JP7748412B2 - Secondary battery inspection method and secondary battery manufacturing method - Google Patents

Description

The present invention relates to a method for inspecting secondary batteries and a method for manufacturing secondary batteries.

When manufacturing secondary batteries, a capacity test is sometimes performed to determine the quality of the secondary battery, using the capacity of the secondary battery as an indicator. For example, Patent Document 1 discloses a method for manufacturing secondary batteries that includes a capacity test process after the initial charging process and high-temperature aging process.

Japanese Patent Application Laid-Open No. 2021-015745

However, during the manufacturing of secondary batteries, gas generated during the initial charging process or other processes can accumulate in layers between the positive and negative electrode plates of the electrode assembly, which face each other via a separator, and cannot fully escape to the outside. When a capacity test is conducted on a secondary battery that contains a gas layer within the electrode assembly, the test capacity obtained is smaller than the test capacity of a secondary battery that does not contain a gas layer. For this reason, it has been found that it may not be possible to properly determine the quality of a secondary battery based on the size of the test capacity.

The present invention was made in consideration of this current situation, and provides a secondary battery inspection method that can properly inspect the test capacity of a secondary battery, and a method for manufacturing a secondary battery using this method.

(1) One aspect of the present invention for solving the above problem is a method for testing a secondary battery that includes a case and an electrode assembly housed in the case, the method comprising: an SOC adjustment step for adjusting the SOC of the secondary battery to a test start SOC; an inspection capacity measurement step for measuring an inspection capacity by performing constant current charging or constant current discharging on the secondary battery over an inspection SOC range from the inspection start SOC to the inspection end SOC, which is a portion of the SOC range from 0% to 100% SOC; a gas correlation quantity acquisition step for acquiring a gas correlation quantity that correlates with the amount of gas present between the positive and negative plates of the electrode assembly; a correction step for obtaining a capacity correction value corresponding to the acquired gas correlation quantity based on a previously obtained relationship between the gas correlation quantity and a capacity correction value, and obtaining a corrected inspection capacity from the measured inspection capacity and the capacity correction value; and a determination step for determining the quality of the secondary battery using the corrected inspection capacity.

In testing this secondary battery, in addition to measuring the test capacity of the secondary battery, a gas correlation quantity that correlates with the amount of gas in the electrode body is obtained, and a capacity correction value is obtained based on the relationship between the gas correlation quantity and the capacity correction value. A corrected test capacity is then obtained from the test capacity and the capacity correction value, and the quality of the secondary battery is determined using the corrected test capacity. In this way, the test capacity can be appropriately corrected for secondary batteries with different amounts of gas in the electrode body, and the quality of the secondary battery can be appropriately determined based on the corrected test capacity.

Secondary batteries include lithium ion secondary batteries, sodium ion secondary batteries, and calcium ion secondary batteries. Electrode bodies for secondary batteries include stacked electrode bodies, cylindrical wound electrode bodies, and flat wound electrode bodies.

The test start SOC, test end SOC, and test SOC range can be selected from within an SOC range of 0-100% SOC. However, selecting a wide test SOC range will increase the amount of electricity charged or discharged by the constant current charge or constant current discharge in the test capacity measurement process, and the test will take longer. For this reason, it is recommended to select the test start SOC and test end SOC so that the test SOC range is, for example, 50% or less, preferably 20% or less. Furthermore, the larger the test current passed through the secondary battery during constant current charge or constant current discharge, the shorter the time required to complete the constant current charge or discharge. Therefore, it is recommended to set the test current, for example, below the maximum current that can be passed through the secondary battery, at 1 C or more, preferably 5 C or more.

Any suitable physical quantity can be used as the gas correlation quantity correlated with the amount of gas in the electrode body, as long as it is a gas correlation quantity that changes depending on the amount of gas in the electrode body. For example, the transmission intensity of ultrasonic waves irradiated from the outside and transmitted through the electrode body of a secondary battery can be measured at each predetermined position on the electrode body or over the entire predetermined area of the electrode body, and the obtained transmission intensity values can be integrated or averaged. Furthermore, in the case of a laminated or flat wound electrode body, the elasticity value in the thickness direction at each position on the electrode body can be measured, and the obtained integrated elasticity value can be used.

(2) In the power storage device described in (1) above, the gas correlation quantity acquisition process may be an ultrasonic irradiation process for obtaining the gas correlation quantity based on the transmission intensity of ultrasonic waves irradiated onto the secondary battery and transmitted through the electrode body.

When ultrasonic waves are irradiated onto a secondary battery from the outside, the intensity of the transmitted ultrasonic waves that pass through the electrode body is lower in parts where a gas layer is present than in parts of the electrode body where there is no gas layer. This is because a portion of the transmitted ultrasonic waves is reflected by the gas layer. Therefore, if a gas correlation quantity that correlates with the gas amount is obtained from the transmitted ultrasonic intensity during the ultrasonic irradiation process, the test capacity can be appropriately corrected according to the gas amount.

As mentioned above, examples of gas correlation quantities include the integrated value or average value obtained by measuring the transmitted ultrasonic wave intensity at each predetermined position on the electrode body or over the entire predetermined area of the electrode body and integrating the obtained intensity values.

(3) In the secondary battery inspection method described in (1) or (2) above, the inspection capacity measurement step may be a secondary battery inspection method in which the inspection capacity is measured by performing constant current charging or constant current discharging at a test current of 5 C or more over the inspection SOC range of 20% or less.

In the test capacity measurement step of this test method, the test capacity is measured by constant-current charging or constant-current discharging at a test current of 5 C or more over a test SOC range of 20% or less. By measuring the test capacity at a large test current over a narrow test SOC range, the test capacity measurement step can be completed in a short time. On the other hand, it has been found that measuring the test capacity at a large test current over such a narrow test SOC range can easily cause the resulting test capacity to vary depending on the amount of gas in the electrode body. Localized battery action is unlikely to occur in areas where a gas layer exists between the positive and negative electrode plates. This is thought to be why the secondary battery is less likely to be charged or discharged at a large test current in a short time, resulting in a small test capacity.
In contrast, in the present invention, a capacity correction value corresponding to the gas correlation quantity is obtained in the correction process, and a corrected test capacity is obtained from the measured test capacity and the capacity correction value, so that the decrease in test capacity due to the presence of a gas layer can be corrected, and the quality of the secondary battery can be appropriately determined in the judgment process.

(4) Another solution is a method for manufacturing a secondary battery that includes an inspection step in which secondary batteries whose test capacity has not been inspected are inspected using the secondary battery inspection method described in any one of (1) to (3), and a sorting step in which secondary batteries that are judged to be good in the judgment step are retained.

In this secondary battery manufacturing method, secondary batteries whose test capacity has not yet been inspected are inspected using the inspection method described above, and secondary batteries that are judged to be good in the sorting process are retained. This allows the test capacity to be properly inspected, and secondary batteries with good test capacity can be manufactured.

3 is a flowchart showing the procedure for inspecting and manufacturing a battery according to an embodiment. 10A and 10B are explanatory diagrams illustrating how the intensity of ultrasonic waves transmitted through a battery is acquired in an ultrasonic irradiation step according to an embodiment. 10 is a graph showing the relationship between the integrated value of the intensity of the obtained transmitted ultrasonic waves and the capacitance correction value. FIG. 10 is an explanatory diagram showing an example of the test capacity and corrected test capacity of each sample battery.

(Embodiment)
A lithium ion secondary battery (hereinafter simply referred to as battery) 1 according to an embodiment of the present invention will be described below with reference to Figures 1 to 4. Battery 1 is a rectangular, sealed lithium ion secondary battery that is installed in vehicles such as hybrid cars, plug-in hybrid cars, and electric cars, as well as in various devices.

The battery 1 of this embodiment (see Figure 2) is composed of a case 5, an electrode assembly 2 housed within the case 5, a positive terminal 6P and a negative terminal 6N fixed to the case 5, and an insulating member (not shown) that provides insulation between these and the case 5. The case 5 is made of metal (aluminum in this embodiment) and has a rectangular box shape. The electrode assembly 2 is covered within the case 5 by a bag-shaped insulating film (not shown). The case 5 also contains an electrolyte 3, some of which is impregnated within the electrode assembly 2 and some of which accumulates at the bottom of the case 5. Note that in this embodiment, the vertical direction in Figure 2 is referred to as the height direction HH, the left-right direction as the thickness direction TH, and the front-to-back direction perpendicular to the paper surface as the width direction WH.

The electrode assembly 2 housed within the case 5 is a so-called flat wound electrode assembly, consisting of a strip-shaped positive electrode plate 2P and a strip-shaped negative electrode plate 2N wound with a pair of strip-shaped separators 2S between them, and pressed flat in the thickness direction TH (left-right direction in the figure) in Figure 2. This electrode assembly 2 is housed within the case 5 in a horizontal position with its axis 2X aligned with the width direction WH.

The positive electrode terminal 6P is made of an aluminum plate and is connected to the positive electrode current collector (not shown) of the electrode body 2 inside the case 5, and is also extended to the outside of the case 5. The negative electrode terminal 6N is made of a copper plate and is connected to the negative electrode current collector (not shown) of the electrode body 2 inside the case 5, and is also extended to the outside of the case 5.

As described below, after completing the initial charging step S2, the battery 1 may have a gas layer GS, where gas such as hydrogen has accumulated, locally formed between the positive electrode plate 2P and the negative electrode plate 2N, separated by the separator 2S, in various locations within the electrode assembly 2. This is thought to be because the gas generated during the initial charging step was unable to escape to the outside of the electrode assembly 2. In such cases, it is thought that the battery reaction is locally difficult to occur in the gas-interposed portion 2G between the positive electrode plate 2P and the negative electrode plate 2N, where the gas layer GS is present. For this reason, when a battery 1 having a gas-interposed portion 2G is charged or discharged for a short period of time, particularly when charging or discharging is performed for a short period of time with a large charging or discharging current, resulting in a small change in SOC, the gas-interposed portion 2G does not contribute to charging or discharging, and the capacity of the battery 1 appears to be reduced.

However, even if a gas-interposed portion 2G is present within the electrode body 2 of the battery 1, if the battery is charged or discharged over a long period of time, for example, if a small charging or discharging current is used for a long period of time, causing a large change in SOC (for example, a change across the entire SOC range from 0-100%), there will not be much difference in the amount of electricity charged or discharged compared to a battery 1 that does not have a gas-interposed portion 2G. This is thought to be because the gas-interposed portion 2G also contributes to charging or discharging through the area surrounding the gas-interposed portion 2G due to the diffusion of Li ions within the positive electrode active material layer or negative electrode active material layer.

When inspecting the capacity of manufactured batteries 1 and selecting only good batteries 1, the test capacity CP of the battery 1 may be measured. In this case, to measure the test capacity CP of the battery 1 in a short time and determine whether it is good or bad, a large charge or discharge current Ich is passed as the test current, and the battery is charged or discharged for only a short time, resulting in a small change in SOC. However, as mentioned above, when measuring this test capacity CP, if a gas-containing portion 2G is present in the battery 1, the resulting test capacity CP will be affected by the presence of the gas-containing portion 2G and measured as a small value. As a result, a battery 1 that should have been determined to be good may be determined to be defective, or a battery 1 that should have been determined to be defective may be determined to be good.

Therefore, in the manufacturing process of battery 1 of this embodiment described below, and in the inspection process S5 thereof, the inspection capacity CP is corrected, and the quality of battery 1 is determined using the corrected inspection capacity CPp. The manufacturing of battery 1 according to this embodiment is described below (see Figures 1 and 2).

First, in the uncharged battery assembly process S1, an uncharged battery 1 is assembled. Specifically, the electrode body 2 is fabricated, and the positive and negative terminals 6P and 6N fixed to the case lid 5L are connected to the positive and negative current collectors (not shown) of the electrode body 2, respectively. The electrode body 2 is covered with a bag-shaped insulating film (not shown) and placed inside the case body 5B. The entire periphery of the case lid 5L is laser welded to the case body 5B to form the case 5. Next, electrolyte 3 is injected into the case 5 through an injection hole (not shown) provided in the case lid 5L, impregnating the electrode body 2 with the electrolyte 3.

Then, in the initial charging step S2, the battery 1 is initially charged. Specifically, CC charging is performed at a constant current of 10 C up to an SOC of 80%. This causes a SEI coating to be formed on the surfaces of the negative electrode active material particles (not shown) of the negative electrode plate 2N and the positive electrode active material particles (not shown) of the positive electrode plate 2P, resulting from the decomposition of a portion of the electrolyte 3. Most of the gases generated during this initial charging, such as hydrogen gas, are released to the outside of the electrode body 2 through the gap between the positive electrode plate 2P and the negative electrode plate 2N. However, some batteries 1 are manufactured in which gas accumulates between the positive electrode plate 2P and the negative electrode plate 2N in various locations on the electrode body 2, forming a gas layer GS, as shown in Figure 2.

After the initial charging step S2, a sealing step S3 follows, in which a filling plug (not shown) is welded to the filling hole to hermetically seal the case 5. Furthermore, in the high-temperature aging step S4, the battery 1 is left in an environment at 60°C for 20 hours.

Then, in the inspection process S5, the quality of the battery 1 is inspected based on the inspection capacity CP. Specifically, first, in the SOC adjustment process S51, the battery 1 is charged to 90% SOC using 10C CCCV charging (cut off at 1 hour) in a room temperature environment, and the inspection start SOC of each battery 1 is adjusted to 90%.

Next, in the test capacity measurement step S52, the magnitude of the CC discharge test current Ich is set to 5C or more, specifically 10C. Then, the SOC of battery 1 is CC discharged over a range of 20% or less from the test start SOC to the test end SOC, specifically over a 10% test SOC range from 90% SOC to 80% SOC. This test capacity measurement step S52 takes a short time, approximately 6 minutes, because discharge is terminated after CC discharge only, and no CV discharge is performed. The amount of electricity discharged from battery 1 during this time is obtained as the test capacity CP.

Next, in the ultrasonic irradiation process (a type of gas correlation quantity acquisition process) S53, an integrated value SG of the transmitted ultrasonic wave intensity IG, which correlates with the gas amount GSA in the electrode body 2, is obtained as shown in Figure 2. Specifically, first, the battery 1 is placed on a movable table MT. This movable table MT is a table that can move the placed battery 1 in the height direction HH (up and down in Figure 2) and the width direction WH (direction perpendicular to the paper surface in Figure 2).

The ultrasonic transmitter UST, connected to the controller CTL and directed in the thickness direction TH, emits irradiated ultrasonic waves US1 toward the battery 1 placed on the moving table MT. A portion of the irradiated ultrasonic waves US1 irradiated toward the battery 1 passes through the case 5 and electrode body 2 in the thickness direction TH as transmitted ultrasonic waves US2, and is emitted from the battery 1 as transmitted ultrasonic waves US3. The transmitted ultrasonic waves US3 are received by the ultrasonic receiver USR, and the magnitude of the transmitted ultrasonic waves US3, or the transmitted ultrasonic intensity IG, is obtained in the controller CTL. In this embodiment, the ultrasonic transmitter UST and ultrasonic receiver USR are used at a distance from the battery 1, but they may also be used in contact with the battery 1.

If a gas layer GS exists within the electrode body 2 and is present on the path of the passing ultrasonic wave US2, the acoustic impedance of the gas layer GS differs significantly from the acoustic impedance of the positive electrode plate 2P, negative electrode plate 2N, separator 2S, and other components impregnated with the electrolyte 3 that make up the electrode body 2. As a result, a portion of the passing ultrasonic wave US2 is reflected at the interface between the gas layer GS and the positive electrode plate 2P, etc. This reduces the transmitted ultrasonic wave intensity IG of the transmitted ultrasonic wave US3 that reaches the ultrasonic receiver USR compared to when no gas layer GS exists on the path of the passing ultrasonic wave US2. It is believed that the greater the number of gas layers GS present on the path of the passing ultrasonic wave US2, i.e., the greater the gas volume GSA, the greater the degree of reduction in the transmitted ultrasonic wave intensity IG. In other words, the transmitted ultrasonic wave intensity IG is a value that correlates with the gas volume GSA in the area through which the passing ultrasonic wave US2 passes.

Furthermore, the gas layer GS is believed to exist locally within the electrode assembly 2. This is because the gas layer GS is formed when gas generated in association with the formation of an SEI coating on each positive electrode plate 2P or negative electrode plate 2N accumulates between the positive electrode plate 2P and the negative electrode plate 2N. Therefore, the battery 1 is moved in the height direction HH and the width direction WH using the moving table MT, and the transmitted ultrasonic intensity IG is measured at each of multiple locations on the battery 1 where flat portions of the electrode assembly 2 exist in the thickness direction TH. For example, the battery 1 is moved using the moving table MT to obtain the transmitted ultrasonic intensity IG at a total of 50 locations, five in the height direction HH and ten in the width direction WH. The sum of these values is then used as the integrated value SG of the transmitted ultrasonic intensity IG. This integrated value SG correlates with the gas amount GSA across substantially the entire area of the electrode assembly 2. Using this integrated value SG, the test capacitance CP can be appropriately corrected according to the gas amount GSA, as described below.

However, as mentioned above, even if a gas-containing portion 2G is present within the electrode body 2 of the battery 1, if charging or discharging is performed over a long period of time with a small charging or discharging current, causing a large change in SOC (for example, the entire range of SOC from 0-100%), it has been found that there is little difference in the amount of electricity charged or discharged compared to a battery 1 that does not have a gas-containing portion 2G.

Therefore, in this embodiment, the aforementioned test capacity CP and the integrated value SG of the transmitted ultrasonic intensity IG were obtained in advance for multiple sample batteries 1. In addition, the discharge capacity of each battery 1 was measured by CCCV discharge (3-hour cutoff) from 100% to 0% SOC, with a discharge current of 1/2C during CC discharge. As described above, this discharge capacity value is measured by long-term discharge over a wide SOC range from 100% to 0% at a small discharge current (1/2C or less in this embodiment), and is therefore less affected by the presence or absence of a gas-containing portion 2G within the electrode body 2 of the battery 1. Therefore, from the multiple sample batteries 1, multiple batteries 1 (three in this embodiment) with approximately the same measured discharge capacity values are selected. Note that, hereinafter, the three selected batteries 1 are referred to as sample batteries SP1 to SP3. Of the selected sample batteries SP1 to SP3, the test capacity CP obtained for sample battery SP1, which had the largest integrated value SG of transmitted ultrasonic wave intensity IG, was used as the reference, and the difference in test capacity CP between sample battery SP1 and sample battery SP2, and the difference in test capacity CP between sample battery SP1 and sample battery SP3, were defined as ΔCP. Figure 3 is a graph plotting the integrated value SG and difference ΔCP for each of sample batteries SP1 to SP3.

Figure 3 shows that, even though sample batteries SP1 to SP3 have approximately the same discharge capacity, differences in the integrated value SG, which is the gas correlation quantity, result in differences in test capacity CP. Because sample batteries SP1 to SP3 have approximately the same discharge capacity, it is likely that if the gas amounts GSA contained within the electrode body 2 were approximately the same, the resulting test capacity CP values would also be approximately the same. Therefore, for sample batteries SP2 and SP3, adding the aforementioned difference ΔCP to the resulting test capacity CP can be corrected to be the same as the test capacity CP of sample battery SP1, which has a smaller gas amount GSA. In other words, Figure 3 shows that the difference ΔCP can be used as a capacity correction value to correct the resulting test capacity CP to be the same as the test capacity CP of sample battery SP1, which has a smaller gas amount GSA, depending on the magnitude of the integrated value SG.

Therefore, in this embodiment, after obtaining the integrated value SG in the ultrasonic irradiation step S53, in the correction step S54, a capacity correction value ΔCP corresponding to the integrated value SG is obtained using the graph in Figure 3, and a correction is made by adding this to the test capacity CP to calculate the corrected test capacity CPp (CPp = CP + ΔCP). For example, Figure 4 shows the test capacity CP and corrected test capacity CPp obtained for sample batteries SP1 to SP4. In Figure 4, the corrected test capacity CPp for sample battery SP1 is equal to the test capacity CP. It can also be seen that the corrected test capacity CPp for sample batteries SP2 and SP3 is approximately equal to the corrected test capacity CPp for sample battery SP1.

In Figure 4, CPmin indicates the lower capacity limit, and CPmax indicates the upper capacity limit. In other words, the range from CPmin to CPmax, sandwiched between two dashed lines, is the pass range CPG for the test capacity CP (corrected test capacity CPp). Looking at the pre-correction test capacity CP, both the test capacity CP and the corrected test capacity CPp for sample batteries SP1 and SP2 are within the pass range CPG. However, the test capacity CP for sample battery SP3 is outside the pass range CPG. This is because the amount of gas GSA contained within the electrode body 2 is large, resulting in a small test capacity CP. In contrast, the corrected test capacity CPp for sample battery SP3 is found to be within the pass range CPG. Thus, according to this embodiment, calculating the corrected test capacity CPp can prevent a battery 1 that should be considered a good product from being deemed defective.

However, as with sample battery SP4, there are cases where the test capacity CP is within the pass range CPG, but the corrected test capacity CPp is outside the pass range CPG. Thus, according to this embodiment, by calculating the corrected test capacity CPp, it is possible to prevent the problem of determining that a battery 1 that should actually be considered defective is a good product.

Therefore, in the judgment step S55, the calculated corrected test capacity CPp is used to judge whether the battery 1 is good or bad. Specifically, as described above, it is determined whether the corrected test capacity CPp falls within the pass range CPG. Thus, in the inspection step S5, the quality of the battery 1 can be appropriately judged based on the corrected test capacity CPp.

Then, in the sorting process S6, batteries 1 that are judged to be good (OK) in the evaluation process S55 are retained, and batteries 1 that are judged to be defective (NG) are rejected as defective. In this way, good batteries 1 whose corrected test capacity CPp falls within the pass range CPG can be manufactured.

The present invention has been described above in accordance with the embodiments and Examples 1 to 6, etc. However, the present invention is not limited to the embodiments, etc., and can be modified and applied as appropriate within the scope of the gist of the present invention.
For example, in the embodiment, in the ultrasonic irradiation step S53, the integrated value SG of the transmitted ultrasonic intensity IG is obtained, but instead, the average value of the transmitted ultrasonic intensity IG may be calculated and used to carry out the subsequent steps.

1, SP1, SP2, SP3 battery (secondary battery)
2 Electrode body 2X (of electrode body) central axis 2P Positive electrode plate 2N Negative electrode plate 2G Gas interposed portion GS Gas layer GSA Gas amount US3 Transmitted ultrasonic wave IG Transmitted ultrasonic wave intensity SG Integrated value (gas correlation amount) (of transmitted ultrasonic wave intensity)
S4 High temperature aging step S5 Inspection step S51 SOC adjustment step S52 Inspection capacity measurement step S53 Ultrasonic wave irradiation step (gas correlation amount acquisition step)
S54 Correction step S55 Judgment step S6 Selection step CP Test capacitance ΔCP Capacitance correction value CPp Corrected test capacitance CPG Pass range

Claims (4)

A method for inspecting a secondary battery including a case and an electrode assembly housed in the case, comprising:
an SOC adjusting step of adjusting the SOC of the secondary battery to an inspection start SOC;
a test capacity measurement step of measuring a test capacity by performing constant current charging or constant current discharging on the secondary battery over a test SOC range from the test start SOC to the test end SOC, which is a part of an SOC range from 0% to 100% SOC;
a gas correlation quantity acquisition step of acquiring a gas correlation quantity correlated with the amount of gas present between the positive electrode plate and the negative electrode plate of the electrode body;
a correction step of obtaining the capacitance correction value corresponding to the acquired gas correlation quantity based on a relationship between the gas correlation quantity and a capacitance correction value obtained in advance, and obtaining a corrected test capacitance from the measured test capacitance and the capacitance correction value;
and a determining step of determining whether the secondary battery is good or bad using the corrected test capacity. 2. The method for inspecting a secondary battery according to claim 1,
The gas correlation quantity acquisition step includes:
The method for inspecting a secondary battery includes an ultrasonic irradiation step of obtaining the gas correlation quantity from the transmitted intensity of ultrasonic waves that are irradiated onto the secondary battery and transmitted through the electrode body. 2. The method for inspecting a secondary battery according to claim 1 ,
The test capacitance measuring step includes:
A method for testing a secondary battery, comprising: measuring the test capacity by performing constant current charging or constant current discharging at a test current of 5 C or more over the test SOC range of 20% or less. an inspection step of inspecting a secondary battery whose inspection capacity has not yet been inspected by the method for inspecting a secondary battery according to any one of claims 1 to 3;
a sorting step of retaining the secondary batteries that are determined to be good in the determination step.