the above formulas (M1a) to (M1e) is used, the current density I (t) can be calculated by the same method as the above formula (M3a).

The boundary condition setting unit 350 calculates the reaction current density (lithium generation amount) j _j ^Li from the current density I (t) calculated by the current estimation unit 330 using the above formula (23) or (23 ′). . Then, the boundary condition setting unit 350 updates the boundary condition in the equation (M2b) using the equation (8 ′).

  The resistance change rate estimation unit 360 calculates the resistance change rate gr represented by the above equation (31).

  Resistance Ra changes in accordance with changes in local SOC θ and battery temperature T. Therefore, by performing an experiment using the secondary battery 10 in the initial state, a map showing the relationship between the resistance Ra, the local SOC θ, and the battery temperature T can be acquired in advance. This map can be stored in the memory 30a. The resistance Ra changes not only due to changes in the local SOC θ and the battery temperature T but also due to aging due to use (charging / discharging) of the secondary battery 10.

  The resistance change rate calculation unit 360 calculates the resistance change rate gr using the following equation (31). The resistance change rate calculation unit 360 outputs information regarding the calculated resistance change rate gr to the current estimation unit 330, the determination unit 370, and the resistance increase amount estimation unit 390.

  In the above formula (31), the open circuit voltage U (θ) is a value estimated by the open circuit voltage estimation unit 320, and V (t) is the battery voltage Vb obtained from the monitoring unit 21. Ran is a value specified from a map indicating the relationship between the battery temperature T, the local SOC θ, and the resistance Ra by specifying the battery temperature T and the local SOC θ. The current density I (t) is a value obtained by dividing the current value Ib measured by the current sensor 22 by the unit electrode plate area.

  The determination unit 370 includes a timer 371 and determines whether or not the high-rate resistance increase has been eliminated. The determination unit 370 performs the processing described with reference to FIGS. Information regarding the on / off of the ignition switch is input to the determination unit 370, and when the ignition switch is switched from on to off, the determination unit 370 determines that the secondary battery 10 is left unattended.

  The storage unit 380 stores a resistance change rate gr (hereinafter referred to as gr (t0)) when the high-rate resistance increase is eliminated. The resistance change rate gr (t0) is a value calculated by the resistance change rate calculation unit 360. The resistance increase amount estimation unit 390 calculates (estimates) the high rate resistance increase amount ΔRh.

  There is an error between the current density (referred to as estimated current density) I (t) estimated by the current estimation unit 330 and the current density (referred to as measured current density) I (t) obtained from the measured current Ib of the current sensor 21. When this occurs, a high rate resistance rise occurs. The estimated current density I (t) and the measured current density I (t) are current densities obtained at the same timing. The occurrence of high rate resistance rise will be described below.

  The battery model described above is derived on the assumption that all current flows through the active material 18 and participates in the electrochemical reaction. However, in actuality, particularly when the temperature is low, an electric double layer capacitor is generated at the interface between the electrolyte and the active material, so that the battery current is an electrochemical reaction current component involved in the electrochemical reaction and the capacitor flowing through the capacitor. The current component may be shunted. In this case, it is preferable to construct the battery model equation so that the capacitor current component is separated from the electrochemical reaction current component.

In the above-described basic battery model, lithium ion Li ⁺ in the reaction at the surface of the electrodes 12 and 15, the lithium ion Li ⁺ diffusion in the active material 18 of the electrodes 12, 15, and the lithium ion Li ⁺ diffusion in the electrolyte Has been modeled. On the other hand, the simplified battery model applied to the battery state estimation unit 300 is based on the assumption that the reaction in the electrode thickness direction is uniform in the basic battery model. It is configured under the assumption that the concentration of lithium ion Li ⁺ is constant.

If the lithium ion Li ⁺ concentration in the electrolyte, ie, the salt concentration of the electrolyte, is sufficiently high, the above assumptions in the simplified battery model can be satisfied. When the salt concentration of the electrolytic solution is sufficiently high, even if the salt concentration of the electrolytic solution in the electrode changes due to charge / discharge, the influence of the change in the salt concentration on the reaction resistance is small. Therefore, the current density I (t) can be estimated with high accuracy.

  On the other hand, the above assumption in the simplified battery model does not take into account the increase in reaction resistance that occurs when the salt concentration of the electrolyte in the electrode is low. This increase in reaction resistance is called high-rate resistance increase. For this reason, an error occurs between the current density I (t) estimated by the simplified battery model and the current density corresponding to the detected current Ib by the current sensor 22. Considering this point, it is possible to estimate the high-rate resistance increase (index) based on the current density error. For example, by simplifying the diffusion equation of the salt concentration (lithium ion concentration) of the electrolytic solution, the salt concentration change in the electrolytic solution in the electrode can be estimated by the following equations (32) and (33).

In the above formulas (32) and (33), ΔCe is the difference between the salt concentration of the electrolytic solution in the negative electrode and the salt concentration of the electrolytic solution in the positive electrode (see FIG. 7). Deff is the effective diffusion coefficient of the electrolytic solution, εe is the volume fraction of the electrolytic solution, t ₊ ⁰ is the transport number of lithium ion Li ⁺ , and F is the Faraday constant. Δt is a time interval (time increment) for performing the current density estimation process, and Δx is a diffusion distance (see FIG. 7). T is the battery temperature and I (t) is the current density.

  For example, when the secondary battery 10 is discharged, the salt concentration difference ΔCe is the sum of the amount of increase in the salt concentration at the negative electrode and the amount of decrease in the salt concentration at the positive electrode, as shown in FIG. The amount of increase and decrease in salt concentration is the amount of change with respect to the average salt concentration.

  Correlation between the salt concentration difference ΔCe of the electrolyte between the electrodes estimated by the above formulas (32) and (33) and the current estimation error (Im−Ir) (Im is the estimated current density and Ir is the measured current density) Is shown in FIG. According to FIG. 17, the current estimation error tends to increase when the salt concentration difference ΔCe increases.

  Therefore, the value of the current estimation error (Im−Ir) when the salt concentration difference ΔCe is large can be used as the high rate resistance increase amount. Here, as a condition that the salt concentration difference ΔCe is large, for example, a condition that the value of the salt concentration difference ΔCe is greater than or equal to a predetermined value set in advance, or a value of the salt concentration difference ΔCe is set in advance. There is a condition that it exists within a predetermined range. In this embodiment, the difference between the estimated current density Im and the measured current density Ir is used. However, the present invention is not limited to this, and the ratio of the estimated current density Im and the measured current density Ir can also be used.

  The current estimation error (Im-Ir) occurs in the region where the salt concentration difference ΔCe is large. The increase in the battery resistance caused by the decrease in the salt concentration of the electrolyte in the electrode is caused by the actual secondary battery. 10 and the battery model are considered to be different. On the other hand, the voltage change amount ΔV due to the increase in battery resistance is equal between the actual secondary battery 10 and the battery model. For this reason, the following equation (34) is established, where Rr is an increase in battery resistance that actually appears and Rm is an increase in battery resistance in the battery model.

  In this embodiment, the following formula (35) is defined in relation to the above formula (34).

  ΔV (t1) indicates a voltage drop amount of the secondary battery 10. Ir (t1) is the current density obtained from the detected current Ib by the current sensor 22, and Rr (t1) is the battery resistance when the detected current Ib is obtained. Im (t1) is a current density I (t) estimated by the current estimation unit 330, and Rm (t1) is a battery resistance corresponding to the current density I (t) estimated by the current estimation unit 330. . Im (t0) is a current density when the high-rate resistance increase is eliminated by leaving the secondary battery 10 left, and Rm (t0) is a battery resistance corresponding to the current density Im (t0).

  In the above equation (35), the relationship of the following equation (36) is established.

  In the above formula (36), the battery resistance Rm (t1) may include a high rate resistance increase amount, and the battery resistance Rm (t1) is the battery resistance Rm ( higher than t0).

  According to the above formula (M1f), the above formula (35) can be expressed by the following formula (37).

  In the above equation (37), the value (I × Rd) relating to the component that does not affect the increase in the high-rate resistance is omitted. Further, it is assumed that the temperature T (t0) is the temperature T (t1). Assuming this, the equation (37) is expressed by the following equation (38).

  The above equation (38) can be transformed into the following equation (39).

  According to the above equation (39), if the resistance change rates gr (t1) and gr (t0) are calculated and the current density I (t1) is estimated by the current estimation unit 330, a high-rate resistance increase has occurred. The current density I (t0) when there is no current can be estimated.

  The deterioration of the secondary battery 10 can be divided into wear deterioration and high rate deterioration. Therefore, as shown by the following formula (40), the high rate resistance increase amount ΔRh includes the resistance Rr of the secondary battery 10 in which high rate deterioration and wear deterioration have occurred, and the resistance Rs of the secondary battery 10 in which only wear deterioration has occurred. It is equivalent to the difference.

  When the battery current Ir is multiplied by both sides of the above formula (40), the voltage drop amount ΔVhr due to the high rate resistance rise can be calculated as shown in the following formula (41).

  Assuming that the estimated resistance Rm calculated from the estimated current density Im is small and can be ignored, the resistance Rs can be regarded as the estimated resistance Rm. Therefore, the above formulas (40) and (41) are expressed by the following formulas (42) and (43).

  On the other hand, since the increase in the high-rate resistance can be observed as an error between the estimated current Im and the measurement current Ir, the voltage drop amount ΔVhm accompanying the increase in the high-rate resistance is expressed by the following formula (44).

  In the above equation (44), ΔI is a current estimation error.

  Assuming that the voltage drop amount ΔVhr as the measured value is equal to the voltage drop amount ΔVhm as the estimated value, the following equation (45) is obtained from the above equations (42) to (44).

  The following formula (46) is obtained from the above formula (45).

  Moreover, if the said Formula (35) is used, high rate resistance raise amount (DELTA) Rh (t1) can be represented by a following formula (47).

  The correction coefficient ξ included in the equation (47) is expressed by the following equation (48).

  According to the above equation (48), no high-rate resistance increase has occurred based on the resistance change rates gr (t1), gr (t0) and the current density Im (t1) estimated by the current estimation unit 330. Current density Im (t0). If the current density Im (t0) is calculated, the battery resistance Rm (t0) can be calculated (estimated) based on the above equation (35). That is, the battery resistance Rm (t0) can be calculated by dividing the voltage drop amount ΔV (t1) by the current density Im (t0).

  If the current density Im (t0) and the battery resistance Rm (t0) can be calculated, the high rate resistance increase ΔRh (t1) can be calculated using the above equation (47).

  On the other hand, as shown in the following formula (49), the high rate resistance increase rate γ can be defined. The high rate resistance increase rate γ can be used to evaluate the high rate resistance increase.

  As a method for evaluating the high rate resistance increase using the high rate resistance increase rate γ, for example, an allowable value γlim is set, and when the high rate resistance increase rate γ exceeds the allowable value γlim, a high rate resistance increase occurs. Can be determined. The allowable value γlim is set based on the high rate resistance increase amount ΔRh (t1) and the battery resistance Rm (t0) when no high rate resistance increase occurs. Battery resistance Rm (t0) corresponds to resistance due to wear deterioration. Here, in consideration of the life of the secondary battery 10, if the resistance due to wear deterioration and the high rate resistance increase ΔRh (t1) are determined in advance, the allowable value γlim can be set.

  Further, when the high rate resistance increase rate γ exceeds the allowable value γlim, it can be determined that the deterioration due to the high rate resistance increase has occurred. When deterioration due to the increase in the high-rate resistance occurs, the input / output of the secondary battery 10 can be limited. As a case where input / output of the secondary battery 10 is restricted, at least one control parameter can be restricted among voltage, current, and power. Since the method of restricting input / output is well known, detailed description thereof is omitted.

  On the other hand, by setting the cancellation value γa, it can also be determined whether or not the increase in the high-rate resistance has been canceled. The cancellation value γa is a value lower than the allowable value γlim, and can be determined in advance.

  As shown in the above equation (49), by defining the high rate resistance increase rate γ, the high rate resistance increase rate γ can be calculated simply by obtaining the current densities Im (t1) and Ir (t1). Compared with the case of calculating the high rate resistance increase amount ΔRh, the calculation load can be reduced.

  Next, the process of the battery state estimation part 300 is demonstrated using the flowchart shown in FIG. The process shown in FIG. 18 is executed at a predetermined cycle.

  The battery state quantity estimation unit 300 acquires the battery voltage Vb based on the output of the monitoring unit 21 in step S301, and acquires the battery temperature Tb based on the output of the temperature sensor 23 in step S302.

  In step S303, battery state estimation unit 300 (diffusion estimation unit 310) calculates local SOC θ based on the lithium concentration distribution at the time of the previous calculation using equation (M2b). In step S304, battery state estimation unit 300 (open voltage estimation unit 320) calculates open voltage U (θ) from local SOC θ obtained in step S303.

  In step S305, the battery state estimation unit 300 (current estimation unit 330) calculates (estimates) the current density Im (t) using the above formula (M1f). For the estimated current density Im (t), the battery voltage Vb, the open circuit voltage U (θ) obtained in step S304, and the parameter value set by the parameter setting unit 340 are substituted into the above equation (M3a). Obtained by.

  If the estimated current density Im (t) (same as Im (t1)) is obtained, the estimated resistance Rm (t1) can be calculated using the above equation (35). The resistance change rate calculation unit 360 calculates the resistance change rate gr by using the detected current Ib from the current sensor 22 and the above equation (31). Specifically, in the above formula (31), the value estimated by the open-circuit voltage estimation unit 320 is used as the open-circuit voltage U (θ), and the battery voltage Vb acquired from the monitoring unit 21 is used as the voltage V (t). be able to. Further, the resistance Ran can be specified from the battery temperature Tb and the local SOC θ by using a map showing the relationship between the battery temperature Tb, the local SOC θ and the resistance Ran. As the current density I (t), the current density I (t) specified from the detection current Ib by the current sensor 22 can be used.

In step S306, the battery state estimation unit 300 (boundary condition setting unit 350) calculates the reaction current density (lithium generation amount) j _j ^Li from the estimated current density I (t) obtained in step S305. Moreover, the battery state estimation part 300 (boundary condition setting part 350) sets the boundary condition (active material interface) in the active material interface of said Formula (M2b) using the calculated reaction current density.

  In step S307, the battery state estimation unit 300 (diffusion estimation unit 310) calculates the lithium ion concentration distribution inside the active material model using the above formula (M2b), and calculates the estimated value of the lithium ion concentration in each region. Update. Here, the lithium ion concentration (updated value) in the outermost peripheral region is used for calculating the local SOC θ in step S303 when the process shown in FIG. 18 is performed next time.

  Next, the learning process of the resistance change rate gr will be described with reference to the flowchart shown in FIG. The process illustrated in FIG. 19 is performed by the determination unit 370 when the ignition switch is switched from off to on.

  In step S401, the determination unit 370 measures the time t2 using the timer 371 from the timing when the ignition switch is switched from OFF to ON. In step S402, the determination unit 370 determines whether or not the measurement time t2 acquired in step S401 exceeds the allowable time ta. The allowable time ta is a time during which the influence of the high-rate resistance rise can be ignored, and can be set in advance. In the time zone immediately after the ignition switch is turned on, it is difficult for the high-rate resistance to increase, so this time zone is set as the allowable time ta. Information regarding the allowable time ta can be stored in the memory 30a in advance, and the determination unit 370 can read information regarding the allowable time ta from the memory 30a.

  When the measurement time t2 is shorter than the allowable time ta, the determination unit 370 stores the resistance change rate gr (t0) calculated by the resistance change rate calculation unit 360 in the storage unit 380 in step S403. The determination unit 370 acquires the resistance change rate gr from the resistance change rate calculation unit 360. When the measurement time t2 is shorter than the allowable time ta, the determination unit 370 stores the resistance change rate gr acquired from the resistance change rate calculation unit 360. Store in 380.

  When the measurement time t2 is longer than the allowable time ta, the determination unit 370 ends the process without storing the resistance change rate gr in the storage unit 380. When the measurement time t2 is longer than the allowable time ta, the resistance change rate gr (t1) calculated by the resistance change rate calculation unit 360 is output to the resistance increase amount estimation unit 390.

  In the process in step S101 of FIG. 4, the controller 30 (determination unit 370) acquires the resistance change rate gr (t0) stored in the storage unit 380. The storage unit 380 stores the latest resistance change rate gr (t0) acquired, and the determination unit 370 can acquire the latest resistance change rate gr (t0). Since the resistance change rate gr (t0) stored in the storage unit 380 is the resistance change rate when the high-rate deterioration is eliminated, the wear deterioration amount ΔRa can be calculated from the resistance change rate gr (t0). .

  Here, a method of calculating the wear deterioration amount ΔRa from the resistance change rate gr (t0) (processing in step S102 in FIG. 4) will be described. According to the above formula (M1f), the resistance Rm of the secondary battery 10 is represented by the following formula (50).

  By using the resistance change rate gr (t0) when the high rate deterioration is eliminated as the resistance change rate gr shown in the above equation (50), the resistance Rm (t0) where the high rate degradation is eliminated can be calculated. . Since the resistance Rm (t0) includes the initial resistance Rini, the wear deterioration amount ΔRa is calculated by subtracting the initial resistance Rini from the resistance Rm (t0) as shown in the following equation (51). be able to.

  Here, as shown in the above formula (50), the resistance Rm depends on the temperature and the local SOC θ. Therefore, when calculating the wear deterioration amount ΔRa, the temperature and the SOC are set in the resistance Rm (t0) and the initial resistance Rini. It is preferable to align. If the wear deterioration amount ΔRa is calculated, as described with reference to FIG. 4, the high rate deterioration allowable amount ΔRhlim can be calculated, or the elimination time τlim can be calculated.

  On the other hand, the resistance increase amount estimation unit 390 calculates the resistance change rate gr (t0) stored in the storage unit 380 and the resistance change rate gr (t1) obtained from the resistance change rate calculation unit 360 from the above equation (48). By substituting into, the correction coefficient ξ is calculated. Further, the resistance increase amount estimation unit 390 calculates the estimated current density Im (t0) from the correction coefficient ξ and the estimated current density Im (t1) using the above equation (48). If the estimated current density Im (t0) is calculated, the estimated resistance Rm (t0) can be calculated from the above equation (35).

  The resistance increase amount estimation unit 390 calculates the high rate resistance increase amount ΔRh (t1) using the above equation (47). Specifically, the amount of increase in the high-rate resistance is calculated by substituting the measured current density Ir (t1), the estimated current density Im (t1), the correction coefficient ξ, and the estimated resistance Rm (t0) into the equation (47). ΔRh (t1) can be calculated.

  According to the present embodiment, the high rate resistance increase amount ΔRh included in the resistance increase amount Rr of the secondary battery 10 can be specified by using the formula (47). Here, according to the above formula (42) or (47), the battery resistance Rm when no increase in the high-rate resistance occurs is used, but there is a possibility that the battery resistance Rm includes the amount of increase in the high-rate resistance. is there.

  Therefore, in this embodiment, by using the correction coefficient ξ, the current density Im (t0) and the resistance Rm (t0) when the high rate resistance increase does not occur can be specified, and the high rate resistance increase amount ΔRh can be specified. The estimation accuracy can be improved. Specifically, by using the ratio (correction coefficient ξ) between the resistance change rate gr when the high rate resistance increase does not occur and the resistance change rate gr when the high rate resistance increase occurs, the current density is obtained. Im (t1) and battery resistance Rm (t1) can be converted into current density Im (t0) and battery resistance Rm (t0) when no high-rate resistance increase occurs.

  In this embodiment, Im is the estimated current density and Ir is the measured current density, but the present invention is not limited to this. The current value obtained by multiplying the estimated current density by the electrode surface area may be Im, and the measured current value may be Ir.

  In this embodiment, the correction coefficient ξ is calculated using the resistance change rates gr (t1) and gr (t0), but the present invention is not limited to this. As shown in the following formula (52), the correction coefficient ξ can also be calculated using the resistance change rate and the capacity maintenance rate.

  The capacity maintenance ratio is a value obtained by dividing the capacity of a single electrode in a deteriorated state by the capacity of a single electrode in an initial state. When the secondary battery deteriorates, the capacity of the single electrode is reduced from the capacity in the initial state.

  The capacity retention rate k1 of the positive electrode is represented by the following formula (53).

  Here, Q1_ini is the capacity of the positive electrode 15 when the secondary battery 10 is in the initial state, and can be specified in advance through experiments or the like. ΔQ1 is an amount by which the capacity of the positive electrode 15 decreases with deterioration. The capacity maintenance ratio k1 can be calculated by comparing the full charge capacity after deterioration with the full charge capacity in the initial state.

  The capacity retention rate k2 of the negative electrode is represented by the following formula (54).

  Here, Q2_ini is the capacity of the negative electrode 12 when the secondary battery 10 is in the initial state, and can be specified in advance by experiments or the like. ΔQ2 is an amount by which the capacity of the negative electrode 12 decreases with deterioration. The capacity maintenance rate k2 can be calculated by comparing the full charge capacity after deterioration with the full charge capacity in the initial state.

  Regarding the capacity retention ratio k shown in the above formula (52), the capacity retention ratio in at least one of the positive electrode 15 and the negative electrode 12 can be considered. On the other hand, when considering the capacity retention ratio k, the above equation (50) can be expressed by the following equation (55).

  In the above formula (55), the resistance change rate gr (t0) obtained when the high-rate deterioration was eliminated as the resistance change rate gr, and the resistance change rate gr (t0) was obtained as the capacity maintenance rate k. If the capacity retention ratio at the time is used, the resistance Rm and the wear deterioration amount ΔRa of the secondary battery 10 when the high rate deterioration is eliminated can be obtained.

  According to the above equation (50), the resistance Rm (t0) and the wear deterioration amount ΔRa cannot be calculated unless the resistance change rate gr (t0) is learned. Since the resistance change rate gr depends on the high rate deterioration, if the high rate deterioration is not eliminated, the resistance Rm (t0) and the wear deterioration amount ΔRa can be calculated based on the resistance change rate gr (t0). Can not. On the other hand, the capacity maintenance rate k does not depend on the high rate deterioration but depends on the wear deterioration. Therefore, even if the high rate deterioration is not eliminated, the capacity maintenance rate k corresponding to the wear deterioration can be learned.

  Therefore, according to the above equation (55), even if the resistance change rate gr (t0) cannot be learned, the resistance Rm reflecting the capacity maintenance rate k can be calculated by learning the capacity maintenance rate k. it can. Thereby, the wear deterioration amount ΔRa calculated from the above equations (55) and (51) is made closer to the actual wear deterioration amount than the wear deterioration amount ΔRa calculated from the above equations (50) and (51). Thus, the estimation accuracy of the wear deterioration amount ΔRa can be improved.

  Here, as the wear deterioration progresses, the capacity retention rate k decreases. Therefore, according to the above formula (55), the resistance Rm and the wear deterioration amount ΔRa increase according to the decrease in the capacity retention rate k. Become. As described above, if the wear deterioration amount ΔRa is increased, the elimination time τlim is shortened. Therefore, the elimination time τlim is shortened as the capacity maintenance rate k is decreased.

  Here, a method for estimating the capacity maintenance rates k1 and k2 will be described.

  Regarding the wear deterioration of the secondary battery 10, two phenomena can be considered. The two phenomena are a decrease in single electrode capacity at the positive electrode and the negative electrode, and a corresponding shift in composition between the positive electrode and the negative electrode. The decrease in single electrode capacity indicates a decrease in lithium ion acceptance ability in each of the positive electrode and the negative electrode. A decrease in lithium ion acceptance capacity means a decrease in active materials and the like that function effectively for charge and discharge.

  The open potential shown in FIG. 20 includes the positive electrode open potential U11 and the negative electrode open potential U21 when the secondary battery 10 is in the initial state (the state in which the secondary battery 10 is not deteriorated), and the positive electrode open when the secondary battery 10 is in the deteriorated state. The potential U11 and the negative electrode open potential U21 are shown. FIG. 20 schematically shows a change in the unipolar open potential due to a decrease in the unipolar capacity.

In Figure 20, Q_L1 in the axis of the positive electrode capacity in the initial state of the secondary battery 10, a capacity corresponding to theta _L local SOC shown in FIG. 15A. Q_H11 is a capacity corresponding to θ _H of the local SOC shown in FIG. 15A in the initial state of the secondary battery 10. Further, Q_L2 on the axis of the negative electrode capacity is a capacity corresponding to θ _L of the local SOC shown in FIG. 15B in the initial state of the secondary battery 10, and Q_H21 is in the initial state of the secondary battery 10 in FIG. 15B. This is the capacity corresponding to the local SOC θ _H.

  In the positive electrode, when the capacity for receiving lithium ions decreases, the capacity corresponding to the local SOC θ changes from Q_H11 to Q_H12. Further, when the lithium ion receiving ability is reduced in the negative electrode, the capacity corresponding to the local SOC θ changes from Q_H21 to Q_H22.

  Even if the secondary battery 10 deteriorates, the relationship between the local SOC θ1 and the positive electrode open potential U1 (the relationship shown in FIG. 15A) does not change. Therefore, when the relationship between the local SOC θ1 and the positive electrode open potential U1 is converted into the relationship between the positive electrode capacity and the positive electrode open potential, a curve indicating the relationship between the positive electrode capacity and the positive electrode open potential is shown in FIG. Therefore, the amount of the deterioration is reduced with respect to the initial curve.

  Also, when the relationship between the local SOC θ2 and the negative electrode open potential U2 is converted into the relationship between the negative electrode capacity and the negative electrode open potential, a curve indicating the relationship between the negative electrode capacity and the negative electrode open potential is shown in FIG. The amount of deterioration is reduced with respect to the initial curve.

  FIG. 21 schematically shows a shift in composition correspondence between the positive electrode and the negative electrode. The deviation corresponding to the composition means that the combination of the composition of the positive electrode (θ1) and the composition of the negative electrode (θ2) is deviated from the initial state of the secondary battery 10 when charging and discharging are performed using the pair of the positive electrode and the negative electrode. It shows that it is.

  The curves showing the relationship between the monopolar compositions θ1 and θ2 and the open circuit potentials U1 and U2 are the same as the curves shown in FIGS. 15A and 15B. Here, when the secondary battery 10 deteriorates, the axis of the negative electrode composition θ2 shifts by Δθ2 in the direction in which the positive electrode composition θ1 decreases. As a result, the curve indicating the relationship between the negative electrode composition θ2 and the negative electrode open-circuit potential U2 shifts in the direction in which the positive electrode composition θ1 becomes smaller than the curve in the initial state by Δθ2.

The composition of the negative electrode corresponding to the composition θ1fix of the positive electrode is “θ2fix_ini” when the secondary battery 10 is in the initial state, but becomes “θ2fix” after the secondary battery 10 is deteriorated. In FIG. 21, the negative electrode composition θ _L shown in FIG. 15B is set to 0, which indicates a state in which all lithium ions in the negative electrode are removed. In FIG. 21, the composition (θ2) of the negative electrode is shifted with respect to the composition (θ1) of the positive electrode, but this is not restrictive. That is, due to the deterioration of the secondary battery 10, the composition of the positive electrode (θ1) and the composition of the negative electrode (θ2) are relatively shifted.

  In this embodiment, the above-described two deterioration phenomena are modeled by introducing three deterioration parameters into the battery model. As the three deterioration parameters, a positive electrode capacity retention ratio (also referred to as a single electrode capacity retention ratio), a negative electrode capacity retention ratio (also referred to as a single electrode capacity retention ratio), and a composition correspondence shift amount are used. A method for modeling two deterioration phenomena will be described below.

  FIG. 22 is a schematic diagram for explaining a shift in composition correspondence between the positive electrode and the negative electrode.

  When the secondary battery 10 is deteriorated, the capacity when the negative electrode composition θ2 is 1 is (Q2_ini−ΔQ2). The composition-corresponding deviation capacity ΔQs between the positive electrode and the negative electrode is a capacity corresponding to the deviation amount Δθ2 of the negative electrode composition axis with respect to the positive electrode composition axis. Thereby, the relationship of the following formula (56) is established.

  The following formula (57) is obtained from the above formula (54) and the above formula (56).

  When the secondary battery 10 is in the initial state, the positive electrode composition θ1fix_ini corresponds to the negative electrode composition θ2fix_ini. When the secondary battery 10 is in a deteriorated state, the positive electrode composition θ1fix corresponds to the negative electrode composition θ2fix. Further, the deviation in correspondence with the composition is based on the positive electrode composition θ1fix in the initial state. That is, the positive electrode composition θ1fix and the positive electrode composition θ1fix_ini have the same value.

  When the secondary battery 10 deteriorates and the composition correspondence shifts between the positive electrode and the negative electrode, the positive electrode composition θ1fix and the negative electrode composition θ2fix after deterioration of the secondary battery 10 are expressed by the following formulas (58) and (59). Have the relationship.

  The meaning of the above formula (59) will be described. When the positive electrode composition θ1 changes (decreases) from 1 to θ1fix due to deterioration of the secondary battery 10, the amount A of lithium ions released from the positive electrode is expressed by the following formula (60).

  In the above formula (60), the value of (1-θ1fix) indicates the change in the positive electrode composition due to the deterioration of the secondary battery 10, and the value of (k1 × Q1_ini) is the positive electrode capacity after the deterioration of the secondary battery 10. Is shown.

  If all the lithium ions released from the positive electrode are taken into the negative electrode, the negative electrode composition θ2fix is expressed by the following formula (61).

  In the above formula (61), the value of (k2 × Q2_ini) indicates the negative electrode capacity after deterioration of the secondary battery 10.

  On the other hand, when there is a composition correspondence shift (Δθ2) between the positive electrode and the negative electrode, the negative electrode composition θ2fix is expressed by the following formula (62).

  The shift amount Δθ2 corresponding to the composition can be expressed using the shift capacity ΔQs corresponding to the composition by the above formula (57). Accordingly, the negative electrode composition θ2fix is expressed by the above formula (59).

  In the battery model in this example, the decrease in single electrode capacity is reflected in the electrode thickness and the active material volume fraction, as shown in the following formulas (63) to (66).

  Here, L10 and L20 indicate the thickness of the positive electrode and the thickness of the negative electrode in the initial state, respectively. εs0,1 and εs0,2 indicate the volume fraction of the positive electrode active material and the volume fraction of the negative electrode active material in the initial state, respectively.

  The open-circuit voltage OCV when the capacity of the single electrode (positive electrode or negative electrode) decreases due to the deterioration and the relative composition correspondence between the positive electrode and the negative electrode occurs is calculated by the following equation (67). In addition, since the salt concentration distribution exists inside the active material when the current flows through the secondary battery 10 or immediately after the charge / discharge of the secondary battery 10 is stopped, the salt concentration on the surface of the active material And the average salt concentration inside the active material does not match. When determining the open circuit voltage OCV, the secondary battery 10 is in a sufficiently relaxed state, so there is no salt concentration distribution inside the active material, and the salt concentration on the surface of the active material and the average salt inside the active material The concentration is the same.

  In the above formula (67), θ1ave and θ2ave represent the average charge rates inside the active material in the positive electrode and the negative electrode, respectively, and are defined by the following formula (68). In the following formula (68), Csave, i is an average salt concentration inside the active material.

  The relationship represented by the following formula (69) is established between θ1ave and θ2ave.

  Further, λ shown in the above formula (69) is defined by the following formula (70).

  FIG. 23 is a diagram for explaining a relational expression established between the average charging rate θ1ave inside the positive electrode active material and the average charging rate θ2ave inside the negative electrode active material. In FIG. 23, it is assumed that the positive electrode composition θ1fix and the negative electrode composition θ2fix correspond to each other. Furthermore, the positive electrode occludes all lithium ions released from the negative electrode, whereby the negative electrode composition changes from θ2fix to θ2ave, and the positive electrode composition changes from θ1fix to θ1ave.

  Since the change amount of lithium in the positive electrode and the change amount of lithium in the negative electrode are equal, assuming that the electrode plate area of the positive electrode and the negative electrode is S, the following formula (63) to (66) and the above formula (68) 71) is established.

  By solving the above equation (71), the above equations (69) and (70) are established.

  As described above, by calculating the average charging rate θ1ave inside the positive electrode active material and the average charging rate θ2ave inside the negative electrode active material, the above formula (67) can be used to reduce the capacity of the single electrode due to deterioration and the positive electrode and It is possible to calculate the change characteristic of the open-circuit voltage when the composition correspondence shift between the negative electrodes occurs. θ1ave and θ2ave are associated with the positive electrode composition θ1fix and the negative electrode composition θ2fix, as shown in the above formula (69).

  As shown in the above formula (61), the negative electrode composition θ2fix includes a positive electrode capacity retention ratio k1, a negative electrode capacity retention ratio k2, and a composition-corresponding shift capacity ΔQs. Therefore, by estimating the positive electrode capacity retention rate k1, the negative electrode capacity retention rate k2, and the composition-corresponding deviation capacity ΔQs, θ1ave and θ2ave after deterioration of the secondary battery 10 can be estimated. Thereby, the change characteristic of the open circuit voltage of the secondary battery 10 which changes with deterioration of the secondary battery 10 can be estimated.

  FIG. 24 is a flowchart showing a process of estimating (searching) the deterioration parameter. The process shown in FIG. 24 is executed by the controller 30.

  In step S501, the controller 30 first sets an upper limit value ΔQs (H) and a lower limit value ΔQs (L) of the composition correspondence deviation capacity ΔQs in order to calculate the optimum composition correspondence deviation capacity ΔQs. In the first search process of the composition-corresponding deviation capacity ΔQs, predetermined values are used as the upper limit value ΔQs (H) and the lower limit value ΔQs (L).

  In step S502, the controller 30 specifies a candidate value ΔQs (E) of the composition-corresponding displacement capacity ΔQs within the range of the upper limit value ΔQs (H) and the lower limit value ΔQs (L). For example, the controller 30 specifies an intermediate value between the upper limit value ΔQs (H) and the lower limit value ΔQs (L) as the candidate value ΔQs (E).

  In step S503, the controller 30 specifies the positive electrode capacity retention ratio k1 and the negative electrode capacity retention ratio k2 from the candidate value ΔQs (E) of the current composition correspondence deviation capacity ΔQs. If a map showing the correspondence between the composition-corresponding deviation capacity ΔQs and the single electrode capacity maintenance ratios k1 and k2 is obtained in advance by experiments or the like, the single electrode capacity maintenance ratio k1 and k2 corresponding to the candidate value ΔQs (E) are specified can do.

  Note that the positive electrode capacity retention rate k1 can be calculated from the composition-corresponding displacement capacity ΔQs by using a function with the composition-corresponding displacement capacity ΔQs and the positive electrode capacity retention ratio k1 as variables. Further, the negative electrode capacity retention rate k2 can be calculated from the composition-corresponding displacement capacity ΔQs by using a function with the composition-corresponding displacement capacity ΔQs and the negative electrode capacity retention ratio k2 as variables.

  In step S504, the controller 30 calculates a change characteristic of the open-circuit voltage with respect to the local SOC θi based on the composition-corresponding deviation capacity ΔQs and the single electrode capacity maintenance ratios k1 and k2 specified in steps S502 and S503.

  In step S505, the controller 30 determines the positive electrode corresponding to the open circuit voltage OCV (H) based on the change characteristic of the open circuit voltage calculated in step S504 and the open circuit voltage OCV (H) when starting the current integration process. An average charging rate (average SOC θ1_1) inside the active material is calculated.

  In step S506, the controller 30 determines the positive electrode corresponding to the open circuit voltage OCV (L) based on the change characteristic of the open circuit voltage calculated in step S504 and the open circuit voltage OCV (L) when the current integration process is finished. An average charging rate (average SOC θ1_2) inside the active material is calculated. The open circuit voltage OCV (H) is higher than the open circuit voltage OCV (L), and when the degradation parameter search process is performed, the assembled battery 100 (secondary battery 10) is discharged.

  In step S507, the controller 30 needs to flow until the open circuit voltage changes from OCV (H) to OCV (L) on the battery model based on the average SOCθ1_1 and the average SOCθ1_2 calculated in steps S505 and S506. An integrated current value ΔQ12 is calculated (estimated). Specifically, the controller 30 calculates a current integrated value (estimated value) ΔQ12 using the following equation (72). In the following formula (72), S represents the area of the electrode plate.

  In step S508, the controller 30 compares the current integrated value (estimated value) ΔQ12 and the current integrated value (actually measured value) ΔQ11. The current integrated value (actual value) ΔQ11 is a value obtained by integrating the current value detected by the current sensor 22 until the open circuit voltage changes from OCV (H) to OCV (L).

  When the current integrated value (estimated value) ΔQ12 is larger than the current integrated value (actually measured value) ΔQ11, the process of step S509 is performed, and when the current integrated value (estimated value) ΔQ12 is smaller than the current integrated value (actually measured value) ΔQ11. The process of step S510 is performed.

  In step S509, the controller 30 replaces the upper limit value ΔQs (H) in the next calculation of the composition correspondence deviation capacity ΔQs with the current composition correspondence deviation capacity candidate value ΔQs (E). Thereby, in the next search process, the candidate value ΔQs (E) is set within the range of ΔQs (L) to ΔQs (E).

  In step S510, the controller 30 replaces the lower limit value ΔQs (L) in the next calculation of the composition correspondence deviation capacity ΔQs with the current composition correspondence deviation capacity candidate value ΔQs (E). Thereby, in the next search process, the candidate value ΔQs (E) is set within the range of ΔQs (E) to ΔQs (H).

  In step S511, the controller 30 determines whether or not the difference between the upper limit value ΔQs (H) and the lower limit value ΔQs (L) (ΔQs (H) −ΔQs (L)) is smaller than a predetermined value ΔQs (min). When the difference (ΔQs (H) −ΔQs (L)) is smaller than the predetermined value ΔQs (min), the processing shown in FIG. 24 is ended. On the other hand, when the difference (ΔQs (H) −ΔQs (L)) is larger than the predetermined value ΔQs (min), the process returns to step S502.

  By repeating the process shown in FIG. 24 until the difference (ΔQs (H) −ΔQs (L)) becomes smaller than the predetermined value ΔQs (min), the current integrated value (estimated value) ΔQ12 and the current integrated value (actually measured value) are obtained. ) The composition-corresponding deviation capacity ΔQs is estimated so that the difference (estimation error) in ΔQ11 is minimized. That is, the composition-corresponding deviation capacity ΔQs is estimated so that the estimation error with respect to the change in the open circuit voltage (change from OCV (H) to OCV (L)) is minimized (for example, 0).

  As a result, the optimum deterioration parameters (composition-corresponding displacement capacity ΔQs, positive electrode capacity retention rate k1 and negative electrode capacity retention rate k2) with respect to the calculated open circuit voltages OCV (H), OCV (L) and current integrated value (actually measured value) ΔQ11. ) Can be calculated. If the optimum deterioration parameter (especially, the unipolar capacity retention ratios k1 and k2) can be calculated, the resistance Rm can be calculated by substituting the unipolar capacity retention ratios k1 and k2 into the above equation (55).

The basic battery model described above is based on the assumption that the reaction in the thickness direction of the electrodes 12 and 15 is uniform and the assumption that the concentration of lithium ions Li ⁺ in the electrodes 12 and 15 is constant. It is configured. Instead of the basic battery model, a battery model that considers the overvoltage Δφ _e (t) due to the difference in lithium ion concentration between the electrodes 12 and 15 can be used.

In the above equation (11), it is assumed that the voltage drop due to DC resistance and the overvoltage due to the difference in lithium ion concentration are independent. In this case, as shown in the following formula (73), the overvoltage Δφ _ej (x, t) due to the difference in lithium ion concentration between the electrodes 12 and 15 and the difference in lithium ion concentration between the electrodes 12 and 15. A relationship with ΔC _ej (x, t) is obtained.

When the overvoltage Δφ _e (t) is obtained from the above equation (73), the following equation (74) is obtained.

  In the above formula (74), Ce and ini indicate the concentration of lithium ions when the secondary battery 10 is in the initial state.

  When the above equation (74) is linearly approximated (linear approximation), the following equation (75) is obtained.

  The density difference shown in the above equation (75) can be obtained from the above equations (32) and (33), and can be expressed by the following equations (32'a) and (33 ').

  Since the equation (32′a) is an equation relating to the difference in lithium ion concentration between the electrodes 12 and 15, as shown in the equation (33 ′), the coefficients α and β shown in the equation (33) Defines different coefficients αe, βe.

  When the time change Δt advances n times, the above equation (32′a) can be expressed by the following equation (32′b).

  If the concentration difference ΔCe shown in the above equation (32′b) is substituted into the above equation (75), the overvoltage Δφe (t) can be obtained.

  On the other hand, in the above formula (M1b), when the overvoltage Δφe (t) is considered, it can be expressed by the following formula (M1g).

  Similarly, in the above formula (M1e), when the overvoltage Δφe (t) is considered, it can be expressed by the following formula (M1h).

  When the above equation (M1h) is linearly approximated (linear approximation), the following equation (M1i) is obtained.

  In the battery model considering the overvoltage Δφe (t), the current density I (t) can be calculated using the above formula (M1i). That is, in the process of calculating the current density I (t) using the above formula (M1f), the overvoltage Δφe (t) calculated from the above formula (75) and the above formula (32′b) may be considered.

  Further, in the battery model considering the overvoltage Δφe (t), the correction coefficient ξ can be obtained as follows.

  When the voltage drop amounts ΔV (t0) and ΔV (t1) at times t0 and t1 are obtained using the above formula (M1i), they are represented by the following formulas (76) and (77). Time t0 is the time when the high-rate resistance rise is eliminated, and time t1 is the time when the current value or the like is detected.

  If the above equations (76), (77) and the above equation (48) are used, the correction coefficient ξ can be expressed by the following equation (78).

  If the resistance change rate gr and the capacity maintenance rate k are used, the correction coefficient ξ can be expressed by the following equation (79).

  The above formulas (78) and (79) have the relationship shown in the following formula (80).

The correction coefficient ξ can be calculated based on the above formulas (78) and (79). If some parameters shown in the above formulas (78) and (79) are set as assumed values, the correction coefficient ξ is corrected. Calculation of the coefficient ξ can be simplified. For example, it can be assumed that the temperature T (t0) is equal to the temperature T (t1), or that the direct current pure resistance Rd (T, t0) is equal to the direct current pure resistance Rd (T, t1). Also, it is assumed that the exchange current density i ₀ (θ, T, t0) is equal to the exchange current density i ₀ (θ, T, t1), or that the overvoltage Δφe (t0) is equal to the overvoltage Δφe (t1). Can be.

100: assembled battery, 10: secondary battery, 21: monitoring unit, 22: current sensor,
23: Temperature sensor, 24: Current limiting resistor, 31: Inverter,
32: Motor generator, 30: Controller, 30a: Memory,
11n: negative electrode terminal, 11p: positive electrode terminal, 12: negative electrode, 15: positive electrode, 14: separator
13, 16: current collector plate, 18: active material, 18p, 18n: active material model,
300: battery state estimation unit, 310: diffusion estimation unit, 320: open circuit voltage estimation unit,
330: current estimation unit, 340: parameter setting unit, 350: boundary condition setting unit,
360: resistance change rate calculation unit, 370: determination unit, 371: timer, 380: storage unit,
390: Resistance increase estimation unit

Claims (10)

A secondary battery for charging and discharging;
A controller that determines that the first deterioration component generated due to the deviation of salt concentration in the secondary battery is eliminated when the time during which the secondary battery is not charged or discharged is a predetermined time or longer. Have
The controller calculates a resistance increase amount of a second deterioration component generated due to wear of the secondary battery, and shortens the predetermined time according to an increase in the resistance increase amount. .   The controller calculates an allowable amount that allows an increase in the resistance of the first deterioration component from an upper limit value that allows an increase in the resistance of the secondary battery, and excludes the increase in the resistance of the second deterioration component. The battery system according to claim 1, wherein the predetermined time is shortened in accordance with a decrease in capacity.   2. The controller according to claim 1, wherein the controller specifies a resistance increase amount of the second deterioration component by calculating a resistance of the secondary battery in a state where the first deterioration component is eliminated. 2. The battery system according to 2.   The controller calculates a resistance change rate representing a ratio of a current resistance of the secondary battery to an initial resistance of the secondary battery in a state where the first deterioration component is eliminated, and the resistance change rate is The battery system according to claim 1, wherein the predetermined time is shortened in response to the increase.   The controller calculates a capacity maintenance ratio indicating a ratio of capacity when the second deterioration component is generated with respect to an initial capacity in at least one of the positive electrode and the negative electrode, and the capacity maintenance ratio is reduced. The battery system according to claim 1, wherein the predetermined time is shortened. A determination method for determining a deterioration state of a secondary battery that performs charge and discharge,
When the time during which the secondary battery is not charged / discharged is a predetermined time or more, it is determined that the first deterioration component generated due to the salt concentration bias in the secondary battery is eliminated,
Calculating a resistance increase amount of the second deterioration component caused by wear of the secondary battery, and shortening the predetermined time according to an increase in the resistance increase amount;
A discrimination method characterized by that. From the upper limit value that allows the resistance increase of the secondary battery, excluding the resistance increase amount of the second deterioration component, to calculate the allowable amount that allows the resistance increase due to the first deterioration component,
The determination method according to claim 6, wherein the predetermined time is shortened according to a decrease in the allowable amount.   The determination according to claim 6 or 7, wherein when the first deterioration component is eliminated, the resistance increase amount of the second deterioration component is specified by calculating the resistance of the secondary battery. Method.   When the first deterioration component is eliminated, a resistance change rate representing a ratio of the current resistance of the secondary battery to the initial resistance of the secondary battery is calculated, and the resistance change rate is increased. The determination method according to claim 6, wherein the predetermined time is shortened. In at least one of the positive electrode and the negative electrode, a capacity maintenance ratio representing a ratio of capacity when the second deterioration component is generated to initial capacity is calculated,
The determination method according to claim 6, wherein the predetermined time is shortened according to a decrease in the capacity maintenance rate.