JP2014202630A - Battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate a potential of a single electrode (a positive electrode or a negative electrode) of a deteriorated secondary battery.SOLUTION: A battery system includes: sensors (21, 22, 23) for detecting a current value, a voltage value, and temperature of a secondary battery (10); and a controller (30) for estimating a potential of a single electrode of the secondary battery. A controller substitutes a value detected by the sensor into a linear regression model formula using a resistance change rate, which is a ratio between a resistance component of the secondary battery in an initial state and a resistance component of the current secondary battery, as a calculation parameter, and applies a least-square method, to calculate a resistance change rate. The controller uses the resistance change rate calculated on a reaction resistance of a single electrode included in the resistance component and a reaction resistance of the single electrode in the initial state, to calculate a reaction resistance of the current single electrode, and uses an open-circuit potential and an amount of change in potential to be generated by the reaction resistance of the single electrode, to calculate the potential of the current single electrode.

Description

  The present invention relates to a battery system for estimating a potential at a single electrode of a secondary battery.

  The DC resistance of the secondary battery includes a pure electric resistance (pure resistance) against the movement of electrons and a charge transfer resistance (reaction resistance) that acts equivalently as an electric resistance when a reaction current is generated at the active material interface. Is included. In Patent Document 1, the rate of change related to pure resistance and the rate of change related to reaction resistance are estimated by using the successive least squares method. Thereby, when the direct current resistance of the secondary battery is increased due to aging, it is possible to grasp the increase in each of the pure resistance and the reaction resistance.

JP 2008-241246 A (paragraphs [0073], [0162] to [0167])

  In patent document 1, the change rate regarding a pure resistance and reaction resistance is estimated by prescribing | regulating the single spherical active material model which has the characteristic averaged in the negative electrode and the positive electrode. Here, in an actual secondary battery, there are a negative electrode and a positive electrode, respectively, and reaction resistances in the negative electrode and the positive electrode may be different from each other. For this reason, even if the change rate regarding reaction resistance is estimated using a single spherical active material model, the potentials of the negative electrode and the positive electrode cannot be grasped.

  A battery system according to the present invention includes a sensor that detects a current value, a voltage value, and a temperature in a secondary battery, and a controller that estimates a potential at a single electrode (positive electrode or negative electrode) of the secondary battery. Here, a current sensor can be used as a sensor for detecting a current value, a voltage sensor can be used as a sensor for detecting a voltage value, and a temperature sensor can be used as a sensor for detecting a temperature.

  The controller calculates the resistance change rate by applying the least square method by substituting the detection values (current value, voltage value, and temperature) of the sensor into a linear regression model expression using the resistance change rate as a calculation parameter. Here, the resistance change rate is the ratio of the resistance component of the secondary battery in the initial state to the resistance component of the current secondary battery. The initial state is a state in which the secondary battery has not deteriorated. Since the resistance component of the secondary battery that has deteriorated deviates from the resistance component in the initial state, the resistance change rate changes.

  The resistance component includes a unipolar reaction resistance. For this reason, the controller can calculate the reaction resistance in the current unipolar using the resistance change rate calculated for the unipolar reaction resistance and the unipolar reaction resistance in the initial state. The resistance change rate related to the reaction resistance is the ratio of the reaction resistance in the initial state and the current monopolar, so if the resistance change rate related to the reaction resistance and the reaction resistance in the initial state are specified, the reaction resistance in the current monopolar is calculated. can do. Thereby, even after the deterioration of the secondary battery proceeds, the unipolar reaction resistance reflecting the deterioration state can be calculated.

  The controller calculates the current unipolar potential using the unipolar open-circuit potential and the amount of change in potential associated with the calculated unipolar reaction resistance. If the reaction resistance at the current monopolar is calculated, the amount of change in monopolar potential associated with this reaction resistance can be calculated. Since this change amount is a change amount with respect to the open potential of the single electrode, the current potential of the single electrode can be calculated from the change amount and the open potential of the single electrode.

  According to the present invention, as described above, the reaction resistance for each single electrode can be calculated, and the potential for each single electrode can be calculated based on this reaction resistance. As described above, since the unipolar reaction resistance reflecting the deterioration state of the secondary battery can be calculated, a value reflecting the deterioration state of the secondary battery can be obtained for the potential of each single electrode. Therefore, it is possible to grasp the unipolar potential after the secondary battery has deteriorated.

  The linear regression model formula can be expressed by the following formula (I).

In the above formula (I), U ₁ and U ₂ are open potentials of the positive electrode and the negative electrode, and V is a voltage value detected by a sensor (voltage sensor). _{R rn, 1, R rn,} 2 is a reaction resistance of the positive electrode and the negative electrode in the initial _{state, I EC, 1, I EC} , 2 is the current value of the electrochemical component flowing in the positive electrode and the negative electrode. R _dn is the pure resistance of the secondary battery in the initial state, and I is the current value detected by the sensor (current sensor).

gr1 ₁ is a resistance change rate related to the reaction resistance of the positive electrode, and the resistance change rate gr1 ₁ is represented by a ratio between the reaction resistance of the positive electrode in the initial state and the reaction resistance of the current positive electrode (particularly after deterioration). gr1 ₂ is the resistance change ratio for the reaction resistance of the negative electrode, the rate of change in resistance gr1 ₂ is represented by the ratio of the reaction resistance of the negative electrode in the initial state, the reaction resistance of the negative electrode current (especially after degradation). gr2 is a resistance change rate related to the pure resistance included in the resistance component, and the resistance change rate gr2 is a ratio of the pure resistance in the secondary battery in the initial state to the pure resistance in the current secondary battery (particularly after deterioration). It is represented by

Using a linear regression model formula shown in above-mentioned formula (I), by calculating the rate of change in resistance gr1 _1, as described above, it can be calculated the reaction resistance in the current of the positive electrode. Then, the reaction resistance of the calculated positive, based on the open-circuit potential U ₁ of the positive electrode, it is possible to calculate the current of the positive electrode potential. Further, using a linear regression model formula shown in above-mentioned formula (I), by calculating the rate of change in resistance gr1 _2, as described above, it can be calculated reaction resistance in the current of the negative electrode. Then, the reaction resistance of the negative electrode was calculated, based on the open-circuit potential U ₂ of the negative electrode, it is possible to calculate the current of the negative electrode potential.

Open-circuit potential U ₁ of the positive electrode, a local SOC at the interface of the positive electrode active material, depending on the temperature of the secondary battery. Therefore, if the correspondence relationship between the open-circuit potential U ₁ , the local SOC and the secondary battery temperature is obtained in advance, the open-circuit potential U ₁ is specified by specifying the local SOC and the secondary battery temperature. can do. The open circuit potential U ₁ changes according to a local change in the SOC, but also changes as the temperature of the secondary battery changes. Therefore, not only the local SOC, by also taking into account the temperature of the secondary battery, the open-circuit potential U ₁ can be accurately estimated.

Like the open-circuit potential U _1, open-circuit potential U ₂ of the negative electrode, a local SOC at the interface of the negative electrode active material, depending on the temperature of the secondary battery. Therefore, if the correspondence relationship between the open-circuit potential U ₂ , the local SOC, and the secondary battery temperature is obtained in advance, the open-circuit potential U ₂ can be specified by specifying the local SOC and the secondary battery temperature. can do. Open-circuit potential U ₂ will vary in response to changes in local SOC, also vary according to the temperature of the secondary battery is changed. Therefore, not only the local SOC, by also taking into account the temperature of the secondary battery, the open-circuit potential U ₂ can be accurately estimated.

The reaction resistance R _{rn, 1} of the positive electrode depends on the local SOC at the interface of the positive electrode active material and the temperature of the secondary battery. Therefore, if the correspondence relationship between the reaction resistance R _{rn, 1} , the local SOC and the temperature of the secondary battery is obtained in advance, the reaction resistance R _rn is determined by specifying the local SOC and the temperature of the secondary battery. _{, 1} can be specified. Similar to the reaction resistance R _{rn, 1} , the reaction resistance R _{rn, 2} of the negative electrode depends on the local SOC at the interface of the negative electrode active material and the temperature of the secondary battery. Therefore, if the correspondence relationship between the reaction resistance R _{rn, 2} , the local SOC and the temperature of the secondary battery is obtained in advance, the reaction resistance R _rn is determined by specifying the local SOC and the temperature of the secondary battery. _{, 2} can be specified.

  When controlling charging / discharging of the secondary battery, the secondary battery can be charged / discharged so that the calculated monopolar potential does not reach a predetermined threshold potential. If the positive electrode potential and the negative electrode potential are calculated as described above, the voltage value of the secondary battery can be calculated. That is, the potential difference between the positive electrode potential and the negative electrode potential is the voltage value of the secondary battery. Therefore, it is possible to grasp the voltage value of the secondary battery when the unipolar potential reaches the threshold potential, and it is also possible to grasp the voltage value range where the unipolar potential does not reach the threshold potential.

  A voltage value detected by a sensor (voltage sensor) is used as a parameter for controlling charging / discharging of the secondary battery. Therefore, in order to prevent the unipolar potential from reaching the threshold potential, the detected voltage value may be changed within a voltage value range in which the unipolar potential does not reach the threshold potential. The threshold potential can be determined in advance in consideration of secondary reactions that may occur in the secondary battery.

  The secondary reaction is a reaction different from the chemical reaction involved in charging / discharging of the secondary battery, and it is necessary to suppress the secondary reaction when using the secondary battery. The secondary reaction includes a reaction that occurs due to the positive electrode potential and a reaction that occurs due to the negative electrode potential. For this reason, the threshold potential can be set for each of the positive electrode potential and the negative electrode potential.

  According to the present invention, since the unipolar potential reflecting the deterioration state of the secondary battery can be calculated, the charge / discharge of the secondary battery is controlled so that the unipolar potential does not reach the threshold potential. , Secondary reactions can be suppressed. In addition, by grasping the unipolar potential reflecting the deterioration state of the secondary battery, it is possible to suppress the secondary reaction without excessively limiting the secondary battery charging / discharging. The secondary battery can be charged and discharged within a range in which the reaction can be suppressed. Thereby, the input / output performance of the secondary battery can be sufficiently exhibited while suppressing the secondary reaction.

It is a figure which shows the structure of a battery system. It is the schematic which shows the structure of a secondary battery. It is a figure which shows the relationship between positive electrode open electric potential and local SOC of a positive electrode active material model. It is a figure which shows the relationship between negative electrode open circuit potential and local SOC of a negative electrode active material model. It is a figure which shows the relationship between a diffusion coefficient and battery temperature. It is a flowchart which shows the process which estimates the resistance change rate regarding reaction resistance (a positive electrode, a negative electrode) and pure resistance. It is a flowchart which shows the process which estimates SOC of a secondary battery. It is a figure which shows the relationship between the positive electrode potential, the negative electrode potential, and the voltage value of a secondary battery. It is a flowchart which shows the process which controls charging / discharging of a secondary battery.

  Examples of the present invention will be described below.

  FIG. 1 is a diagram showing the configuration of the battery system of this example. The battery system shown in FIG. 1 can be mounted on a vehicle. Vehicles 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 or a fuel cell in addition to an assembled battery described later as a power source for running the vehicle. In PHV, an assembled battery can be charged using power from an external power source in HV. The EV includes only an assembled battery, which will be described later, as a power source of the vehicle, and can charge the assembled battery by receiving power supply from an external power source. The external power source is a power source (for example, commercial power source) provided separately from the vehicle outside the vehicle.

  In the present embodiment, an assembled battery mounted on a vehicle will be described, but the present invention is not limited to this. That is, the present invention can be applied to any system that charges and discharges a secondary battery.

  The assembled battery 1 has a plurality of secondary batteries 10 connected in series. As the secondary battery 10, for example, a lithium ion secondary battery can be used. The number of secondary batteries 10 can be appropriately set based on the required output of the assembled battery 1 and the like. The assembled battery 1 can also include a plurality of secondary batteries 10 connected in parallel. The monitoring unit (voltage sensor) 21 detects the voltage value of the assembled battery 1 or detects the voltage value Vb of each secondary battery 10. The monitoring unit 21 outputs the detection result to the controller 30.

  The current sensor 22 detects the current value Ib flowing through the assembled battery 1 and outputs the detection result to the controller 30. In this embodiment, the current value Ib at the time of discharging is a positive value, and the current value Ib at the time of charging is a negative value. The temperature sensor 23 detects the temperature Tb of the assembled battery 1 (secondary battery 10) and outputs the detection result to the controller 30. By using the plurality of temperature sensors 23, it becomes easy to detect the temperature Tb of the secondary batteries 10 arranged at different positions.

  The controller 30 includes a memory 31, and the memory 31 stores various information for the controller 30 to perform predetermined processing (for example, processing described in the present embodiment). In this embodiment, the memory 31 is built in the controller 30, but the memory 31 may be provided outside the controller 30.

  A system main relay SMR-B is provided on the positive electrode line PL connected to the positive electrode terminal of the assembled battery 1. System main relay SMR-B is switched between on and off by receiving a control signal from controller 30. A system main relay SMR-G is provided on the negative electrode line NL connected to the negative electrode terminal of the assembled battery 1. 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 current limiting resistor 24 are connected in parallel to the system main relay SMR-G. System main relay SMR-P and current limiting resistor 24 are connected in series. System main relay SMR-P is switched between on and off by receiving a control signal from controller 30.

  The current limiting resistor 24 is used to suppress an inrush current from flowing through the capacitor 25 when the assembled battery 1 is connected to a load (specifically, the inverter 26). Capacitor 25 is connected to positive electrode line PL and negative electrode line NL, and is used to smooth voltage fluctuations between positive electrode line PL and negative electrode line NL.

  When connecting the assembled battery 1 to the inverter 26, the controller 30 first switches the system main relay SMR-B from off to on and switches the system main relay SMR-P from off to on. As a result, a current flows through the current limiting resistor 24.

  Next, the controller 30 switches the system main relay SMR-G from off to on and switches the system main relay SMR-P from on to off. Thereby, the connection between the assembled battery 1 and the inverter 26 is completed, and the battery system shown in FIG. 1 is in a start-up state (Ready-On). Information about on / off of the ignition switch of the vehicle is input to the controller 30, and the controller 30 activates the battery system shown in FIG. 1 in response to the ignition switch switching from off to on.

  On the other hand, when the ignition switch is switched from on to off, the controller 30 switches the system main relays SMR-B and SMR-G from on to off. Thereby, the connection between the assembled battery 1 and the inverter 26 is cut off, and the battery system shown in FIG. 1 is in a stopped state (Ready-Off).

  The inverter 26 converts the DC power output from the assembled battery 1 into AC power, and outputs the AC power to the motor / generator 27. As the motor generator 27, for example, a three-phase AC motor can be used. The motor / generator 27 receives AC power from the inverter 26 and generates kinetic energy for running the vehicle. The kinetic energy generated by the motor / generator 27 is transmitted to the wheels so that the vehicle can run.

  On the other hand, when the vehicle is decelerated or stopped, the motor / generator 27 converts kinetic energy generated during braking of the vehicle into electric energy (AC power). The inverter 26 converts the AC power generated by the motor / generator 27 into DC power and outputs the DC power to the assembled battery 1. Thereby, the assembled battery 1 can store regenerative electric power.

  In this embodiment, the assembled battery 1 is connected to the inverter 26, but the present invention is not limited to this. Specifically, a booster circuit can be provided in the current path between the assembled battery 1 and the inverter 26. By using the booster circuit, the output voltage of the assembled battery 1 can be boosted. The booster circuit can step down the output voltage from the inverter 26 to the assembled battery 1.

  Next, the battery model used in the present embodiment will be described. This battery model is used to dynamically estimate the behavior inside the secondary battery 10 in consideration of the electrochemical reaction inside the secondary battery 10.

  As shown in FIG. 2, the secondary battery 10 includes a negative electrode (also referred to as an electrode) 12, a positive electrode (also referred to as an electrode) 15, and a separator 14. The separator 14 is located between the negative electrode 12 and the positive electrode 15 and contains an electrolytic solution. 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 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 of the secondary battery 10.

  Each of the negative electrode 12 and the positive electrode 15 includes a spherical active material aggregate. In the battery model of this example, as shown in FIG. 2, the active material of the negative electrode 12 is represented as one spherical active material model 18n, and the active material of the positive electrode 15 is represented as one spherical active material model 18p. ing.

When the secondary battery 10 is discharged, a chemical reaction that releases lithium ions Li ⁺ and electrons e ⁻ is performed at the interface of the active material model 18 n of the negative electrode 12 (interface of the active material model 18 n and the electrolyte). Further, at the interface of the active material model 18p of the positive electrode 15 (the interface between the active material model 18p and the electrolyte), a chemical reaction that absorbs lithium ions Li ⁺ and electrons e ⁻ is performed. On the other hand, when the secondary battery 10 is charged, a reaction reverse to the chemical reaction described above is performed. 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 charging current Ib (Ib <0) or a discharging current Ib (Ib> 0) is generated.

Voltage value Vb of the secondary battery 10, based on the following equation (1), is calculated from the current value I, the open circuit voltage value (OCV) U and DC resistance _{R a} of the secondary battery 10. Here, the current value I indicates a current value per unit electrode plate area. That is, current value I (I = Ib / S) is obtained by dividing current value Ib detected by current sensor 22 by electrode plate area S in negative electrode 12 and positive electrode 15. Hereinafter, the “current value” and the “current estimation value” described in the battery model of this example indicate the current values per unit electrode plate area described above unless otherwise specified.

As shown in the above equation (1), the open circuit voltage value U depends on θ indicating a local SOC (State of Charge) at the interface between the active material models 18n and 18p. That is, the open circuit voltage value U changes in accordance with the change in local SOC θ. Further, as shown in the above formula (1), the direct current resistance _Ra depends on the local SOC θ and the battery temperature Tb. That is, in response to at least one of changes in the local SOCθ and battery temperature Tb, DC resistance R _a is changed.

The DC resistance _{R a} of the secondary battery 10 includes a pure resistance _{R d} and reaction resistance _{R r.} The pure resistance R _d is a pure electrical resistance against the movement of the electron e ^{− in} each of the negative electrode 12 and the positive electrode 15. The reaction resistance R _r is a charge transfer resistance that acts equivalently as an electric resistance when a reaction current is generated at the interface between the active material models 18n and 18p.

Considering that the open-circuit voltage value U of the secondary battery 10 is expressed by the difference between the open-circuit potentials of the negative electrode 12 and the positive electrode 15, and that the direct-current resistance _Ra includes the pure resistance _Rd and the reaction resistance _Rr. The above formula (1) is represented by the following formula (2).

In the above formula (2), U ₁ is the open-circuit potential of the positive electrode 15 when the secondary battery 10 is in the initial state, and depends on the local SOC θ ₁ at the interface of the active material model 18p. That is, the positive electrode open potential U ₁ changes in accordance with the change in local SOC θ ₁ . For this reason, when the secondary battery 10 is in the initial state, if the correspondence between the positive electrode open potential U ₁ and the local SOC θ ₁ is obtained by experiments or the like, the local SOC θ ₁ is calculated to calculate the local SOC θ _1. it is possible to identify the potential U _1.

Here, the initial state is a state in which the secondary battery 10 is not deteriorated, for example, a state immediately after the secondary battery 10 is manufactured. The correspondence relationship between the positive electrode open potential U ₁ and the local SOC θ ₁ can be expressed as a map or a function, and information regarding this correspondence relationship can be stored in the memory 31. In general, the positive electrode opening potential U ₁ and the local SOC θ ₁ have the relationship shown in FIG.

U ₂ is the open-circuit potential of the negative electrode 12 when the secondary battery 10 is in the initial state, and depends on the local SOC θ ₂ at the interface of the active material model 18n. That is, the negative electrode open-circuit potential U ₂ changes according to the change in local SOC θ ₂ . Therefore, when the secondary battery 10 is in the initial state, if the correspondence relationship between the negative electrode open potential U ₂ and the local SOC θ ₂ is obtained by experiments or the like, the local SOC θ ₂ is calculated to calculate the local SOC θ _2. it is possible to identify the potential U _2.

The correspondence relationship between the negative electrode open-circuit potential U ₂ and the local SOC θ ₂ can be expressed as a map or a function, and information regarding this correspondence relationship can be stored in the memory 31. In general, negative electrode open-circuit potential U ₂ and local SOC θ ₂ have the relationship shown in FIG.

According to the above formula (2), the open-circuit potentials U ₁ and U ₂ are specified based on the local SOCs θ ₁ and θ ₂ , but are not limited thereto. Specifically, the open circuit potentials U ₁ and U ₂ are likely to depend not only on the local SOCs θ ₁ and θ ₂ but also on the temperature Tb of the secondary battery 10. For this reason, the estimation accuracy of the open-circuit potentials U ₁ and U ₂ can be improved by considering not only the local SOCs θ ₁ and θ ₂ but also the battery temperature Tb.

If the correspondence relationship between the positive electrode opening potential U ₁ , the local SOC θ ₁ and the battery temperature Tb is obtained by experiments or the like, the positive electrode opening potential U ₁ can be specified by specifying the local SOC θ ₁ and the battery temperature Tb. it can. Specifically, when the secondary battery 10 is in the initial state, the correspondence relationship between the positive electrode open potential U ₁ , the local SOC θ ₁ and the battery temperature Tb can be obtained. This correspondence can be expressed as a map or a function, and information regarding this correspondence can be stored in the memory 31.

Similarly, if the correspondence relationship between the negative electrode open-circuit potential U ₂ , the local SOC θ ₂ and the battery temperature Tb is obtained through experiments, the negative electrode open-circuit potential U ₂ is specified by specifying the local SOC θ ₂ and the battery temperature Tb. can do. Specifically, when the secondary battery 10 is in the initial state, the correspondence relationship between the negative electrode open-circuit potential U ₂ , the local SOC θ _2, and the battery temperature Tb can be obtained. This correspondence can be expressed as a map or a function, and information regarding this correspondence can be stored in the memory 31.

_{R r, 1} represented by the above formula (2) is a reaction resistance of the cathode 15, depending on local SOC [theta] ₁ at the interface temperature Tb and the positive electrode active material model 18p of the secondary battery 10. Therefore, when the secondary battery 10 is in the initial state, if the correspondence (map or function) of the reaction resistance R _{r, 1} , the battery temperature Tb, and the local SOC θ ₁ is obtained in advance by experiments or the like, the battery temperature By specifying Tb and local SOC θ ₁ , the reaction resistance R _{r, 1} can be specified.

R _{r, 2} is a reaction resistance of the negative electrode 12, it depends on the local SOC [theta] ₂ at the interface temperature Tb and the anode active material model 18n of the secondary battery 10. Therefore, when the secondary battery 10 is in the initial state, if the correspondence relationship (map or function) of the reaction resistance R _{r, 2} , the battery temperature Tb, and the local SOC θ ₂ is obtained in advance by experiments or the like, the battery temperature By specifying Tb and local SOC θ ₂ , the reaction resistance R _{r, 2} can be specified.

R _d is a pure resistance and depends on the temperature Tb of the secondary battery 10. For this reason, when the secondary battery 10 is in the initial state, if the correspondence (map or function) between the pure resistance _Rd and the battery temperature Tb is obtained in advance by experiments or the like, by specifying the battery temperature Tb, The pure resistance _Rd can be specified. The current value I multiplied by the pure resistance _Rd is a total current value obtained by combining the current value of the electrochemical component and the current value flowing through the electric double layer capacitor. As described above, the current value I is defined as a current per unit electrode plate area.

In the above formula (2), IEC _{, 1} is the current value of the electrochemical component flowing in the active material model 18p, and IEC _{, 2} is the current value of the electrochemical component flowing in the active material model 18n. The current values _{IEC, 1} , _{IEC, 2} are expressed by the following formulas (3), (4).

C ₁ shown in the above formula (3) is an electric double layer capacitor capacity in the positive electrode 15, and C ₂ shown in the above formula (4) is an electric double layer capacitor capacity in the negative electrode 12. T represents time (calculation cycle). Ψ ₁ and Ψ ₂ shown in the above formulas (3) and (4) are expressed by the following formulas (5) and (6).

[Psi ₁ in the previous operation _cycle, and [psi _2, [psi ₁ in the current calculation _cycle, by using the [psi _2, the formula (5), the discretizing (6), the formula (2) to (6) By providing them simultaneously, the current value (total) I and the current value (electrochemical component) _{IEC, 1} and _{IEC, 2} can be calculated from the detected voltage value Vb and battery temperature Tb.

On the other hand, local SOCs θ ₁ and θ ₂ are defined by the following formula (7). In the following formula (7), when j is “1”, the positive electrode 15 is shown, and when j is “2”, the negative electrode 12 is shown. In other formulas, the subscript j has the same meaning.

In the above formula (7), c _se is the average lithium concentration at the interface of the active material models 18n, 18p, and c _{s, max} is the critical lithium concentration in the active material models 18n, 18p. The lithium concentration c _s inside the active material models 18n and 18p has a distribution in the radial direction of the active material models 18n and 18p. This lithium concentration distribution is defined by the diffusion equation of the polar coordinate system, as shown in the following formula (8).

In the above equation (8), D _s is a diffusion coefficient of lithium in the active material models 18p and 18n, and depends on the temperature Tb of the secondary battery 10. Therefore, when the secondary battery 10 is in the initial state, if determined by an experiment correspondence between battery temperature Tb and the diffusion coefficient D _s (the map or function), by detecting the battery temperature Tb, diffusion The coefficient D _s can be specified. Correspondence between the battery temperature Tb and the diffusion coefficient _{D s,} the active material model 18p, obtained in each of 18n. In general, as shown in FIG. 5, as the temperature Tb of the secondary battery 10 increases, the diffusion coefficient D _s is increased.

  The boundary conditions of the diffusion equation shown in the above equation (8) are set as shown in the following equations (9) and (10).

  The above equation (9) indicates that the concentration gradient at the center of the active material models 18n and 18p is “0”. Here, r is the diameter of the active material models 18n and 18p, and the diameter r being 0 indicates the center of the active material models 18n and 18p. When lithium enters and exits at the interface between the active material models 18n and 18p, the lithium concentration at the interface between the active material models 18n and 19p changes. The above formula (10) shows the change in the lithium concentration at the interface between the active material models 18n and 18p.

In the above equation (10), ε _s is the volume fraction of each active material model 18n, 18p. a _s is a active material model 18n, the surface area of 18p per unit volume of each electrode 12, 15. The radius r, volume fraction ε _s, and surface area a _s are determined from measurement results obtained by various electrochemical measurement methods. F is a Faraday constant.

In the above formula (10), j ^Li is the amount of lithium produced per unit volume / time. If the reaction in the thickness direction of the electrode 12, 15 is assumed to be uniform, by using the thickness L and the current value _{I EC} of the electrodes 12 and 15, the lithium production quantity ^{j Li,} by the following formula (11) expressed.

DC resistance R _a as described by the above formula (1) is not only dependent on the battery temperature Tb and local SOC [theta], also depends on the deterioration state of the secondary battery 10. It is known that the secondary battery 10 is deteriorated depending on the use state, and if the deterioration of the secondary battery 10 proceeds, the direct current resistance _Ra is likely to increase. Here, since the direct resistance R _a includes the pure resistance R _d and the reaction resistance R _r , the pure resistance R _d and the reaction resistance R _r also depend on the deterioration state of the secondary battery 10. Specifically, as the secondary battery 10 deteriorates, the pure resistance _Rd and the reaction resistance Rr _tend to increase.

To calculate the reaction resistance R _r corresponding to the deterioration of the secondary battery 10 can be as shown in the following formula (12), defines the rate of change in resistance gr1.

In the above formula (12), R _rn is a reaction resistance when the secondary battery 10 is in the initial state, and can be measured in advance by an experiment or the like. Here, since the reaction resistance R _rn depends on the battery temperature Tb and the local SOC θ, if the correspondence (map or function) of the reaction resistance R _rn , the battery temperature Tb and the local SOC θ is obtained in advance, the battery temperature By specifying Tb and local SOC θ, the reaction resistance R _rn can be calculated.

On the other hand, R _r is the current reaction resistance of the secondary battery 10, and the reaction resistance R _r becomes higher than the reaction resistance R _{rn as} the deterioration of the secondary battery 10 proceeds. Here, if the secondary battery 10 is not deteriorated, the reaction resistance R _r becomes equal to the reaction resistance R _rn , and the resistance change rate gr 1 becomes “1”. On the other hand, when the deterioration of the secondary battery 10 progresses and the reaction resistance R _r becomes higher than the reaction resistance R _rn , the resistance change rate gr1 becomes higher than “1”. According to the above equation (12), it is possible to grasp the current reaction resistance R _r of the secondary battery 10 by estimating the resistance change rate gr1.

  In the battery model of this example, reaction resistance (charge transfer resistance) is generated at the interface between the active material models 18n and 18p. Therefore, the above equation (12) is expressed by the negative electrode 12 (active material model 18n) and the positive electrode 15 ( Each of the active material models 18p) can be expressed by the following formulas (13) and (14).

Gr1 ₁ represented by the above formula (13) is the resistance change ratio for the reaction resistance _{R r} of the positive electrode 15, gr1 ₂ represented by the above formula (14) is a resistance change ratio for the reaction resistance _{R r} of the negative electrode 12. According to the equation (13), by estimating the rate of change in resistance gr1 _1, it is possible to grasp the reaction resistance R _r in the current of the positive electrode 15. Further, according to the above formula (14), by estimating the rate of change in resistance gr1 _2, it is possible to grasp the reaction resistance R _r in the current of the negative electrode 12.

Meanwhile, in order to calculate the pure resistance R _d in accordance with the deterioration of the secondary battery 10 can be as shown in the following formula (15), defines the rate of change in resistance gr2.

In the above formula (15), R _dn is a pure resistance when the secondary battery 10 is in the initial state, and can be measured in advance by an experiment or the like. Here, since the pure resistance R _dn depends on the battery temperature Tb, if the correspondence (map or function) between the pure resistance R _dn and the battery temperature Tb is obtained in advance, the battery temperature Tb can be determined by specifying the battery temperature Tb. The resistance R _dn can be calculated.

On the other hand, R _d is the current pure resistance of the secondary battery 10, and if the secondary battery 10 deteriorates, the pure resistance R _d becomes higher than the pure resistance R _dn . Here, unless the secondary battery 10 is degraded, pure resistance R _d is equal to the pure resistance R _dn, the resistance change ratio gr2 is "1". On the other hand, when the deterioration of the secondary battery 10 progresses and the pure resistance R _d becomes higher than the pure resistance R _dn , the resistance change rate gr2 becomes higher than “1”. According to the equation (15), by estimating the rate of change in resistance gr2, it can grasp the pure resistance R _d in the current of the secondary battery 10.

The resistance change rates gr1 ₁ , gr1 ₂ , and gr2 described above can be calculated (estimated) using a sequential least square method with a forgetting factor described below. First, the sequential least square method with a forgetting factor will be described.

  According to the sequential least square method, in the system represented by the linear regression model represented by the following equation (16), the parameter Θ represented by the following equation (16) is the time update represented by the following equations (17) to (19). The equation is estimated by sequentially calculating with the initial conditions of the following equations (20) and (21). Here, the estimated value of the parameter Θ is indicated by Θ #.

In the above formulas (17) and (19), λ is a forgetting factor, and usually the forgetting factor λ is smaller than “1.0”. P is a covariance matrix, and the initial value P (0) of the above equation (21) is a matrix obtained by multiplying the diagonal element of the unit matrix I by a constant γ, and γ is usually about 10 ² to 10 ^3. Use a large value of. The initial value Θ # ₀ of the parameter (estimated value) Θ # is usually a zero vector.

By using such a sequential least square method with a forgetting factor, the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 can be estimated as follows. First, the above formula (2) can be transformed into the following formula (22).

As shown in the above equation (22), the above equation (2) can be expressed in the form of the above equation (16). Therefore, if the above-described sequential least square method is used, the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 as the parameter Θ can be calculated (estimated). In this embodiment, the estimation method using the sequential least square method is described, but the present invention is not limited to this. Specifically, the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 can be calculated (estimated) by using another least square method such as a collective least square method.

As described above, the reaction resistance R _r depends on the battery temperature Tb and the local SOC, and the pure resistance R _d depends on the battery temperature Tb. In particular, the reaction resistance R _r and the pure resistance R _d are easily affected by the battery temperature Tb. Here, if it is attempted to directly estimate the reaction resistance R _r and the pure resistance R _d from the battery temperature Tb or the like, this estimation process needs to sufficiently follow the change in the battery temperature Tb. However, when the follow-up speed of the estimation process with respect to the change in the battery temperature Tb is increased, fluctuations in the estimated value are likely to increase due to noise or disturbance. In other words, hardly stably estimate the reaction resistance R _r and pure resistance R _d.

On the other hand, the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 described above change in accordance with the deterioration of the secondary battery 10, but the speed at which the deterioration of the secondary battery 10 proceeds is faster than the speed at which the battery temperature Tb changes. Very slow. Therefore, when estimating the rate of change in resistance _{gr1 1,} gr1 2, gr2, compared with when estimating the reaction resistance _{R r} and pure resistance _{R d} directly is not necessary to increase the speed of following estimation process. Therefore, the resistance change rates gr1 ₁ , gr1 ₂ , gr2 can be stably estimated.

Further, in this embodiment, since the sequential least square method with a forgetting factor is used, in estimating the resistance change rate gr1 ₁ , gr1 ₂ , gr2, the current state of the secondary battery 10 rather than the past state. The state of the secondary battery 10 is easily reflected. That is, the weighting for the current state of the secondary battery 10 is made larger than the weighting for the state of the secondary battery 10 in the past. Thereby, the resistance change rates gr1 ₁ , gr1 ₂ , gr2 can be accurately estimated in consideration of the current state of the secondary battery 10.

Next, the process of estimating the resistance change rates gr1 ₁ , gr1 ₂ , gr2 will be described with reference to the flowchart shown in FIG. Here, the process shown in FIG. 4 is executed by the controller 30.

In step S101, the controller 30 acquires the current state of the secondary battery 10. The acquired battery state includes the voltage value Vb detected by the monitoring unit 21, the battery temperature Tb detected by the temperature sensor 23, the negative electrode 12 (negative electrode active material model 18n) and the positive electrode 15 (positive electrode active material model 18p). Local SOCs θ ₁ and θ ₂ are included. Local SOCs θ ₁ and θ ₂ can be estimated using the battery model described above. Processing for estimating local SOCs θ ₁ and θ ₂ will be described later.

In step S102, the controller 30 calculates reaction resistances R _{rn, 1} , R _{rn, 2} and pure resistance R _dn when the secondary battery 10 is in the initial state. As described above, the reaction resistance R _{rn, 1} can be calculated from the battery temperature Tb and the local SOC θ ₁ , and the reaction resistance R _{rn, 2} can be calculated from the battery temperature Tb and the local SOC θ ₂ . Moreover, the pure resistance _Rdn can be calculated from the battery temperature Tb.

In step S103, the controller 30 calculates the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 by using the sequential least square method as described above. If the resistance change rates gr1 ₁ , gr1 ₂ , gr2 are calculated, the reaction resistances R _{r, 1} , R _{r, 2} and the pure resistance R _d in the current secondary battery 10 can be grasped.

Further, by calculating the resistance change rates gr1 ₁ and gr1 ₂ , the current potential (monopolar potential) at the negative electrode 12 and the positive electrode 15 can be estimated. Specifically, the following equation (23), based on (24) can calculate the positive electrode potential _{E 1} and the negative electrode potential _{E 2} in the secondary battery 10 of the current (after degradation).

The deterioration of the rechargeable battery 10 progresses, the positive electrode potential E ₁ and the negative electrode potential E ₂ is changed to the cathode open-circuit potential U ₁ and the negative electrode open-circuit potential U ₂ when the secondary battery 10 is in the initial state. Specifically, the equation (23), as shown in (24), the positive electrode potential _{E 1} and the negative electrode potential _{E 2,} the reaction resistance _R r, _1, varies depending on the _{R r, 2.}

Specifically, as shown in the equation (23), the positive electrode potential _{E 1} after the degradation has progressed in the secondary battery 10, to the positive electrode open-circuit potential _{U 1, "R r, 1} × _{I EC, 1} ”changes. Further, as shown in the above formula (24), the negative electrode potential E ₂ after the deterioration of the secondary battery 10 proceeds is “R _{r, 2} × _{IEC, 2} ” with respect to the negative electrode open circuit potential U ₂ . It changes by the amount of change.

If the resistance change rates gr1 ₁ and gr1 ₂ are calculated as described above, the reaction resistances R _{r, 1} , R _{r, 2} can be calculated _, and therefore the positive electrode potential E after the deterioration of the secondary battery 10 proceeds. ₁ and the negative electrode open-circuit potential E ₂ can be grasped.

The process of estimating the resistance change rates gr1 ₁ , gr1 ₂ , gr2 can be performed only when a predetermined condition is satisfied. When the resistance of the secondary battery 10 increases with deterioration, not only the direct current resistance _Ra but also the diffusion resistance tends to increase. The diffusion resistance is a resistance component when lithium diffuses inside the active material, and the diffusion resistance increases due to a decrease in the diffusion rate of lithium in the active material. In a state where the diffusion resistance is likely to increase, not only the increase in the direct current resistance R _a (reaction resistance R _r and pure resistance R _d ) but also the diffusion resistance of the calculated resistance change rate gr1 ₁ , gr1 ₂ , gr2. The increase is easily reflected, and the estimation accuracy of the resistance change rates gr1 ₁ , gr1 ₂ , gr2 is lowered.

Therefore, a state in which the diffusion rate of lithium in the active material is likely to decrease is specified in advance, and in such a state, the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 can be prevented from being estimated. In other words, the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 can be estimated when the state is not specified in advance. Here, as a state where the diffusion rate of lithium tends to decrease, there is a state in which the lithium concentration is extremely biased in the active material.

  The state in which the lithium concentration is extremely biased can be grasped based on the current value Ib (charge rate or discharge rate) flowing through the secondary battery 10. Specifically, as the absolute value of the current value Ib increases, the lithium concentration tends to be biased in the active material. Therefore, the boundary (the first value) of the current value Ib (absolute value) when an extreme bias of the lithium concentration occurs. 1 threshold) can be set in advance. Thereby, when the current value Ib (absolute value) is equal to or greater than the first threshold value, it can be determined that the lithium concentration is extremely biased.

On the other hand, as the current value Ib flowing through the secondary battery 10 decreases, the ratio of the detection error of the current sensor 22 to the detected current value Ib increases. In this case, as described above, when the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 are calculated, the detection error of the current sensor 22 is reflected on the calculated resistance change rates gr1 ₁ , gr1 ₂ , and gr2. As a result, the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 may not be accurately estimated.

For this reason, a boundary (second threshold) in consideration of the detection error of the current sensor 22 is set in advance, and when the absolute value of the current value Ib is smaller than the second threshold, the resistance change rates gr1 ₁ , gr1 ₂ , gr2 Can be avoided. In other words, when the absolute value of the current value Ib is larger than the second threshold value, the resistance change rates gr1 ₁ , gr1 ₂ , gr2 can be estimated. Here, the second threshold is a value smaller than the first threshold described above.

In the present embodiment, as shown in FIG. 5, the diffusion coefficients D _s1 and D _s2 in the active material models 18n and 18p are specified based on the correspondence relationship between the diffusion coefficient D _s and the battery temperature Tb. It is not limited to. Specifically, when the diffusion coefficients D _s1 and D _s2 change as the secondary battery 10 deteriorates, the diffusion coefficients D _s1 and D _s2 are changed according to the deterioration state of the secondary battery 10. be able to.

  First, similarly to the resistance change rates gr11, gr12, and gr2, the diffusion coefficient change rate gd can be appropriately set as shown in the following formula (25).

In the above formula (25), D _sn is a diffusion coefficient when the secondary battery 10 is in the initial state, and D _s is a diffusion coefficient in the current secondary battery 10. The diffusion coefficient D _sn can be obtained in advance by experiments or the like, and information regarding the diffusion coefficient D _sn can be stored in the memory 31. If the diffusion coefficient change rate gd is estimated, the current diffusion coefficient D _s can be calculated based on the above equation (25).

  The diffusion coefficient change rate gd can specify the diffusion coefficient change rate gd corresponding to the actual state of the secondary battery 10 by performing a search process as described below. As this search processing, for example, a known GSM method (golden division method) can be used. Specific search processing for the diffusion coefficient change rate gd is described in Japanese Patent Application Laid-Open No. 2008-241246.

  First, if the above formula (1) is used, the current value (estimated value) I flowing through the secondary battery 10 can be calculated by detecting the voltage value Vb and the temperature Tb in the secondary battery 10. This current value (estimated value) I is usually equal to the current value Ib obtained from the detected value of the current sensor 22. The current value (detected value) Ib here is a value obtained by dividing the current value Ib detected by the current sensor 22 by the electrode plate area S in the negative electrode 12 and the positive electrode 15.

Open-circuit voltage value U and DC resistance _{R a} shown in the equation (1) is locally SOC [theta] _1, it varies according to the theta _2. Further, the local SOCs θ ₁ and θ ₂ are calculated based on the above formula (8). Here, according to the above formula (25), the above formula (8) can be transformed into the following formula (26).

According to the above equation (26), the local SOCs θ ₁ and θ ₂ can be calculated while changing the diffusion coefficient change rate gd. The local SOC [theta] _1, based on the theta _2, the open-circuit voltage value U and DC resistance R _a can be identified, based on the open-circuit voltage value U and DC resistance R _a, the current value (estimated value) I Can be calculated. Here, the diffusion coefficient change rate gd can be searched so that the error between the current value (estimated value) I and the current value (detected value) Ib is minimized.

When calculating the current value (estimated value) I, open-circuit voltage value U, the above formula (1) can be calculated seen, from the positive electrode open-circuit potential U ₁ and the negative electrode open-circuit potential U ₂ (2). The positive electrode open potential U ₁ can be calculated from the local SOC θ ₁ , and the negative electrode open potential U ₂ can be calculated from the local SOC θ ₂ .

Further, as described above, if the resistance change rates gr1 ₁ , gr1 ₂ , and gr2 are calculated, the reaction resistances R _{r, 1} , R _{r, 2} and the pure resistance R _d reflecting the deterioration state of the secondary battery 10 are calculated. can do. Here, since the direct current resistance _Ra is a value obtained by summing the reaction resistances R _{r, 1} , R _{r, 2} and the pure resistance R _d , the direct current resistance _Ra is calculated as the direct current resistance Ra when searching for the diffusion coefficient change rate gd. The sum of the reaction resistances R _{r, 1} , R _{r, 2} and the pure resistance R _d can be used.

The diffusion coefficient change rate gd is can be calculated in each of the negative electrode 12 and positive electrode 15, a change in the diffusion coefficient D _s is some cases dominant even in only one of the negative electrode 12 and positive electrode 15. In this case, changes in the diffusion coefficient D _s is about dominant single pole (negative electrode 12 or positive electrode 15), it is possible to search for the diffusion coefficient change rate gd as described above. On the other hand, the single-pole change in the diffusion coefficient D _s is not dominant (positive electrode 15 or negative electrode 12), without searching the diffusion coefficient change rate gd, the diffusion coefficient D _s which is specified from the relationship shown in FIG. 5 Can be used.

Next, processing for estimating local SOCs θ ₁ and θ ₂ will be described. The local SOCs θ ₁ and θ ₂ are calculated when estimating the SOC of the secondary battery 10. Hereinafter, the process of estimating the SOC of the secondary battery 10 will be described with reference to FIG. FIG. 7 is executed by the controller 30.

In step S <b> 201, the controller 30 detects the voltage value Vb of the secondary battery 10 based on the output of the monitoring unit 21. In step S202, the controller OCV 30 detects the temperature Tb of the secondary battery 10 based on the output of the temperature sensor 23. In step S203, the controller 30 calculates local SOCs θ ₁ and θ ₂ in the active material models 18n and 18p based on the lithium concentration distribution obtained in the previous calculation. The local SOCs θ ₁ and θ ₂ are calculated using the above equation (7).

In step S204, the controller 30 calculates the positive electrode open-circuit potential _{U 1} and the negative electrode open-circuit potential _{U 2.} Since the local SOC θ ₁ of the positive electrode active material model 18p is calculated by the process of step S203, the positive electrode open-circuit potential U ₁ corresponding to the local SOC θ ₁ can be calculated using the correspondence shown in FIG. . Similarly, in the processing in step S203, since the local SOC [theta] ₂ of the negative electrode active material model 18n is calculated, using a correspondence relationship shown in FIG. 4, to calculate the negative electrode open-circuit potential _{U 2} corresponding to local SOC [theta] ₂ be able to.

In step S205, the controller 30 calculates the current values _{IEC, 1} , _{IEC, 2} based on the above formulas (2) to (6). In step S206, the controller 30 sets the boundary condition shown in the above equation (10) in the active material models 18n and 18p. Through the process of step S205, since the current value _{I EC, 1, I EC,} 2 are calculated, based on the above equation (11), the active material model 18n, be calculated lithium production quantity ^{j Li} in 18p it can. If the lithium generation amount j ^Li is calculated, the boundary condition shown in the above equation (10) can be set.

In step S207, the controller 30 calculates the lithium concentration distribution in the active material models 18n and 18p. Specifically, the controller 30 calculates the lithium concentration distribution in the active material models 18n and 18p by solving the diffusion equation shown in the above equation (8) based on the boundary condition set in the process of step S206. . Here, the diffusion coefficient D _s shown in the above equation (8) is specified using the correspondence relationship shown in FIG. 5 prepared for each active material model 18n, 18p.

When solving the diffusion equation shown in the above equation (8), the lithium concentration in the active material models 18n and 18p is determined using the diffusion equation discretized by the position and time in the active material models 18n and 18p. c _{s, k} (t + Δt) is calculated. Here, k indicates the position when the active material models 18n and 18p are discretized in the radial direction. Δt represents a discrete time (calculation cycle). The lithium concentration distribution calculated in step S207 is used in step S203 when the process shown in FIG. 7 is performed next time.

In step S208, the controller 30 calculates the SOC of the secondary battery 10. First, the controller 30 calculates the average lithium concentration c _save inside each active material model 18n, 18p based on the following equation (27).

In the above equation (27), N is the number of divisions when the active material models 18n and 18p are discretized in the radial direction. Since the lithium concentration c _{s, k} is calculated by the process of step S207, the average lithium concentration c _save can be calculated by using the above equation (27).

If the correspondence relationship (map or function) between the average lithium concentration c _save and the SOC of the secondary battery 10 is obtained in advance by experiments or the like, the SOC corresponding to the calculated average lithium concentration c _save can be calculated. Information regarding the correspondence relationship between the average lithium concentration c _save and the SOC can be stored in the memory 31. In the present embodiment, the average lithium concentration c _save is calculated in each of the active material models 18n and 18p. By using at least one of these average lithium concentrations c _save , as described above, the secondary battery 10 The SOC can be calculated.

As described above, in this embodiment, it is possible to grasp the positive electrode potential E ₁ and the negative electrode potential E ₂ after degradation of the secondary battery 10 has progressed. Thereby, a secondary reaction that can occur in the secondary battery 10 can be grasped. Examples of the secondary reaction include lithium deposition, elution of the current collector plate 13 in the negative electrode 12, structural change of the positive electrode 15, and decomposition of the electrolytic solution. These secondary reactions include positive electrode potential. generated in response to a change in E ₁ and the negative electrode potential _{E 2.} Therefore, as described above, by grasping the positive electrode potential E ₁ and the negative electrode potential E ₂ after degradation of the secondary battery 10 has progressed, it is possible to prevent the side-reactions occur.

Negative electrode potential E ₂ lithium deposition potential (e.g., 0 [V]) when lower than, sometimes lithium is precipitated. Therefore, in order to suppress deposition of lithium, as the negative electrode potential E ₂ is not lower than the lithium deposition potential, it is necessary to control the charging and discharging of the secondary battery 10.

Here, the positive electrode potential E ₁ and the negative electrode potential E ₂ have the relationship shown in FIG. In FIG. 8, the vertical axis indicates the potential, and the horizontal axis indicates the capacity. The potential difference between the positive electrode potential E ₁ and the negative electrode potential E ₂ becomes the voltage value Vb of the secondary battery 10. As can be seen from the relationship shown in FIG. 8, as the voltage value of the secondary battery 10 Vb (or volume) is increased, the negative electrode potential E ₂ tends to decrease. Therefore, within the scope of a voltage value lower than the voltage value Vb when the negative electrode potential E ₂ reaches the lithium deposition potential, by controlling the charging and discharging of the secondary battery 10 (particularly, charge), the negative electrode potential E ₂ Can be suppressed from lowering than the lithium deposition potential, and lithium deposition can be suppressed.

As described above, when grasped positive electrode potential E ₁ and the negative electrode potential E ₂ after degradation has proceeded in the secondary battery 10, to identify the voltage value Vb when the negative electrode potential E ₂ reaches the lithium deposition potential that Can do. The voltage value Vb at this time can be set as the upper limit voltage value when controlling charging / discharging of the secondary battery 10. The setting information of the upper limit voltage value can be stored in the memory 31, and the controller 30 controls charging / discharging of the secondary battery 10 so that the voltage value Vb of the secondary battery 10 does not become higher than the upper limit voltage value. .

On the other hand, the elution of the current collector plate 13 may be generated in response to the negative electrode potential E ₂ is increased. For this reason, in order to suppress elution of the current collector plate 13, charging of the secondary battery 10 is performed so that the negative electrode potential E ₂ does not rise above the potential (referred to as elution potential) that causes elution of the current collector plate 13. It is necessary to control the discharge. As can be seen from the relationship shown in FIG. 8, as the voltage value of the secondary battery 10 Vb (or volume) is reduced, the negative electrode potential E ₂ is likely to rise. Therefore, within the scope of the higher voltage value than the voltage value Vb when the negative electrode potential E ₂ reaches the dissolution potential, by controlling the charging and discharging of the secondary battery 10 (in particular, discharge), a negative electrode potential E ₂ The rise from the elution potential can be suppressed, and the elution of the current collector plate 13 can be suppressed.

As described above, that degradation of the secondary battery 10 when grasping the positive electrode potential E ₁ and the negative electrode potential E ₂ after traveling, to identify the voltage value Vb when the negative electrode potential E ₂ reaches the dissolution potential it can. The voltage value Vb at this time can be set as the lower limit voltage value when controlling charging / discharging of the secondary battery 10. The setting information of the lower limit voltage value can be stored in the memory 31, and the controller 30 controls charging / discharging of the secondary battery 10 so that the voltage value Vb of the secondary battery 10 does not become lower than the lower limit voltage value. .

On the other hand, structural changes in the positive electrode 15 may be the positive electrode potential E ₁ is generated in response to a decrease. For this reason, in order to suppress the structural change of the positive electrode 15, the charging / discharging of the secondary battery 10 is performed so that the positive electrode potential E ₁ does not fall below the potential that causes the structural change of the positive electrode 15 (referred to as the structural change potential). Need to control. As can be seen from the relationship shown in FIG. 8, the positive electrode potential E ₁ tends to decrease as the voltage value Vb (or capacity) of the secondary battery 10 decreases. Therefore, within the scope of the higher voltage value than the voltage value Vb at which the positive electrode potential E ₁ reaches the structural changes potential, the charge and discharge (in particular, discharge) of the secondary battery 10 by controlling the positive electrode potential E ₁ Can be suppressed from lowering than the structural change potential, and the structural change of the positive electrode 15 can be suppressed.

As described above, when grasped positive electrode potential E ₁ and the negative electrode potential E ₂ after degradation of the secondary battery 10 has progressed, to identify the voltage value Vb at which the positive electrode potential E ₁ reaches a structural change potential Can do. The voltage value Vb at this time can be set as the lower limit voltage value when controlling charging / discharging of the secondary battery 10. The setting information of the lower limit voltage value can be stored in the memory 31, and the controller 30 controls charging / discharging of the secondary battery 10 so that the voltage value Vb of the secondary battery 10 does not become lower than the lower limit voltage value. .

On the other hand, decomposition of the electrolyte solution may be generated in response to the positive electrode potential E ₁ is increased. Therefore, in order to suppress the decomposition of the electrolyte solution, positive electrode potential E ₁ is, so as not to rise above the potential (referred decomposition potential) for generating a decomposition of the electrolyte solution, to control the charging and discharging of the secondary battery 10 There is a need. As can be seen from the relationship shown in FIG. 8, as the voltage value of the secondary battery 10 Vb (or volume) is increased, the positive electrode potential E ₁ is likely to rise. Therefore, within the range of the voltage value lower voltage value than Vb when the positive electrode potential E ₁ reaches the decomposition potential, by controlling the charging and discharging of the secondary battery 10 (particularly, charge), the positive electrode potential E ₁ It is possible to suppress the rise from the decomposition potential, and to suppress the decomposition of the electrolytic solution.

As described above, when grasped positive electrode potential E ₁ and the negative electrode potential E ₂ after degradation of the secondary battery 10 has progressed, that the positive electrode potential E ₁ identifies a voltage value Vb at the time of reaching the decomposition potential it can. The voltage value Vb at this time can be set as the upper limit voltage value when controlling charging / discharging of the secondary battery 10. The setting information of the upper limit voltage value can be stored in the memory 31, and the controller 30 controls charging / discharging of the secondary battery 10 so that the voltage value Vb of the secondary battery 10 does not become higher than the upper limit voltage value. .

  If the reaction that occurs first among the secondary reactions that occur in the negative electrode 12 and the positive electrode 15 is known, the charging / discharging of the secondary battery 10 is based on the potential (threshold potential) when this reaction occurs. Can be controlled. This threshold potential corresponds to the lithium deposition potential, elution potential, structure change potential, and decomposition potential described above.

  If the secondary reaction that occurs first is suppressed, as a result, other secondary reactions can also be suppressed. As described above, an upper limit voltage value or a lower limit voltage value is set according to the content of the secondary reaction. For this reason, when charging / discharging of the secondary battery 10 is controlled, an upper limit voltage value and a lower limit voltage value are set in consideration of a secondary reaction that occurs first.

  Next, processing for controlling charging / discharging of the secondary battery 10 will be described with reference to a flowchart shown in FIG. The process shown in FIG. 9 is executed by the controller 30.

In step S301, the controller 30 calculates the positive electrode potential _{E 1} and the negative electrode potential _{E 2} of the secondary battery 10. How to calculate the positive electrode potential E ₁ and the negative electrode potential E ₂ are as described above. As described above, each time the deterioration of the secondary battery 10 progresses, the positive electrode potential E ₁ and the negative electrode potential E ₂ is changed.

In step S302, the controller 30 sets the upper limit voltage value _{V U_lim} and lower limit voltage value _{V l_lim.} As described above, if a secondary reaction that occurs first is specified in advance, a threshold potential for suppressing this secondary reaction can be specified. Information regarding this threshold potential can be stored in the memory 31.

Once you have identified the threshold potential, can be based on positive electrode potential _{E 1} and the negative electrode potential _{E 2} calculated in the processing in step S301, it calculates the upper limit voltage value _{V U_lim} and lower limit voltage value _{V l_lim.} That is, by calculating the positive electrode potential E ₁ and the negative electrode potential E ₂ , as described above, the voltage value Vb when the positive electrode potential E ₁ or the negative electrode potential E ₂ reaches the threshold potential can be specified. a value Vb, can be set as the upper limit voltage value _{V U_lim} or lower limit voltage value _{V l_lim.}

Information about the set upper limit voltage value _{V U_lim} and lower limit voltage value _{V L_lim} can be stored in the memory 31. Here, the threshold potential for suppressing a side reaction is used as a fixed value, at least one of the upper limit voltage value _{V U_lim} and lower limit voltage value _{V L_lim} the positive electrode potential _{E 1} and the negative electrode potential _{E 2} It changes as it changes. That is, in response to the positive electrode potential _{E 1} and the negative electrode potential _{E 2} is changed, the upper limit voltage value _{V U_lim} and lower limit voltage value _{V L_lim} is updated.

In step S <b> 303, the controller 30 detects the voltage value Vb of the secondary battery 10 based on the output of the monitoring unit 21. In step S304, the controller 30 determines whether or not the voltage value Vb detected in the process of step S303 is higher than the upper limit voltage value V _{u_lim} . When the voltage value Vb is higher than the upper limit voltage value _{Vu_lim} , the controller 30 performs the process of step S305. On the other hand, when the voltage value Vb is lower than the upper limit voltage value V _{u_lim} , the controller 30 performs the process of step S306.

In step S305, the controller 30 restricts input (charging) of the secondary battery 10 (the assembled battery 1). Specifically, the controller 30 reduces the upper limit power _{Win_lim} that can allow the input of the secondary battery 10. When controlling the charging and discharging of the secondary battery 10, the input power W _in the secondary battery 10 is to be no higher than the upper limit electric power W _{In_lim} input of the secondary battery 10 is controlled.

Therefore, the input of the secondary battery 10 is limited by reducing the upper limit power _{Win_lim} . Here, reducing the upper limit electric power _{W In_lim} also include the ability to limit power _{W In_lim} set to 0 [kW]. If the upper limit power _{Win_lim} is set to 0 [kW], the secondary battery 10 is not charged.

In step S306, the controller 30 determines whether or not the voltage value Vb detected in the process of step S303 is lower than the lower limit voltage value _{Vl_lim} . When the voltage value Vb is lower than the lower limit voltage value _{Vl_lim} , the controller 30 performs the process of step S307. On the other hand, when the voltage value Vb is higher than the lower limit voltage value _{Vl_lim} , the controller 30 ends the process shown in FIG.

In step S307, the controller 30 limits the output (discharge) of the secondary battery 10 (the assembled battery 1). Specifically, the controller 30 reduces the upper limit power W _{out_lim} that can allow the output of the secondary battery 10. When controlling the charging and discharging of the secondary battery 10, the output power _{W out} of the secondary battery 10 so as not higher than the upper limit electric power _{W Out_lim,} the output of the secondary battery 10 is controlled.

Therefore, the output of the secondary battery 10 is suppressed by reducing the upper limit power W _{out_lim} . Here, reducing the upper limit electric power _{W Out_lim} also include the ability to limit power _{W Out_lim} set to 0 [kW]. If the upper limit power W _{out_lim} is set to 0 [kW], the secondary battery 10 is not discharged.

In case of controlling the charging and discharging of the secondary battery 10, in order to suppress any side reaction mentioned above, the upper limit voltage value V _{U_lim} and lower limit voltage value V _{L_lim,} previously assumed deterioration of the secondary battery 10 fixed It is also possible to set the value. However, when the current deterioration state of the secondary battery 10 does not reach the deterioration state assumed in advance, the input / output of the secondary battery 10 is excessively limited. As a result, the input / output performance of the secondary battery 10 cannot be sufficiently exhibited. On the other hand, when the current deterioration state of the secondary battery 10 progresses more than the deterioration state assumed in advance, the secondary reaction cannot be suppressed.

In this embodiment, since the positive electrode potential E ₁ and the negative electrode potential E ₂ in the current secondary battery 10 are estimated, the upper limit voltage value V _{u_lim} and the lower limit voltage value V corresponding to the current deterioration state of the secondary battery 10. _{l_lim} can be set. That is, while grasping the deteriorated state of the secondary battery 10, it is possible to change the upper limit voltage value _{V U_lim} and lower limit voltage value _{V l_lim.} Thereby, it can suppress that the input-output of the secondary battery 10 is restrict | limited too much, suppressing a secondary reaction. In other words, the input / output performance of the secondary battery 10 can be sufficiently exhibited within a range in which a secondary reaction can be suppressed.

1: assembled battery, 10: secondary battery, 12: negative electrode, 14: separator, 15: positive electrode,
13, 16: current collector plate, 18n: negative electrode active material model, 18p: positive electrode active material model,
21: monitoring unit, 22: current sensor, 23: temperature sensor, 24: current limiting resistor,
25: capacitor, 26: inverter, 27: motor generator
30: Controller, 31: Memory, PL: Positive line, NL: Negative line,
SMR-B, SMR-G, SMR-P: System main relay

Claims (7)

A sensor for respectively detecting a current value, a voltage value and a temperature in the secondary battery;
A controller for estimating a potential at a single electrode of the secondary battery,
The controller is
Substituting the value detected by the sensor into a linear regression model equation using the resistance change rate, which is the ratio of the resistance component of the secondary battery in the initial state and the current resistance component of the secondary battery, as a calculation parameter By applying the square method, the resistance change rate is calculated,
Using the resistance change rate calculated for the unipolar reaction resistance included in the resistance component and the unipolar reaction resistance in the initial state, the current unipolar reaction resistance is calculated,
Using the open potential of the monopolar and the amount of change in potential associated with the calculated reaction resistance of the monopolar, calculate the current potential of the monopolar.
A battery system characterized by that. The linear regression model formula is represented by the following formula (I):

In the above formula (I), U ₁ and U ₂ are open-circuit potentials of the positive electrode and the negative electrode, V is a voltage value detected by the sensor, and R _{rn, 1} and R _{rn, 2} are initial states _{IEC, 1} , _{IEC, 2} are current values of electrochemical components flowing through the positive electrode and the negative electrode, and R _dn is an initial value of the secondary battery in the initial state. It is a pure resistance, I is a current value detected by the sensor, gr1 ₁ is the rate of change of resistance relating to the reaction resistance of the positive electrode, and gr1 ₂ is the rate of change of resistance relating to the reaction resistance of the negative electrode. , Gr2 is the resistance change rate related to the pure resistance included in the resistance component.
The battery system according to claim 1. The controller is
The current positive electrode potential is calculated using the current positive electrode reaction resistance calculated from the resistance change rate gr1 ₁ and the open-circuit potential U ₁ .
The current and reaction resistance of the negative electrode which is calculated from the rate of change in resistance gr1 _2, with said open-circuit potential U _2, to calculate the potential of the current of the negative electrode,
The battery system according to claim 2. The open circuit potentials U ₁ and U ₂ change according to local SOC at the interface between the positive electrode active material and the negative electrode active material and the temperature of the secondary battery. Battery system. _{3. The} reaction resistances R _{rn, 1} , R _{rn, 2} change according to local SOC at the interface between the positive electrode active material and the negative electrode active material and the temperature of the secondary battery. To 4. The battery system according to any one of items 4 to 4.   When the controller controls charging / discharging of the secondary battery, the controller changes the voltage value of the secondary battery within a voltage value range in which the calculated potential of the single electrode does not reach a predetermined threshold potential. The battery system according to any one of claims 1 to 5, wherein: The battery system according to claim 6, wherein the threshold potential is a potential that generates a secondary reaction different from a chemical reaction involved in charge / discharge of the secondary battery.