Secondary battery inspection method

Abstract

In order to inspect a secondary battery (11) in a short time, the resistance (R2, R3) of a secondary battery to be used by applying a surface pressure of a prescribed range (Pmin-Pmax) is measured in a state where at least a surface pressure (P2, P3) lower than the prescribed range is applied to the secondary battery, and the quality of the secondary battery is determined on the basis of at least the measured resistance value.

Description

Secondary battery inspection method

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

[0002] As an inspection method for inspecting whether or not a short circuit has occurred in an all-solid-state battery assembly in a manufacturing process of a secondary battery, a method is known in which the all-solid-state battery assembly is restrained by a restraining jig and cooled to increase its resistance, and a voltage is applied to the all-solid-state battery assembly and the resulting current is measured to determine whether or not a short circuit has occurred (Patent Document 1). In this inspection method, the cooling temperature appropriate for increasing the resistance of the all-solid-state battery assembly is −45° C. to −300° C. (See paragraph

[0058] of the same document).

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

[0004] However, as with the above-mentioned conventional technology, there is a problem in that it takes a long time to cool the all-solid-state battery assembly to a level of −45° C. or lower.

[0005] The problem to be solved by the present invention is to provide a method for testing a secondary battery that can be completed in a short time.

[0006] The present invention solves the above problem by measuring the resistance of a secondary battery that is used by applying a surface pressure within a predetermined range while applying a surface pressure at least lower than the predetermined range, and determining whether the secondary battery is good or bad based at least on the measured resistance value.

[0007] According to the present invention, a secondary battery can be inspected in a short time.

[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 graph for explaining the principle of the secondary battery inspection method according to the present invention. FIG. 3 is a flowchart showing the procedure of the secondary battery inspection method according to one embodiment of the present invention. FIG. 4 is a graph showing an example of a surface pressure-resistance curve and an acceptable range in the secondary battery inspection method according to one embodiment of the present invention. FIG. 5 is a graph showing an example of an SOC-circuit voltage curve and an upper limit voltage, a lower limit voltage, and an SOC measurable range in the secondary battery inspection method according to one embodiment of the present invention. FIG. 6 is a graph showing surface pressure-resistance curves at low and high temperatures in the secondary battery inspection method according to one embodiment of 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 with a predetermined range of applied surface pressure. Here, a secondary battery used with a predetermined range of applied surface pressure refers to a secondary battery that is charged or discharged while a predetermined range of pressure is applied in the stacking direction of the positive electrode, negative electrode, and electrolyte. The secondary battery used with a predetermined range of applied surface pressure is not particularly limited, but may be, for example, an all-solid-state battery or a semi-solid-state battery. 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 11 that can be inspected by the inspection method of this embodiment is not particularly limited, but examples thereof include secondary batteries containing metallic lithium or metallic silicon as a negative electrode active material. The secondary battery 11 of this embodiment is configured such that a stack of a positive electrode layer, a negative electrode layer, an electrolyte layer, a positive electrode current collector, and a negative electrode current collector is housed in an exterior member such as a laminate film, and a positive electrode terminal 111 and a negative electrode terminal 112 are led out from the exterior member.

[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 a surface pressure to a main surface of a secondary battery 11, 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 predetermined range of surface pressure to the main surface of the secondary battery 11 will do.

[0013] The charging / discharging device 13 of this embodiment has its input / output terminals connected to the positive terminal 111 and negative terminal 112 of the secondary battery 11, respectively, and measures the resistance of the secondary battery 11 when charging or discharging. When measuring the resistance of the secondary battery 11 when charging, a constant current I is passed between the positive terminal 111 and negative terminal 112 of the secondary battery 11, and the voltage V between the positive terminal 111 and 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 ０is used as the reference, and the voltage deviation ΔV (= V １ -V ０ ) to determine the resistance value R. When measuring the resistance of the secondary battery 11 during discharge, the secondary battery 11 is discharged from the positive terminal 111 and the negative terminal 112 at a constant current I, 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. 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 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. Furthermore, the controller 15 calculates the slope a of the resistance value versus surface pressure from two or more resistance values ​​Rn thus obtained. It then determines whether these calculated resistance values ​​Rn and slope a are within a pre-stored pass range. This procedure will be described in detail 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 predetermined range has a specific profile with respect to the applied surface pressure. FIG. 2 is a graph showing the relationship between the resistance (Ω) of the all-solid-state secondary battery 11 and the surface pressure (MPa) applied to the main surface of the secondary battery 11. In the same figure, the curve shown as "Passed Secondary Battery" represents an example of the characteristics of a normal secondary battery without any defects. In contrast, the curve shown as "Failed Secondary Battery (High Resistance)" represents an example of the characteristics of an abnormal secondary battery with a defect in which the internal resistance of the battery is higher than the reference value, and the curve shown as "Failed Secondary Battery (Slight Short Circuit)" represents an example of the characteristics of an abnormal secondary battery with a slight short circuit defect inside the battery.

[0017] In a secondary battery 11 used with a surface pressure within such a predetermined range, the surface pressure to be applied when charging and discharging is predetermined as a design specification. This is the predetermined range Pmin to Pmax (both inclusive, the same applies below), and the secondary battery 11 as a product is used with a surface pressure within this predetermined range Pmin to Pmax applied to charge and discharge the required power. While this surface pressure within the predetermined range Pmin to Pmax is not uniquely defined, it can be defined, for example, by finding an approximate line of the resistance value within this predetermined range and defining it as a range where the deviation from this approximate line is, for example, 10% or less. The value of the predetermined range is a characteristic value determined for each design specification of the secondary battery 11.

[0018] However, as shown in Figure 2, when a surface pressure in the predetermined range Pmin to Pmax is applied to the secondary battery 11, the change in resistance ΔR1 with respect to the change in surface pressure is small, so the accuracy of the pass / fail determination is relatively low. In contrast, in a low surface pressure range (<Pmin) lower than the predetermined range Pmin to Pmax, the change in resistance ΔR2 with respect to the change in surface pressure is large, as shown in Figure 2, so the accuracy of the pass / fail determination is relatively high. Therefore, the secondary battery inspection method of this embodiment utilizes this sensitivity characteristic of resistance with respect to surface pressure.

[0019] Next, the procedure for the secondary battery inspection method according to this embodiment will be described. {Preparation} For each secondary battery 11 after the manufacturing process, before performing finished product inspection, the resistance characteristics (resistance-surface pressure curve) relative to the applied surface pressure are acquired in advance for each design specification of the secondary battery. A pass range for the acquired resistance-surface pressure curve is also set in advance. FIG. 4 is a graph showing an example of a surface pressure-resistance curve and a pass range in the secondary battery inspection method according to one embodiment of the present invention. The standard surface pressure-resistance curve for the secondary battery 11 to be inspected is shown by a solid line, and the pass range is shown by a dotted line. The pass range shown by the dotted line in FIG. 4 can be the lower and upper absolute values ​​of the resistance value acceptable for a passing product. Furthermore, in a low surface pressure range below Pmin, in addition to the lower and upper absolute values, a pass range is also predetermined for the slope a of the resistance measured at two or more points, e.g., amin≦a≦amax. The slope a of the resistance measured at two or more points can be determined using a known linear regression method, such as the least squares method.

[0020] FIG. 5 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. A secondary battery 11 is generally defined to have an upper limit voltage Vmax and a lower limit voltage Vmin during use, and it is recommended to use the secondary battery 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 charging curve in the same figure. Similarly, when measuring the resistance during discharging, the voltage of the secondary battery 11 may reach the lower limit voltage Vmin, as shown in the discharging curve in the same figure. Therefore, the SOCmax (second predetermined value) when the upper limit voltage is reached and the SOCmin (first predetermined value) when the lower limit voltage is reached are determined in advance, and in the inspection process, the SOC of the secondary battery 11 is inspected within a range where SOCmin≦SOC≦SOCmax so that the voltage of the secondary battery 11 does not exceed the upper limit voltage Vmax or fall below the lower limit voltage Vmin.

[0021] 6 is a graph showing the surface pressure-resistance curves at low and high temperatures in a secondary battery inspection method according to one embodiment of the present invention, comparing secondary batteries 11 with the same design specifications. When the environmental temperature at which the resistance 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 preferably performed in a relatively low-temperature environment, at a temperature below room temperature (e.g., 0 to 35°C), although this is not particularly limited.

[0022] <<Inspection Process>> After the above preparations are completed, the secondary battery 11 to be inspected after the manufacturing process is set on the fixed platen 121 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 and the negative terminal 112 of the secondary battery 11, respectively, before starting the inspection using the inspection method of this embodiment. Note that initial charging may be performed before starting the inspection. Fig. 3 is a flowchart showing the steps of the secondary battery inspection method according to one embodiment of the present invention.

[0023] In step S1, the movable platen 122 is brought close to the secondary battery 11 set on the fixed platen 121 of the inspection system 1 shown in FIG. 1, and a pressure actuator 123 applies a surface pressure P1 within a predetermined range Pmin to Pmax. In this state, the charge / discharge device 13 discharges the secondary battery 11 to a fully discharged state SOC of 0%, and then a constant current I is passed through the secondary battery 11, measuring the time t until the secondary battery 11 reaches a fully charged state SOC of 100%. The current value I and the time t are integrated to obtain a battery capacity C (unit: Ah). In step S2, the system determines whether the determined battery capacity C is within a predetermined acceptable range Cmin≦C≦Cmax. If the determined battery capacity C is not within the predetermined acceptable range Cmin≦C≦Cmax, the system proceeds to step S11, where a rejection determination is made, and the inspection process ends. If the determined battery capacity C is within the acceptable range Cmin≦C≦Cmax, the system proceeds to step S3.

[0024] In the next step S3, with the surface pressure P1 applied to the secondary battery 11, the secondary battery 11 is discharged or charged by the charge / discharge device 13 so that the SOC of the secondary battery 11 falls within the range of SOCmin≦SOC≦SOCmax shown in FIG. 5, and then a constant current I1 is passed through the secondary battery 11 to charge it, and the voltage V1 at that time is measured by the voltmeter 14. Then, the resistance value R1=ΔV1 / I1 of the secondary battery 11 at the surface pressure P1 is calculated (closed circuit voltage V １ and the open circuit voltage V of the secondary battery 11 measured in advance. ０ The difference between ΔV1 and V １ -V ０ ), in the next step S4, it is determined whether the obtained resistance value R1 is within a preset pass range R1min≦R1≦R1max. If the obtained resistance value R1 is not within the preset pass range R1min≦R1≦R1max, the process proceeds to step S11, where a fail determination is made, and the inspection process is terminated. If the obtained resistance value R1 is within the pass range R1min≦R1≦R1max, the process proceeds to step S5.

[0025] In the next step S5, the pressure actuator 123 is controlled to set the surface pressure to be applied to the secondary battery 11 to an arbitrary surface pressure P2 within a low surface pressure range lower than Pmin. With the surface pressure P2 applied to the secondary battery 11, the secondary battery 11 is discharged or charged by the charge / discharge device 13 so that the SOC of the secondary battery 11 falls within the range of SOCmin≦SOC≦SOCmax shown in FIG. 5, and then a constant current I2 is passed through the secondary battery 11 to charge it, and the voltage V2 at that time is measured by the voltmeter 14.

[0026] In the next step S6, the pressure actuator 123 is controlled to set the surface pressure to be applied to the secondary battery 11 to an arbitrary surface pressure P3 (≠P2) within a low surface pressure range lower than Pmin. With the surface pressure P3 applied to the secondary battery 11, the secondary battery 11 is discharged or charged by the charge / discharge device 13 so that the SOC of the secondary battery 11 falls within the range of SOCmin≦SOC≦SOCmax shown in FIG. 5, and then a constant current I3 is passed through the secondary battery 11 to charge it, and the voltage V3 at that time is measured by the voltmeter 14.

[0027] In the following step S7, the resistance value R2 of the secondary battery 11 at the surface pressures P2 and P3 is calculated from the voltages V2 and V3 measured in steps S5 and S6, and the resistance value R2 is calculated as R2 = ΔV2 / I2 (closed circuit voltage V ２ and the open circuit voltage V of the secondary battery 11 measured in advance. ０ The difference between these is ΔV2 = V ２ -V ０ ) and R3 = ΔV3 / I3 (closed circuit voltage V ３ and the open circuit voltage V of the secondary battery 11 measured in advance. ０ The difference between these is ΔV3 = V ３ -V ０ ) is calculated, and then the slope a = (R3 - R2) / (P3 - P2) is calculated from the surface pressures P2 and P3 and the resistance values ​​R2 and R3.

[0028] Then, in the next step S8, it is determined whether the determined resistance values ​​R2 and R3 are within the predetermined pass ranges R2min≦R2, R3≦R2max. If the determined resistance values ​​R2 and R3 are not within the predetermined pass ranges R2min≦R2, R3≦R2max, the process proceeds to step S11, where a fail determination is made, and the inspection process ends. If the determined resistance values ​​R2 and R3 are both within the pass ranges R2min≦R2, R3≦R2max, the process proceeds to step S9.

[0029] In step S9, it is determined whether the slope a found in step S7 is within a predetermined pass range a min ≦ a ≦ a max. If the found slope a is not within the predetermined pass range a min ≦ a ≦ a max, the process proceeds to step S11, where a fail judgment is made, and the inspection process ends. If the found slope a is within the pass range a min ≦ a ≦ a max, the process proceeds to step S10, where a pass judgment is made, and the inspection process ends.

[0030] As described above, according to the secondary battery inspection method of this embodiment, the resistances R2 and R3 of the secondary battery 11 are measured while applying surface pressures P2 and P3 that are lower than the predetermined range Pmin to Pmax to the secondary battery 11 used under these conditions, and the quality of the secondary battery 11 is determined based on at least the measured resistance values ​​R2 and R3. This makes it possible to measure resistance values ​​that are highly sensitive to surface pressure, thereby enabling secondary batteries to be inspected in a short time.

[0031] 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 secondary battery can be inspected with high accuracy.

[0032] According to the secondary battery inspection method of this embodiment, the resistance of the secondary battery 11 is measured while applying two or more levels of surface pressure P2, P3 that are lower than the predetermined range Pmin to Pmax, so that it is possible to measure a resistance gradient that is highly sensitive to surface pressure, thereby enabling the secondary battery to be inspected with high accuracy.

[0033] According to the secondary battery inspection method of this embodiment, a slope a of the resistance values ​​relative to the applied surface pressures P2 and P3 is calculated from two or more resistance values ​​R2 and R3 measured while applying two or more surface pressures P2 and P3 that are lower than the predetermined range Pmin to Pmax, and the quality of the secondary battery 11 is determined based on whether the slope a is within a predetermined pass range amin≦a≦amax, making it possible to measure a slope of the resistance values ​​that is highly sensitive to surface pressure. As a result, the secondary battery can be inspected with high accuracy.

[0034] According to the secondary battery inspection method of this embodiment, the quality of the secondary battery is determined based on whether two or more resistance values ​​R2, R3 measured while applying two or more levels of surface pressure P2 and P3 lower than the predetermined range Pmin to Pmax are within a predetermined pass range R2min≦R2, R3≦R2max, making it possible to measure a resistance gradient that is highly sensitive to surface pressure, thereby enabling accurate inspection of the secondary battery.

[0035] According to the secondary battery inspection method of this embodiment, the resistance R1 of the secondary battery is measured while applying a surface pressure P1 within the predetermined range Pmin to Pmax, thereby improving the inspection accuracy of the secondary battery 11. As a result, the secondary battery can be inspected with high accuracy.

[0036] According to the secondary battery inspection method of this embodiment, the quality of the secondary battery 11 is determined based on whether the resistance value R1 measured while applying a surface pressure P1 within the predetermined range Pmin to Pmax is within a predetermined pass range R1min≦R1≦R1max, thereby improving the inspection accuracy of the secondary battery 11. As a result, the secondary battery can be inspected with high accuracy.

[0037] According to the secondary battery testing method of this embodiment, the resistance of the secondary battery 11 is measured while the secondary battery 11 is being discharged or charged, and when the resistance is measured while the secondary battery 11 is being discharged, the SOC of the secondary battery 11 is equal to or greater than a first predetermined value SOCmin, and when the resistance is measured while the secondary battery 11 is being charged, the SOC of the secondary battery 11 is equal to or less than a second predetermined value SOCmax, thereby preventing the voltage value from becoming unmeasurable. As a result, the secondary battery can be tested with high accuracy.

[0038] According to the secondary battery inspection method of this embodiment, the resistance of the secondary battery 11 is measured while the secondary battery 11 is being charged. If a micro-short circuit occurs due to the presence of dendrites in the battery cell, measuring while charging makes it easier to detect the micro-short circuit than measuring while discharging, because the dendrites grow due to the charging current. As a result, the secondary battery can be inspected with high accuracy.

[0039] According to the secondary battery inspection method of this embodiment, the resistance of the secondary battery 11 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 secondary battery can be inspected with high accuracy.

[0040] REFERENCE SIGNS LIST 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

Claims

1. A method for inspecting a secondary battery, which comprises applying a surface pressure within a predetermined range to the secondary battery, measuring the resistance of the secondary battery while applying a surface pressure at least lower than the predetermined range, and determining whether the secondary battery is good or bad based on at least the measured resistance value.

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

3. A method for inspecting a secondary battery according to claim 1 or 2, wherein the resistance of the secondary battery is measured while applying two or more levels of surface pressure lower than the predetermined range.

4. A method for inspecting a secondary battery as described in claim 3, wherein the slope of the resistance value versus the applied surface pressure is determined from two or more resistance values ​​measured while applying two or more levels of surface pressure lower than the specified range, and the quality of the secondary battery is determined based on whether the determined slope is within a specified acceptable range.

5. A method for inspecting a secondary battery as described in claim 3 or 4, in which the quality of the secondary battery is determined based on whether or not two or more resistance values ​​measured while applying two or more levels of surface pressure lower than the specified range are within a specified pass range.

6. The method for inspecting a secondary battery according to any one of claims 3 to 5, wherein the resistance of the secondary battery is measured while the surface pressure within the predetermined range is applied.

7. A method for inspecting a secondary battery according to claim 6, wherein the quality of the secondary battery is determined based on whether or not the resistance value measured when the specified range of surface pressure is applied is within a specified acceptable range.

8. A method for inspecting a secondary battery according to any one of claims 1 to 7, wherein the resistance of the secondary battery is measured while the secondary battery is being discharged or charged, and when the resistance is measured while the secondary battery is being discharged, the SOC of the secondary battery is equal to or greater than a first predetermined value, and when the resistance is measured while the secondary battery is being charged, the SOC of the secondary battery is equal to or less than a second predetermined value.

9. The method for inspecting a secondary battery according to claim 8, wherein the resistance of the secondary battery is measured while the secondary battery is being charged.

10. The method for inspecting a secondary battery according to any one of claims 1 to 9, wherein the resistance of the secondary battery is measured in an environment below room temperature.

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