JP2020173928A - Deterioration estimation method of all-solid battery - Google Patents

Abstract

To provide a deterioration estimation method of an all-solid battery, capable of estimating an all-solid battery crack with high accuracy.SOLUTION: A deterioration estimation method of an all-solid battery includes: a step of acquiring internal-pressures P1, P2 and voltages V1, V2 in an arbitrary period of the all-solid battery; a step of calculating an internal-pressure variation amount ΔP from the internal-pressures P1, P2; a step of obtaining charging rates SOC1, SOC2 corresponding to the voltages V1, V2; a step of calculating a charging rate variation amount ΔSOC from the charging rates SOC1, SOC2; a step of acquiring a threshold value ΔPlim corresponding to the charging rate variation amount ΔSOC; and a step of determining whether or not the absolute value of the internal-pressure variation amount ΔP exceeds the absolute value of the threshold value ΔPlim, and when a determination is made in the determination step that the absolute value of the internal-pressure variation amount ΔP exceeds the absolute value of the threshold value ΔPlim, such an estimation is made that a crack occurs in the all-solid battery.SELECTED DRAWING: Figure 1

Description

The present application relates to a method for estimating deterioration of an all-solid-state battery.

The secondary battery deteriorates by repeating charging and discharging. Therefore, it is important to check how much the secondary battery has deteriorated. So far, methods for determining deterioration of various secondary batteries have been developed.

Patent Document 1 describes the measured values of the voltage V and the internal pressure P of the secondary battery, the relationship diagram between the voltage and the pressure in the predetermined reference state, and the relationship diagram between the pressure and the capacity in the predetermined reference state. It discloses a system for determining the deterioration state of a secondary battery, which calculates the amount of deterioration (capacity deterioration) according to the amount of decrease in internal pressure. Patent Document 2 calculates the fatigue ratio within the fatigue limit from the estimated stress applied to the electrode body exterior film and the temperature difference between the predetermined time before and the current temperature, and determines the deterioration of the electrode body exterior film. Deterioration of the electrode body exterior film. The judgment method is disclosed. Patent Document 3 discloses a secondary battery system that determines cell deterioration based on the pressure of an electrode body. Patent Document 4 measures the pressure and temperature of a secondary battery housed in a housing, and calculates the remaining capacity, the fully charged capacity, and the like based on the measured pressure and temperature and a preset correlation. The method of estimating the state of the secondary battery is disclosed.

Japanese Unexamined Patent Publication No. 2013-92398 JP 2015-115100 JP-A-2015-153509 Japanese Unexamined Patent Publication No. 2006-12761

In an all-solid-state battery, if a material having a large expansion / contraction rate during charging / discharging, such as metal Li, is used for the negative electrode, the internal pressure of the battery increases / decreases with the expansion / contraction of the negative electrode during charging / discharging. At that time, the solid electrolyte may not be able to follow the internal pressure fluctuation and may crack. As a result, the ionic conductive function of the solid electrolyte may be partially lost, or a material having a large expansion / contraction rate during charging / discharging of metal Li or the like may grow in cracks and cause a short circuit, which causes a problem. There is. With the methods of Patent Documents 1 to 4, it is difficult to detect cracks in an all-solid-state battery with high accuracy.

Therefore, it is an object of the present application to provide a deterioration estimation method for an all-solid-state battery that can estimate the cracking of the all-solid-state battery with high accuracy.

In the prior art, the fluctuation of the voltage of the all-solid-state battery was detected to estimate the cracking of the solid electrolyte, but the fluctuation of the voltage caused by the cracking was slight, it was difficult to distinguish it from noise, and the detection sensitivity was low. .. Therefore, as a result of diligent studies, the present inventor monitors fluctuations in the internal pressure during charging and discharging, and detects whether or not the fluctuations in the internal pressure exceed a predetermined threshold value, thereby increasing the cracking of the solid electrolyte. We have found that it can be estimated accurately, and completed the present invention.

As described above, based on the above findings, the present application is a method for estimating deterioration of an all-solid-state battery as one means for solving the above problems, in which the start point of an arbitrary period of the method is t ₁ and the end point is t _2. Then, the step of acquiring the internal pressures P ₁ , P ₂ and the voltages V ₁ and V ₂ in the above period of the all-solid-state battery, and the step of calculating the internal pressure fluctuation amount ΔP from the above internal pressures P ₁ and P _2. , The step of acquiring the charge rates SOC ₁ and SOC ₂ corresponding to the above voltages V ₁ and V ₂ based on the V-SOC map in the normal state obtained in advance, and the charge rate fluctuation from the charge rates SOC ₁ and SOC _2. The step of calculating the amount ΔSOC, the step of acquiring the threshold value ΔP _lim corresponding to the charge rate fluctuation amount ΔSOC based on the ΔSOC−ΔP _lim map in the normal state obtained in advance, and the absolute value of the internal pressure fluctuation amount ΔP are A step of determining whether or not the absolute value of the threshold value ΔP _lim is exceeded is provided, and it is determined that the absolute value of the internal pressure fluctuation amount ΔP exceeds the absolute value of the threshold value ΔP _{lim in} the determination step. In this case, the deterioration estimation method of the all-solid-state battery, which presumes that the all-solid-state battery is cracked, is disclosed.

According to the deterioration estimation method of the all-solid-state battery disclosed in the present application, the cracking of the solid electrolyte can be estimated with high accuracy.

It is a flowchart of the deterioration estimation method 10 of an all-solid-state battery. It is the schematic of the evaluation battery used in an Example. This is the result of the charge / discharge test. (A) is a diagram showing a time-voltage relationship, (b) is a diagram showing a time-internal pressure relationship, and (c) is a time (s) -voltage fluctuation ΔV / Δt (mV /). It is a figure which showed the relationship of s), and (d) is a figure which showed the relationship of time (s) -surface pressure fluctuation ΔP / Δt (kPa / s).

[Deterioration estimation method for all-solid-state battery 10]
The deterioration estimation method 10 of the all-solid-state battery of the present disclosure (hereinafter, may be referred to as “deterioration estimation method 10”) will be described. FIG. 1 shows a flowchart of the deterioration estimation method 10.

The deterioration estimation method 10 is a deterioration estimation method for an all-solid-state battery. Here, the start point of an arbitrary period in the deterioration estimation method 10 is t ₁ , and the end point is t ₂ . Then, the degradation estimation method 10, as shown in FIG. 1, the internal pressure _P 1, step S1 to acquire the _{P 2} and the voltage _V 1, _{V 2} (hereinafter in the period of the all-solid-state battery, "internal pressure, voltage sometimes referred obtaining step S1 "and.), in step S2 (hereinafter to calculate the internal pressure variation amount ΔP from the internal pressure P _1, P _2, is sometimes referred to as" internal pressure variation amount calculating step S2 ".) And step S3 to acquire the charge rates SOC ₁ and SOC ₂ corresponding to the above voltages V ₁ and V ₂ based on the V-SOC map in the normal state obtained in advance (hereinafter, “charge rate acquisition step S3””. In addition, step S4 (hereinafter, may be referred to as "charge rate fluctuation amount calculation step S4") for calculating the charge rate fluctuation amount ΔSOC from the charge rate SOC ₁ and SOC ₂ and the normal obtained in advance. Step S5 (hereinafter, may be referred to as “threshold acquisition step S5”) for acquiring the threshold value ΔP _lim corresponding to the charge rate fluctuation amount ΔSOC based on the ΔSOC−ΔP _lim map in the above state, and the internal pressure fluctuation amount. A step S6 (hereinafter, may be referred to as “determination step S6”) for determining whether or not the absolute value of ΔP exceeds the absolute value of the threshold value ΔP _lim is provided.

Further, the deterioration estimation method 10 may have a step of notifying the result of the determination step S6 (hereinafter, may be referred to as "notification step S7").
Hereinafter, each configuration of the deterioration estimation method 10 will be further described.

<All-solid-state battery>
The all-solid-state battery that can be used in the deterioration estimation method 10 is not particularly limited. That is, the power generation element is not particularly limited as long as it is an all-solid-state battery including a positive electrode, a solid electrolyte layer, a negative electrode, and the like. A material having a large expansion / contraction rate during charging / discharging, such as metal Li, may be used for the negative electrode, but the present invention is not limited to this, and a known material can be appropriately selected depending on the intended purpose. The material constituting the positive electrode and the solid electrolyte layer is not particularly limited, and a known material can be appropriately selected depending on the intended purpose. Further, the all-solid-state battery may be sealed with an exterior member such as laminated metal.
Since the all-solid-state battery expands and contracts during charging and discharging, the internal pressure of the all-solid-state battery increases or decreases. Therefore, the all-solid-state battery (mainly the solid electrolyte layer) may be cracked. In the deterioration estimation method 10, such cracks are estimated with high accuracy.

<Internal pressure and voltage acquisition step S1>
The internal pressure and voltage acquisition step S1 is a step of acquiring the internal pressures P ₁ , P ₂ and the voltages V ₁ and V ₂ of the all-solid-state battery in an arbitrary period (t ₁ , t ₂ ) of the deterioration estimation method 10.
Here, the arbitrary period is a period for calculating the internal pressure fluctuation amount ΔP and the like, which will be described later. Therefore, in order to estimate the deterioration of the all-solid-state battery with high accuracy, the length of the arbitrary period is preferably a unit time. However, a period wider than the unit time may be used. Also, any period, the beginning of the degradation estimation method 10 may start point t _1.
The internal pressure and voltage corresponding to t ₁ are P ₁ and V ₁ , respectively, and the internal pressure and voltage corresponding to t ₂ are P ₂ and V ₂ , respectively.

<Internal pressure fluctuation amount calculation step S2>
Internal pressure variation amount calculating step S2 is a step of calculating the internal pressure variation amount ΔP from the internal pressure P _1, P _2. The internal pressure variation amount ΔP is the difference between the internal pressure _P 1, _{P 2.}

<Charging rate acquisition step S3>
The charge rate acquisition step S3 is a step of acquiring the charge rates SOC ₁ and SOC ₂ corresponding to the voltages V ₁ and V ₂ based on the V-SOC map in the normal state obtained in advance.

Here, the "normal state" refers to the state of an all-solid-state battery that has not deteriorated such as cracks. Therefore, the "V-SOC map in a normal state" refers to a V-SOC map obtained by using an all-solid-state battery in a normal state. When the deterioration estimation method 10 is performed, it is preferable to obtain a V-SOC map in advance by using an all-solid-state battery in a normal state having the same configuration as the all-solid-state battery used in the deterioration estimation method 10.

<Calculation of charge rate fluctuation amount S4>
The charge rate fluctuation amount calculation S4 is a step of calculating the charge rate fluctuation amount ΔSOC from the charge rates SOC ₁ and SOC ₂ . The charge rate fluctuation amount ΔSOC is the difference between the charge rates SOC ₁ and SOC ₂ .

<Threshold acquisition step S5>
The threshold value acquisition step S5 is a step of acquiring the threshold value ΔP _lim corresponding to the charge rate fluctuation amount ΔSOC based on the ΔSOC−ΔP _lim map obtained in advance in the normal state.
The "ΔSOC-ΔP _lim map in a normal state" refers to a ΔSOC-ΔP _lim map obtained by using an all-solid-state battery in a normal state. The threshold value ΔP _lim is an upper limit value of the internal pressure fluctuation amount corresponding to the charge rate fluctuation amount when charging / discharging is performed using an all-solid-state battery in a normal state. Therefore, the threshold value ΔP _lim is a value used to determine whether the internal pressure fluctuation amount ΔP is due to cracking of the all-solid-state battery or a mere noise signal when the deterioration estimation method 10 is performed, which will be described later. In the determination step S6, the cracking of the all-solid-state battery is estimated depending on whether or not the absolute value of the internal pressure fluctuation amount ΔP exceeds the absolute value of the threshold value ΔP _lim .
In this way, when the deterioration estimation method 10 is performed, a ΔSOC−ΔP _lim map must be obtained in advance using an all-solid-state battery in a normal state having the same configuration as the all-solid-state battery used in the deterioration estimation method 10. Is good.

<Judgment step S6>
Decision step S6 the absolute value of the internal pressure variation amount [Delta] P is a step of determining whether or not exceeded (| ΔP |) is the absolute value of the threshold _{ΔP lim (| | ΔP lim)} .
If it is determined in the determination step S6 that | ΔP | exceeds | ΔP _lim |, it is presumed that the all-solid-state battery is cracked. As a result, the deterioration estimation method 10 can estimate the cracking of the all-solid-state battery with high accuracy.

Further, when it is determined in the determination step S6 that | ΔP | does not exceed | ΔP _lim |, it is preferable to perform steps S1 to S6 in the same manner in the next period continuous with the above arbitrary period. .. Then, this may be continued until the deterioration estimation method 10 is completed. More specifically, it can be said that the deterioration estimation method 10 preferably detects whether or not | ΔP | exceeds | ΔP _lim | while monitoring the internal pressure and voltage of the all-solid-state battery. At this time, the deterioration estimation method 10 may be performed while using an all-solid-state battery.

<Notification step S7>
The deterioration estimation method 10 may further include a step of notifying the result of the determination step S6. The result of the determination step S6 is the result of determination as to whether or not | ΔP | exceeds | ΔP _lim |. In the notification step S7, only the case where | ΔP | exceeds | ΔP _lim | may be notified, and the results of both the case where | ΔP | exceeds | ΔP _lim | and the case where | ΔP | exceeds | You may notify.

The deterioration estimation method 10 for the all-solid-state battery has been described above. As described above, the all-solid-state battery deterioration estimation method of the present disclosure can be said to be an indispensable method for determining battery deterioration and improving safety because cracks in the all-solid-state battery can be estimated with high accuracy. ..

The deterioration estimation method 10 for the all-solid-state battery can be performed while using, for example, the all-solid-state battery. The detection of the internal pressure and voltage of the all-solid-state battery can be obtained by using a known sensor. For example, the internal pressure of an all-solid-state battery can be obtained by installing a sensor on the positive electrode side or the negative electrode side. A sensor may be attached to the positive electrode side of the all-solid-state battery as in the embodiment described later. However, the location of the sensor is not limited to this. Further, the analysis performed in steps S2 to S6 may be performed using an electronic computer including an arithmetic unit such as a computer. Further, parameters such as internal pressure, voltage, internal pressure fluctuation amount, and the result of determination may be displayed on an external display.

Hereinafter, the deterioration estimation method for the all-solid-state battery of the present disclosure will be further described with reference to Examples.

An evaluation battery is manufactured by using an all-solid lithium secondary battery in which a negative electrode (metal Li), a solid electrolyte layer, and a positive electrode (copper foil) are laminated, and further installing an internal pressure measuring unit on the surface of the copper foil. did. A schematic diagram of the evaluation battery is shown in FIG.

The method for producing the all-solid-state lithium secondary battery is as follows. A solid electrolyte layer was prepared by pressing at a pressure of 6 ton / cm ² using 101.7 mg of a sulfide-based solid electrolyte (Li ₂ SP ₂ S _5- based material containing LiBr and LiI). Then, the metal Li foil was arranged on one surface of the solid electrolyte layer, the copper foil was arranged on the other surface of the solid electrolyte layer, and press molding was performed at a pressure of 1 ton / cm ² . As a result, an all-solid-state lithium secondary battery was produced.

A charge / discharge test was performed using the above evaluation battery. The absolute value of the threshold value ΔP _lim (| ΔP _lim |) was 0.5 kPa / s.
First, the evaluation battery was allowed to stand in a constant temperature bath at 25 ° C. for 1 hour to make the cell temperature uniform. Next, a constant current having a current density of 435 μA / cm ² was passed through the evaluation battery to charge the battery (Li precipitation), and charging was stopped when the charging capacity reached 4.35 mAh / cm ² . After 10 minutes, it was also planned to discharge (Li dissolve) at a constant current with a current density of 435 μA / cm ² and finish when 1.0 V arrives, but a deterioration mode (crack) occurs before reaching 1.0 V. Therefore, the test was completed.

The results of the test are shown in FIG. FIG. 3A is a diagram showing the relationship of time (s) -voltage (V), and FIG. 3B is a diagram showing the relationship of time (s) -surface pressure (MPa), and (c). ) Is a diagram showing the relationship of time (s) -voltage fluctuation ΔV / Δt (mV / s), and (d) shows the relationship of time (s) -surface pressure fluctuation ΔP / Δt (kPa / s). It is a figure. The surface pressure can be read as the internal pressure.

The cracking of the battery (cracking of the solid electrolyte layer) in the above test was caused by the sudden decrease in the electrode thickness as the metal Li was dissolved, and the solid electrolyte layer caused the springback phenomenon. Regarding this, it is examined whether or not the cracking of the solid electrolyte layer could be estimated based on FIGS. 3A to 3D.
First, when focusing on the voltage of the all-solid-state battery, the battery resistance increased and the voltage increased slightly due to the cracking of the solid electrolyte layer (Fig. 3 (a)), but it was converted into the voltage fluctuation amount and plotted. Then (FIG. 3 (c)), it was found that the signal was discriminated as a noise signal. Therefore, it was found that the estimation method focusing on voltage is not an effective means.
On the other hand, when focusing on the internal pressure of the all-solid-state battery, the internal pressure fluctuated greatly at the time when the solid electrolyte cracked (FIG. 3 (b)). Then, when this was converted into the amount of internal pressure fluctuation and plotted (FIG. 3 (d)), it was found that cracks in the solid electrolyte layer could be detected with high sensitivity.
From the above results, it was found that the cracking of the all-solid-state battery can be estimated with high accuracy by paying attention to the fluctuation of the internal pressure.

Claims (1)

In the deterioration estimation method of the all-solid-state battery, when the start point of an arbitrary period of the method is t ₁ and the end point is t ₂ .
The step of acquiring the internal pressures P ₁ , P ₂ and the voltages V ₁ , V ₂ in the period of the all-solid-state battery, and
Calculating the internal pressure variation amount ΔP from the internal pressure P _1, P _2,
Based on the V-SOC map in the normal state obtained in advance, the steps of acquiring the charge rates SOC ₁ and SOC ₂ corresponding to the voltages V ₁ and V ₂ and
The step of calculating the charge rate fluctuation amount ΔSOC from the charge rate SOC ₁ and SOC ₂ and
Based on the ΔSOC−ΔP _lim map obtained in advance in the normal state, the step of acquiring the threshold value ΔP _lim corresponding to the charge rate fluctuation amount ΔSOC, and
A step of determining whether or not the absolute value of the internal pressure fluctuation amount ΔP exceeds the absolute value of the threshold value ΔP _lim is provided.
If it is determined in the determination step that the absolute value of the internal pressure fluctuation amount ΔP exceeds the absolute value of the threshold value ΔP _lim , it is estimated that the all-solid-state battery is cracked.
Deterioration estimation method for all-solid-state batteries.

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