JP2009289757A - Method of manufacturing laminated secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a laminated secondary battery with productivity enhanced. <P>SOLUTION: The method of manufacturing the laminated secondary battery includes a cell element forming step of forming an electronic conductive insulation layer between electrodes, an inspection step of inspecting short circuiting between electrodes of the cell elements obtained by the previous step to separate products into accepted products which are determined without short circuiting and rejected products which are determined with short circuiting, a laminated battery cell element forming step laminating a plurality of sheets of the accepted products separated by the above step, and a packaging step of housing the laminated cell elements obtained by the above step. The inspection step applies an AC signal between the electrodes of the secondary battery before charging to measure its impedance (1), and determines an existence of short circuit between electrodes based on the differences of the measured results of the impedance of a normal cell and a short-circuiting cell presented on a complex plane. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a stacked secondary battery, and more particularly, to a method for manufacturing a stacked secondary battery with improved productivity.

  In recent years, various devices such as a camera-integrated VTR device, an audio device, a portable computer, and a mobile phone have been reduced in size and weight, and there is an increasing demand for higher performance of batteries as power sources of these devices. In particular, in order to cope with the downsizing of the device main body, it is required to simultaneously reduce the size of the battery and ensure the capacity, that is, to increase the energy density. Under such circumstances, lithium secondary batteries are capable of realizing a high energy density and are being actively developed because they have a high voltage.

  Known electrolytes for lithium batteries include (1) a non-aqueous electrolyte comprising a lithium salt and a non-aqueous solvent, (2) a gel electrolyte containing a non-aqueous electrolyte in a polymer, and (3) a solid electrolyte. Yes. When a non-aqueous electrolyte is used, a separator is disposed between the positive electrode and the negative electrode. When a gel electrolyte or a solid electrolyte is used, these layers are disposed between the positive electrode and the negative electrode. The separator can be omitted.

  A lithium secondary battery that has been put into practical use has a cylindrical structure in which a positive and negative thin electrode plate and a separator that separates the electrode plates from each other are spirally wound. And as an electrode board, what made electrode active materials, such as a lithium compound, adhere to conductive foil, such as copper foil and aluminum foil, is used. Such a secondary battery is assembled as follows.

  First, the positive and negative electrode plates and the two separators wound on the reels are unwound from the reel, and the separator, the negative electrode plate, the separator, and the positive electrode plate are stacked in a spiral shape by a winder. The positive and negative electrode plates are electrically joined to the positive and negative electrode plates, respectively, to form a cylindrical battery element. Next, a short circuit inspection is performed on the battery element (dry state), and only acceptable products are sent to the next step and canned, and an electrolytic solution is injected to obtain a battery. The short circuit inspection is a method of performing a direct current continuity test, an alternating current continuity test, a high voltage insulation test, and the like on the semi-finished battery element before injecting the electrolytic solution, and is properly used depending on the purpose.

  On the other hand, the stacked secondary battery that has been attracting attention recently has a structure in which a battery element composed of a pair of flat positive and negative electrodes and their electron conductive insulating layers is stacked. The thickness can be reduced compared to the secondary battery, and further, there is an advantage that it can be formed into a sheet shape or a card shape.

  However, the stacked secondary battery is still in the examination stage, and there are many problems to be solved about the manufacturing method considering its productivity. This invention is made | formed in view of such a situation, The objective is to provide the manufacturing method of the laminated type secondary battery with improved productivity.

That is, the gist of the present invention is that a battery element forming step having a battery function for forming an electron conductive insulating layer comprising a gel electrolyte layer or a solid electrolyte layer that ionically bonds them between electrodes, the step Inspecting the short circuit between the electrodes of the battery element obtained in the above, the inspection process to classify the acceptable product judged as no short circuit and the rejected product judged as short-circuited, multiple acceptable products sorted in the process Including a stacked battery element forming step of stacking and connecting in parallel, and a packaging step of storing the stacked battery element obtained in the process in a case, and the inspection step includes (1) electrodes of the secondary battery before the first charge applying an AC signal of the impedance was measured between, you determine the presence or absence of a short circuit between the electrodes based on the measurement result the difference in impedance of the normal rechargeable battery and short-circuit the battery represented in the complex plane, that Method for producing a multilayer type lithium secondary battery according to symptoms, resides in.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the laminated type secondary battery with improved productivity is provided, and the industrial value of this invention is large.

(A) is side explanatory drawing of the cell unit of an example of the secondary battery with which the short circuit inspection method of this invention is applied, (b) is upper surface explanatory drawing of the cell unit shown to (a). The typical explanatory view of an example of the short circuit inspection device used at an inspection process. Explanatory drawing of the measurement example of the impedance of the normal battery and short circuit battery which were represented to the complex number plane. Explanatory drawing of an example of the method of determining a short circuit from the measurement result of the impedance represented on the complex number plane. Explanatory drawing of another example of the method of determining a short circuit from the measurement result of the impedance represented on the complex number plane. Explanatory drawing of another example of the method of determining a short circuit from the measurement result of the impedance represented on the complex plane. The typical explanatory view of other examples of the short circuit inspection device used at an inspection process. Schematic explanatory drawing of still another example of a short circuit inspection device used in the inspection process. Explanatory drawing of an example of the short circuit determination method using the time change of a voltage. Explanatory drawing of another example of the short circuit determination method using the time change of a voltage. (A) is a partial cross-sectional side view of an example of a laminated secondary battery obtained by the production method of the present invention, and (b) is an example of the laminated secondary battery shown in (a) (the case lid is opened). FIG.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1A is an explanatory side view of an example of a battery element, and FIG. 1B is an explanatory top view of the battery element shown in FIG.
FIG. 2 is a schematic explanatory view of an example of a short-circuit inspection apparatus used in the inspection process according to the present invention, FIG. 3 is an explanatory view of an example of measuring impedances of a normal battery and a short-circuit battery expressed in a complex plane, and FIG. FIG. 5 is an explanatory diagram of an example of a technique for determining a short circuit from an impedance measurement result represented on a complex plane; FIG. 5 is an explanatory diagram of another example of a technique for determining a short circuit from an impedance measurement result represented on a complex plane; FIG. 6 is an explanatory diagram of still another example of a technique for determining a short circuit from the impedance measurement result represented on the complex plane. In each of the complex planes, the vertical axis represents the complex imaginary part Z ″, and the horizontal axis represents the complex real part Z ′.

FIG. 7 is a schematic explanatory view of another example of the short-circuit inspection apparatus used in the inspection process according to the present invention.
FIG. 8 is a schematic explanatory diagram of still another example of a short-circuit inspection apparatus used in the inspection process according to the present invention, FIG. 9 is an explanatory diagram of an example of a short-circuit determination method using time change of voltage, and FIG. It is explanatory drawing of another example of the short circuit determination method using the time change of a voltage.

  FIG. 11A is a partial cross-sectional side view of an example of a stacked secondary battery obtained by the manufacturing method of the present invention, and FIG. 11B is a stacked secondary battery shown in FIG. It is a plane explanatory view of an example (state where the case lid is opened).

  The manufacturing method of the present invention includes a battery element forming process, an inspection process, a laminated battery element forming process, and a packaging process. When a gel electrolyte or a solid electrolyte is used as the electrolyte, these layers are disposed between the positive electrode and the negative electrode, and the parator can be omitted.

<Inspection process> In this process, a short circuit between the electrodes of the battery element obtained in the battery element formation process described later is inspected, and a pass product determined to be short-circuited and a reject product determined to be short-circuited. Sort. In the case of a secondary battery in which a gel electrolyte or a solid electrolyte is used as an electrolyte, a gel electrolyte layer or a solid electrolyte layer is formed as an electron conductive insulating layer between a pair of electrodes and has a battery function. The battery element that is inspected.

  In the case of a battery element that does not have a battery function, the inspection process can be performed by a DC continuity test, an AC continuity test, a high voltage insulation test, and the like according to a conventionally known method.

  In the case of a battery element having a battery function, the inspection process needs to be performed by a method different from the above. The reason is as follows. That is, in the method based on the direct current continuity test, it cannot be distinguished whether the observed continuity is due to a short circuit or due to a charging process for a battery element that has already been injected with an electrolyte and functions as a battery. Even in the AC continuity test, it cannot be distinguished whether the observed continuity is due to a short circuit or the electrolyte. The high voltage insulation test cannot be used because a high voltage is applied to a functioning battery and even the battery may be destroyed.

  Of course, since the battery element already functions as a battery, it is possible to detect a defective product by charging itself. However, the initial charging is usually performed over a day or more, and depending on the degree of short circuit, abnormal behavior may finally appear at the stage where the charging has progressed considerably. Therefore, the production efficiency is very low in the method of determining a defect from the abnormal behavior during charging.

Therefore, when the battery element includes the present invention, a battery function, the inspection process, and measuring the impedance by applying an AC signal between the electrodes of the illustrated (1) first charge before the secondary battery or less Inspection method (see FIGS. 2 to 6), (2) Inspection method for measuring voltage between electrodes of secondary battery before initial charge (see FIG. 7), (3) Between electrodes of secondary battery before initial charge Among the inspection methods (refer to FIGS. 8 to 10) for measuring the change with time of the voltage between the electrodes during energization and / or after being opened, the method (1) is used.

  (1) Inspection method for measuring impedance: Impedance Z is a resistance value including a phase component measured when an AC signal having a frequency f is applied between electrodes, and is measured with a measured voltage V expressed in a complex number. It means a value obtained from current I by Z = V / I. The complex number Z is expressed as Z = Z ′ + iZ ″ by its real part Z ′ and imaginary part Z ″. i is the square root of -1. The complex plane is represented by taking a complex real part Z ′ on the x-axis on the xy plane and a complex imaginary part Z ″ on the y-axis, and the measured impedance value Z = Z ′ + iZ ″ is expressed in coordinates ( x, y) = (Z ′, Z ″). Z ′ and Z ″ are values related to the characteristics of the battery and can be used for evaluating the state of the battery. Further, the trajectory drawn by the points (Z ′, Z ″) measured for a plurality of frequencies can be derived by performing an appropriate analysis.

That is, the impedance of the battery shows a specific impedance locus according to the used electrode type, electrolyte type, electrode area, electrode thickness, electrolyte layer thickness, temperature, and the like. When the electrodes are not short-circuited, the impedance trajectory in the state before the first charge is linear on the low frequency side, and in particular shows a behavior in which Z ″ diverges. As shown in the figure, it can be seen from the fact that the external resistor R is connected in parallel in the equivalent circuit of the battery, the impedance locus tends to draw an arc on the low frequency side. The divergence becomes more prominent as it goes to the low frequency side.

  The inspection method (1) in the present invention has been completed based on the above facts, and it is determined whether or not there is a short circuit between the electrodes based on the difference in the measurement results of the impedance of the normal battery and the short circuit battery expressed in the complex plane. It is a method to do. In addition, although measuring the impedance between battery electrodes is known per se, the measurement of the impedance so far is for evaluation of interface resistance, charge double layer capacity, bulk resistance of the electrolyte layer, etc. This is done to elucidate the behavior of cycle deterioration from the change over time, and there is no example in which impedance is measured to judge the presence or absence of a short circuit between electrodes having an electrolyte as in the present invention.

  In the above inspection method, an AC signal is applied between electrodes, a current flowing between the electrodes, a voltage between the electrodes and a phase difference are measured, and an impedance between the electrodes is measured, which is called a so-called LCR tester. It is possible to use a known measuring device called a so-called impedance analyzer. Examples of the impedance analyzer include a model “SI1260 / SI1267” manufactured by Solartron, and examples of the LCR tester include a model “3502C high tester” manufactured by Hioki Electric Co., Ltd.

  The short circuit inspection apparatus (30) shown in FIG. 2 uses an impedance analyzer (20). Then, the positive electrode measurement terminals (8) and (9) adapted to be in electrical contact with the positive electrode terminal (4) of the battery and the negative electrode measurement adapted to be in electrical contact with the negative electrode terminal (5) of the battery. Terminals (10) and (11) and terminal retainers (6) and (7) for respectively pressing the positive terminal (4) and the negative terminal (5) are provided. Each of the measurement terminals (8), (9), (10) and (11) is connected to the impedance analyzer (20) side by means of lead wires (12), (13), (14) and (15), respectively. The terminals (16) and (17) are connected to the device side terminals (18) and (19). However, in the above device side terminals, (16) and (19) are device side terminals for voltage measurement, and (17) and (18) are device side terminals for current measurement.

  With the above configuration, for example, when an AC measurement signal having a frequency f is applied between the device-side terminals (16) and (19), the current flowing between the electrodes via the device-side terminals (17) and (18) is reduced. The phase difference with respect to strength and voltage can be measured, thereby further measuring the impedance between the positive and negative electrode plates of the battery. In order to increase the measurement accuracy of impedance, it is preferable that the measurement unit including the battery to be measured is kept at a constant temperature. In the above example, the voltage is applied to measure the current, but conversely, the current is applied to measure the voltage.

  The inspection method (1) in the present invention can be performed in the manner shown in the following steps 11 to 14 using the short circuit inspection apparatus (30) as described above.

(Step 11)
The positive terminal (4) is positioned on the terminal retainer (6), the negative terminal (5) is positioned on the terminal retainer (7), and is disposed in the short circuit inspection device (30). Further, the terminal retainers (6) and ( 7) is operated to bring each terminal into contact with the measurement terminal.

(Step 12)
An AC measurement signal is applied between the device side terminals (16) and (19) of the impedance analyzer (20), and if necessary, the impedance between the positive and negative electrodes of the battery is measured at a plurality of frequencies.

(Step 13)
When the measurement result of the impedance is out of the specified range, it is considered that the electrodes are short-circuited, and the inspected battery element is excluded as a defective product.

(Step 14)
When the measurement result of the impedance is within the specified range, the inspected battery element is sent to the next process as an acceptable product, and a plurality of battery cell units are stacked.

  Specifically, the determination of the short circuit by the above impedance measurement can be performed as follows.

  In the measurement example of the impedance of the normal battery and the short-circuit battery shown in FIG. 3, the impedance is measured over the range of 1 MHz to 20 mHz for the four batteries B1 to B4 before charging, and the obtained result is plotted on the impedance complex plane. It was obtained. As a result of actually charging and checking, it was confirmed that B1 to B3 batteries were normal, but B4 was short-circuited. When the result of impedance measurement is plotted on the impedance complex plane in this way, the short-circuited battery shows a very characteristic trajectory and can be easily identified. An improved method for determining a short circuit from the impedance measurement result is as follows.

(Short-circuit determination method shown in FIG. 4)
This determination method is a method in which the frequency of the AC signal to be measured is single, and the presence or absence of a short circuit is determined based on the position of the measurement point on the complex plane of the measured impedance.

  That is, the value of the normal battery impedance is on the locus M (see FIG. 3), and the measured value measured at the frequency F1 is in the region A1. However, in the short-circuit battery, for example, the measured value is a value represented by Z1. Furthermore, it may be a value represented by Z1a or Z1b depending on the degree of short circuit. In the present invention, it is determined that a short circuit has not occurred in the battery when the measured impedance value measured at the frequency F1 is in the region A1. More simply, the boundary line L can be used as a short-circuit determination criterion, and the determination can be made when the value of Z ″ exceeds Z ″ 1. In this case, since the determination can be made based on only a single numerical value, the apparatus is simplified. Since the location of the region A1 or the boundary line L may change depending on the frequency, the region or value that is normalized by the inspection frequency is reset. For example, in the case of measurement at the frequency F2, the measurement value of the normal battery is in the region A2, and in the case of the short-circuit battery, for example, the value is represented by Z2. Furthermore, since the location of the region A1 or the boundary line L may change depending on the configuration of the battery to be measured, a value that is normalized by the configuration of the battery to be inspected is reset.

  The frequency of the AC signal used for the measurement is usually 100 Hz to 0.1 mHz, preferably 10 Hz to 10 mHz. If the frequency is too high, it will be difficult to determine whether it is normal or short-circuited. If it is too low, the measurement will take time and the efficiency of the inspection will be reduced. The amplitude voltage of the AC signal used for the measurement is usually 100 mV to 1 μV, preferably 50 mV to 100 μV. If the amplitude voltage is too high, the accuracy of the inspection decreases due to the progress of charging or the like, and an excessive voltage is applied to the battery. If it is too low, the determination accuracy of the short circuit decreases from the viewpoint of the measurement accuracy.

(Short-circuit determination method shown in FIG. 5)
In this determination method, the frequency of the AC signal to be measured is two points, and the presence / absence of a short circuit is determined based on the inclination of the two points on the impedance complex plane.

  That is, when the impedance is measured at two points of the frequencies F3 and F4 for the battery to be measured, the impedance values of the normal battery are represented by Z3a and Z4b, and the slope of the straight line Y1 connecting these is S1. However, in the short-circuit battery, for example, the measured value is a value represented by Z3b and Z4b, and the slope of the straight line Y2 connecting these is S2. Therefore, a value in a range centering on S1 and allowing a measurement error is set, and if the slope is in this range, it can be determined that a short circuit has not occurred. In this case, since the determination is made from the relative positional relationship between the two measurement points, it is possible to determine with high accuracy and high accuracy with respect to the measurement time.

  (Short-circuit determination method shown in FIG. 6) In this determination method, the frequency of the AC signal to be measured is 3 points or more, and the presence or absence of a short circuit is determined by an arc approximated from 3 or more measurement points on the impedance complex plane. It is a method to do.

  That is, when the impedance is measured at four points of frequencies F5, F6, F7, and F8 for the measured battery, the impedance value of the normal battery is represented by Z5a, Z6a, Z7a, and Z8a, and each point is indicated by an arc. In the case of approximation, the arc cannot be approximated or the arc S1 has a very large radius. However, in the short-circuit battery, for example, the measured values are values represented by Z5b, Z6b, Z7b, and Z8b, and can be satisfactorily approximated by the arc S2. As the radius of the arc, a value correlated with the resistance of the short-circuit portion is obtained. Therefore, a reference value is set according to the required inspection accuracy, and when the radius of the approximate arc is greater than or equal to the reference value, it can be determined that no short circuit has occurred. The number of impedance measurement points can be from a minimum of three points. A larger number allows more accurate determination. However, when the number is too large, the measurement time becomes longer and the efficiency decreases.

  (2) Inspection method for measuring voltage: In a secondary battery having no abnormality, depending on the type of electrode used, the type of electrolyte, the temperature, etc., at the stage where the positive electrode and the negative electrode are ionically bonded, The inherent interelectrode voltage is shown. If the positive and negative terminals have not been conducted in the state before the initial charge, this value is in a certain range including variation. When the electrodes are short-circuited, the inherent inter-terminal voltage is discharged through the short circuit, and the measured voltage is close to zero. In addition, when foreign matter or the like is mixed in the electrode or electrolyte, the measured voltage differs from the voltage unique to the system.

  The inspection method (2) in the present invention has been completed based on the above facts, and is a method for determining the presence / absence of abnormality of the battery from the value of the voltage between the electrodes, and the voltage between the electrodes is within a certain range. The battery is accepted. And it is preferable that the measurement of said voltage measures an open voltage from the stability. In addition, the secondary battery to be inspected is preferably subjected to the inspection without the positive electrode and the negative electrode being conducted. Specifically, it is preferable to prevent the positive and negative terminals from coming into contact with a common metal plate. As a result, the accuracy of the inspection can be increased.

  In the above inspection method, a known measuring device called a voltmeter, which is a device for measuring a voltage between electrodes, can be used. For voltage measurement, a voltage measurement function associated with a charging device or another inspection device can be used. Since devices related to battery evaluation and inspection usually have a voltage measurement function in many cases, it is preferable to use the function because the cost can be reduced.

  The short circuit inspection apparatus (30) shown in FIG. 7 uses the voltage measurement apparatus (21) as a measurement for measuring the voltage between the electrodes. Then, the positive electrode measurement terminals (8) and (9) adapted to be in electrical contact with the positive electrode terminal (4) of the battery and the negative electrode measurement adapted to be in electrical contact with the negative electrode terminal (5) of the battery. Terminals (10) and (11) and terminal retainers (6) and (7) for respectively pressing the positive terminal (4) and the negative terminal (5) are provided. The positive electrode measuring terminal (8) and the negative electrode measuring terminal (11) are connected to the device side terminals (16) and (19) of the voltage measuring device (21) by lead wires (12) and (15), respectively. The short-circuit inspection device (30) shown in FIG. 7 further includes a current test device (22), and the device-side terminals (17) and (18) of the current test device (22) are respectively connected to the positive electrode measuring terminal ( 8) and (9) or the negative electrode measurement terminals (10) and (11) can be connected.

  With the above configuration, the open voltage of the battery can be measured by measuring the voltage between the device side terminals (16) and (19) of the voltage measuring device (21). In order to increase the voltage measurement accuracy, it is preferable that the measurement unit including the battery to be measured be kept at a constant temperature.

  The inspection method (2) in the present invention can be performed in the manner shown in the following steps 21 to 25 using the short-circuit test apparatus (30) as described above.

(Step 21)
The positive terminal (4) is positioned on the terminal retainer (6), the negative terminal (5) is positioned on the terminal retainer (7), and is disposed in the short-circuit test apparatus (30). Further, the terminal retainers (6) and ( 7) is operated to bring each terminal into contact with the measurement terminal.

(Step 22)
First, the relays (1) and (2) are opened, and a continuity test is performed through the device-side terminals (17) and (18) of the conduction test device (22). If there is continuity, it is determined that there is no problem in contact between the positive electrode measuring element (8) and the positive electrode terminal (4). Next, the relays (1) and (2) are closed, the relays (3) and (4) are opened, and a continuity test is performed between the device-side terminals (17) and (18) of the conduction test device (22). If there is conduction, it is determined that there is no problem in contact between the negative electrode measuring element (11) and the negative electrode terminal (5). Next, the relays (3) and (4) are closed. If there is a problem with the contact of the terminal, the process returns to step 1 to recontact the terminal.

(Step 23)
The voltage between the device side terminals (16) and (19) of the voltage measuring device (21) is measured. At this time, the open voltage can be measured by measuring in a mode in which no current flows.

(Step 24)
If the voltage measurement result is outside the specified range, it is considered that the battery is abnormal, and the inspected battery element is excluded as a defective product.

(Step 25)
When the voltage measurement result is within the specified range, the inspected battery element is sent to the next process as an acceptable product, and a plurality of battery cell units are stacked.

  Since the voltage measurement is not easily affected by the contact condition of the terminals, step 22 may be omitted to speed up the inspection and simplify the equipment.

  (3) Inspection method for measuring change with time of voltage: When the electrodes are not short-circuited, the voltage is increased or decreased by energization, and is slightly restored after being released. When the electrodes are short-circuited, a part of the energized current passes through the short-circuited portion, so that the voltage change rate becomes slow. When the degree of short circuit is large, the voltage does not change from a constant value. In addition, after the electrode is opened, the voltage is restored to the initial value with time because the discharge occurs through the short-circuit portion. Since these voltages are sufficiently low, these changes can be interpreted by treating the secondary battery before charging approximately as the capacitor C, regarding the short circuit portion as the short circuit resistance R, and assuming a parallel circuit of CR.

  The inspection method (3) in the present invention has been completed based on the above facts, and is a method for determining the presence or absence of a short circuit between electrodes based on the change over time of the measured voltage. The voltage during energization is measured as a change in the voltage of the secondary battery, and the voltage after the energization is stopped and released is measured as a change in the open voltage of the battery over time. Although the time-dependent change of the voltage during energization can be measured continuously or intermittently by the same voltmeter, it is preferably measured continuously. Although the change with time of the open voltage can be measured continuously or intermittently by the same voltmeter, productivity can be improved by measuring twice with a fixed time interval. Alternatively, the measurement may be performed at different time intervals using different voltmeters. In this case, the time required for the battery to be measured to occupy the terminal of the measuring instrument can be shortened, so that productivity is further improved.

  The direction of energization may be either charging or discharging, but the charging direction is preferable. The energization control may be based on voltage or current. A method of energizing until a predetermined voltage is obtained by a constant current is particularly preferable because control is easy. The amount of current to be energized is usually C / 10 to C / 100,000, preferably C / 100 to C / 1000. The higher the amount of current, the faster the measurement, but the measured value tends to be unstable and current control may be required. In the case of a lithium secondary battery, the predetermined voltage is usually 1 mV to 1 V, preferably 3 to 100 mV, and more preferably 5 to 50 mV. If the voltage is too high, it takes a long time to measure and an excessive voltage is applied to the battery before charging, which is not preferable. If the voltage is too low, the measurement accuracy decreases. After the inspection is completed, the residual voltage may be removed from the battery by short-circuiting the electrodes externally or energizing in the opposite direction as necessary.

  In the above inspection method, for example, a known measuring device called a voltmeter, which is a device for measuring a voltage between electrodes, can be used. For voltage measurement, a voltage measurement function associated with a charging device or other inspection device can be used. Furthermore, a known current supply device called a current source, which is a device for energizing between electrodes, can be used. When the presence or absence of a short circuit is determined based on the voltage increase rate and / or the increase curve during energization, the above two devices are used in combination. Moreover, you may use the apparatus which has the function of said 2 apparatuses in the same apparatus. For convenience, a charging device can be used. A similar device can also be used when the presence / absence of a short circuit is determined based on the voltage decrease rate and / or the decrease curve after opening. Further, after the voltage measuring devices 1 and 2 are arranged on the production line, the voltage is measured in the device 1, the voltage is again measured in the device 2, and the voltage at the time when the measured battery is transported from the device 1 to the device 2 The change with time may be measured.

  The short circuit inspection apparatus (30) shown in FIG. 8 uses the voltage measurement apparatus (21) as a measurement for measuring the voltage between the electrodes. Then, the positive electrode measurement terminals (8) and (9) adapted to be in electrical contact with the positive electrode terminal (4) of the battery and the negative electrode measurement adapted to be in electrical contact with the negative electrode terminal (5) of the battery. Terminals (10) and (11) and terminal retainers (6) and (7) for respectively pressing the positive terminal (4) and the negative terminal (5) are provided. The positive electrode measuring terminal (8) and the negative electrode measuring terminal (11) are connected to the device side terminals (16) and (19) of the voltage measuring device (21) by lead wires (12) and (15), respectively. The short-circuit inspection device (30) shown in FIG. 8 further includes an electrical current test device (22), and the device side terminals (17) and (18) of the electrical current test device (22) are connected to the positive electrode measurement terminal ( 8) and (9) or the negative electrode measurement terminals (10) and (11) can be connected. Depending on the form of measurement, a controller (23) connected to the cables (24) and (25) for controlling energization and voltage measurement is provided.

  With the above configuration, the voltage of the battery is measured by energizing the battery to be measured by the current test device (22) and measuring the voltage between the device side terminals (16) and (19) of the voltage measuring device (21). I can do it. In order to increase the voltage measurement accuracy, it is preferable that the measurement unit including the battery to be measured be kept at a constant temperature.

  The inspection method (3) in the present invention can be performed in the manner shown in the following steps 31 to 35 using the short circuit inspection device (30) as described above.

(Step 31)
The positive terminal (4) is positioned on the terminal retainer (6), the negative terminal (5) is positioned on the terminal retainer (7), and is disposed in the short circuit inspection device (30). Further, the terminal retainers (6) and ( 7) is operated to bring each terminal into contact with the measurement terminal.

(Step 32)
First, the relays (1) and (2) are opened, and a continuity test is performed through the device-side terminals (17) and (18) of the conduction test device (22). If there is continuity, it is determined that there is no problem in contact between the positive electrode measuring elements (8) and (9) and the positive electrode terminal (4). Next, the relays (1) and (2) are closed, the relays (3) and (4) are opened, and a continuity test is performed between the device-side terminals (17) and (18) of the conduction test device (22). If there is continuity, it is determined that there is no problem in contact between the negative electrode measuring elements (10) and (11) and the negative electrode terminal (5). Next, the relays (3) and (4) are closed. If there is a problem with the contact of the terminal, the process returns to step 1 to recontact the terminal.

(Step 33)
First, the voltage between the device side terminals (16) and (19) of the voltage measuring device (21) is measured and set to a voltage measurement value of 1. Next, the relays (2) and (3) are opened, and the conduction test device (22) is operated for 10 seconds. Next, the relays (2) and (3) are closed, and the voltage between the device side terminals (16) and (19) of the voltage measurement device (21) is measured to obtain a voltage measurement value of 2.

(Step 34)
When the difference between the voltage measurement value 1 and the voltage measurement value 2 is equal to or less than the specified value, the battery is considered to be abnormal, and the inspected battery element is excluded as a defective product.

(Step 35)
When the measured voltage value is within the specified range, the inspected battery element is sent to the next process as an acceptable product, and a plurality of battery cell units are stacked.

  Since the voltage measurement is not easily affected by the contact condition of the terminals, step 2 may be omitted to speed up the inspection and simplify the equipment.

  In the inspection method (3) in the present invention, the above steps 33 and 34 can be replaced with the following steps 33-1 and 34-1.

(Step 33-1)
First, the relays (2) and (3) are closed, and the conduction test device (22) is operated for a maximum of 10 seconds. During the energization, the voltage between the device side terminals (16) and (19) of the voltage measuring device (21) is continuously observed, and the energization is stopped when the measured voltage value becomes the measured voltage value 3, and the relay Open the electrodes by opening (2) and (3). Next, after the release, the voltage between the device side terminals (16) and (19) of the voltage measuring device (21) is continuously measured for a certain time to obtain a voltage curve 1.

(Step 34-1)
The voltage curve 1 is approximated by an exponential function: V = A × exp (−t / T)), and the relaxation time T is calculated. Here, V is the measured voltage, A is a constant, and t is the measurement time. When the relaxation time T is less than a certain value, it is considered that the battery is abnormal, and the inspected battery element is excluded as a defective product.

  Specifically, the determination of the short circuit by the voltage measurement can be performed as follows.

(Short-circuit determination method shown in FIG. 9)
In FIG. 9, curve (a) shows a case where the short circuit is not caused, (b) shows a case where the light is short-circuited, and (c) shows a case where the material is severely short-circuited. These curves are created based on data obtained as follows. That is, the current test is performed until the voltage between the electrodes reaches 30 mV using the above-described current test device (22). On the other hand, whether or not there is a short circuit is confirmed by actual charging. In the case of a short circuit, the voltage increase rate was slow, and in the case of a severe short circuit, the voltage increase stopped at a constant value and did not reach 30 mV. Therefore, as shown in the short circuit determination method shown in FIG. 9, in the present invention, it is possible to determine the presence or absence of a short circuit based on the rising speed and / or rising curve of the voltage during energization. For example, as shown in FIG. 9, it is possible to determine that a battery that satisfies the criteria such as the time to reach the voltage V1 within t1 or the voltage value at the time t2 equal to or higher than V2 is normal.

(Short-circuit determination method shown in FIG. 10)
In FIG. 10, curve (a) shows a case where the short circuit is not caused, (b) shows a case where the light is short-circuited, and (c) shows a case where the material is severely short-circuited. These curves are created based on data obtained as follows. That is, a constant current is applied using the above-described conduction test device (22), and after the interelectrode voltage reaches 30 mV, the energization is stopped and the change over time of the interelectrode open voltage is measured. As a result, the presence / absence and the extent of the short-circuit were confirmed, and when the short-circuit was not performed, the voltage decrease rate was slow, and the voltage decrease rate was increased according to the degree of the short-circuit. Therefore, as shown in the short circuit determination method shown in FIG. 10, in the present invention, it is possible to determine the presence or absence of a short circuit based on the voltage decrease rate and / or the decrease curve after opening. For example, as shown in FIG. 10, the voltage value at time t3 is V4 or more, the ratio of the voltage at time t3 to the voltage V3 immediately after opening is a certain value or more, and the initial slope of the curve is more than a certain value. It can be determined that the battery is normal.

By the way, in the case of a lithium secondary battery, even if it is not completely short-circuited, if insulation is impaired as much as possible, dendrite is generated from there and short-circuiting proceeds. Thus, in the lithium secondary battery, it is important to understand the extent of the short circuit as described above.

Specific examples of secondary batteries targeted by the present invention include lithium secondary batteries, nickel / cadmium secondary batteries, nickel / hydrogen secondary batteries, etc., and gel electrolytes or solid electrolytes were used as electrolytes. Secondary batteries are preferred. In particular, when an inspection method for measuring impedance is employed in the above-described inspection step, high-accuracy and high-speed inspection can be performed on a battery whose opposing electrode area is less than 200 cm ² . And since the short circuit in a lithium secondary battery carries the danger of ignition, the short circuit test | inspection is important also on safety. In the following, a lithium secondary battery using a gel electrolyte will be mainly described. In this case, an electrode forming step is provided before the battery element forming step.

<Electrode formation process>
In this step, a positive electrode and a negative electrode are formed. In the case of a lithium secondary battery using a gel electrolyte, the positive electrode and / or the negative electrode include, for example, an active material containing layer provided on a current collector and capable of occluding and releasing lithium ions, and ions formed in the layer. Mobile phase. In addition, any one electrode (usually negative electrode) can also be comprised with metals themselves, such as lithium foil.

  In the above electrode, a positive electrode active material layer having voids and / or a negative electrode active material layer having voids is formed on a current collector, and an electrolytic solution for forming a gel electrolyte is applied to the surface of the active material layer. It can be formed by a step of forming a gel electrolyte after impregnating with. Here, the gel electrolyte is a substance mainly composed of an electrolytic solution and a gelled polymer, the electrolytic solution is held in a polymer network, and the fluidity as a whole is remarkably lowered. In the case of such a gel electrolyte, characteristics such as ion conductivity are similar to those of a normal electrolytic solution, but fluidity and volatility are remarkably suppressed and safety is improved.

  The positive electrode active material layer having voids and / or the negative electrode active material layer having voids are formed by applying an electrode coating material containing an active material, a binder and a solvent on a current collector and drying. I can do it. The gel electrolyte can be obtained by (1) a method of cooling a polymer to room temperature by using an electrolyte containing a polymer that can be gelled by cooling in a heated state, or (2) electrolysis containing a monomer. It can be formed by a method of polymerizing a monomer using a liquid.

  As the current collector, a metal foil such as an aluminum foil or a copper foil is usually used, and the thickness is appropriately selected, but is usually 1 to 50 μm, preferably 1 to 30 μm.

Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. As the transition metal, Fe, Co, Ni, Mn and the like are used. Specific examples of the inorganic compound used for the positive electrode active material include transition metal oxides such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ , lithium such as lithium nickelate, lithium cobaltate, and lithium manganate. And transition metal sulfides such as TiS ₂ , FeS, and MoS ₂ . Examples of the positive electrode active material made of an organic compound include polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, and N-fluoropyridinium salts. The particle size of the positive electrode active material is usually 1 to 30 μm, preferably 1 to 10 μm.

  Examples of the negative electrode active material include carbon-based active materials such as graphite and coke. Moreover, as a negative electrode active material, lithium alloys, such as oxides and sulfates, such as silicon, tin, zinc, manganese, iron, and nickel, lithium metal, Li-Al, Li-Bi-Cd, Li-Sn-Cd, Lithium transition metal nitride, silicon and the like can also be used. The particle size of the negative electrode active material is usually 1 to 50 μm, preferably 15 to 30 μm.

  Examples of the binder include inorganic compounds such as silicate and glass and various resins. Examples of the binder resin include alkane polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene, unsaturated polymers such as polybutadiene and polyisoprene, polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N—. Polymers having a ring such as vinylpyrrolidone, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide, and other acrylic polymers, Fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride and polytetrafluoroethylene, CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide, polyvinylidene such as polyvinyl acetate and polyvinyl alcohol Alcohol polymers, polyvinyl chloride, halogen-containing polymers such as polyvinylidene chloride, conductive polymers such as polyaniline. The molecular weight of these resins is usually 10,000 to 3,000,000, preferably 100,000 to 1,000,000.

  If necessary, the electrode can contain additives that exhibit various functions such as a conductive material and a reinforcing material. The conductive material is not particularly limited as long as it can be mixed with an active material in an appropriate amount to impart conductivity, and usually includes carbon powders such as acetylene black, carbon black and graphite, and fibers and foils of various metals. . In order to increase the stability and life of the battery, trifluoropropylene carbonate, vinylene carbonate, catechol carbonate, 1,6-Dioxaspiro [4,4] nonane-2,7-dione, 12-crown-4-ether, etc. Can be used. Furthermore, various inorganic and organic spherical, plate-like, rod-like, and fibrous fillers can be used as the reinforcing material.

  In preparation of the electrode coating material, the amount of the binder to be added to 100 parts by weight of the active material is usually 0.1 to 30 parts by weight, preferably 1 to 20 parts by weight. An example of the solvent used is N-methylpyrrolidone. In addition, a ball mill, a sand mill, a biaxial kneader, or the like is used for preparing the electrode paint.

The electrolytic solution mainly includes a lithium salt and a solvent. LiPF ₆ or LiClO ₄ is preferred as the lithium salt. As the solvent, one or a mixture of two or more selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and acyclic carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is preferable. The concentration of the lithium salt in the electrolytic solution is usually 0.5 to 2.5 mol / L.

  In order to increase the stability, performance, and life of the battery, the electrolyte includes, for example, trifluoropropylene carbonate, vinylene carbonate, catechol carbonate, 1,6-Dioxaspiro [4,4] nonane-2,7-dione, 12- Additives such as crown-4-ether may be added.

  The molecular weight of the gelled polymer forming the gel electrolyte is usually 10,000 to 5,000,000, preferably 100,000 to 1,000,000.

  Specific examples of the gelable polymer used for forming the gel electrolyte include polymers having a ring such as polyvinyl pyridine and poly-N-vinyl pyrrolidone, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, Acrylic derivative polymers such as poly (methyl acrylate), poly (ethyl acrylate), poly (acrylic acid), poly (methacrylic acid) and polyacrylamide, fluororesins such as polyvinyl fluoride and polyvinylidene fluoride, CNs such as polyacrylonitrile and polyvinylidene cyanide Examples thereof include group-containing polymers, polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol, and halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride.

  As the monomer used for forming the gel electrolyte, a reactive unsaturated group-containing monomer is preferably used, and specific examples thereof include acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, methacrylic acid. Ethyl acid, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N diethylaminoethyl acrylate, N, N dimethyl Aminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile, N-vinyl pyrrolidone, diethylene glycol Diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, and the like.

  Examples of the method for polymerizing the monomer include a method using heat, ultraviolet rays, and electron beams, but a method using ultraviolet rays is preferable from the viewpoint of productivity. In this case, in order to effectively advance the reaction, a polymerization initiator that reacts with ultraviolet rays can be blended in the electrolytic solution. Examples of the ultraviolet polymerization initiator include benzoin, benzyl, acetophenone, benzophenone, Michler's ketone, biacetyl, benzoyl peroxide and the like. On the other hand, in thermal polymerization, a polymerization initiator can be used for reaction control. As thermal polymerization initiators, 1,1-di (tertiarybutylperoxy) -3,3,5-trimethylcyclohexane, 2,2-bis- [4,4-di (tertiarybutylperoxycyclohexyl) propane ], 1,1-di (tertiary butyl peroxy) -cyclohexane, tertiary butyl peroxy-3,5,5-trimethyl hexanonate, tertiary butyl peroxy-2-ethyl hexanonate, dibenzoyl per Examples include oxides.

  The ratio of the polymer in the gel electrolyte is usually 0.1 to 80% by weight, preferably 1 to 50% by weight. The ratio of the polymer to the solvent is usually 0.1 to 50% by weight, preferably 1 to 30% by weight.

<Battery element formation process>
In this step, an electron conductive insulating layer is formed between the electrodes obtained in the electrode step. Here, the electron conductive insulating layer in the case of a lithium secondary battery using a gel electrolyte is an electrolyte layer that ionically bonds the positive electrode and the negative electrode, that is, a gel electrolyte layer. In the case of a lithium secondary battery using a solid electrolyte, the electron conductive insulating layer is a solid electrolyte layer.

  The gel electrolyte layer is obtained by gelling the electrolyte solution for forming the gel electrolyte. The formation of the electrolyte layer between the electrodes is as follows. (1) In the electrode forming step, when applying the electrolyte for forming the gel electrolyte on the surface of the active material layer having the gap, the gap is impregnated and gelled. Gelation is performed after an amount sufficient to form an electrolyte layer is formed, and then a method of laminating a positive electrode and a negative electrode through an electrolyte layer formed on an electrode, or (2) The electrode forming step can be performed by a method of sandwiching a gel electrolyte sheet formed separately.

  In particular, the method (1) is characterized in that at least one gel electrolyte of the positive electrode and the negative electrode and at least a part of the gel electrolyte constituting the electrolyte layer are continuous. The thickness of the gel electrolyte constituting the electrolyte layer continuous with the gel electrolyte of the positive electrode and / or the negative electrode is usually 1 to 100 μm, preferably 5 to 50 μm. The positive electrode, the electrolyte layer, and the negative electrode are preferably laminated in a flat manner.

The battery element illustrated in FIGS. 1A and 1B includes a positive electrode (1) and a negative electrode (2) and an electrolyte (3) (gel electrolyte layer or solid electrolyte layer) that ionically bonds them. It consists Te that. Contact name connected positive terminal to the sign (4) is positive (1) in FIG. 1, reference numeral (5) represents a negative terminal connected to the negative electrode (2), both are subjected to the above-described inspection process This is a necessary element.

<Laminated battery element formation process>
In this step, a plurality of acceptable products (battery elements) sorted in the inspection step described above are stacked. The number of stacked layers is appropriately determined depending on the required voltage and capacity, but is usually 2 to 25, preferably 2 to 10. In the present invention, since the short circuit inspection is performed at the stage of the battery element before stacking as described above, an advantage that rejected products can be eliminated from the manufacturing process at an early stage occurs, and productivity is improved. In particular, when a large number of battery elements are stacked in the stacked battery element forming step, the above advantages are remarkable. The numerous inspection processes described above are appropriately selected depending on the type of secondary battery to be manufactured.

<Packaging process>
In this step, the laminated battery element obtained in the above step is housed in a case. As the case, a shape-variable case having flexibility, flexibility, flexibility and the like is preferably used. Examples of the material include plastic, polymer film, metal film, rubber, and a thin metal plate. Specific examples of the case include a bag made of a polymer film such as a plastic bag, a vacuum packaging bag or vacuum pack made of a polymer film, a vacuum packaging bag or vacuum pack made of a laminate material of a metal foil and a polymer film. And a can formed of plastic, or a case in which the periphery is sandwiched between plastic plates and fixed by welding, bonding, fitting, or the like.

  Each of the above steps is performed in the following environment. In other words, the first half of the electrode formation process (the process of forming an active material layer having voids on the current collector) does not contain an electrolyte solution, and moisture is removed by a subsequent drying process, so moisture management is necessary. It can be performed in a normal atmosphere. The other steps are performed in a room (dry room) that is dehumidified.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded.
The raw materials used were pretreated as follows. That is, the powder was vacuum-dried at 240 ° C. for 24 hours, the resin and the lithium salt were dried at 110 ° C. for 4 hours, and the monomer was dehydrated with molecular sieves. Further, as the electrolytic solution, an electrolytic solution dehydrated in advance for a lithium battery was used. In the following examples, “parts” means “parts by weight”.

Example 1
<Preparation of electrode paint>
A positive electrode paint and a negative electrode paint were prepared by kneading and dispersing in a ball mill for 8 hours according to the following composition.

[Table 1]
(Positive electrode coating composition)
LiCoO ₂ (active material): 90.0 parts Acetylene black (conductive material): 5.0 parts Polyvinylidene fluoride (binder): 5.0 parts N-methylpyrrolidone (solvent): 100.0 parts

[Table 2]
(Negative electrode coating composition)
Graphite (active material): 90.0 parts Polyvinylidene fluoride (binder): 10.0 parts N-methylpyrrolidone (solvent): 150.0 parts

<Preparation of electrolyte>
The raw materials used for the preparation of the electrolytic solution are as follows. And it melt | dissolved at 110 degreeC according to the composition shown below, and prepared uniform electrolyte solution.

[Table 3]
(Electrolytic solution composition)
Propylene carbonate (PC) (electrolytic solution): 40.8 parts
Ethylene carbonate (EC) (electrolyte): 40.8 parts
LiClO ₄ (supporting electrolyte): 10.4 parts
Polyacrylonitrile (molecular weight: 150,000): 8.0 parts

<Electrode forming step and battery element forming step>
First, a positive electrode coating material was applied to a 20 μm thick aluminum foil with a doctor blade so as to have a film thickness of 100 μm and dried to obtain a sheet on which a positive electrode active material layer having voids was formed. Thereafter, a calendar process was performed to obtain a final layer thickness of about 80 μm. Similarly to the above, a negative electrode coating material was applied on a copper foil having a thickness of 20 μm so as to have a thickness of 100 μm and dried to obtain a sheet on which a negative electrode active material layer having voids was formed. Thereafter, a calendar process was performed to obtain a final layer thickness of about 70 μm. All the steps up to here were performed in a normal environment. Then, after re-drying the coating film at 120 ° C., it was punched into a predetermined shape.

  Next, the electrolyte solution heated to 90 ° C. was applied and impregnated on each of the above sheets with a doctor blade. At that time, by setting the blade gap larger than usual, an amount more than the amount that fills the gap was applied, and the electrolyte was present on the surface. Then, it cooled to 0 degreeC, the electrolyte solution impregnated and the electrolyte solution which exists on the surface were gelatinized, the gel electrolyte which followed the space | gap in an active material layer and an electrolyte layer was formed, and the positive electrode and the negative electrode were obtained.

<Inspection process>
Next, the positive electrode and the negative electrode were laminated with the electrolyte layer side inside, and a battery element composed of the positive electrode, the electrolyte layer, and the negative electrode was formed, and the battery element was inspected for the presence or absence of a short circuit as follows. That is, as shown in FIGS. 1A and 1B, the positive electrode terminal (4) and the negative electrode terminal (5) are connected to the positive electrode and the negative electrode, respectively, and the impedance analyzer (30) of the short-circuit inspection device (30) shown in FIG. 20), measure the impedance by applying an AC signal (frequency: 1 Hz, amplitude voltage: 10 mV) between the electrodes before the first charge, and according to the short-circuit determination method shown in FIG. Sorted into rejected products.

<Laminated battery element formation process and packaging process>
Next, the above three acceptable battery elements are stacked so that the same poles overlap each other, and after attaching the collective positive electrode terminal and the collective negative electrode terminal to each positive electrode terminal and each negative electrode terminal, enclose them in a vacuum pack with a lid. Then, a stacked lithium secondary battery was prepared (see FIG. 11).

1: Positive electrode 2: Negative electrode 3: Electrolyte layer 4: Positive electrode terminal 5: Negative electrode terminal 6, 7: Terminal presser 8, 9, 10, 11: Measurement terminals 12, 13, 14, 15: Lead wires 16, 17, 18, 19: Device side terminal 20: Impedance analyzer 21: Voltage measuring device 22: Energization test device 23: Controller 24, 25: Cable 30: Short circuit inspection device 40: Collective positive terminal 50: Collective negative terminal 60: Case 61: Case lid Ry1: Relay 1
Ry2: Relay 2
Ry3: Relay 3
Ry4: Relay 4

Claims (5)

A battery element forming step having a battery function for forming an electron conductive insulating layer comprising a gel electrolyte layer or a solid electrolyte layer that ionically bonds them between electrodes, and an electrode of the battery element obtained in the step Inspecting the short circuit between the inspection products that are judged as having no short circuit and the rejecting products that are judged to be short-circuiting, laminating a plurality of acceptable products sorted in the relevant process and connecting them in parallel Including a battery element forming process and a packaging process in which the laminated battery element obtained in the process is housed in a case, and the inspection process includes (1) applying an AC signal between the electrodes of the secondary battery before the first charge. Measuring the impedance and determining the presence or absence of a short circuit between the electrodes based on the difference in impedance measurement results of a normal battery and a short-circuit battery represented on a complex plane. A method for manufacturing a secondary battery. The manufacturing method according to claim 1 , wherein in (1), the frequency of the AC signal to be measured is single, and the presence or absence of a short circuit is determined based on the position of the measurement point on the complex plane of the measured impedance. The manufacturing method according to claim 1 , wherein in (1), the frequency of the AC signal to be measured is two points, and the presence or absence of a short circuit is determined based on the slope of the two points on the impedance complex plane. 2. The manufacturing according to claim 1 , wherein in (1), the frequency of the AC signal to be measured is three or more, and the presence or absence of a short circuit is determined by an arc approximated from three or more measurement points on the impedance complex plane. Method. In the above (1), The process according to any one of claims 1 to 4, at least one point of the frequency of the AC signal to be measured is 10Hz or less.