JP2021163632A - Secondary battery deterioration estimation method, life estimation method and control device - Google Patents

Abstract

To provide a secondary battery deterioration estimation method, life estimation method and control device, capable of using an in-vehicle lithium ion secondary battery until a target life by accurately estimating a deterioration in a secondary battery and controlling the secondary battery.SOLUTION: A secondary battery can be used until a target life by: acquiring deterioration information up to now from a step of calculating deviation capacity ΔQ corresponding to a positive and negative electrode composition to calculate the deviation capacity ΔQ corresponding to a positive and negative electrode composition, by multiplying a difference between an amount of decrease in negative electrode capacity ΔQNE and an amount of decrease in positive electrode capacity ΔQPE by a lapsed time Δt by an ECU mounted on a vehicle, the amount of decrease in negative electrode capacity and the amount of decrease in positive electrode capacity being calculated in a step of calculating an amount of decrease in negative electrode capacity and in a step of calculating an amount of decrease in positive electrode capacity, respectively (S10); determining input information of conditions to be predicted in future (S11); estimating deterioration at the end of a life target period (S12-17); determining whether the life target is reachable by comparing the estimated deterioration with a preset threshold (S18); and, if it is determined that the life target is not reachable, controlling such that an SOC usage area with a less deterioration amount is used (S20).SELECTED DRAWING: Figure 6

Description

The present invention relates to a deterioration estimation method, a life estimation method, and a control device for a secondary battery, and more specifically, a deterioration estimation method for estimating the deterioration degree of a positive electrode and a negative electrode to estimate the deterioration of a secondary battery with higher accuracy. , Life estimation method, and control device.

As is well known, a secondary battery such as a lithium ion secondary battery is used as a power source for portable electronic devices and as a power source for electric vehicles and hybrid vehicles.
For example, in the case of lithium-ion secondary batteries mounted on vehicles, in addition to deterioration factors such as temperature environment and elapsed time, deterioration factors such as charge / discharge status by the user, frequency of use, and SOC status of the secondary battery used are also deterioration factors. Contributes greatly as. Therefore, the degree of deterioration cannot be estimated simply from the elapsed time and the mileage.

Therefore, Patent Document 1 discloses a method of estimating the deterioration of a lithium ion secondary battery by using the positive electrode / negative electrode composition-corresponding deviation capacity ΔQ, which is a factor of reducing the capacity of the lithium ion secondary battery. Specifically, the film formation current density i at the negative electrode is obtained by the following Tafel equation (formula (5)).

ここで、ｉ_０を交換電流密度、αを移動係数、Ｆをファラデー定数、Ｒを気体定数、Ｔを絶対温度、Ｕ_sideを被膜形成電位、Ｕ_ＮＥを負極開放電位とする。

Here, 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 formation potential, and _UNE is the negative electrode open potential.

Then, it is calculated for each period Δt, and the product of i and Δt is integrated to calculate the deviation capacity ΔQ corresponding to the positive and negative electrode compositions.
According to such a method, the degree of deterioration of the lithium ion secondary battery can be estimated.

JP-A-2017-190979

However, in the conventional invention, only the side reaction at the negative electrode is considered in the calculation of the deviation capacity ΔQ corresponding to the positive / negative electrode composition, and the influence of the side reaction at the positive electrode is not considered to be small. There was a problem that the value of the capacitance ΔQ could be overestimated.

The present invention solves the above problems, and an object of the present invention is to provide a method for estimating deterioration of a secondary battery, a method for estimating the life of a secondary battery, and a control device for more accurately estimating the degree of deterioration of the secondary battery. be.

To solve the above problems, in the secondary battery of the degradation estimation method of the present invention, a film formation current density of the negative electrode and i _NE, the exchange current density of side reactions that occur with a _NE on the negative electrode, the b _NE negative electrode when a side reaction overvoltage term occurring in, the negative electrode capacity to calculate the capacity decrease amount Delta] Q _NE in the negative electrode by multiplying the elapsed time Δt based on the film-forming current density i _NE of the negative electrode which is calculated by the stated formula (1) When the step of calculating the amount of decrease and the positive electrode film forming current density are _iPE , a _PE is the exchange current density of the side reaction occurring on the positive _{electrode, and b PE} is the overvoltage term of the side reaction occurring on the positive electrode. (2) a step of positive electrode capacity decrease amount calculation for calculating a capacity decrease amount Delta] Q _PE in the positive electrode by multiplying the elapsed time Δt based on the film-forming current density i _PE of the positive electrode calculated by the negative electrode capacity decrease amount calculation From the difference between the negative electrode capacity reduction amount ΔQ _NE calculated in the step of and the positive electrode capacity reduction amount ΔQ _PE calculated in the positive electrode capacity reduction amount calculation step, the positive and negative electrode composition correspondence deviation capacity ΔQ is calculated. It is characterized by including a step of calculating the capacity ΔQ. Incidentally, the same also with the present invention so as to determine the positive and negative electrodes discrepancy capacity ΔQ by multiplying the elapsed time Δt a film formation current density i _NE and the positive electrode film formation current density of the negative electrode to the difference between the i _PE.

Further, in the step of calculating the amount of decrease in the negative electrode capacity, 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 formation potential, and _UNE is the negative electrode. open-circuit potential, when the U _PE as a positive electrode open-circuit potential based on the negative electrode film forming the current density i _NE calculated by otherwise equation (3) to calculate the negative electrode side reaction current value I _{SR (NE),} the positive electrode capacity decrease amount in the calculation step, it is also stated formula (4) by calculating the positive electrode film formation current density i on the basis of the _PE positive electrode side reaction current value I _{SR (PE).}

In this case, in the step of calculating the negative electrode capacity reduction amount and the step of calculating the positive electrode capacity reduction amount, the positive electrode capacity reduction amount ΔQ _PE and the negative electrode capacity reduction amount are used by using the values obtained by declining the side reaction current value according to the elapsed time. You can also calculate the ΔQ _NE.

Further, in the step of calculating the amount of decrease in negative electrode capacity and the step of calculating the amount of decrease in positive electrode capacity, a storage step of storing the secondary battery under specific conditions and a battery full capacity before and after storage of the stored secondary battery a step of the battery capacity decrease amount measurement for measuring a capacity decrease amount Q _loss, comprising the steps of self-discharge capacity measurement for measuring a self-discharge capacity Q _SD before and after storage of the secondary battery the storage, the capacity decrease amount Q _loss and from self-discharge capacity Q _SD, and a step of degradation characteristic acquisition for obtaining the secondary reaction current value of the positive and negative electrodes in a particular condition during the storage, based on secondary reactions current value of the positive electrode and the negative electrode in the step of the degradation characteristic acquisition It is also possible to estimate the deterioration.

It should be noted that this can be particularly preferably carried out when the secondary battery is a lithium ion secondary battery.
Further, the secondary battery life estimation method of the present invention is a life estimation method for estimating the life of the secondary battery by estimating the deterioration of the secondary battery at a future time tmax, and is the above-mentioned lithium ion secondary battery. Degradation estimation step of the secondary battery for calculating the positive / negative composition correspondence deviation capacity ΔQ of t1 at the time of life estimation using the deterioration estimation method of, and positive / negative composition correspondence deviation capacity calculated in the deterioration estimation step of the secondary battery. Based on ΔQ and conditions, the step of estimating the life of the secondary battery at which the deterioration of the secondary battery at the time tmax is estimated by integrating the deterioration of the secondary battery from the time of life estimation t1 to the future life target time tmax. It is characterized by having and.

Further, in the step of estimating the life of the secondary battery, the cumulative distribution function obtained based on the probability density function derived from the cell SOC or the cell temperature accumulated as a condition in the step of estimating the deterioration of the secondary battery is used. As a reference function, it is also possible to generate a random number and integrate the deterioration of the secondary battery from t1 at the time of life estimation to tmax in the future time by Monte Carlo simulation.

Further, by comparing the deterioration of the secondary battery at the time tmax estimated in the step of estimating the life of the secondary battery with the preset threshold of deterioration of the secondary battery, the secondary battery has a time tmax. It is also possible to further include a step of determining the life of the secondary battery, which determines whether or not the deterioration in the above-mentioned is less than the threshold value and reaches the end of life.

Further, when it is determined in the step of determining the life of the secondary battery that the secondary battery cannot reach the life at the time tmax, the cell SOC condition in the step of estimating the life of the secondary battery can be changed. It is also preferable to further include a re-determination step of re-determining whether or not the life can be reached.

Further, if it can be determined in the re-determination step that the life can be reached when the conditions are changed, a control step of controlling the cell SOC of the secondary battery according to the conditions of the cell SOC may be provided. preferable.

The secondary battery control device of the present invention includes a voltage sensor that detects the cell voltage of the secondary battery, a temperature sensor that detects the cell temperature of the secondary battery, a CPU, and a memory, and the cell is derived from the voltage sensor. It is a control device for a secondary battery including a computer for estimating SOC, and constitutes a control means for executing the above-mentioned method for estimating the life of the secondary battery. The secondary battery is mounted on a vehicle, and the computer can be suitably implemented by a computer mounted on the vehicle.

According to the method for estimating deterioration of a secondary battery of the present invention, the degree of deterioration of a secondary battery can be estimated more accurately.

The figure which shows schematic the whole structure of the vehicle which mounts the lithium ion secondary battery which concerns on this embodiment. A graph showing (a) the capacitance-OCP characteristics of the positive electrode and the negative electrode before deterioration, and (b) a graph showing the capacitance-OCP characteristics of the positive electrode and the negative electrode after deterioration. In this embodiment, (a) a graph showing the capacitance-OCP characteristics of the positive electrode and the negative electrode before deterioration, and (b) a graph showing the capacitance-OCP characteristics of the positive electrode and the negative electrode after deterioration. The flowchart which calculates the positive electrode composition correspondence deviation capacity ΔQ integrated from the time t ₀ of this embodiment to a predetermined time t _1. FIG. 3A is a schematic diagram comparing ΔQ of the present embodiment shown in FIG. 3 with ΔQ of the prior art shown in FIG. The flowchart which shows the procedure of the deterioration suppression control method by life estimation. The block diagram which shows the structure of the device of deterioration characteristic acquisition. A flowchart showing a procedure for acquiring deterioration characteristics. (A) is a figure which shows the cell SOC, (b) is a figure which shows the method of determining the input information of a cell temperature TB. (A)-(c) Schematic diagram showing a model of film growth. An equation showing the relationship between the amount of film formed and the side reaction current value. The graph which shows the attenuation rate of the current value with respect to the reciprocal of the coating amount. A table showing the relationship between the elapsed time, the amount of film formation, and the side reaction current value. The graph which compares the deterioration degree estimation result of the prior art with the deterioration degree estimation result of this embodiment. The figure which shows the relationship between the deterioration amount and SOC.

A deterioration estimation method, a life estimation method, a control method, and a control device for a secondary battery, which are embodiments of the present invention, will be described with reference to FIGS. 1 to 15. In the present embodiment, an in-vehicle lithium ion secondary battery 1 will be described as an example of the secondary battery.

<Outline of the configuration of this embodiment>
The deterioration estimation method of the lithium ion secondary battery 1 of the present embodiment estimates the deterioration state of the lithium ion secondary battery 1 mounted on the vehicle 10. In the estimation, the deviation capacitance ΔQ corresponding to the positive and negative electrode compositions of the positive electrode and the negative electrode _{is calculated individually for ΔQ PE} and ΔQ _NE , respectively, based on the cell voltage VB and the cell temperature TB measured sequentially, and the lithium ion secondary battery 1 is estimated. Estimate the deterioration state. As a result of the prediction based on the estimation, it may be determined that the deteriorated state of the lithium ion secondary battery 1 becomes larger than the assumed threshold value by the expected life in the used SOC region. In that case, control is performed so as to avoid the used SOC region of the lithium ion secondary battery 1 used so far and select the used SOC region in which the progress of deterioration is slowed down.

<Overall configuration of vehicle equipped with lithium-ion secondary battery>
First, the vehicle 10 on which the lithium ion secondary battery 1 of the present embodiment is mounted will be briefly described.

FIG. 1 is a diagram schematically showing an overall configuration of a vehicle 10 equipped with a lithium ion secondary battery 1 according to an embodiment. The vehicle 10 shown in FIG. 1 is a hybrid vehicle. The vehicle 10 includes a control device 18 for a lithium ion secondary battery 1, a PCU (Power Control Unit) 30, motor generators 41 and 42, an engine 50, a power split device 60, and a drive shaft 70. , The drive wheel 80 is provided.

The control device 18 of the lithium ion secondary battery includes the lithium ion secondary battery 1, the monitoring unit 20 that constantly monitors the cell voltage VB, the current IB, and the cell temperature TB of the lithium ion secondary battery 1, and the cell voltage thereof. It includes a memory 102 that stores VB, current IB, and cell temperature TB, and an ECU (electronic control unit) 100 that includes a CPU 101 that processes these.

<Motor generator 42>
The motor generator 42 mainly operates as an electric motor, and drives the drive wheels 80 with a large current supplied from the lithium ion secondary battery 1 at the time of sudden acceleration. On the other hand, when the vehicle is braking or on a downward slope, the motor generator 42 operates as a generator to regenerate a large current and supply a large current to the lithium ion secondary battery 1.

In such an in-vehicle lithium ion secondary battery 1, the progress of deterioration may differ depending on the usage environment. For example, the environmental temperature changes from low temperature to high temperature and the cell temperature TB changes from low temperature to high temperature, high rate charging / discharging is performed, and the charging / discharging situation changes from low cell SOC to high cell SOC. This is the case.

<Lithium-ion secondary battery monitoring unit 20>
The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects the cell voltage VB. The current sensor 22 detects the current IB input / output to / from the lithium ion secondary battery 1. The temperature sensor 23 detects the cell temperature TB for each block. Each sensor outputs a signal indicating the detection result to the ECU 100. These cell voltage VB and current IB are stored as cell temperature TB and cell voltage VB at regular time intervals as the history of the lithium ion secondary battery 1.

<Cell voltage VB, current IB, cell temperature TB, cell SOC>
In the present embodiment, the cell voltage VB, the current IB, and the cell are used every Δt (for example, 0.1 second) from the _{start time t 0} when the lithium ion secondary battery 1 is mounted on the vehicle 10 and during its operation. Temperature TB is measured and recorded, and deterioration is determined. The ECU 100 estimates the cell SOC from the measured cell voltage VB and the deviation capacity ΔQ corresponding to the positive / negative electrode composition, calculates a new deviation capacity ΔQ corresponding to the positive / negative electrode composition, and accumulates and stores the value.

(Action of Embodiment)
In the present embodiment, the lithium ion secondary battery 1 and the vehicle 10 on which the lithium ion secondary battery 1 is mounted can exert the following actions.

<Calculation of deviation capacity ΔQ corresponding to positive / negative electrode composition of the prior art>
Next, the principle of deterioration estimation of the present invention will be described. For the sake of explanation, the conventional technique will be described first. FIG. 2 is a graph showing (a) positive electrode / negative electrode capacity-OCP (Open circuit potential) characteristics (relationship between battery capacity and positive electrode / negative electrode open potential at that time), (b). It is a graph which shows the OCP characteristic after deterioration. The graph shown in FIG. 2A is a graph showing the characteristics of the battery before initial deterioration, which is specified from the composition of the electrodes and the like. If the cell voltage VB is known, the open potential _VNE and the open potential VNE according to the capacities of the negative electrode and the positive electrode You can see V _PE. As can be seen from FIG. 2 (a), the graph _{U NE0} graph _{U PE} and negative OCP positive electrode OCP has a irregular curve. In particular, the negative electrode has a stepped graph due to the absorption and diffusion of lithium ions. Here, the cell voltage VB is the potential difference between _{the positive electrode potential V PE0} and the negative electrode potential V _NE0. Then, the relative positional relationship between the chart _{U NE} graphs _{U PE} and negative OCP positive electrode OCP shown in FIG. 2 (a), the capacity of the positive and negative electrodes, the cell voltage VB will change. At this time, the deviation capacity ΔQ corresponding to the positive and negative electrode compositions does not occur.

Therefore, in Patent Document 1, the deterioration of the lithium ion secondary battery is estimated by using the "positive electrode composition correspondence deviation capacity ΔQ" for the capacity decrease which is a factor of the deterioration of the lithium ion secondary battery. The “positive electrode composition correspondence deviation capacity ΔQ” is the amount of fluctuation in the battery capacity due to the deviation of the correspondence between the local charge rate on the surface of the positive electrode active material and the local charge rate on the surface of the negative electrode active material from the initial state.

FIG. 2B is a graph showing the capacitance-OCP characteristics of the positive electrode and the negative electrode after deterioration in the prior art. ΔQ of the prior art will be described with reference to FIG. 2 (b). As the deterioration progresses due to use from the state shown in FIG. 2 (a), the amount of volume reduction ΔQ _NE due to a side reaction at the negative electrode decreases as shown in FIG. 2 (b). Therefore, the position of a point on the graph U _NE0 of the negative electrode OCP is, from the initial position, displacement at the position of a point on the graph U _NE1 of the negative electrode OCP shown on the left side, the positive and negative electrodes discrepancy capacity ΔQ indicated by the leftward arrow Occurs.

Here, the cell voltage VB is the potential difference between _{the potential V PE of} the positive electrode and the potential V _{NE of the negative electrode.} Then, the cell voltage VB becomes the potential difference of <positive potential V _PE0 -negative potential V _{NE1 > from the potential difference of <positive potential V PE0} -negative potential V _NE0 >, and the potential difference is small as shown in FIG. 2 (a). Become. Then, there will be a difference in the correspondence between the detected cell voltage VB and the capacity.

Therefore, the deterioration due to use is estimated using the Tafel equation or the like, and the deviation capacity ΔQ corresponding to the positive and negative electrode compositions is calculated. This ΔQ is integrated at any time, and when the positive electrode potential V _PE and the negative electrode potential V _NE are calculated from the cell voltage VB, the deviation capacity ΔQ corresponding to the positive and negative electrode compositions is referred to.

In Patent Document 1, since it is assumed that the positive electrode composition-corresponding deviation capacity ΔQ does not change in the positive electrode, it is equal to the decrease in the _{capacity decrease amount ΔQ NE due to a side reaction in the negative electrode.}
<Characteristics of calculation of deviation capacity ΔQ corresponding to positive / negative electrode composition of this embodiment>
FIG. 3A is a graph showing the SOC-OCP characteristics of the positive electrode and the negative electrode before deterioration of the present embodiment. Conventionally, it has been known that a positive electrode causes a side reaction in the same manner as a negative electrode, but it is not well known what kind of side reaction acts and how. Also, it was not easy to estimate future side reaction currents. Furthermore, the effect of the positive electrode side reaction was thought to be small. Therefore, it can be said that there was an impediment to considering only the deterioration of the negative electrode and the deviation of the positive electrode, which simply complicates the process. Therefore, those skilled in the art did not consider the side reaction of the positive electrode in Cited Document 1 as shown in FIG. 2 (b).

However, the present inventor analyzes what kind of characteristics the lithium ion secondary battery 1 itself has, and then what kind of side reaction occurs on the positive electrode and how it works. It was clarified that the effect was not small by experiments, and the present invention was reached. It was also experimentally confirmed that the reaction rate of the side reaction can be defined by the Tafel equation for the positive electrode as well as the negative electrode.

<Calculation of deviation capacity ΔQ corresponding to positive / negative electrode composition of this embodiment>
FIG. 3A is a graph showing the SOC-OCP characteristics of the positive electrode and the negative electrode before deterioration of the present embodiment. FIG. 3B is a graph showing the SOC-OCP characteristics of the positive electrode and the negative electrode after deterioration of the present embodiment. According to the findings of the present inventor, in reality, as shown in FIG. 3 (b), a volume decrease ΔQ _PE due to a side reaction also occurs at the positive electrode. When the positive electrode capacity decrease ΔQ _{PE occurs, the position on the point U PE0} on the graph of the positive electrode OCP shown in FIG. 3A _{shifts to the left position by the ΔQ PE} indicated by the arrow pointing to the left, and the point U on the graph. It becomes _PE1.

That is, the decrease in the cell voltage VB is caused by both an increase in _{the potential VNE} of the negative electrode and a decrease in the _{potential V PE of the positive electrode.} Conventionally, as shown in FIG. 2B, the decrease in the cell voltage VB was considered to be entirely due to the increase in _{the potential VNE of the negative electrode.} In other words, it was considered that _{ΔQ = ΔQ NE.} However, in the present embodiment, reduction of the cell voltage VB is assumed to result from both a decrease in the rise and the positive potential V _PE negative electrode potential V _NE, in which it was decided to analyze isolate them respectively.

In the present embodiment, the cell voltage VB before the deviation occurs is _{the potential difference of <positive potential V PE0} -negative potential V _NE0 > as shown in FIG. 3 (a), but when the deviation occurs, FIG. 3 (b) ), The potential difference is <positive potential V _PE1 -negative potential V _NE1>.

In the present embodiment, as shown in FIG. 3B, as a result of allocating the decrease in the cell voltage VB to the increase in _{the potential V NE of the negative electrode and the decrease in the potential V PE of the positive electrode, the cell voltage VB is the same voltage.} as also, the rise in the potential V _NE of the negative electrode shown in FIG. 3 (b) of the present embodiment than the rise in the potential V _NE of the negative electrode shown in prior art FIG. 2 (b) has become smaller.

In other words this for Delta] Q, Delta] Q of this embodiment from the relationship that Delta] Q _NE conventional Delta] Q _NE> the present embodiment, becomes smaller than the conventional Delta] Q.
Furthermore, the relationship that Delta] Q _NE conventional Delta] Q _NE> the present embodiment, the displacement due to the decrease in capacity decrease amount Delta] Q _NE due to side reactions in the anode, and the deviation due to side reactions decrease in capacity decrease amount Delta] Q _PE by the positive electrode, It is offset and the ΔQ becomes smaller. That is, the relationship is ΔQ = ΔQ _{NE − ΔQ PE.} Therefore, the ΔQ of the present embodiment is even smaller than that of the conventional ΔQ.

That is, the present inventor has found that in the conventional method, even if the cell voltage VB is the same voltage, there is a possibility that ΔQ may be overestimated. In the present embodiment, the _{deterioration of ΔQ NE} and ΔQ _PE is calculated accurately. By using ΔQ derived from this, the cell voltage VB is correctly distributed to the positive electrode potential VPE and the negative electrode potential VNE, and the deterioration of each of _{ΔQ NE} and ΔQ _{PE is calculated accurately.} By repeating this, the deviation capacitance ΔQ corresponding to the positive and negative electrode compositions can always be estimated more accurately.

<Calculation of deviation capacity ΔQ corresponding to positive and negative electrode composition>
<Calculation of deviation capacity ΔQ corresponding to positive / negative electrode composition of the present invention>
Here, in the present invention, the elapsed time Δt is obtained by multiplying the negative electrode film forming current density _{iNE by the elapsed time Δt to obtain the decrease in the capacitance decrease amount ΔQ NE} due to the side reaction in the negative electrode, and the positive electrode film forming current density is set to the _iPE by the elapsed time Δt. _{It is also possible to obtain the capacity decrease ΔQ PE} due to the side reaction in the positive electrode by multiplying by, and to obtain the positive electrode / negative electrode composition-corresponding deviation capacity ΔQ from these differences. Then, in any case, it is necessary to calculate _{ΔQ NE} and ΔQ _{PE, respectively.}

Of course, the difference between the side reaction current value I _{SR (NE)} at the negative electrode and the side reaction current value I _{SR (PE)} at the positive electrode is multiplied by the elapsed time Δt, and the deviation capacity ΔQ (t _{0) corresponding to the positive and negative electrode composition of the elapsed time Δt.} The total amount of ~ t ₁ ) may be calculated. Here, a method of calculating ΔQ according to the present embodiment of such a procedure will be described with reference to FIG.

<Procedure for calculating the deviation capacity ΔQ corresponding to the positive and negative electrode compositions of this embodiment>
FIG. 4 is an example of a flowchart for calculating the positive / negative electrode composition-corresponding deviation capacity ΔQ integrated _{from the time t 0} of the present embodiment to the predetermined time t ₁ based on such a method.

Hereinafter, the procedure will be described with reference to FIG. First, the calculation of ΔQ (t _{0 to t 1} ) is started (S1). Here, the time t ₀ is the start of the estimation of the deterioration of the lithium ion secondary battery 1. Further, the time t ₁ is the time when the estimation of the deterioration of the lithium ion secondary battery 1 is completed. Δt is the elapsed time _{from time t 0} to time t _1. The time t ₂ is the measurement interval time. For example, 0.1 seconds.

Subsequently, the cell voltage VB of the lithium ion secondary battery 1 to be inspected and the cell temperature T, which is the environmental temperature of the cell, are measured (S2). The cell voltage VB and the cell temperature TB are measured by the voltage sensor 21 and the temperature sensor 23 (FIG. 1) of the monitoring unit 20 of the vehicle 10 on which the lithium ion secondary battery 1 is mounted.

Following the process of S2, the negative electrode potential _VNE is calculated from the cell voltage VB and the cell temperature TB (S3). Since ΔQ = 0 at time t ₀ , the cell voltage VB can be divided into the positive electrode potential V _PE and the negative electrode potential V _NE according to the graph of FIG. 3 (a).

The side reaction current value _{ISR (NE)} at the negative electrode is calculated from the negative electrode potential V _NE and the cell temperature TB (S4).
_{In parallel with the processing of S3, the positive electrode potential V PE} is calculated from the cell voltage VB and the cell temperature TB following the processing of S2 (S5). The side reaction current value I _{SR (PE)} at the positive electrode is calculated from the positive electrode potential V _PE (S6).

_{From the I SR (NE)} calculated in S4 and _{the I SR (PE)} calculated in S6, ΔQ (t _{0 to t 1} ) = (I _{SR (NE)} −I _{SR (PE)} ) × Δt is calculated. .. That is, the difference between the side reaction current value I _{SR (NE)} at the negative electrode and the side reaction current value I _{SR (PE)} at the positive electrode is multiplied by the elapsed time Δt, and the deviation capacity ΔQ (t _{0) corresponding to the positive and negative electrode composition of the elapsed time Δt.} Calculate the total capacity of ~ t _{1) (S7).}

In this process, Δt is sequentially processed from time t0 to time t1. When this process is completed, ΔQ (t _{0 to t 1} ) is calculated at the next process. In this way, ΔQ (t _{n-1 to t n} ) is calculated _{during the processing of t n to t n + 1.} Therefore, as shown in FIG. 3B, the cell voltage VB acquired in S2 can divide the cell voltage VB into the positive electrode potential V _PE and the negative electrode potential V _{NE according} to the ΔQ already calculated and accumulated. By repeating this, the cell voltage VB can be accurately _{divided into the positive electrode potential V PE} and the negative electrode potential V _{NE according} to the ΔQ calculated at that time, and the processing of S3 and S5 can be performed.

<Vaccine side reaction current values for negative and positive electrodes I _{SR (NE) and} I _{SR (PE)} >
_{Here, the volume reduction ΔQ NE} and ΔQ _PE due to side reactions at the negative electrode and the positive electrode, that is, the side reaction current value I _{SR (NE)} at the negative electrode and the side reaction current value I _{SR (PE) at the} positive electrode are obtained as follows. Be done.

The negative electrode side reaction current value _{ISR (NE)} is the following _{equation (6), where a NE} is the exchange current density of the _{side reaction that occurs on the negative electrode and b NE} is the overvoltage term of the side reaction that occurs on the negative electrode.

により負極における容量低下量ΔＱ_ＮＥを算出することができる。

Therefore, the amount of decrease in capacity ΔQ _NE at the negative electrode can be calculated.

The positive electrode side reaction current value _{ISR (PE)} is the following _{equation (7), where a PE} is the exchange current density of the side reaction that occurs on the positive electrode and b _PE is the overvoltage term of the side reaction that occurs on the positive electrode.

により正極における容量低下量ΔＱ_ＰＥを算出することができる。

Therefore, the amount of decrease in capacity at the positive electrode ΔQ _PE can be calculated.

<How to determine the _{decrease in capacity ΔQ NE} due to side reactions at the negative electrode>
Next, a method of specifically obtaining a decrease in the _{volume reduction amount ΔQ NE and} a decrease in the capacity reduction amount ΔQ _PE due to a side reaction in the negative electrode and the positive electrode will be described using these equations.

Here, first, the negative electrode will be described. _{The volume reduction ΔQ NE} due to a side reaction at the negative electrode can be obtained by using the Tafel equation as described in Patent Document 1.
That is, the decrease in the capacity decrease amount ΔQ _NE due to the side reaction at the negative electrode _{integrates the negative electrode side reaction current value ISR (NE)} between Δt. The negative electrode side reaction current value _{ISR (NE)} can be calculated based on the negative electrode coating formation current density _iNE. Negative film formation current density i _NE, based on the cell voltage VB and cell temperature TB, can be obtained by the following Tafel equation.

<Calculation of negative electrode side reaction current value _{ISR (NE) by Tafel equation>}
In the present embodiment, the negative electrode film forming current density _iNE is obtained by the Tafel equation (formula (3)) shown below.

ここで、ｉ_０を交換電流密度、αを移動係数、Ｆをファラデー定数、Ｒを気体定数、Ｔを絶対温度、Ｕ_sideを被膜形成電位、Ｕ_ＮＥを負極開放電位とする。

Here, 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 formation potential, and _UNE is the negative electrode open potential.

<Calculation of _{capacity reduction amount ΔQ NE} corresponding to negative electrode composition using Tafel's equation>
For details on how to obtain the film formation current density i at the negative electrode by the Tafel equation (number (3)), refer to paragraphs 0024 to 0081 of Cited Document 1, in particular, the calculation of the displacement capacitance ΔQ corresponding to the positive and negative electrode compositions using the Tafel equation. Since the method is described in detail in paragraphs 0076 to 0081, detailed description is omitted here.

_{The exchange current density i 0} of the formula (3) is a substantially constant value because the formation rate of the SEI (solid electrolyte interphase) film becomes substantially constant when charging / discharging is repeated several times after the production of the lithium ion secondary battery 1 is completed. Calm down. Therefore, a map corresponding to the cell temperature TB may be created in advance by a test or the like and read from this map.

The transfer coefficient α may be set to 0.5, for example, assuming that the charge / discharge efficiencies are the same. Further, the reductive decomposition of the electrolytic solution, which is the main factor of film formation, occurs continuously when the negative electrode open potential is 0.6 V to 1.0 V. Therefore, for example, the film formation potential Uside is 0.6 V, 0.8 V or 1. It may be set as 0.0V.

<Vaccine side reaction current value _{ISR (PE) at the} positive electrode>
Conventionally, it has been considered that the deviation capacity ΔQ corresponding to the positive and negative electrode compositions is mainly affected by the formation of an SEI film (a side reaction) on the surface of the negative electrode. The coating formed on the negative electrode includes LiF, Li ₂ Co _{3, and the} like in addition to SEI, but the negative electrode side reaction current _{ISR (PE)} was estimated by the Tafel equation described above.

The present inventor considered the film formed by the positive electrode in the same manner, made a hypothesis that it could be estimated by the Tafel equation in the same manner, and found that this hypothesis was correct by experiments.

_{Therefore, also for the positive electrode, iPE} is calculated for the film formation current density at the positive electrode by the Tafel equation of the following formula (4) based on the cell voltage VB and the cell temperature TB.
Here, the exchange current density i _0, move coefficient alpha, Faraday constant F, the gas to R constant, absolute temperature T, the film formation potential U _side, the U _PE positive electrode open-circuit potential.

そして、この正極被膜形成電流密度をｉ_ＰＥに基づいて、正極副反応電流値Ｉ_{ＳＲ（ＰＥ）}を算出する。

Then, the positive electrode side reaction current value _{ISR (PE)} is calculated based on the positive electrode film forming current density of _iPE.

<Total capacity of _{deviation capacity ΔQ (t 0 to t 1} ) corresponding to positive and negative electrode compositions>
Then, in S7 of the follow chart shown in FIG. 4, ΔQ (t0 to t1) = (from _{the negative electrode side reaction current value I SR (NE)} calculated in this way and the positive electrode side reaction current value I _{SR (PE).} I _{SR (NE)} -I _{SR (PE)} ) × Δt is calculated. That is, the difference between the side reaction current value I _{SR (NE)} at the negative electrode and the side reaction current value I _{SR (PE)} at the positive electrode is multiplied by the elapsed time Δt, and the deviation capacity ΔQ (t _{0) corresponding to the positive / negative electrode composition of the elapsed time Δt.} Calculate the total capacity of ~ t _{1) (S7).}

<Comparison between ΔQ of the present embodiment and ΔQ of the prior art>
5 (a) shows ΔQ of the prior art shown in FIGS. 2 (a) and 2 (b), and FIG. 5 (b) shows ΔQ of the present embodiment shown in FIGS. 3 (a) and 3 (b). It is a schematic diagram which compares these easily. In the conventional determination of deterioration shown in Patent Document 1, the upper figure of FIG. 5A shows a state in which there is no deviation corresponding to the positive and negative electrode compositions before deterioration. From this state, when the negative electrode capacity decrease amount ΔQ _NE deviates by 3 squares as shown in the lower figure of FIG. 5A, the positive electrode capacity-corresponding deviation capacity ΔQ becomes 3 squares.

On the other hand, in ΔQ of the present embodiment, from the state where there is no deviation shown in the upper part of FIG. 5B, the negative electrode capacity decrease amount ΔQ _NE is 3 as shown in the lower part of FIG. The mass is off. At this time, since the positive electrode capacity reduction amount Delta] Q _PE of positive electrode 1 _PE is shifted to 1 mass fraction same direction as in FIG. 5 (b), the deviation is canceled, the positive and negative electrodes discrepancy capacity Delta] Q is 2 mass fraction It becomes. That is, as compared with the conventional deterioration estimation method, the deterioration estimation method of the present embodiment does not overestimate ΔQ. It can be seen that ΔQ can be estimated more accurately.

Strictly speaking, as described above, ΔQ _NE itself is also reduced in the present embodiment as compared with the prior art, but is omitted here for the sake of brevity.
<Deterioration suppression control method for lithium-ion secondary batteries>
The life of the lithium ion secondary battery that suppresses the deterioration of the lithium ion secondary battery 1 based on the deviation capacity ΔQ corresponding to the positive and negative electrode compositions estimated by the deterioration estimation method of the lithium ion secondary battery 1 of the present embodiment. The estimation method and the deterioration suppression control method will be described. In the present embodiment, the deterioration state of the lithium ion secondary battery 1 in the future can be predicted based on the history of the cell SOC θ, the cell voltage VB, and the cell temperature TB. Then, by controlling the usage band of the cell SOCθ as needed based on this result, the life of the lithium ion secondary battery 1 can be extended.

<Procedure of control method for suppressing deterioration of lithium ion secondary battery>
FIG. 6 is a flowchart of a deterioration suppression control method for the lithium ion secondary battery 1 that suppresses deterioration of the lithium ion secondary battery 1 of the present embodiment.

The calculation is started when the lithium ion secondary battery 1 is mounted on the vehicle 10 (calculation start). It is not always necessary to determine whether or not the life target can be reached. For example, the timing of turning on the ignition or once every few days may be set regardless of the ignition. The calculation is repeated every measurement interval time Δt, for example, and is continuously calculated from t0 to the life target period tmax.

Prior to the start of the calculation, the deterioration characteristic data is read. The deterioration characteristic data is measured at the time of shipment from the factory by the procedure for acquiring the deterioration characteristics shown in FIG. Then, the deterioration characteristic data is readable and stored in advance in a memory 102 (FIG. 1) such as a ROM of the ECU 100 of the vehicle 10.

Here, a procedure for acquiring deterioration characteristics will be described with reference to FIG.
<Procedure for acquiring deterioration characteristics>
For accurate prediction, it is important to acquire the deterioration characteristics of the lithium ion secondary battery 1, which is the reference for the prediction, that is, the rate of deterioration. Therefore, before the lithium ion secondary battery 1 is mounted on the vehicle, or the lithium ion secondary battery 1 mounted on the vehicle is removed from the vehicle and set in a device for acquiring deterioration characteristics for measurement. Then, "preservation" is performed under a specific preset temperature, time, and charge / discharge conditions, and the rate of deterioration peculiar to the lithium ion secondary battery 1 is obtained from the difference in the measured values of the side reaction currents before and after that. Is measured separately for the positive electrode and the negative electrode. Accurately calculate _{the negative electrode capacity reduction amount ΔQ NE} and the positive electrode capacity reduction amount ΔQ _PE of the lithium ion secondary battery 1 by correcting the measured value of this side reaction current under the conditions expected in the future. Can be done.

<Configuration of equipment for acquiring deterioration characteristics of lithium-ion secondary batteries>
FIG. 7 is a block diagram showing a configuration of an apparatus for acquiring deterioration characteristics of the lithium ion secondary battery 1. The configuration of the device for acquiring deterioration information of the lithium ion secondary battery 1 of the present embodiment includes a well-known charging / discharging device 3, a cell voltage measuring device 4, a cell current measuring device 5, a thermometer 6, and a heat retaining device 7. Further, a control device 8 composed of a well-known computer provided with an interface for controlling these is provided. The control device 8 includes a CPU 81 and a memory 82. The memory 82 includes a RAM and a ROM.

These function as a storage means for storing the lithium ion secondary battery 1 under specific conditions as a configuration of an apparatus for acquiring deterioration characteristics of the lithium ion secondary battery 1. It also functions as a battery capacity reduction amount measuring means for measuring _{the capacity reduction amount Q loss} of the battery full capacity before and after storage of the stored lithium ion secondary battery 1. Also functions as a self-discharge amount measuring means for measuring a self-discharge capacity Q _SD before and after the storage was a lithium ion secondary battery 1 storage. Also, the measured volume reduction amount Q _loss and self-discharge capacity Q _SD, using the previously obtained relation between the secondary reaction rate environment of use, and deterioration of the positive electrode in the environment of use envisaged, the deterioration amount of the negative electrode It functions as a deterioration amount calculation means for calculating each of the above.

<Flowchart for acquiring deterioration characteristics>
Next, with reference to the flowchart of FIG. 8, the deterioration characteristic acquisition which is the premise of the life estimation method and the deterioration suppression control method of the lithium ion secondary battery of the present embodiment will be described. In the procedure for acquiring the deterioration characteristics, the individual difference in the deterioration rate of the lithium ion secondary battery 1 can be found by measuring the side reaction current value and self-discharge peculiar to the lithium ion secondary battery 1.

Here, first, prior to the explanation of this flowchart, the terms used in the explanation will be described in advance.
“T1 (° C)” is an arbitrary storage temperature (for example, 50 ° C).

“T1 (h)” is an arbitrary storage period (for example, 24 hours).
“V1 (V)” is full from the voltage of 3.0 (V) at which the cell voltage VB is completely discharged (in this embodiment, the cell voltage VB in the fully discharged state with 0% cell SOC is referred to as “lower limit voltage”). A voltage (for example, 3.8 (V)) arbitrarily set between 4.1 (V) of charging (cell SOC 0 to 100%, referred to as "upper limit voltage" in this embodiment), in this embodiment. , "Reference voltage". In this embodiment, it is used as a reference voltage for measuring the self-discharge capacity and is also an arbitrary initial cell voltage VB for storage.

"Q1 (Ah)" is a battery having a cell voltage VB of a lower limit voltage of 3.0 (V) to an upper limit voltage (fully charged cell voltage VB = 4.1 (V) (here, cell SOC 100% voltage)). It is the full capacity of the pre-storing battery whose capacity has been measured.

It is the section capacitance before storage measured from the lower limit voltage 3.0 (V) of "Q2 (Ah)" to the reference voltage V1 = 3.8 (V).
“Q3 (Ah)” is the remaining capacity after storage, which is discharged from the reference voltage V1 = 3.8 (V) to the lower limit voltage of 3.0 (V) after storage.

“Q4 (Ah)” is the full capacity of the battery after storage measured from the lower limit voltage of 3.0 (V) to the upper limit voltage of 4.1 (V).
“ _QSD (Ah)” is the self-discharge capacity during the storage period obtained from the difference between the section capacity Q2 before storage and the remaining capacity Q3 after storage.

“Q _loss (Ah)” is a capacity decrease amount obtained from the difference between the battery full capacity before storage Q1 and the battery full capacity after storage.
“ _{ISR (NE) 0} (A)” is a negative electrode side reaction current (velocity) determined by _{the self-discharge capacity QSD (Ah) ÷ storage time t1 (h).}

“I _{SR (PE) 0} (A)” is _{based on the difference from the vaccine current (velocity) I SR (NE) 0} of the negative electrode and the quotient of the volume reduction amount Q loss (Ah) ÷ storage time t1 (h). This is the obtained side reaction current (velocity) of the positive electrode.

In this embodiment, it is defined as described above.
<Procedure of flowchart for acquiring deterioration characteristics>
Next, using these definitions, the procedure for acquiring the deterioration characteristics of the lithium ion secondary battery 1 will be described with reference to the flowchart of FIG.

First, when the process of acquiring deterioration characteristics is started (START), the battery is charged from the lower limit voltage 3.0 (V) of the cell SOC 0% at the time of complete discharge to the full charge of the upper limit voltage 4.1 (V) of the cell SOC 100%. The battery full capacity Q1 (Ah) before storage is measured (S101).

Next, the section capacitance Q2 (Ah) before storage is measured by charging in the voltage section from the lower limit voltage 3.0 (V) to the reference voltage V1 = 3.8 (V) (S102).
Subsequently, while adjusting the voltage to the reference voltage V1 = 3.8 (V), it is stored at an arbitrary temperature T1 (for example, 50 ° C.) for an arbitrary time t1 (for example, 24 hours) (S104). This procedure corresponds to the "save step". Therefore, this storage is performed under conditions in which the starting cell voltage, the storage temperature T1, and the storage time t1 are always constant.

After adjusting the voltage to the reference voltage V1 = 3.8 (V) before storage, the battery is discharged to the lower limit voltage of 3.0 (V) after storage, and the remaining capacity Q3 (Ah) after storage is measured (S105). ). Subsequently, the battery is fully charged from the lower limit voltage of 3.0 (V) to the upper limit voltage of 4.1 (V), and the battery full capacity Q4 (Ah) after storage is measured (S106). In this case, the voltage is specified. This is because after storage, the full charge capacity is lower than before storage due to deterioration of the active material / electrolyte, formation of a film, and the like.

Then, the difference between the section capacity Q2 (Ah) before storage and the remaining capacity Q3 (Ah) after storage is obtained. Compared to the section capacity Q2 before storage, the remaining capacity Q3 after storage has a decrease in capacity due to self-discharge. That is, the self-discharge amount of the storage time t1 can be obtained by obtaining these in the voltage section from the same lower limit voltage 3.0 (V) to the reference voltage V1 = 3.8 (V). _{By this procedure, the self-discharge capacity QSD} is calculated from the electric capacity reduced to the storage time t1 (S107). This procedure corresponds to the “step of measuring the amount of self-discharge”.

Next, the self-discharge capacity _QSD (Ah) is divided by the storage time t1 (h) to calculate the side reaction current (velocity) I _{SR (NE) 0} (A) of the negative electrode (S108).
Further, the capacity reduction amount Q _loss (Ah) is calculated from the difference between the battery full capacity Q1 (Ah) before storage and the battery full capacity Q4 (Ah) after storage (S109).

Finally, from the difference between the side reaction current (velocity) I _{SR (NE) 0} (A) of the negative electrode and the quotient (A) obtained by dividing the volume reduction amount Q _loss (Ah) by the storage time t1 (h), the positive electrode The side reaction current (velocity) I _{SR (PE) 0} (A) of is calculated (S110).

_{As described above, the side reaction current (velocity) I SR (NE) 0} (A) of the negative electrode of the lithium ion secondary battery and the side reaction current (velocity) I _{SR (PE) 0} of the positive electrode in the predetermined storage section of the present embodiment. The procedure for acquiring the deterioration identification for measuring (A) is completed (END).

_{By such a procedure, the side reaction current (velocity) I SR (PE) 0} of the positive electrode under the conditions of the reference voltage V1 (V) for starting storage, the storage temperature T1 (° C), and the storage time t1 (h) ( A) and the side reaction current (velocity) I _{SR (NE) 0} (A) of the negative electrode can be measured. That is, the deterioration characteristic that serves as a reference for the lithium ion secondary battery 1 is clarified. This procedure may be performed for each cell, but if the lithium ion secondary battery 1 has the same configuration, a sampling inspection without 100% inspection is sufficient.

The above is the procedure for acquiring the deterioration characteristics of the lithium ion secondary battery 1.
Next, returning to FIG. 6, the step of “acquisition of deterioration information up to now (S10)”, which is processed after the calculation of the flowchart of the deterioration suppression control method for the lithium ion secondary battery is started, will be described.

<Acquisition of deterioration information up to now (S10)>
Here, deterioration information from the start time t0 to the current time t1 is acquired (S10).
This is a sequential integration of the positive and negative electrode composition-corresponding deviation capacitance ΔQ actually measured, stored, processed and calculated by the ECU 100 of the control device 18 of the vehicle 10 in the steps S11 to S16. Therefore, in the first round of processing, there is no deterioration of the lithium ion secondary battery 1, and ΔQ is also zero. Therefore, this "deterioration information up to now" is zero. From the second round, deterioration information is accumulated in sequence. By this procedure, it is possible to know the state of deterioration of the lithium ion secondary battery 1 accumulated from the start of use to the present, and it is possible to predict further deterioration from this state as a starting point.

<Determination of input information (S11)>
After the procedure of acquiring deterioration information (S10) up to now is completed, the input information is next determined (S11). The method for controlling the lithium ion secondary battery that suppresses the deterioration of the lithium ion secondary battery 1 of the present embodiment needs to predict the deterioration of the lithium ion secondary battery 1 when the life of the lithium ion secondary battery 1 is reached in the future.

FIG. 9 is a diagram showing a method of determining input information.
Although the deterioration up to the present was found in S10, the cell SOC and the cell temperature TB for estimating the future deterioration are estimated from the cell voltage VB and the cell temperature TB accumulated by the ECU 100 of the vehicle 10.

The past cell SOC (%), cell voltage VB (V), and cell temperature TB (° C) are stored in the memory 102 by the ECU 100 of the vehicle 10.
FIG. 9A is a diagram showing a method of estimating cell SOC (%) for estimating future deterioration. The probability density function PDF (probability distribution function) is derived from the accumulated past cell SOC (%). The probability density function PDF shows the existence probability with an upwardly convex graph. In this example, it has a peak at approximately 50-60%. From this, the cumulative probability (cumulative probabilities), that is, the cumulative distribution function CDF (cumulative distribution function), is derived. It is an upward-sloping graph showing a cumulative probability of 0 to 100%.

Next, by Monte Carlo simulation, a random number is generated to determine the coordinates of the vertical axis, and the cell SOCθ is virtually determined using this cumulative distribution function CDF as a reference function.
On the other hand, FIG. 9B is a diagram showing a method of estimating the cell temperature TB (° C) for estimating future deterioration. The cell temperature TB is processed in the same manner as the cell SOC. The accumulated past cell temperature TB (° C) is derived from the probability density function PDF. The probability density function PDF shows the existence probability with an upwardly convex graph. In this example, it has a peak at approximately 30 ° C. From this, the cumulative distribution function CDF, which is the accumulation of these, is derived. It is an upward-sloping graph showing a cumulative probability of 0 to 100%.

Next, by Monte Carlo simulation, a random number is generated to determine the coordinates of the vertical axis, and the cell temperature TB (° C) is virtually determined using this cumulative distribution function CDF as a reference function.

From the cell SOC θ (%) and the cell temperature TB (° C) determined in this way, the input information of the time t2 at that time is determined. In this way, the cell SOC θ (%) and the cell temperature TB (° C) are determined every time t2.

<Creation of OCV after deterioration (S12)>
Then, the side reaction current value generated at that time t2 is calculated by the cell SOC θ and the cell temperature TB determined in the input information determination (S11), and the deviation capacity ΔQ corresponding to the positive and negative electrode compositions is calculated.

As described in FIG. 3 (b), the deterioration progresses the negative electrode open-circuit potential of the graph U respectively graphs in point diagram on the graph U _PE point and the positive electrode open-circuit potential of the _NE U _NE, along the graph U _PE left Shift in the direction. Then, the position of a point on the graph U _'PE point and the positive electrode open-circuit potential of the graph U' _NE of the negative electrode open-circuit potential shown in FIG. From _{V PE1} on the graph _{U 'PE} of _{V NE1} and positive open-circuit potential of the graph _{U' NE} of the negative electrode open-circuit potential at this time, to estimate the OCV after deterioration.

_{<V'PE, V'NE} calculated (S13)>
Based on the information input is determined, calculates positive electrode potential _V'PE, the negative electrode potential _{V'NE.
<Calculate I SR (PE)} and I _{SR (NE)} based on electric potential (S14)>
The positive electrode potential _V'PE calculated in S13, based on the negative electrode potential _V'NE, side reactions current _{I SR} in the positive electrode _(PE), to calculate a side reaction current value _{I SR (NE)} in the negative electrode (S14).

<Vaccine side reaction current values for negative and positive electrodes I _{SR (NE) and} I _{SR (PE)} >
_{Here, the volume reduction ΔQ NE} and ΔQ _PE due to side reactions at the negative electrode and the positive electrode, that is, the side reaction current value I _{SR (NE)} at the negative electrode and the side reaction current value I _{SR (PE) at the} positive electrode are as follows as described above. Is required in this way.

The negative electrode side reaction current value _{ISR (NE)} is the following _{equation (6), where a NE} is the exchange current density of the _{side reaction that occurs on the negative electrode and b NE} is the overvoltage term of the side reaction that occurs on the negative electrode.

により負極における副反応電流値Ｉ_{ＳＲ（ＮＥ）}を算出することができる。

This allows the side reaction current value _{ISR (NE)} at the negative electrode to be calculated.

The positive electrode side reaction current value _{ISR (PE)} is the following _{equation (7), where a PE} is the exchange current density of the side reaction that occurs on the positive electrode and b _PE is the overvoltage term of the side reaction that occurs on the positive electrode.

により正極における副反応電流値Ｉ_{ＳＲ（ＰＥ）}を算出することができる。

This allows the side reaction current value _{ISR (PE)} at the positive electrode to be calculated.

_{<Add I SR (PE)} and I _{SR (NE)} considering the temperature and the amount of deterioration to the accumulated side reaction amount (S15)>
Based on the input cell temperature TB, the side reaction current value I _{SR (PE)} at the positive electrode calculated in S14, and the side reaction current value I _{SR (NE)} at the negative electrode, the positive electrode capacity decrease amount ΔQ _PE and the negative electrode capacity decrease Find the quantity ΔQ _NE .

<Calculation of negative electrode side reaction current value _{ISR (NE) by Tafel equation>}
In the present embodiment, the negative electrode film forming current density _iNE is obtained by the Tafel equation (formula (3)) shown below.

ここで、ｉ_０を交換電流密度、αを移動係数、Ｆをファラデー定数、Ｒを気体定数、Ｔを絶対温度、Ｕ_sideを被膜形成電位、Ｕ_ＮＥを負極開放電位とする。

Here, 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 formation potential, and _UNE is the negative electrode open potential.

<Calculation of negative electrode side reaction current value _{ISR (PE) by Tafel equation>}
Even in the positive electrode, to calculate a film formation current density i _PE at the positive electrode by Tafel equation of formula (4).

Here, 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 formation potential, and _UNE is the negative electrode open potential.

そして、この正極被膜形成電流密度をｉ_ＰＥに基づいて、正極副反応電流値Ｉ_{ＳＲ（ＰＥ）}を算出する。

Then, the positive electrode side reaction current value _{ISR (PE)} is calculated based on the positive electrode film forming current density of _iPE.

<Attenuation of the side reaction current value of the positive and negative electrodes according to the film growth>
In the Tafel equation, the thickness of the SEI coating is not considered. Therefore, Delta] Q _PE, in the calculation of Delta] Q _NE, according to the film formation amount at each elapsed time, Delta] Q _PE, a Delta] Q _NE is calculated using a value obtained by attenuating the side reaction current value.

FIG. 10 is a schematic view showing a model of film growth. FIG. 11 is an equation showing the relationship between the amount of film formed and the side reaction current value. FIG. 12 is a graph showing the attenuation rate of the current value with respect to the reciprocal of the coating amount. FIG. 13 is a table showing the relationship between the elapsed time, the amount of film formation, and the side reaction current value. FIG. 14 is a graph comparing the deterioration degree estimation result of the prior art and the deterioration degree estimation result of the present embodiment. With reference to FIGS. 10 to 14, the attenuation of the side reaction current values of the positive and negative electrodes according to the film growth will be described.

_{As shown in FIG. 10A, the time t 0} immediately after assembling the lithium ion secondary battery 1 (before conditioning) is a state in which the current collector foil 1c and the mixture 1a are bonded together, and the SEI coating 1sei is formed. Not formed. Depending on the use, at time _{t 1,} the SEI film 1sei as shown in FIG. 10 (b), it is formed. Further continued use, grows thicker SEI film 1sei as shown in FIG. 10 (c) When it is time _{t 2.} This SEI coating 1sei acts as a resistor and obstructs the flow of current. The side reaction current value I depends on the thickness x. The side reaction current value I is proportional to 1 / x as shown in FIG. 11 (k is a coefficient). Then, when calculating ΔQ in (t _{1 to t 2} ), it is attenuated due to the relationship between “1 / Σ subcurrent value × t / mAh” and “adverse reaction current value attenuation rate /%” shown in FIG. calculating the ΔQ in _(t 1 ~t ₂₎ with a side reaction current value at was _(t 1 ~t _2).

As a result, as shown in FIG. 13, as the time _{elapses from t 1 to t 2 to t n} , the coating amount is cumulatively thickened, and the side reaction current value I is the reciprocal of the thickness x. It becomes smaller in proportion to.
In the present embodiment, since the attenuation of the side reaction current values of the positive and negative electrodes described above according to the film growth is taken into consideration, as shown in FIG. 14, the method of estimating the deterioration of the present embodiment is Tafel by the conventional technique. It is possible to estimate the deterioration closer to the actual deterioration than the deterioration estimation method using only the equation.

<Calculation of ΔQ from the difference in the amount of deterioration of the positive and negative electrodes (S16)>
Further, the explanation will be continued by returning to the flowchart of FIG. The deviation capacity ΔQ corresponding to the positive / negative electrode composition is calculated from the difference between the positive electrode capacity decrease amount ΔQ _PE and the negative electrode capacity decrease amount ΔQ _NE.

<Completion of calculation of life target period (S17)>
The processing of S11 to S16 _{is performed every time t n} , and if the life target period t max is not completed _{, the process returns to S11 and the processing is continued for the next time t n + 1} (S17: NO → S11).

On the other hand, when the processes of S11 to S16 _{are performed every time t n} and the life target period tmax is completed, it is determined whether or not the life can reach the target (S17: YES → S18).
<Achievable life target (S18)>
The deviation capacity ΔQ corresponding to the positive and negative electrode composition is integrated up to the life target period tmax, and as a result, it is compared with the threshold value of the deviation capacity ΔQ corresponding to the positive and negative electrode composition set in advance. The calculation is finished assuming that the performance can be maintained.

On the other hand, the deviation capacity ΔQ corresponding to the positive and negative electrode composition is integrated up to the life target period tmax, and as a result, it is compared with the threshold value of the deviation capacity ΔQ corresponding to the positive and negative electrode composition set in advance. It is determined that the life target cannot be reached because the predetermined performance cannot be maintained (S18: NO).

<Relationship between deterioration amount and SOC>
Here, FIG. 15 is a diagram showing the relationship between the amount of deterioration and SOC. Normally, in a hybrid vehicle, the SOC usage range is fully charged (100%) so that the secondary battery can receive regenerative power and can immediately supply power to the motor when requested. ) And the state where the battery is not charged at all (0%) is controlled to be approximately in the middle (50 to 60%). However, as a result of the simulation, if it is found that the current SOC use area control deteriorates and the performance cannot be maintained until the life target period tmax, it is necessary to use the SOC use area with a small amount of deterioration. It is necessary to perform charge / discharge control by the PCU 30 so as to limit the SOC usage range to a limited range. Here, in the ECU 100, when the original used SOC area is changed to the used SOC area after the correspondence, whether or not the performance can be maintained up to the life target period tmax is determined by changing the setting of the used SOC area and again in S10 to S18. Perform processing. The setting of the used SOC area is 60 to 70% if the currently used SOC area is 50 to 60%. However, the charging rate needs to have a certain margin from the fully charged state (100%) and the completely uncharged state (0%). Further, if the currently used SOC range is 50 to 60%, it may be set to 40 to 50%, and the simulation may be performed a plurality of times to select the used SOC range with the least deterioration.

(Effect of embodiment)
(1) In the deterioration estimation method of the lithium ion secondary battery 1 of the present embodiment, the deterioration is determined separately for the positive electrode and the negative electrode, and the deterioration is divided into the positive electrode capacity decrease amount ΔQ _PE and the negative electrode capacity decrease amount ΔQ _{NE, respectively.} Since it is estimated, it can be estimated accurately.

(2) In particular, the negative electrode capacity reduction amount ΔQ _NE and the positive electrode capacity reduction amount ΔQ _PE are divided and analyzed, and the positive and negative electrode composition-corresponding deviation capacity ΔQ is obtained from the difference between them. Therefore, the deviation capacity ΔQ corresponding to the positive and negative electrode compositions is not overestimated, and an accurate estimation can be made.

(3) In the embodiment, the lithium ion secondary battery 1 having no usage history immediately after production can be stored under specific conditions, and the deterioration characteristics peculiar to the lithium ion secondary battery 1 can be measured. Using this deterioration rate, it is possible to estimate the life based on the deviation capacity ΔQ corresponding to the positive and negative electrode compositions.

(4) Therefore, from the start of use of the lithium ion secondary battery 1, the future life can be more reliably estimated from the viewpoint of the deviation capacity ΔQ corresponding to the positive and negative electrode compositions.
(5) In addition, since the vehicle 10 actually equipped with the lithium ion secondary battery 1 actually measures and accumulates the past cell SOC, cell voltage VB, and cell temperature TB, and estimates deterioration based on these, the deterioration is estimated. Deterioration from the past to the present can be estimated extremely accurately.

(6) Furthermore, by performing a simulation based on past data, it is possible to make an accurate and realistic estimation even in the future.
(7) Moreover, since these are calculated based on the theory such as the Tafel equation, accurate estimation can be performed even in a vehicle.

(8) Further, since ΔQ is obtained in consideration of the attenuation of the side reaction current value of the positive electrode and the negative electrode according to the coating growth, it is possible to estimate the deterioration closer to the actual deterioration.
(9) Further, in the control method of the lithium ion secondary battery 1 of the present embodiment, the deterioration status of the lithium ion secondary battery 1 is matched based on the deterioration estimation method of the lithium ion secondary battery 1 of the present embodiment. Can be controlled.

(10) In particular, it can be determined whether or not the lithium ion secondary battery 1 can maintain its performance up to the life target period tmax. Furthermore, if it is found that the lithium ion secondary battery 1 cannot maintain its performance until the life target period tmax, the used SOC range with a small amount of deterioration should be used without replacing the lithium ion secondary battery 1. Therefore, it is possible to extend the life.

(11) It is possible to select the optimum SOC usage range by comparing the deterioration by simulation and selecting which of the used SOC areas has less deterioration.
(12) Since these can be processed by the in-vehicle ECU 100, appropriate control can always be performed based on accurate information from the start of use of the lithium ion secondary battery 1.

(13) Since the control of the lithium ion secondary battery 1 is not a limitation of charging, the regenerative current from the vehicle can be used up without wasting it.
(Modification example)
The present invention is not limited to the above embodiment, and can be carried out as follows.

The control device 18 for the lithium ion secondary battery according to the present embodiment has been described by taking as an example a configuration mounted on an electric vehicle. The electric vehicle is typically a hybrid vehicle (including a plug-in hybrid vehicle), but is not limited thereto. The lithium ion secondary battery control device 18 according to the present embodiment can be applied to all vehicles that generate electric power using electric power supplied from the lithium ion secondary battery. Therefore, the electric vehicle may be an electric vehicle or a fuel cell vehicle.

〇 Further, the application of the method for estimating the life of the lithium ion secondary battery according to the present embodiment is not limited to the vehicle, and may be, for example, a stationary battery mounted on a building.
-In the present embodiment, the secondary battery has been described by taking a lithium ion secondary battery as an example, but the secondary battery is not limited to the lithium ion secondary battery, but is a nickel hydrogen secondary battery, and further in the future. Sodium ion secondary batteries, lithium air secondary batteries, etc., which are assumed in the above, are not excluded.

〇 The estimation method of the embodiment can be performed at the time of a new vehicle. In that case, the battery model data is supplied instead of the past data.
〇 Since the secondary battery inspection method of the embodiment can be carried out at any time, it can be used not only for inspection of availability of shipment at the time of manufacturing the lithium ion secondary battery, but also for the lithium ion secondary battery recovered from the used vehicle. Can be done at the time of resale. Moreover, it is natural that it can be simply used for determining the deterioration of the secondary battery for other purposes.

○ The flowcharts shown in FIGS. 4, 6 and 8 are examples, and the order thereof can be changed, and steps can be added, deleted or changed.
〇 In the embodiment, _{the difference between the side reaction current value I SR (NE)} at the negative electrode and the side reaction current value I _{SR (PE)} at the positive electrode is multiplied by the elapsed time Δt, and the deviation capacity ΔQ corresponding to the positive / negative electrode composition of the elapsed time Δt. The total capacity of (t _{0 to t n) is calculated.} On the other hand, by multiplying the negative electrode film forming current density _iNE by the elapsed time Δt, the capacity decrease due to a side reaction in the negative electrode ΔQ _NE is obtained, and by multiplying the positive electrode film forming current density _iPE by the elapsed time Δt, the positive electrode is used. Obtain the _{volume reduction ΔQ PE} due to the side reaction. Then, it can also be carried out by obtaining the deviation capacity ΔQ corresponding to the positive and negative electrode compositions from these differences.

〇 The main point of the present invention is to calculate the deviation capacity ΔQ corresponding to the positive / negative electrode composition based on the negative electrode capacity reduction amount ΔQ _NE and the positive electrode capacity reduction amount ΔQ _PE. Therefore, the calculation method of the negative electrode capacity reduction amount ΔQ _NE and the positive electrode capacity reduction amount ΔQ _PE is not limited to the embodiment.

〇 The elements illustrated in the embodiment can be implemented by replacing each other.
○ Further, it goes without saying that the present invention can be implemented by a person skilled in the art by adding, deleting or changing its structure, or by changing the category, as long as it does not deviate from the scope of claims.

1 ... Lithium ion secondary battery 1A ... Cell 1 _NE ... Negative electrode 1 _PE ... Positive electrode 1a ... Mixing material 1c ... Current collecting foil 1sei ... SEI coating 2 ... Life estimation device 3 ... Charging / discharging device 4 ... Cell voltage measuring device 5 ... Cell Current measuring device 6 ... Thermometer 7 ... Heat retaining device 8 ... Control device 81 ... CPU
82 ... Memory 10 ... Vehicle 18 ... Control device 20 ... Monitoring unit 21 ... Voltage sensor 22 ... Current sensor 23 ... Temperature sensor 30 ... PCU
100 ... ECU
101 ... CPU
102 ... Memory t ₀ ... (Start of use) time t ₁ ... (ΔQ calculation) time t ₂ ... (Next ΔQ calculation) time t ₃ ... (Life estimation interval) time t _n, t _{n + 1} ... (Repeat) ) Time tmax ... Life target period Δt ... Elapsed time VB ... Cell voltage TB ... Cell temperature IB ... Current θ ... Cell SOC
_UNE ... Graph of (negative electrode open potential) U _PE ... Graph of (positive electrode open potential) V _PE ... Positive electrode potential V _NE ... Negative electrode potential i _NE ... Negative electrode film formation current density i _PE ... Positive electrode film formation current density I ... Side reaction Current value I _{SR (NE)} ... Side reaction current value at the negative electrode I _{SR (PE)} ... Side reaction current value at the positive electrode Q ... Capacity ΔQ ... positive and negative electrodes discrepancy capacity Delta] Q _{NE ...} negative electrode capacity decrease Delta] Q _{PE ...} positive electrode capacity decrease amount Q1 ... before storage battery full capacity Q2 ... before storage interval capacity Q3 ... residual capacity Q4 ... after storage battery full capacity after storage.
Q _SD (Ah) ... Self-discharge capacity during storage period Q _loss (Ah) ... Capacity reduction amount T1 (° C) ... Storage temperature V1 (V) ... Reference voltage (initial voltage for storage)

Claims (12)

A film formation current density of the negative electrode and i _NE,
When a _NE is the exchange current density of the side reaction that occurs on the negative electrode and b _NE is the overvoltage term of the side reaction that occurs on the negative electrode, the following equation (1)

A step of the negative electrode capacity decrease amount calculation for calculating a capacity decrease amount Delta] Q _NE in the negative electrode by multiplying the elapsed time Δt based on the film-forming current density i _NE of the negative electrode which is calculated by,
Let the positive electrode film formation current density be _iPE .
When a _PE is the exchange current density of the side reaction that occurs on the positive electrode and b _PE is the overvoltage term of the side reaction that occurs on the positive electrode, the following equation (2)

A step of positive electrode capacity decrease amount calculation for calculating a capacity decrease amount Delta] Q _PE in the positive electrode by multiplying the elapsed time Δt based on the film-forming current density i _PE of the positive electrode calculated by,

From the difference between the negative electrode capacity reduction amount ΔQ _{NE calculated in the negative electrode capacity reduction amount calculation step and the positive electrode capacity reduction amount ΔQ PE} calculated in the positive electrode capacity reduction amount calculation step, the positive electrode capacity reduction amount ΔQ PE is calculated. A method for estimating deterioration of a secondary battery, which comprises a step of calculating a deviation capacity ΔQ corresponding to a positive and negative electrode composition. In the step of calculating the amount of decrease in negative electrode capacity,
i ₀ the exchange current density, transfer coefficient of alpha, Faraday constant F, when the gas the R constant, absolute temperature T, the film formation potential U _side, a negative electrode open-circuit potential of the U _NE, the U _PE as a positive electrode open-circuit potential ,
The following formula (3)

The negative electrode side reaction current value _{ISR (NE)} was calculated based on the negative electrode film formation current density _{iNE calculated in}
In the step of calculating the amount of decrease in positive electrode capacity,
The following formula (4)

The method for estimating deterioration of a secondary battery according to claim 1, wherein the positive electrode side reaction current value ISR (PE) is calculated based on the positive electrode film formation current density iPE. In the step of calculating the negative electrode capacity reduction amount and the step of calculating the positive electrode capacity reduction amount, the positive electrode capacity reduction amount ΔQ _PE and the negative electrode capacity reduction amount ΔQ _NE are calculated using the values obtained by attenuated the side reaction current value according to the elapsed time. The method for estimating deterioration of a secondary battery according to claim 2, wherein the calculation is performed. In the step of calculating the negative electrode capacity reduction amount and the step of calculating the positive electrode capacity reduction amount,
Preservation steps to preserve the rechargeable battery under specific conditions,
The step of measuring the amount of decrease in battery capacity before and after the storage of the stored secondary battery and measuring the amount of decrease in capacity of the battery full capacity Q _loss , and the step of measuring the amount of decrease in battery capacity.
A step of self-discharge capacity measurement for measuring a self-discharge capacity Q _SD before and after storage of the secondary battery the storage,
This includes a step of acquiring deterioration characteristics for obtaining the side reaction current values of the positive electrode and the negative electrode under the specific conditions at the time of storage from the capacity reduction amount Q _loss and the self-discharge capacity Q _SD.
The method for estimating deterioration of a secondary battery according to any one of claims 1 to 3, wherein the deterioration is estimated based on the side reaction current values of the positive electrode and the negative electrode by the step of acquiring the deterioration characteristics. The method for estimating deterioration of a secondary battery according to any one of claims 1 to 4, wherein the secondary battery is a lithium ion secondary battery. It is a life estimation method that estimates the life of the secondary battery by estimating the deterioration of the secondary battery at the future time tmax.
A step of estimating deterioration of a secondary battery for calculating a deviation capacity ΔQ corresponding to a positive / negative electrode composition at t1 at the time of life estimation using the method for estimating deterioration of a lithium ion secondary battery according to any one of claims 1 to 5.
Based on the positive / negative composition correspondence deviation capacity ΔQ calculated in the step of estimating the deterioration of the secondary battery and the conditions, the time is accumulated by integrating the deterioration of the secondary battery from t1 at the time of life estimation to the time tmax which is the future life target. A method for estimating the life of a secondary battery, which comprises a step of estimating the life of the secondary battery for estimating the deterioration of the secondary battery at tmax. In the step of estimating the life of the secondary battery, the cumulative distribution function obtained based on the stochastic density function derived from the cell SOC and the cell temperature accumulated as the conditions in the step of estimating the deterioration of the secondary battery is referred to as a reference function. The method for estimating the life of a secondary battery according to claim 6, wherein a random number is generated and the deterioration of the secondary battery is integrated from t1 at the time of estimating the life to tmax in the future time by Monte Carlo simulation. By comparing the deterioration of the secondary battery at the time tmax estimated in the step of estimating the life of the secondary battery with the preset threshold of deterioration of the secondary battery, the secondary battery deteriorates at the time tmax. The method for estimating the life of a secondary battery according to claim 6 or 7, further comprising a step of determining the life of the secondary battery for determining whether or not the battery reaches the life below the threshold value. When it is determined in the step of determining the life of the secondary battery that the secondary battery cannot reach the life at the time tmax, the life is reached by changing the cell SOC condition in the step of estimating the life of the secondary battery. The method for estimating the life of a secondary battery according to any one of claims 6 to 8, further comprising a step of re-determining whether or not the battery can be reached. In the re-judgment step
The ninth aspect of the present invention is characterized in that the control step of controlling the cell SOC of the secondary battery is provided according to the condition of the cell SOC when it can be determined that the life can be reached when the conditions are changed. How to estimate the life of a secondary battery. A voltage sensor that detects the cell voltage of the secondary battery,
A temperature sensor that detects the cell temperature of the secondary battery,
A secondary battery control device having a CPU and a memory, and a computer that estimates cell SOC from the voltage sensor.
A control device for a secondary battery, which comprises a control means for executing the life estimation method according to claim 10. The secondary battery control device according to claim 11, wherein the secondary battery is mounted on a vehicle, and the computer is a computer mounted on the vehicle.

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