JP6668905B2 - Battery deterioration estimation device - Google Patents

Description

  The present invention relates to a battery, and more particularly to an apparatus for estimating deterioration of a lithium ion secondary battery.

  2. Description of the Related Art A power supply system is used in which power is supplied to a load by a chargeable / dischargeable secondary battery, and the chargeable / dischargeable secondary battery can be charged even during operation of the load as needed. Typically, a hybrid vehicle or an electric vehicle including a motor driven by a secondary battery as a driving force source is equipped with such a power supply system. In these power supply systems, the stored power of the secondary battery is used as the driving power of the motor as a driving power source, the generated power when the motor generates regenerative power, and the power generated by the rotation of the engine. This secondary battery is charged by the generated power or the like. In such a power supply system, it is required that the state estimating device for the secondary battery accurately output a state of charge (SOC) for a fully charged state.

  In particular, in the case of a hybrid vehicle, the charging rate is set to a fully charged state (100%) so that the secondary battery can receive regenerative power and can immediately supply power to the electric motor when requested. ), And control is required to be performed in the vicinity (50-60%) of the state where the battery is not charged at all (0%).

  Also, if the secondary battery is overdischarged or overcharged, the battery may be deteriorated and its life may be shortened. Therefore, in the use form of the secondary battery in which charge and discharge are repeatedly performed with the intermediate SOC as a control target as described above, the charge amount of the secondary battery is sequentially grasped to limit excessive charge and discharge. From the viewpoint of charge / discharge control, it is highly necessary to accurately estimate the state of the secondary battery (for example, see Patent Document 1). For this reason, a model formula and a state estimating device for specifying the state of the lithium ion secondary battery have been proposed (for example, see Patent Document 2). Patent Literature 1 describes a battery model formula assuming lithium deposition.

  Of the plurality of parameters in the battery model formula, three parameters that change according to the change in the state of the secondary battery are the positive electrode capacity retention rate, the negative electrode capacity retention rate, the local charge rate on the surface of the positive electrode active material, and the negative electrode activity. A method has been proposed for estimating the state of a secondary battery using the positive / negative electrode composition correspondence shift capacity, which is the amount of change in the battery capacity due to a change from the initial state of the correspondence relationship of the local charge rate on the surface of the substance (for example, Patent Document 3). Further, it is considered that the positive electrode capacity retention rate, the negative electrode capacity retention rate, and the displacement capacity corresponding to the positive / negative electrode composition are mainly affected by the SEI film formation (side reaction) on the negative electrode surface. The Tafel equation which defines the reaction rate of this side reaction is described.

  Patent Document 3 proposes a technique for simultaneously searching for three deterioration parameters of a positive electrode capacity retention rate, a negative electrode capacity retention rate, and a displacement capacity corresponding to positive and negative electrode compositions, and estimating a state change due to deterioration in a secondary battery. Have been. According to such a technique, the state of the secondary battery can be accurately estimated even when, for example, electrode wear and deposition of a reaction-related substance (for example, deposition of metallic lithium) occur simultaneously.

  However, when the three parameters relating to the battery state to be estimated are collectively identified as in the technique described in Patent Document 3, the calculation load becomes extremely large. Therefore, for example, in an environment in which arithmetic processing capacity and memory capacity are restricted, such as an electronic control unit (ECU: Electronic Control Unit) mounted on a vehicle, it is practical to estimate the battery state by such a method. Can be difficult.

JP 2014-32825 A JP 2008-243373 A Japanese Patent No. 5537236

Vijay A. Sethuraman, Venkat Srinivasan, and John NewmanVijai, "Analysis of Electrochemical Lithiation and Delithiation Kineticsin Silicon", Journal of The Electrochemical Society (ECS), 2013 160 (2) pp A394-A403

  Therefore, an object of the present invention is to accurately estimate the deterioration state of a lithium ion secondary battery with a low calculation load.

電池容量の変化に対する開放電圧の変化を示す開放電圧曲線を測定する測定部と、前記ずれ容量算出部が算出した前記正負極組成対応ずれ容量を用い、前記測定部によって測定された開放電圧曲線実測値と略一致する開放電圧曲線推定値を特定する前記正極容量維持率と前記負極容量維持率とを算出する容量維持率算出部と、前記ずれ容量算出部が算出した前記正負極組成対応ずれ容量と、前記容量維持率算出部が算出した前記正極容量維持率と、前記容量維持率算出部が算出した前記負極容量維持率と、を用いて前記リチウムイオン二次電池の劣化状態を推定する劣化推定部と、を有することを特徴とする。 The battery deterioration estimating device of the present invention has a positive electrode capacity retention ratio that is a ratio of the positive electrode capacity in the deteriorated state to the positive electrode capacity in the initial state, and a negative electrode capacity retention ratio that is a ratio of the negative electrode capacity in the deteriorated state to the negative electrode capacity in the initial state. , The positive and negative electrode composition correspondence displacement capacity, which is the amount of change in battery capacity due to the change from the initial state of the correspondence between the local charge rate on the positive electrode active material surface and the local charge rate on the negative electrode active material surface. A battery deterioration estimating apparatus for estimating deterioration of a lithium ion secondary battery, wherein i ₀ is an exchange current density, α is a transfer coefficient, F is a Faraday constant, R is a gas constant, T is an absolute temperature, and U _side is an absolute temperature. The film formation current density i is calculated for each predetermined period Δt according to the following equation (I) using the film formation potential U ₂ as the negative electrode open potential, and the product of the calculated film formation current density i and the predetermined period Δt is integrated. The positive and negative electrode composition A displacement volume calculating section for calculating a capacity Ozure,

A measurement unit that measures an open-circuit voltage curve indicating a change in the open-circuit voltage with respect to a change in battery capacity, and an open-circuit voltage curve actually measured by the measurement unit using the positive-negative electrode composition corresponding displacement capacity calculated by the displacement capacity calculation unit. A capacity maintenance ratio calculating unit that calculates the positive electrode capacity maintenance ratio and the negative electrode capacity maintenance ratio that specify an open-circuit voltage estimated value that substantially matches the value, and the positive and negative electrode composition-related shift capacities calculated by the shift capacity calculation unit And a deterioration estimating a deterioration state of the lithium ion secondary battery using the positive electrode capacity maintenance ratio calculated by the capacity maintenance ratio calculation unit and the negative electrode capacity maintenance ratio calculated by the capacity maintenance ratio calculation unit. And an estimating unit.

  The present invention can accurately estimate the state of deterioration of a lithium ion secondary battery with a low calculation load.

It is a conceptual diagram which shows the internal structure of a lithium ion secondary battery. FIG. 5 is a diagram illustrating a change characteristic of an open circuit voltage with respect to a local change in SOC of a lithium secondary battery. FIG. 3 is a diagram illustrating a change in the open potential of the positive electrode with a decrease in the positive electrode capacity of the lithium secondary battery and a change in the open potential of the negative electrode with a decrease in the negative electrode capacity. FIG. 3 is a diagram for explaining a difference in composition correspondence between a positive electrode and a negative electrode of a lithium secondary battery. FIG. 3 is a diagram illustrating a shift in composition correspondence due to deterioration of a lithium secondary battery. FIG. 4 is a diagram illustrating a change in open-circuit voltage (open-circuit voltage curve) with respect to the battery capacity of a lithium secondary battery. Positive electrode capacity maintenance rate k _1, negative electrode capacity maintenance rate k _2, is an illustration of a calculation method will to match the open-circuit voltage curve actually measured open-circuit voltage curve estimated by changing the positive and negative electrodes discrepancy capacity Delta] Q _s. 1 is a system diagram illustrating a configuration of an electric vehicle equipped with a battery deterioration estimation device according to an embodiment of the present invention. It is a functional block diagram of a battery deterioration estimation device of an embodiment of the present invention. 5 is a flowchart showing an operation of calculating a positive / negative electrode composition correspondence shift capacity ΔQ _s in the battery deterioration device according to the embodiment of the present invention using the Tafel equation. 5 is a flowchart illustrating a deterioration estimation operation in the battery deterioration estimation device according to the embodiment of the present invention. It is explanatory drawing which shows the detection of an open-circuit voltage curve (actually measured value) and the open-circuit voltage curve (estimated value) in the battery deterioration estimation apparatus of embodiment of this invention. FIG. 5 is an explanatory diagram of a voltage error ΔV. 5 is a flowchart of an operation for calculating a positive / negative electrode composition corresponding displacement capacity ΔQ _s from a positive / negative electrode composition corresponding displacement capacity ΔQ _s2 due to film formation by a Tafel equation based on a positive / negative electrode composition corresponding displacement capacity ΔQ _s1 derived from lithium deposition.

<Lithium ion secondary battery and characteristic formula>
Before describing the battery deterioration estimating device 40 of the embodiment of the present invention, a lithium ion secondary battery (battery 10) for which the battery deterioration estimating device 40 of the present embodiment estimates deterioration and its characteristic formula will be briefly described. .

As shown in FIG. 1, the lithium ion secondary battery includes a negative electrode, a separator containing an electrolytic solution, and a positive electrode. Each of the negative electrode and the positive electrode is composed of an aggregate of spherical active materials. During discharging of the lithium ion secondary battery, a chemical reaction is performed on the interface of the active material of the negative electrode to release lithium ions Li ⁺ and electrons e ⁻ . On the other hand, on the interface of the active material of the positive electrode, a chemical reaction for absorbing lithium ions Li ⁺ and electrons e ⁻ is performed. At the time of charging the lithium ion secondary battery, a reaction opposite to the above-described reaction is performed.

  The negative electrode is provided with a current collector that absorbs electrons, and the positive electrode is provided with a current collector that emits electrons. The current collector plate of the negative electrode is formed of, for example, copper and connected to the negative electrode terminal. The current collector plate of the positive electrode is made of, for example, aluminum and is connected to the positive electrode terminal. Transfer of lithium ions between the positive electrode and the negative electrode via the separator allows charging and discharging of the lithium ion secondary battery.

  Here, the state of charge inside the lithium ion secondary battery differs depending on the lithium concentration distribution in each of the active materials of the positive electrode and the negative electrode.

  The output voltage of the lithium ion secondary battery is represented by the following equation (1).

ここで、ＯＣＶは、リチウムイオン二次電池の開放電圧、Ｒ_aは、リチウムイオン二次電池の全体における抵抗、Ｉは、リチウムイオン二次電池に流れる電流である。抵抗Ｒ_aは、負極および正極で電子の移動に対する純電気的な抵抗と、活物質界面での反応電流発生時に等価的に電気抵抗として作用する電荷移動抵抗とが含まれる。

Here, OCV is the open-circuit voltage of the lithium ion secondary battery, _Ra is the resistance of the entire lithium ion secondary battery, and I is the current flowing through the lithium ion secondary battery. The resistance _Ra includes a pure electric resistance against movement of electrons between the negative electrode and the positive electrode, and a charge transfer resistance equivalently acting as an electric resistance when a reaction current is generated at the active material interface.

θ ₁ is a local charge rate on the surface of the positive electrode active material (hereinafter, the charge rate is referred to as SOC; SOC is an abbreviation of State Of Charge), and θ ₂ is a local charge rate on the surface of the negative electrode active material. SOC. The resistance _Ra has characteristics that change according to changes in θ ₁ , θ ₂ and the battery temperature. In other words, the resistance R _a is, theta _1, can be expressed as a function of theta ₂ and battery temperature.

The local SOCs θ ₁ and θ ₂ are represented by the following equation (2).

ここで、Ｃ_se,iは、活物質（正極または負極）の界面におけるリチウム濃度（平均値）であり、Ｃ_s,i,maxは、活物質（正極または負極）における限界リチウム濃度である。限界リチウム濃度とは、正極や負極におけるリチウム濃度の上限値である。正極、負極の局所的ＳＯＣθ₁、θ₂は、それぞれ、０と１（０％と１００％）の間で変化する。

Here, C _{se, i} is the lithium concentration (average value) at the interface of the active material (positive electrode or negative electrode), and C _{s, i, max} is the limit lithium concentration in the active material (positive electrode or negative electrode). The limit lithium concentration is the upper limit of the lithium concentration in the positive electrode or the negative electrode. The local SOCs θ ₁ and θ ₂ of the positive electrode and the negative electrode change between 0 and 1 (0% and 100%), respectively.

The positive electrode open potential U ₁ has a characteristic that changes in accordance with local SOC θ ₁ on the surface of the positive electrode active material, and the negative electrode open potential U ₂ has a characteristic that changes in accordance with local SOC θ ₂ on the surface of the negative electrode active material. have. FIG. 2 shows the relationship between the local SOC θ _{1 and the} positive electrode open potential U ₁ when the lithium ion secondary battery is in the initial state, and the relationship between the local SOC θ ₂ and the negative electrode open potential U ₂ .

As shown in FIG. 2, open-circuit voltage OCV of the lithium ion secondary battery is expressed as a potential difference of the positive electrode open-circuit potential U ₁ and the negative electrode open-circuit potential U _2. The initial state refers to a state in which the lithium ion secondary battery has not deteriorated, for example, a state immediately after the manufacture of the lithium ion secondary battery.

As shown in FIG. 2, when the lithium ion secondary battery is in the initial state and is almost fully charged, that is, when the open voltage OCV of the lithium ion secondary battery is VH shown in FIG. to have been moved, the local SOC [theta] ₂ of the negative electrode θ _H2 (= 1) negative electrode open-circuit potential U ₂ in the lowest, the positive electrode open-circuit potential U ₁ local SOC [theta] ₁ of the positive electrode at θ _L1 (= 0) is most Is getting higher. Conversely, when the discharge is close to complete discharge, that is, when the open-circuit voltage OCV of the lithium ion secondary battery is VL shown in FIG. 2, all lithium has moved to the positive electrode, and the local SOC θ _{1 of the} positive electrode is θ _H1 (= 1) at the positive electrode open-circuit potential U ₁ is the lowest, the negative electrode open-circuit potential with local SOC [theta] ₂ of the negative electrode θ _L2 (= 0) is the highest. Data indicating these characteristics (U ₁ , U ₂ ) can be stored in the memory 42 shown in FIG. 8 in advance as a map.

  The open-circuit voltage OCV of a lithium ion secondary battery has a characteristic of decreasing as the discharge proceeds. Further, in the deteriorated lithium ion secondary battery, the amount of voltage drop for the same discharge time is larger than in the initial state lithium ion secondary battery. This indicates that the deterioration of the lithium ion secondary battery causes a decrease in the full charge capacity and a change in the open-circuit voltage curve. In the present embodiment, the change of the open-circuit voltage curve due to the deterioration of the lithium ion secondary battery is modeled as two phenomena that are considered to occur inside the lithium ion secondary battery in the deteriorated state.

  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 the single-electrode capacity indicates a decrease in the capacity of accepting lithium in each of the positive electrode and the negative electrode. The decrease in the capacity for accepting lithium means that the active material or the like that effectively functions for charge and discharge is reduced.

Figure 3 is a variation of the positive electrode open-circuit potential U ₁ due to a reduction in positive electrode capacity and the change of the negative electrode open-circuit potential U ₂ due to a reduction in the negative electrode capacity is schematically shown. 3, Q_L1 on the axis of the positive electrode capacity is a capacity corresponding to the local SOC θ _L1 (= 0) in FIG. 2 in the initial state of the lithium ion secondary battery. Q_H11 is a capacity corresponding to the local SOC θ _H1 (= 1) in FIG. 2 in the initial state of the lithium ion secondary battery. Further, Q_L2 on the axis of the negative electrode capacity is a capacity corresponding to the local SOC θ _L2 (= 0) in FIG. 2 in the initial state of the lithium ion secondary battery, and Q_H21 is a capacity in the initial state of the lithium ion secondary battery. , The capacity corresponding to the local SOC θ _H2 (= 1) in FIG.

When the capacity of accepting lithium in the positive electrode decreases, the capacity corresponding to the local SOC θ _H1 (= 1) changes from Q_H11 to Q_H12. Further, when the capacity for accepting lithium in the negative electrode is reduced, the capacity corresponding to the local SOC θ _H2 (= 1) changes from Q_H21 to Q_H22.

Here, even if the lithium ion secondary battery deteriorates, the relationship between the local SOC θ ₁ and the positive electrode open potential U ₁ (the relationship shown in FIG. 2) does not change. Therefore, the relationship between local SOC [theta] ₁ and positive electrode open-circuit potential U _1, is converted into the positive electrode capacity and the relationship of the positive electrode open-circuit potential U _1, as shown in FIG. 3, the positive electrode open-circuit potential U ₁ for the positive electrode capacity of the deteriorated state The curve showing the relationship is in a state in which the curve of the initial state is reduced by the amount of deterioration of the lithium ion secondary battery.

Similarly, the negative electrode open-circuit potential U ₂ relationship to the local SOC [theta] _2, is converted into the relationship of the negative electrode capacity and the negative electrode open-circuit potential U _2, as shown in FIG. 3, the negative electrode open-circuit potential U ₂ for the negative electrode capacity of the deteriorated state The curve showing the relationship is in a state in which the curve of the initial state is reduced by the amount of deterioration of the lithium ion secondary battery.

FIG. 4 schematically shows the correspondence of the composition between the positive electrode and the negative electrode. The difference in the composition correspondence means that when charging and discharging are performed using a pair of a positive electrode and a negative electrode, the combination of the composition of the positive electrode (θ ₁ ) and the composition of the negative electrode (θ ₂ ) is changed to the initial state of the lithium ion secondary battery. This indicates that the position is shifted.

The curves showing the relationship between the positive SOC and the negative anode open potential U ₁ , U ₂ with respect to the local SOC θ ₁ , θ ₂ of the positive electrode and the negative electrode are the same as the curves shown in FIG. Here, when deterioration of the lithium ion secondary battery, the axis of the anode composition theta ₂ is shifted in the direction the positive electrode composition theta ₁ is smaller by [Delta] [theta] _2. Accordingly, the curve showing the negative electrode relationship between the open voltage U ₂₂ for the negative electrode compositions theta ₂ of the axis of the deteriorated state, to the curve showing the relationship between the negative electrode open-circuit potential U ₂₁ for the negative electrode compositions theta ₂ of the axis of the initial state, [Delta] [theta] only ₂ minute shifts in the direction of the positive electrode composition theta ₁ is reduced.

The composition of the negative electrode corresponding to the composition θ _1fix of the positive electrode is “θ _2fix _ _ini ” when the lithium ion secondary battery is in the initial state, but becomes “θ _2fix ” after the lithium ion secondary battery is deteriorated. .

In the present embodiment, the two deterioration phenomena described above are modeled by introducing three deterioration parameters into the battery model. The three deterioration parameters are a positive electrode capacity retention rate k ₁ , a negative electrode capacity retention rate k _2, and a shift capacity ΔQ _s corresponding to the positive and negative electrode compositions. A method for modeling the two deterioration phenomena will be described below.

The positive electrode capacity maintenance rate k _1, means the ratio of the positive electrode capacity of the deteriorated state for the positive electrode capacity in the initial state. Here, it is assumed that the positive electrode capacity is reduced by an arbitrary amount from the capacity in the initial state after the lithium ion secondary battery is in a deteriorated state. At this time, the positive electrode capacity retention ratio k ₁ is represented by the following equation (3).

Here, Q ₁ _ _ini represents the positive electrode capacity when the lithium ion secondary battery is in the initial state (Q_H11 shown in FIG. 3), Delta] Q ₁ is a positive electrode capacity when the lithium ion secondary battery has degraded The amount of decrease is shown. Thus positive electrode capacity when the lithium ion secondary battery becomes deteriorated state (Q_H12 shown in FIG. 3) becomes _{(Q 1 _ ini -ΔQ 1)} . Also, k ₁ decreases from ₁ in the initial state. Here, the positive electrode capacity Q _{1 _ini} in the initial state can be obtained in advance from the theoretical capacity or the charged amount of the active material.

The negative electrode capacity maintenance rate k _2, means the ratio of the negative electrode capacity of the deteriorated state of the negative electrode capacity in the initial state. Here, it is assumed that the negative electrode capacity is reduced by an arbitrary amount from the capacity in the initial state after the lithium ion secondary battery is in a deteriorated state. At this time, the negative electrode capacity retention ratio k ₂ is represented by the following equation (4).

Here, Q ₂ _ _ini represents a negative electrode capacity (Q_H21 shown in FIG. 3) when the lithium ion secondary battery is in the initial state, Delta] Q ₂ is the negative electrode capacity when the lithium ion secondary battery has degraded The amount of decrease is shown. Therefore, the negative electrode capacity (Q_H22 shown in FIG. 3) when the lithium ion secondary battery is in a deteriorated state is (Q _{2 # ini−} ΔQ ₂ ). Also, k ₂ decreases from 1 in the initial state. Here, the negative electrode capacity Q _{2 _ini} in the initial state can be obtained in advance from the theoretical capacity or the charged amount of the active material.

  FIG. 5 is a schematic diagram for explaining a difference in composition correspondence between the positive electrode and the negative electrode.

When the lithium ion secondary battery becomes deteriorated state, the negative electrode capacity when the negative electrode composition theta ₂ is 1, the _{(Q 2 _ ini -ΔQ 2)} . Further, the positive / negative electrode composition displacement capacity ΔQ _s is a capacity corresponding to the displacement Δθ ₂ of the negative electrode composition axis θ ₂ with respect to the positive electrode composition axis θ ₁ . Thereby, the relationship of the following equation (5) is established. The positive / negative electrode composition correspondence shift capacity ΔQ _s is a correspondence relationship between a local SOC θ ₁ which is a local charge rate on the surface of the positive electrode active material and a local SOC θ ₂ which is a local charge rate on the surface of the negative electrode active material. 5 shows the amount of change in battery capacity due to a change from the initial state.

  The following equation (6) is obtained from the equations (4) and (5).

When the lithium ion secondary battery is in the initial state, the positive electrode composition theta _1fix _ _ini corresponds to the negative electrode composition _θ 2fix _ _ini. When the lithium ion secondary battery is in a deteriorated state, the positive electrode composition theta _1fix corresponds to the negative electrode composition _θ 2fix. Further, the deviation of the composition correspondence is based on the positive electrode composition θ _1fix in the initial state. That is, the positive electrode composition θ _1fix and the positive electrode composition θ _{1fix — ini} have the same value.

In the case where the composition correspondence between the positive electrode and the negative electrode is caused by the deterioration of the lithium ion secondary battery, the positive electrode composition θ _1fix and the negative electrode composition θ _2fix after the deterioration of the lithium ion secondary battery are _expressed by the following formula (7). , (8).

The meaning of equation (8) will be described. When lithium is released from the positive electrode by charging while the lithium ion secondary battery is in a deteriorated state, the positive electrode composition θ ₁ decreases from ₁ . When the positive electrode composition θ ₁ decreases from 1 to θ _1fix , the amount of lithium released from the positive electrode is represented by the following equation (9).

ここで、（１−θ_1fix）の値は、リチウムイオン二次電池の充電による正極組成θ₁の減少分を示し、（ｋ₁×Ｑ₁__ini）の値は、リチウムイオン二次電池の劣化後における正極容量を示している。

Here, the value of (1−θ _1fix ) indicates a decrease in the positive electrode composition θ ₁ due to charging of the lithium ion secondary battery, and the value of (k ₁ × Q _{1 — ini} ) indicates the value of the lithium ion secondary battery. It shows the positive electrode capacity after deterioration.

_Assuming that all the lithium released from the positive electrode is taken into the negative electrode, the negative electrode composition θ _2fix is represented by the following formula (10).

ここで、（ｋ₂×Ｑ₂__ini）の値は、リチウムイオン二次電池の劣化後における負極容量を示している。

Here, the value of (k ₂ × Q _{2 — ini} ) indicates the negative electrode capacity of the lithium ion secondary battery after deterioration.

On the other hand, when there is a deviation (Δθ ₂ ) corresponding to the composition between the positive electrode and the negative electrode, the negative electrode composition θ _2fix after deterioration is represented by the following equation (11).

The shift amount Δθ ₂ corresponding to the composition can be expressed by the equation (6) using the shift capacitance ΔQ _s corresponding to the positive and negative electrode compositions. Thereby, the negative electrode composition θ _2fix after deterioration is expressed by the above equation (8).

As shown in FIG. 5, the open-circuit voltage OCV when the lithium ion secondary battery is in a deteriorated state is expressed as a potential difference of the positive electrode open-circuit potential U ₁₁ and the negative electrode open-circuit potential U ₂₂ in a degraded state. That is, if the three deterioration parameters, ie, the positive electrode capacity retention rate k ₁ , the negative electrode capacity retention rate k ₂ , and the positive / negative electrode composition correspondence shift capacity ΔQ _s are specified, the negative electrode open potential when the lithium ion secondary battery is in the deteriorated state is determined. it can be identified U _22, as a potential difference of the negative electrode open-circuit potential U ₂₂ and the positive electrode open-circuit potential U _11, it is possible to calculate the open circuit voltage OCV.

That is, the positive electrode capacity in the initial state Q ₁ _ _ini, since the negative electrode capacity Q ₂ _ _ini can be obtained in advance from the theoretical capacity and charge of the active material, positive electrode capacity maintenance rate k ₁ is a three degradation parameters, When the negative electrode capacity retention ratio k ₂ and the positive / negative electrode composition corresponding displacement capacity ΔQ _s can be specified, the deteriorated negative electrode composition θ _2fix can be calculated using Expression (8). Further, the shift amount Δθ ₂ corresponding to the composition can be calculated using the equation (6). Now, as shown in FIG. 5, may be a positive electrode composition theta ₁ the deteriorated state to identify the negative electrode composition axis theta ₂ 0 position and the negative electrode composition theta _2Fix the deteriorated state with respect to the position of 1. Then, from the positions of 0 and θ _2fix, the position where the negative electrode composition axis θ ₂ in the deteriorated state becomes 1 can be specified as shown in FIG.

Even deteriorated lithium ion secondary battery, the relationship of the positive electrode open-circuit potential U ₁ for local SOC [theta] ₁ of the positive electrode, the relationship between the negative electrode open-circuit potential U ₂ for the local SOC [theta] ₂ of the negative electrode (the relationship shown in FIG. 2) is not changed . Thus, if a particular 0 and 1 positions of the negative electrode composition axis theta ₂ of the deterioration state for 1 and 0 position of the positive electrode composition theta ₁ of the deterioration state, between 1 and 0 of the positive electrode composition theta ₁ a degraded 2 drawing a curve showing the relationship between the positive electrode open-circuit potential U ₁ for local SOC [theta] ₁ of the positive electrode shown in the negative electrode open for local SOC [theta] ₂ of the negative electrode shown in FIG. 2 between 1 and 0 of the positive electrode composition theta ₁ a degraded When a curve showing the relationship between potential U _2, each curve, the positive electrode open-circuit potential U ₁₂ deteriorated state shown in FIG. 5, a negative electrode open-circuit potential U _22. As described above, when the curves indicating the positive electrode open potential U ₁₂ and the negative electrode open potential U ₂₂ can be specified, the open circuit voltage OCV of the deteriorated lithium secondary battery can be calculated.

As described above, when the three deterioration parameters, ie, the positive electrode capacity retention rate k ₁ , the negative electrode capacity retention rate k ₂ , and the positive / negative electrode composition correspondence shift capacity ΔQ _s are specified, the open circuit voltage OCV of the deteriorated state lithium secondary battery is calculated. Can be.

In the lithium ion secondary battery in the initial state, the positive electrode capacity retention rate k ₁ and the negative electrode capacity retention rate k ₂ are 1, and the positive / negative electrode composition correspondence displacement capacity ΔQ _s is 0. ) Is equal to a value (actually measured value) when the open circuit voltage OCV of the lithium ion secondary battery in the initial state (new) is measured.

  As shown in FIG. 6, the open circuit voltage OCV of the lithium ion secondary battery increases as the battery capacity (A × h) increases, that is, as the secondary battery is charged. Hereinafter, a change curve of the open-circuit voltage OCV with respect to the battery capacity (A × h) is referred to as an open-circuit voltage curve. The open-circuit voltage curve shifts from the initial state to the left side in the figure when deteriorated, as shown by the one-dot chain line and the broken line in FIG.

As described above, the open-circuit voltage OCV of the deteriorated state lithium secondary battery is calculated from the three deterioration parameters, ie, the positive electrode capacity retention rate k ₁ , the negative electrode capacity retention rate k ₂ , and the positive / negative electrode composition correspondence shift capacity ΔQ _s. since it is, it is possible to positive electrode capacity maintenance rate k _1, negative electrode capacity maintenance rate k _2, the positive and negative electrodes discrepancy capacity Delta] Q _s to calculate the open-circuit voltage curve of the lithium secondary battery.

Therefore, the battery deterioration estimating device 40 of the present embodiment uses the positive electrode capacity retention ratio k ₁ , the negative electrode capacity retention ratio k ₂ , and the positive / negative electrode composition corresponding shift capacity ΔQ _s of the three deterioration parameters. ΔQ _s is calculated and specified in advance by a battery model formula (formulas (12) and (13)) and a Tafel formula (formula (14)) which will be described later, and the open-circuit voltage curve (estimated value) is determined by the open-circuit voltage. The convergence calculation is performed as shown in FIG. 7 by changing the positive electrode capacity retention ratio k ₁ and the negative electrode capacity retention ratio k ₂ so as to substantially match the curve (actually measured value). k _1, negative electrode capacity maintenance rate k _2, and estimates the capacity deterioration of the lithium ion secondary battery to identify the positive and negative electrodes discrepancy capacity Delta] Q _s.

<Model formula of lithium ion battery>
Next, lithium for calculating the positive / negative electrode composition correspondence shift capacity ΔQs from the measured terminal voltage V of the lithium ion battery and the battery absolute temperature T, which is applied in the battery deterioration estimating device 40 of the present embodiment described later. The model formula of the ion battery will be briefly described.

  Equations (12) and (13) below assume that the chemical reaction in each of the positive electrode and the negative electrode is uniform, and that the lithium ion concentration in each active material model does not depend on the position in the circumferential direction. And a simplified battery model formula.

In equation (12), V is the voltage between terminals, U is the electrode potential, I is the current density, θ is the local SOC, R is the gas constant, T is the battery absolute temperature, F is the Faraday coefficient, α is the transfer coefficient, i ₀ is the exchange current density, D _s is the diffusion coefficient, L is the electrode thickness, k ^eff is the effective ionic conductivity of the electrolyte, c _s is the lithium concentration of the active material, r is the radius of the active material, and t is time. . The subscript 1 indicates a positive electrode, and 2 indicates a negative electrode.

The first term on the right side of the equation (12) indicates an open circuit voltage (OCV) determined by the concentration of the reactant (lithium) on the surface of the active material, and the second term on the right side indicates the overvoltage (η ₁ ^♯− η ₂ ^♯ ). And the third term on the right side indicates a voltage drop due to the battery current. That is, the DC pure resistance of the secondary battery is represented by Rd (T) in the equation (12).

Further, in the equation (13), the diffusion coefficients D _s1 and D _s2 used as parameters defining the diffusion rate of lithium as a reactant have a temperature dependency, and therefore, the battery absolute temperature T , A map for setting the diffusion coefficients D _s1 and D _s2 as battery parameter values is created and stored in the memory 42 shown in FIG. Similar maps are created for the exchange current density i ₀ and the DC resistance Rd and stored in the memory 42.

Further, regarding the positive electrode open potential U ₁ and the negative electrode open potential U ₂ in the equation (12), the change in the positive electrode open potential U _{1 with} respect to the local SOC θ ₁ of the positive electrode as described with reference to FIG. A map showing a change in the negative electrode open potential U ₂ with respect to the local SOC θ ₂ is created and stored in the memory 42 shown in FIG.

Then, using the voltage value Vb of the battery 10 detected by the voltage sensor 31 shown in FIG. 8, the temperature Tb detected by the temperature sensor 33, and the above parameters stored in the memory 42, the equations (12) and ( by solving 13), it is possible to calculate the negative electrode open-circuit potential U ₂ used in expression Tafel described later (equation (14)).

<Calculation of Positive / Negative Electrode Composition Corresponding Displacement Capacity ΔQ _s Using Tafel Equation>
It is considered that the shift capacity ΔQ _s corresponding to the positive / negative electrode composition is mainly affected by the SEI film formation (side reaction) on the negative electrode surface. And the film formation current density i can be calculated by the following equation (14). Equation (14) is sometimes referred to as Tafel equation.

式（１４）において、ｉ₀は交換電流密度、αは移動係数、Ｆはファラデー定数、Ｒはガス定数、Ｔは電池絶対温度、Ｕ_sideは被膜形成電位、Ｕ₂は負極開放電位である。

In the equation (14), i ₀ is the exchange current density, α is the transfer coefficient, F is the Faraday constant, R is the gas constant, T is the battery absolute temperature, U _side is the film formation potential, and U ₂ is the negative electrode open potential.

When charge and discharge are repeated several times after the completion of the manufacture of the lithium ion secondary battery, the exchange current density i _{0 in} the equation (14) is settled to a substantially constant value because the formation speed of the SEI film becomes substantially steady. For this reason, as described above, a map corresponding to the battery absolute temperature T may be created in advance by a test or the like, and read from this map. In addition, as a test for determining the exchange current density i ₀ , as described in Non-Patent Document 1, lithium ion whose charge and discharge characteristics are in a steady state by repeating charge and discharge several times after the completion of manufacturing is described. performed a plurality of times of charging and discharging the secondary battery (lithium ion secondary battery after the completion of aging), is determined based on the amount of movement in the transverse direction of the negative electrode open-circuit potential U ₂ of characteristic curves for the battery capacity at that time You may do so.

The transfer coefficient α may be set to 0.5, for example, assuming that the charge and discharge efficiency is the same. Further, the reductive decomposition of the electrolytic solution, which is a main factor of the film formation, occurs continuously when the negative electrode open potential is 0.6 V to 1.0 V. For example, the film formation potential U _{side is set} to 0.6 V, 0.8 V or It may be set as 1.0V.

The shift capacity ΔQ _s corresponding to the positive / negative electrode composition is obtained by integrating the film formation current density i calculated by the equation (14) with time as shown in the equation (15).

具体的には、式（１４）によって周期Δｔごとに被膜形成電流密度ｉを計算し、（ｉ×Δｔ）を積算して求める。この計算は、リチウムイオン二次電池の使用を開始した直後、例えば、リチウムイオン二次電池が搭載された電動車両１００が完成後、最初にイグニッションスイッチがオンとなった時から積算を開始する。

Specifically, the film formation current density i is calculated for each period Δt by the equation (14), and (i × Δt) is integrated. This calculation is started immediately after the use of the lithium ion secondary battery is started, for example, when the ignition switch is first turned on after the completion of the electric vehicle 100 equipped with the lithium ion secondary battery.

<Configuration of battery deterioration estimation device>
Next, the configuration of the battery deterioration estimation device 40 of the present embodiment will be described. First, the battery deterioration estimating device 40 according to the embodiment of the present invention mounted on the electric vehicle 100 will be described with reference to FIG. The electric vehicle 100 includes a battery 10, an inverter 13 connected to the battery 10 via the positive electrode line 11 and the negative electrode line 12, a motor generator 14 which is a vehicle driving motor driven and controlled by the inverter 13, A main ECU 70 that controls the operation of the motor generator 14, a battery deterioration estimating device 40 that estimates the deterioration of the battery 10, a state of the battery 10 that is monitored, and the SOC, Win (maximum chargeable power), and Wout (maximum discharge) of the battery 10. And a battery ECU 60 that outputs the potential power to the main ECU 70. The electric vehicle 100 further includes an external power supply connector 15 connected to the positive electrode line 11 and the negative electrode line 12 and capable of charging the battery 10 with an external power supply.

  The battery 10 is provided with a voltage sensor 31 for detecting a voltage value Vb and a temperature sensor 33 for detecting a temperature Tb. Further, a current sensor 32 for detecting a current value Ib of the battery 10 is attached to the positive electrode line 11. The detection signals of the voltage sensor 31, the current sensor 32, and the temperature sensor 33 are input to a battery deterioration estimating device 40 which is a battery deterioration estimating device. The detection signals of the voltage sensor 31, the current sensor 32, and the temperature sensor 33 are also input to the battery ECU 60.

  The battery 10 is a chargeable / dischargeable secondary battery such as a lithium ion secondary battery. Motor generator 14 receives electric power output from battery 10, drives electric vehicle 100, converts kinetic energy generated during braking of electric vehicle 100 into electric power, and charges battery 10. Therefore, while the electric vehicle 100 is running, the battery 10 repeatedly charges and discharges. The current value Ib from the battery 10 is such that the discharge current is positive (+) and the charging current is negative (-).

  The battery deterioration estimating device 40 includes a CPU 41 that internally performs information processing and calculations, a memory 42 that stores a control program, control data, and the like, and a sensor interface 43 to which the voltage sensor 31, the current sensor 32, and the temperature sensor 33 are connected. And a computer in which a CPU 41, a memory 42, and a sensor interface 43 are mutually connected by a data bus 44. Further, the battery ECU 60 and the main ECU 70 are also computers including a CPU for performing information processing and calculations, and a memory for storing control programs, control data, and the like. The battery ECU 60 is a higher-level control device of the battery deterioration estimating device 40, and the main ECU 70 is a higher-level control device of the battery ECU 60. The battery deterioration estimation device 40 and the battery ECU 60 are connected by a data bus 45, and are configured to exchange data with each other. Further, the battery ECU 60 and the main ECU 70 are also connected by the data bus 46 so that data can be exchanged with each other. The data bus 44 of the battery deterioration estimating device 40 is also connected to the data buses 45 and 46.

In the memory 42, diffusion coefficients D _s1 and D _s2 , exchange current density i ₀ , DC resistance Rd, and local voltage of the positive electrode for calculating the negative electrode open potential U ₂ using the equations (12) and (13) are stored. change of the positive electrode open-circuit potential U ₁ for SOC [theta] _1, and the map of the map or the like showing the change of the negative electrode open-circuit potential U ₂ for the local SOC [theta] ₂ of the negative electrode, transfer coefficient alpha, Faraday constant F, the gas constant R, the film-forming potential U _side Etc. are stored.

  Next, functional blocks of the battery deterioration estimating device 40 of the present embodiment will be described with reference to FIG. As shown in FIG. 9, the battery deterioration estimating device 40 of the present embodiment includes a displacement capacity calculating unit 51, a measuring unit 52, a capacity maintenance ratio calculating unit 53, and a deterioration estimating unit 54.

The displacement capacity calculation unit 51 uses the voltage value Vb of the battery 10 detected by the voltage sensor 31 shown in FIG. 8, the temperature Tb detected by the temperature sensor 33, and the parameters stored in the memory 42 to obtain the equation (12). , (13) to calculate the negative electrode open potential U ₂ . Then, the film formation current density i is calculated for each predetermined period Δt by the equation (14), and the product of the calculated film formation current density i and the predetermined period Δt is integrated as shown in the equation (15). The positive / negative electrode composition displacement capacity ΔQ _s is calculated and stored in the memory 42 (steps S101 to S106 shown in FIG. 10).

  The measuring unit 52 calculates the battery 10 at time t1 based on the voltage value Vb of the battery 10 detected by the voltage sensor 31 shown in FIG. 8, the current value Ib detected by the current sensor 32, and the temperature Tb detected by the temperature sensor 33. The OCV (t1) and the OCV (t2) of the battery 10 at the time t2 are detected, and the charging / discharging current between the time t1 and the time t2 is integrated to obtain an open-circuit voltage curve which is a change characteristic of the OCV to the battery capacity. (Actual measured value) is detected and stored in the memory 42 (Steps S201 to S205 shown in FIG. 11).

The capacity retention ratio calculation unit 53 uses the positive / negative electrode composition correspondence deviation capacity ΔQ _s read from the memory 42 and the set candidate of the positive electrode capacity retention ratio k ₁ and the set candidate of the negative electrode capacity retention ratio k ₂ to open-circuit voltage curve. (estimated value) is calculated, perform iterative calculation until identifying a positive electrode capacity maintenance rate k ₁ and negative electrode capacity maintenance rate k ₂ which coincides with the open-circuit voltage curve stored in the memory 42 (measured value), identified the positive electrode capacity storing maintenance rate k ₁ and negative electrode capacity maintenance rate k ₂ and the open-circuit voltage curve and (estimated value) in the memory 42 (S212 from step S206 shown in FIG. 11).

The deterioration estimating unit 54 calculates the positive / negative electrode composition corresponding shift capacity ΔQ _s calculated by the shift capacity calculation unit 51, the positive capacity maintenance rate k ₁ and the negative capacity maintenance rate k ₂ calculated by the capacity maintenance rate calculation unit 53, and the open-circuit voltage curve ( ) Is calculated and output from the estimated value). The deterioration state value is, for example, a full charge capacity of the battery 10 or an open-circuit voltage curve (estimated value) of the battery 10.

  The deterioration state value of the battery 10 output by the deterioration estimating unit 54 is input to the battery ECU 60. The battery ECU 60 uses the voltage value Vb of the battery 10 detected by the voltage sensor 31 shown in FIG. 8, the current value Ib detected by the current sensor 32, the temperature Tb detected by the temperature sensor 33, and the deterioration state value. The battery status values such as SOC, Win (maximum chargeable power), and Wout (maximum dischargeable power) are output to the main ECU 70. The main ECU 70 controls the inverter 13 and the motor generator 14 using these battery state values to drive the electric vehicle 100.

  The functional blocks of the battery deterioration estimating device 40 of the present embodiment as described above mainly include the CPU 41 and the memory 42 included in the battery deterioration estimating device 40 and the programs read from the memory 42 and executed by the CPU 41. Implemented by software.

<Calculation of Positive / Negative Electrode Composition-Related Displacement Capacity ΔQ _s Using Tafel Equation (Equation (14))>
Next, the operation of the battery deterioration estimating device 40 will be described with reference to FIGS. First, with reference to FIG. 10, calculation of the shift capacitance ΔQ _s corresponding to the positive and negative electrode compositions by the shift capacitance calculating unit 51 will be described.

As described above, the calculation of the positive / negative electrode composition corresponding displacement capacity ΔQ _s is performed immediately after the use of the battery 10 is started, for example, when the ignition switch is first turned on after the completion of the electric vehicle 100 on which the battery 10 is mounted. Starts counting when it reaches the end. When the ignition switch is turned on for the first time, the displacement capacitance calculating unit 51 repeatedly executes steps S101 to S106 shown in FIG. 10 at predetermined intervals Δt (for example, 0.1 seconds).

As shown in step S101 of FIG. 10, the displacement capacity calculation unit 51 detects the voltage value Vb of the battery 10 with the voltage sensor 31 shown in FIG. 8, and detects the temperature Tb with the temperature sensor 33. As shown in step S102 of FIG. 10, the shift capacitance calculation unit 51 determines whether the diffusion coefficients D _s1 and D _s2 stored in the memory 42, the exchange current density i ₀ , the DC resistance Rd, and the positive electrode opening for the positive local SOC θ ₁ are stored. A map such as a map showing a change in the potential U _1, a change in the negative electrode open potential U ₂ with respect to the local SOC θ ₂ of the negative electrode, and data such as a transfer coefficient α, a Faraday constant F, a gas constant R, and a film formation potential U _side are read. , as shown in step S103 of FIG. 10, equation (12), to calculate the negative electrode open-circuit potential U ₂ using equation (13). Then, the shift capacitance calculating unit 51 calculates the film formation current density i according to the equation (14) as shown in step S104 in FIG. 10, and as shown in step S105 in FIG. by integrating the product of the Δt to calculate the positive and negative electrodes discrepancy capacity Delta] Q _s (equation (15)), as shown in step S106, and stores the calculated negative electrodes discrepancy capacity Delta] Q _s in the memory 42.

Even when the ignition switch is off and the electric vehicle 100 is stopped, the open voltage OCV of the battery 10 decreases due to self-discharge. Therefore, even when the electric vehicle 100 is stopped, the displacement capacity calculation unit 51 acquires the voltage value Vb, the temperature Tb, and the time t of the battery 10 from the battery monitoring unit, and executes steps S101 to S106 in FIG. The composition-dependent displacement capacity ΔQ _s is integrated.

If the data of the voltage value Vb and the temperature Tb of the battery 10 cannot be obtained while the electric vehicle 100 is stopped, the voltage value Vb and the temperature Tb of the battery 10 when the ignition switch is turned off, and then the ignition switch Is turned on, the voltage value Vb and the temperature Tb of the battery 10 are complemented by linear interpolation or an exponential function or the like to calculate the voltage value Vb and the temperature Tb of the battery 10 for each period Δt, and the calculated complement values are used. the S106 from step S101 in FIG. 10 may be performed the integration of the positive and negative electrodes discrepancy capacity Delta] Q _s running Te.

<Operation of battery deterioration estimation device>
Next, the operation of estimating the deterioration of the battery 10 will be described with reference to FIGS. The deterioration estimation of the battery 10 is such that the electric vehicle 100 is traveling a predetermined distance or a predetermined time has elapsed after the end of the previous deterioration estimation, and the SOC of the battery 10 is low enough to obtain an open-circuit voltage curve by charging. Alternatively, the control is executed when the SOC of the battery 10 is high enough to obtain an open-circuit voltage curve by discharging and the battery 10 is in a relaxed state. The determination condition that the battery 10 is relaxed is, for example, that the maximum concentration difference of the lithium ion concentration in the active material in the battery model is equal to or less than a predetermined concentration difference, and the absolute value of the battery current is a predetermined value. It is a condition that is less than or equal to the value. Specifically, when the battery 10 is charged by an external power supply from a state where the SOC of the battery 10 is low, or when the electric vehicle 100 is stopped, the deterioration estimation operation of the battery 10 is executed.

  Hereinafter, as an example, a case will be described in which an external power supply is connected to the external power supply connector 15 shown in FIG. 8 and the deterioration estimation operation of the battery 10 is performed when the battery 10 is charged by the external power supply.

As shown in step S201 in FIG. 11, the measuring unit 52 detects the open voltage OCV of the battery 10 by the voltage sensor 31 at time t1 when the external power supply is connected to the external power supply connector 15 and charging of the battery 10 by the external power supply is started. (T1) is detected. When the current value Ib is flowing, the voltage value Vb, the current value Ib, and the temperature Tb may be detected, and the open circuit voltage OCV (t1) of the battery 10 may be calculated by the following equation (16).

OCV = Vb + Ra × Ib (16)

In the equation (16), Ra is a DC internal resistance of the battery 10. Since the DC internal resistance Ra changes according to the temperature Tb of the battery 10, a map indicating the relationship between the temperature Tb and the DC internal resistance Ra is stored in the memory 42, and the DC internal resistance Ra is determined from the map based on the detected temperature Tb. May be obtained and calculated by equation (16). As shown in FIG. 12, at time t1, the capacity of the battery 10 is Q (t1) (A × h).

In addition, as shown in step S202 of FIG. 11, the measuring unit 52 starts integrating the charging current to the battery 10 at time t1. The current is integrated by multiplying the product of the current value Ib detected by the current sensor 32 and the period Δt at every period Δt (for example, 0.1 second) as in the following equation (17).

Integrated current value (A × h) = Σ (Ib × Δt) (17)

  As shown in step S203 of FIG. 11, the measuring unit 52 detects the open voltage OCV (t2) of the battery 10 by the voltage sensor 31 at the time t2 when the charging of the battery 10 ends. When the current value Ib is flowing, as described above, the voltage value Vb, the current value Ib, and the temperature Tb are detected, and the open-circuit voltage OCV (t2) of the battery 10 is calculated by Expression (16). May be.

Further, as shown in step S204 of FIG. 11, the measurement unit 52 ends the integration of the current at time t2. As shown in FIG. 12, the capacity of the battery 10 at time t2 is Q (t2) (A × h) obtained by adding the integrated current value to the battery capacity Q (t1) at time t1.

Q (t2) = Q (t1) + Integrated current value (18)

  Then, as shown in step S205 in FIG. 11, the measuring unit 52 stores an open-circuit voltage curve (actually measured value) as shown by a solid line in FIG.

Capacity maintenance rate calculation unit 53, as shown in step S206 of FIG. 11, reads out the positive and negative electrodes discrepancy capacity Delta] Q _s of capacity calculation unit 51 deviated from the memory 42 is calculated. Further, capacity maintenance rate calculation unit 53, as shown in step S207 of FIG. 11, to set the candidate value of positive electrode capacity maintenance rate k ₁ and the candidate value of the negative electrode capacity maintenance rate k _2. Since the positive electrode capacity retention rate k ₁ and the negative electrode capacity retention rate k ₂ change between 0 and 1, for example, 20 candidate values may be set for each 0.05 unit.

Capacity maintenance rate calculation unit 53, as shown in step S208 of FIG. 11, the candidate value of positive electrode capacity maintenance rate k ₁ set in positive and negative electrodes discrepancy capacity Delta] Q _s and step S207 that read from the memory 42 and the negative electrode capacity As described above with reference to FIG. 5 using the candidate value of the maintenance rate k ₂ , the open circuit voltage OCV is calculated as the potential difference between the negative open circuit potential U ₂₂ and the positive open circuit voltage U ₁₁ of the battery 10. An open-circuit voltage curve (estimated value) indicated by a broken line in FIG. 12 is calculated.

  The capacity maintenance ratio calculation unit 53 calculates the voltage error ΔV and the capacity error ΔQ as shown in step S209 of FIG. The voltage error ΔV is calculated by comparing the open-circuit voltage curve (estimated value) and the open-circuit voltage curve (actually measured value), as shown in FIG. The voltage error ΔV may be a voltage error at a specific battery capacity, or may be an average value of the voltage errors between two open voltage curves. Further, the capacity error ΔQ is calculated by using the open-circuit voltage curve (estimated value) to determine the capacity Q1 between the open-circuit voltage OCV (t1) before charging (time t1) and the open-circuit voltage OCV (t2) after charging (time t2). Is calculated. In addition, the charged capacity Q2 can be calculated from the integrated current value integrated in steps S202 and S204 in FIG. By calculating the difference between the capacitances Q1 and Q2, the absolute value (| Q1-Q2 |) of the capacitance error ΔQ can be obtained.

  After calculating the voltage error ΔV and the capacity error ΔQ, the capacity maintenance ratio calculation unit 53 proceeds to step S210 in FIG. 11 and calculates an evaluation function f (ΔV, ΔQ) for the voltage error ΔV and the capacity error ΔQ. As the evaluation function f (ΔV, ΔQ), for example, a value obtained by weighting and adding the voltage error ΔV and the capacitance error ΔQ can be used.

  As shown in step S210 of FIG. 11, the capacity maintenance ratio calculation unit 53 calculates the evaluation function f (ΔV, ΔQ) calculated from the currently set deterioration parameter by using the evaluation function f calculated from the previously set deterioration parameter. A minimum value determination process is performed to determine whether the value is smaller than f (ΔV, ΔQ). If the current evaluation function f (ΔV, ΔQ) is smaller than the previous evaluation function f (ΔV, ΔQ), the current evaluation function f (ΔV, ΔQ) is stored in the memory 42. If the current evaluation function f (ΔV, ΔQ) is larger than the previous evaluation function f (ΔV, ΔQ), the previous evaluation function f (ΔV, ΔQ) remains stored in the memory 42.

The capacity maintenance ratio calculation unit 53 proceeds to step S211 in FIG. 11 and determines whether or not the positive electrode capacity maintenance ratio k ₁ and the negative electrode capacity maintenance ratio k ₂ have been changed in all search ranges. If the capacity maintenance ratio k ₁ and the negative electrode capacity maintenance ratio k ₂ have been changed, the process proceeds to step S212. On the other hand, if it has not been changed in all search ranges, the process returns to step S207.

Thus, the capacity maintenance rate calculation unit 53, positive electrode capacity maintenance rate k _1, until it is changed in the entire search range negative electrode capacity maintenance rate k ₂ executes steps S207 Repeat step S211. When all the searches have been completed, the process proceeds to step S212 in FIG. 11, where the evaluation function f (ΔV, ΔQ) that becomes the minimum value is specified, and the open-circuit voltage curve from which this evaluation function (minimum value) is obtained is specified. At the same time, the positive electrode capacity maintenance ratio k ₁ and the negative electrode capacity maintenance ratio k ₂ that define the open-circuit voltage curve (estimated value) are specified, and the specified open-circuit voltage curve (estimated value), the positive electrode capacity maintenance ratio k ₁ , and the negative electrode capacity maintenance ratio k ₂ is stored in the memory 42.

The deterioration estimating unit 54 calculates the positive / negative electrode composition corresponding shift capacity ΔQ _s calculated by the shift capacity calculation unit 51, the positive capacity maintenance rate k ₁ and the negative capacity maintenance rate k ₂ calculated by the capacity maintenance rate calculation unit 53, and the open-circuit voltage curve ( ) Is calculated and output from the estimated value). The deterioration state value is, for example, the full charge capacity of the battery 10 in the deteriorated state shown in FIG. 12, the deterioration capacity from the initial state, the open-circuit voltage curve of the battery 10 (estimated value), and the like.

As described above, the battery deterioration estimating apparatus 40 of the present embodiment uses the following three parameters as the positive electrode capacity retention rate k ₁ , the negative electrode capacity retention rate k ₂ , and the positive / negative electrode composition correspondence displacement capacity ΔQ _s. (14), the positive and negative electrode composition correspondence shift capacity ΔQ _s is specified in advance by the equation (15), and candidate values are searched for only the positive electrode capacity maintenance rate k ₁ and the negative electrode capacity maintenance rate k ₂ of the two deterioration parameters. , The positive-negative electrode composition correspondence shift capacity ΔQ _s , the positive-electrode capacity maintenance rate k ₁ , the negative-electrode capacity maintenance rate k ₂ , and the open-circuit voltage curve (estimated value) are specified to estimate the deterioration of the battery 10. Can be accurately estimated.

  In the embodiment described above, the deterioration of the battery 10 is estimated when the battery 10 is charged by the external power supply. For example, the open-circuit voltage OCV is detected while the electric vehicle 100 is stopped, and the deterioration of the battery 10 is estimated. Can also be performed.

  It is difficult to obtain an open-circuit voltage curve (actually measured value) except during external charging. However, when the battery 10, which is a lithium ion secondary battery, is in a relaxed state, it is located on the open-circuit voltage curve (actually measured value). Several open circuit voltages OCV can be measured. Here, when a current flows through the battery 10 or immediately after the current is interrupted, an accurate open-circuit voltage OCV cannot be measured due to a difference in lithium concentration in the active material.

  On the other hand, if the time has elapsed since the power supply to the battery 10 was cut off, the battery is in a relaxed state, and an accurate open circuit voltage OCV can be measured in a state where there is no lithium concentration difference. The case where the battery 10 is in the relaxed state includes, for example, when the electric vehicle 100 is stopped. Therefore, while the electric vehicle 100 is stopped, the open circuit voltage OCV (actually measured value) when the battery 10 has a specific capacity can be obtained.

  If a specific open circuit voltage OCV (actual measurement value) at a specific capacity can be measured, the voltage error ΔV can be obtained by comparing the open circuit voltage OCV (actual measurement value) with an open circuit voltage curve (estimated value). Further, by measuring a plurality of open-circuit voltages OCV (actually measured values), the capacitance error ΔQ can be obtained as described above. Specifically, the capacity Q1 between two points of the open-circuit voltage OCV (actually measured value) is calculated using the open-circuit voltage curve (estimated value). If the integrated current value for obtaining the open-circuit voltage OCV (actually measured value) at two points is measured, the capacity Q2 can be calculated from the integrated current value. Then, if the difference (| Q1-Q2 |) between the capacitance Q1 and the capacitance Q2 is obtained, the absolute value of the capacitance error ΔQ can be obtained.

If the voltage error ΔV and the capacity error ΔQ can be calculated, the minimum value of the evaluation function f (ΔV, ΔQ) is determined in the same manner as described above, and the positive electrode capacity maintenance rate k ₁ and the negative electrode capacity maintenance rate k ₂ are calculated. The evaluation function f (ΔV, ΔQ) that is the minimum value is specified by changing the entire search range. Then, the open-circuit voltage curve from which the evaluation function (minimum value) was obtained was specified, and the positive electrode capacity maintenance ratio k ₁ and the negative electrode capacity maintenance ratio k ₂ that define the open-circuit voltage curve (estimated value) were specified and specified. The open-circuit voltage curve (estimated value), the positive electrode capacity maintenance rate k ₁ , and the negative electrode capacity maintenance rate k ₂ are stored in the memory 42.

<Calculation of Positive / Negative Electrode Composition Displacement Capacity ΔQ _s from Positive / Negative Electrode Composition Displacement Capacity ΔQ _s1 Derived from Lithium Deposition and Positive / _Negative Electrode Composition Displacement Capacity ΔQ _{s2 Due} to Discharge>
As explained above, the degradation capacity of the battery 10 is a lithium ion secondary battery, positive electrode capacity maintenance rate k _1, negative electrode capacity maintenance rate k _2, is represented by positive and negative electrodes discrepancy capacity Delta] Q _s, usually, The positive / negative electrode composition correspondence displacement capacity ΔQ _s can be expressed by self-discharge. However, it used the way and the battery 10, use environment (particularly, the negative electrode open-circuit potential U ₂ is like tends cold state and 0V) by, there is a possibility that lithium deposition occurs. Since the precipitation of lithium affects the displacement capacity ΔQ _s corresponding to the positive and negative electrode compositions, under such conditions, if only the negative electrode SEI film formation is considered as a side reaction, the capacity estimation accuracy may be reduced. . Therefore, in the following embodiment, the deterioration of the battery 10 is estimated by adding a battery model for estimating the amount of deposited lithium.

The displacement capacity ΔQ _s1 corresponding to the positive / negative electrode composition derived from lithium deposition is calculated by adding the change amount of the deposition amount of the reaction-related substance from the previous deposition amount to the previous deposition amount according to the following equations (19) and (20). The current deposition amount, which is the deposition amount of the reaction-related substance at the time of estimation, is calculated.

式（１９）中、添字ｃは今回推定された値であることを表し、添え字ｐは前回推定された値であることを表し、ＱＬｉは反応関与物質の析出量（に対応する電荷量）を表し、ｉ₂は反応関与物質の析出電流密度を表し、Ａ２は反応関与物質の析出反応表面積を表し、そしてΔｔは周期を示す。すなわち、式（１９）の右辺第２項は、反応関与物質の析出量の前回析出量からの変化量に相当する。

In the equation (19), the subscript c represents the value estimated this time, the subscript p represents the value estimated last time, and QRi represents the amount of deposition of the reaction-related substance (the charge amount corresponding to). , I ₂ represents the deposition current density of the reaction participating substance, A 2 represents the deposition reaction surface area of the reaction participating substance, and Δt represents the period. That is, the second term on the right side of the equation (19) corresponds to the amount of change in the deposition amount of the reaction-related substance from the previous deposition amount.

Similar to the calculation of the previously described positive and negative electrodes discrepancy capacity Delta] Q _s, the calculation of the positive and negative electrodes discrepancy capacity Delta] Q _s2 after electric vehicle 100 battery 10 is mounted is completed, first the ignition switch is turned on Then, the integration is started, and thereafter, steps S301 to S308 shown in FIG. 14 are repeatedly executed at predetermined intervals Δt (for example, 0.1 seconds).

As shown in step S301 in FIG. 14, the displacement capacity calculation unit 51 calculates the displacement capacity ΔQ _s1 corresponding to the positive and negative electrode compositions derived from lithium deposition by using equations (19) and (20). In addition, as in steps S101 to S105 of FIG. 10, the displacement capacity calculation unit 51 detects the voltage value Vb of the battery 10 detected by the voltage sensor 31 illustrated in FIG. Using the temperature Tb and the parameters stored in the memory 42, the equations (12) and (13) are solved to calculate the negative electrode open potential U _2, and the film forming current density i is calculated by the equation (14) to a predetermined period Δt. As shown in equation (15), the product of the calculated film formation current density i and the predetermined period Δt is integrated to calculate the positive / negative electrode composition correspondence shift capacity ΔQ _s2 due to film formation.

After calculating the shift capacity ΔQ _s1 corresponding to the positive / negative electrode composition derived from lithium deposition and the shift capacity ΔQ _s2 corresponding to the positive / negative electrode composition due to film formation, the shift capacity calculating unit 51 proceeds to step S307 in FIG. the process proceeds to step S308 in FIG. 14 the sum of the positive and negative electrodes discrepancy capacity Delta] Q _s2 by the corresponding capacity shift Delta] Q _s1 and the film formed as a positive and negative electrodes discrepancy capacity Delta] Q _s, the positive and negative electrodes discrepancy capacity Delta] Q _s in the memory 42 Store.

The battery deterioration estimating device 40 uses the positive / negative electrode composition corresponding shift capacity ΔQ _s calculated as described above, and in the same manner as described above with reference to FIGS. ), The positive electrode capacity maintenance ratio k ₁ and the negative electrode capacity maintenance ratio k ₂ are specified, and the deterioration state value of the battery 10 is calculated and output from these values. The deterioration state value is, for example, a full charge capacity or a deterioration capacity of the battery 10 or an open voltage curve of the battery 10.

According to the embodiment described above, that the negative electrode open-circuit potential U ₂ that may lithium deposition occurs even if the battery 10 is used in a low temperature easily becomes 0V, thereby accurately estimate the deterioration state of the battery 10 it can.

Reference Signs List 10 battery, 11 positive electrode line, 12 negative electrode line, 13 inverter, 14 motor generator, 15 external power connector, 31 voltage sensor, 32 current sensor, 33 temperature sensor, 40 battery deterioration estimation device, 41 CPU, 42 memory, 43 sensor interface , 44, 45 and 46 a data bus, 51 displacement volume calculating section, 52 measuring unit, 53 capacity maintenance ratio calculation unit, 54 deterioration estimating unit, 60 battery ECU, 70 main ECU, 100 electric vehicle, k ₁ positive electrode capacity maintenance rate, k ₂ negative electrode capacity maintenance rate, Delta] Q _s positive and negative electrodes discrepancy capacity, Delta] t period.

Claims (1)

A positive electrode capacity retention ratio which is a ratio of the deteriorated state positive electrode capacity to the initial state positive electrode capacity,
A negative electrode capacity retention ratio which is a ratio of the negative electrode capacity in the deteriorated state to the negative electrode capacity in the initial state;
Based on the positive and negative electrode composition correspondence shift capacity, which is the amount of change in battery capacity due to a change from the initial state of the correspondence between the local charge rate on the positive electrode active material surface and the local charge rate on the negative electrode active material surface. A battery deterioration estimating device for estimating deterioration of a lithium ion secondary battery,
The film is formed by the following formula (I), where i ₀ is the exchange current density, α is the transfer coefficient, F is the Faraday constant, R is the gas constant, T is the absolute temperature, U _side is the film forming potential, and U ₂ is the negative electrode opening potential. A displacement capacity calculating unit that calculates a current density i for each predetermined cycle Δt, and integrates a product of the calculated film forming current density i and a predetermined cycle Δt to calculate the positive / negative electrode composition corresponding displacement capacity;

A measuring unit that measures an open-circuit voltage curve indicating a change in open-circuit voltage with respect to a change in battery capacity;
Using the positive-negative electrode composition-dependent displacement capacity calculated by the displacement capacity calculation unit, the positive electrode capacity retention ratio and the negative electrode that specify an open-circuit voltage curve estimated value that substantially matches the open-circuit curve actual measurement value measured by the measurement unit A capacity maintenance ratio calculation unit for calculating a capacity maintenance ratio,
The positive and negative electrode composition corresponding shift capacity calculated by the shift capacity calculation unit, the positive electrode capacity maintenance ratio calculated by the capacity maintenance ratio calculation unit, and the negative electrode capacity maintenance ratio calculated by the capacity maintenance ratio calculation unit, And a deterioration estimating unit for estimating a deterioration state of the lithium ion secondary battery using the same.

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