Method for inspecting secondary battery

Abstract

In order to inspect the contact pressure distribution of a secondary battery (11) in a laminate (M), a characteristic profile of the resistance value of the laminate with respect to an applied contact pressure is acquired for the laminate of the secondary battery that is used while being applied with a contact pressure in a normal contact pressure range (Pmin to Pmax), an approximate straight line (L1) of the resistance value with respect to the contact pressure in the normal contact pressure range of the characteristic profile is acquired, a contact pressure range in which the deviation between the resistance value of the approximate straight line and the resistance value of the laminate is equal to or less than a specific value is defined as an inspection contact pressure range (P2min to P2max) in a contact pressure range that is lower than the normal contact pressure range of the characteristic profile, a contact pressure (P2) included in the inspection contact pressure range is applied to the laminate and the resistance value of the laminate is measured, and the quality of the laminate is determined on the basis of at least the measured resistance value of the laminate.

Description

Secondary battery inspection method

[0001] The present invention relates to a method for inspecting a secondary battery.

[0002] In a known method for inspecting a battery pack that includes a stack of multiple secondary batteries and a restraint band that compresses and restrains the stack in the stacking direction, a compressive force along the stacking direction is applied to the stack to which the restraint band is attached, the compressive force when a change in the shape of the restraint band satisfies a specified condition is obtained as a restraint load on the stack by the restraint band, and if the obtained restraint load is greater than a first threshold value, the battery pack is determined to be abnormal (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2020-13776

[0004] The above-mentioned conventional technology can measure the absolute value of the load applied to the stack. However, it has a problem in that it cannot measure the surface pressure distribution (in-plane pressure distribution / in-plane pressure variation) of the secondary batteries in the stack. If the secondary batteries constituting the stack are tilted and the surface pressure distribution becomes uneven, there is a risk of reduced durability or short-circuiting during charging.

[0005] The problem to be solved by the present invention is to provide a method for inspecting a secondary battery that can inspect the surface pressure distribution of secondary batteries in a stack.

[0006] The present invention solves the above problem by obtaining a characteristic profile of resistance value versus surface pressure for a secondary battery stack, obtaining an approximate straight line of resistance value versus surface pressure within a normal surface pressure range of the characteristic profile, determining an inspection surface pressure range as a surface pressure range in which the deviation between the resistance value of the approximate line and the resistance value of the stack is equal to or less than a predetermined value within a surface pressure range lower than the normal surface pressure range of the characteristic profile, applying a surface pressure included in the inspection surface pressure range to the stack to measure the resistance value of the stack, and determining whether the stack is good or bad based on the measured resistance value of the stack.

[0007] According to the present invention, it is possible to inspect the surface pressure distribution of the secondary batteries in the stack.

[0008] FIG. 1 is a diagram showing an example of an inspection system for carrying out the secondary battery inspection method according to the present invention. FIG. 2 is a characteristic profile diagram showing the relationship between surface pressure and resistance value, for explaining the principle of the secondary battery inspection method according to the present invention. FIG. 3 is a diagram showing a battery module, for explaining the principle of the secondary battery inspection method according to the present invention. FIG. 4 is a characteristic profile diagram showing the relationship between surface pressure and resistance value, for explaining the principle of the secondary battery inspection method according to the present invention. FIG. 5 is a characteristic profile diagram showing the relationship between surface pressure and resistance value for each SOC state, for the secondary battery inspection method according to the present invention. FIG. 6 is a graph showing an example of an SOC-circuit voltage curve, an upper limit voltage, a lower limit voltage, and an SOC measurable range, for the secondary battery inspection method according to the present invention. FIG. 7 is a characteristic profile diagram showing the relationship between surface pressure and resistance value in a low temperature environment and a high temperature environment, for explaining the principle of the secondary battery inspection method according to the present invention.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A secondary battery inspection method according to an embodiment of the present invention inspects a secondary battery used under a predetermined surface pressure range (hereinafter referred to as the normal surface pressure range), and a stack of multiple secondary batteries is used as an inspection target. Here, a secondary battery used under a surface pressure within the normal surface pressure range refers to a secondary battery that is charged or discharged while a pressure within the normal surface pressure range is applied in the stacking direction of the positive electrode, negative electrode, and electrolyte. Examples of secondary batteries used under a surface pressure within the normal surface pressure range include, but are not limited to, all-solid-state batteries and semi-solid-state batteries. An all-solid-state battery refers to a rechargeable secondary battery that uses a solid electrolyte as the electrolyte, and also includes a solid electrolyte containing a small amount of liquid material. Furthermore, a semi-solid-state battery refers to a rechargeable secondary battery that uses a gel electrolyte as the electrolyte.

[0010] The secondary battery that can be inspected by the inspection method of this embodiment is not particularly limited, and examples thereof include secondary batteries containing metallic lithium or metallic silicon as the negative electrode active material. The secondary battery 11 of this embodiment is configured by housing a battery element, including a laminated positive electrode layer, a negative electrode layer, an electrolyte layer, a positive electrode current collector, and a negative electrode current collector, in an exterior member such as a laminate film, and extending a positive electrode terminal 111 and a negative electrode terminal 112 from the exterior member. As shown in FIG. 1 , five secondary batteries 11 are stacked with their main surfaces facing each other and connected in series and / or parallel to form a stack M. When this stack M is used in a vehicle, a pressure mechanism 16 such as a cable tie is separately provided (see FIG. 3 ), and a surface pressure within the normal surface pressure range is applied to the battery module.

[0011] 1 is a diagram showing an example of an inspection system for carrying out a secondary battery inspection method according to the present invention. The inspection system 1 of this embodiment includes a pressure device 12 that applies surface pressure to the main surfaces of secondary batteries 11 that constitute a laminate M, a charge / discharge device 13 that applies a constant current between a positive terminal 111 and a negative terminal 112 of the secondary battery 11 to charge the secondary battery 11 and discharge the constant current from the positive terminal 111 and the negative terminal 112 of the secondary battery 11, a voltmeter 14 that detects the voltage between the positive terminal 111 and the negative terminal 112 of the secondary battery 11, and a controller 15 that controls the pressure device 12 and the charge / discharge device 13, reads measurements from the voltmeter 14, and performs various calculations.

[0012] The pressure device 12 of this embodiment has a fixed platen 121, a movable platen 122, and a pressure actuator 123. The movable platen 122 is moved toward and away from the fixed platen 121 by the pressure actuator 123, applying and removing a desired surface pressure to the secondary battery 11 placed on the fixed platen 121. The pressure actuator 123 is driven by a control signal from the controller 15, thereby controlling the surface pressure applied to the main surface of the secondary battery 11. Note that the pressure device 12 shown in the figure is an example for implementing the secondary battery inspection method according to the present invention, and is not intended to be limited to this type of pressure device 12. Any pressure device 12 that can apply a surface pressure within the normal surface pressure range to the main surface of the secondary battery 11 will suffice.

[0013] The charge / discharge device 13 of this embodiment has its input / output terminals connected to the positive terminal 111 of the secondary battery 11 at one end of the stack M and the negative terminal 112 of the secondary battery 11 at the other end, respectively, and measures the resistance of the secondary battery 11 during charging or discharging. When measuring the resistance of the secondary battery 11 during charging, a constant current I is passed between the positive terminal 111 of the secondary battery 11 at one end of the stack M and the negative terminal 112 of the secondary battery 11 at the other end, and the voltage V between the positive terminal 111 and the negative terminal 112 of the secondary battery 11 at this time is measured with a voltmeter, and the resistance value R is calculated from the equation: resistance value R = voltage value ΔV / current value I. Note that the voltage value ΔV is calculated based on the open circuit voltage V of the secondary battery 11. ０ , closed circuit voltage V １ The voltage difference V １ -V ０ = ΔV. Since a secondary battery has an electromotive force and the voltage is not 0 when no current is flowing, the voltage value V when the current value is 0 ０ is used as the reference, and the voltage deviation ΔV (= V １ -V ０ ) to determine the resistance value R. Furthermore, when measuring the resistance of the secondary battery 11 during discharge, a constant current I is discharged from the positive electrode terminal 111 of the secondary battery 11 at one end of the laminate M and the negative electrode terminal 112 of the secondary battery 11 at the other end, and the voltage V between the positive electrode terminal 111 and the negative electrode terminal 112 of the secondary battery 11 at this time is measured with a voltmeter, and the resistance value R is calculated from the equation: resistance value R = voltage value ΔV / current value I. In the embodiment shown in FIG. 1 , the voltmeter 14 is provided separately from the charge / discharge device 13, but a charge / discharge device 13 with a built-in voltmeter 14 may also be used.

[0014] The charging / discharging device 13 of this embodiment can also measure the SOC (State of Charge) and battery capacity of the secondary battery 11. The SOC of the secondary battery 11 is an index representing the state of charge or charging rate, with a fully charged state being 100% and a fully discharged state being 0%. The battery capacity C of the secondary battery 11 can be calculated by passing a constant current I through the secondary battery 11 with a fully discharged SOC of 0% and measuring the time t until the fully discharged SOC reaches 100%. The current value I and the time t are integrated to obtain the battery capacity C, It (unit: Ah). Alternatively, the secondary battery 11 with a fully charged SOC of 100% can be discharged at a constant current I and measuring the time t until the fully discharged SOC reaches 0%, and the battery capacity C can be calculated by integrating the current value I and the time t, It (unit: Ah).

[0015] The controller 15 of this embodiment controls the pressure actuator 123 of the pressure device 12 to adjust the surface pressure applied to the stack M of the secondary battery 11, which is the object to be inspected, to a predetermined value. The controller 15 of this embodiment also controls the charge / discharge device 13, reads the voltage value V measured during charging or discharging, and calculates the resistance value R (= ΔV / I) of the secondary battery 11. It then determines whether the calculated resistance value Rn is within a pre-stored non-defective range. Furthermore, the controller 15 calculates the tilt amount ΔC of the stack M from the calculated resistance value Rn. Details of this procedure will be described later.

[0016] Now, like an all-solid-state battery or a semi-solid-state battery, the resistance of a secondary battery 11 used by applying a surface pressure within a normal surface pressure range has a specific profile with respect to the applied surface pressure. Fig. 2 is a characteristic profile diagram showing the relationship between the resistance (Ω) of the laminate M of the secondary battery 11 made of an all-solid-state battery and the surface pressure (MPa) applied to the main surface of the laminate M of the secondary battery 11. In the figure, the black circles indicate measurement points.

[0017] In the stack M of the secondary battery 11 that is used by applying a surface pressure within such a normal surface pressure range, the surface pressure to be applied when charging and discharging is determined in advance as a design specification. ｍｉｎ ~P ｍａｘ(both ends are included, the same applies below), and the stack M of the secondary battery 11 as a product is within this normal surface pressure range P ｍｉｎ ~P ｍａｘ The bearing is used in a state where a surface pressure of this range is applied. ｍｉｎ ~P ｍａｘ Although the surface pressure is not uniquely defined, it can be defined as a range in which the absolute value of the deviation from the approximate line L1 is, for example, 0 to 0.5% (both ends included) by finding an approximate line L1 of the resistance values ​​actually measured in this normal surface pressure range using, for example, the least squares method. The value of the normal surface pressure range is a characteristic value determined for each design specification of the secondary battery 11.

[0018] In contrast, the normal surface pressure range P ｍｉｎ ~P ｍａｘ Lower surface pressure range (<P ｍｉｎ 2 ), a characteristic profile is shown in which the change in resistance relative to the change in surface pressure is relatively large. Therefore, the secondary battery inspection method of this embodiment utilizes this sensitivity characteristic of resistance to surface pressure. Then, an approximation line L2 of the resistance values ​​actually measured in this low surface pressure range is obtained using, for example, the least squares method, and a surface pressure near the intersection of this approximation line L2 and the approximation line L1 of the normal surface pressure range is applied to obtain the resistance value, thereby making it possible to inspect the degree or magnitude of the surface pressure distribution of the secondary battery 11 in the stack M. More specifically, in a surface pressure range lower than the normal surface pressure range of the characteristic profile, the range of surface pressure in which the deviation between the resistance value of the approximation line L1 of the normal surface pressure range and the resistance value of the stack M is equal to or less than a predetermined value is defined as the inspection surface pressure range P2. ｍｉｎ ~P2 ｍａｘ This inspection surface pressure range P2 ｍｉｎ ~P2 ｍａｘ is applied to the laminate M to measure the resistance value of the laminate M. Here, it is more preferable that the absolute value of the deviation between the resistance value of the approximate straight line L1 in the inspection surface pressure range and the resistance value of the laminate M is 0.5 to 5% (both ends included).

[0019] Fig. 3 is a diagram illustrating the principle of the secondary battery inspection method according to the present invention, showing a battery module that is a stack M. The left diagram of Fig. 3 shows a battery module in which a stack M, which is made up of five stacked secondary batteries 11, is pressed using a pressing mechanism 16, where the surface pressure from the pressing mechanism 16 acts uniformly on the stack M and the amount of tilt ΔC of the stack M is 0. In contrast, the right diagram of Fig. 3 shows a battery module in which a stack M, which is also made up of five stacked secondary batteries 11, is pressed using a pressing mechanism 16, where the surface pressure from the pressing mechanism 16 acts non-uniformly on the stack M and the amount of tilt of the stack M is ΔC (>0). Fig. 4 is a characteristic profile diagram illustrating the relationship between surface pressure and resistance value, illustrating the principle of the secondary battery inspection method according to the present invention.

[0020] As shown in the left diagram of FIG. 3, when the surface pressure by the pressure mechanism 16 acts uniformly on the laminate M and the tilt amount ΔC of the laminate M is 0, the inspection surface pressure range P2 is near the intersection of the approximate line L1 of the normal surface pressure range and the approximate line L2 of the low surface pressure range. ｍｉｎ ~P2 ｍａｘ When the surface pressure P2 included in the above is applied to the stack M, the surface pressure P2 is applied evenly within the surface of the secondary battery 11, and the measured resistance value of the stack M becomes R2 as shown in FIG.

[0021] In contrast, as shown in the right diagram of Fig. 3, when the surface pressure from the pressure mechanism 16 acts non-uniformly on the laminate M and the amount of tilt of the laminate M is ΔC, a surface pressure P3 greater than the surface pressure P2 acts on one side of the laminate M, and a surface pressure P1 smaller than the surface pressure P2 acts on the other side of the laminate M. Therefore, the measured resistance value of the laminate M is a resistance value that is a combination of the resistance value R3 due to the surface pressure P3 and the resistance value R1 (= R3 + ΔR) due to the surface pressure P1, as shown in Fig. 4. Therefore, compared to when the surface pressure distribution is uniform as shown in the left diagram of Fig. 3, when the surface pressure distribution is non-uniform as shown in the right diagram of Fig. 3, the measured resistance value of the laminate M is larger.

[0022] The larger the tilt amount ΔC of the laminate M, the smaller the surface pressure P1 becomes when surface pressure P2 is applied, and the larger the surface pressure P3 becomes. Therefore, the resistance value R1 in FIG. 4 becomes larger, and since the resistance value R3 remains substantially the same, the measured resistance value of the laminate M becomes larger. FIG. 9 is a graph showing an example of the resistance value versus the tilt amount ΔC of the battery module in the secondary battery inspection method according to the present invention. The relationship between the resistance value and the tilt amount ΔC of the battery module can be determined from the characteristic profile of the resistance value of the laminate M versus surface pressure shown in FIG. 2.

[0023] Next, the procedure of the secondary battery inspection method according to this embodiment will be described. <<Preparation>> Before carrying out finished product inspection or the like for each laminate M of the secondary battery 11 after the manufacturing process, a characteristic profile of the resistance value with respect to the applied surface pressure (resistance value-surface pressure curve) as shown in FIG. 2 is acquired in advance for each design specification of the laminate M of the secondary battery 11. In addition, in this acquired characteristic profile of the resistance value-surface pressure, a normal surface pressure range P ｍｉｎ ~P ｍａｘ The approximate line L1 of the resistance value versus the surface pressure is obtained in advance. The approximate line L1 can be obtained using a known linear regression method such as the least squares method. In addition, the approximate line L1 of the resistance value versus surface pressure characteristic profile obtained in this ｍｉｎ ~P ｍａｘ In the lower surface pressure range, the range of surface pressure in which the deviation between the resistance value of the approximate line L1 and the resistance value of the laminate M is equal to or less than a predetermined value as shown in FIG. 2 is defined as an inspection surface pressure range P2. ｍｉｎ ~P2 ｍａｘ Furthermore, in the inspection of this embodiment, a non-defective range (a range that passes the inspection) for the resistance value of the measured laminate M is set in advance.

[0024] FIG. 5 is a characteristic profile diagram showing the relationship between surface pressure and resistance value during discharge and charge in a secondary battery inspection method according to one embodiment of the present invention, comparing the laminate M of a secondary battery 11 having the same design specifications. When measuring the resistance value of the laminate M of the secondary battery 11, measuring the resistance value while discharging from the laminate M results in a larger absolute value of the resistance value and a larger amount of fluctuation in the low surface pressure range than when measuring the resistance value while charging the laminate M. In other words, sensitivity to surface pressure is high. Therefore, it can be said that the inspection method of this embodiment more preferably measures the resistance value of the laminate M while discharging from the laminate M.

[0025] FIG. 6 is a characteristic profile diagram showing the relationship between surface pressure and resistance value for each SOC state in a secondary battery inspection method according to one embodiment of the present invention, comparing stacks M of secondary batteries 11 with the same design specifications while discharging. When measuring the resistance value of the stack M of a secondary battery 11 while discharging a stack M with a relatively low SOC, the absolute value of the resistance value is larger and the amount of fluctuation in the low surface pressure range is also larger than when measuring the resistance value while discharging a stack M with a relatively high SOC. In other words, the sensitivity to surface pressure is higher. Therefore, it can be said that the inspection method of this embodiment is more preferable for measuring the resistance value of a stack M with a relatively low SOC.

[0026] FIG. 7 is a graph showing an example of an SOC-circuit voltage curve, an upper limit voltage, a lower limit voltage, and an SOC measurable range in a secondary battery inspection method according to one embodiment of the present invention. The stack M of the secondary battery 11 generally has a predetermined upper limit voltage Vmax and a predetermined lower limit voltage Vmin during use, and it is recommended to use the secondary battery 11 within this voltage range Vmax to Vmin in order to prevent battery degradation. When implementing the inspection method of this embodiment, when measuring the resistance during charging, the voltage of the secondary battery 11 may reach the upper limit voltage Vmax, as shown in the charge curve in the figure. Similarly, when measuring the resistance during discharge, the voltage of the secondary battery 11 may reach the lower limit voltage Vmin, as shown in the discharge curve in the figure. Therefore, the SOC max when the upper limit voltage is reached and the SOC min when the lower limit voltage is reached are determined in advance, and in the inspection process, the inspection is performed within the SOC range of the secondary battery 11, where SOC min≦SOC ≦SOC max, so that the voltage of the stack M of the secondary battery 11 under test does not exceed the upper limit voltage Vmax or fall below the lower limit voltage Vmin.

[0027] FIG. 8 is a characteristic profile diagram showing the relationship between surface pressure and resistance value at low and high temperatures in a secondary battery inspection method according to one embodiment of the present invention, comparing the laminate M of a secondary battery 11 with the same design specifications. When the environmental temperature at which the resistance value of the laminate M of the secondary battery 11 is measured is relatively low, the absolute value of the resistance value is larger and the amount of fluctuation in the low surface pressure range is also larger than when the environmental temperature is relatively high. In other words, the sensitivity to surface pressure is high. Therefore, the inspection method of this embodiment is performed in a relatively low temperature environment, although not particularly limited thereto, at a temperature below room temperature (e.g., 0 to 35°C), preferably below 35°C, and more preferably below 0°C.

[0028] <<Inspection Process>> After the above preparations are completed, the stack M of secondary batteries 11 that has undergone the manufacturing process and is the object to be inspected is set between the fixed platen 121 and the movable platen 122 of the inspection system 1 shown in Fig. 1, and the input / output terminals of the charge / discharge device 13 are connected to the positive terminal 111 of the secondary battery 11 at one end of the stack M and the negative terminal 112 of the secondary battery 11 at the other end, respectively, and then inspection using the inspection method of this embodiment is started. Note that if the SOC of the stack M is low, for example, initial charging may be performed before starting the inspection.

[0029] The movable platen 122 is moved closer to the stack M of secondary batteries 11 set between the fixed platen 121 and the movable platen 122 of the inspection system 1 of FIG. 1, and the pressure actuator 123 is operated to apply an inspection surface pressure within the inspection surface pressure range P ２ｍｉｎ ~P ２ｍａｘ With the surface pressure P2 applied to the stack M of the secondary batteries 11, the stack M of the secondary batteries 11 is discharged or charged by the charge / discharge device 13 so that the SOC of the stack M of the secondary batteries 11 falls within the range of SOCmin≦SOC≦SOCmax shown in FIG. 7 , and then a constant current I2 is discharged from the stack M of the secondary batteries 11, and the voltage V2 at that time is measured by the voltmeter 14.

[0030] The resistance value R2 of the stack M of the secondary battery 11 at the surface pressure P2 from the measured voltage V2 is calculated as follows: R2 = ΔV2 / I2 (closed circuit voltage V ２ and the open circuit voltage V of the stack M of the secondary battery 11 measured in advance. ０ The difference between these is ΔV2 = V ２ -V ０ ) is calculated. Then, it is determined whether the calculated resistance value R2 is within a predetermined pass range R2min≦R2≦R2max. If the calculated resistance value R2 is not within the predetermined pass range R2min≦R2≦R2max, a fail determination is made and the inspection process is terminated.

[0031] If the obtained resistance value R2 is not within a preset pass range R2min≦R2≦R2max, the slope ΔC (see the right diagram in FIG. 3) of the laminate M relative to the resistance value R2 may be obtained by referring to the resistance-slope characteristic shown in FIG. 9, which is calculated in advance from the characteristic profile diagram shown in FIG. 2. Furthermore, this obtained slope ΔC may be fed back to the laminate M that has been determined to be unacceptable, and the pressure mechanism 16 may be adjusted to correct the slope ΔC to zero.

[0032] In the inspection method of the present embodiment described above, the tilt amount ΔC of the stack M of the secondary battery 11 is inspected to inspect the degree or magnitude of the surface pressure distribution of the secondary battery 11 in the stack M, but the resistance value and battery capacity within the normal surface pressure range may also be inspected at the same time.

[0033] As described above, according to the method for inspecting a secondary battery of this embodiment, the normal surface pressure range P ｍｉｎ ~P ｍａｘ For the stack M of the secondary battery 11 used by applying a surface pressure of 100 kJ / s, a characteristic profile of the resistance value of the stack M relative to the applied surface pressure is obtained, and the normal surface pressure range P ｍｉｎ ~P ｍａｘ An approximate straight line L1 of the resistance value relative to the surface pressure in the normal surface pressure range P ｍｉｎ ~P ｍａｘ In the lower surface pressure range, the range of surface pressure in which the deviation between the resistance value of the approximate straight line and the resistance value of the laminate is equal to or less than a predetermined value is defined as an inspection surface pressure range P2. ｍｉｎ ~P2 ｍａｘ and the inspection surface pressure range P2 ｍｉｎ ~P2 ｍａｘ The surface pressure P2 included in the above is applied to the stack M to measure the resistance value R2 of the stack M, and the quality of the stack M of the secondary battery 11 is determined based on at least the measured resistance value R2 of the stack M, so that the degree or magnitude of the surface pressure distribution of the secondary battery 11 in the stack M can be accurately inspected.

[0034] According to the secondary battery inspection method of this embodiment, the inspection surface pressure range P2 ｍｉｎ ~P2 ｍａｘSince the absolute value of the deviation between the resistance value of the approximate straight line L1 and the resistance value of the laminate M is 0.5 to 5%, it is possible to accurately specify an inspection surface pressure range suitable for inspecting the degree or magnitude of the surface pressure distribution. As a result, it is possible to accurately inspect the degree or magnitude of the surface pressure distribution of the secondary battery 11.

[0035] According to the secondary battery inspection method of this embodiment, the secondary battery 11 is an all-solid-state battery or a semi-solid-state battery, and therefore has good sensitivity of the resistance value to the surface pressure, so that the degree or magnitude of the surface pressure distribution of the secondary battery 11 can be inspected with high accuracy.

[0036] According to the secondary battery inspection method of this embodiment, the resistance value of the laminate M is measured while discharging the secondary battery 11, and the resistance value of the laminate M is determined from the amount of voltage drop during discharge relative to the open circuit voltage before discharge.As a result, the sensitivity of the resistance value to surface pressure is good, and the degree or magnitude of the surface pressure distribution of the secondary battery 11 can be inspected with high accuracy.

[0037] According to the method for inspecting a secondary battery of this embodiment, the SOC of the stack M is set to a predetermined value or less, and the measurement of the resistance value is performed at the predetermined value or less that does not reach the lower limit voltage, so that it is possible to prevent the voltage value from becoming unmeasurable. As a result, it is possible to inspect the degree or magnitude of the surface pressure distribution of the secondary battery 11 with high accuracy.

[0038] According to the secondary battery inspection method of this embodiment, the resistance of the laminate M is measured in an environment below room temperature, so the sensitivity of the resistance value to the surface pressure is better than when measuring in an environment above room temperature, and as a result, the degree or magnitude of the surface pressure distribution of the secondary battery 11 can be inspected with high accuracy.

[0039] According to the secondary battery inspection method of this embodiment, the inspection surface pressure range P2 ｍｉｎ ~P2 ｍａｘ The quality of the laminate M is determined based on whether the resistance value of the laminate M measured by applying a surface pressure P2 is within a predetermined acceptable range, so that the degree or magnitude of the surface pressure distribution of the secondary battery 11 can be inspected with high accuracy.

[0040] According to the secondary battery inspection method of this embodiment, the inspection surface pressure range P2 ｍｉｎ ~P2 ｍａｘ The tilt amount ΔC of the laminate M is estimated from the resistance value of the laminate M measured by applying a surface pressure P2 of 1000 mV, and the correction amount for the tilt of the laminate M that is determined not to be within the predetermined acceptable range is calculated, so that the tilt amount of the laminate M that is determined not to be within the predetermined acceptable range can be efficiently corrected.

[0041] DESCRIPTION OF SYMBOLS 1... Inspection system 11... Secondary battery 111... Positive electrode terminal 112... Negative electrode terminal 12... Pressure device 121... Fixed platen 122... Movable platen 123... Pressure actuator 13... Charging / discharging device 14... Voltmeter 15... Controller 16... Pressure mechanism M... Laminate

Claims

1. A method for inspecting a secondary battery, comprising: obtaining a characteristic profile of the resistance value of a stack of a secondary battery used by applying a surface pressure within a normal surface pressure range to the stack against the applied surface pressure; obtaining an approximation line of the resistance value against the surface pressure in the normal surface pressure range of the characteristic profile; determining an inspection surface pressure range as a surface pressure range in which the deviation between the resistance value of the approximation line and the resistance value of the stack is equal to or less than a predetermined value within a surface pressure range lower than the normal surface pressure range of the characteristic profile; applying a surface pressure included in the inspection surface pressure range to the stack to measure the resistance value of the stack; and judging the quality of the stack based on at least the measured resistance value of the stack.

2. The method for inspecting a secondary battery according to claim 1, wherein the absolute value of the deviation between the resistance value of the approximate straight line and the resistance value of the laminate in the inspection surface pressure range is 0.5 to 5%.

3. The method for inspecting a secondary battery according to claim 1 or 2, wherein the secondary battery is an all-solid-state battery or a semi-solid-state battery.

4. A method for inspecting a secondary battery according to any one of claims 1 to 3, wherein the resistance value of the stack is measured while discharging the secondary battery, and the resistance value of the stack is calculated from the amount of voltage drop during discharge relative to the open circuit voltage before discharge.

5. The method for inspecting a secondary battery according to claim 4, wherein the SOC of the stack is equal to or less than a predetermined value, and the measurement of the resistance value is performed when the SOC is equal to or less than the predetermined value that does not reach a lower limit voltage.

6. The method for inspecting a secondary battery according to any one of claims 1 to 5, wherein the resistance value of the laminate is measured in an environment below room temperature.

7. A method for inspecting a secondary battery according to any one of claims 1 to 6, in which the quality of the laminate is determined based on whether the resistance value of the laminate measured by applying a surface pressure within the inspection surface pressure range is within a predetermined acceptable range.

8. A secondary battery inspection method as described in claim 7, wherein the amount of tilt of the stack is estimated from the resistance value of the stack measured by applying a surface pressure within the inspection surface pressure range, and the amount of correction for the tilt of a stack determined not to be within the specified non-defective range is calculated.

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