JP4609046B2 - Laminated battery inspection method - Google Patents

Description

  The present invention relates to a method for inspecting the hermeticity of an outer case in a battery using a laminated film having a metal foil as an intermediate layer, such as a polymer lithium ion secondary battery, as the outer case.

  The battery outer case needs to be sealed with a strong material such as a metal can because the electrolytic solution made of the solvent and the electrolyte dissolved in it is liquid, but the electrolyte is solidified or gelled Etc. have been proposed, and non-solid materials such as metal cans have been used as exterior cases. As one of them, a laminate film having a metal foil as an intermediate layer is used as an outer case of a battery, and the weight and thickness can be reduced compared to a battery using a metal can.

  When using a laminate film with this metal foil as an intermediate layer as an exterior case and sealing the power generation element, arrange the power generation element so that it is sandwiched between two laminate films larger than the power generation element, and heat the part where the laminate films meet Then, heat-welding resins in the inner layer of the laminate film are welded together and sealed, or the power generation element is housed in a bag-like laminate film and the sealing portion is heated to heat the inner layer of the laminate film. A method of sealing by welding weldable resins together is employed.

  However, when the lead portion is pulled out as an external terminal from the power generation element, the lead portion is pulled out from the sealed portion of the laminate film. The metal foil is exposed on the end face of the laminate film. The metal foil and the lead part come into contact with each other, or the heat-welding resin in the inner layer of the laminate film melts too much due to heating during sealing. As a result, the metal foil is exposed, the metal foil and the lead portion come into contact with each other, and there is a problem that the metal foil is short-circuited with both the positive electrode lead, the negative electrode lead, or both the positive and negative electrode leads.

  Moreover, in the apparatus using a battery, the metal foil which comprises the intermediate | middle layer of a laminate film may contact with a part of apparatus circuit, and may be electrically connected to a positive electrode or a negative electrode.

  On the other hand, the metal foil constituting the middle layer of the laminate film is electrically insulated from the power generation element by the heat welding resin of the inner layer of the power generation element and the laminate film. By doing so, when a minute crack occurs in the heat-welding resin layer of the inner layer of the laminate film, the metal foil may be exposed, and this portion may come into contact with the electrolyte inside the battery. When the metal foil is in contact with the electrolyte inside the battery and insulation between the metal foil and the positive and negative electrode leads cannot be maintained, the metal foil becomes a potential on the shorted lead side, and part of the battery is charged and discharged. A phenomenon occurs in which a battery is formed, the metal foil is repeatedly dissolved and deposited, and the metal foil becomes sparse. As this phenomenon progresses, the metal foil has holes, and the metal foil can no longer serve as a barrier layer to prevent moisture from entering from the outside of the battery. The nature will be impaired.

Therefore, it is indispensable to establish an electrical insulation state between the metal foil constituting the middle layer of the laminate film and the positive electrode lead or the negative electrode lead of the power generation element. For this reason, a resin layer composed of three layers is used as a sealing material in the lead part (see, for example, Patent Document 1), or an insulating film is formed with an ultraviolet curable resin on the exposed portion of the metal foil at the end of the laminate film. Thus, a device for maintaining insulation is proposed (see, for example, Patent Document 2).
JP 2000-268789 A Japanese Patent Laid-Open No. 2004-87422

  However, in the process of sealing the sealing part of the laminated battery, the lead is deformed, the inner heat-welding resin layer is melted too much, the lead and the metal foil are short-circuited, or the inner layer is extremely thin. If the battery is charged / discharged in a state where the insulation between the positive and negative electrode leads and the metal foil cannot be maintained, and the heat-welding resin in the inner layer of the laminate film is cracked, the metal is linked with the charging / discharging of the battery. As the foil melts and precipitates, the metal foil becomes partially roughened, preventing the ingress of moisture from the outside of the battery, and the water and electrolyte react to generate gas, causing the laminate battery to swell. Will not function as a battery.

  Whether the heat-welding resin in the inner layer of the laminate film is cracked is a problem that cannot be determined even by conducting an insulation test between the metal foil and the positive and negative electrode leads.

  Therefore, the present invention provides the moisture resistance of the battery due to the progress of dissolution / deposition of the metal layer even when the electrical insulation between the metal foil and the lead portion is impaired and the heat-welding resin of the inner layer of the laminate film is cracked. An object of the present invention is to provide an inspection method for electrically determining whether or not a crack that lowers moisture resistance of a metal foil is contained in a heat-welding resin layer of an inner layer of a laminate film. To do.

In order to solve the above-mentioned conventional problems, the inspection method of the present invention includes a positive electrode plate, a separator holding an electrolyte, and an electrode plate group consisting of a negative electrode plate in an outer case made of a laminate film having a metal foil as an intermediate layer. In the method for inspecting a battery in which the positive electrode lead and the negative electrode lead connected to one end of each of the positive electrode plate and the negative electrode plate are pulled out from the seal portion of the outer case, the heat weldability of the inner layer of the laminate film is stored When the resin layer is cracked and the metal foil and the electrolyte are in contact with each other, and the electrical insulation between the metal foil and the lead portion is damaged, the voltage of the partial battery is the measured by applying a current between the metal foil, heat welding cracks the laminated film inner layer to lower the moisture resistance of the metal foil from the voltage of the partial cell It characterized by examining whether the entered resin layer, as the current value, it is preferable discharge by constant resistance of 100Keiomega～1emuomega, or a discharge by 1μA~10μA current.

According to this invention, it can be test | inspected whether the crack which reduces the moisture resistance of metal foil is contained in the heat welding resin layer of a laminate film inner layer .

  Hereinafter, an embodiment of an inspection method of the present invention will be described with reference to the drawings.

  In FIG. 1, the longitudinal cross-sectional schematic of the polymer lithium ion secondary battery which is one Example of this invention is shown.

  A positive electrode plate 5 formed by applying the positive electrode active material layer 3 to the positive electrode current collector 1 and a negative electrode plate 6 formed by applying the negative electrode active material layer 4 to the negative electrode current collector 2 are interposed via the separator 11. The electrode plate group 12 is arranged in an insulated state and the positive electrode current collector plate 7 and the negative electrode current collector plate 8 are laminated so as to sandwich them. The electrode plate group 12 is composed of three layers of a heat-welding resin layer, a metal foil layer, and a surface resin layer. It is housed in an outer case 13 made of a laminated film having a structure, and the electrolyte is held in the separator 11 in a polymerized state (not shown).

  A positive electrode lead 9 is welded to the positive electrode current collector plate 7, and one end of the negative electrode lead 10 is welded to the negative electrode current collector plate 8, and the positive electrode lead 9 and the negative electrode lead 10 are arranged to face each other. The seal portion from which the positive electrode lead 9 is pulled out of the outer case 13 and the other seal portion from which the negative electrode lead 10 is pulled out are sealed by thermal welding.

As a method for inspecting the hermeticity of such a laminated battery, a current is passed between the positive electrode lead or the negative electrode lead and the metal foil, and a crack in the heat-welding resin layer of the inner layer of the outer case occurs from the amount of voltage change. Inspect the presence or absence of contact between the metal layer and the electrolyte.
The direction of the current flowing between the metal foil and the lead portion may be either direction, but it is preferable to flow the current in the direction in which the metal foil is dissolved and precipitated. In addition, in order to charge and discharge a current through a partial battery formed by minute cracks in the heat-welding resin layer of the laminate film inner layer, an electric current may be forced to flow using an external power source. Alternatively, a fixed resistor may be connected between the metal foil and the lead portion to supply current from the battery.

  The voltage is measured immediately after the current starts to flow or immediately after the fixed resistor is connected, because a specific voltage determined by the formed partial battery is generated. Therefore, it is preferable to measure the voltage after a certain time. . When the metal foil is made of a material different from the power generation element of the battery, the voltage of the partial battery rapidly decreases even with a small current. Moreover, when the area of the crack of the heat-welding resin is large, the capacity of the partial battery is increased, and the voltage attenuation is reduced with respect to the discharge capacity.

  Although it differs depending on the battery system, as a result of examination by the inventors, in order to continue the discharge reaction of the partial battery formed by minute cracks in the heat-weldable resin layer of the laminate film, the discharge with a current of 1 μA to 10 μA, Or it turned out that a partial battery voltage needs to be 0.8V or more even after discharging 50 ms to 2000 ms with a constant resistance of 100 kΩ to 1 MΩ. In the partial battery formed by the crack of the heat-welding resin layer, if the voltage remains in the partial battery even if the partial battery is discharged, only when the charge / discharge reaction continuously occurs, The metal foil constituting one layer becomes rough due to the charge / discharge reaction, and a path through which moisture from the outside enters is formed. Conversely, when no voltage remains due to the discharge of the partial battery, the charging / discharging reaction does not continue, so the metal foil constituting the middle layer of the laminate film does not become roughened, and the path through which moisture from the outside enters Will not be formed. It was found that the boundary of the partial battery voltage at that time was 0.8V. Thus, in order to determine the presence or absence of micro cracks in the heat-welding resin layer of the laminate film inner layer, discharge with a constant resistance of 100 kΩ to 1 MΩ or discharge with a current of 1 μA to 10 μA is performed for a time of 50 ms to 2000 ms. It is preferable to measure the voltage after elapse of time, and to determine that a voltage less than 0.8V is a non-defective product and that 0.8V or more is a defective product.

Hereinafter, the inspection method of the present invention will be described in detail. However, the inspection method of the present invention is not limited to these examples.
Example 1
In FIG. 1, first, a positive electrode plate 5 formed by applying a positive electrode active material layer 3 to a positive electrode current collector 1 made of aluminum foil, and a negative electrode active material layer 4 applied to a negative electrode current collector 2 made of copper foil. A separator 11 made of a microporous film made of polypropylene resin is disposed between the negative electrode plates 6 formed in this way. The positive electrode current collector plate 7 made of aluminum and the negative electrode current collector plate 8 made of copper are laminated so as to sandwich them, thereby constituting an electrode plate group 12. A positive electrode lead 9 is welded to the positive electrode current collector plate 7 made of aluminum, and a negative electrode lead 10 is welded to the negative electrode current collector plate 8 made of copper. The active material layer application surfaces of the positive electrode plate 5 and the negative electrode plate 6 are opposed to the separator 11. The positive electrode lead 9 and the negative electrode lead 10 are arranged so as to face each other, and the electrode plate group 12 is fixed with a tape (not shown).

  Furthermore, an exterior case 13 composed of a laminate film having a three-layer structure of a heat-welding resin layer composed of a polypropylene (hereinafter abbreviated as PP) resin layer, a metal layer composed of an aluminum foil, and a surface layer composed of a PP resin layer from the inside. The electrode plate group 12 is accommodated therein.

  The seal portion of the laminate film 13 from which one positive electrode lead 9 is pulled out is thermally welded together with the positive electrode lead 9 and sealed. A polymer precursor mixed with a non-aqueous electrolyte is injected from the seal portion of the laminate film 13 from which the other negative electrode lead 10 is drawn.

  As a pre-sealing treatment, charging is performed at a constant current of 0.7 mA for 8 hours, and vacuum deaeration (−100 MPa, 10 seconds) is performed. Thereafter, the battery was heated at 60 ° C. for 15 minutes to give a polymer precursor as a polymer. The sealing part of the laminate film is thermally welded together with the negative electrode lead 10 and sealed.

  In the polymer lithium ion secondary battery thus obtained, when an aluminum foil that is the same kind of metal as the positive electrode current collector 1 is used as a metal foil constituting the middle layer of the laminate film, the aluminum foil and the negative electrode The lead 10 was connected with a fixed resistance having a resistance value of 1 MΩ, and the voltage applied to the fixed resistance after 200 ms had elapsed after the connection was measured.

  The potential of the aluminum foil with respect to the negative electrode lead 10 has an electromotive force of 1.7 V in an unloaded state, but the voltage applied to the fixed resistor is rapidly attenuated by connecting the fixed resistor. Those having a voltage applied to the fixed resistance after 200 ms of 0.8 V or more were determined as defective. When the battery having a voltage applied to the fixed resistance of 0.8 V or higher was disassembled and the PP resin heat-welding resin layer as the inner layer of the laminate film was observed with a microscope, minute cracks were observed.

Further, a defective battery n = 10 (average voltage 1.3 V) with a voltage applied to the fixed resistance after 200 ms has passed after the fixed resistor connection is 0.8 V or more and a non-defective battery n = 10 (less than 0.8 V) ( For the average voltage of 0.1 V), as a holed acceleration test of the aluminum foil constituting the middle layer of the laminate film, the negative electrode lead 10 and the aluminum foil constituting the middle layer of the laminate film were short-circuited, and 60 ° C. It was left in a hot and humid tank of -90% RH. Two weeks later, the batteries were taken out from the high-temperature and high-humidity tank and observed. As a result, the batteries of 0.8 V or higher were swollen by 1.0 mm or more for both n = 10. This is presumably because moisture entered from the outside of the battery, reacted with the non-aqueous electrolyte, and gas was generated. Batteries with a voltage of less than 0.8 V were not observed even when n = 10. Although insulation was not maintained between the negative electrode lead 10 and the aluminum foil constituting the middle layer of the laminate film, it was confirmed that sufficient moisture resistance was ensured.
(Example 2)
In the polymer lithium ion secondary battery obtained in the same manner as in Example 1, a fixed resistance of 100 kΩ was connected, and after 50 ms, a fixed resistance of 1 MΩ was connected, and after 2000 ms, at a constant current of 1 μA. After 2000 ms, the voltage after 50 ms was measured at a constant current of 10 μA.

As a result, in each case, the battery having a voltage of 0.8 V or higher was disassembled, and when the thermal resin layer made of PP resin as the inner layer of the laminate film was observed with a microscope, minute cracks were observed. .
In addition, as a result of performing the same aluminum foil perforation acceleration test as in Example 1 on defective batteries n = 10 having a voltage of 0.8 V or higher and non-defective batteries n = 10 having a voltage of less than 0.8 V, the voltage was reduced to 0.1. Batteries of 8V or higher were swollen by 1.0 mm or more for both n = 10, but no battery swollen was observed for batteries of less than 0.8V at n = 10.
From the above, a discharge with a constant resistance of 100 kΩ to 1 MΩ or a discharge with a current of 1 μA to 10 μA is performed between the aluminum foil constituting the middle layer of the laminate film and the negative electrode lead, and a time of 50 ms to 2000 ms has elapsed. It was clarified that the presence or absence of cracks in the inner layer of the laminate film can be determined by measuring the voltage after the treatment, and setting a value less than 0.8 V as a non-defective product and a value of 0.8 V or more as a defective product.

  The inspection method of the present invention can easily inspect the sealing property of an outer case made of a laminate film having a metal foil as an intermediate layer, and can obtain a highly reliable laminate battery. Useful as a power source for equipment.

1 is a schematic vertical sectional view of a polymer lithium ion secondary battery according to an embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Negative electrode collector 3 Positive electrode active material layer 4 Negative electrode active material layer 5 Positive electrode plate 6 Negative electrode plate 7 Positive electrode current collector plate 8 Negative electrode current collector plate 9 Positive electrode lead 10 Negative electrode lead 11 Separator 12 Electrode plate group 13 Exterior Case

Claims (2)

A positive electrode plate, an electrode plate group consisting of a separator for holding an electrolyte, and a negative electrode plate are housed in an outer case made of a laminate film having a metal foil as an intermediate layer, and one end of each of the positive electrode plate and the negative electrode plate is connected. In the battery inspection method in which the positive electrode lead and the negative electrode lead are drawn to the outside from the seal portion of the outer case, the heat-welding resin layer of the inner layer of the laminate film is cracked, and the metal foil and the electrolyte are in contact with each other. The voltage of the partial battery formed in a state and when the electrical insulation between the metal foil and the lead part is impaired is measured by passing a current between the lead and the metal foil, and the part and wherein the crack to reduce the moisture resistance of the metal foil from the voltage of the battery is examined whether the entered heat-welding resin layer of the laminated film inner layer Inspection method of the laminate battery that. 2. The method for inspecting a laminated battery according to claim 1, wherein the current value is a discharge with a constant resistance of 100 kΩ to 1 MΩ or a discharge with a current of 1 μA to 10 μA.