Testing methods for lithium-ion secondary batteries, manufacturing methods for lithium-ion secondary batteries

Abstract

To estimate the extent of the impact of minute foreign matter remaining in lithium-ion secondary battery cells, and to suppress self-discharge failure while suppressing the increase in initial resistance. [Solution] In the lithium-ion secondary battery manufacturing method, the spike creek defect rate is determined by a spike creek inspection step (S1), the ΔOCV is estimated from the spike creek defect rate, and the ΔOCV defect rate is estimated by determining a ΔOCV defect based on a threshold (S2). The average ΔOCV is estimated based on the ΔOCV defect rate (S3), and the amount of plating additive to smooth the metal surface of minute foreign matter is determined using a predetermined calculation formula (S4). The procedure of adding the determined amount of plating additive to the non-aqueous electrolyte (S5) and the conditioning process including initial charging are performed. Furthermore, aging conditions consisting of temperature and time conditions are determined based on the amount of plating additive added (S7), and aging is performed according to the aging conditions (S8).

Description

[Technical Field]

[0001] This invention relates to a method for inspecting lithium-ion secondary batteries and a method for manufacturing lithium-ion secondary batteries, and more particularly to a method for inspecting lithium-ion secondary batteries and a method for manufacturing lithium-ion secondary batteries that suppress self-discharge and initial resistance. [Background technology]

[0002] Lithium-ion secondary batteries generally use copper foil as the negative electrode current collector and aluminum foil as the positive electrode current collector. When manufacturing the negative and positive electrode plates, these metal foils are cut and shaped to predetermined dimensions. During this process, minute foreign matter, such as fine metal fragments, may remain in the lithium-ion secondary battery cell. Furthermore, even if a short circuit does not occur at that stage, the presence of such minute foreign matter may cause metal deposition on the negative electrode plate due to the potential. This occurs because the metal foreign matter mixed into the cell first dissolves due to the positive electrode potential. Then, the dissolved metal foreign matter ions move to the negative electrode via the separator. At the negative electrode potential, the metal foreign matter ions change from ions to metal and deposit on the negative electrode. This can then cause a short circuit in the future due to dendrites, etc. Such minute foreign matter remaining in the lithium-ion secondary battery cell can cause chemical and physical short circuits, leading to self-discharge.

[0003] Patent Document 1 discloses an invention that reduces the short-circuit failure rate by thermally melting burr foreign matter that causes self-discharge generated on the positive or negative electrode by high-voltage pulse discharge in advance. Furthermore, Patent Document 2 describes how insulating powder can be scattered on part or all of the positive electrode, negative electrode, and separation membrane to reduce internal short circuits and low-voltage failures due to self-discharge.

[0004] Such an invention can reduce the impact of minute foreign matter remaining in the lithium-ion secondary battery cell. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-135145 [Patent Document 2] Special Publication No. 2009-535780 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, while it is possible to reduce the impact of minute foreign matter remaining in lithium-ion secondary battery cells, it is not possible to estimate in advance the extent of the impact of such minute foreign matter remaining in lithium-ion secondary battery cells.

[0007] The problem that the present invention's method for inspecting lithium-ion secondary batteries and manufacturing lithium-ion secondary batteries aims to solve is to estimate the extent of the influence of minute foreign matter remaining in the cells of a lithium-ion secondary battery. Furthermore, based on such estimation, the aim is to suppress self-discharge failure while suppressing the increase in initial resistance. [Means for solving the problem]

[0008] To solve the aforementioned problems, the present invention provides a method for inspecting lithium-ion secondary batteries, comprising: a step of performing a spike-creek inspection, in which pulse discharge of a set voltage is performed on the positive and negative electrodes of the lithium-ion secondary battery before the injection of a non-aqueous electrolyte, and if current is detected, it is determined to be defective; a step of determining the spike-creek defect rate in the spike-creek inspection; a step of estimating the ΔOCV defect rate, which is the ratio of cells that cause OCV defects due to self-discharge by minute foreign matter remaining in the cells of the lithium-ion secondary battery, from the spike-creek defect rate; and a step of calculating the average ΔOCV, which is estimated based on the ΔOCV defect rate.

[0009] The step of estimating the ΔOCV failure rate may be carried out by assuming that the size distribution of the minute foreign matter mixed in the cell follows a normal distribution, and estimating the ΔOCV failure rate from the spike creek failure rate, based on the proportion of the distribution of minute foreign matter that is larger than the lower limit size that causes self-discharge due to the minute foreign matter.

[0010] The step of calculating the average ΔOCV may be carried out assuming that the ΔOCV defect rate of the cell follows a normal distribution, and the corresponding average ΔOCV may be estimated from its relationship with the ΔOCV defect rate.

[0011] Furthermore, the present invention provides a method for manufacturing a lithium-ion secondary battery, characterized by the steps of obtaining the average ΔOCV estimated by the above-mentioned lithium-ion secondary battery inspection method, and adding a plating additive to the non-aqueous electrolyte that smooths the metal surface of the minute foreign matter formed on the electrode plate, according to the average ΔOCV estimated by the inspection method.

[0012] Furthermore, for example, the plating additive can be made of a polymer that has a film-forming effect, and the plating additive can be polyethylene glycol (PEG).

[0013] The plating additive added to the non-aqueous electrolyte may also include a step of determining the amount of plating additive to add, such that the amount of additive is such that "(average ΔOCV when the spike creek defect rate is X%) - (average ΔOCV when the spike creek defect rate is 0%) = ΔV" suppresses ΔV.

[0014] The lithium-ion secondary battery may include LiBOB in the non-aqueous electrolyte and comprises a step of determining the amount of plating additive to add, which is determined from the average ΔOCV; a step of determining aging conditions, which consist of temperature and time conditions for the lithium-ion secondary battery, based on the amount of plating additive to add; and an aging step of performing aging according to the aging conditions.

[0015] The aforementioned aging conditions can be determined so that the initial resistance is set. [Effects of the Invention]

[0016] According to the lithium-ion secondary battery inspection method and lithium-ion secondary battery manufacturing method of the present invention, it is possible to estimate the extent of the influence of minute foreign matter remaining in the lithium-ion secondary battery cell. Furthermore, based on such estimation, it is possible to suppress self-discharge failure while suppressing the increase in initial resistance. [Brief explanation of the drawing]

[0017] [Figure 1] This flowchart shows some of the steps involved in the manufacturing method of the lithium-ion secondary battery according to this embodiment. [Figure 2] This graph shows the relationship between the size distribution of foreign objects found in cells and the probability of their presence. [Figure 3] This graph shows the relationship between the spike creek defect rate and the ΔOCV defect rate. [Figure 4] This graph shows the relationship between the ΔOCV defect rate and the average ΔOCV. [Figure 5] This graph shows the relationship between ΔV and the addition ratio of plating additives. [Figure 6] This graph shows the relationship between the addition ratio of plating additives and the initial resistance. [Figure 7] This graph shows the relationship between initial resistance and aging temperature. [Figure 8] This is a schematic diagram illustrating the smoothing of sulfur-based plating additives. [Figure 9] This is a schematic diagram illustrating the smoothing effect of amine-based plating additives. [Figure 10] This is a schematic diagram illustrating the smoothing of polymer-based plating additives. [Figure 11] This is a perspective view showing a schematic representation of the external configuration of the lithium-ion secondary battery cell of this embodiment. [Figure 12] This is a schematic diagram showing the configuration of the wound electrode body. [Modes for carrying out the invention]

[0018] (Outline of this embodiment) The following describes the inspection method and manufacturing method of the lithium-ion secondary battery of the present invention, using an embodiment of the manufacturing method of lithium-ion secondary battery cell 1 (see Figure 11) as an example, with reference to Figures 1 to 12. The lithium-ion secondary battery will be described using cell 1, which is a single cell that constitutes a battery pack for driving hybrid vehicles (HV, PHV) and electric vehicles (BEV), as an example. However, this embodiment is an example for illustrative purposes only, and the present invention is not limited to this embodiment.

[0019] <Conventional Technology> As described in the background technology section, while Patent Documents 1 and 2 can reduce the influence of minute foreign matter remaining in the lithium-ion secondary battery cell 1, they cannot estimate the extent of the influence of minute foreign matter remaining in the lithium-ion secondary battery cell.

[0020] In the method described in Patent Document 1, minute foreign matter can only be determined by whether or not it was thermally melted by pulsed discharge, and excessive pulsed discharge may adversely affect the electrode body. In the method described in Patent Document 2, internal short circuits can certainly be suppressed by forming an electrode assembly by scattering insulating powder on the surface of the separation membrane or the electrode placed opposite the separation membrane. However, excessive scattering may increase the initial resistance and adversely affect the battery performance.

[0021] <Principle of this embodiment> The inventors believe that by first performing a spike creek inspection (Figure 1: S1), the spike creek defect rate DR can be calculated. S [%] As shown in Figure 3, ΔOCV defect rate DR O We obtained the finding that it is possible to estimate the [%]. Furthermore, as shown in Figure 4, this ΔOCV defect rate DR OThe average ΔOCV[%] can be calculated from [%]. A high average ΔOCV[%] indicates that the lot for cell 1 is prone to so-called chemical shorting.

[0022] When such chemical short circuits are likely to occur, the plating additive PA is added to suppress their growth. The plating additive PA reduces the average ΔOCV and the spike-creek defect rate DR. S The growth of minute foreign matter MF is suppressed so that the ΔV[%] becomes 0[%]. As shown in Figures 8-10, the plating additive PA can suppress the growth of minute foreign matter MF depending on the amount added. Therefore, as shown in Figure 5, the amount of plating additive PA to be added is determined according to ΔV[%]. As a result, the ΔV[%] of the product can be made 0[%].

[0023] However, although the addition of the plating additive PA can reduce the product's ΔV[%] to 0[%], the initial resistance R is as shown in Figure 6. ini A problem arises where the [%] increases. This is thought to be due to an increase in resistance caused by the formation of a film on the negative electrode. In lithium-ion secondary batteries, the initial resistance R ini LiBOB (LiB(C2O4)2, lithium bisoxalate borate) is added to suppress the increase in [%]. LiBOB forms a film of its own origin, suppressing the excessive formation of a film of SEI, which has high resistance. However, LiBOB film formation requires a certain amount of time. Since LiBOB film formation depends on temperature T[%], it proceeds efficiently in the aging process (S8) performed in a high-temperature environment. As shown in Figure 7, the aging temperature T[%] is increased in this aging process (S8) compared to normal. In this case, even in the same aging process (S8) time, the LiBOB film is formed more efficiently, and the initial resistance R ini [%] can be suppressed to a set level. Based on this finding, the inventors have determined the initial resistance R ini We have discovered a method for inspecting a lithium-ion secondary battery of this embodiment that suppresses self-discharge failure while suppressing an increase in [%], and a method for manufacturing a lithium-ion secondary battery using this method.

[0024] <Outline of the procedure of this embodiment> FIG. 1 is a flowchart showing a part of the procedure of the method for manufacturing a lithium ion secondary battery according to this embodiment. Based on the above findings, the following procedure is performed in this embodiment. Hereinafter, a part of the procedure of the method for manufacturing a lithium ion secondary battery according to this embodiment will be outlined with reference to this flowchart. First, on the premise of the cell 1 in which the source process, assembly process, and drying process (not shown) are completed, a spike leak inspection of minute foreign matter MF remaining in the cell 1 of the lithium ion secondary battery is performed (FIG. 1: S1). Based on the result of this spike leak inspection, the size and distribution state of the minute foreign matter MF in the cell 1 are estimated. From this, the spike leak failure rate DR of the spike leak inspection S Furthermore, the failure rate (ΔOCV failure rate DR) due to an abnormal decrease in the voltage [V] of the open circuit voltage OCV due to self-discharge is estimated (S2). From this, the average of the voltage drop amount due to self-discharge (average ΔOCV V [%]) is estimated (S3). The amount of the plating additive PA added to the non-aqueous electrolyte 13 is determined according to how much the average ΔOCV [%] has decreased compared to the average ΔOCV [%] when the spike leak failure rate DR AV [%] is 0% (S4). The non-aqueous electrolyte 13 added with the determined amount of the plating additive PA is injected into the cell 1 (S5). Thereafter, a conditioning process including initial charging is performed (S6). Next, according to the amount of the plating additive PA added, the conditions in the aging process are determined (S7). Then, the aging process is performed according to the determined aging conditions (S8). Thereafter, it is shipped through post-processes such as an inspection process (not shown).

[0025] Next, each process will be described in detail. <Spike leak inspection> ​​In this embodiment, a "spike creek test (Figure 1: S1)" is performed. A spike creek test involves assembling a lithium-ion secondary battery cell 1 as shown in Figure 11, and after the drying process, before injecting the non-aqueous electrolyte 13, applying a voltage to the positive electrode external terminal 14 and the negative electrode external terminal 15. For example, a voltage of 500[V] is applied for 0.5[sec]. As shown in Figure 12, the positive electrode plate 3 and the negative electrode plate 2 are separated by an insulating separator 4, and normally, no current flows between the positive electrode plate 3 and the negative electrode plate 2 after the drying process and before injecting the non-aqueous electrolyte 13. However, if there are conductive minute foreign matter MF between the positive electrode plate 3 and the negative electrode plate 2, a current may flow directly or through sparks when a high voltage is applied between the positive electrode plate 3 and the negative electrode plate 2, depending on the gap. This gap generally depends on the size of the minute foreign matter MF. If a current flows during this spike creek test, it can be seen that minute foreign matter MF larger than a certain size is mixed in the cell 1. However, objects smaller than a certain size cannot be detected by the spike creek test. Nevertheless, if many cells 1 are judged as defective in the spike creek test, it is presumed that there is a high probability that there are small, minute foreign objects (MF) that cannot be detected by the spike creek test.

[0026] <Spike Creek Defect Rate DR S [%]> Through this type of spike creek inspection, the ratio of cells that conduct electricity (i.e., defective cells) out of all inspected cells is called the "Spike Creek Defect Rate DR". S [%]"

[0027] <ΔOCV defective rate DR O [%]> Figure 2 is a graph showing the relationship between the size distribution of minute foreign matter MFs mixed in cell 1 and the probability of their presence. Assume that the size distribution of minute foreign matter MFs mixed in cell 1 follows a normal distribution. Then, the spike creek defect rate DR... S From the [%], the size distribution of minute foreign matter MF remaining in cell 1, which was deemed good based on the Spike Creek test results, can be estimated.

[0028] In Figure 2, the size of the minute foreign matter MF that leaks in the spike creek test is set to 100%. Such a cell 1 is considered defective in the spike creek test and is therefore rejected. In the spike creek test, if the size of the minute foreign matter is less than 100%, it will not be judged as defective. In other words, if the size of the minute foreign matter is less than 100%, no leakage current flows in the spike creek test and it is judged as a good product. However, subsequent use of cell 1 may cause minute short circuits if the minute foreign matter MF dissolved at the positive electrode precipitates and grows on the negative electrode. For example, experiments by the inventors have shown that in this embodiment, the probability of a minute short circuit occurring in subsequent use of cell 1 is low if the size of the minute foreign matter MF is less than 50% of the minimum size that is considered defective in the spike creek test.

[0029] Here, in Figure 2, the spike creek defect rate DR S Graph G1 when [%] is 0[%] and spike creek defect rate DR S Graph G2, when [%] is 0.1[%], shows the size distribution of minute foreign matter MF contained within cell 1.

[0030] Spike Creek Defect Rate DR S If [%] is 0[%], there is no area S2 in graph G1 that exceeds 100[%] of the x-axis. Therefore, graph G1 cannot be estimated. On the other hand, the DR (Damage Reduction Rate) of Spike Creek S If [%] is 0.1[%], then the area S1 between the x-axis and graph G2 in the portion where graph G2 exceeds 100[%] of the x-axis is considered to be 0.1[%] of the total area between the x-axis and graph G2. Here, we assume that the size distribution of minute foreign matter MF follows a normal distribution. Then, the spike creek defect rate DR S When [%] is 0.1[%], the probability [%] of the presence of minute foreign matter MF is thought to be as shown in graph G2.

[0031] Based on the above findings, the spike creek defect rate DR, which is considered poor in spike creek inspection, is S If [%] is 0.1[%], it can be estimated that the size distribution of minute foreign matter MF will have an area S2 as shown in graph G2. Similarly, the spike creek defect rate DR S As the percentage increases, the area S2 also increases. Therefore, assuming that the size distribution of minute foreign matter MF follows a normal distribution, the spike creek defect rate DR S If the percentage [%] is known, a graph of the size distribution of minute foreign matter MF at that time can be drawn. If graph G2 can be drawn, the area S1 can be derived by integrating over the portion from 50% to 100% of the minute foreign matter size. That is, ΔOCV defect rate DR O [%] can be estimated.

[0032] The steps for estimating the ΔOCV failure rate are: Spike Creek Failure Rate DR S [%] represents the ΔOCV failure rate DR, which is the percentage of cells in a lithium-ion secondary battery that exhibit OCV failure due to self-discharge caused by minute foreign matter (MF) remaining within the cell 1. O Estimate [%].

[0033] Spike Creek Defect Rate DR S From [%], the presence of minute foreign matter MF remaining in cell 1 of the lithium-ion secondary battery can be estimated. Self-discharge caused by this minute foreign matter MF results in a defect in the difference ΔOCV from the reference OCV0[V] of cell 1. Therefore, the spike creek defect rate DR S [%] represents the ΔOCV defect rate DR, which is the percentage of cells with a poor ΔOCV. O [%] can be estimated.

[0034] The percentage of cells in which the OCV[V] drops abnormally compared to the reference OCV0[V] due to self-discharge in the future is called the "ΔOCV failure rate DR". OLet's define it as [%]. Here, "reference OCV 0[V]" is the expected average ΔOCV[V] when a voltage drop occurs due to minute foreign matter (G2 in Figure 2) that may be present when the spike creek defect rate DRs is 0[%].

[0035] In other words, in this embodiment, the spike creek defect rate DR S If the percentage is known, the ΔOCV defect rate DR O [%] can be estimated. Figure 3 shows the spike creek defect rate DR. S [%] and ΔOCV defect rate DR O This graph shows the relationship with [%]. The horizontal axis represents the spike creek defect rate DR. S [%] The vertical axis represents the ΔOCV defect rate DR O [%] indicates a percentage.

[0036] As mentioned above, the Spike Creek defect rate DR S From [%], the size distribution of the present minute foreign matter MF can be estimated, and the larger the size of the present minute foreign matter MF, the larger the voltage abnormality failure rate due to self-discharge [%]. Based on the above findings, the inventors experimentally confirmed this relationship. As a result, as shown in Figure 3, the spike creek failure rate DR S [%] and ΔOCV defect rate DR O It was demonstrated that there is a strong correlation between [%] and the given values, and that this relationship can be approximated by a linear function.

[0037] <Average ΔOCV and ΔV> Figure 4 shows the ΔOCV defect rate DR. O This graph shows the relationship between [%] and the average ΔOCV [%]. Here, "average ΔOCV" is the ΔOCV defect rate DR. O This shows the difference in percentage between the average OCV[V] of cell 1, estimated from [%], and the reference OCV0[V]. In Figure 4, the spike creek defect rate DR is shown. S The average ΔOCV when [%] is X[%] is "Average ΔOCV X Let's define "ΔV" as "ΔV = average ΔOCV". X- Defined as "Reference OCV0". Alternatively, an approximation curve can be expressed as an equation from the measured plot points. Then, from this equation, the spike creek defect rate DR S The increase in [%] gives us the increase in the average ΔOCV, which is ΔV[%]. In other words, the spike creek defect rate DR S To set the average ΔOCV when [%] is X[%] to the baseline OCV0[V], the OCV[%] needs to be increased by ΔV[%]. Since the ΔOCV[%] of cell 1 is assumed to follow a normal distribution, the ΔOCV defect rate DR is as shown in Figure 4. O As the percentage increases, the average ΔOCV[%] also increases.

[0038] In other words, if ΔV[%], which indicates the magnitude of the difference between the average ΔOVC[%] and the reference OCV0, is large, it can be concluded that the lot of cell 1 is prone to developing chemical short circuits. <Plating additive PA> Here, we will explain "plating additive PA". As the name suggests, "plating additive PA" in this application is an additive added to the electrolyte when performing a plating treatment. Such plating additives are usually added in the plating treatment for the purpose of smoothing the plated layer. The main roles of plating additives are surface shape control and film property control. In terms of surface shape control, the adsorption of the additive onto the plated surface, the reaction control or acceleration effect, or the consumption of electricity makes it possible to smooth, polish, or fill holes in the plated surface.

[0039] In this embodiment, although no plating treatment is performed, if minute foreign matter MF made of metal precipitates, adheres, and grows on the surface of the negative electrode plate 2, forming convex shapes such as dendrites on the positive electrode plate 3 side, it becomes easier for minute short circuits to occur. In such cases, by adding the plating additive PA to the non-aqueous electrolyte 13, the convex parts originating from the minute foreign matter MF can be smoothed and miniaturized, thereby suppressing chemical minute short circuits.

[0040] Plating additives PA include polyether compounds (polymers) such as polyethylene glycol. Other typical plating additives include sulfur compounds such as bis(3-sulfopropyl) disulfide (brighteners) and quaternary amine compounds such as Nusgreen B (levelers). The following describes each type of plating additive.

[0041] Figure 8 is a schematic diagram illustrating the smoothing effect of the sulfur-based plating additive PA. As shown in Figure 8, the sulfur-based plating additive PA has the function of smoothing the surface of precipitates by promoting the deposition of minute foreign matter MF in the depressions of the precipitates.

[0042] Figure 9 is a schematic diagram illustrating the smoothing effect of the amine-based plating additive PA. As shown in Figure 9, the amine-based plating additive PA smooths the surface of precipitates by suppressing the deposition of protrusions in the precipitated areas of minute foreign matter MF.

[0043] Figure 10 is a schematic diagram illustrating the smoothing effect of the polymer-based plating additive PA. As shown in Figure 10, the polymer-based plating additive PA forms a monolayer on the surface of precipitated minute foreign matter MF, thereby suppressing crystal growth and miniaturizing the particles.

[0044] The present invention can be implemented using any type of plating additive, but in this embodiment, polyethylene glycol (PEG), a polymer-based polyether compound, is used as an example of the plating additive PA. Of course, it is not limited to this.

[0045] <ΔV[%] and the addition ratio of plating additive PA R AD Relationship > Figure 5 shows ΔV[%](ΔV=average ΔOCV). X -Base OCV0) and the addition ratio of plating additive PA R AD This graph shows the relationship between the two. The horizontal axis represents ΔV [%]. The vertical axis represents the addition ratio R of the plating additive PA to the non-aqueous electrolyte 13. AD This shows the addition ratio R. ADThere are no units. As can be seen from this graph, the addition ratio R of the plating additive PA when eliminating ΔV[%] shown in Figure 4. AD This can be determined. For example, if ΔV[%] is 125[%], the addition ratio of the plating additive PA R AD R AD If ΔV[%] is 1 and ΔV[%] is 25[%], then the addition ratio of the plating additive PA is R. AD is R AD It turns out that setting it to 2 is the correct approach.

[0046] <Initial resistance R of plating additive PA> ini Relationship with [%] Figure 6 shows the addition ratio R of the plating additive PA. AD and initial resistance R ini This graph shows the relationship in percentages. The horizontal axis represents the addition ratio R of the plating additive PA to the non-aqueous electrolyte 13. AD The vertical axis represents the initial resistance R when the plating additive PA is not added. ini Initial resistance R when [%] is set to 100[%] ini [%]. The dotted line is an approximation curve derived from numerous plotted points. Here, the addition ratio R of the plating additive PA. AD R is relatively small AD In case 2, the initial resistance R ini [%] is approximately 117[%]. On the other hand, the addition ratio R of the plating additive PA AD R is relatively common AD In the case of 1, the initial resistance R ini It can be seen that the percentage (%) becomes approximately 123%.

[0047] <LiBOB(LiB(C2O4)2、リチウムビスオキサラートボレート)> Lithium-ion secondary batteries use a non-aqueous electrolyte 13, but the non-aqueous electrolyte 13 decomposes at the potential [V] of the negative electrode during charging. For this reason, in the conditioning process (S6), following a predetermined procedure, a film of SEI (Solid Electrolyte Interphase) with a thickness of several to tens of nanometers is formed at the interface between the negative electrode active material and the non-aqueous electrolyte 13 during the initial charge. SEI is necessary to suppress the decomposition of the non-aqueous electrolyte 13 during subsequent charging and discharging, but SEI itself has high resistance and consumes Li and the non-aqueous electrolyte 13, so it is undesirable for it to grow to a thickness greater than necessary.

[0048] Therefore, it is known that additives are used in the non-aqueous electrolyte 13 to suppress such an increase in initial resistance and capacity degradation. For example, LiBOB-based film-forming agents are often used as additives. When LiBOB is added to the non-aqueous electrolyte 13, the initial resistance of cell 1 is high in the initial stages of use because it takes time for the LiBOB-derived film to form. Subsequently, as the formation of the LiBOB-derived film progresses, the initial resistance of cell 1 R ini [%] becomes lower. The formation rate of the LiBOB-derived film changes depending on the temperature conditions, so the initial resistance R ini To suppress the noise level to the target value set by [%], it is necessary to set appropriate aging conditions (temperature [%] and time [h]) during the aging process (S8).

[0049] <Initial resistance R ini Relationship between [%] and aging temperature T[%]> Figure 7 shows the initial resistance R. ini This graph shows the relationship between [%] and the aging temperature T[%]. Here, assuming an aging time [h] in a standard production process, the aging temperature [%] is shown when the standard aging temperature of 60[°C] is set to 100[%]. Also, the initial resistance R[mΩ] after the aging process performed at an aging time [h] and aging temperature T[%] in a standard production process is set to 100[%]. iniThis is shown in [%]. As shown in Figure 7, the initial resistance R after the aging process at the standard aging temperature T=100[%] ini [%] represents the result of performing the aging process at an aging temperature T[%] of approximately 120[%], which corresponds to the initial resistance R ini We confirmed that the [%] improved significantly to approximately 80[%]. Although not shown in the figure, we similarly changed the aging temperature[%] and identified the relationship as a linear function from numerous plotted points using methods such as the least squares method. As a result, the initial resistance R ini The relationship between [%] and aging temperature [%] has become clear. Therefore, the target initial resistance R ini By performing the aging process at an aging temperature [%] to achieve [%], the initial resistance R of the final product is determined. ini It can be set to [%].

[0050] <Lithium-ion rechargeable battery> Figure 11 is a perspective view showing a schematic representation of the external configuration of cell 1 of the lithium-ion secondary battery of this embodiment. First, the configuration of the lithium-ion secondary battery of this embodiment, which is an example of the present invention, will be described.

[0051] As shown in Figure 11, the lithium-ion secondary battery is configured as a cell battery. The lithium-ion secondary battery has a plate-shaped rectangular parallelepiped battery case 11 with an opening on the top. An electrode body 12 is housed inside the battery case 11. The battery case 11 is filled with a non-aqueous electrolyte 13 from an injection port 18. The battery case 11 is made of a metal such as an aluminum alloy and forms a sealed battery case with a lid. The lithium-ion secondary battery also has a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging power. The positive electrode external terminal 14 is electrically connected to the positive electrode current collector terminal 16 inside the battery case 11 via the lid. The negative electrode external terminal 15 is electrically connected to the negative electrode current collector terminal 17 inside the battery case 11 via the lid. The positive electrode current collector terminal 16 is electrically connected to the positive electrode current collector portion 33 (see Figure 12) of the electrode body 12. Furthermore, the negative electrode current collector terminal 17 is electrically connected to the negative electrode current collector section 23 (see Figure 12) of the electrode body 12.

[0052] The lid has an injection port 18 for injecting the non-aqueous electrolyte 13. This injection port 18 is sealed after injection, and the cell case of cell 1 is completely sealed. <Electrode body 12> Figure 12 is a schematic diagram showing the configuration of the wound electrode body 12. The electrode body 12 is made up of a number of stacked negative electrode plates 2, positive electrode plates 3, and separators 4 placed between them. The stacked negative electrode plates 2, positive electrode plates 3, and separators 4 are wound together to form a flat shape. The negative electrode plate 2 has a negative electrode composite layer 22 formed on a negative electrode current collector 21 made of copper foil, which serves as the base material. A negative electrode current collector 23 is provided on one end in the width direction W (winding axis direction) perpendicular to the winding direction (winding direction L). The negative electrode current collector 23 has no negative electrode composite layer 22 formed on it, and the negative electrode current collector 21 is exposed.

[0053] The positive electrode plate 3 has a positive electrode composite layer 32 formed on a positive electrode current collector 31 made of aluminum foil, which serves as the base material. As shown in Figure 12, the positive electrode current collector 33 is provided on the other end (opposite side from the negative electrode current collector 23) in the width direction W (winding axis direction) perpendicular to the winding direction (winding direction L) of the positive electrode current collector 31. The positive electrode composite layer 32 is not formed on the positive electrode current collector 33, and the metal of the positive electrode current collector 31 is exposed.

[0054] <Laminated structure of electrode body 12> As shown in Figure 12, the basic configuration of the electrode body 12 of the lithium-ion secondary battery includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4.

[0055] The negative electrode plate 2 has a negative electrode composite material layer 22 on both sides of the negative electrode current collector 21, which serves as the negative electrode base material. One end of the negative electrode current collector 21 is a negative electrode current collector portion 23 in which metal is exposed. The positive electrode plate 3 has a positive electrode composite material layer 32 on both sides of the positive electrode current collector 31, which serves as the positive electrode base material. The other end of the positive electrode current collector 31 is a positive electrode current collector portion 33 where metal is exposed.

[0056] A laminate is formed by stacking a negative electrode plate 2 and a positive electrode plate 3 with a separator 4 in between. As shown in Figure 9, this laminate is wound longitudinally around a winding axis to form a wound electrode body 12 that is flattened as shown in Figure 6.

[0057] <Nonaqueous electrolyte 13> The non-aqueous electrolyte 13 of the lithium-ion secondary battery of this embodiment shown in Figure 11 is a composition obtained by dissolving a lithium salt in an organic solvent. Examples of lithium salts that can be used include LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butanesultone; or phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One or more of these can be mixed and used as the non-aqueous electrolyte 13. However, the composition of the non-aqueous electrolyte 13 is not limited to these.

[0058] In this embodiment, EC (ethylene carbonate) is used as the organic solvent. Furthermore, in this embodiment, as described above, a compound having a lithium salt is added as an additive for the film-forming material. In this embodiment, lithium bisoxalate borate (LiBOB, LiB(C2O4)2, hereinafter referred to as "LiBOB") is added.

[0059] Furthermore, polyethylene glycol (PEG), a polymer-based polyether compound, is added as a plating additive PA. <Components of electrode body 12> Next, we will describe the components that make up the electrode body 12: the negative electrode plate 2, the positive electrode plate 3, and the separator 4.

[0060] <Negative electrode plate 2> As shown in Figure 12, the negative electrode plate 2 is constructed by forming a negative electrode composite material layer 22 on both sides of the negative electrode current collector 21, which is the negative electrode substrate. In the source process, the negative electrode composite material paste is applied to the negative electrode current collector 21. Subsequently, the negative electrode plate 2 is completed through drying, pressing, and cutting processes.

[0061] In this embodiment, the negative electrode current collector 21 is made of Cu foil. The negative electrode current collector 21 serves as the base material for the negative electrode composite layer 22 and also functions as a current collector that collects electricity from the negative electrode composite layer 22. One end of the negative electrode current collector 21 is a negative electrode current collector section 23 where the metal surface is exposed and the negative electrode composite layer 22 is not formed thereon. In other words, the negative electrode active material particles are electrically connected to the negative electrode external terminal 15 via the negative electrode current collector 21, the negative electrode current collector section 23, and the negative electrode current collector terminal 17.

[0062] The negative electrode composite layer 22 consists of a negative electrode active material as the raw material, and a binder (binding agent) and additives as auxiliary materials. The raw material and auxiliary materials are mixed with an organic solvent to produce a negative electrode composite paste. This negative electrode composite paste is applied to the negative electrode current collector 21. The applied negative electrode composite paste is dried and then shaped and pressed to complete the negative electrode plate 2.

[0063] In this embodiment, the negative electrode active material is powdered graphite particles GP, which consist of graphite having a layered structure, and lithium ions Li + It is a material capable of absorbing and releasing substances. <Positive plate 3> As shown in Figure 11, the positive electrode plate 3 is composed of a positive electrode current collector 31, which is the positive electrode substrate, and a positive electrode composite layer 32 coated thereon. In the source process, the positive electrode composite layer 32 is applied to the positive electrode current collector 31 by coating it with a positive electrode composite paste. Subsequently, the positive electrode plate 3 is completed through drying, pressing, and cutting processes.

[0064] The positive electrode plate 3 is constructed by forming a positive electrode composite material layer 32 on both sides of a positive electrode current collector 31, which is a positive electrode substrate. In this embodiment, the positive electrode current collector 31 is made of aluminum foil. The positive electrode current collector 31 serves as a base material for the positive electrode composite material layer 32 and also functions as a current collector that collects electricity from the positive electrode composite material layer 32.

[0065] First, although Al foil was used as an example for the positive electrode substrate constituting the positive electrode current collector 31, it can be made of a conductive material consisting of a metal with good conductivity, for example. As a material with good conductivity, in addition to Al foil, materials containing Al alloys can be used. The composition of the positive electrode current collector 31 is not limited to this.

[0066] The positive electrode composite layer 32 is formed by coating the positive electrode composite paste onto the positive electrode current collector 31 and drying it. The positive electrode composite layer 32 contains positive electrode active material particles as well as additives such as conductive additives, binders, and dispersants.

[0067] The positive electrode active material particles contain a lithium transition metal oxide having a layered crystalline structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. Preferably, the transition metal elements contained in the lithium transition metal oxide are at least one of Ni, Co, and Mn. The positive electrode active material of this embodiment is exemplified by a ternary system called NCM, which has a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0068] Furthermore, the positive electrode active material in this embodiment is not limited to having a lithium transition metal oxide containing all of Ni, Co, and Mn. It may also have a composition containing, for example, Al.

[0069] <Separator 4> The separator 4 is a highly insulating nonwoven fabric, such as one made of porous resin, for holding the non-aqueous electrolyte 13 between the negative electrode plate 2 and the positive electrode plate 3. As the separator 4, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, or lithium-ion or ion-conductive polymer electrolyte membranes can be used alone or in combination. In this embodiment, both outer surfaces are made of polypropylene (PP), which has high mechanical strength and excellent heat resistance. The interior is made of polyethylene (PE), which shuts down at high temperatures.

[0070] (Operation of this embodiment) <Manufacturing method for lithium-ion secondary batteries> Next, we will briefly explain the manufacturing method of lithium-ion secondary batteries.

[0071] <Pre-process> First, in the so-called source process, the negative electrode plate 2, positive electrode plate 3, separator 4, battery case 11 with a cover, and various terminals 14-17 are manufactured individually.

[0072] Next, in the assembly process, the negative electrode plate 2, positive electrode plate 3, and separator 4 are stacked and wound to manufacture the electrode body 12. Various terminals 14-17 and a cover are attached to the electrode body 12 and then placed in the battery case 11. After that, the cover is sealed by laser welding or the like.

[0073] Cell 1, assembled through the assembly process, then moves on to a drying process to remove internal moisture. In the drying process, the inside is dried using heating, airflow, etc. Normally, a non-aqueous electrolyte 13 is injected during this post-injection step. However, in this embodiment, a spike creek test (S1) is performed.

[0074] Next, some steps of the manufacturing method for the lithium-ion secondary battery of this embodiment will be explained with reference to the flowchart Figure 1. <Steps for Spike Creek Testing (S1)> In the step of spike leak inspection (S1), pulse discharge of the voltage set on the positive and negative electrodes of the lithium-ion secondary battery before injecting the non-aqueous electrolyte 13 is performed, and if there is conduction, it is determined as defective. In the spike leak inspection, if there is a minute foreign matter MF larger than a certain size, leakage occurs and it is determined as defective. A cell 1 in which current has conducted, that is, leaked, in the spike leak inspection is determined as defective. The spike leak defect rate DR S In the step of obtaining [%], among all the cells 1 inspected, the ratio of the cells 1 determined as defective is obtained, and the spike leak defect rate DR S [%] is calculated.

[0075] <(Step of estimating ΔOCV defect rate (S2))> In the step of estimating the ΔOCV defect rate (S2), assuming that the size distribution of the minute foreign matter MF mixed in the cell 1 follows a normal distribution, the spike leak defect rate DR S [%] is used to estimate the size distribution of the minute foreign matter MF remaining in these cells 1.

[0076] The spike leak defect rate DR S [%] is used to determine that when the difference ΔOCV between the open circuit voltage OCV of the cell 1 due to self-discharge caused by the minute foreign matter MF remaining in the cell 1 of the lithium-ion secondary battery is greater than the threshold value, it is determined as an OCV defect, and the ΔOCV defect rate DR O [%] is estimated.

[0077] <(Step of calculating and obtaining average ΔOCV (S3))> In the step of calculating the average ΔOCV (S3), the average ΔOCV [%] is estimated based on the ΔOCV defect rate DR O [%]. The step of calculating the average ΔOCV (S3) estimates the corresponding average ΔOCV [%] from the relationship with the ΔOCV defect rate DR O [%] on the premise that the ΔOCV defect rate DR O [%] of the cell 1 follows a normal distribution.

[0078] Here, the spike leak defect rate DR SWhen [%] is X[%], the average ΔOCV is defined as average ΔOCV X and the spike leak failure rate DR S When the average ΔOCV when [%] is 0[%] is defined as the reference OCV0, ΔV = average OCV X - can be obtained from the reference OCV0. By setting this ΔV to ΔV = 0, the OCV is corrected.

[0079] <Step (S4) for determining the amount of plating additive added> In the step (S4) for determining the amount of plating additive added, the plating additive PA to be added to the non-aqueous electrolyte 13 is calculated. It is set to the amount that suppresses ΔV = 0 as described above. When a plating additive PA such as polyethylene glycol is added to the non-aqueous electrolyte 13, the ΔOCV of the cell 1 can be decreased according to the addition ratio R AD and thus the average ΔOCV [%] can be decreased. The addition ratio R of the plating additive PA required to make ΔV [%] 0[%] AD is as shown in Fig. 5. However, as shown in Fig. 6, the initial resistance R ini [%] deteriorates as the plating additive PA is added.

[0080] <Step (S5) of injecting liquid / plating additive addition> In the step (S5) of injecting liquid / plating additive addition, a predetermined amount of the non-aqueous electrolyte 13 is injected into the cell 1 in which the drying process has been completed. At this time, according to the estimated average ΔOCV [%], the plating additive PA for smoothing the metal surface of the fine foreign matter formed on the electrode plate is added to the non-aqueous electrolyte 13 at the addition ratio R AD which is the determined ratio. In this embodiment, the plating additive PA contains polyethylene glycol (PEG) made of a polymer having a film-forming action. After the liquid injection is completed, the injection port 18 is sealed to seal the battery case of the cell 1.

[0081] <Conditioning process (initial charge) (S6)> In the conditioning process (initial charge) (S6), the initial charge is performed. In the initial charge, while activating the lithium-ion secondary battery, a SEI film is formed on the negative electrode plate 2.

[0082] <Steps for determining aging conditions (S7)> In the step of determining the aging conditions (S7), the addition ratio R of the plating additive PA is determined. AD Based on this, the aging conditions are determined, consisting of the temperature T[%] and time[h] of the aging process. If the aging time[h] is constant, the temperature T[%] is determined. The aging conditions are set as shown in Figure 7, with an initial resistance R ini The aging temperature T[%] is determined so that it becomes [%].

[0083] Furthermore, the promotion of LiBOB film formation depends on the amount of energy obtained by combining the aging temperature T[%] and time [h]. Therefore, it is not limited to the condition of aging temperature T[%] alone, but can also be achieved by keeping the aging temperature T[%] constant and extending the time [h]. Of course, it can also be adjusted by using both.

[0084] <Aging Steps (S8)> In the aging step (S8), aging is performed according to the aging conditions determined in the aging condition determination step (S7). In this embodiment, the aging conditions are, for example, a temperature of 60 [°C] and a time of 24 [h], but it goes without saying that this is not limited to these conditions.

[0085] <Post-process> Once the steps in the flowchart shown in Figure 1 are completed, necessary tests such as OCV testing, initial resistance testing, and self-discharge testing are performed, and the finished product is shipped.

[0086] (Effects of this embodiment) (1) The lithium-ion secondary battery inspection method and lithium-ion secondary battery manufacturing method of this embodiment have the effect of being able to estimate the extent of the influence of minute foreign matter MF remaining in the lithium-ion secondary battery cell 1.

[0087] (2) Also, based on such estimations, the initial resistance R iniThis has the effect of suppressing self-discharge failure while also suppressing the increase in [%]. (3) In this embodiment, the spike creek inspection step (S1) is performed by the spike creek defect rate DR S Calculate the percentage (%). Spike Creek defect rate DR S [%] ΔOCV failure rate DR due to self-discharge caused by minute foreign matter MF remaining in cell 1 O [%] is estimated (S2). This ΔOCV defect rate DR O From [%], the average ΔOCV, which is the difference between cell 1's reference OCV0[V] and the current OCV, is estimated and obtained (S3). This has the effect of allowing the future state of cell 1 to be estimated in real time during the manufacturing process.

[0088] (4) Step (S2) of estimating the ΔOCV defect rate assumes that the distribution of the size of minute foreign matter MF mixed in cell 1 follows a normal distribution, and the ΔOCV defect rate DR O [%] is estimated. Here, the spike creek defect rate DR is used. S [%] The ΔOCV failure rate DR is calculated from the percentage of the distribution of minute foreign matter MF that is larger than the lower limit size at which self-discharge occurs due to minute foreign matter MF. O This estimates the percentage [%]. Therefore, the spike creek test alone has the effect of being able to estimate future abnormalities in the OCV[V] of cell 1.

[0089] (5) The step (S3) for calculating the average ΔOCV is the ΔOCV defect rate DR of cell 1. O Assuming that [%] follows a normal distribution, the ΔOCV defect rate DR O The corresponding mean ΔOCV[%] is estimated from its relationship with [%]. Therefore, the future OCV[V] of cell 1 can be estimated simply by performing a spike creek test.

[0090] (6) In accordance with the obtained average ΔOCV[%], a plating additive PA is added to the non-aqueous electrolyte 13 to smooth the metal surface of the minute foreign matter MF formed on the negative electrode plate 2. Therefore, by adding an appropriate amount of the plating additive PA to the non-aqueous electrolyte 13 according to the conditions of minute foreign matter MF generation, the OCV[V] of cell 1 can be optimized.

[0091] (7) The plating additive PA in this embodiment is polyethylene glycol (PEG) made of a polymer that has a film-forming effect. Therefore, it effectively suppresses the generation of dendrites and the like, and does not adversely affect the non-aqueous electrolyte 13 or the electrode body 12.

[0092] (8) The plating additive PA is provided in a step (S4) of determining the amount of plating additive to add, such that (average ΔOCV when the spike creek defect rate is X%) - (average ΔOCV when the spike creek defect rate is 0%) = ΔV, and the amount of additive is such that ΔV is suppressed. This has the effect of being able to determine an appropriate amount to optimize the future OCV [V] of cell 1.

[0093] (9) The non-aqueous electrolyte 13 contains LiBOB and is aged (S8). This activates LiBOB and the initial resistance R ini It has the effect of suppressing [%] (10) The aging conditions are the set initial resistance R ini The process includes a step (S7) for determining aging conditions, which consists of temperature T [°C] and time [h], based on the amount of plating additive PA added so that the result is [%]. The aging process is performed according to these aging conditions, and the initial resistance R ini This has the effect of allowing you to set a value to [%].

[0094] (Another example) In this embodiment, as an example of a lithium-ion secondary battery, we have given cell 1, which constitutes a drive battery pack mounted on a vehicle, as shown in Figures 11 and 12. However, as long as the present invention can be implemented, its purpose, shape, etc., are not limited.

[0095] ○The flowchart shown in Figure 1 is just one example; for instance, the procedure for determining the aging conditions (S7) may be performed before the procedure for injecting the solution / adding the plating additive (S5). Furthermore, those skilled in the art can change the order of the procedures, add or delete procedures, or modify them as appropriate.

[0096] ○The numerical values, numerical ranges, thresholds, etc., mentioned in this embodiment can be appropriately optimized and implemented by those skilled in the art. The graphs shown in Figures 2-7 are merely examples of implementation, and the method is not necessarily limited to graphs. The desired relationship can also be expressed using relational equations, tables, or other methods.

[0097] ○While polyethylene glycol (PEG), which consists of a polymer with film-forming properties, was given as an example of the plating additive PA, the type is not limited to sulfur-based plating additives, amine-based plating additives, etc., as long as the invention can be implemented.

[0098] ○In this embodiment, the aging process (S8) is assumed to be performed at a constant temperature, but it is not limited to this, and the temperature conditions may be changed during the aging process (S8). In this case as well, it is controlled by the accumulated energy (heat).

[0099] ○This embodiment is merely one example for explaining the present invention, and it goes without saying that those skilled in the art can add, delete, or modify its configuration to implement it. [Explanation of symbols]

[0100] 1…Cell (Lithium-ion secondary battery) 11…Battery case 12...Electrode body 13...Nonaqueous electrolyte 14…Positive external terminal 15…Negative external terminal 16…Positive current collection terminal 17... Negative current collection terminal 18…Injection port 2… Negative plate 21...Negative electrode current collector 22...Negative electrode composite material layer 23... Negative electrode current collector 3…Positive plate 31...Positive electrode current collector 32…Positive electrode composite layer 33…Positive electrode current collector 4... Separator G1, G2... Graph S1, S2…Area MF...Micronized foreign body PA…Plating Additive R AD ...addition ratio of plating additive PA DR S [%]...Spike Creek defect rate ΔOCV[%]...Ratio to the reference OCV0[V] DR V [%]…ΔOCV defective rate ΔV[%]…Average OCV X The ratio of the difference relative to the standard OCV0[V] Average ΔOCV X ...Average ΔOCV when the spike creek defect rate is X[%] Reference OCV 0[V]...Average OCV[V] when the spike creek defect rate is 0[%] R ini [%]…Initial resistance T[%]...Aging temperature

Claims

1. The spike creek test involves performing pulse discharges of a set voltage on the positive and negative electrodes of a lithium-ion secondary battery before injecting a non-aqueous electrolyte, and determining if the battery is defective if current flows through. The steps include determining the spike creek defect rate in the aforementioned spike creek inspection, Steps include: estimating the ΔOCV failure rate, which is the ratio of cells that experience OCV failure due to self-discharge caused by minute foreign matter remaining in the lithium-ion secondary battery cells, from the spike creek failure rate; A step of calculating the average ΔOCV, which estimates the average ΔOCV based on the aforementioned ΔOCV defect rate. A method for inspecting a lithium-ion secondary battery, characterized by comprising the following features.

2. The step of estimating the ΔOCV defect rate is as follows: The method for inspecting a lithium-ion secondary battery according to claim 1, characterized in that, assuming that the size distribution of the minute foreign matter mixed in the cell follows a normal distribution, the ΔOCV failure rate is estimated from the spike creek failure rate by the proportion of the distribution of minute foreign matter that is larger than the lower limit size that causes self-discharge due to the minute foreign matter.

3. The steps for calculating the average ΔOCV are as follows: The method for inspecting a lithium-ion secondary battery according to claim 1, characterized in that, assuming that the ΔOCV defect rate of the cell follows a normal distribution, the corresponding mean ΔOCV is estimated from the relationship with the ΔOCV defect rate.

4. A step of obtaining the average ΔOCV estimated by the lithium-ion secondary battery inspection method described in claim 1, A method for manufacturing a lithium-ion secondary battery, characterized by adding a plating additive to the non-aqueous electrolyte that smooths the metal surface of the minute foreign matter formed on the electrode plate, according to the average ΔOCV estimated by the inspection method described above.

5. The method for producing a lithium-ion secondary battery according to claim 4, characterized in that the plating additive comprises a polymer having a film-forming effect.

6. The method for producing a lithium-ion secondary battery according to claim 4, characterized in that the plating additive includes polyethylene glycol (PEG).

7. The method for manufacturing a lithium-ion secondary battery according to claim 4, comprising the step of determining the amount of plating additive to be added to the non-aqueous electrolyte such that the amount of plating additive is such that when "(average ΔOCV when the spike creek defect rate is X%) - (average ΔOCV when the spike creek defect rate is 0%) = ΔV", the amount of plating additive is such that ΔV is suppressed.

8. The lithium-ion secondary battery contains LiBOB in the non-aqueous electrolyte. A step of determining the amount of plating additive to add, in which the amount of the plating additive to add is determined from the average ΔOCV, A step of determining aging conditions, which involves determining aging conditions consisting of temperature and time conditions for the lithium-ion secondary battery based on the amount of the plating additive added, An aging step in which aging is performed according to the aforementioned aging conditions, A method for manufacturing a lithium-ion secondary battery according to claim 4, characterized by comprising the above.

9. The method for manufacturing a lithium-ion secondary battery according to claim 8, characterized in that the aging conditions are determined so that the initial resistance is set.

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