Secondary battery self-discharge inspection method and secondary battery manufacturing method

Abstract

To provide a self-discharge testing method of a secondary battery, in which a secondary battery can be shifted to a self-discharge test in a short standby time after being adjusted to have a first battery voltage, and a manufacturing method for a secondary battery using this method.SOLUTION: A battery 10 includes an electrode body 30 including a positive electrode plate 31 having a positive electrode active material layer 312 and a negative electrode plate 32 having a negative electrode active material layer 322. The negative electrode active material layer includes a facing part 322F that faces the positive electrode active material layer and a non-facing part 322N that does not face. A self-discharge testing method for the battery includes a voltage adjusting step S4 of adjusting a battery voltage VB to a first battery voltage VB1, and a self-discharge testing step S5 of keeping the battery in a terminal open state for a predetermined period IH and testing the self-discharge state of the battery on the basis of the change in battery voltage generated in the predetermined period. In the voltage adjusting step S4, the first battery voltage has the level at which a variation convergence time KTC of a fluctuation amount ΔV of the battery voltage due to Li diffusion that relieves the concentration difference ΔC between a facing part concentration CF, which is the Li concentration of the facing part, and a non-facing part concentration CN, which is the Li concentration of the non-facing part, is within 17 hours from an adjustment completion time Tc.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for inspecting a self-discharge of a secondary battery and a method for manufacturing a secondary battery. [Background technology]

[0002] In manufacturing secondary batteries, a self-discharge inspection is carried out to detect the magnitude of self-discharge and to determine whether or not a short circuit has occurred. For example, Patent Document 1 shows a method of inspecting a secondary battery for short circuits, which includes an SOC adjustment step of discharging a secondary battery (hereinafter also referred to as a battery) that has been initially charged in an initial activation step to adjust the SOC value, and a self-discharge step of leaving the SOC-adjusted battery, i.e., a battery adjusted to a predetermined battery voltage, to self-discharge, and detects whether or not a short circuit has occurred based on the amount of voltage drop of the battery in the self-discharge step. This is because a short-circuited battery will experience a larger voltage drop during the same period of the self-discharge step compared to a non-shorted battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-134395 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when a battery is set to a certain battery voltage and then left to stand, as described above, the battery voltage of a short-circuited battery drops significantly in the same period of time compared to a non-shorted battery. This is because self-discharge occurs, in which the charge stored in the battery is discharged through the short-circuited part in the battery. In this case, assuming that the resistance value of the short-circuited part does not change over time, the discharge current is generally constant, so the battery voltage of a short-circuited battery drops at a generally constant rate, except for the range in which the battery voltage changes nonlinearly with the amount of stored charge, such as when the battery's SOC is low (for example, when the SOC is 10% or less). However, it goes without saying that the rate of drop increases as the resistance value of the short-circuited part decreases.

[0005] However, the cause of the change in battery voltage that occurs when a battery is adjusted to a specified battery voltage VB and then left to stand is not only the drop in battery voltage due to self-discharge as described above, as will be explained below.

[0006] First, consider the case where the battery is adjusted to a specified battery voltage VB by CCCV charging to the target voltage. In this case, CC charging (constant current charging) is performed until the battery voltage VB reaches the target voltage (cut-off voltage value). When the battery voltage VB reaches the target voltage, charging is switched to CV charging (constant voltage charging). Then, the battery current IB flowing through the battery gradually decreases over time. Then, CV charging is terminated when the battery current IB reaches the cut-off current value. This means that the battery has been charged to the target battery voltage. However, at the end of this CCCV charging, a battery current IB of the cut-off current value flows through the battery.

[0007] When a battery is expressed by an equivalent circuit (see FIG. 3 described later), it is represented by a battery capacity Cs, a parallel resistance Rp connected in parallel to the battery capacity Cs and equivalent to the insulation resistance of the battery capacity Cs, and a series resistance Rs connected in series to these parallel circuits and indicating the resistance of each part of the battery. As described above, since the battery includes the series resistance Rs, when the battery current IB flows through the battery, the apparent battery voltage VB appears to be higher by the voltage drop that occurred in the series resistance Rs than the battery capacity voltage VCs (equivalent to the open battery voltage) of the battery capacity Cs. Conversely, just before the CCCV charging is completed, the battery voltage VB is equal to the target battery voltage, but just after the completion of the CCCV charging, the battery voltage VB drops by the voltage that occurred in the series resistance Rs. This is because the battery current IB is no longer supplied from the outside when the CCCV charging is completed (IB=0). The voltage change caused by stopping the flow of the battery current IB (a decrease in the battery voltage VB in the case of charging, and an increase in the battery voltage VB in the case of discharging) occurs promptly, for example, within a few seconds to a few minutes, after the adjustment of the battery voltage VB by CCCV charging or the like is completed.

[0008] In addition, at the battery manufacturing stage, a battery that is not short-circuited (a good product) is initially charged. After that, charging and discharging are performed for capacity inspection and the like. Furthermore, the battery voltage VB may be adjusted to a predetermined value by charging such as CCCV charging, and then the battery may be left for a further period, after which a self-discharge inspection of the battery may be performed to check for the presence or absence of a short circuit. In this case, due to the presence of the aforementioned series resistor Rs, the battery voltage VB drops immediately after the adjustment of the battery voltage VB is completed. However, even after that, the voltage continues to drop over time. However, over a period of about 100 to several hundred days, the rate of voltage drop gradually slows down, and finally the battery voltage becomes roughly constant. This behavior of the voltage drop over a long period of time is believed to be due to the fact that the formation of an SEI film on the surface of the active material particles due to the reaction between the active material particles and the electrolyte slows down over time, and the drop in battery voltage due to such film formation subsides. In other words, when manufacturing a battery through initial charging and charging / discharging, the amount of battery voltage drop that occurs during this inspection period varies depending on the length of time that has elapsed since the completion of adjustment to a predetermined battery voltage by charging or discharging until the start of a self-discharge inspection or short-circuit inspection. In addition, the amount of battery voltage drop also varies depending on the length of the period from the voltage measurement before leaving it alone to the voltage measurement after leaving it alone (leaving it alone period).

[0009] In addition to these, a change in the battery voltage VB associated with a change in the negative electrode potential due to the diffusion of charge carrier atoms (e.g., Li atoms) in the negative electrode active material layer is also considered. In a battery, the negative electrode active material layer is made larger in area than the positive electrode active material layer, and the positive electrode plate and the negative electrode plate are arranged so that there is a negative electrode active material layer facing any part of the positive electrode active material layer. This is to ensure that the Li ions released from the positive electrode active material layer during charging are received by the negative electrode active material layer. Therefore, in the negative electrode active material layer of the negative electrode plate, in addition to the facing part facing the positive electrode active material layer via the separator, there is a non-facing part located around this facing part and not facing the positive electrode active material layer. However, in this case, for example, during charging, Li is inserted into the facing part of the negative electrode active material layer, but Li is not inserted into the non-facing part. For this reason, a difference (Li concentration difference) occurs in the amount of Li (Li concentration) per unit area (or unit volume) between the facing part and the non-facing part, and the local negative electrode potentials may also differ from each other. Specifically, the negative electrode potential of the facing part with a high Li concentration is low, while the negative electrode potential of the non-facing part with a low Li concentration is relatively high. The negative electrode potential generated in the negative plate is mainly determined by the negative electrode potential of the facing part, but it is also determined by the negative electrode potential of the non-facing part. The battery voltage VB observed from the outside is obtained as the difference between the positive electrode potential and the overall negative electrode potential.

[0010] However, the Li concentration difference between the facing portion and the non-facing portion of the negative electrode active material layer is gradually alleviated by Li diffusion over time, and after a sufficient amount of time has passed, the Li concentration difference is eliminated, and the facing portion and the non-facing portion have the same Li concentration. Accordingly, the local negative electrode potential difference between the facing portion and the non-facing portion is also gradually eliminated, and the change (increase or decrease) in the negative electrode potential of the negative electrode plate and the change (decrease or increase) in the battery voltage VB also become smaller over time. Such a change in battery voltage due to Li diffusion depends on the temperature of the battery and the magnitude of the Li concentration difference, and is generally eliminated within several days to one week, for example, when the battery is left at room temperature.

[0011] For this reason, when a battery self-discharge test is performed after adjusting the battery voltage VB to a predetermined value by CCCV charging or the like, the battery self-discharge test cannot be performed immediately after the voltage adjustment. That is, it is necessary to wait for one to several days after the completion of the voltage adjustment until the change in the battery voltage VB due to Li diffusion between the facing portion and the non-facing portion settles down to a certain extent before starting the self-discharge test. This is because, when detecting the presence or absence of a short circuit or the self-discharge state of the battery from the decrease rate of the battery voltage VB in the self-discharge test, if there is also a change in the battery voltage VB due to Li diffusion, there is a risk that the self-discharge state cannot be detected properly or the detection accuracy will decrease. The voltage change caused by the SEI film formation is a voltage change that occurs during the manufacturing stage after the battery is first charged. As described above, it takes more than 100 days for the voltage change caused by the SEI film formation to disappear, so if the self-discharge test is started within a few days after the completion of the voltage adjustment, it can be considered that a roughly linear voltage drop occurs, and the impact on the self-discharge test is small.

[0012] The present invention has been made in consideration of the current situation, and provides a self-discharge inspection method for a secondary battery that can transition to a self-discharge inspection with a short waiting time after adjusting the secondary battery to a first battery voltage, and a method for manufacturing a secondary battery using this inspection method. [Means for solving the problem]

[0013] (1) One aspect of the present invention for solving the above problem is a method for inspecting a self-discharge of a secondary battery, the method comprising: a voltage adjustment step of charging or discharging the secondary battery to adjust a battery voltage to a first battery voltage; and a self-discharge inspection step of holding the secondary battery in an open terminal state for a predetermined period of time and inspecting a state of self-discharge of the secondary battery from a change in the battery voltage that occurs during the predetermined period of time, the voltage adjustment step adjusting the first battery voltage based on a fluctuation convergence time of an amount of fluctuation in the battery voltage due to diffusion of the charge carrier atoms that alleviates a concentration difference between an opposing portion concentration, which is a concentration of charge carrier atoms present in the opposing portion, and a non-opposing portion concentration, which is a concentration of the charge carrier atoms present in the non-opposing portion, of the negative electrode active material layer. a change in the battery voltage of the secondary battery of a preceding sample is investigated from the time when the battery voltage is adjusted to the first battery voltage in the voltage adjustment step until the battery voltage starts to decrease along a straight line, the straight line is extended back in time to the time when the adjustment is completed, a one-hour deviation amount that is the difference between the battery voltage one hour after the adjustment completion time and the value on the straight line is obtained, and the elapsed time at which the deviation amount between the acquired battery voltage and the value on the straight line has decreased to a magnitude of 10% of the one-hour deviation amount is obtained as the fluctuation convergence time, This is a method for testing the self-discharge of a secondary battery, the self-discharge period of which is within 17 hours from the completion of adjustment.

[0014] In this method for inspecting self-discharge of a secondary battery, the magnitude of the first battery voltage in the voltage adjustment step is set to a magnitude that causes the fluctuation convergence time of the amount of fluctuation in the battery voltage due to the diffusion of charge carrier atoms such as Li to be within 17 hours (within about 0.7 days) from the completion of adjustment. By setting the magnitude of the first battery voltage in this manner, it is possible to reduce the total amount of fluctuation in the battery voltage due to the diffusion of Li, etc., and to shorten the fluctuation convergence time to 17 hours or less, compared to a case in which the fluctuation convergence time is 24 hours or more (for example, one day to several days). Therefore, when the self-discharge inspection process, which measures the magnitude of self-discharge and determines the presence or absence of a short circuit from the amount and rate of decrease in the battery voltage, is started immediately after the completion of the voltage adjustment, the influence of the fluctuation in the battery voltage due to the diffusion of charge carrier atoms can be reduced and the self-discharge inspection can be performed accurately. Alternatively, when the self-discharge inspection process is started after the fluctuation in the battery voltage due to the diffusion of charge carrier atoms has become sufficiently small, the self-discharge inspection process can be started earlier and the self-discharge inspection can be completed earlier.

[0015] The fluctuation convergence time of the fluctuation amount of the battery voltage VB can be determined, for example, as follows. That is, the change in the battery voltage VB is investigated from the time when the battery voltage VB is adjusted to the first battery voltage in the voltage adjustment process until the battery voltage VB starts to drop along a straight line. Next, the above-mentioned straight line is extended back in time to the time when the adjustment is completed, and the difference between the battery voltage one hour after the adjustment completion (voltage after one hour) and the value on the straight line L (straight line value after one hour) is calculated. Deviation Then, the difference between the acquired battery voltage VB and the value on the above-mentioned straight line L (straight line value) is calculated. Deviation The amount is 1 hour later. Deviation The time it takes for the fluctuation to decrease to 10% of the original amount is defined as the fluctuation convergence time.

[0016] Examples of the "secondary battery" include a lithium ion secondary battery, a sodium ion secondary battery, etc. Furthermore, the "charge carrier atom" is, for example, a Li atom in a lithium ion secondary battery, and a Na atom in a sodium ion secondary battery. An example of the "negative electrode active material layer" is a layer containing a negative electrode active material made of a carbon-based material such as graphite into which charge carrier atoms such as Li atoms can be inserted. In addition, the "self-discharge test" includes tests to measure the magnitude of the battery's self-discharge, i.e., the magnitude of the aforementioned parallel resistance Rp, to determine whether the battery is short-circuited, and to classify the battery according to the magnitude of its self-discharge. The "diffusion of charge carrier atoms" includes both forward diffusion, in which charge carrier atoms such as Li move from the opposing portion to the non-opposing portion of the negative electrode active material layer, and reverse diffusion, in which charge carrier atoms such as Li move from the non-opposing portion to the opposing portion.

[0017] (2)(1) A method for inspecting self-discharge of a secondary battery, wherein the voltage adjustment process adjusts the first battery voltage to a magnitude such that the fluctuation convergence time is within 5 hours from the completion of the adjustment.

[0018] In this method for inspecting self-discharge of a secondary battery, the first battery voltage is set to a value that causes the fluctuation to converge within 5 hours (approximately 0.2 days). Therefore, if the self-discharge inspection process is started immediately after the completion of the voltage adjustment, the self-discharge inspection can be performed more accurately. Alternatively, the self-discharge inspection process can be started earlier.

[0019] In the method for inspecting a self-discharge of a secondary battery according to (3) or (1) or (2), the self-discharge inspection step includes a pre-discharge voltage measurement step of measuring a pre-discharge battery voltage of the secondary battery, a leaving step of leaving the secondary battery whose pre-discharge battery voltage has been measured in an open terminal state for the predetermined period of time, a post-discharge voltage measurement step of measuring a post-discharge battery voltage of the secondary battery after the leaving step, and a comparison between the pre-discharge battery voltage and the post-discharge battery voltage of the secondary battery. The difference voltage between these Between This is the voltage drop per unit time divided by the period of time the device was left unused. The method for inspecting a secondary battery for self-discharge preferably includes a measuring step of obtaining an actual voltage drop rate, and a self-discharge determination step of determining the magnitude of self-discharge of the secondary battery using the actual voltage drop rate of the secondary battery.

[0020] In the above-mentioned method for testing self-discharge of a secondary battery, in addition to the voltage adjustment process of adjusting the battery voltage to the first battery voltage, the battery voltage before leaving the battery unused and then the actual voltage drop rate are measured, so that it is possible to properly detect whether the battery is short-circuited and the magnitude of self-discharge, etc.

[0021] (4) Alternatively, the method for manufacturing a secondary battery may include an initial charging step of initially charging the secondary battery to an initial voltage, an adjustment inspection step of inspecting the magnitude of self-discharge of the secondary battery by a self-discharge inspection method for a secondary battery described in any one of (1) to (3), and a discharge step of discharging the secondary battery determined to be short-circuited in the self-discharge inspection step.

[0022] In this method of manufacturing a secondary battery, after initial charging, a self-discharge test is performed in the adjustment inspection process, and batteries determined to be short-circuited are discharged in the discharge process. In this way, only batteries determined not to be short-circuited can be manufactured. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is an explanatory diagram of a battery according to an embodiment. [Diagram 2] FIG. 2 is an explanatory diagram illustrating the opposing positional relationship between a positive electrode plate and a negative electrode plate that are stacked by winding in the embodiment. [Diagram 3] 2 is an equivalent circuit of a battery according to an embodiment. [Figure 4] 3 is a flowchart showing a manufacturing process of a battery according to an embodiment. [Diagram 5] 1 is a graph showing an example of a change in battery voltage after a voltage adjustment process for the batteries of Examples 1 and 2 and Comparative Examples 1 and 2, in which no short circuit has occurred. [Figure 6] FIG. 1 is an explanatory table for explaining the concentration and diffusion movement of Li in the positive electrode active material layer and the negative electrode active material layer of the batteries of Examples 1 and 2 and Comparative Examples 1 and 2, in which column (a) shows the state before the first charge, column (b) shows the state at the completion of the first charge, column (c) shows the state after high-temperature aging, column (d) shows the state at the completion of adjustment, and column (e) shows the state after the completion of adjustment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] (Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows a longitudinal cross-sectional view of a battery 10 according to this embodiment (Examples 1 and 2 and Comparative Examples 1 and 2 described below). The battery 10 is a rectangular sealed lithium ion secondary battery that can be mounted in vehicles such as hybrid cars, plug-in hybrid cars, and electric cars, drones, and various devices.

[0025] The battery 10 is composed of a case 11, an electrode assembly 30 housed inside the case 11, and a positive terminal 21 and a negative terminal 25 that are supported by the case 11 and connected to the electrode assembly 30 inside the case 11 and protrude outside the case 11 (upward in Figure 1).

[0026] Of these, the case 11 is a rectangular parallelepiped box made of metal (aluminum in this embodiment). The case 11 has a case body 12 in the shape of a rectangular cylinder with a bottom having an opening 12P at the upper AHU in the battery height direction AH, and a rectangular plate-like lid 15 that seals the opening 12P. The battery height direction AH, battery width direction BH, and battery thickness direction CH will be described as the directions shown in FIG. 1.

[0027] A positive electrode terminal 21 made of aluminum is fixed to the lid body 15 in a state insulated from the lid body 15 by a positive electrode insulating member 24. Specifically, of the positive electrode terminal 21, a positive electrode internal terminal member 22 is connected to a positive electrode current collecting portion 35 (described later) of the electrode body 30 at a connection portion 22C, and also penetrates the lid body 15 and is conductively connected to a positive electrode external terminal member 23.

[0028] Furthermore, a negative electrode terminal 25 made of copper is fixed to the lid body 15 in a state insulated from the lid body 15 by a negative electrode insulating member 28. Specifically, of the negative electrode terminal 25, a negative electrode internal terminal member 26 is connected to a negative electrode current collecting portion 36 (described later) of the electrode body 30 at a connection portion 26C, and also penetrates the lid body 15 and is conductively connected to a negative electrode external terminal member 27.

[0029] The case 11 also contains an electrolyte 40 together with the electrode body 30, a part of which is impregnated in the electrode body 30 and a part of which is pooled at the bottom of the case 11. The electrode body 30 is also covered with an insulating film 50 in the shape of a rectangular bag with a bottom that is open at the upper AHU in the battery height direction AH.

[0030] The electrode assembly 30 is a flat wound type electrode assembly that is generally in the shape of a flat rectangular parallelepiped and is formed by winding a band-shaped positive electrode plate 31 and a band-shaped negative electrode plate 32 together with two band-shaped separators 33 made of a resin porous film interposed therebetween around an axis 30X and then flattening them by crushing them. Therefore, as shown in Fig. 2, the positive electrode plates 31 and the negative electrode plates 32 are alternately stacked with the separators 33 interposed therebetween.

[0031] The belt-shaped positive electrode plate 31 has a positive electrode active material layer 312 on each of the two main surfaces of a positive electrode current collector foil 311 made of a rectangular aluminum foil. The belt-shaped negative electrode plate 32 has a negative electrode active material layer 322 containing graphite particles (not shown) as a negative electrode active material on each of the two main surfaces of a negative electrode current collector foil 321 made of a rectangular copper foil. The belt-shaped positive electrode plate 31 has a positive electrode plate main body portion 31M in which the positive electrode active material layer 312 overlaps each of the two main surfaces of the positive electrode current collector foil 311, and a positive electrode plate current collector portion 31S in which the positive electrode current collector foil 311 extends and is exposed on one side WH1 (the right side in FIG. 2) in the electrode width direction WH. In addition, the strip-shaped negative electrode plate 32 includes a negative electrode plate main body 32M in which the negative electrode active material layers 322 are overlapped on both main surfaces of the negative electrode current collector foil 321, and a negative electrode current collector foil 321 that extends and is exposed on the other side WH2 (the left side in FIG. 2) in the electrode width direction WH. negative Plate current collector 3 2 It has S.

[0032] 2, the width direction dimension of the negative electrode plate main body portion 32M (negative electrode active material layer 322) of the negative electrode plate 32 is made larger than the width direction dimension of the positive electrode plate main body portion 31M (positive electrode active material layer 312) of the positive electrode plate 31. Moreover, the positive electrode plate 31 is disposed such that the positive electrode active material layer 312 faces the negative electrode active material layer 322 of the negative electrode plate 32 without fail, via the separator 33. That is, the negative electrode active material layer 322 of the negative electrode plate 32 has, in addition to a facing portion 322F facing the positive electrode active material layer 312, non-facing portions 322N located on both sides (left and right in FIG. 2) of the facing portion 322F in the electrode width direction WH and not facing the positive electrode active material layer 312.

[0033] In the electrode body 30, a positive electrode current collecting portion 35 formed by exposing a positive electrode current collecting portion 31S of the positive electrode plate 31 while being wound in a spiral shape is provided on one side BH1 (the right side in FIG. 1) in the battery width direction BH along the axis 30X, and a negative electrode current collecting portion 36 formed by exposing a negative electrode current collecting portion 32S of the negative electrode plate 32 while being wound in a spiral shape is provided on the other side BH2 (the left side in FIG. 1). The central portion of the axis 30X, sandwiched between the positive electrode current collecting portion 35 and the negative electrode current collecting portion 36, is a main portion 34 formed by overlapping and winding a positive electrode plate main portion 31M and a negative electrode plate main portion 32M.

[0034] In this embodiment, the positive electrode current collecting portions 35 of the electrode body 30 are laser-welded to the connection portion 22C of the positive electrode internal terminal member 22 at the connection portion 35C in close contact with each other in the battery thickness direction CH, and can be electrically connected to circuit members outside the battery 10 by the positive electrode internal terminal member 22 and the positive electrode external terminal member 23 that form the positive electrode terminal 21. Also, the negative electrode current collecting portions 36 of the electrode body 30 are laser-welded to the connection portion 26C of the negative electrode internal terminal member 26 in close contact with each other in the battery thickness direction CH, and can be electrically connected to circuit members outside the battery 10 by the negative electrode internal terminal member 26 and the negative electrode external terminal member 27 that form the negative electrode terminal 25.

[0035] In addition, the electrode body 30 is supported by the lid body 15 via the positive electrode terminal 21 and the negative electrode terminal 25 . In addition, the connection between the connection portion 35C of the positive electrode current collecting portion 35 of the electrode body 30 and the connection portion 22C of the positive electrode internal terminal member 22, and the connection between the connection portion 36C of the negative electrode current collecting portion 36 and the connection portion 26C of the negative electrode internal terminal member 26 can also be made by other methods, such as ultrasonic welding or crimping.

[0036] The battery 10 is represented in terms of DC by an equivalent circuit shown in FIG. 3. That is, the equivalent circuit of the battery 10 is composed of a battery capacity Cs of the battery 10, a parallel resistance Rp that forms a parallel circuit with the battery capacity Cs and corresponds to the insulation resistance of the battery 10, and a series resistance Rs that is connected in series to the parallel circuit consisting of the battery capacity Cs and the parallel resistance Rp and corresponds to the resistance of each part of the battery. Therefore, when the battery current IB does not flow to the battery 10, the battery voltage VB (open voltage) is equal to the battery capacity voltage VCs generated at the battery capacity Cs. On the other hand, when a charging current IBC is flowing toward the battery 10, the apparent battery voltage VB is the sum of the battery capacity voltage VCs and the voltage (voltage drop) generated at the series resistance Rs by the charging current IBC. Conversely, when a discharging current IBC is flowing from the battery 10, the apparent battery voltage VB is the battery capacity voltage VCs minus the voltage (voltage drop) generated at the series resistance Rs by the discharging current IBC. When the battery 10 is short-circuited, the magnitude of the parallel resistance Rp is smaller than when the battery 10 is not short-circuited, and the charge stored in the battery capacity Cs is gradually discharged by self-discharge through the parallel resistance Rp, causing a gradual decrease in the battery voltage VB.

[0037] Next, the manufacture of the battery 10 will be described with reference to Fig. 4. First, an uncharged battery 10 is manufactured. The manufacture of a sealed battery 10 having a rectangular parallelepiped case 11 is well known, so a description thereof will be omitted. In the initial charging step S1 (see FIG. 4), first, the uncharged battery 10 is initially charged by CCCV charging at room temperature to set the initial voltage VB0 to VB0 = 3.800 V. In this embodiment, for example, initial charging is performed by CCCV charging at a constant current of 7 C, a cut voltage of 3.800 V, and a cut current of 0.3 C in an environment of 25° C., to set the initial voltage VB0 of the battery 10 to 3.800 V.

[0038] Next, in a high-temperature aging step S2, each initially charged battery 10 is subjected to high-temperature aging in an open state by leaving it in an environment of 50 to 80° C. for 10 to 200 hours (for example, 18 hours in an environment of 70° C. in this embodiment). After the high-temperature aging step S2, the battery 10 is cooled, and then in a capacity inspection step S3, the battery 10 is charged to SOC 100%, and then the battery 10 is discharged to SOC 0% to measure the capacity of the battery 10 (discharge capacity in the case of the above-mentioned method).

[0039] Next, in a voltage adjustment step S4, the battery voltage VB of each battery 10 is charged to a first voltage VB1 at room temperature. At this time, the first voltage VB1 is set to a value slightly smaller than the initial voltage VB0 in the initial charging step S1. In this embodiment (corresponding to Example 1), for example, CCCV charging is performed in an environment of 25°C with a constant current of 7C, a cutoff voltage of 3.750V, and a cutoff current of 0.3C. That is, after the initial charging, the battery voltage VB of the battery 10 that has undergone high-temperature aging is temporarily adjusted to the first voltage VB1 (VB1=3.750V in this embodiment).

[0040] Next, in the self-discharge inspection process S5, a self-discharge inspection is performed on the battery 10 after the voltage adjustment process S4. Specifically, first, in the pre-discharge voltage measurement process S51, the pre-discharge second voltage VB2a, which is the battery voltage VB of the battery 10 at that time, is measured. As described above, in the voltage adjustment process S4, the battery voltage VB of the battery 10 is temporarily set to the first voltage VB1 by CCCV charging. However, immediately after the completion of CCCV charging, the battery voltage VB drops (for example, about 1 to 5 mV) within a few seconds to a few minutes of elapsed time KT from the adjustment completion time Tc. The battery current IB, which is the cut current that was flowing at the end of CCCV charging, does not flow due to the completion of CV charging. As a result, the voltage drop that occurred in the series resistance Rs in the equivalent circuit (see FIG. 3) does not occur, and the battery voltage VB drops. In addition, even if the battery 10 is not short-circuited, the battery voltage VB fluctuates over time due to the above-mentioned SEI generation in the positive electrode active material layer and the diffusion of Li between the facing portion 322F and the non-facing portion 322N of the negative electrode active material layer 322 (see FIG. 5). For this reason, the second pre-discarded voltage VB2a of the battery 10 is measured prior to the next-described discontinuous step S52.

[0041] If the battery 10 under test is short-circuited (slightly short-circuited), the charge stored in the battery 10 (battery capacity Cs: see FIG. 3) is discharged through a low-resistance parallel resistor Rp that occurs at the short-circuited portion (not shown). For this reason, assuming that the resistance value of the short-circuited portion (parallel resistor Rp) does not change, the discharge will be at a roughly constant current, and the battery voltage VB of the battery 10 will drop at a roughly constant rate. In other words, if the battery 10 is short-circuited, the change will be a combination of the aforementioned fluctuation in the battery voltage VB when the battery 10 is not short-circuited (see FIG. 5) plus a constant-rate drop in the battery voltage VB due to the constant-current discharge of the short-circuited portion.

[0042] Next, in the leaving-alone process S52, the battery 10 with the positive electrode terminal 21 and the negative electrode terminal 25 in an open state is left alone in an environment of 25°C for a predetermined leaving-alone period IH (in the first embodiment, IH ≥ 5.0 days (IH ≥ 120 hours)) in an unconstrained or slightly constrained state. Then, in the post-leaving-alone voltage measurement process S53, the post-leaving-alone second voltage VB2b, which is the battery voltage VB of the battery 10 after leaving alone, is measured.

[0043] Subsequent decrease rate calculation In process S54, the difference voltage (second voltage decrease amount ΔVB2) between the pre-leaving-alone second voltage VB2a and the post-leaving-alone second voltage VB2b is divided by the actual leaving-alone period IH to calculate the second voltage decrease rate DVB2 (=ΔVB2 / IH), which is the second voltage decrease amount per unit time (for example, per day or per hour).

[0044] The length of the leaving-alone period IH may vary depending on whether weekends are included within the leaving-alone period IH, whether there is a delay in the post-leaving-alone voltage measurement process S53, etc., and the timing at which the post-leaving-alone voltage measurement process S53 can be performed for each lot of the leaving-alone process S52 may be different. Therefore, in the short-circuit determination process S55 described later, it is easier to compare with the determination criteria by using a decrease rate such as the second voltage decrease rate DVB2 rather than using the difference voltage (second voltage decrease amount ΔVB2) between the pre-leaving-alone second voltage VB2a and the post-leaving-alone second voltage VB2b.

[0045] Then, in the short-circuit determination process S55, the presence or absence of a short circuit in the battery 10 is determined based on the second voltage decrease rate DVB2 obtained for the battery 10. Specifically, it is determined whether the second voltage decrease rate DVB2 is greater than the threshold decrease rate THD2 (DVB2 > THD2). If the answer is No, that is, if the second voltage decrease rate DVB2 is less than the threshold decrease rate THD2 (DVB2 < THD2), it is assumed that no short circuit has occurred in the battery 10. Thus, the short-circuit determination process S55 is terminated, and the battery 10 is completed.

[0046] If the short circuit determination step S55 judges that the battery 10 is short-circuited, that is, if the second voltage drop rate DVB2 is greater than the threshold drop rate THD2 (DVB2>THD2), the battery 10 is determined to be short-circuited, and the process proceeds to the discharge step S6. In the discharge step S6, the defective battery 10N determined to be short-circuited is discharged from the manufacturing process. In the short circuit determination step S55, the second voltage drop rate DVB2 is compared with the threshold drop rate THD2 to determine only whether or not the battery 10 is short circuited. However, the degree of self-discharge can also be classified into three or more ranks based on the magnitude of the second voltage drop rate DVB2.

[0047] In the manufacturing method and self-discharge inspection method for battery 10 described above, in addition to the voltage adjustment step S4 of adjusting the battery voltage VB to the first voltage VB1, the second voltage before leaving the battery 10 is measured, and then the second voltage drop rate DVB2 is actually measured. Therefore, it is possible to appropriately detect whether or not the battery 10 is short-circuited, the magnitude of self-discharge, etc.

[0048] In addition, in this manufacturing method for battery 10, after initial charging, a self-discharge inspection is performed in an adjustment inspection process (voltage adjustment process S4 and self-discharge inspection process S5), and batteries 10 determined to be short-circuited are discharged in a discharge process S6. In this way, only batteries 10 determined not to be short-circuited can be manufactured.

[0049] Next, the relationship between the initial voltage VB0 at which the battery 10 is initially charged in the initial charging process S1 and the first voltage VB1 reached in the voltage adjustment process S4 (in this embodiment (Example 1), VB0 = 3.800 V, VB1 = 3.750 V) and the change in the battery voltage VB after the voltage adjustment process S4 (after the adjustment completion time Tc) will be examined.

[0050] The first voltage VB1 reached in the voltage adjustment step S4 is the same (VB1=3.750V), while the initial voltage VB0 in the initial charging step S1 is different. The change in the battery voltage VB after the voltage adjustment step S4 (after the adjustment completion time Tc) of each example will be described with reference to FIG. 5 and FIG. 6. Here, in Comparative Example 1, the initial voltage VB0 is 3.750 (same as VB1). In Example 1 corresponding to the above-mentioned embodiment, the initial voltage VB0 is 3.800 (0.050V=50mV higher than VB1). In Example 2, the initial voltage VB0 is 3.900 (0.150V=150mV higher than VB1). Furthermore, in Comparative Example 2, the initial voltage VB0 is 4.000 (0.250V=250mV higher than VB1).

[0051] FIG. 5 shows a graph of the change in the voltage drop ΔVB1 from the first voltage VB1 (VB1=3.750V) with respect to the elapsed time KT after the adjustment completion time Tc in each example. In the battery 10 of Comparative Example 1 (VB0=3.750V, VB1=3.750V) shown by the long dashed line in FIG. 5, the voltage drop ΔVB1 dropped by about -1.3mV in a very short time (within a few minutes of elapsed time KT) after the adjustment completion time Tc. Furthermore, when the elapsed time KT was 1 hour (KT=1hr), the voltage drop ΔVB1 dropped to about -1.8mV. After that, the battery voltage VB dropped sharply, but the drop in the battery voltage VB gradually became gentler as time passed, and it can be seen that the battery voltage VB dropped almost linearly after the elapsed time KT was about 72 hours or more.

[0052] Also, in the battery 10 of Example 1 (same as the embodiment, VB0=3.800V, VB1=3.750V) shown by the solid line in FIG. 5, the voltage drops by about ΔVB1=-1.3mV in a very short time (within a few minutes of elapsed time KT) after the adjustment completion time Tc. Furthermore, when the elapsed time KT was 1 hour (KT=1hr), the voltage drops to about ΔVB1=-2.1mV. Thereafter, the battery voltage VB dropped sharply, but the voltage drop ΔVB1 was smaller than that of Comparative Example 1. Then, the drop in the battery voltage VB gradually became gentler as time passed, and it can be seen that the battery voltage VB dropped almost linearly after the elapsed time KT was about 48 hours.

[0053] In the battery 10 of Example 2 (VB0=3.900V, VB1=3.750V) shown by the dashed line in FIG. 5, the voltage drop amount ΔVB1 dropped by about -1.3mV in a very short time (within a few minutes of elapsed time KT) after the adjustment completion time Tc. Furthermore, when the elapsed time KT was 1 hour (KT=1hr), the voltage drop amount ΔVB1 dropped to about -1.5mV. However, unlike Comparative Example 1 and Example 1, it can be seen that the battery voltage VB dropped almost linearly after the elapsed time KT reached 2 hours. That is, in the battery 10 of Example 2, unlike the batteries 10 of Comparative Example 1 and Example 1, there was almost no period during which the drop in the battery voltage VB gradually became gentler with the passage of time.

[0054] Furthermore, in the battery 10 of Comparative Example 2 (VB0=4.000V, VB1=3.750V) shown by the short dashed line in FIG. 5, the voltage drop amount ΔVB1 dropped by about -1.3mV in a very short time (within a few minutes of elapsed time KT) after the adjustment completion time Tc. Also, when the elapsed time KT was 1 hour (KT=1hr), the voltage drop amount ΔVB1 dropped to about -1.5mV. However, unlike the above three examples, the battery voltage VB increased (the voltage drop amount ΔVB1 increased) until the elapsed time KT reached about 24 hours. Then, after maintaining a substantially constant battery voltage VB, it can be seen that the battery voltage VB dropped almost linearly after the elapsed time KT reached about 60 hours.

[0055] First, let us consider the behavior of the battery voltage VB (voltage drop ΔVB1) after the adjustment completion time Tc in the battery 10 of Comparative Example 1. The reason why the battery voltage VB drops significantly to the first voltage VB1 within a few minutes immediately after the adjustment completion time Tc is understood to be because, as described above, the battery current IB no longer flows through the series resistor Rs due to the completion of CCCV charging. This change is considered to be similar in the other three examples (Examples 1 and 2 and Comparative Example 2).

[0056] On the other hand, in the battery 10 of Comparative Example 1, the battery voltage VB drops almost linearly after the elapsed time KT=72 hours, which is considered to be due to the voltage drop caused by the formation of an SEI film on the surface of the active material particles described above. This voltage drop due to the formation of the SEI film is a voltage drop that lasts for about several tens to several hundreds of days, so it appears to be an approximately linear voltage drop in the period of several days to about one week (up to 170 hours) after the adjustment completion time Tc. The linear voltage drop after the elapsed time KT=48 hours in the battery 10 of Example 1, the linear voltage drop after the elapsed time KT=2 hours in the battery 10 of Example 2, and the linear voltage drop after the elapsed time KT=60 hours in the battery 10 of Comparative Example 2 are also considered to be voltage drops caused by the formation of the SEI film described above.

[0057] On the other hand, in the battery 10 of Comparative Example 1, the voltage drop occurring after a few minutes have passed since the adjustment completion time Tc and before 72 hours have passed (KT=72 hrs), excluding the effect of the voltage drop caused by the above-mentioned SEI coating film formation, is considered to be due to the above-mentioned fluctuation in Li concentration (Li diffusion) between the facing portion 322F and the non-facing portion 322N of the negative electrode active material layer 322. This fluctuation in Li concentration will be explained using FIG. 6. FIG. 6 is an explanatory table for explaining the Li concentration and Li diffusion in the positive electrode active material layer 312 and the negative electrode active material layer 322 of each battery 10. Among them, column (a) shows the Li concentration in the positive electrode active material layer 312 and the facing portion 322F and the non-facing portion 322N of the negative electrode active material layer 322 before the initial charge, column (b) shows the Li concentration at the completion of the initial charge, column (c) shows the Li concentration at the completion of the high-temperature aging, column (d) shows the Li concentration at the completion of the adjustment, and column (e) shows the Li concentration at the positive electrode active material layer 312 and the facing portion 322F and the non-facing portion 322N of the negative electrode active material layer 322 after the adjustment is completed.

[0058] First, in the battery 10 of Comparative Example 1, before the initial charge shown in section (a), Li is present in the positive electrode active material layer 312 but not in the negative electrode active material layer 322. However, after the initial charge step S1 shown in section (b) in which the battery voltage VB is set to an initial voltage VB0 (VB0=3.750 V in Comparative Example 1) is performed (after the initial charge), part of the Li in the positive electrode active material layer 312 moves to the facing portion 322F of the negative electrode active material layer 322 that faces the positive electrode active material layer 312 and is inserted into the negative electrode active material. However, at this point, Li is not present in the non-facing portion 322N of the negative electrode active material layer 322 that does not face the positive electrode active material layer 312. That is, a concentration difference ΔC occurs between the facing portion concentration CF, which is the Li concentration in the facing portion 322F, and the non-facing portion concentration CN, which is the Li concentration in the non-facing portion 322N, and so as to alleviate this concentration difference ΔC, Li atoms diffuse forward from the facing portion 322F to the non-facing portion 322N, as shown by the outward arrow. Therefore, after the high-temperature aging step S2 in which the battery 10 is left under high temperatures as shown in section (c) (after high-temperature aging), the facing portion concentration CF of the facing portion 322F and the non-facing portion concentration CN of the non-facing portion 322N become roughly equal due to Li forward diffusion, and the concentration difference ΔC is eliminated. The non-facing portion concentration CN at this point (after high-temperature aging) is slightly lower than the facing portion concentration CF after the initial charge as shown in section (b).

[0059] Thereafter, as described above, the capacity inspection step S3 is followed by the voltage adjustment step S4, and the battery voltage VB is charged to a first voltage VB1 (VB1=VB0=3.750V in Comparative Example 1) equal to the initial voltage VB0. Li is supplied to the facing portion 322F from the positive electrode active material layer 312, and at the time Tc at which the adjustment is completed, as shown in section (d), the facing portion concentration CF is approximately the same as that after the initial charge, as shown in section (b). On the other hand, since Li is not supplied to the non-facing portion 322N, the non-facing portion concentration CN after high-temperature aging, as shown in section (c), is maintained. That is, at the time Tc at which the voltage adjustment is completed, as shown in section (d), the facing portion concentration CF is slightly higher than the non-facing portion concentration CN, and a concentration difference ΔC occurs. Then, after the time Tc at which the adjustment is completed, Li atoms diffuse forward from the facing portion 322F to the non-facing portion 322N, as shown by the outward arrow in section (e), in order to eliminate this concentration difference ΔC. As a result, the facing portion concentration CF gradually decreases, while the non-facing portion concentration CN gradually increases, until the facing portion concentration CF and the non-facing portion concentration CN are made equal.

[0060] The local negative electrode potential at each portion of the negative electrode active material layer 322 is affected by the Li concentration at that portion. That is, the higher the Li concentration, the lower the local negative electrode potential at that portion. The negative electrode potential of the negative electrode plate 32 is a potential obtained by combining the local negative electrode potentials at each portion. However, in the negative electrode active material layer 322 of the battery 10 of this embodiment, the area of ​​the facing portion 322F is larger than the area of ​​the non-facing portion 322N (see FIG. 2), so that the negative electrode potential of the negative electrode plate 32 is approximately equal to the negative electrode potential of the facing portion 322F. The battery voltage VB is the difference voltage between the positive electrode potential of the positive electrode plate 31 (positive electrode active material layer 312) and the negative electrode potential of the negative electrode plate 32.

[0061] Therefore, after the adjustment completion time Tc at which the first voltage VB1 is set in the voltage adjustment step S4, the negative electrode potential of the facing portion 322F and further the negative electrode potential of the negative electrode plate 32 gradually increase as the facing portion concentration CF gradually decreases due to Li forward diffusion over the elapsed time KT, and the battery voltage VB gradually decreases. Note that, in Comparative Example 1, the decrease in the battery voltage VB due to Li diffusion ends approximately 72 hours (KT=72 hrs) after the adjustment completion time Tc, as shown by the long dashed line in FIG.

[0062] The reason why the battery voltage VB decreases due to forward Li diffusion after the adjustment completion time Tc shown in section (e) of this comparative example 1 can also be said to be because the initial voltage VB0 was set to be equal to the first voltage VB1, and therefore the non-facing portion concentration CN was a lower Li concentration than the facing portion concentration CF at the adjustment completion time Tc shown in section (d).

[0063] Next, consider the behavior of the battery voltage VB (voltage drop amount ΔVB1) in the battery 10 in Examples 1 and 2. The drop in the battery voltage VB immediately after the adjustment completion time Tc, the linear voltage drop in the battery 10 in Example 1 after the elapsed time KT=48 hours, and the linear voltage drop in the battery 10 in Example 2 after the elapsed time KT=2 hours have already been described. On the other hand, in the battery 10 of Examples 1 and 2, the voltage drop occurring after a few minutes have passed since the adjustment completion time Tc and before 48 hours or 2 hours have passed, excluding the effect of the voltage drop caused by the above-mentioned formation of the SEI coating, is considered to be due to the above-mentioned fluctuation in the Li concentration in the facing portion 322F and the non-facing portion 322N of the negative electrode active material layer 322. The fluctuation in the Li concentration in the battery 10 of Examples 1 and 2 will also be described with reference to FIG.

[0064] First, in the batteries 10 of Examples 1 and 2, before the initial charge shown in FIG. 6(a), Li exists in the positive electrode active material layer 312 but does not exist in the negative electrode active material layer 322, as in Comparative Example 1. However, after the initial charge step S1 shown in FIG. 6(b) in which the battery voltage VB is set to an initial voltage VB0 (VB0=3.800V in Example 1, VB0=3.900V in Example 2) is performed (after the initial charge), Li is inserted into the negative electrode active material of the facing portion 322F. At this point, Li does not exist in the non-facing portion 322N of the negative electrode active material layer 322 that does not face the positive electrode active material layer 312. However, compared to Comparative Example 1, the Li concentration (facing portion concentration CF) in the facing portion 322F is increased by the amount that the initial voltage VB0 is increased.

[0065] Thereafter, in order to reduce the concentration difference ΔC, Li atoms diffuse forward from the facing portion 322F to the non-facing portion 322N. Therefore, after the high-temperature aging step S2 shown in section (c) is performed (after high-temperature aging), the facing portion concentration CF of the facing portion 322F and the non-facing portion concentration CN of the non-facing portion 322N become approximately equal due to Li forward diffusion, and the concentration difference ΔC is eliminated. The non-facing portion concentration CN at this point (after high-temperature aging) is slightly lower than the facing portion concentration CF after the initial charge shown in section (b). However, compared to Comparative Example 1, the non-facing portion concentrations CN of the batteries 10 of Examples 1 and 2 are relatively high.

[0066] Thereafter, the voltage adjustment step S4 is performed through the capacity inspection step S3 as described above, and the battery voltage VB is charged to the first voltage VB1 (VB1=3.750V in Examples 1 and 2 as in Comparative Example 1). Then, Li is supplied from the positive electrode active material layer 312 to the facing portion 322F, and at the time Tc at which adjustment is completed as shown in section (d), the facing portion concentration CF is approximately the same as that after the initial charge as shown in section (b). On the other hand, since Li is not supplied to the non-facing portion 322N, the non-facing portion concentration CN after high-temperature aging as shown in section (c) is maintained. However, unlike Comparative Example 1, at the time Tc at which adjustment is completed as shown in section (d), the facing portion concentration CF is approximately the same as the non-facing portion concentration CN. That is, compared to Comparative Example 1, the concentration difference ΔC at the time Tc at which voltage adjustment is completed is small (Example 1), or hardly occurs (Example 2). For this reason, in Examples 1 and 2, as can be seen from the fact that no arrow is shown in column (e) after the adjustment completion time Tc, the diffusion movement of Li atoms between the facing portion 322F and the non-facing portion 322N is smaller (Example 1) or hardly occurs (Example 2) compared to Comparative Example 1.

[0067] Therefore, after the adjustment completion time Tc in the voltage adjustment process S4, in Example 1 shown by the solid line in Fig. 5, the decrease in the battery voltage VB due to the forward Li diffusion ends in a short time (approximately after 48 hours have passed (KT=48 hrs)) compared to Comparative Example 1 shown by the long dashed line. Also, in Example 2 shown by the dashed and dotted line in Fig. 5, the decrease in the battery voltage VB due to the forward Li diffusion hardly occurs and ends in an extremely short time (within 2 hours (KT≦2 hrs)).

[0068] In these Examples 1 and 2, the voltage drop ΔVB1 due to Li diffusion does not fluctuate much after the adjustment completion time Tc. This can be attributed to the fact that, by making the initial voltage VB0 appropriately larger than the first voltage VB1, at the adjustment completion time Tc shown in column (d), the non-facing portion concentration CN is approximately the same Li concentration as the facing portion concentration CF.

[0069] Next, consider the behavior of the battery voltage VB (voltage drop amount ΔVB1) in the battery 10 of Comparative Example 2. The drop in the battery voltage VB immediately after the adjustment completion time Tc and the linear voltage drop after the elapsed time KT=60 hours in the battery 10 of Comparative Example 2 have already been described. On the other hand, in the battery 10 of Comparative Example 2, the increase and maintenance of the voltage drop ΔVB1 (i.e., the increase in the battery voltage VB) that occurs after a few minutes have passed since the adjustment completion time Tc and before 60 hours have passed, excluding the influence of the voltage drop caused by the formation of the SEI coating, is also considered to be due to the aforementioned fluctuation in the Li concentration in the facing portion 322F and the non-facing portion 322N of the negative electrode active material layer 322. The fluctuation in the Li concentration in the battery 10 of Comparative Example 2 will also be described with reference to FIG.

[0070] First, in the battery 10 of Comparative Example 2, before the initial charge shown in FIG. 6(a), Li is present in the positive electrode active material layer 312 but not in the negative electrode active material layer 322, as in Comparative Example 1 and Examples 1 and 2. However, after the initial charge step S1 shown in (b) in which the battery voltage VB is set to an initial voltage VB0 (VB0=4.000V in Comparative Example 2) is performed (after the initial charge), Li is inserted into the negative electrode active material of the facing portion 322F. At this point, Li is not present in the non-facing portion 322N of the negative electrode active material layer 322. However, compared to Comparative Example 1 and Examples 1 and 2, the Li concentration (facing portion concentration CF) in the facing portion 322F is further increased by the amount that the initial voltage VB0 is further increased.

[0071] Then, in order to reduce the concentration difference ΔC, Li atoms diffuse forward from the facing portion 322F to the non-facing portion 322N. For this reason, after the high-temperature aging step S2 in which the battery 10 is left under high temperatures as shown in section (c) (after high-temperature aging), the facing portion concentration CF of the facing portion 322F and the non-facing portion concentration CN of the non-facing portion 322N become roughly equal due to Li forward diffusion, and the concentration difference ΔC is eliminated. The non-facing portion concentration CN at this point (after high-temperature aging) is slightly lower than the facing portion concentration CF after the first charge as shown in section (b). However, compared to the other three examples, the comparative example 2 The non-opposing portion concentration CN of the battery 10 is even higher.

[0072] Thereafter, as described above, the capacity inspection step S3 is followed by the voltage adjustment step S4, and the battery voltage VB is charged to the first voltage VB1 (VB1=3.750V in Comparative Example 2 as in the other three examples). Then, Li is supplied from the positive electrode active material layer 312 to the facing portion 322F, and at the time Tc at which adjustment is completed as shown in section (d), the facing portion concentration CF becomes approximately the same as that after the initial charge as shown in section (b). On the other hand, since Li is not supplied to the non-facing portion 322N, the non-facing portion concentration CN after high-temperature aging as shown in section (c) is maintained. However, unlike the other three examples, at the time Tc at which adjustment is completed as shown in section (d), the facing portion concentration CF becomes a "lower" concentration than the non-facing portion concentration CN. That is, at the time Tc at which voltage adjustment is completed, a concentration difference ΔC that is the opposite (negative) to that of the other three examples is generated. Therefore, in this Comparative Example 2, after the adjustment completion time Tc, back diffusion of Li atoms occurs from the non-facing portion 322N to the facing portion 322F, as shown by the inward arrow in section (e).

[0073] Therefore, in Comparative Example 2, as the elapsed time KT passes after the adjustment completion time Tc in the voltage adjustment process S4, the opposing portion concentration CF gradually increases due to Li reverse diffusion, and the negative electrode potential of the opposing portion 322F and further the negative electrode potential of the negative electrode plate 32 gradually decrease, the battery voltage VB gradually increases, and the voltage reduction amount ΔVB1 also increases. Note that in Fig. 5, the increase in the battery voltage VB of the battery 10 in Comparative Example 2 subsides after about 24 hours has elapsed, but this is because the effect of the voltage reduction due to the formation of the SEI coating described above is included, and the increase in the battery voltage VB due to Li reverse diffusion ends about 60 hours (KT = 60 hrs) after the adjustment completion time Tc, as shown by the short dashed line in Fig. 5.

[0074] In Comparative Example 2, the increase in the voltage drop ΔVB1 (increase in battery voltage VB) due to this Li back-diffusion after the adjustment completion time Tc can also be attributed to the fact that the initial voltage VB0 was made too larger than the first voltage VB1, resulting in the non-facing portion concentration CN being a higher Li concentration than the facing portion concentration CF at the adjustment completion time Tc shown in column (d).

[0075] Therefore, the battery voltage VB due to the Li diffusion movement between the facing portion 322F and the non-facing portion 322N as described above Deviation The fluctuation convergence time KTC of the amount (fluctuation amount) ΔV is determined as follows, using a graph showing the change in the voltage drop amount ΔVB1 (or the first voltage VB1) during the elapsed time KT after the adjustment completion time Tc, as shown in FIG. 5. First, the change in the battery voltage VB is investigated from the adjustment completion time Tc at which the battery voltage VB is adjusted to the first voltage VB1 in the voltage adjustment process S4 until the battery voltage VB starts to drop along the line L (lines La to Ld in FIG. 5 for Comparative Examples 1 and 2 and Examples 1 and 2) (for example, over the elapsed time KT=144 hours). Next, the above-mentioned line L (lines La to Ld) is extended back in time (to the left in FIG. 5) to the adjustment completion time Tc (elapsed time KT=0). Next, the one-hour convergence time VTC, which is the difference between the battery voltage VB one hour after the adjustment completion time Tc (KT=1 hour) (hereinafter referred to as the one-hour voltage V1h) and the value on the line L (hereinafter referred to as the one-hour straight line value VL1h), is determined. DeviationThe amount ΔV1h (= V1h-VL1h, ΔV1ha to ΔV1hd) is obtained. Deviation Regarding the amount ΔV1h, for convenience of description, in FIG. 5, the voltage V1ha after one hour, the linear value VL1h1a after one hour, and the linear value VL1h1a after one hour for Comparative Example 1 are shown. Deviation Only the amount ΔV1ha is illustrated. Then, the relationship between the acquired battery voltage VB and the values ​​on the above-mentioned line L (hereinafter referred to as line values ​​VL, VLa to VLd) Deviation After 1 hour, the amount ΔV (=VB-VL, ΔVa~ΔVd) Deviation The elapsed time KT at which the magnitude of the quantity ΔV1h (ΔV1ha to ΔV1hd) has decreased to 10% is defined as the fluctuation convergence time KTC (KTCa to KTCd).

[0076] As shown in FIG. 5, the fluctuation convergence time KTCa of the battery 10 of Comparative Example 1 was 24.5 hours (KTCa=24.5 hrs). The fluctuation convergence time KTCb of the battery 10 of Example 1 was 13.2 hours (KTCb=13.2 hrs). The fluctuation convergence time KTCc of the battery 10 of Example 2 was 1.8 hours (KTC c = 1.8 hrs). Furthermore, the fluctuation convergence time KTCd of the battery 10 of Comparative Example 2 was 38.7 hours (KTCd = 38.7 hrs).

[0077] In this way, the fluctuation convergence time KTC is obtained in advance for the battery 10 of the preceding sample of the same product number or lot, and, for example, an initial voltage VB0 is selected that provides a convergence time KTC of 17.0 hours or less (KTC≦17.0 hrs). For example, according to Comparative Examples 1 and 2 and Examples 1 and 2 shown in Fig. 5, the fluctuation convergence time KTC can be set to within 17.0 hours by setting the initial voltage VB0 to a value within the range of 3.78 to 3.95 V for the first voltage VB1 of 3.750 V.

[0078] In this way, when the battery voltage VB is adjusted to the first voltage VB1 in the voltage adjustment step S4, the magnitude of the first voltage VB1 is set so that the fluctuation convergence time KTC of the fluctuation amount ΔV of the battery voltage VB due to Li diffusion is within 17 hours (within about 0.7 days) from the adjustment completion time Tc. Then, when the self-discharge inspection step S5 is started immediately after the adjustment completion time Tc, the influence of the fluctuation of the battery voltage VB due to Li diffusion can be reduced and the self-discharge inspection can be performed accurately. Alternatively, when the self-discharge inspection step S5 is started after the fluctuation of the battery voltage VB due to Li diffusion becomes sufficiently small, the self-discharge inspection step S5 can be started earlier, for example, one day after the adjustment completion time Tc, and the self-discharge inspection can be completed earlier.

[0079] Alternatively, for example, the initial voltage VB0 may be selected such that the fluctuation convergence time KTC is 5.0 hours or less (KTC≦5.0 hrs). For example, according to Comparative Examples 1 and 2 and Examples 1 and 2 shown in FIG. 5, by setting the initial voltage VB0 to a value within the range of 3.84 to 3.92 V for the first voltage VB1=3.750 V, Variation The convergence time KTC can be reduced to within 5.0 hours.

[0080] In this way, the first voltage VB1 is set to a value that makes the fluctuation convergence time KTC within 5 hours (within about 0.2 days). Then, when the self-discharge inspection process S5 is started immediately after the adjustment completion time Tc, the self-discharge inspection can be performed more accurately. Alternatively, the self-discharge inspection process S5 can be started earlier.

[0081] Although the present invention has been described above based on the embodiments (Examples 1 and 2), it goes without saying that the present invention is not limited to the embodiments and can be modified as appropriate without departing from the spirit of the present invention. For example, in Examples 1 and 2 and Comparative Examples 1 and 2, the first voltage VB1 adjusted in the voltage adjustment step S4 was fixed (VB1 = 3.750 V), while the initial voltage VB0 in the preceding initial charging step S1 was made different for each example, to obtain a range of the initial voltage VB0 appropriate for setting the fluctuation convergence time KTC to, for example, within 17.0 hours or 5.0 hours or less, and the initial voltage VB0 within this range was selected. However, the first voltage VB1 in the voltage adjustment step S4 may be set to a value that shortens the fluctuation convergence time KTC, for example, within 17.0 hours (KTC≦17.0 hrs) or within 5.0 hours (KTC≦5.0 hrs). Therefore, contrary to Examples 1 and 2, in the preceding sample battery 10, the initial voltage VB0 may be fixed (for example, VB0 = 3.750 V), while the first voltage VB1 in the voltage adjustment step S4 may be varied for each example to obtain a range of the first voltage VB1 appropriate for setting the fluctuation convergence time KTC to, for example, within 17.0 hours or 5.0 hours or less, and the first voltage VB1 to be set in the voltage adjustment step S4 may be selected from within this range.

[0082] Also, in the embodiment, in the manufacturing process of the battery 10, in the capacity inspection step S3, the battery 10 is charged to SOC 100%, then the battery 10 is discharged to SOC 0% to measure the capacity of the battery 10, and then in the voltage adjustment step S4, the battery voltage VB is set to the first voltage VB1 by charging. However, in the capacity inspection step, the battery 10 may be discharged to SOC 0%, then the battery 10 is charged to SOC 100% to measure the charge capacity of the battery 10, and then in the voltage adjustment step S4, the battery voltage VB may be set to the first voltage VB1 by discharging.

[0083] In the embodiment and the like, the relationship between the first voltage VB1 in the voltage adjustment step S4 performed prior to the self-discharge inspection step S5 and the initial voltage VB0 in the initial charging step S1 in the manufacturing process of the battery 10 has been considered. However, the present invention can also be applied to batteries 10 that have already been manufactured and released onto the market, such as batteries 10 already used in devices such as vehicles, and batteries 10 for reuse collected from the market. That is, when performing a self-discharge inspection on such a battery 10, the first voltage VB1 adjusted in the voltage adjustment step prior to the self-discharge inspection step may be set to a magnitude such that the fluctuation convergence time KTC of the fluctuation amount ΔV of the battery voltage VB caused by Li diffusion between the facing portion 322F and the non-facing portion 322N is within 17.0 hours or within 5.0 hours, for example. [Explanation of symbols]

[0084] 10 Battery (secondary battery) 10N Defective battery (secondary battery determined to be short circuited) 21 Positive terminal 25 Negative terminal 30 Electrode body 31 Positive electrode plate 312 Cathode active material layer 32 Negative plate 322 Negative electrode active material layer 322F facing section 322N Non-opposing part CF Opposing area concentration CN non-opposing area concentration ΔC concentration difference 34 Main body Cs (of a battery) Battery capacity VCs Battery capacity voltage Rs (battery) series resistance Rp (battery) parallel resistance IB battery current IBc charging current IBd discharge current VB Battery voltage VB0 Initial voltage VB1 1st voltage (1st battery voltage) ΔVB1 Voltage drop ΔV, ΔVa~ΔVd Deviation(variation in battery voltage due to diffusion of charge carrier atoms) ΔV1h, ΔV1ha~ΔV1hd 1 hour later Deviation amount VB2a Second voltage before storage (battery voltage before storage) VB2b Second voltage after storage (battery voltage after storage) DVB2 2nd voltage drop rate (actual voltage drop rate) When Tc adjustment is completed KT Elapsed Time KTC, KTCa~KTCd Fluctuation convergence time S1 Initial charging process S4 Voltage adjustment process (adjustment inspection process) S5 Self-discharge inspection process (adjustment inspection process) S51 Voltage measurement process before storage S52 Leaving process IH leaving period (predetermined period) S53 Voltage measurement process after storage S54 Decrease amount calculation process (actual measurement process) S55 Short circuit determination process (self-discharge determination process) S6 discharge process

Claims

1. An electrode assembly including a positive electrode plate including a positive electrode active material layer and a negative electrode plate including a negative electrode active material layer, The negative electrode active material layer includes a facing portion facing the positive electrode active material layer and a non-facing portion not facing the positive electrode active material layer. A method for testing a self-discharge of a secondary battery, comprising: a voltage adjustment step of charging or discharging the secondary battery to adjust the battery voltage to a first battery voltage; a self-discharge inspection step of holding the secondary battery in an open terminal state for a predetermined period of time and inspecting a self-discharge state of the secondary battery from a change in the battery voltage that occurs during the predetermined period of time; The voltage adjustment step includes: The first battery voltage, a fluctuation convergence time of the amount of fluctuation in the battery voltage due to diffusion of the charge carrier atoms that alleviates a concentration difference between a facing portion concentration, which is a concentration of charge carrier atoms present in the facing portion, and a non-facing portion concentration, which is a concentration of the charge carrier atoms present in the non-facing portion, in the negative electrode active material layer, the fluctuation convergence time is set to be within 17 hours from the completion of adjustment in which the battery voltage is adjusted to the first battery voltage in the voltage adjustment step, a change in the battery voltage is investigated until the battery voltage starts to decrease along a straight line, the straight line is extended backward in time to the completion of adjustment, a one-hour deviation amount that is the difference between the battery voltage one hour after the completion of adjustment and a value on the straight line is obtained, and the elapsed time at which the deviation amount between the acquired battery voltage and the value on the straight line has decreased to 10% of the one-hour deviation amount is obtained in advance as the fluctuation convergence time, and the fluctuation convergence time is set to be within 17 hours from the completion of adjustment. A method for testing secondary batteries for self-discharge.

2. 2. The method for inspecting a self-discharge of a secondary battery according to claim 1, The voltage adjustment step includes: The first battery voltage, The fluctuation convergence time is set to be within 5 hours from the completion of the adjustment. A method for testing secondary batteries for self-discharge.

3. 2. The method for inspecting a self-discharge of a secondary battery according to claim 1, The self-discharge inspection step includes: a pre-discharge voltage measuring step of measuring a pre-discharge battery voltage of the secondary battery; a step of leaving the secondary battery, the pre-discarded battery voltage of which has been measured, in an open terminal state for the predetermined period of time; a post-standing voltage measuring step of measuring a post-standing battery voltage of the secondary battery after the post-standing step; a measuring step of obtaining an actual voltage drop rate, which is an amount of voltage drop per unit time, by dividing a difference voltage between the pre-discarded battery voltage and the post-discarded battery voltage of the secondary battery by a period of discarding between them; and a self-discharge determination step of determining the degree of self-discharge of the secondary battery using the actual measured voltage drop rate of the secondary battery. A method for testing secondary batteries for self-discharge.

4. an initial charging step of initially charging the secondary battery to an initial voltage; An adjustment inspection step of inspecting the magnitude of self-discharge of the secondary battery by the method for inspecting self-discharge of a secondary battery according to any one of claims 1 to 3; and a discharge step of discharging the secondary battery determined to be short-circuited in the self-discharge inspection step. A method for manufacturing a secondary battery.

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