JP7571571B2 - Battery Inspection Method - Google Patents

Description

This application relates to a battery inspection method.

Lithium-ion batteries have been in practical use for some time. Lithium-ion batteries have a high voltage and high energy capacity and are used in a wide range of fields, but depending on the battery configuration, moisture in the air can have a detrimental effect. For example, the ionic conductivity of the sulfide solid electrolyte used in solid-state batteries decreases when exposed to moisture. Therefore, when operating lithium-ion batteries, it is important to determine the deterioration state of the battery.

Patent Document 1 discloses a method for estimating or predicting the degradation state of a sulfide-based solid battery, which calculates the amount of moisture that has permeated into the sulfide-based solid battery based on the temperature and relative humidity of the sulfide-based solid battery, and estimates or predicts the degradation state of the battery based on the calculated amount of moisture that has permeated. In addition, Patent Document 1 discloses, as a specific embodiment, a technology that uses the moisture permeation rate (moisture permeation coefficient) of the battery to calculate the amount of moisture that has permeated.

JP 2015-53139 A

As mentioned above, Patent Document 1 uses the moisture permeability coefficient of the battery to calculate the moisture permeation amount. However, this moisture permeability coefficient is the moisture permeability coefficient of the battery in its initial state. Since the moisture permeability coefficient increases as the battery deteriorates, the technology in Patent Document 1 does not take into account the state of the battery after deterioration, and there is room for improvement in the accuracy of estimating the moisture permeation amount.

In view of the above, the object of this application is to provide a battery inspection method that can calculate the amount of moisture permeation more accurately than conventional methods and determine the deterioration state of a battery.

As one means for solving the above problem, the present disclosure provides a battery inspection method for inspecting the deterioration state of a battery based on the amount of moisture permeation between time t0 and t1, the method comprising the steps of acquiring the temperature T1 and relative humidity H1 applied to the battery between time t0 and t1, acquiring a deterioration coefficient a based on the acquired temperature T1 and relative humidity H1, calculating the moisture permeation coefficient P(t1, T1) at time t1 and temperature T1 using the acquired deterioration coefficient a, calculating the amount of moisture permeation between time t0 and t1 based on the calculated moisture permeation coefficient P(t1, T1), the time between time t0 and t1, the relative humidity H1, and the permeation resistance of the battery, and judging the deterioration state of the battery from the calculated amount of moisture permeation.

The battery inspection method disclosed herein calculates P(t1, T1) using the deterioration coefficient a. In other words, the moisture permeability coefficient is calculated taking into account the state of the battery after deterioration. Therefore, it is possible to calculate the moisture permeability with greater accuracy than conventional methods and determine the deterioration state of the battery.

1 is a flowchart of a battery inspection method 10. FIG. 11 is a diagram for explaining a degradation coefficient map. FIG. 13 is a diagram for explaining a temperature dependency map. FIG. 4 is a diagram for explaining the relationship between the water concentration and resistance of a battery.

The battery inspection method of the present disclosure will be described using battery inspection method 10, which is one embodiment.

Battery inspection method 10 is a method for inspecting the deterioration state of a battery based on the amount of moisture permeation between times t0 and t1.

"Time t0→t1" refers to the inspection period. Battery inspection method 10 inspects the battery during the inspection period and determines the deterioration state of the battery. Time t0 is the start of the inspection period, and time t1 is the end of the inspection period. Typically, time t0 is the time when the battery in the initial state is operated, and time t1 is the time when process S1 is started. In other words, time t0→t1 is the elapsed time from when the battery in the initial state is operated to when process S1 is started.

The battery used in the battery inspection method 10 is a battery in which the electrode elements are sealed in an exterior body. The electrode elements are known electrode elements such as a positive electrode, a negative electrode, an electrolyte layer, a positive electrode current collector, and a negative electrode current collector. The exterior body is, for example, a known laminate seal material. Such a battery can be produced by housing the battery elements inside the exterior body and then welding the ends of the exterior body.

The type of electrode element sealed inside the battery is not particularly limited, and may be an electrode element of a liquid battery or an electrode element of a solid battery. That is, the battery used in the battery inspection method 10 may be a liquid battery or a solid battery. However, from the viewpoint of the necessity of inspection, it is preferable that the battery includes a battery element that is deteriorated by moisture that penetrates. For example, if the battery is a solid battery, a solid battery including a sulfide solid electrolyte is included. This is because the ionic conductivity of the sulfide solid electrolyte decreases due to moisture. The battery configuration may be a known configuration.

Normally, the exterior body (sealing part) has a certain moisture permeability coefficient as one of its material properties. It is also known that the exterior body deteriorates due to the environmental load (temperature, relative humidity) in which the battery is placed, and the moisture permeability coefficient increases accordingly. Therefore, in order to accurately estimate the amount of moisture that has permeated into the battery, it is necessary to correct the moisture permeability coefficient by taking into account the deterioration of the battery (deterioration of the exterior body).

In battery inspection method 10, as described below, the moisture permeability coefficient is calculated taking into account the state of the battery after degradation. Therefore, it is possible to calculate the moisture permeability with greater accuracy than conventional methods and to determine the state of degradation of the battery. Each step of battery inspection method 10 is described below.

Figure 1 shows a flowchart of battery inspection method 10. As shown in Figure 1, battery inspection method 10 has steps S1 to S5. Battery inspection method 10 may also have step S6 after step S5.

<Step S1>
Step S1 is a step of acquiring the temperature T1 and relative humidity H1 applied to the battery during the time period from t0 to t1. Here, in this specification, "temperature" refers to the temperature of the environment in which the battery is placed. "Relative humidity" refers to the relative humidity of the environment in which the battery is placed. The temperature and relative humidity can be measured by known measuring devices. The measurement frequency can be set to any frequency. For example, every hour or every day. The temperature T1 and relative humidity H1 applied to the battery during the time period from t0 to t1 refer to the average relative temperature and average relative humidity, respectively.

<Step S2>
Step S2 is a step of acquiring a deterioration coefficient a based on the temperature T1 and relative humidity H1 acquired in step S1. The deterioration coefficient a is a coefficient for correcting the moisture permeability coefficient of the battery at time t0 to the moisture permeability coefficient of the battery in a deteriorated state. Such a deterioration coefficient a can be acquired, for example, from a deterioration coefficient map.

The deterioration coefficient map is obtained in advance. For example, the deterioration coefficient map can be obtained as follows. First, a test (storage test) is performed in which a battery having the same configuration as the battery used in the battery inspection method 10 is used to store the battery for a predetermined time in an environment of a predetermined temperature and relative humidity. Next, the moisture permeability coefficient of the battery after the storage test is calculated. This operation is performed multiple times by changing the temperature and relative humidity of the battery. Then, using the obtained moisture permeability coefficient of the battery after the test, the increase rate of the moisture permeability of the battery after the test relative to the moisture permeability coefficient of the battery in the initial state at a predetermined temperature is calculated, and the increase rate is set as the deterioration coefficient. The obtained deterioration coefficient is related to the temperature and relative humidity of the battery. In this way, the deterioration coefficient map can be obtained. For such a deterioration coefficient map, it is necessary to obtain a deterioration coefficient map for the moisture permeability coefficient of the battery in the initial state at each temperature. This is because the moisture permeability coefficient has temperature dependency.

A specific example of a deterioration coefficient map is shown in FIG. 2. The left diagram of FIG. 2 is a diagram for explaining the increase rate (deterioration coefficient) of the moisture permeability of a battery after testing relative to the moisture permeability coefficient of the battery in the initial state at 25°C when the relative humidity is 50% RH. The right diagram of FIG. 2 is a schematic diagram showing a deterioration coefficient map in which the obtained deterioration coefficients are mapped (not shown) in a graph with the storage temperature on the horizontal axis and the storage relative humidity on the vertical axis. Here, the deterioration coefficient map shown in the right diagram of FIG. 2 is a diagram similar to the left diagram of FIG. 2, and can be created by obtaining multiple diagrams obtained by changing the relative humidity. This deterioration coefficient map is a deterioration coefficient map of the moisture permeability coefficient of a battery in the initial state at 25°C (deterioration coefficient map at 25°C). As mentioned above, since the moisture permeability coefficient has temperature dependency, it is necessary to obtain a deterioration coefficient map at each temperature.

Next, a method for obtaining the deterioration coefficient a from the deterioration coefficient map will be described. First, if the temperature T1 obtained in step S1 is 25°C and the relative humidity H1 is 50% RH, the deterioration coefficient map for 25°C is selected (Figure 2). Then, from Figure 2, the deterioration coefficient a corresponding to a storage temperature of 25°C and a storage relative humidity of 50% RH is obtained. In this way, a deterioration coefficient map is selected based on the temperature T1, and the deterioration coefficient a corresponding to the temperature T1 and the relative humidity H1 is obtained.

<Step S3>
Step S3 is a step of calculating a moisture permeability coefficient P(t1, T1) at time t1 and temperature T1 using the deterioration coefficient a obtained in step S2. Specific methods for calculating the moisture permeability coefficient P(t1, T1) include, for example, the following two methods.

The first method is to calculate the moisture permeability coefficient P(t1,T1) from the product of the deterioration coefficient a and the moisture permeability coefficient P(t0,T1) at time t0 and temperature T1 (P(t1,T1)=a×P(t0,T1)). The moisture permeability coefficient P(t0,T1) at time t0 and temperature T1 is obtained in advance. Specifically, after leaving the battery in a thermo-hygrostat at temperature T1 and relative humidity H1 for an arbitrary period of time (a period of time that does not cause the effects of deterioration), the amount of moisture in the battery (amount of moisture permeation) is measured, and the amount of moisture can be calculated from the formula (1) described below.

The second method is to calculate the moisture permeability coefficient P(t1, T1) using a temperature dependency map. In detail, the temperature dependency of the moisture permeability coefficient is first obtained, the moisture permeability coefficient after deterioration at the reference temperature T is obtained, and then the moisture permeability coefficient at T1 is calculated from the temperature dependency map.

The temperature dependency of the moisture permeability coefficient is, for example, as shown in the left diagram of Figure 3. The vertical axis of the left diagram of Figure 3 is the permeability coefficient, and the horizontal axis is the temperature. The solid line shows the relationship between the temperature and the moisture permeability coefficient before deterioration, and the dashed line shows the relationship between the temperature and the moisture permeability coefficient after deterioration. The temperature and moisture permeability coefficient after deterioration (dashed line) are the temperature and moisture permeability coefficient before deterioration multiplied by the deterioration coefficient a. The reference temperature T is the temperature that is the reference for the temperature dependency map. In Figure 3, it is set to 25°C. The temperature dependency map is as shown in the right diagram of Figure 3. The horizontal axis of the right diagram of Figure 3 is the temperature, and the vertical axis shows the moisture permeability coefficient after deterioration at each temperature when the reference temperature T is set to 25°C. The differences between the left diagram and the right diagram are as follows. The left diagram shows an example of the change in the moisture permeability coefficient at the initial stage and after deterioration when a certain deterioration is performed, and the right diagram shows the map of the permeability coefficient at each temperature when the permeability coefficient at the reference temperature of 25°C changes due to systematic deterioration.

Specifically, the moisture permeability coefficient P(t1, T1) is calculated as follows. First, the moisture permeability coefficient P(t1, T) after deterioration at the reference temperature T is calculated from the product of the deterioration coefficient a and the moisture permeability coefficient P(t0, T) at time t0 and reference temperature T (P(t1, T) = a x P(t0, T)). The moisture permeability coefficient P(t0, T) at the reference temperature T is obtained in the same manner as the method for obtaining P(t0, T1) described above. Next, the moisture permeability coefficient P(t1, T1) at temperature T1 is obtained from the temperature dependency map.

Here, when the second method is used, there is an advantage that it is necessary to obtain only the degradation coefficient map for the reference temperature in step S2. Specifically, in step S2, the degradation coefficient a at temperature T1 can be obtained using the degradation coefficient map for the reference temperature. In this way, when the second method is used, it is not necessary to create degradation coefficient maps for each temperature in advance.

<Step S4>
Step S4 is a step of calculating the amount of moisture permeation between times t0 and t1 based on the moisture permeation coefficient P(t1, T1) calculated in step S3, the time (elapsed period) between times t0 and t1, the relative humidity H1, and the permeation resistance of the battery. The permeation resistance is a physical quantity specific to the battery, and is calculated by the seal length (permeation length) L/seal cross-sectional area (permeation cross-sectional area) S. The seal length is the width of the part (sealed part) where the exterior body is welded (the length of the sealed part from the outside to the inside of the battery), and the seal cross-sectional area is the thickness of the sealed part x the length of the sealed outer periphery.

Specifically, the water permeation amount is calculated by the following formula (1).
Moisture permeability = moisture permeability coefficient x elapsed time x relative humidity / permeation resistance (1)

<Step S5>
Step S5 is a step of determining the deterioration state of the battery from the moisture permeation amount calculated in step S4. Specifically, first, the moisture concentration in the battery is calculated from the moisture permeation amount, and then the resistance increase amount during the time period from t0 to t1 is calculated from the moisture concentration. Then, it is determined whether the calculated resistance increase amount exceeds a predetermined threshold value.

The moisture concentration in the battery can be calculated from the moisture permeation amount by a known method. For example, the moisture concentration at time t1 can be calculated by adding up the moisture amount in the battery at time t0 and the moisture permeation amount calculated in step S4 and dividing by the battery volume. In addition, the resistance increase amount between time t0 and t1 can be calculated by obtaining the relationship between the moisture concentration and resistance in the battery in advance and calculating the resistance increase amount from the difference between the resistance value obtained from the moisture concentration at time t0 and the resistance value obtained from the moisture concentration at time t1. Figure 4 shows an example of the relationship between the moisture concentration and resistance in the battery. Figure 4 can be obtained by the above-mentioned storage test. The predetermined threshold is an index for determining the deterioration state of the battery and can be set based on the target battery performance.

If it is determined in step S5 that the resistance increase exceeds the predetermined threshold (resistance increase > threshold), it is determined that the deterioration has progressed sufficiently, and step S6 is performed. If it is determined in step S5 that the resistance increase does not exceed the predetermined threshold (resistance increase ≦ threshold), it is determined that the deterioration has not progressed sufficiently, and step S1 is performed again.

<Step S6>
Step S6 is an optional step, and is a step of changing the battery control when it is determined in step S5 that the resistance increase exceeds a predetermined threshold (resistance increase>threshold). The change in battery control is not particularly limited, and can be set appropriately according to the device in which the battery is mounted. For example, there are the following. First, a battery replacement diagram is set up. This can encourage battery replacement. Second, when the battery is mounted on a vehicle, the resistance increase calculated in step S5 is replaced with the capacity deterioration amount to correct the cruising distance. Third, based on the resistance increase calculated in step S5, the maximum current value at which Li does not precipitate is corrected.

The battery inspection method of the present disclosure has been described above using the battery inspection method 10, which is one embodiment. The battery inspection method of the present disclosure calculates P(t1, T1) using the deterioration coefficient a. In other words, the moisture permeability coefficient is calculated taking into account the state of the battery after deterioration. Therefore, it is possible to calculate the moisture permeability with higher accuracy than conventional methods and to determine the deterioration state of the battery.

Claims (1)

A method for inspecting a deterioration state of a battery based on a moisture permeation amount during a time period from t0 to t1, comprising the steps of:
acquiring a temperature T1 and a relative humidity H1 applied to the battery during a time period t0→t1;
acquiring a deterioration coefficient a based on the acquired temperature T1 and relative humidity H1;
calculating a moisture permeability coefficient P(t1, T1) at the time t1 and the temperature T1 using the acquired deterioration coefficient a;
Calculating the amount of moisture permeated during the time t0→t1 based on the calculated moisture permeability coefficient P(t1, T1), the time during the time t0→t1, the relative humidity H1, and the permeation resistance of the battery;
and determining a deterioration state of the battery from the calculated moisture permeation amount.
Battery testing methods.