JP2005209528A - Secondary battery inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery inspection method which can detect a secondary battery that will have the risk of a micro short circuit sooner or later even if the micro short circuit does not occur at the moment of the inspection, since the inspection method can detect incorporation of a minute amount of metal impurities. <P>SOLUTION: The method can bring the state of the micro short circuit between electrodes by decreasing an initial charging temperature IT, increasing the viscosity of an electrolyte, and increasing the height H of copper deposited on a negative electrode 5, even when a minute amount of copper piece 12, such that does not make the micro short circuit occur in a conventional charging manner, is incorporated into an electrode. Therefore, the method can detect the battery having the electrode, into which a minute amount of the copper is incorporated, by detecting the micro short circuit. Preferably, the initial charging temperature IT is set in a range from -20°C to 5°C. This can detect nearly half the secondary batteries having the incorporation of copper, and can improve the reliability of the secondary batteries. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention detects defective products of a secondary battery, and particularly relates to a secondary battery inspection method for detecting a small amount of metal impurities mixed in an electrode.

  When metal impurities or metal wear debris from the battery manufacturing facility are mixed in the positive electrode of the secondary battery, they are dissolved electrochemically by the potential of the positive electrode during the initial charge, and diffuse in the electrolyte and reach the negative electrode. However, it may be deposited at the potential of the negative electrode to cause a micro short between the positive and negative electrodes. Then, by detecting the presence or absence of such a micro short circuit, it is possible to detect the mixing of metal impurities. Patent Documents 1 and 2 are shown below as examples.

  FIG. 6 shows a method for determining the micro short-circuit failure of the secondary battery disclosed in Patent Document 1. The defective battery sorting method of Patent Document 1 includes three steps. After selecting a plurality of batteries of a predetermined production unit and charging each battery, the terminal voltage V101 of each battery is measured and recorded in the pre-aging voltage measurement step 101, and the battery is subjected to the battery in the aging process for a predetermined time. , The terminal voltage V102 of each battery is measured in the post-aging voltage measurement calculation step 102, and the V102 average value and standard deviation σ for a plurality of batteries in a predetermined manufacturing unit are calculated. Next, ΔV is calculated and recorded in the voltage difference calculation calculation step 103 before and after aging, and the ΔV average value and standard deviation σ of the voltage difference before and after aging for each of a plurality of batteries in a predetermined manufacturing unit are calculated. From these measurement results, in post-aging voltage determination first step 104, the post-aging voltage V102 is compared with the post-aging voltage lower limit standard value set in advance for each battery, and is lower than the post-aging voltage lower limit standard value. If it is, it is determined as a defective product.

  FIG. 7 shows a method for detecting a micro short between electrodes disclosed in Patent Document 2. When the battery is cooled to bring the electrolyte into a solid state, ion migration and diffusion in the electrolyte does not occur, and the charge transfer reaction resistance and electric double layer at the interface between the positive electrode, the negative electrode active material and the electrolyte The capacity can be neglected, and can be considered as an approximately simple circuit as shown in FIG. 7 (R121 is an electric resistance by a separator mainly interposed between the positive electrode and the negative electrode, C122 is a capacitor component on the battery structure, and R123 is Sealing plate, current collector plate, case, and electrical resistance of wiring part when measuring impedance). Here, since the electric resistance R121 is a component that is greatly affected by a micro short circuit, and C122 is a capacitance generated by a capacitor component between both electrodes, the electrode group such as the opposing area of both electrodes and the distance between the electrodes is not suitable. It is a component that is greatly affected by the configuration state. When a short-circuited battery is discharged for a long time after charging, the discharge capacity decreases, or when the battery voltage drops, the resistance of foreign matter such as deposited metal that short-circuits the positive and negative electrodes rather than the electrical resistance of the separator itself However, since it is lower by two digits or more, for example, the electrical resistance due to the separator can be ignored, and the resistance value of R121 can be said to be the resistance of foreign matters. Therefore, the presence or absence of a short circuit can be determined based on the resistance value of the electric resistance R121.

Further, Patent Documents 3 to 5 and the like are also disclosed for other secondary battery inspection methods.
JP 2001-228224 A (paragraph 0008, FIG. 1) JP 2003-45500 (paragraphs 0023-0024, FIG. 2 and FIG. 3) JP-A-4-65067 JP 2002-343446 A JP 2000-88933 A

  The detection methods of Patent Documents 1 and 2 are generally performed at room temperature. At this time, metal impurities deposited on the negative electrode are widely diffused and deposited on the negative electrode. Therefore, since the deposited metal impurities may not reach the positive electrode, there are secondary batteries that do not lead to the occurrence of microshorts. In addition, when the amount of metal impurities mixed in the secondary battery is very small, the probability of occurrence of a micro short circuit further decreases. However, in secondary batteries containing metal impurities, the metal impurities are deposited on the negative electrode even if no micro short-circuit has occurred. When a compressive force is applied when the case is stored, a micro short circuit is caused later due to the deposition portion of the metal impurities, which may cause a problem in that the battery performance may deteriorate. Therefore, it is necessary to remove such a secondary battery as a defective product in an inspection process before shipment as much as possible. However, the detection methods of Patent Document 1 and Patent Document 2 are problematic because the secondary battery in which minute metal impurities are mixed cannot be detected with high accuracy because the initial charging is performed in a room temperature environment.

  The present invention has been made to solve at least one of the above-described problems of the prior art, and can detect the mixing of a minute amount of metal impurities that are difficult to detect. An object of the present invention is to provide a method for inspecting a secondary battery that can detect a secondary battery that may cause a defect due to a minute amount of metal impurities in the future.

  In order to achieve the above object, the secondary battery inspection method according to claim 1 includes performing an initial charge of the secondary battery at a predetermined temperature at which metal impurities are localized and deposited on the electrode; And a micro-short detection step of detecting a micro-short between the positive electrode and the negative electrode after the initial charging step.

  The first charging is a charging process when charging is performed for the first time after manufacturing the secondary battery. The predetermined temperature is a temperature at which metal impurities are localized and deposited on the electrode. The micro short is a minute short between the positive electrode and the negative electrode of the secondary battery. As a cause of generation, for example, a case where metal ions are generated by depositing on the negative electrode can be mentioned. In the micro short detection step, a micro short is inspected. Examples of the inspection method include a method of measuring a voltage drop value in an aging (self-discharge) process. In the initial charge step, the initial charge is performed at a predetermined temperature at which metal impurities are localized and deposited on the electrode, so that metal impurities and the like can be deposited on the negative electrode with a peak shape having a sharp peak shape. Thus, it is possible to make a state in which a micro short circuit is likely to occur between the electrodes. By detecting a micro short in the micro short detection step, it is possible to detect a secondary battery mixed with a trace amount of metal impurities.

  As a result, since it is possible to detect a minute amount of metal contamination that cannot be detected by the conventional metal impurity detection method, even if there is no problem at the time of the inspection, a micro short circuit will occur in the future, and the battery performance will be improved. It is possible to remove a secondary battery having a possibility of deterioration by inspection, and the reliability of the secondary battery can be improved.

  The secondary battery inspection method according to claim 2 is the secondary battery inspection method according to claim 1, wherein the predetermined temperature in the initial charging step is within a range from -20 ° C to 15 ° C. Features.

  In a region where the predetermined temperature is −20 (° C.) or lower, metal ions, which are electrolyte ions, may be deposited on the negative electrode of the secondary battery, and microshorts may occur between the electrodes. In addition, in a region where the predetermined temperature is 15 (° C.) or more, the metal impurities are widely diffused and deposited on the negative electrode so as to have a gentle mountain shape. The detection accuracy of metal impurities does not increase. That is, as compared with the case where the predetermined temperature is room temperature, by setting the predetermined temperature within a range from −20 ° C. to 15 ° C., it is possible to detect the mixing of a minute amount of metal with high accuracy. Therefore, even if no micro short circuit has occurred, metal impurities are deposited on the negative electrode. It is possible to remove a secondary battery that may cause a micro short-circuit due to the depositing portion and deteriorate the battery performance as a defective product, and improve the reliability of the secondary battery. More preferably, the predetermined temperature is in the range of -20 ° C to 5 ° C. Thereby, the secondary battery in which the metal impurity is mixed can be detected more reliably.

  The secondary battery inspection method according to claim 4 is the secondary battery inspection method according to claim 1, wherein the micro-short detection step includes an aging step of leaving the charged secondary battery and an aging step end. And an inspection step of measuring a voltage value of the secondary battery later.

  In the aging step, the charged secondary battery is left unattended. In the inspection step, the voltage value of the secondary battery is measured after the aging step. Then, for example, a difference value between the voltage value before aging and the voltage value after aging is calculated, and if the difference value is larger than a predetermined reference value, it is determined that a micro short-circuit has occurred, and the difference value is the reference value. If the value is smaller than the value, it is determined that no micro-short has occurred.

  Thereby, since the micro short circuit can be detected in the micro short circuit detection step, the secondary battery mixed with a trace amount of metal impurities can be detected and removed as a defective product.

  According to the present invention, since it is possible to detect the mixing of a minute amount of metal impurities, even if a micro short circuit does not occur at the time of inspection, there is a possibility that a micro short circuit due to the metal impurity may occur in the future. The battery can be removed as a defective product, and an inspection method capable of improving the reliability of the secondary battery can be provided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a secondary battery inspection method and inspection apparatus according to the present invention will be described below in detail with reference to FIGS. FIG. 1 shows a partially enlarged sectional view of an electrode 11 of a secondary battery inspected by the inspection method according to the present invention. The electrode 11 is configured by sandwiching the positive electrode 4 and the negative electrode 5 with a separator 6 interposed therebetween. The positive electrode 4 is composed mainly of lithium nickelate (LiNiO2), and the negative electrode 5 is composed mainly of graphite. The separator 6 is made of polypropylene having a thickness of 25 (μm). The electrode 11 having this laminated structure is wound, a positive electrode current collector and a negative electrode current collector (not shown) are connected to the positive electrode 4 and the negative electrode 5, and an electrolyte is injected and sealed after being housed in a battery case (not shown). Thus, a secondary battery is formed. The electrolyte was 1.0 (mol / L) of lithium hexafluorophosphate (LiPF6) as a solute in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 3. What was melt | dissolved in the density | concentration was used.

  The experimental conditions will be described. The inspection apparatus (not shown) for a secondary battery according to the present invention includes a thermostat, and the thermostat is provided with a temperature control unit that can control the secondary battery to a predetermined temperature, and a charging unit that charges the secondary battery. ing. The temperature control unit of the thermostatic bath makes it possible to set the temperature of the secondary battery to a predetermined temperature. As the experimental sample, two types of secondary batteries were prepared: a mixed secondary battery in which 1 (μg) of copper was mixed in 1 (mm 2) of the positive electrode surface, and a non-mixed secondary battery in which copper was not mixed. The secondary battery of the experimental sample is not charged. The temperature of the secondary battery when the secondary battery is initially charged is defined as the initial charge temperature IT. The temperature inside the thermostatic chamber was set to −30, −20, 5, 15, 25, 60 (° C.) by the temperature controller, and the secondary battery was charged for the first time at each temperature. The number of experimental samples is 20 samples of mixed secondary battery and non-mixed secondary battery when the temperature in the tank is 15 (° C.), and mixed secondary battery and non-mixed battery at other tank temperatures. Ten samples of the secondary battery were tested.

  The experimental procedure is shown in the flowchart of FIG. The experimental flow is roughly divided into an initial charge / discharge process (steps S1 to S3), an aging process (steps S4 and S5), and an inspection process (steps S6 and S7). In step S1, by leaving an uncharged secondary battery in the thermostat for 5 hours, the initial charge temperature IT is set to any of −30, −20, 5, 15, 25, 60 (° C.). After the setting, the secondary battery is charged for the first time. The initial charging is performed by constant current-constant voltage charging (CCCV charging), and the current value during charging is 1/4 (C), the voltage value is 4.1 (V), and the charging time is 6 (hours).

  After the secondary battery is charged for the first time, the temperature inside the thermostatic chamber is set to 25 ° C. with the secondary battery inserted, and the secondary battery is left in the thermostatic bath for 5 hours so that the temperature of the secondary battery is approximately room temperature. To 25 ° C. Thereafter, constant current discharge is performed in step 2. The current value of constant current discharge is 1 (C), and the voltage value is 3 (V). After the constant current discharge in step S2 is completed, a charge / discharge repetition process is performed in step S3 after 10 minutes of rest time in which no charge / discharge is performed. The charging / discharging repetition process includes constant current-constant voltage charging (current 1 (C), voltage 4.1 (V), time 1.5 (hour), rest time 10 (minutes)), constant current discharging (current 1 (C) is a process in which one cycle combining voltage 3 (V) and pause time 10 (min)) is repeated for two cycles.

  In step S4, the secondary battery is charged for aging. Charging is performed by constant current-constant voltage charging (current 1 (C), voltage 3.75 (V), time 1.5 (hours)). After the aging charge is completed, the pre-aging voltage measurement of the secondary battery is performed, and the pre-aging voltage IV is obtained. The secondary battery for which the pre-aging voltage measurement has been completed is left aging (self-discharge) for 12 days in an environment of 25 ° C. in step S5.

  After the aging process is completed, the post-aging voltage measurement is performed in step S6, and the post-aging voltage AV is obtained. In step S7, a voltage drop value DV, which is a difference value between the pre-aging voltage IV obtained in step S4 and the post-aging voltage AV obtained in step S6, is calculated, and it is determined whether the product is a self-discharge defective product. The Specifically, a secondary battery having a voltage drop value DV of 25 (mV) or more is determined as a self-discharge defective product due to the occurrence of a micro short, and a secondary battery having a voltage drop value of 25 (mV) or less. Is determined not to be a self-discharge defective product because there is no occurrence of a micro short circuit.

  The experimental results are shown in the table in FIG. 3A and the graph in FIG. In FIG. 3B, the horizontal axis represents the initial charge temperature IT, and the vertical axis represents the self-discharge failure rate DR (%). Here, the self-discharge defective rate DR is a generation rate of self-discharge defective products with respect to the number of samples subjected to the charge experiment at a certain initial charge temperature IT. First, the self-discharge failure rate DR in the mixed secondary battery mixed with copper will be examined. In the mixed secondary battery, the higher the self-discharge defective rate DR, the more sensitive the battery mixed with copper as a defective product, and the higher the inspection accuracy for mixing metal impurities, which is preferable. 3A and 3B, the self-discharge failure rate DR of the mixed secondary battery when the initial charging temperature IT is 25 ° C is 5 (%), and the initial charging temperature IT is 15 (° C). It can be seen that there is a singular point where the self-discharge defective rate DR rises discontinuously at a temperature between the initial charging temperature IT of 25 (° C.) and 15 (° C.). In addition, when the initial charging temperature IT is in the range of 15 (° C.) to −20 (° C.), the self-discharge defective rate DR of the mixed secondary battery increases in proportion to the decrease in the initial charging temperature IT. It can be seen that the inspection accuracy of the detection of the mixing of metal impurities increases as the temperature IT during the initial charge decreases.

  In the mixed secondary battery, the mechanism by which the self-discharge failure rate DR increases as the initial charging temperature IT decreases will be described with reference to FIGS. FIG. 4A shows a state of the electrode 11 before the first charge in which the copper piece 12 is mixed on the surface of the positive electrode 4. The electrode 11 is in a state immersed in the electrolytic solution. Although the copper piece 12 exists between the positive electrode 4 and the separator 6, since the insulation between the copper piece 12 and the negative electrode 5 is maintained by the separator 6, a micro short circuit occurs between the positive and negative electrodes through the copper piece 12. Not done. When the secondary battery in the state of FIG. 4 (A) is initially charged, the copper piece 12 is electrochemically dissolved into copper ions by the voltage bias between the positive and negative electrodes during the initial charge, Spread. Since copper ions have a bivalent positive charge, an electrostatic force having a vector in the direction of the negative electrode 5 acts on the copper ions during charging of the secondary battery. Accordingly, the copper ions pass through the separator 6 and move toward the negative electrode 5, and are deposited on the negative electrode 5. At this time, the shape of copper deposited on the negative electrode 5 varies greatly depending on the initial charge temperature IT, and when the initial charge temperature IT is high, a gentle mountain-shaped precipitate shape as shown in FIG. When the temperature of the initial charging temperature IT is low, the precipitated copper 12b having a sharp mountain-shaped precipitation shape as shown in FIG.

  The relationship between the initial charging temperature IT and the precipitated copper deposition shape will be described with reference to FIG. FIG. 5 shows the force acting on the copper ions 13 in the electrolytic solution. The direction from the positive electrode 4 to the negative electrode 5 is defined as the Z direction, and the direction parallel to the positive electrode 4 and the negative electrode 5 is defined as the X direction. Moreover, although the copper ion 13 passes the separator 6, it demonstrates on the assumption that the separator 6 does not exist in FIG. First, how the precipitation shape is determined when the initial charging temperature IT is as high as 25 ° C. or higher will be described with reference to FIG. The electrostatic force EF1 having a positive vector in the Z direction acts on the copper ion 13, and the magnitude of the force is a constant value during charging. Moreover, although the force received from the electrolyte solution which is a fluid acts on the copper ion 13, if the distance DD between the positive electrode 4 and the negative electrode 5 is small, if the force in the Z direction can be ignored, X is in a direction parallel to the electrode. Receive direction force. Here, since the force received from the electrolytic solution is not constant depending on the state of the electrolytic solution, the maximum value of the force that can be received is defined as the maximum fluid force HF1 and is shown in FIG. Therefore, the direction of the resultant force vector of the electrostatic force EF1 and the maximum fluid force HF1 received by the copper ions 13 is within the range of the diffusion angle θ1 as shown in FIG.

  On the other hand, how the precipitation shape is determined when the initial charging temperature IT is in the range of −20 (° C.) to 15 (° C.) and is low will be described with reference to FIG. The copper ion 13 is subjected to an electrostatic force EF1 having a vector in the positive direction in the Z direction and a maximum fluid force HF2 received from the electrolyte in the X direction. Here, the electrolyte has a property that the viscosity increases as the temperature IT at the first charge decreases, and the fluidity of the electrolyte decreases as the viscosity increases, so the maximum flow that is the force in the X direction. The physical strength HF2 is smaller than the maximum fluid force HF1 in FIG. However, the magnitude of the electrostatic force EF1, which is the force in the Z direction, is constant during charging regardless of the initial charging temperature IT. Therefore, the direction of the resultant force vector received by the copper ions 13 is within the range of the diffusion angle θ2, as shown in FIG. As the initial charging temperature IT decreases, the viscosity of the electrolyte increases, so the maximum fluid force HF2 decreases and the diffusion angle θ2 also decreases.

  As described above, when the charging temperature IT is high, the copper ions 13 move toward the negative electrode 5 with a wide diffusion angle θ1, and therefore have a precipitation width W1 and a precipitation height H1 as shown in FIG. 4B. The precipitated copper 12a is deposited in a gentle mountain shape. On the other hand, since the copper ion 13 diffuses at a narrow diffusion angle θ2 when the temperature at the initial charging time IT is low, a sharp peak having a precipitation width W2 and a precipitation height H2, as shown in FIG. The deposited copper 12b is localized and deposited in a mountain shape. And since the mass of the mixed copper piece 12 is constant, the precipitation height H2 of the precipitation copper 12b is higher than the precipitation height H1 because the precipitation width W2 of the precipitation copper 12b is narrower than the precipitation width W1 of the precipitation copper 12a. Become.

  That is, as the initial charging temperature IT decreases, the precipitation width W2 of the precipitated copper 12b is narrow, the mountain-like peak is sharp, and the precipitation height H2 tends to increase. As the precipitation width W2 of the precipitated copper 12b becomes narrower and the precipitation height H2 becomes higher, the tip 14 of the precipitated copper 12b breaks through the separator 6 and contacts the positive electrode 4 as shown in FIG. Therefore, the probability of a self-discharge defective product increases due to a voltage drop exceeding a specified value when left after charging. Therefore, in the mixed secondary battery in which copper is mixed, a phenomenon occurs in which the self-discharge defective rate DR increases as the initial charge temperature IT decreases.

  Further, when examining the self-discharge defective rate DR of the non-mixed secondary battery not containing copper, the non-mixed secondary battery erroneously detected a battery not mixed with copper as the self-discharge defective rate DR increased as a defective product. This is not preferable. Therefore, from the experimental data, it can be seen from FIGS. 3A and 3B that the self-discharge failure rate DR of the non-mixed secondary battery is 0 (when the initial charging temperature IT is in the range of 60 (° C.) to −20 (° C.). %), No false detection has occurred and the inspection accuracy is good, but the self-discharge defective rate DR when the temperature IT at the initial charge is −30 (° C.) is 20 (%), and the false detection It can be seen that occurs. This mechanism will be described. When the secondary battery is charged, lithium ions in the electrolytic solution are occluded in the numerous pores of the negative electrode 5. However, the viscosity of the electrolyte solution increases as the temperature IT during the first charge decreases, and lithium ions are not occluded in the negative electrode 5 as the viscosity increases, so that the lithium ions that are not occluded are deposited on the negative electrode 5 as lithium metal. Then, the tip of the lithium metal deposited in the same manner as in FIG. 4C comes into contact with the positive electrode 4, thereby causing a micro short and a self-discharge failure. Therefore, in the method for detecting a metal impurity of the present invention, it can be seen that the region where the initial charging temperature IT is −30 (° C.) or less is not preferable because erroneous detection occurs.

  As a result, in the secondary battery inspection method of the present invention, even when a small amount of copper piece 12 that does not cause a micro short-circuit in the conventional charging method is mixed in the electrode, the temperature IT at the first charge is lowered. By increasing the viscosity of the electrolyte, increasing the deposition height H of the deposited copper deposited on the negative electrode 5 and making the deposited shape into a sharp mountain shape, the electrodes can be brought into a micro-short state. By detecting, it is possible to determine a battery in which a trace amount of copper is mixed in the electrode as a defective product. That is, according to the detection method of the present invention, it is possible to detect a minute amount of metal contamination that cannot be detected by the conventional metal impurity detection method. When a force is applied that causes the negative electrode to come close to the negative electrode, secondary batteries that may cause the occurrence of micro-shorts due to the deposition of metal impurities and deteriorate the battery performance may be removed as defective products. This is possible, and the reliability of the secondary battery can be increased.

  In the inspection process of the present invention, the temperature range of the initial charge IT is set to a temperature of 15 (° C.) or less, which can increase the sensitivity of detecting the occurrence of micro-shorts in the mixed secondary battery mixed with copper. If a non-mixed non-mixed secondary battery is not erroneously detected as a defective product within a range of −20 (° C.) or higher, a mixed secondary battery mixed with a small amount of copper pieces 12 can be obtained. It can be removed with high accuracy. And preferably, if the temperature IT at the time of initial charge is in the range of −20 (° C.) to 5 (° C.), the mixed secondary battery can be removed by inspection as a defective self-discharge with a higher probability. The reliability of the battery can be further improved.

  In addition, the current value at the time of the constant current-constant voltage charge in the first charge step is 2 (C) or less, preferably a value in the vicinity of 1/4 (C). As shown in FIG. 4C, when the tip 14 of the deposited copper 12b breaks through the separator 6 and comes into contact with the positive electrode 4 to generate a micro short circuit, if the current amount is large, the current suddenly flows through the contact portion. As a result of the flow, a spark is generated at the tip portion 14, the tip portion 14 is lost, a non-contact state is detected, and a micro short circuit is not detected. This is because the battery cannot be removed as a defective product. However, such a problem can be avoided if a current value of about 1/4 (C) is used.

  The present invention is not limited to the above-described embodiment, and it goes without saying that various improvements and modifications can be made without departing from the spirit of the present invention. In the present embodiment, copper is used as the metal impurity, but the present invention is not limited to this, and it is needless to say that it may be a metal such as iron or other alloy that is often used in ordinary equipment and may be mixed. .

  In this embodiment, the electrolytic solution is a solution in which lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Not limited to. For example, it may be composed of a mixed solvent of ethylene carbonate (EC) and one or more solvents selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), gamma butyrolactone (GBL) and the like. .

  Moreover, although the positive electrode 4 of the secondary power supply of this embodiment used lithium nickelate (LiNiO2) as a main component, it is not restricted to this. For example, the lithium-containing transition metal oxide contained in the positive electrode is a composite oxide of lithium and one or more transition metals selected from the group consisting of V, Fe, Co, Mn, Ni, W, and Zn, such as cobalt acid. Lithium (LiCoO2) may be used. In the present embodiment, the secondary battery is a so-called lithium ion secondary battery, but is not limited thereto, and may be, for example, a nickel hydride secondary battery. In other words, the secondary battery inspection method of the present invention can be used without depending on the type of secondary battery.

  Moreover, although the micro short detection step of the present embodiment is a method of measuring a voltage drop value in an aging (self-discharge) process, it is not limited thereto. For example, a method of detecting a micro short by measuring the electrical resistance of the separator, the capacitor component on the battery structure, the sealing plate, the current collector plate, the case, and the electrical resistance of the wiring part when measuring the impedance. Needless to say, it may be.

It is a partial expanded sectional view of the electrode 11 of a secondary battery. It is a flowchart figure of the experimental procedure in this embodiment. It is a figure which shows the experimental result in this embodiment. It is a partial expanded sectional view of the electrode 11 in which the copper piece 12 was mixed. It is a figure which shows the force which acts on the copper ion 13. FIG. It is a flowchart figure of the method of determining the micro short defect of the secondary battery in a prior art. It is a figure which shows the detection method of the micro short circuit between electrodes in a prior art.

Explanation of symbols

4 Positive electrode 5 Negative electrode 6 Separator 7 Electrolytic solution 12 Copper piece 13 Copper ion DR Self-discharge failure rate IT Initial charging temperature EF1 Electrostatic force HF1, HF2 Maximum fluid force θ1, θ2 Diffusion angle W1, W2 Precipitation width H1, H2 Precipitation height 12a, 12b Precipitated copper 14 Tip

Claims (4)

An initial charge step of performing an initial charge of the secondary battery at a predetermined temperature at which metal impurities are localized and deposited on the electrode;
A method for inspecting a secondary battery, comprising: a micro-short detection step of detecting a micro-short between the positive electrode and the negative electrode after the initial charging step.   2. The method for inspecting a secondary battery according to claim 1, wherein the predetermined temperature in the initial charging step is within a range from −20 ° C. to 15 ° C. 3.   3. The method for inspecting a secondary battery according to claim 2, wherein the predetermined temperature in the initial charging step is more preferably in a range from −20 ° C. to 5 ° C. 4. The micro short detection step includes an aging step of leaving the charged secondary battery,
2. The secondary battery inspection method according to claim 1, further comprising: an inspection step of measuring a voltage value of the secondary battery after the aging step is completed.

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