JP7727682B2 - Inspection method for lithium ion storage devices and manufacturing method for device group - Google Patents

Description

The present invention relates to a method for inspecting lithium-ion storage devices and a method for manufacturing a group of devices using the same.

When manufacturing electricity storage devices such as lithium-ion secondary batteries, it is preferable to be able to predict deterioration. Patent Document 1 discloses a battery deterioration prediction system that can improve the accuracy of predicting deterioration of secondary batteries through which large currents flow.

Japanese Patent Application Laid-Open No. 2022-007946

As employed in Patent Document 1, secondary batteries are evaluated based on the magnitude of battery capacity and battery resistance.
However, it has been found that even batteries with good battery capacity and resistance values may experience significant deterioration with subsequent use (repeated charging and discharging) compared to other batteries. The reason for this is that batteries with localized performance unevenness in the electrode assembly tend to deteriorate locally with use, compared to batteries with little localized performance unevenness in the electrode assembly, which is thought to result in more deterioration across the entire battery. However, localized performance unevenness in the electrode assembly cannot be detected by measuring the average characteristics of the entire battery, such as battery capacity and battery resistance.

The inventors therefore conducted research to find a new method for evaluating batteries and found that one of the causes of localized performance unevenness in electrode bodies is that the amount (thickness) of the SEI coating formed on the negative electrode active material particles varies depending on the location of the negative electrode active material layer in the negative electrode plate used in the electrode body. Specifically, if there are areas in the negative electrode active material layer where the amount of SEI coating is locally greater (thicker) or less (thinner) than areas with an average amount of SEI coating, then with subsequent use of the battery, deterioration will progress in the areas with a greater or lesser amount of SEI coating than in areas with an average amount of SEI coating, and deterioration will also progress when viewed from the perspective of the battery as a whole.

The present invention was made in light of this knowledge and provides a method for inspecting lithium ion storage devices that makes it possible to predict the degree of deterioration, and a method for manufacturing a group of devices that are less likely to deteriorate using this inspection method.

(1) One aspect of the present invention for solving the above-mentioned problems is a method for inspecting a lithium ion storage device, the method comprising: an electrolyte solution containing lithium; a positive electrode plate having a positive electrode active material layer; a negative electrode plate having a coated negative electrode active material layer on which a lithium-containing Li-containing SEI coating is formed; an electrode body having a separator interposed between the positive electrode active material layer and the coated negative electrode active material layer and permeated with the electrolyte solution; and a case accommodating the electrode body and the electrolyte solution, wherein the Li-containing S of the coated negative electrode active material layer is detected. The method for inspecting a lithium ion storage device includes: a degradation step of subjecting the lithium ion storage device to a degradation test that thickens the EI coating; a negative electrode plate removal step of dismantling the lithium ion storage device that has been degraded in the degradation step and removing the negative electrode plate; a removal step of washing and removing the electrolyte adhering to the removed negative electrode plate; and a Li amount distribution acquisition step of examining the linear distribution or planar distribution in the width direction or length direction of the Li amount contained in the Li-containing SEI coating of the coated negative electrode active material layer.

In this method for inspecting a lithium-ion storage device (hereinafter simply referred to as the device), the device is disassembled, the negative electrode plate is removed, the negative electrode plate is washed to remove any adhering electrolyte, and the distribution of the amount of Li contained in the Li-containing SEI coating formed on the coated negative electrode active material layer is investigated. This makes it possible to determine the distribution of the amount of SEI coating formed on the negative electrode active material particles in the coated negative electrode active material layer of the negative electrode plate of the device's electrode body from the distribution of Li. Thus, the presence or absence and degree of localized uneven distribution of the SEI coating makes it possible to predict the degree of degradation, such as whether the device will deteriorate quickly or slowly if used.

Note that examples of lithium ion storage devices include lithium ion secondary batteries and capacitors such as lithium ion capacitors. The electrode body housed in the device may be a laminated electrode body or a wound electrode body. Examples of wound electrode bodies include cylindrical wound electrode bodies and flat wound electrode bodies.

The electrolyte may be a non-aqueous electrolyte obtained by dissolving a supporting salt in an organic solvent. Examples of organic solvents used in the electrolyte include cyclic carbonates such as propylene carbonate and ethylene carbonate (EC), and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate, and ethyl methyl carbonate (EMC).

_Examples of supporting salts to be dissolved in the electrolytic solution include _lithium salts that can _serve as electrolytes, such as _LiBF4 , _LiAsF6 , _LiPF6 , _LiCF3SO3 , LiN( _SO2CF3 ) ₂ , _LiN ( _SO2C2F5 ) ₂ , and LiN( _SO2CF3 ) _{( SO2C4F9} ) _. These salts may be used alone or in mixtures of two or more thereof _, but are not limited to these.

Methods for examining the distribution of Li content in the Li content distribution acquisition process include ICP-MS, ICP-OES, XPS, AES, and EDS.

The Li amount distribution data to be acquired may be any data on the distribution of Li amount in a specified range to be investigated, such as linear distribution data obtained in a linear range extending in a desired direction, such as the width or length direction of the negative electrode active material layer, or surface distribution data in a desired circular or rectangular range.

(2) The method for inspecting a lithium ion storage device according to (1) above, wherein the electrolyte is a P-containing electrolyte containing a supporting salt containing phosphorus, and the coated negative electrode active material layer of the negative electrode plate has a LiP-containing SEI coating that also contains phosphorus, the Li-containing SEI coating being formed on the phosphorus-free negative electrode active material layer, and the method for inspecting a lithium ion storage device may further include a P amount distribution acquisition step, which is performed instead of the Li amount distribution acquisition step or together with the Li amount distribution acquisition step, of examining a linear distribution or a planar distribution of the P amount contained in the LiP-containing SEI coating of the coated negative electrode active material layer in the width direction or the length direction .

In this device inspection method, the device's electrolyte is a phosphorus-containing electrolyte, and the coated negative electrode active material layer contains a LiP-containing SEI coating that contains not only lithium but also phosphorus, while the negative electrode active material layer does not contain phosphorus. Additionally, the method includes a phosphorus amount distribution acquisition step performed instead of or in conjunction with the Li amount distribution acquisition step. Therefore, the distribution of the amount of the SEI coating formed on the negative electrode active material particles in the coated negative electrode active material layer of the negative electrode plate of the device's electrode body can be determined from the phosphorus amount distribution or the distribution of the phosphorus amount and the lithium amount distribution. Even in this way, the degree of deterioration of the device when used can be predicted from the presence or absence and degree of localized SEI coating unevenness.
Furthermore, by measuring the distribution of the Li amount and the distribution of the P amount in the same region, it is possible to more reliably detect the presence or absence and degree of local uneven distribution of the SEI film and predict the progress of deterioration of the device.

An example of a phosphorus-containing supporting salt is LiPF _6. Methods for examining the distribution of P content include ICP-MS, ICP-OES, XPS, AES, and EDS.

The P content distribution data to be obtained may be P content distribution data for a specified range to be investigated, such as linear distribution data obtained for a range extending linearly in a desired direction, such as the width or length of the negative electrode active material layer, or planar distribution data for a desired circular or rectangular range. Furthermore, when obtaining Li content distribution in addition to P content distribution, it is preferable to obtain P content and Li content at the same position. This makes it easier to compare the distributions of the two elements.

(3) Another aspect is a method for manufacturing a device group consisting of a plurality of lithium ion storage devices, the method comprising: an electrode body having an electrolyte solution, a positive electrode plate having a positive electrode active material layer, a negative electrode plate having a coated negative electrode active material layer in which a lithium-containing SEI coating containing lithium is formed on negative electrode active material particles, a separator interposed between the positive electrode active material layer and the coated negative electrode active material layer, and the electrolyte solution permeated therein; and a case accommodating the electrode body and the electrolyte solution, the method comprising the steps of: selecting a sample device from an undetermined device group consisting of a plurality of the lithium ion storage devices; The method for manufacturing a device group includes: a degradation step of subjecting the sample device to a degradation test in which the Li-containing SEI coating of the film-coated negative electrode active material layer is thickened; a negative electrode plate removal step of disassembling the degraded sample device and removing the negative electrode plate; a removal step of washing and removing the electrolyte adhering to the removed negative electrode plate; a Li amount distribution acquisition step of examining a linear distribution or a planar distribution of the Li amount contained in the Li-containing SEI coating of the film-coated negative electrode active material layer in the width direction or the length direction; and a determination step of selecting the sample device and determining whether the device group is good or bad based on the obtained Li amount distribution.

In this device group manufacturing method, a sample device is selected from the device group and subjected to a degradation test. The sample device is then disassembled to remove the negative electrode plate, which is then washed to remove any adhering electrolyte, and the distribution of Li contained in the Li-containing SEI coating formed on the coated negative electrode active material layer is investigated. This allows the distribution of Li amounts to be determined from the distribution of Li amounts, which allows the distribution of the amount of SEI coating formed on the negative electrode active material particles in the coated negative electrode active material layer of the negative electrode plate of the electrode body of the sample device to be determined. In addition, the presence or absence and degree of localized uneven distribution of the SEI coating on the sample device allows the degree of degradation to be predicted and selected when using the undetermined device group from which the sample device was obtained. In this way, a good device group with slow degradation characteristics can be manufactured.

One method for selecting sample devices from a device group in the selection process is to randomly select one or more sample devices from the multiple devices that make up the device group. It is also possible to select the first, last, or intermediate device manufactured from a device group that makes up a production lot. Sample devices can also be selected based on device characteristics, such as selecting a sample device with a pre-tested characteristic, such as battery capacity, that has the average size of the device group.

(4) The method for manufacturing a device group of (3), further comprising the steps of: (a) preparing a device group including a negative electrode active material layer having a negative electrode active material layer free of phosphorus and a LiP-containing SEI coating that also contains phosphorus; (b) preparing a device group including a negative electrode active material layer having a negative electrode active material layer free of phosphorus and a LiP-containing SEI coating that also contains phosphorus; (c) preparing a device group including a negative electrode active material layer having a negative electrode active material layer free of phosphorus and a LiP-containing SEI coating that also contains phosphorus; (d) preparing a device group including a negative electrode active material layer having a negative electrode active material layer free of phosphorus and a LiP-containing SEI coating that also contains phosphorus; (e) preparing a device group including a negative electrode active material layer having a negative electrode active material layer free of phosphorus and a LiP-containing SEI coating that also contains phosphorus; (f ...g) preparing a device group including a negative electrode active material layer free of phosphorus and a LiP-containing SEI coating that also contains phosphorus;

In this device group manufacturing method, the electrolyte of each device is a phosphorus-containing electrolyte, and the coated negative electrode active material layer contains a LiP-containing SEI coating that contains phosphorus in addition to lithium while not containing phosphorus. Additionally, a P amount distribution acquisition process is performed on the sample device in place of or in addition to the Li amount distribution acquisition process. Therefore, the P amount distribution or the P and Li amount distribution can be used to determine the amount of SEI coating formed on the negative electrode active material particles in the coated negative electrode active material layer of the negative electrode plate of the device's electrode body. In this way, the presence or absence and degree of localized SEI coating unevenness can be used to predict and select the degree of degradation that will occur when using the untested device group from which the sample device was obtained, enabling the production of a high-quality device group with slow degradation characteristics.

(5) In the device group manufacturing method of (3), the judgment step may be a device group manufacturing method in which the pass/fail judgment of the unjudged device group is performed using the minimum and maximum Li amount values in the obtained Li amount distribution.

This device group manufacturing method uses the minimum and maximum Li amounts in the assessment process, making it easy to assess the pass/fail status of unassessed device groups.

In the device group manufacturing method (6) or (4), the judgment step may be a device group manufacturing method in which the pass/fail of the undetermined device group is determined using the minimum and maximum P amounts in the obtained P amount distribution, or using the minimum and maximum P amounts and the minimum and maximum Li amounts in the obtained Li amount distribution.

In this device group manufacturing method, the pass/fail judgment of the unjudged device group can be performed simply by using the minimum and maximum P amounts in the judgment process, or more reliably by using the minimum and maximum P amounts, as well as the minimum and maximum Li amounts.

(7) Furthermore, in the method for manufacturing a device group described in any one of (3) to (6), the degradation step may be a step of reducing the capacity of the sample device until the capacity maintenance rate becomes smaller than a predetermined value.

In this device group manufacturing method, the capacity of the sample device is reduced in the degradation process until the capacity retention rate becomes smaller than a predetermined value. This makes it possible to appropriately determine the quality of the sample device, and ultimately the quality of the undetermined device group, using the Li amount distribution obtained in the Li amount distribution acquisition process or the P amount distribution obtained in the P amount distribution acquisition process.

Incidentally, a forced degradation test to reduce the capacity of a sample device can be performed by conducting a charge-discharge cycle test in which charging and discharging are repeated over a predetermined SOC range. In this sample device, the amount of SEI coating formed on the negative electrode active material particles in the coated negative electrode active material layer can be increased quickly, allowing for early determination of the quality of the device group.

FIG. 1 is a partially cutaway perspective view of a battery according to an embodiment and first and second modified embodiments. FIG. 10 is a perspective view of a flat wound electrode body according to the embodiment and modified embodiments 1 and 2. FIG. 10 is an explanatory diagram showing the positive electrode plate, the negative electrode, and the separator in a flat wound electrode assembly according to the embodiment and modified examples 1 and 2. FIG. 10 is an explanatory diagram showing a state in which a negative electrode SEI coating is formed on a negative electrode active material particle of a coating-coated negative electrode active material layer according to the embodiment and modified examples 1 and 2. 3 is a flowchart showing a manufacturing process of a battery pack according to an embodiment. 1 is a graph showing an example of the distribution of the amount of Li contained in a strip-shaped coated negative electrode active material layer obtained from degraded good batteries of a good product lot and defective batteries of a defective product lot. 1 is a graph showing the relationship between the capacity maintenance rate of good batteries from a degraded good product lot and defective batteries from a defective product lot and the Li fluctuation rate obtained from the distribution of Li amounts. 10 is a flowchart showing a manufacturing process of a battery pack according to a first modified embodiment. 1 is a graph showing an example of the distribution of P amounts contained in strip-shaped coated negative electrode active material layers obtained from degraded good batteries from a good product lot and defective batteries from a defective product lot. 10 is a graph showing the relationship between the capacity maintenance rate of good batteries from a degraded good product lot and defective batteries from a defective product lot and the P fluctuation rate obtained from the P amount distribution. 10 is a flowchart showing a manufacturing process of a battery pack according to a second modified embodiment.

(Embodiment)
Hereinafter, a battery group GB (an example of a device group) including a plurality of batteries 1 (an example of a lithium ion power storage device) that are lithium ion secondary batteries according to an embodiment of the present invention, and the manufacture thereof, will be described with reference to Figures 1 to 7. The plurality of batteries 1 belonging to this battery group GB are each a prismatic, sealed lithium ion secondary battery, and are installed in vehicles such as hybrid cars, plug-in hybrid cars, and electric cars, as well as in various devices.

The battery 1 of this embodiment includes a rectangular parallelepiped case 7 and an electrode assembly 2 and electrolyte 6 housed inside the case 7. Made of metal (aluminum in this embodiment), the rectangular parallelepiped box-shaped case 7 comprises a bottomed, square cylindrical case body 7H and a lid 7L located at the upper BH1 in the height direction BH. A positive electrode terminal 8P and a negative electrode terminal 8N are fixed to the lid 7L via an insulating member 9. A liquid filling hole 7LH for filling the electrolyte 6 is drilled in the lid 7L, and after filling, the hole is sealed with a liquid filling plug 7LP. The electrode assembly 2 is covered in a bag-shaped insulating film (not shown) inside the case 7. A portion of the electrolyte 6 housed in the case 7 is impregnated into the electrode assembly 2, and the remainder accumulates at the bottom of the case 7.

The electrode assembly 2 (see Figures 2 and 3) is a so-called flat-wound electrode assembly, consisting of a strip-shaped positive electrode plate 3 and a strip-shaped negative electrode plate 4 wound with a pair of strip-shaped separators 5 between them, pressed flat in the thickness direction CH, and housed in the case 7. The electrode assembly 2 is housed in the case 7 in a horizontal position with the winding axis AX aligned with the width direction AH (the left-right direction in Figure 1).

In the flat-wound electrode assembly 2, a positive current collecting portion 2P, on which the current collecting portion 3S of the positive electrode plate 3 is wound, is provided on one side XH1 in the axial direction XH along the winding axis AX (in this embodiment, this corresponds to one side AH1 in the width direction AH of the battery 1; upper side in Figure 2). Conversely, a negative current collecting portion 2N, on which the current collecting portion 4S of the negative electrode plate 4 is wound, is provided on the other side XH2 in the axial direction XH (in this embodiment, this corresponds to the other side AH2 in the width direction AH of the battery 1; lower side in Figure 2). The portion between the positive current collecting portion 2P and the negative current collecting portion 2N is a main body portion 2H, on which the positive electrode plate 3 and negative electrode plate 4 are wound with a separator 5 interposed between them.

The positive electrode terminal 8P is made of an aluminum plate bent into a predetermined shape. The inner connection portion 8PI, which forms one end of the positive electrode terminal 8P, is connected to the positive electrode current collector 2P, which is located on one side AH1 in the width direction AH of the electrode body 2. Meanwhile, the other end of the positive electrode terminal 8P extends outside the case 7 (specifically, onto the lid 7L) to form the external terminal 8PO. The negative electrode terminal 8N is made of a copper plate bent into a predetermined shape. The inner connection portion 8NI, which forms one end of this negative electrode terminal 8N, is connected to the negative electrode current collector 2N, which is located on the other side AH2 in the width direction AH of the electrode body 2. Meanwhile, the other end of the negative electrode terminal 8N extends outside the case 7 (specifically, onto the lid 7L) to form the external terminal 8NO.

The electrolyte 6 is a non-aqueous electrolyte containing an organic solvent 6V and a supporting salt 6S. In this embodiment, the organic solvent 6V is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a weight ratio of 3:4:3. _LiPF6 is used as the supporting salt 6S containing P. The concentration of _LiPF6 in the electrolyte 6 is 1.1 mol/L.

As shown in FIG. 3 , the strip-shaped positive electrode plate 3 of the electrode body 2 includes a positive electrode foil 3F made of aluminum foil and a positive electrode active material layer 3A laminated on both surfaces of the positive electrode foil 3F. The positive electrode active material layer 3A is composed of positive electrode active material particles, conductive particles, and a binder (not shown). In this embodiment, the positive electrode active material particles are lithium transition metal composite oxide particles, specifically, for example, lithium nickel cobalt manganese composite oxide particles. The conductive particles are, for example, acetylene black (AB). The binder is, for example, polyvinylidene fluoride (PVDF). At the end of one side WH1 (upper side in FIG. 3 ) of the strip-shaped positive electrode plate 3 in the width direction WH, the positive electrode active material layer 3A is not present on the positive electrode foil 3F, forming a current collecting portion 3S where the positive electrode foil 3F is exposed. Meanwhile, the remaining portion of the positive electrode plate 3 is a positive electrode portion 3P in which positive electrode active material layers 3A are laminated on both surfaces of a positive electrode foil 3F. As can be seen from Figures 2 and 3, the width direction WH (the vertical direction in Figure 3) of the positive electrode plate 3 and the like coincides with the axial direction XH, and one side WH1 coincides with one side XH1.

On the other hand, the strip-shaped negative electrode plate 4 of the electrode body 2 includes a negative electrode foil 4F made of copper foil and a coated negative electrode active material layer 4A laminated on both surfaces of the negative electrode foil 4F. This coated negative electrode active material layer 4A includes a negative electrode active material layer 4AB made of negative electrode active material particles 4AP and a binder (not shown) that does not contain P, and a negative electrode SEI coating 4AC formed in a coating state around the negative electrode active material particles 4AP during the initial charging process described below. In this embodiment, graphite particles are used as the negative electrode active material particles 4AP. Furthermore, carboxymethyl cellulose (CMC), for example, is used as the binder. At the end of the other side WH2 (lower in Figure 3) of the strip-shaped negative electrode plate 4 in the width direction WH, the coated negative electrode active material layer 4A is not present on the negative electrode foil 4F, forming a current collecting portion 4S where the negative electrode foil 4F is exposed. Meanwhile, the remaining portion of the negative electrode plate 4 is the negative electrode portion 4N, in which a coated negative electrode active material layer 4A is laminated on both surfaces of the negative electrode foil 4F.

The pair of strip-shaped separators 5 in the electrode assembly 2 are made of porous resin. As shown in FIG. 3, the separators 5 are wound and stacked between the negative electrode plate 4 and the positive electrode plate 3. The negative electrode plate 4 and negative electrode portion 4N are slightly wider in the width direction WH than the positive electrode plate 3 and positive electrode portion 3P. Furthermore, the negative electrode portion 4N is arranged so as to cover the entire positive electrode portion 3P in the width direction WH, i.e., so that the coated negative electrode active material layer 4A faces the positive electrode active material layer 3A at every position on the positive electrode active material layer 3A. The separator 5 is also slightly wider in the width direction WH than the negative electrode portion 4N and positive electrode portion 3P. Furthermore, the separator 5 is arranged so as to cover the entire negative electrode portion 4N and positive electrode portion 3P in the width direction WH, i.e., so that the separator 5 covering the positive electrode active material layer 3A and the coated negative electrode active material layer 4A is present at every location of the positive electrode active material layer 3A and the coated negative electrode active material layer 4A.

In addition, by performing initial charging after the electrolyte solution 6 has permeated the electrode body 2 of the battery 1, as shown in FIG. 4, a negative electrode SEI coating 4AC containing Li and P is formed around the negative electrode active material particles 4AP that constitute the coated negative electrode active material layer 4A formed on the negative electrode foil 4F of the negative electrode plate 4. The negative electrode SEI coating 4AC is derived from the organic solvent 6V and supporting salt 6S containing P (phosphorus) contained in the electrolyte solution 6. The formation of this negative electrode SEI coating 4AC enables stable charging and discharging of the battery 1 with low resistance, compared to when the negative electrode SEI coating 4AC is not formed or is insufficiently formed.

When manufacturing the battery 1, the electrode assembly 2 is connected to the positive electrode terminal 8P and the negative electrode terminal 8N and housed in the case 7. The electrolyte 6 is then poured into the case 7. The electrolyte 6 then permeates from the outer side XHO to the inner side XHI in the axial direction XH of the electrode assembly 2, i.e., from one side XH1 and the other side XH2, toward the interior of the electrode assembly 2. Specifically, the electrolyte 6 permeates along the positive electrode plate 3, negative electrode plate 4, and separator 5 from one side WH1 and the other side WH2 in the width direction WH (the upper and lower sides in FIG. 3 ), which coincide with the axial direction XH, toward the center line ML of the width direction WH of the negative electrode active material layer 4AB, i.e., toward the inner side WHI in the width direction WH.

After a predetermined waiting time TT has elapsed since the start of the liquid injection, a power source (not shown) is connected to the positive electrode terminal 8P and the negative electrode terminal 8N, and a voltage is applied to the electrode body 2 of the battery 1 via the positive electrode terminal 8P and the negative electrode terminal 8N to perform initial charging. That is, a voltage is applied between the positive electrode plate 3 and the negative electrode plate 4 of the electrode body 2 in a predetermined initial charging pattern, and an anode SEI coating 4AC made of electrolyte 6 is formed on the anode active material particles 4AP in the anode active material layer 4AB of the negative electrode plate 4, forming a coated anode active material layer 4A (see Figure 4). In this embodiment, initial charging was performed using an initial charging pattern of 0.5C-CCCV charging (SOC 85%). The liquid injection hole 7LH is then sealed with the liquid injection plug 7LP.

Next, the sealed batteries 1 are subjected to high-temperature aging by being left in a 60°C environment for 25 hours. Furthermore, various tests are conducted on the batteries 1 to complete the batteries 1. This unassessed battery group manufacturing process S1 produces an unassessed battery group GBB, which is made up of a large number of batteries 1 and is managed by a single manufacturing lot number, etc., and whose deterioration prediction, as described below, has not yet been assessed (see Figure 5).

However, depending on the battery 1, the anode SEI coating 4AC formed on the anode active material layer 4AB by the electrolyte 6 during initial charging may not be formed uniformly over the entire coated anode active material layer 4A, resulting in location-specific variations (unevenness) in the amount and composition of the anode SEI coating 4AC.

Thus, even in a battery 1 in which unevenness occurs in the negative electrode SEI coating 4AC formed on the film-coated negative electrode active material layer 4A, various characteristics such as battery capacity and battery resistance are good at the initial stage of use. However, it has been found that a battery 1 in which unevenness occurs in the negative electrode SEI coating 4AC deteriorates significantly as it is repeatedly charged and discharged with subsequent use, compared to the deterioration state of a battery 1 in which unevenness occurs in the negative electrode SEI coating 4AC.
It was thought that this was because in a battery 1 in which unevenness occurs in the negative electrode SEI coating 4AC and localized uneven performance exists in the electrode body 2, deterioration progresses locally as the battery 1 is used, and therefore deterioration is likely to progress even when viewed as a whole.

(Li amount distribution investigation)
Therefore, we prepared a defective battery 1N, which showed significant degradation despite being used in the same manner, and a good battery 1G, which showed relatively slow degradation and maintained good characteristics. Each battery 1G and 1N was discharged to 0% SOC and disassembled in a glove box under an inert atmosphere to remove the electrode assembly 2. The electrode assembly 2 was then unwound (see FIG. 3 ) to remove the strip-shaped negative electrode plate 4. A negative electrode sample (not shown) including a region for measuring the Li content distribution was obtained from this negative electrode plate 4. For example, the flattened portion of the negative electrode plate 4 was cut in the width direction WH (the vertical direction in FIG. 3 ) to obtain a tape-shaped negative electrode sample extending in the width direction WH.

The negative electrode sample was then washed with EMC to remove the electrolyte 6. This removed Li, _LiPF6 , and other elements contained in the electrolyte 6. Next, ICP-MS was used to obtain the distribution of the amount of Li contained in the negative electrode SEI coating 4AC formed on the coated negative electrode active material layer 4A in a desired measurement region of the negative electrode sample. Specifically, the ICP-MS was used to measure the amount of Li AL at each width direction position WP in a linear measurement region extending in the width direction WH.

Figure 6 shows the results of measuring the distribution of Li content AL for good battery 1G and defective battery 1N. The horizontal axis of the graph in Figure 6 represents the widthwise position WP, measured in mm from the edge 4AE1 on one side WH1 in the widthwise direction WH of the negative electrode plate 4 shown in Figure 3 toward the other side WH2 in the widthwise direction WH. On the other hand, the vertical axis of the graph in Figure 6 represents the relative value indicating the relative magnitude of the Li content AL.

Figure 6 shows that the distribution of Li content AL in the good battery 1G, shown by the solid line, was almost constant regardless of the widthwise position WP. In other words, it can be seen that there was very little variation (unevenness) in the Li content AL in the widthwise direction WH in the coated negative electrode active material layer 4A. From these results, it can be seen that in the good battery 1G, the amount (thickness) of the negative electrode SEI coating 4AC formed in the coated negative electrode active material layer 4A was also almost constant regardless of the widthwise position WP, with only slight variation (unevenness).

On the other hand, the distribution of the Li content AL of the defective battery 1N, shown by the dashed line in Figure 6, contained localized areas, specifically areas near the widthwise position WP of 28 to 37 mm and 42 to 49 mm, where the Li content AL was significantly greater than in other areas. This indicates that the Li content AL contained in the negative electrode SEI coating 4AC in the defective battery 1N exhibited significant variations (unevenness) at the widthwise position WP. This indicates that the amount (thickness) of the negative electrode SEI coating 4AC formed on the coated negative electrode active material layer 4A in the defective battery 1N also existed locally in significantly larger areas, resulting in significant variations (unevenness) at the widthwise position WP. Furthermore, in areas where the amount of negative electrode SEI coating 4AC was abnormally large, localized abnormal degradation of battery characteristics occurred, specifically, localized reductions in battery capacity and localized increases in battery resistance occurred. This is thought to have caused the overall battery characteristics of defective battery 1N to deteriorate significantly compared to those of good battery 1G. It is also assumed that the above-mentioned localized abnormal increase in the amount (thickness) of negative electrode SEI coating 4AC gradually accumulated as the battery was used.

(Investigation of Li variation ratio)
Therefore, a plurality of unused good-quality batteries 1G from the same lot (good-quality lot) as the good-quality battery 1G used in the investigation shown in Fig. 6, and a plurality of unused defective batteries 1N from the same lot (defective lot) as the defective battery 1N used in the investigation shown in Fig. 6, are prepared. A predetermined charge-discharge cycle test, specifically a forced deterioration test based on a charge-discharge cycle test in which 1C CCCV charging and 1C CCCV discharging are repeated in the range of SOC 20 to 80%, is performed on each of the good-quality batteries 1G and the defective batteries 1N, causing the negative electrode SEI coating 4AC to thicken over time and causing deterioration in each of the batteries 1G and 1N.

In this embodiment, forced degradation tests were conducted on multiple good batteries 1G and defective batteries 1N, with seven levels of capacity retention, including a case where no forced degradation test was conducted (test time 0 hours). That is, the forced degradation tests were conducted until the time when the good batteries 1G or defective batteries 1N were estimated to reach a predetermined capacity retention, and the battery capacities of the removed good batteries 1G and defective batteries 1N were measured. The capacity retention rates CC of the batteries 1G and 1N were calculated from the pre-test battery capacities obtained before the forced degradation test. Note that the number of cycles and test times of the charge-discharge cycle tests conducted on good batteries 1G and defective batteries 1N that achieved approximately the same capacity retention rates CC were different from each other.

Then, in the same manner as in the Li content AL distribution investigation described above, the good battery 1G and the defective battery 1N were disassembled, and a Li content AL distribution similar to that shown in Figure 6 was obtained using the negative electrode sample of the negative electrode plate 4. Next, as shown in Figure 6, the minimum Li content LI and maximum Li content LX were obtained from the Li content AL distribution, and the Li fluctuation ratio RL was calculated using RL = LX/LI. Specifically, the minimum Li content GLI and maximum Li content GLX were obtained from the Li content AL distribution of the good battery 1G. The Li fluctuation ratio RL of the good battery 1G was calculated using RL = GLX/GLI. Similarly, the minimum Li content NLI and maximum Li content NLX were obtained from the Li content AL distribution of the defective battery 1N, and the Li fluctuation ratio RL of the defective battery 1N was calculated using RL = NLX/NLI.

Figure 7 shows the changes in capacity retention rate CC and Li fluctuation ratio RL obtained from multiple good batteries 1G and multiple bad batteries 1N. Figure 7 shows that for good batteries 1G, shown by the solid line, the Li fluctuation ratio RL remains roughly the same even as the capacity retention rate CC gradually decreases over time as the aforementioned forced degradation test is performed. This means that for good batteries 1G, even as they deteriorate, the amount (thickness) of the negative electrode SEI coating 4AC remains roughly uniform in the width direction WH, with no unevenness.

In contrast, in the defective battery 1N, the Li fluctuation ratio RL was roughly the same as that of the good battery 1G at the beginning of the aforementioned forced degradation test, i.e., until the capacity retention rate CC reached approximately 97%. However, unlike the good battery 1G, as the forced degradation test was extended and the capacity retention rate CC decreased beyond 97%, the Li fluctuation ratio RL increased as the capacity retention rate CC decreased. By performing the forced degradation test, abnormal formation of the negative electrode SEI coating 4AC occurred in specific areas of the coated negative electrode active material layer 4A, and the abnormal formation area expanded to the surrounding area. Furthermore, in the abnormal formation area, the abnormally formed negative electrode SEI coating 4AC made it difficult for the battery reaction to occur, resulting in a local decrease in battery capacity and an increase in battery resistance. This is thought to have resulted in a decrease in battery capacity, etc., for the electrode body 2 of the defective battery 1N as a whole.

These results show that for a certain battery 1, before the aforementioned forced degradation test is conducted, or after a short-term forced degradation test is conducted to slightly degrade the battery, and at a stage when the capacity retention rate CC is maintained at approximately 97% or higher, even if this battery 1 is disassembled and the aforementioned Li amount distribution investigation is conducted to obtain the distribution of Li amount AL (see Figure 6), it is not possible to properly determine whether this battery 1 is a good battery 1G or a defective battery 1N.

However, if the aforementioned forced degradation test is performed until the capacity retention rate CC reaches 95% or less, and then the aforementioned Li amount distribution investigation is performed, it is possible to determine whether the battery 1 is a good battery 1G or a bad battery 1N. Specifically, for example, as shown by the dashed-dotted line in Figure 7, a threshold value RLT (RLT = 2.0 in Figure 7) is set for the Li fluctuation ratio RL, and if the obtained Li fluctuation ratio RL is smaller than the threshold value RLT, the battery is determined to be a good battery 1G, and if it is larger than the threshold value RLT, the battery is determined to be a bad battery 1N. This also makes it possible to determine whether the undetermined battery group GBB to which the battery 1 belongs is a good battery group GBG consisting of good batteries 1G, or a bad battery group GBN consisting of bad batteries 1N (see Figure 5).

(Manufacturing of battery groups)
In this embodiment, a battery group GB that comprises a single production lot and includes a large number of batteries 1 is manufactured as follows: First, in an unassessed battery group manufacturing step S1, a known method is used to manufacture an unassessed battery group GBB that comprises a single production lot and includes a large number of batteries 1 (see FIG. 1, for example). It is assumed that each battery 1 has already undergone high-temperature aging and initial charging.

Next, in the selection step S2, one or a small number of sample batteries 1S are selected from the large number of batteries 1 belonging to the undetermined battery group GBB. In the subsequent degradation step S3, the selected sample battery 1S is subjected to the aforementioned forced degradation test. Specifically, the aforementioned forced degradation test is conducted to reduce the capacity of the sample battery 1S until the capacity retention rate CC of the sample battery 1S falls to a predetermined value of 95% or less, specifically, approximately 95-93%. By conducting this forced degradation test (charge-discharge cycle test), the amount of negative electrode SEI coating 4AC formed on the negative electrode active material particles 4AP of the coated negative electrode active material layer 4A in the sample battery 1S can be quickly increased, allowing for early determination of the quality of the undetermined battery group GBB.

After the forced degradation test is completed, in the negative electrode plate removal process S4, the sample battery 1S is discharged to 0% SOC and disassembled in a glove box under an inert atmosphere, and the electrode assembly 2 is removed. The electrode assembly 2 is then unwound to remove the strip-shaped negative electrode plate 4. A negative electrode sample (not shown) including a region for measuring the Li content distribution is obtained from this negative electrode plate 4. For example, the flattened portion of the negative electrode plate 4 is cut in the width direction WH (the vertical direction in Figure 3) to obtain a tape-shaped negative electrode sample extending in the width direction WH.

In the removal step S5, the removed negative electrode sample of the negative electrode plate 4 is washed with EMC to remove the attached electrolyte 6. As a result, Li, LiPF ₆ , and the like contained in the electrolyte 6 are removed from the negative electrode sample of the negative electrode plate 4.

In the Li amount distribution acquisition step S6, the distribution of the Li amount AL contained in the negative electrode SEI coating 4AC formed on the coated negative electrode active material layer 4A is obtained for the desired measurement area using IPC-MS, as described above (see Figure 6).

Then, in the judgment step S7, the quality of the unjudged battery group GBB from which the sample battery 1S was obtained is judged based on the obtained distribution of Li amount AL. Specifically, as described above, for example, the minimum Li amount LI and maximum Li amount LX are obtained from the distribution of Li amount AL to calculate the Li fluctuation ratio RL. The obtained Li fluctuation ratio RL is compared with a predetermined threshold value RLT, and if the Li fluctuation ratio RL is greater than the threshold value RLT (RL > RLT), the sample battery 1S is judged to be a defective battery 1N. At the same time, the unjudged battery group GBB to which the sample battery 1S belongs is judged to be a defective battery group GBN (NG in the judgment step S7). Processing such as disposal is then carried out.

Conversely, for example, if the Li fluctuation ratio RL is smaller than the threshold value RLT (RL<RLT), the sample battery 1S is determined to be a good battery 1G (GOOD in determination step S7). At the same time, the undetermined battery group GBB to which the sample battery 1S belongs is determined to be a good battery group GBG. In this way, a good battery group GB (good battery group GBG) with slow degradation characteristics can be manufactured.

In this way, in this embodiment, the minimum Li amount LI and maximum Li amount LX are used in the determination step S7, making it possible to easily determine whether the undetermined battery group GBB is good or bad.

(Variation 1)
In the above-described embodiment, when manufacturing the battery group GB, the distribution of the Li amount AL was obtained from the negative electrode sample of the negative electrode plate 4 of the sample battery 1S, and this Li amount distribution was used to determine the quality of the sample battery 1S and the undetermined battery group GBB to which this sample battery 1S belongs (see Figure 5).
However, the electrolyte 6 of the battery 1 described above is a phosphorus-containing electrolyte containing a supporting salt 6S, specifically LiPF _6. Therefore, during initial charging, the negative electrode SEI coating 4AC formed on the negative electrode active material particles 4AP contains P in addition to Li.

(Distribution survey of P content)
Therefore, in this modified embodiment 1, instead of obtaining the Li amount distribution (see FIG. 6 ), the distribution of the P amount AP in the negative electrode sample obtained from the negative electrode plate 4 is obtained. That is, as in the embodiment, an ICP-MS is used to obtain the distribution of the P amount AP contained in the negative electrode SEI coating 4AC formed on the coated negative electrode active material layer 4A for the desired measurement region of the negative electrode sample obtained for the aforementioned good battery 1G and defective battery 1N (see FIG. 9 ). The horizontal axis of the graph in FIG. 9 also represents the width direction position WP, which is indicated by the dimension (mm) measured from the edge 4AE1 on one side WH1 in the width direction WH to the other side WH2 in the width direction WH, of the negative electrode plate 4 shown in FIG. 3 . Meanwhile, the vertical axis of the graph in FIG. 9 represents a relative value indicating the relative magnitude of the P amount AP.

As can be easily understood by comparing FIG. 9 with FIG. 6, in the good battery 1G shown by the solid line in FIG. 9, the distribution of the P amount AP, like the distribution of the Li amount AL, is approximately constant regardless of the widthwise position WP. In other words, it can be seen that the variation (unevenness) in the widthwise direction WH of the P amount AP contained in the negative electrode SEI coating 4AC formed in the coated negative electrode active material layer 4A of the good battery 1G is also very slight, just like the variation in the Li amount AL. From these results, it can be seen that in the good battery 1G, the amount (thickness) of the negative electrode SEI coating 4AC formed in the coated negative electrode active material layer 4A is also approximately constant regardless of the widthwise position WP, and the variation (unevenness) is very slight.

On the other hand, the distribution of P content AP for defective battery 1N, shown by the dashed line in Figure 9, is similar to the distribution of Li content AL for defective battery 1N, shown by the dashed line in Figure 6. Specifically, there were localized areas, specifically near widthwise positions WP of 28 to 37 mm and 42 to 49 mm, where the P content AP was significantly greater than in other areas. In other words, it can be seen that in defective battery 1N, the P content AP contained in the negative electrode SEI coating 4AC also varied significantly across the widthwise position WP. This P content AP distribution also reveals that in defective battery 1N, the amount (thickness) of the negative electrode SEI coating 4AC formed on the coated negative electrode active material layer 4A also varied significantly across the widthwise position WP, resulting in significant variations across the widthwise position WP. This likely resulted in significant deterioration in the overall battery characteristics of defective battery 1N compared to those of non-defective battery 1G.

(Investigation of P fluctuation ratio)
In this modified example 1, the P fluctuation ratio RP was investigated (see FIG. 10 ) in the same manner as in the embodiment, using negative electrode samples of the negative electrode plates 4 of multiple good batteries 1G and multiple defective batteries 1N used in the investigation of the Li fluctuation ratio RL (see FIG. 7 ). As shown in FIG. 9 , the minimum P value PI and the maximum P value PX were obtained from the P amount AP values, and the P fluctuation ratio RP was calculated by RP = PX/PI. Specifically, the minimum P value GPI and the maximum P value GPX were obtained from the distribution of the P amount AP of the good battery 1G. The P fluctuation ratio RP of the good battery 1G was calculated by RP = GPX/GPI. Similarly, the minimum P value NPI and the maximum P value NPX were obtained from the distribution of the P amount AP of the defective battery 1N, and the P fluctuation ratio RP of the defective battery 1N was calculated by RL = NLX/NLI.

Figure 10 shows the trends in the capacity retention rate CC and P fluctuation ratio RP for good battery 1G and bad battery 1N. As in the embodiment (see Figure 7), in Figure 10, for good battery 1G, even though the capacity retention rate CC decreases due to the forced degradation test described above, the P fluctuation ratio RP remains at approximately the same value. In other words, the trends in the P fluctuation ratio RP in Figure 10 also show that for good battery 1G, even as it deteriorates, the amount (thickness) of the negative electrode SEI coating 4AC remains approximately uniform in the width direction WH, and no unevenness occurs.

In contrast, as in the embodiment (see Figure 7), the defective battery 1N had a P fluctuation ratio RP roughly similar to that of the good battery 1G until the capacity retention rate CC reached approximately 97%. However, once the capacity retention rate CC decreased beyond 97%, the P fluctuation ratio RP increased as the capacity retention rate CC decreased. By conducting the forced degradation test, an abnormally formed negative electrode SEI coating 4AC was formed in a specific region of the coated negative electrode active material layer 4A. In this region, the abnormally formed negative electrode SEI coating 4AC made it difficult for the battery reaction to occur, and it is believed that a significant decrease in battery capacity, etc., occurred in the electrode body 2 of the defective battery 1N as a whole.

From these results, as in the embodiment, if the aforementioned forced degradation test is performed until the capacity retention rate CC falls to 95% or less, and then a distribution survey of the P amount AP is performed, it is possible to determine whether the battery 1 is a good battery 1G or a bad battery 1N. Specifically, for example, as shown by the dashed-dotted line in Figure 10, a threshold value RPT (RPT = 2.0 in Figure 10) can be set for the P fluctuation ratio RP, and if the obtained P fluctuation ratio RP is smaller than the threshold value RPT, the battery can be determined to be a good battery 1G. Furthermore, it is also possible to determine whether the undetermined battery group GBB to which the battery 1 belongs is a good battery group GBG consisting of good batteries 1G, or a bad battery group GBN consisting of bad batteries 1N (see Figure 8).

(Manufacturing of battery groups)
Therefore, in this modified embodiment 1, a battery group GB is manufactured that comprises a single manufacturing lot and includes a large number of batteries 1. Specifically, in the manufacturing method of the battery group GB shown in Fig. 8, the undetermined battery group manufacturing step S1 to the removal step S5 are the same as the manufacturing method of the battery group GB shown in the embodiment (see Fig. 5).

However, in the P amount distribution acquisition step S16 of this modified embodiment, which replaces the Li amount distribution acquisition step S6 of the embodiment, ICP-MS is used to obtain the distribution of the P amount AP contained in the negative electrode SEI coating 4AC formed on the coated negative electrode active material layer 4A for the desired measurement region of the negative electrode sample (see Figure 9).

Then, unlike the judgment step S7 in the embodiment, in judgment step S17, the quality of the unjudged battery group GBB from which the sample battery 1S was obtained is judged based on the distribution of the obtained P amount AP. Specifically, as described above, the minimum P amount PI and maximum P amount PX are obtained from the distribution of the P amount AP to calculate the P fluctuation ratio RP. The obtained P fluctuation ratio RP is then compared with a predetermined threshold value RPT, and if the P fluctuation ratio RP is greater than the threshold value RPT (RP > RPT), the sample battery 1S is judged to be a defective battery 1N, and the unjudged battery group GBB to which the sample battery 1S belongs is judged to be a defective battery group GBN (NG in judgment step S17).

Conversely, for example, if the P fluctuation ratio RP is smaller than the threshold value RPT (RP<RPT), the sample battery 1S is determined to be a good battery 1G (GOOD in determination step S17), and the undetermined battery group GBB to which the sample battery 1S belongs is determined to be a good battery group GBG. Thus, even in this modified embodiment 1, it is possible to manufacture a good battery group GB (good battery group GBG) that exhibits slow degradation characteristics.

In this way, in this modified embodiment 1, the minimum P amount value PI and the maximum P amount value PX are used in the determination step S17, making it possible to easily determine whether the undetermined battery group GBB is good or bad.

(Variation 2)
In the above-described embodiment and variant 1, when manufacturing the battery group GB, the Li amount distribution or the P amount distribution was obtained from the negative electrode sample of the negative electrode plate 4 of the sample battery 1S, and only one of the obtained Li amount distribution or the P amount distribution was used to determine the quality of the sample battery 1S and the undetermined battery group GBB to which this sample battery 1S belongs (see Figures 5 and 8).

In contrast, in this modified embodiment 2, both the Li amount distribution (see Figure 6) and the P amount distribution (see Figure 9) are obtained from the negative electrode sample of the negative electrode plate 4 of the sample battery 1S, and the quality of the sample battery 1S and the undetermined battery group GBB to which this sample battery 1S belongs is determined using these two obtained Li amount distribution and P amount distribution.

(Manufacturing of battery groups)
That is, in this modified embodiment 2, a battery group GB is manufactured that constitutes a single manufacturing lot and includes a large number of batteries 1. Specifically, in the manufacturing method of the battery group GB shown in Fig. 11 , the undetermined battery group manufacturing step S1 to the removal step S5 are the same as the manufacturing method of the battery group GB in the embodiment and modified embodiment 1 shown in Figs.

However, in the LiP amount distribution acquisition step S26 of this modified embodiment 2, ICP-MS is used to obtain the distribution of the Li amount AL and the distribution of the P amount AP contained in the negative electrode SEI coating 4AC formed on the coated negative electrode active material layer 4A for the desired measurement region of the negative electrode sample (see Figures 6 and 9). In other words, the LiP amount distribution acquisition step S26 is a step that combines the Li amount distribution acquisition step S6 in the embodiment and the P amount distribution acquisition step S16 in modified embodiment 1.

Then, in the judgment step S27 of this modified embodiment 2, the quality of the unjudged battery group GBB from which the sample battery 1S was obtained is judged based on the obtained distribution of Li amount AL and distribution of P amount AP. Specifically, as described above, the minimum Li amount LI and maximum Li amount LX are obtained from the distribution of Li amount AL to calculate the Li fluctuation ratio RL. The minimum P amount PI and maximum P amount PX are also obtained from the distribution of P amount to calculate the P fluctuation ratio RP. The obtained Li fluctuation ratio RL is compared with a predetermined threshold value RLT, and the P fluctuation ratio RP is compared with a predetermined threshold value RPT. If at least one of the following is true: the Li fluctuation ratio RL is greater than the threshold value RLT (RL > RLT) and the P fluctuation ratio RP is greater than the threshold value RPT (RP > RPT), the sample battery 1S is judged to be a defective battery 1N. At the same time, the undetermined battery group GBB to which the sample battery 1S belongs is determined to be a defective battery group GBN (NG in determination step S27).

Conversely, for example, if the Li fluctuation ratio RL is smaller than the threshold value RLT (RL<RLT) and the P fluctuation ratio RP is smaller than the threshold value RPT (RP<RPT), the sample battery 1S is determined to be a good battery 1G (GOOD in determination step S27). At the same time, the undetermined battery group GBB to which the sample battery 1S belongs is determined to be a good battery group GBG. Thus, even in this modified embodiment 2, a good battery group GB (good battery group GBG) with slow degradation characteristics can be manufactured.

In this way, in this modified embodiment 2, in the judgment step S27, in addition to the minimum Li amount value LI and the maximum Li amount value LX, the minimum P amount value PI and the maximum P amount value PX are also used to make the judgment, so that the quality of the unjudged battery group GBB can be more reliably judged.

The present invention has been described above in accordance with the embodiment and modified forms 1 and 2, but it goes without saying that the present invention is not limited to the embodiment, etc., and can be modified and applied as appropriate within the scope of the gist of the present invention.
For example, in the embodiment and modified examples 1 and 2, examples were shown in which, in a deteriorated defective battery 1N, there are localized areas in the lithium content distribution and phosphorus content distribution where the lithium content AL and phosphorus content AP are larger than other areas (see FIGS. 6 and 9 ). However, conversely, there may be defective batteries 1N where there are localized areas where the lithium content AL and phosphorus content AP are smaller than other areas. Even in this case, the quality of the undetermined battery group GBB can be determined by, for example, obtaining the minimum lithium content LI and the maximum lithium content LX from the lithium content distribution to calculate the lithium fluctuation ratio RL, or by obtaining the minimum phosphorus content PI and the maximum phosphorus content PX from the phosphorus content distribution to calculate the phosphorus fluctuation ratio RP.

1. Battery (lithium ion storage device)
1G Good battery 1N Bad battery 1S Sample battery (sample device)
GB Battery group (device group)
GBB Undetermined battery group (undetermined device group)
GBG: Good battery group GBN: Defective battery group 2: Electrode body 3: Positive electrode plate 3A: Positive electrode active material layer 4: Negative electrode plate 4A: Negative electrode active material layer (coated negative electrode active material layer)
4AB Negative electrode active material layer ML Center line WP (of the negative electrode active material layer) Width direction position 4AE1 (One side in the width direction) Edge 4AP Negative electrode active material particles 4AC Negative electrode SEI coating (Li-containing SEI coating, LiP-containing SEI coating)
AL Li amount AP P amount LX, GLX, NLX Maximum Li amount LI, GLI, NLI Minimum Li amount PX, GPX, NPX Maximum P amount LI, GPI, NPI Minimum P amount RL Li fluctuation ratio RLT Threshold value RP P fluctuation ratio RPT Threshold value 6 Electrolyte 6V Organic solvent 6S Supporting salt (supporting salt containing P)
7 Case XH Axial direction
S7 Li amount distribution determination step S17 P amount distribution determination step S27 LiP amount distribution determination step

Claims (7)

an electrolyte solution containing lithium ;
an electrode body having a positive electrode plate having a positive electrode active material layer, a negative electrode plate having a coated negative electrode active material layer on which a Li-containing SEI coating containing lithium is formed, and a separator interposed between the positive electrode active material layer and the coated negative electrode active material layer, and permeated with the electrolyte;
A method for inspecting a lithium ion storage device including the electrode body and a case that accommodates the electrolyte,
a degradation step of subjecting the lithium ion storage device to a degradation test in which the Li-containing SEI coating of the coating-coated negative electrode active material layer is thickened;
a negative electrode plate removal step of dismantling the deteriorated lithium ion storage device and removing the negative electrode plate;
a removing step of washing and removing the electrolyte adhering to the removed negative electrode plate;
and a Li amount distribution acquisition step of examining the linear or planar distribution of the Li amount contained in the Li-containing SEI coating in the width direction or length direction of the coated negative electrode active material layer. 2. A method for inspecting a lithium ion storage device according to claim 1, comprising:
the electrolyte is a P-containing electrolyte containing a supporting salt containing phosphorus,
The coated negative electrode active material layer of the negative electrode plate is
the Li-containing SEI coating, which is a LiP-containing SEI coating that also contains phosphorus, is formed on a negative electrode active material layer that does not contain phosphorus,
A method for inspecting a lithium ion storage device, comprising a P amount distribution acquisition step, which is performed instead of or together with the Li amount distribution acquisition step, of examining a linear distribution or a planar distribution of the P amount contained in the LiP-containing SEI coating of the coated negative electrode active material layer in the width direction or the longitudinal direction . an electrolyte solution containing lithium ;
an electrode body having a positive electrode plate having a positive electrode active material layer, a negative electrode plate having a coated negative electrode active material layer on which a Li-containing SEI coating containing lithium is formed, and a separator interposed between the positive electrode active material layer and the coated negative electrode active material layer, and permeated with the electrolyte;
A method for manufacturing a device group including a plurality of lithium ion storage devices each including the electrode body and a case containing the electrolyte solution, the method comprising:
a selection step of selecting a sample device from an undetermined device group consisting of a plurality of the lithium ion electricity storage devices;
a degradation step of subjecting the sample device to a degradation test in which the Li-containing SEI coating of the coating-coated negative electrode active material layer of the sample device is thickened;
a negative electrode plate removal step of dismantling the deteriorated sample device and removing the negative electrode plate;
a removing step of washing and removing the electrolyte adhering to the removed negative electrode plate;
a Li amount distribution acquisition step of examining a linear distribution or a planar distribution of the Li amount contained in the Li-containing SEI coating of the coating-coated negative electrode active material layer in a width direction or a length direction ;
and a determining step of determining whether the sample devices in the undetermined device group are good or bad based on the obtained distribution of Li amounts. 4. A method for manufacturing a group of devices according to claim 3, comprising the steps of:
the electrolyte is a P-containing electrolyte containing a supporting salt containing phosphorus,
The coated negative electrode active material layer of the negative electrode plate is
the Li-containing SEI coating, which is a LiP-containing SEI coating that also contains phosphorus, is formed on a negative electrode active material layer that does not contain phosphorus,
a P amount distribution acquisition step, which is performed instead of the Li amount distribution acquisition step or together with the Li amount distribution acquisition step, of examining a linear distribution or a planar distribution of the P amount contained in the LiP-containing SEI coating of the coated negative electrode active material layer in the width direction or the longitudinal direction ;
The determination step includes:
A method for manufacturing a device group, in which the pass/fail judgment of the unjudged device group from which the sample devices are obtained is performed using the P content distribution instead of or in addition to the Li content distribution. 4. A method for manufacturing a group of devices according to claim 3, comprising the steps of:
The determination step includes:
The method for manufacturing a group of devices includes determining the pass/fail of the group of undetermined devices using the minimum and maximum values of the amount of Li in the obtained distribution of the amount of Li. 5. A method for manufacturing a group of devices according to claim 4, comprising the steps of:
The determination step includes:
Using the minimum and maximum P amounts in the obtained P amount distribution, or
Using the minimum value of the P amount, the maximum value of the P amount, and the minimum value of the Li amount and the maximum value of the Li amount in the obtained distribution of the Li amount,
A method for manufacturing a group of devices, in which the pass/fail judgment of the group of unjudged devices is performed. A method for manufacturing a device group according to any one of claims 3 to 6, comprising:
The degradation step includes:
The method for manufacturing a group of devices comprises the step of reducing the capacity of the sample devices until the capacity retention rate becomes smaller than a predetermined value.