JP7582282B2 - Inspection method for solid-state batteries - Google Patents

Description

This disclosure relates to a method for inspecting solid-state batteries.

JP 2013-210333 A (Patent Document 1) describes a method for inspecting the internal resistance of a secondary battery that can detect the internal resistance of the secondary battery with high accuracy by reducing the influence of the harness.

JP 2013-210333 A

In all-solid-state lithium batteries (hereafter also referred to as "all-solid-state batteries") that use lithium-ion conductive solid electrolytes, all reaction interfaces are solid-solid interfaces, so poor contacts are more likely to occur inside the unit cells (inside the cells) than in liquid batteries, where the reaction interfaces are solid-liquid interfaces. For example, if a unit cell with poor contact is used as a battery pack, the poor contacts may gradually worsen due to use in a low-constraint state or exposure to mechanical loads, and an abnormality may be discovered during the battery's usage stage.

The purpose of this disclosure is to inspect for poor contacts inside solid-state batteries.

The disclosed method for inspecting an all-solid-state battery includes measuring a first resistance value, which is the resistance of the all-solid-state battery immediately after the start of charging and discharging at a first temperature, measuring a second resistance value, which is the resistance of the all-solid-state battery immediately after the start of charging and discharging at a second temperature that is lower than the first temperature, and determining an internal contact failure in the all-solid-state battery based on the first resistance value and the second resistance value.

The components of the internal resistance of an all-solid-state battery are roughly composed of reaction resistance and diffusion resistance (reaction/diffusion resistance) Rd, contact resistance Rc, and electronic resistance Re. In an all-solid-state battery, the resistance value (internal resistance) immediately after the start of charging/discharging, for example, 0.1 seconds after the start of charging/discharging, is dominated by the contact resistance Rc and electronic resistance Re inside the battery. If there is poor contact inside the battery, the contact resistance Rc becomes large. The contact resistance Rc and electronic resistance Re change depending on the temperature of the battery. The change in resistance in response to temperature change (temperature sensitivity of resistance) is small for electronic resistance Re and large for contact resistance Rc.

According to this method, a first resistance value, which is the resistance of the all-solid-state battery, is measured immediately after the start of charging/discharging at a first temperature (e.g., 0.1 seconds after the start of charging/discharging), and a second resistance value, which is the resistance of the all-solid-state battery, is measured immediately after the start of charging/discharging at a second temperature (the second temperature is a temperature lower than the first temperature) (e.g., 0.1 seconds after the start of charging/discharging). The difference between the first resistance value and the second resistance value correlates with the magnitude of the contact resistance Rc of the all-solid-state battery. Therefore, it is possible to determine internal contact failure of the all-solid-state battery based on the first resistance value and the second resistance value.

In an all-solid-state battery, when the temperature of the battery is -10°C or lower, the contact resistance Rc is the major component of the resistance value immediately after the start of charging and discharging, for example, when 0.1 seconds have elapsed since the start of charging and discharging. Therefore, by measuring the first resistance value at a first temperature that is higher than -10°C and measuring the second resistance value at a second temperature that is lower than -10°C, the magnitude of the contact resistance Rc of the all-solid-state battery can be more accurately determined. Also, when the temperature of the battery is 40°C or higher, the electronic resistance Re is the major component of the resistance value immediately after the start of charging and discharging, for example, when 0.1 seconds have elapsed since the start of charging and discharging (the contact resistance Rc is smaller). Therefore, by measuring the first resistance value at a first temperature that is higher than 40°C and measuring the second resistance value at a second temperature that is lower than -10°C, the magnitude of the contact resistance Rc of the all-solid-state battery can be more accurately determined. Note that "immediately after the start of charging and discharging" refers to the point in time when the resistance value (internal resistance) measured after the start of charging and discharging contains almost no reaction/diffusion resistance components.

The difference between the first resistance value and the second resistance value correlates with the magnitude of the contact resistance Rc of the solid-state battery. Therefore, by appropriately setting the threshold value in advance, it is possible to determine internal contact failure in the solid-state battery based on the first resistance value, the second resistance value, and the threshold value.

Preferably, when the first resistance value is R1, the second resistance value is R2, and the previous threshold value is S, the threshold value S is set as "S = a(R1) + b" (a and b are constants), and if S < R2, it may be determined that an internal contact failure has occurred in the solid-state battery.

According to this method, by setting the threshold value S as a linear expression of the first resistance value R1 in advance through experiments or the like, it becomes possible to determine internal contact failure of the solid-state battery in a relatively simple manner.

According to the present disclosure, it is possible to inspect all-solid-state batteries for poor contacts inside the battery.

1 is a diagram showing an outline of an inspection system for an all-solid-state battery according to an embodiment of the present invention. 6A to 6C are diagrams illustrating the change in resistance value of an all-solid-state battery during discharge. FIG. 1 is a diagram showing the contribution rate (Rc/(Rc+Re)) of contact resistance Rc in the 0.1 second resistance of an all-solid-state battery. FIG. 13 is a diagram illustrating a method for setting a threshold value S. 10 is a flowchart illustrating an example of a defective product determination process executed by an inspection device. FIG. 4 is a diagram showing an example of a determination map.

The following describes in detail the embodiments of the present disclosure with reference to the drawings. Note that the same or corresponding parts in the drawings are given the same reference numerals and their description will not be repeated.

Figure 1 is a diagram showing an outline of an inspection system 100 for an all-solid-state battery according to the present embodiment. The inspection system 100 includes a charger/discharger 40, a voltmeter 50, a temperature sensor 60, a heating/cooling unit 70, and an inspection device 80.

In FIG. 1, the all-solid-state battery SB is a cell (single cell) and includes a positive electrode 1, a negative electrode 2, and a separator layer 3. The positive electrode 1 includes a positive electrode active material layer 11 and a positive electrode current collector 12. The positive electrode active material layer 11 is in close contact with the separator layer 3. The positive electrode active material layer 11 includes positive electrode active material particles and a sulfide solid electrolyte. The positive electrode active material particles may include at least one selected from the group consisting of, for example, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. The negative electrode 2 includes a negative electrode active material layer 21 and a negative electrode current collector 22. The negative electrode active material layer 21 is in close contact with the separator layer 3. The negative electrode active material layer 21 includes negative electrode active material particles and a sulfide solid electrolyte. The negative electrode active material particles may include at least one selected from the group consisting of graphite, Si, SiOx (0<x<2), and Li4Ti5O12. The separator layer 3 is interposed between the positive electrode 1 and the negative electrode 2. The separator layer 3 separates the positive electrode 1 from the negative electrode 2. The separator layer 3 includes a sulfide solid electrolyte.

The charger/discharger 40 performs constant current charging and constant current discharging to the all-solid-state battery SB. The voltmeter 50 measures the voltage of the all-solid-state battery SB. The temperature sensor 60 detects the temperature of the all-solid-state battery SB. The heating/cooling unit 70 adjusts the temperature of the all-solid-state battery SB to a predetermined temperature.

The inspection device 80 is a computer including a CPU (Central Processing Unit), memory, a communication interface, a display, etc. The inspection device 80 includes the following functional blocks: an internal resistance detection unit 81, a threshold storage unit 82, and a defective product determination unit 83.

The internal resistance detection unit 81 detects the internal resistance of the all-solid-state battery SB while performing constant current discharge or constant current charging of the all-solid-state battery SB. In the present embodiment, the charger/discharger 40 detects the internal resistance of the all-solid-state battery SB undergoing constant current discharge. The internal resistance is detected based on the voltage value detected by the voltmeter 50 and the current value flowing through the all-solid-state battery SB due to constant current discharge, and is detected for a predetermined time from the start of discharge. Note that a current sensor may be provided to measure the current input/output to the all-solid-state battery SB, and the current value may be measured.

In this embodiment, the heating and cooling unit 70 adjusts the temperature of the all-solid-state battery SB, and the temperature of the all-solid-state battery SB detected by the temperature sensor 60 is maintained at "-10°C". The internal resistance detection unit 81 detects the internal resistance of the all-solid-state battery SB for a predetermined time from the start of discharge, and outputs the detection result to the defective product determination unit 83. The heating and cooling unit 70 adjusts the temperature of the all-solid-state battery SB, and the temperature of the all-solid-state battery SB detected by the temperature sensor 60 is maintained at "40°C". The internal resistance detection unit 81 detects the internal resistance of the all-solid-state battery SB for a predetermined time from the start of discharge, and outputs the detection result to the defective product determination unit 83.

The threshold storage unit 82 stores (stores) a threshold value S that is set in advance by an experiment or the like. FIG. 2 is a diagram for explaining the change in the resistance value of the solid-state battery SB during discharge. FIG. 2(B) shows the change in the resistance value detected by the internal resistance detection unit 81 when discharging is started at a constant current of 40 A in a state where the SOC (State Of Charge) of the solid-state battery SB is 60%. When discharging is started, the resistance value (internal resistance) of the solid-state battery SB increases over time. FIG. 2(C) shows the resistance value when 0.1 seconds have elapsed since the start of discharging (hereinafter also referred to as the "0.1 second resistance"), and shows the case where the temperature of the solid-state battery SB is 40° C. and the case where the temperature of the solid-state battery SB is -10° C. FIG. 2(A) shows the resistance value when 2 seconds have elapsed since the start of discharging (hereinafter also referred to as the "2 second resistance"), and shows the case where the temperature of the solid-state battery SB is 40° C. and the case where the temperature of the solid-state battery SB is -10° C.

As shown in FIG. 2(A), the 2-second resistance includes a component of reaction/diffusion resistance Rd in the resistance value, but as shown in FIG. 2(C), the 0.1-second resistance does not include a component of reaction/diffusion resistance Rd in the resistance value. The lower the battery temperature, the higher the resistance (internal resistance) of the all-solid-state battery SB becomes, and the contact resistance Rc and electronic resistance Re also change depending on the battery temperature. As shown in FIG. 2(C), the change in resistance value with respect to temperature change (temperature sensitivity of resistance) is small for electronic resistance Re and large for contact resistance Rc (there is almost no change in electronic resistance Re between the resistance value at 40°C and the resistance value at -10°C, but there is a large change in contact resistance Rc).

Figure 3 shows the contribution rate of contact resistance Rc (Rc/(Rc+Re)) in the 0.1 second resistance of the solid-state battery SB. When the battery temperature is -10°C or lower, the contribution rate of contact resistance Rc (the proportion of contact resistance Rc in the 0.1 second resistance) is high. When the battery temperature is 40°C or higher, the contribution rate of contact resistance Rc is 50% or lower.

Due to manufacturing variations (material components, dimensions, etc.), the 0.1 second resistance (electronic resistance Re and contact resistance Rc) may vary (vary) significantly. For this reason, it is difficult to determine the contact resistance Rc using the 0.1 second resistance at -10°C or lower. As described above, the temperature sensitivity of the contact resistance Rc (change in resistance value with respect to temperature change) is large, so by measuring and comparing the 0.1 second resistance at different temperatures, the magnitude of the contact resistance Rc can be estimated without the manufacturing variations, and it becomes possible to inspect the contact failure inside the battery. In particular, by comparing the 0.1 second resistance at a temperature where the contribution rate of the contact resistance Rc (the proportion of the contact resistance Rc in the 0.1 second resistance) is high (-10°C or lower in this embodiment) with a temperature where the contribution rate of the contact resistance Rc is low (40°C or higher in this embodiment), the magnitude of the contact resistance Rc can be estimated more accurately.

Figure 4 is a diagram explaining a method for setting the threshold value S. In Figure 4, the horizontal axis represents the 0.1 second resistance when the temperature of the solid-state battery SB is 40°C, and the vertical axis represents the 0.1 second resistance when the temperature of the solid-state battery SB is -10°C. Hereinafter, the 0.1 second resistance when the temperature of the solid-state battery SB is 40°C will be referred to as the "first resistance value R1," and the 0.1 second resistance when the temperature of the solid-state battery SB is -10°C will also be referred to as the "second resistance value R2."

In FIG. 4, the open circles (○) represent the first resistance value R1 and the second resistance value R2 of good (no contact failure) all-solid-state batteries SB, and 50 or more N (number of samples) are plotted. The black circles (●) represent the first resistance value R1 and the second resistance value R2 of defective (contact failure) all-solid-state batteries SB. Defective all-solid-state batteries SB may be produced, for example, by changing the pressing area during the production of the all-solid-state battery SB from the entire surface to a portion, or by sandwiching an insulating member between the current collector and the active material layer.

The first resistance value R1 and the second resistance value R2 of the good and defective all-solid-state batteries SB are measured, and the data of the first resistance value R1 and the second resistance value R2 of the good products (○) and the data of the first resistance value R1 and the second resistance value R2 of the defective products (●) are plotted as shown in FIG. 4 to find the boundary between the good products and the defective products and set the threshold value S. In this embodiment, as shown in FIG. 4, the threshold value S is expressed by a linear expression with the first resistance value R1 as a variable, and is set as the threshold value S = a (R1) + b (a and b are real constants). Then, the region where the second resistance value R2 is equal to or less than the threshold value S (= a (R1) + b) is set as the good product region, and the region where the second resistance value R2 is greater than the threshold value S (= a (R1) + b) is set as the defective product region.

Referring to FIG. 1, the threshold value S thus set is stored in the threshold value storage unit 82. The defective product determination unit 83 determines whether there is an internal contact failure in the all-solid-state battery SB based on the internal resistance (first resistance value R1, second resistance value R2) of the all-solid-state battery SB detected by the internal resistance detection unit 81 and the threshold value S.

Figure 5 is a flow chart showing an example of a defective product determination process executed by the inspection device 80. First, in step (hereinafter, step is abbreviated as "S") 10, the defective product determination unit 83 calculates (extracts) the resistance value (first resistance value R1) when 0.1 seconds have elapsed since the start of discharge at 40°C from the detection result output from the internal resistance detection unit 81. Next, in S11, the defective product determination unit 83 calculates (extracts) the resistance value (second resistance value R2) when 0.1 seconds have elapsed since the start of discharge at -10°C from the detection result output from the internal resistance detection unit 81, and then proceeds to S12.

In S12, the threshold value S (linear formula for calculating the threshold value S (a(R1)+b)) is read from the threshold value memory unit 82, and the threshold value S is set (threshold value S=a(R1)+b is calculated).

In the next step S13, it is determined whether the second resistance value R2 is greater than the threshold value S (= a(R1) + b). If the second resistance value R2 is equal to or less than the threshold value S (R2 ≦ S (= a(R1) + b)), a negative determination is made and the process proceeds to S14, where the solid-state battery SB is determined to be a non-defective product, and the process ends.

If the second resistance value R2 is greater than the threshold value S (R2>S (=a(R1)+b)), a positive judgment is made and the process proceeds to S15, where the solid-state battery SB is judged to have a large contact resistance Rc, internal contact failure, and is therefore defective, and the process ends.

According to this embodiment, the first resistance value R1, which is the resistance of the all-solid-state battery SB, is measured immediately after the start of discharge (when 0.1 seconds have elapsed since the start of discharge) at 40°C (first temperature), and the second resistance value R2, which is the resistance of the all-solid-state battery SB, is measured immediately after the start of discharge (when 0.1 seconds have elapsed since the start of discharge) at -10°C (second temperature lower than the first temperature). Then, the threshold value S is calculated using the first resistance value R1 from the linear equation (S = a (R1) + b) of the threshold value S stored in the threshold value storage unit 82, and the threshold value S is compared with the second resistance value R2 to determine the internal contact failure of the all-solid-state battery SB, so that the contact failure inside the battery of the all-solid-state battery SB can be inspected.

In the above embodiment, the threshold value S is set as a linear expression (a(R1)+b) with the first resistance value R1 as a variable, and the threshold value S is used to determine whether a product is defective. However, without using the threshold value S, for example, a determination map may be created with the first resistance value R1 and the second resistance value R2 as parameters, and a product defective due to poor contact may be determined by map search. FIG. 6 is a diagram showing an example of a determination map. Such a determination map may be created, and a product defective due to poor contact may be determined by map search.

The threshold value S for determining whether or not a product is defective does not have to be a linear expression (a(R1)+b) with the first resistance value R1 as a variable. For example, the threshold value is set to b and stored in the threshold value storage unit 82. In the defective product determination unit 83, the deviation δ between the first resistance value R1 and the second resistance value R2 is calculated as δ=R2-a(R1). The defective product determination unit 83 may then read the threshold value (=b) from the threshold value storage unit 82, and determine that the all-solid-state battery SB is defective when δ>b (when R2-a(R1)>b). In the above embodiment, the internal resistance is detected when the all-solid-state battery SB is discharged, but the internal resistance may be detected when it is charged.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the claims rather than the description of the embodiments above, and is intended to include all modifications within the meaning and scope of the claims.

1 Positive electrode, 11 Positive electrode active material layer, 12 Positive electrode current collector, 2 Negative electrode, 21 Negative electrode active material layer, 22 Negative electrode current collector, 3 Separator layer, 40 Charger/discharger, 50 Voltmeter, 60 Temperature sensor, 70 Heating/cooling unit, 80 Inspection device, 81 Internal resistance detection unit, 82 Threshold value storage unit, 83 Defective product determination unit, 100 Inspection system, SB All-solid-state battery.

Claims (5)

A method for inspecting an all-solid-state battery, comprising:
Measuring a first resistance value, which is a resistance of the all-solid-state battery immediately after starting charging and discharging at a first temperature;
Measuring a second resistance value, which is a resistance of the all-solid-state battery immediately after starting charging/discharging, at a second temperature that is lower than the first temperature;
determining an internal contact failure in the all-solid-state battery based on the first resistance value and the second resistance value;
A method for inspecting an all-solid-state battery, comprising: The method for inspecting an all-solid-state battery according to claim 1, wherein the first temperature is higher than -10°C, and the second temperature is lower than -10°C. The method for inspecting an all-solid-state battery according to claim 2, wherein the first resistance value and the second resistance value are resistance values 0.1 seconds after the start of constant current discharge or constant current charging. The method for inspecting an all-solid-state battery according to claim 3, wherein the internal contact failure is determined based on the first resistance value, the second resistance value, and a preset threshold value. When the first resistance value is R1, the second resistance value is R2, and the threshold value is S,
5. The method for inspecting an all-solid-state battery according to claim 4, wherein the threshold value S is set as "S = a(R1) + b" (a and b are constants), and when S < R2, it is determined that an internal contact failure occurs in the all-solid-state battery.

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