JP7323417B2 - Method for manufacturing secondary battery - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a method for manufacturing a secondary battery, and more particularly to a method for manufacturing a secondary battery including a short-circuit inspection step.

In the manufacture of secondary batteries, there is a possibility that metallic foreign matter may enter the electrode body when the electrode body is produced by coating and drying the active material or by laminating the electrodes. Such foreign matter can cause a short circuit in the electrode assembly. In general, manufacturing facilities for secondary batteries take various measures (filters, etc.) to prevent foreign matter from entering from the outside. However, there are also foreign substances generated during the manufacturing process, such as when cutting the electrodes. Also, even if foreign matter does not enter, there is a possibility that the active material attached to the cutting blade drips and moves to the opposing active material (active material sag) when cutting the edge of the electrode body, causing a short circuit. Therefore, a method for manufacturing a secondary battery including a short-circuit inspection process has been proposed.

For example, Japanese Patent Application Laid-Open No. 2019-075302 (Patent Document 1) discloses a method for manufacturing a lithium ion secondary battery. In this manufacturing method, a short circuit is determined based on the amount of cell voltage drop per unit time of an uncharged secondary battery.

JP 2019-075302 A JP 2015-103437 A WO2015/136930

In the method for manufacturing a lithium ion secondary battery disclosed in Patent Document 1, the presence or absence of a short circuit in the secondary battery can be determined, but the short circuit location cannot be specified. If the location of the short circuit cannot be identified, the electrode body in which the short circuit has occurred must simply be discarded. However, by specifying the short-circuited portion, the electrode body from which the short-circuited portion is removed can be reused. Alternatively, by grasping locations where short circuits are likely to occur and analyzing the reasons, it is possible to make improvements to prevent short circuits. Therefore, it is desirable that the manufacturing method of the secondary battery including the short-circuit inspection step can identify even the short-circuit location.

The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide a technique capable of identifying a short-circuit location in an electrode body of a secondary battery.

(1) A method for manufacturing a secondary battery according to an aspect of the present disclosure includes first to third steps. The first step is to assemble an electrode body in which a positive electrode current collector, a positive electrode active material layer, a separator layer, a negative electrode active material layer, and a negative electrode current collector are laminated. In the second step, while a current is flowing between the positive electrode current collector and the negative electrode current collector, is a step of measuring the voltage of The plurality of measurement points includes first to third measurement points and a reference point located inside a circular area defined by the first to third measurement points. The measuring step includes measuring a first voltage between the first measurement point and the reference point, measuring a second voltage between the second measurement point and the reference point, measuring a third voltage between the three measurement points and the reference point. A third step is a step of specifying that the short-circuit location in the electrode body is inside the circular region when predetermined conditions regarding the first to third voltages are satisfied.

(2) The reference point is equidistant from each of the first to third measurement points.

(3) Each sign of the first to third voltages is determined so as to correspond to a reference sign when the electrode body is not short-circuited. The predetermined condition is met when the sign of at least one of the first to third voltages is different from the corresponding reference sign.

(4) Each magnitude of the first to third voltages is determined so as to correspond to a reference amount when the electrode body is not short-circuited. The predetermined condition is met when the magnitude of at least one of the first to third voltages is greater than the corresponding reference amount.

When a current is passed between the positive electrode current collector and the negative electrode current collector, a large current flows in the vicinity of the short-circuited portion in the current collector plane. When a short circuit occurs, the sign or magnitude of the voltage (the direction or magnitude of the voltage drop) changes compared to when the short circuit does not occur. This change occurs within a circular area defined by the first to third measurement points. Measuring the voltages between the first to third measurement points and the reference point in the above methods (1) to (4), and determining whether or not predetermined conditions regarding the first to third voltages are established. means to obtain the state of the current drop inside the circular area. Therefore, according to the above methods (1) to (4), the short circuit location can be specified as being inside the circular area.

(5) Each sign of the first to third voltages is determined so as to correspond to a reference sign when the electrode body is not short-circuited. Each magnitude of the first to third voltages is determined so as to correspond to a reference amount when the electrode body is not short-circuited. The predetermined condition is that the sign of at least one of the first to third voltages is different from the corresponding reference sign, and the magnitude of at least one of the first to third voltages corresponds. It is established when it is larger than the reference amount.

In method (5) above, it is determined whether a short circuit occurs inside the circular region based on both the sign and magnitude of the voltage (the direction and magnitude of the voltage drop). By using both the sign and the magnitude of the voltage in this way, it is possible to reduce the possibility of erroneously determining that a short circuit has occurred even though it has not actually occurred.

(6) The plurality of measurement points further includes a fourth measurement point defining a circular area. The measuring step further includes measuring a fourth voltage between the fourth measurement point and the reference point. A straight line connecting two of the first to fourth measurement points and a straight line connecting the remaining two points intersect each other.

According to the above method (6), by measuring voltages at four points and acquiring voltage drops in two intersecting directions, it is possible to improve the accuracy of specifying a short-circuit location (detection rate, which will be described later).

(7) The method for manufacturing a secondary battery further includes the step of removing the short-circuited portion identified in the identifying step and housing the remaining portion of the electrode assembly in an exterior material.

According to the method (7) above, the yield of the secondary battery can be improved by removing only the short-circuited portion and reusing the electrode assembly.

(8) Multiple measurement points are pre-positioned. The step of measuring is a step of measuring a voltage between any two of the plurality of measurement points. The method for manufacturing a secondary battery further comprises a step of selecting measurement points that satisfy a predetermined condition from among the plurality of measurement points as the first to third measurement points and the reference point. The specifying step is a step of specifying a circular area defined by the selected first to third measurement points as a short-circuit location.

In the method (8) above, the voltages are measured at all points previously positioned in the plane of the current collector, and a combination of measurement points that satisfies a predetermined condition is selected from among them. As a result, it is possible to reduce errors caused by variations in measurement positions, and to shorten the time required to identify the short-circuit location.

According to the present disclosure, it is possible to identify a short circuit location in an electrode body of a secondary battery.

1 is a diagram showing a configuration of a secondary battery in Embodiment 1; FIG. It is a figure showing roughly the whole inspection system composition used in a short-circuit inspection process. 4 is a flow chart showing a method for manufacturing a secondary battery according to Embodiment 1. FIG. FIG. 4 is a diagram for explaining voltage measurement points in an electrode body; FIG. 4 is a diagram for explaining in more detail voltage measurement points; FIG. 4 is a diagram for explaining the potential distribution of the positive current collector foil when the electrode assembly is normal; FIG. 4 is a diagram for explaining a potential distribution when a short circuit occurs in an electrode body; FIG. 11 is an exploded perspective view showing the configuration of an inspection jig according to Embodiment 2; FIG. 10 is a diagram showing voltage measurement points of an electrode body according to Embodiment 2; FIG. 2 is a first diagram showing an example of the arrangement and number of measurement points; FIG. 4 is a second diagram showing an example of the arrangement and number of measurement points; FIG. 11 is a third diagram showing an example of the arrangement and number of measurement points; FIG. 4 is an exploded perspective view for explaining current paths in the electrode body; FIG. 4 is a cross-sectional view for explaining a current path in an electrode body; FIG. 5 is a diagram showing an example of voltage measurement results at each measurement point when no short circuit occurs in the electrode body; FIG. 10 is a diagram for explaining current flow in an electrode body in which a short circuit has occurred; FIG. 10 is a diagram showing an example of voltage measurement results at each measurement point when a short circuit occurs in the electrode body; 6 is a flow chart showing a method for manufacturing a secondary battery according to Embodiment 2. FIG. FIG. 10 is a diagram for explaining a technique for improving the accuracy of specifying a short-circuited portion of an electrode body; It is a figure for demonstrating the removal method of a short circuit location.

Hereinafter, this embodiment will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

[Embodiment 1]
<Configuration of secondary battery>
In Embodiment 1 described below, the secondary battery manufactured by the manufacturing method according to the present disclosure is an all-solid battery in which a solid electrolyte is responsible for charge transfer between the positive electrode and the negative electrode. However, secondary batteries that can be manufactured by the manufacturing method according to the present disclosure are not limited to all-solid-state batteries, and may be so-called liquid secondary batteries. Also, the type of the liquid secondary battery is not particularly limited, and may be, for example, a lithium ion secondary battery.

FIG. 1 is a diagram showing the configuration of a secondary battery according to Embodiment 1. FIG. Referring to FIG. 1 , secondary battery 10 includes electrode body 1 . The electrode body 1 includes a positive electrode layer 21 , a negative electrode layer 22 , a separator layer 3 , a positive current collecting foil 41 , a negative current collecting foil 42 , a positive terminal 51 and a negative terminal 52 .

The positive electrode layer 21 contains a positive electrode active material and a solid electrolyte. The positive electrode active material may contain, for example, a lithium-nickel-cobalt-manganese composite oxide. The positive electrode layer 21 may further contain a conductive material, a binder, and the like. In addition, the positive electrode layer 21 corresponds to the "positive electrode active material layer" according to the present disclosure.

The negative electrode layer 22 contains a negative electrode active material and a solid electrolyte. The negative electrode active material may contain, for example, graphite, silicon, or silicon oxide. The negative electrode layer 22 may further contain a conductive material, a binder, and the like. The negative electrode layer 22 corresponds to the "negative electrode active material layer" according to the present disclosure.

The separator layer (insulating layer) 3 is arranged between the positive electrode layer and the negative electrode layer. The separator layer 3 is a solid electrolyte layer containing a solid electrolyte. The solid electrolyte may include, for example, sulfide glass (eg, a mixture of lithium sulfide and phosphorus sulfide). The solid electrolyte layer may further contain a binder, for example. The solid electrolyte contained in each layer of the positive electrode layer 21, the negative electrode layer 22 and the separator layer 3 may be the same or different.

Each layer of the positive electrode layer 21, the negative electrode layer 22, and the separator layer 3 may be formed by, for example, powder molding, or may be formed by applying slurry. Moreover, the positive electrode layer 21, the negative electrode layer 22 and the separator layer 3 may be integrated by, for example, compression molding.

The positive collector foil 41 is electrically connected to the positive electrode layer 21 . Positive current collector foil 41 is, for example, aluminum foil. The negative current collector foil 42 is electrically connected to the negative electrode layer 22 . Negative collector foil 42 is, for example, copper foil. The positive terminal 51 is electrically connected to the positive collector foil 41 . The negative current collector foil 42 is electrically connected to the negative electrode layer 22 .

The electrode body 1 is housed in an exterior material (not shown) such as a pouch made of an aluminum laminate film after the short-circuit inspection step described later. As a result, the secondary battery 10, which is an all-solid battery, is completed.

<Configuration of inspection system>
FIG. 2 is a diagram schematically showing the overall configuration of an inspection system used in the short-circuit inspection process. Referring to FIG. 2 , inspection system 9 includes inspection jig 91 , current generator 92 , voltage measuring device 93 , and control device 94 .

The inspection jig 91 fixes the electrode body 1 to be inspected so that it does not move, and properly electrically insulates the electrode body 1 from the environment during current application. As a material of the inspection jig 91, for example, an insulating resin can be used.

A top view of the inspection jig 91 is shown in the balloon in FIG. The inspection jig 91 is provided with a plurality of (five in this example) measurement conductors (measurement pins). Each measuring pin is a bar-shaped metal, for example a copper bar with a diameter of 2 mm.

The inspection jig 91 is also configured to apply pressure to the electrode body 1 by sandwiching the electrode body 1 from above and below. When the electrode body 1 is not pressurized, the contact state between the components of the electrode body 1 (the positive electrode layer 21, the negative electrode layer 22, the separator layer 3, the positive electrode current collector foil 41 and the negative electrode current collector foil 42) may differ depending on the location. Then, the internal resistance is low where the components are in firm contact, while the internal resistance is high where the contact between the components is loose. As a result, the voltage measurement results may vary depending on the measurement locations. By applying a predetermined pressure to the electrode body 1, the contact state between the components of the electrode body 1 becomes uniform irrespective of the location, so that variations in voltage measurement can be reduced.

The current generator 92 applies a constant current of a predetermined magnitude (for example, about several tens of mA) between the positive electrode terminal 51 and the negative electrode terminal 52 provided on the electrode assembly 1 .

The voltage measuring device 93 measures the voltage between two measuring points (described later) set on the electrode body 1 while the constant current is applied using the current generator 92 . In general, the resistance of the current collector foil is much smaller than the resistance of the positive electrode active material and the negative electrode active material. Therefore, the amount of voltage drop in the positive current collector foil 41 and the negative current collector foil 42 is very small. Therefore, the voltage measuring device 93 is required to have high voltage resolution. For the voltage measuring device 93, for example, a DC voltmeter DM7276 manufactured by HIOKI having a voltage resolution of 10 nV can be used.

The control device 94 is, for example, a microcomputer including a CPU (Central Processing Unit), memory and input/output ports. Controller 94 controls current generator 92 . The control device 94 may be configured to be able to control the voltage between the positive terminal 51 and the negative terminal 52 . The control device 94 receives the result of the voltage measurement by the voltage measuring device 93, determines whether or not there is a short circuit in the electrode body 1, and identifies the location of the short circuit.

When the electrode body 1 is an all-solid battery and a sulfide-based solid electrolyte such as sulfide glass is used, a harmful gas (hydrogen sulfide) may be generated by reaction between sulfur and moisture in the air. Therefore, it is desirable to install at least the inspection jig 91 in a glove box (not shown) so that the electrode body 1 is not exposed to the atmosphere.

<Manufacturing flow of secondary battery>
FIG. 3 is a flow chart showing a method for manufacturing secondary battery 10 according to the first embodiment. Hereinafter, each step in the flowchart may be abbreviated as "S".

Referring to FIG. 3, in S11, an electrode assembling step of assembling electrode assembly 1 of secondary battery 10 is performed. The configuration of the electrode body 1 is as described with reference to FIG. 1, and a known method can be adopted for assembling the electrode body 1, so the description will not be repeated here. In subsequent S12 to S14, S16 and S17, the short-circuit inspection process of the electrode body 1 is performed. The presence or absence of a short circuit in the electrode body 1 is determined by the short circuit inspection step, and the short circuit location is specified.

First, in S12, the control device 94 measures the potential of a plurality of measurement pins with the voltage measurement device 93 while applying a constant current using the current generator 92, thereby measuring each measurement point (positive electrode corresponding to the measurement pin). position on the current collector foil 41) is measured. Further, in S13, the control device 94 determines whether or not there is a short circuit in the electrode body 1 based on the voltage drop measured in S12.

If no short circuit occurs in electrode body 1 (NO in S13), control device 94 determines that electrode body 1 is non-defective (S14). In this case, the electrode assembly 1 is then housed in the exterior material (S15). On the other hand, if there is a short circuit in electrode body 1 (YES in S13), control device 94 determines that electrode body 1 is defective (S15). Then, the controller 94 identifies the location of the short circuit (S17). The principle of determining a short circuit in S13 and the principle of identifying a short circuit location in S17 will be described below.

<Short circuit detection mechanism>
FIG. 4 is a diagram for explaining voltage measurement points in the electrode body 1. FIG. Referring to FIG. 4, in the present embodiment, one of positive current collector foil 41 and negative current collector foil 42 is provided with five measurement points. Although each measurement point is assumed to be provided on the positive current collector foil 41 below, the positive current collector foil 41 may be read as the negative current collector foil 42 as appropriate.

FIG. 5 is a diagram for explaining the voltage measurement points in more detail. Referring to FIG. 5, the positions of measurement points P0 to P4 are determined based on two circles C virtually drawn on positive electrode current collector foil 41. As shown in FIG. The measurement point P0 is located at the center of the circle C. Hereinafter, the measurement point P0 is also referred to as the reference point P0, and the potential of the reference point P0 is also referred to as the reference potential _φ0 . Note that the area defined by the circle C corresponds to the "circular area" according to the present disclosure.

The remaining measurement points P1-P4 are located on the circumference of the circle C. FIG. In this case, the reference point P0 is equidistant from each of the measurement points P1 to P4. The positions of the measurement points P1 to P4 are such that a straight line connecting the measurement points P1 and P3 (the diameter of the circle C) and a straight line connecting the measurement points P2 and P4 intersect each other (more preferably orthogonally). Position is preferred.

In the example shown in FIG. 5, the measurement point P3 is positioned on the positive terminal 51 side, and the measurement point P1 is positioned on the negative terminal 52 side. When a voltage is applied to the electrode body 1, the current flows in the direction from the positive electrode terminal 51 to the negative electrode terminal 52 (the direction from the left side to the right side in the drawing), so the measurement point P3 is upstream in the current flow direction. It can also be said that the measuring point P1 is located downstream. The measurement points P2 and P4 are positioned in a direction perpendicular to the direction of current flow.

At these five measurement points, the potentials of the measurement points P1 to P4 are measured with the potential of the reference point P0 (reference potential φ ₀ ) as a reference. Hereinafter, the voltage (potential difference) between the potential φ1 at the measurement point _P1 and the reference potential _φ0 is referred to as _V1 (see formula (1) below).
V ₁ = φ ₁ - φ ₀ (1)

Similarly, as shown in the following equations (2) to (4), the voltage between the potential _φ2 at the measurement point P2 and the reference potential _φ0 is denoted as _V2 . The voltage between the potential φ3 at the measuring point _P3 and the reference potential _φ0 is denoted as _V3 . The voltage between the potential φ4 at the measuring point _P4 and the reference potential _φ0 is denoted as _V4 .
V ₂ = φ ₂ - φ ₀ (2)
V ₃ =φ ₃ -φ ₀ (3)
V ₄ = φ ₄ - φ ₀ (4)

FIG. 6 is a diagram for explaining the potential distribution of the positive current collecting foil 41 when the electrode body 1 is normal (when no short circuit occurs). 6 and FIG. 7, which will be described later, the potential distribution of the positive current collecting foil 41 is represented by an arrow pointing from a high potential to a low potential (that is, an arrow indicating the direction of current flow).

Referring to FIG. 6, when no short circuit occurs in electrode body 1, current flows from positive electrode terminal 51 on the left side of the drawing to negative electrode terminal 52 on the right side of the drawing. This is because the potential at the measuring point P3 near the positive terminal 51 is the highest, the potential at the central reference point P0 is the next highest, and the potential at the measuring point P1 near the negative terminal 52 is the lowest. Therefore, the voltage _V3 at the measuring point P3 is positive and the voltage _V1 at the measuring point P1 is negative. Also, the voltages V ₂ and V ₄ are both negative. The signs of the voltages V ₁ to V ₄ when the electrode body 1 is not short-circuited correspond to the “reference signs” according to the present disclosure.

As the current flows from upstream to downstream, part of the current branches off in a direction (vertical direction, etc.) that intersects the main flow direction of the current (horizontal direction in the figure), so the magnitude of the current is the downstream direction. becomes smaller. Therefore, the current flowing through the measurement point P3 on the upstream side is larger than the current flowing through the measurement point P1 on the downstream side. Therefore, the magnitude of voltage _V3 (voltage drop between measurement point P3 and reference point P0) is greater than the magnitude of voltage _V1 (voltage drop between measurement point P1 and reference point P0). Also, the magnitude of the voltage _V3 is greater than the magnitudes of the voltages _V2 and _V4 . In FIG. 6, the size relationship of the voltages V ₁ to V ₄ (absolute values) is expressed by the thickness of the arrows. The magnitude of the voltages V ₁ to V ₄ when the electrode body 1 is not short-circuited corresponds to the "reference amount" according to the present disclosure.

FIG. 7 is a diagram for explaining the potential distribution when the electrode body 1 is short-circuited. If there is a short circuit, the current will flow in the direction towards the short circuit. Therefore, in the example shown in FIG. 7A in which the short-circuit location is located in the inner region of the circle C (especially near the center), the voltage _V3 has a positive sign, while the voltages _V1 , _V2 , and _V4 have a positive sign. The sign is negative. In other words, when the electrode body 1 is short-circuited, the directions of the voltage drops at the measurement points P1, P2, and P4 are reversed compared to when the electrode body 1 is normal. The voltages V ₁ , V ₂ and V ₄ also become larger than the voltages V ₁ , V ₂ and V ₄ when the electrode body 1 is normal.

Depending on the mode of the short circuit, a relatively large current may flow through the short circuit. In another example shown in FIG. 7B, the signs of voltages V ₁ and V ₃ are positive, while the signs of voltages V ₂ and V ₄ are negative. In other words, the sign of the voltage _V1 is the same as the sign of the voltage _V1 when the electrode body 1 is normal despite the short circuit. However, in this example, the voltages V ₂ and V ₄ are larger than the voltages V ₂ and V ₄ when the electrode body 1 is normal. In other words, when the electrode body 1 is short-circuited, the voltage drop at the measurement points P2 and P4 becomes greater than when the electrode body 1 is normal.

By comparing the signs and magnitudes of the voltages V ₁ to V ₄ with the signs and magnitudes of the voltages V ₁ to V ₄ in the normal state, it is determined whether or not a short circuit occurs inside the circle C. be able to. Specifically, in this example, when the signs of the voltages V ₁ to V ₄ are all positive, it can be determined that a short circuit has occurred inside the circle C (see FIG. 7A). Also, when two or three of the voltages V ₁ to V ₄ are larger than the reference amount, it can be determined that a short circuit has occurred inside the circle C (see FIG. 7B).

In this example, it was explained that the direction of voltage drop (sign of voltage) changes at all of the measurement points P1, P2, and P4, and the voltage drop at both of the measurement points P2 and P4 increases. However, depending on the location of the short circuit or the mode of the short circuit, only one or two of the measurement points P1, P2, and P4 may change the direction of the voltage drop, or the voltage at one of the measurement points P2 and P4 may change. In some cases, only the descent becomes large. As described above, in the present embodiment, it is sufficient to detect a change in the direction of the voltage drop at at least one of the measurement points P1 to P4. Also, it is sufficient if an increase in the magnitude of the voltage drop can be detected at at least one of the measurement points P1 to P4.

<Verification result>
The inventors prepared a plurality of samples of the secondary battery 10 in which a foreign substance penetrating the separator layer 3 was incorporated, and verified whether or not the short-circuit location of each sample could be identified. Specifically, 10 types of samples with different foreign matter positions were prepared, and measurements were repeated several times for each sample.

A liquid-type lithium ion secondary battery was used for each sample. The capacity of the lithium ion secondary battery was 90mAh. The shape of each of the positive electrode layer 21 and the negative electrode layer 22 was square. The length of each side of the positive electrode layer 21 was 45 mm. The length of each side of the positive electrode layer 21 was 47 mm. An aluminum wire was used as the foreign object. The aluminum wire had a diameter φ of 200 μm and a length of 1 mm. The voltage of the sample was adjusted to 3.7 V, and the voltage between measurement points was measured during charging with a constant current of 20 mA from that state.

When only the voltages V 1 and V 3 at the reference point P 0 and the two measurement points P ₁ and P ₃ aligned in one direction were measured, the ratio (detection rate) of accurately specifying the short circuit location was 50%. On the other hand, when measuring the voltages V ₁ to V ₄ at four measurement points P1 to P4 in two directions in addition to the reference point P0, the detection rate improved to 90%. As an example of specific measurement results, V ₁ =−5 μV, V ₂ =−1 μV, V ₃ =7 μV, and V ₄ =−1 μV when there is no short circuit in the electrode body 1. Met. On the other hand, when the electrode body 1 was short-circuited, V ₁ =8 μV, V ₂ =1.1 μV, V ₃ =11 μV, and V ₄ =1.3 μV. In addition, according to the present embodiment, the short circuit can be detected with high accuracy, which eliminates the need to repeat the measurement many times.

As described above, in Embodiment ₁ , the potential φ ₁ By measuring _∼φ4 , the voltage drop (voltages V ₁ to V ₄ ) at the measurement points P1 to P4 is obtained. When the electrode body 1 is short-circuited, current flows toward the short-circuited portion, thereby forming a unique potential distribution corresponding to the short-circuited portion. Whether or not such a potential distribution is formed can be determined from the direction and/or magnitude of the voltage drop at each measurement point P1-P4. Therefore, according to Embodiment 1, it is possible to identify the short-circuit location in the electrode assembly 1 of the secondary battery 10 .

Further, the voltage measurement at the measurement points P1 to P4 is realized by bringing the measuring pins into contact with the collector foil (the positive collector foil 41 or the negative collector foil 42). Such measurement techniques are less susceptible to disturbances. Furthermore, since current does not flow to the voltage measuring device 93, the current distribution in the plane of the current collecting foil is not disturbed. Therefore, according to the present embodiment, it is possible to identify the short-circuit location with high accuracy.

[Embodiment 2]
In the first embodiment, a relatively simple configuration for measuring voltage drops at four points has been described as an example. In the second embodiment, a configuration in which more measurement pins are provided and voltages at more locations are measured will be described. The overall configuration of the inspection system according to the second embodiment is basically the same as the overall configuration of the inspection system 9 according to the first embodiment (see FIG. 2).

<Configuration of inspection jig>
FIG. 8 is an exploded perspective view showing the configuration of the inspection jig according to Embodiment 2. FIG. Referring to FIG. 8 , inspection jig 91A includes insulating plate 911 , insulating base 912 , fixing screw 913 and a plurality of measuring pins 914 . The insulating plate 911 and the insulating base 912 are fixed by a fixing screw 913 with the electrode assembly 1 sandwiched therebetween. As a result, the electrode body 1 can be electrically insulated from the outside and a necessary pressure can be applied to the electrode body 1 .

A plurality of measuring pins 914 are arranged in a grid pattern on the insulating plate 911 . By selecting any five measurement pins from a plurality of measurement pins 914, it is possible to identify the short-circuited portion of electrode body 1 as in the first embodiment. However, in the second embodiment, the entire surface of the electrode body 1 is subject to the determination of whether or not there is a short circuit.

FIG. 9 is a diagram showing voltage measurement points of the electrode body 1 in the second embodiment. Referring to FIG. 9, in this example, a total of 25 measurement points are provided on a grid of 5 rows×5 columns.

The test system 9 measures the voltage between every two adjacent measuring points. Below, the measurement point is described as P(i, j) using coordinates (i, j) (i, j is a natural number of 5 or less). In FIG. 9, the upper left measurement point is P(1,1), and the lower right measurement point is P(5,5). If the potential of the measurement point P(i, j) is denoted by φ _ij , the voltage V _Xij between two laterally adjacent measurement points is represented by the following equation (5). Similarly, the voltage V _Yij between two vertically adjacent measurement points is represented by the following equation (6).
V _Xij =φ _i(j+1) −φ _ij (5)
V _Yij = φ _(i+1)j - φ _ij (6)

Note that the arrangement and number of measurement points shown in FIG. 9 are merely examples. Each of FIGS. 10 to 12 is a diagram showing an example of the arrangement and number of measurement points. As shown in FIGS. 10 to 12, the arrangement and number of measurement points can be appropriately determined according to the shape of the electrode body 1. FIG.

8 and the upper stages of FIGS. 10 to 12, the positive electrode terminal 51 and the negative electrode terminal 52 are provided on the same side surface of the electrode body 1. As shown in FIG. However, the positions of the positive electrode terminal 51 and the negative electrode terminal 52 in the electrode body 1 are not particularly limited. For example, as shown in the lower part of FIGS. 10 to 12, the positive terminal 51 and the negative terminal 52 may be provided on opposite sides of the electrode body 1. FIG.

<Current path>
FIG. 13 is an exploded perspective view for explaining current paths in the electrode body 1. FIG. FIG. 14 is a cross-sectional view for explaining current paths in the electrode assembly 1. FIG. In FIGS. 13 and 14, arrows schematically indicate the direction of current flowing from the positive terminal 51 to the negative terminal 52 .

13 and 14, when positive electrode current collector foil 41 has a rectangular shape and positive electrode terminal 51 is provided at one end of the diagonal line of the rectangle, current flows from positive electrode terminal 51 to the other diagonal line. It flows on the surface of the positive current collector foil 41 toward the edge. At this time, the current branches to the positive electrode layer 21 . The branched current flows through the separator layer 3 and the negative electrode layer 22 to the negative current collector foil 42 . The current then reaches the negative electrode terminal 52 provided on the negative electrode current collector foil 42 .

FIG. 15 is a diagram showing an example of voltage measurement results at each measurement point P(i, j) when no short circuit occurs in the electrode body 1. In FIG. Referring to FIG. 15 , when electrode body 1 is not short-circuited, the current flowing through positive electrode current collector foil 41 increases as it approaches positive electrode terminal 51 (closer to the upper right). Therefore, the closer the voltage drop between two adjacent measurement points is to the positive terminal 51, the greater the voltage drop.

FIG. 16 is a diagram for explaining current flow in the electrode assembly 1 in which a short circuit has occurred. Referring to FIG. 16, also in this example, the direction of the voltage drop at the measurement point near the short-circuited portion is reversed compared to the normal direction, similarly to the description of FIG. 7A. Although not shown, the magnitude of the voltage drop at the measurement point near the short-circuited portion may be greater than the normal magnitude (see FIG. 7B).

FIG. 17 is a diagram showing an example of voltage measurement results at each measurement point P(i, j) when the electrode body 1 is short-circuited. Referring to FIG. 17, a short circuit occurs in electrode body 1 and a current flows as shown in FIG. 16, causing voltage _VY22 to become negative. As a result, a pattern different from the voltage drop pattern (see FIG. 15) is formed when the electrode body 1 is not short-circuited. From this voltage drop pattern, it can be seen that a current is flowing toward the short circuit. As described above, in the second embodiment, as in the first embodiment, the short-circuit location can be identified based on the direction and magnitude of the voltage drop.

<Manufacturing flow of secondary battery>
FIG. 18 is a flow chart showing a method for manufacturing secondary battery 10 according to the second embodiment. Referring to FIG. 18, the electrode assembling step of S21 is the same as the electrode assembling step of S11 (see FIG. 3) in the first embodiment.

At S22, as explained in FIG. 9, the controller 94 measures the voltages V _Xij and V _Yij between every two adjacent measurement points according to the above equations (5) and (6).

In S23, the control device 94 determines whether or not there is a short circuit in the electrode body 1 based on the voltages V _Xij and V _Yij measured in S22. Specifically, each measurement point is regarded as a reference point, and the direction and magnitude of the voltage drop at the four measurement points above, below, to the left, and to the right around the reference point are determined. Similar to the explanation in FIG. 7(A), the direction of the voltage drop at the four measurement points is reversed compared to normal (see FIG. 7(A)), or the magnitude of the voltage drop at the four measurement points becomes larger than normal (see FIG. 7B), it is determined that a short circuit has occurred inside the circle C defined by the four measurement points. If the direction and magnitude of the voltage drop are the same as normal, it is determined that there is no short circuit inside the circle C.

If there is no short circuit at any point on electrode body 1 (NO in S23), control device 94 determines electrode body 1 to be non-defective (S24). Then, the electrode body 1 is housed in the exterior material (S25).

On the other hand, if there is a short circuit in at least one location (YES in S23), control device 94 determines electrode body 1 to be defective (S26), and identifies the short circuit location (S27). In S27, it may be desired to specify the short circuit location in more detail after roughly specifying the short circuit location. In such a case, the control device 94 may specify the short-circuit location in more detail as necessary (S28).

19A and 19B are diagrams for explaining a technique for improving the accuracy of specifying the short-circuited portion of the electrode body 1. FIG. As shown in FIG. 19, when specifying the short-circuit location in more detail, it is possible to use an inspection jig with a narrower interval between adjacent measurement points than the inspection jig used in S26. . The processes of S22 to S27 are executed again in the area including the short-circuited portion specified in S26. As a result, the short circuit location can be narrowed down to a narrower area. Note that this narrowing down (NO in S28) may be performed twice or more (that is, the short-circuit location may be identified three times or more in total).

Returning to FIG. 18, in the second embodiment, after specifying the short circuit location, the short circuit location is further removed (S29). The remaining normal portions that have not been removed can be reused. For example, the electrode body 1 after removing the short-circuited portion is reused by being housed in an exterior material.

20A and 20B are diagrams for explaining a method of removing short-circuited portions. FIG. As shown in FIG. 20A, the region including the short circuit is removed while leaving the positive electrode terminal 51 and the negative electrode terminal 52 . If there are multiple short-circuit locations, all short-circuit locations are removed (see FIG. 20(B)).

As shown in FIG. 20C, both the positive terminal 51 and the negative terminal 52 are provided on one side of the electrode assembly 1, and the aspect ratio of the electrode assembly 1 is sufficiently smaller than 1. In this case, even if the short-circuited portion is relatively close to the center of the electrode body 1, a wide area including the short-circuited portion can be removed. When removing the short-circuited portion, attention should be paid so that the positive electrode active material of the positive electrode layer 21 does not move (avalanche) toward the negative electrode layer 22 side.

As described above, in Embodiment 2, the presence or absence of a short circuit is determined over the entire surface of the positive electrode current collector foil 41 by providing measurement points over the entire surface of the positive electrode current collector foil 41 . Then, after roughly identifying the short-circuited location, the short-circuited location is identified in more detail using an inspection jig with narrow intervals between measurement points (see FIG. 19). Thus, according to the second embodiment, the short-circuited portion in the electrode body 1 of the secondary battery 10 can be identified with high accuracy. Moreover, it is also possible to reuse the electrode body 1 by removing the short-circuited portion specified with high accuracy.

The embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present disclosure is indicated by the scope of claims rather than the description of the above-described embodiments, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

1 Electrode body 21 Positive electrode layer 22 Negative electrode layer 3 Separator layer 41 Positive electrode current collector foil 42 Negative electrode current collector foil 51 Positive electrode terminal 52 Negative electrode terminal 10 Secondary battery 9 Inspection system 91, 91A Inspection and treatment Tool, 92 current generator, 93 voltage measuring device, 94 control device, 911 insulating plate, 912 insulating base, 913 fixing screw, 914 measuring pin.

Claims (7)

assembling an electrode body in which a positive electrode current collector, a positive electrode active material layer, a separator layer, a negative electrode active material layer and a negative electrode current collector are laminated;
voltage between a plurality of measurement points located on the surface of one of the positive electrode current collector and the negative electrode current collector while current is flowing between the positive electrode current collector and the negative electrode current collector; and measuring
The plurality of measurement points are
first to third measurement points;
and a reference point located inside a circular area defined by the first to third measurement points,
The measuring step includes:
measuring a first voltage between the first measurement point and the reference point;
measuring a second voltage between the second measurement point and the reference point;
measuring a third voltage between the third measurement point and the reference point;
Each sign of the first to third voltages is determined so as to correspond to a reference sign when the electrode body is not short-circuited,
a predetermined condition is established when the sign of at least one of the first to third voltages is different from the corresponding reference sign;
A method of manufacturing a secondary battery, further comprising the step of specifying that a short circuit location in the electrode body is inside the circular region when the predetermined condition is satisfied. assembling an electrode body in which a positive electrode current collector, a positive electrode active material layer, a separator layer, a negative electrode active material layer and a negative electrode current collector are laminated;
voltage between a plurality of measurement points located on the surface of one of the positive electrode current collector and the negative electrode current collector while current is flowing between the positive electrode current collector and the negative electrode current collector; and measuring
The plurality of measurement points are
first to third measurement points;
and a reference point located inside a circular area defined by the first to third measurement points,
The measuring step includes:
measuring a first voltage between the first measurement point and the reference point;
measuring a second voltage between the second measurement point and the reference point;
measuring a third voltage between the third measurement point and the reference point;
each magnitude of the first to third voltages is determined so as to correspond to a reference amount when the electrode body is not short-circuited;
a predetermined condition is satisfied when the magnitude of at least one of the first to third voltages is greater than the corresponding reference amount;
A method of manufacturing a secondary battery, further comprising the step of specifying that a short circuit location in the electrode body is inside the circular region when the predetermined condition is satisfied. assembling an electrode body in which a positive electrode current collector, a positive electrode active material layer, a separator layer, a negative electrode active material layer and a negative electrode current collector are laminated;
voltage between a plurality of measurement points located on the surface of one of the positive electrode current collector and the negative electrode current collector while current is flowing between the positive electrode current collector and the negative electrode current collector; and measuring
The plurality of measurement points are
first to third measurement points;
and a reference point located inside a circular area defined by the first to third measurement points,
The measuring step includes:
measuring a first voltage between the first measurement point and the reference point;
measuring a second voltage between the second measurement point and the reference point;
measuring a third voltage between the third measurement point and the reference point;
Each sign of the first to third voltages is determined so as to correspond to a reference sign when the electrode body is not short-circuited,
each magnitude of the first to third voltages is determined so as to correspond to a reference amount when the electrode body is not short-circuited;
A reference quantity to which the sign of at least one of the first to third voltages is different from the corresponding reference sign and to which the magnitude of at least one of the first to third voltages corresponds A predetermined condition is satisfied when the value is greater than
A method of manufacturing a secondary battery, further comprising the step of specifying that a short circuit location in the electrode body is inside the circular region when the predetermined condition is satisfied. 4. The method of manufacturing a secondary battery according to claim 1, wherein said reference point is equidistant from each of said first to third measurement points. The plurality of measurement points further includes a fourth measurement point that defines the circular area;
the measuring step further includes measuring a fourth voltage between the fourth measurement point and the reference point;
The manufacturing of the secondary battery according to any one of claims 1 to 4, wherein a straight line connecting two of the first to fourth measurement points and a straight line connecting the remaining two points intersect each other. Method. The secondary according to any one of claims 1 to 5 , further comprising the step of removing the short-circuited portion identified in the identifying step and housing the remaining portion of the electrode assembly in an exterior material. Battery manufacturing method. The plurality of measurement points are pre-positioned,
The step of measuring is a step of measuring a voltage between any two of the plurality of measurement points,
further comprising the step of selecting measurement points that satisfy the predetermined condition from among the plurality of measurement points as the first to third measurement points and the reference point;
7. The second step according to any one of claims 1 to 6 , wherein the identifying step is a step of identifying the circular area defined by the selected first to third measurement points as the short circuit location. A method for manufacturing a secondary battery.

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