JP2010153275A - Method for deciding quality of secondary battery, and method for manufacturing secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for deciding the quality of a secondary battery for surely detecting minute short circuit portions in a flat secondary battery, and to provide a method for manufacturing the flat secondary battery. <P>SOLUTION: The quality determination method of the secondary battery includes: a charging process charging the secondary battery for deciding the quality of the secondary battery in which a plate-like electrode body is sealed in a flat case; a voltage-before standing measuring process measuring the open circuit voltage of the secondary battery after charging; a standing process standing the charged secondary battery for the prescribed period of time while pressing in the direction crossing to the electrode body from the outside of the case; a voltage-after standing measuring process measuring the open circuit voltage of the secondary battery after standing; and a determination process deciding as a defective when the voltage decreasing amount from he voltage measured in the voltage-before standing measuring process to the voltage measured in the voltage-after standing measuring process is larger than the prescribed value and deciding as a non-defective in any other cases. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a quality determination method for determining the quality of a secondary battery having a flat electrode body and a manufacturing method including the quality determination method. More specifically, the present invention relates to a method for determining the quality of a secondary battery for determining the presence or absence of a minute short-circuit portion inside the secondary battery and a method for manufacturing the same.

For example, some lithium ion secondary batteries are sealed with a power generation element housed in a flat battery case. Usually, the manufactured secondary battery is first subjected to an initial charge / discharge treatment. Then, various inspections such as short circuit inspection are performed. For example, Patent Document 1 discloses an inspection method for performing a short circuit inspection by charging a secondary battery with a charge / discharge current having a current value larger than the initial charge / discharge current. According to this method, it is said that a minute short-circuit location can be forcibly short-circuited. Therefore, it is said that the inspection can be performed in a short time.
JP 2002-352864 A

  However, the conventional inspection method described above has not been sufficient yet. For example, in a secondary battery in which positive and negative electrode plates are wound and housed in a battery case, the physical distance between the electrode plates is also closely related to the likelihood of a short circuit. For example, when a very small foreign matter is mixed in the battery, a short circuit does not occur even if a large current flows as in Patent Document 1 as it is. However, some flat secondary batteries are considered to be battery packs in which a plurality of secondary batteries are constrained in use.

  If the physical distance between the electrode plates changes from that before the restraint due to this restraint, there is a possibility that the above-mentioned part may be short-circuited. For this reason, there was a concern that the number of short-circuit points in the market would gradually increase. This point is not limited to the wound type but is the same for the stacked type secondary battery in which the electrode plates are stacked and stored.

  The present invention has been made to solve the problems of the conventional inspection method described above. That is, an object of the present invention is to provide a secondary battery quality determination method and a manufacturing method for reliably detecting the presence or absence of a minute short-circuited portion in a flat secondary battery.

  The secondary battery quality determination method of the present invention made for the purpose of solving this problem is a secondary battery quality test for determining the quality of a secondary battery in which a flat electrode body is enclosed in a flat case. The determination method includes a charging step for charging a secondary battery, a voltage measurement step before standing for measuring an open circuit voltage of the secondary battery after charging, and a charged secondary battery crossing the electrode body from the outside of the case. Voltage is applied in the direction of pressure, and is left for a predetermined period of time, a voltage measurement step after leaving the battery to measure the open circuit voltage of the secondary battery after being left, and a voltage after being left to stand from the voltage measured in the voltage measurement step before leaving. A determination step of determining that the product is defective when the amount of voltage drop up to the voltage measured in the measurement step is greater than a predetermined value, and determining that the product is non-defective when the voltage drop is other than that.

  According to the secondary battery quality determination method of the present invention, two voltage measurement steps are included with the leaving step in between. In the leaving step, the secondary battery is pressurized in a direction crossing the electrode body. In the flat type secondary battery, the flat part is pressed in the direction of further flattening. That is, the distance between the positive and negative electrode bodies can be made closer by applying pressure in the direction intersecting the surface of the positive and negative flat electrode bodies. Therefore, if a minute metal piece or the like is mixed between the electrode bodies, it is surely short-circuited by being pressurized. This is a method for determining the quality of a secondary battery for reliably detecting the presence or absence of a minute short-circuited portion.

  Furthermore, in the present invention, it is desirable to perform the measurement process in a low temperature environment of 0 ° C. or less. In this way, at a low temperature, the difference in voltage change between the non-defective product and the defective product appears more conspicuously, and the determination becomes easier.

  Furthermore, in the present invention, it is desirable that the leaving step be performed in a high temperature environment of 45 ° C. or higher and 70 ° C. or lower. By doing so, since the dissolution and deposition of minute metallic foreign matters and the like in the secondary battery proceed faster, determination in a shorter time becomes possible.

  The present invention also relates to a method of manufacturing a secondary battery for manufacturing a secondary battery in which a flat electrode body is sealed in a flat case, and the flat electrode body is sealed in the flat case. The assembly process of the secondary battery, the charging process for charging the secondary battery, the voltage measurement process before leaving to measure the open circuit voltage of the secondary battery after charging, and the charged secondary battery from the outside of the case The step of leaving for a predetermined period of time while applying pressure in the direction intersecting with the voltage, the step of measuring the open circuit voltage after leaving the secondary battery, and the step of measuring the voltage after leaving, and the step of measuring the voltage measured in the voltage measurement step before leaving A secondary step including a determination step of determining that the product is defective when the amount of voltage drop to the voltage measured in the post-voltage measurement step is greater than a predetermined value, and determining that the product is non-defective when it is not It extends to battery manufacturing methods.

  According to the quality determination method and the manufacturing method of the secondary battery of the present invention, it is possible to reliably detect the presence or absence of a minute short-circuit portion in the flat secondary battery.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a determination method for determining the quality of a flat secondary battery and a manufacturing method including the determination method.

  The secondary battery 10 which is the object of this embodiment is a wound type in which positive and negative electrode plates are wound as shown in FIG. In the secondary battery 10, an electrode plate portion 12 and an electrolytic solution 13 are enclosed in a flat box-shaped battery case 11. The battery case 11 is formed by joining a lid 11b to a metal case body 11a. The electrode plate portion 12 is formed by sandwiching a separator between strip-shaped positive and negative electrode plates and winding them together into a flat shape. In FIG. 1, the winding cross section is visible.

  Next, the assembly process of the secondary battery 10 of this embodiment will be described. First, positive and negative electrode plates are respectively prepared to appropriate lengths and wound together with a separator to form an electrode plate portion 12. In addition, a case body 11a and a lid 11b are prepared. Further, the electrode terminal provided on the lid 11 b is connected to the electrode plate portion 12. Further, the electrode plate portion 12 is accommodated in the case main body 11a, and the lid 11b is attached. And electrolyte solution is inject | poured from the injection hole provided in the lid | cover 11b. Seal the inlet and perform initial charge / discharge treatment. This completes the assembly process of the secondary battery 10.

  Next, the flow of the quality determination method of this embodiment for determining quality of the assembled secondary battery 10 will be described. First, the secondary battery 10 assembled as described above is charged until reaching a predetermined voltage value (charging process), and the open circuit voltage is measured. This is the first voltage measurement (voltage measurement step before leaving). This measurement may be performed in parallel with charging, and the voltage value at the end of charging may be used as the first open circuit voltage measurement value. Or you may measure a voltage anew after completion | finish of charge.

  Next, as shown in FIG. 2, the plurality of secondary batteries 10 are restrained by the restraining device 20. Further, pressing force is applied to each secondary battery 10 so that the surfaces of the positive and negative electrode plates are pressed toward each other inside the battery case 11. All electrode terminals of each secondary battery 10 are left open. Leave in this state for 10 to 20 days (leaving step).

  Thereafter, the second open circuit voltage is measured for each secondary battery 10 (voltage measurement step after standing). The first voltage measurement and the second voltage measurement may be performed while being restrained by the restraining device 20, or may be performed while the restraint is released. Then, the quality of the secondary battery 10 is determined based on the difference between the measured values of the open circuit voltage twice before and after being left (determination step).

  The restraining device 20 used here is for pressurizing a plurality of secondary batteries 10 together as shown in FIG. By using this, it is possible to determine the quality of the plurality of secondary batteries 10 in parallel. It is desirable that the pressing force at this time be equal to or higher than the pressing force when a plurality of the secondary batteries 10 are combined and used as a battery pack. For example, it is desirable to apply a pressure of about 700 to 800 kPa or more to each secondary battery 10.

  When restraining the restraint device 20, the secondary batteries 10 are arranged so that the large side surfaces 15 (side surfaces corresponding to the surfaces of the electrode plates) face each other, and the pressure plates 21 are sandwiched therebetween. Further, the outside is sandwiched between the restraining plates 22. Then, as shown by the arrows in the figure, the two constraining plates 22 are pressurized in a direction to approach each other. Thereby, all the inserted secondary batteries 10 are pressurized simultaneously.

  Here, the side surface of the pressure plate 21 is formed slightly smaller than the large side surface 15 of the secondary battery 10. That is, only the portion excluding the edge of the large side surface 15 of the secondary battery 10 is pressurized. This is because, in the large side surface 15 of the battery case 11, at the boundary with the bottom portion 16 and the vicinity of the lid 11 b, the pressure is not easily transmitted to the internal electrode plate portion 12 even if pressure is applied. Thereby, the internal electrode plate part 12 can be appropriately pressed without applying an excessive force to the battery case 11.

  In this embodiment, the positive and negative electrode plates of the secondary battery 10 are each formed by applying an active material to a band-shaped base material. This active material is usually not applied to the side edges of the substrate. Therefore, there are portions where the base material is exposed at both end portions of the electrode plate. The pressure plate 21 of this embodiment desirably presses at least the entire area where the active material is applied in the depth direction in FIG.

  By pressing in this way, the distance between the electrode plates can be reduced inside the secondary battery 10. Therefore, when a very small piece of metal is mixed between the electrode plates, it can be forcibly short-circuited at that point. If there is no short circuit, the voltage will hardly drop even if left under pressure. In other words, the measured values of the open circuit voltage twice before and after the neglect are almost the same.

  However, even if it is a minute one, if there is a short-circuited part, the voltage value to be measured drops because it is gradually discharged inside. The worse the short circuit, the greater the drop. Therefore, in this embodiment, if the width of the open circuit voltage drop before and after being left is larger than a predetermined value, it is determined that there is a short-circuited portion. Thus, by applying pressure with the restraining device 20, even a small short-circuited portion can be reliably detected.

  That is, the presence / absence of a defective portion can be determined based on the difference between the measured values of the two open circuit voltages. Those that are judged to be defective are excluded and do not flow to the next process. By passing only those determined to be non-defective products to the next process, a manufacturing method for manufacturing only good secondary batteries can be obtained.

[Experiment 1]
Furthermore, the present inventor has confirmed from Experiment 1 that, by applying pressure, it is possible to short-circuit a minute short-circuit portion that has been difficult to detect in the past. For this purpose, a secondary battery in a minute short-circuit state was assembled by intentionally mixing a metal piece of about 0.5 mm into the electrolyte. And after performing initial charging / discharging, it restrained to the restraint device 20. FIG. In this experiment 1, it was left at room temperature (around 20 ° C.) while monitoring the open circuit voltage. In Example 1, a pressurized state was applied from the first day to the 19th day. In Example 2, no pressure was applied from the first day to the ninth day, and the pressure state was maintained from the tenth day to the 19th day. In Comparative Example 1, no pressure was applied from the first day to the 19th day.

The result of Experiment 1 is shown in FIG. In Example 1, as indicated by the solid line L1, the open circuit voltage decreased from the first day. In Example 2, as indicated by a broken line L2, the pressure greatly decreased from the 10th day when the pressing was started. In Comparative Example 1, as shown by the alternate long and short dash line L3, it did not drop so much. Therefore, it was confirmed that by applying pressure, the amount of voltage drop increased, and defective products could be reliably determined in a short period of time. In this experiment 1, the voltage was appropriately measured during the standing for verification of the effect. However, according to the present invention, it is not necessarily necessary to measure the standing voltage. This is the same in Experiment 2 described below.
[End of Experiment 1]

  In this embodiment, it is more preferable that the step of measuring the open circuit voltage after being left is performed at a low temperature. For example, it may be performed at 0 ° C. or lower. The micro short circuit product is in a state where current is flowing though it is weak. That is, it is not electrically unloaded. By keeping this at a low temperature, the voltage drop becomes larger. On the other hand, a good product without a short-circuit point is unloaded because no current flows. Therefore, the state does not change even when measured at low temperatures. That is, at a low temperature, the difference in voltage change between the non-defective product and the defective product becomes more prominent. Therefore, since the S / N ratio for determination is improved by measuring at a low temperature, the determination becomes easier.

[Experiment 2]
The inventor further performed Experiment 2 to confirm this point. In Experiment 2, a micro short-circuit product manufactured in the same manner as in Experiment 1 (Example 4) was compared with a good product in which no metal piece was mixed (Comparative Example 2). In either case, after the initial charge and discharge, the restraint device 20 was restrained. While monitoring the open circuit voltage, it was allowed to stand and measure at room temperature (23 ° C.) from day 1 to day 10 and at low temperature (0 ° C.) from day 11.

The results of Experiment 2 are shown in FIG. In this figure, the result of Example 4 is indicated by a solid line L4, and the result of Comparative Example 2 is indicated by a one-dot chain line L5. The difference between Example 4 and Comparative Example 2 was not so great up to the 10th day when measured at room temperature. However, when the measurement was performed at a low temperature from the 10th day, a clear difference was obtained. Therefore, it was confirmed that defective products can be reliably judged in a shorter period of time by measuring at a low temperature.
[End of Experiment 2]

  Furthermore, if the leaving process is performed at a high temperature, it is possible to determine a defective product in a shorter time. For example, it is left in an environment of about 45 to 70 ° C. in a state of being restrained as described above. It has been found that in high temperature conditions, dissolution and precipitation of minute metallic foreign matters in the secondary battery proceed faster. Therefore, this can shorten the neglect period. In other words, it is more desirable that the standing process is at a high temperature and the measurement process is at a low temperature.

  As described in detail above, according to the pass / fail judgment method of this embodiment, the battery is left in a charged state, and the open circuit voltage is measured before and after that. However, if it can be measured properly at the time of charging, measurement before leaving is unnecessary. Moreover, since the center part of the secondary battery 10 is pressurized at the time of leaving, a minute short circuit location can be short-circuited more reliably. In addition, if left in a high temperature environment, the presence or absence of a short circuit can be determined more reliably. Furthermore, if the measurement after standing is performed in a low-temperature environment, the determination is easier. This is a quality determination method for reliably detecting the presence or absence of a minute short-circuited point in a flat secondary battery.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the flat electrode body of the battery that is the subject of the present invention is not limited to the wound type, but can be applied to a stacked type in which a plurality of electrode plates are alternately stacked positively and negatively and stored in a case. Further, as a restraining jig, when all the restrained secondary batteries 10 are determined to be non-defective products, those that can be used as they are as a battery pack may be used.

It is sectional drawing which shows the secondary battery of determination object. It is explanatory drawing which shows the press apparatus of this form. 6 is a graph showing the results of Experiment 1. FIG. 6 is a graph showing the results of Experiment 2. FIG.

Explanation of symbols

10 Secondary battery 11 Battery case 12 Electrode plate part 20 Restraint jig

Claims (4)

In a secondary battery quality determination method for determining quality of a secondary battery in which a flat electrode case is enclosed in a flat case,
A charging process for charging the secondary battery;
A voltage measurement process before leaving to measure the open circuit voltage of the secondary battery after charging;
A leaving step of leaving the charged secondary battery for a predetermined period of time while applying pressure to the electrode body from the outside of the case;
A step of measuring a voltage after being left to measure an open circuit voltage of the secondary battery after being left;
When the voltage drop from the voltage measured in the voltage measurement step before leaving to the voltage measured in the voltage measurement step after leaving is larger than a predetermined value, it is determined as a defective product, and otherwise And a determination step for determining that the battery is a non-defective product. The quality determination method for the secondary battery according to claim 1,
A method for determining a quality of a secondary battery, wherein the measuring step is performed in a low temperature environment of 0 ° C. or less. In the quality determination method of the secondary battery according to claim 1 or 2,
A method for determining a quality of a secondary battery, wherein the leaving step is performed in a high temperature environment of 45 ° C. or higher and 70 ° C. or lower. In a secondary battery manufacturing method for manufacturing a secondary battery in which a flat electrode body is sealed in a flat case,
An assembly process of a secondary battery in which a flat electrode body is enclosed in a flat case;
A charging process for charging the secondary battery;
A voltage measurement process before leaving to measure the open circuit voltage of the secondary battery after charging;
A leaving step of leaving the charged secondary battery for a predetermined period of time while applying pressure to the electrode body from the outside of the case;
A step of measuring a voltage after being left to measure an open circuit voltage of the secondary battery after being left;
When the voltage drop from the voltage measured in the voltage measurement step before leaving to the voltage measured in the voltage measurement step after leaving is larger than a predetermined value, it is determined as a defective product, and otherwise And a determination step for determining that the battery is a non-defective product.

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