Method for estimating irreversible capacity of negative electrode of lithium ion secondary battery and method for manufacturing lithium ion secondary battery

Abstract

To accurately estimate the irreversible capacity of a negative electrode and suppress variations in the initial capacity of a battery cell in the step of manufacturing a lithium ion secondary battery.SOLUTION: A method for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery includes: the step (S16) of predicting a coating film amount-derived irreversible capacity ICC [Ah] derived from a coating film NC of an amorphous carbon on the basis of a coating film amount Ac [g] in graphite particles GP having the coating film NC of the amorphous carbon as the negative electrode active material to be a raw material of the negative electrode plate of a lithium ion secondary battery; the step (S13) of predicting a specific surface area-derived irreversible capacity CA [Ah] derived from a specific surface area BET [m2 / g] after the step (S11) of manufacturing the negative electrode plate; and the step (S18) of calculating a cell battery capacity Cc from the total irreversible capacity ICT [Ah] of the coating film amount-derived irreversible capacity ICC [Ah] and the specific surface area-derived irreversible capacity ICA [Ah].SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery and a method for manufacturing a lithium ion secondary battery, and more particularly to a method for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery that suppresses variation in the initial capacity of battery cells and a method for manufacturing a lithium ion secondary battery. [Background technology]

[0002] Lithium ion secondary batteries are widely used because of their large battery capacity and the ability to charge and discharge at large currents. Such lithium ion secondary batteries are charged by inserting lithium ions of the positive electrode active material into the negative electrode, and discharged by inserting the lithium ions removed from the negative electrode back into the positive electrode. In recent years, negative electrode active materials using graphite have been widely used in such lithium ion secondary batteries. When the negative electrode is graphite, the negative electrode potential at the time of initial charging is about 0.1 V, so reductive decomposition of the carbonate-based organic solvent in contact at the interface occurs. At this time, a coating of SEI (Solid Electrolyte Interphase) with a thickness of several to several tens of nm, which is made of organic matter such as lithium alkyl carbonate or inorganic matter such as lithium salt, is formed at the interface between the negative electrode active material and the non-aqueous electrolyte. The formation of SEI causes the non-aqueous electrolyte to decompose and the lithium ions to be consumed. As a result, the initial discharge capacity decreases to about 80 to 95% of the capacity at the initial charge. The difference between the charged capacity [Ah] and the dischargeable capacity [Ah] at this time is called the "irreversible capacity [Ah]".

[0003] Because the SEI is necessary to protect the negative electrode during subsequent charging and discharging, the occurrence of such irreversible capacity [Ah] is an inevitable phenomenon, but it is undesirable for the initial capacity to vary from one battery cell to another.

[0004] In the invention disclosed in Patent Document 1, a negative electrode composite paste is applied to a copper foil current collector, dried to prepare an electrode, and then the electrode is pressed to a specified electrode density. At this time, a large load is applied to the electrode, which leads to the destruction and peeling of the low-crystalline surface carbonaceous material, which is harder and more brittle than graphite. As a result, the specific surface area [m 2 / g] increases. Then, the graphite inside comes into direct contact with the electrolyte, and as the electrolyte decomposes, lithium ions are consumed, increasing the irreversible capacity [Ah]. In this way, the specific surface area [m 2 It is disclosed that the irreversible capacity [Ah] changes depending on the amount of carbon dioxide per unit area [A / g].

[0005] In addition, in Patent Document 2, the graphite is composed of graphite particles that serve as mother particles and amorphous carbon that covers the surface of the graphite particles. Lithium ions are inserted into the amorphous carbon, but some lithium ions cannot be released during discharge. It is suggested that the irreversible capacity [Ah] of graphite increases when the amount of amorphous carbon coated on the graphite is large [g].

[0006] According to these suggestions, the specific surface area [m 2 It is possible to control the irreversible capacity [Ah] by adjusting the amount of carbon per unit area [g] or the amount of amorphous carbon coating [g]. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-209035 A [Patent Document 2] JP 2017-199510 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, when graphite particles coated with amorphous carbon are delivered as the raw material for the negative electrode active material, there is a problem that the coating is delivered with a certain degree of variation. 2 / g] varies depending on the manufacturing process, which results in variation in the irreversible capacity [Ah] of the produced cell batteries and therefore variation in the capacity [Ah] of each cell battery.

[0009] The problem to be solved by the method for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery and the method for manufacturing a lithium ion secondary battery of the present invention is to accurately estimate the irreversible capacity of the negative electrode and suppress variation in the initial capacity of a battery cell. [Means for solving the problem]

[0010] In order to solve the above problems, the method for estimating the irreversible capacity of the negative electrode of a lithium ion secondary battery of the present invention includes the steps of: obtaining a coating amount Ac [g] of the amorphous carbon coating NC in graphite particles GP having an amorphous carbon coating NC, which is a negative electrode active material that is a raw material for a negative electrode plate 2 of a lithium ion secondary battery 1; and estimating a coating amount-derived irreversible capacity IC derived from the amorphous carbon coating NC from the coating amount Ac [g] obtained in the coating amount obtaining step. C A step of predicting the irreversible capacity derived from the coating amount [Ah]; a step of producing a negative electrode plate by using the graphite particles GP having the amorphous carbon coating NC as a raw material, kneading it with a sub-material to produce a negative electrode composite paste, and coating the produced negative electrode composite paste on a negative electrode current collector to produce the negative electrode plate; and a step of predicting the specific surface area BET [m 2 A step of measuring a specific surface area BET [m 2 / g] specific surface area-derived irreversible capacity IC A A step of predicting the specific surface area-derived irreversible capacity [Ah] and the irreversible capacity IC derived from the coating amount predicted in the step of predicting the coating amount-derived irreversible capacity C [Ah] and the specific surface area-derived irreversible capacity IC predicted in the specific surface area-derived irreversible capacity prediction step A [Ah] and the total irreversible capacity IC T and a step of estimating the total irreversible capacity [Ah].

[0011] In the step of obtaining the coating amount, the specific surface area BET [m 2 / g] and the average diameter (d 50 The coating amount Ac [g] of the graphite particles GP may be obtained based on the surface roughness D [μm].

[0012] In addition to the above-mentioned method for estimating the irreversible capacity of the negative electrode of the lithium ion secondary battery, the total irreversible capacity IC estimated by the step of estimating the total irreversible capacity T The present invention may further include a step of predicting a cell battery capacity Cc [Ah] based on the battery capacity [mAh].

[0013] In the step of predicting the cell battery capacity, the irreversible capacity IC derived from the coating amount predicted in the step of predicting the irreversible capacity derived from the coating amount C [Ah] and the specific surface area-derived irreversible capacity IC predicted in the specific surface area-derived irreversible capacity prediction step A [Ah] and the total irreversible capacity IC T Based on [Ah], cell battery capacity Cc [Ah], design capacity Cc S [Ah], cell battery capacity Cc = Cc S -I C T ...The cell battery capacity Cc [Ah] may be predicted using (Equation 1).

[0014] Based on the cell battery capacity Cc [Ah] predicted in the cell battery capacity prediction step, a preset threshold value Th of the cell battery capacity Cc [Ah] is set. C It is also desirable to have a step of determining whether the cell battery is good or bad by comparing it with [Ah].

[0015] In the step of determining whether or not the battery is defective, if the battery cell capacity Cc [Ah] is insufficient, the aging time to be performed thereafter is adjusted to the design capacity Cc [Ah] that targets the battery cell capacity Cc [Ah].S It is also desirable to provide a step of adjusting the aging time to [Ah]. Effect of the Invention

[0016] The method for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery and the method for manufacturing a lithium ion secondary battery of the present invention have the effect of accurately estimating the irreversible capacity of the negative electrode and suppressing variation in the initial capacity of the battery cell. [Brief description of the drawings]

[0017] [Figure 1] 1 is a graph showing the relationship between the amount of coating Ac [g] and the irreversible capacity IC [mAh]. [Diagram 2] 1 is a graph showing the relationship between the specific surface area BET [m2 / g] and the irreversible capacity IC [mAh]. [Diagram 3] FIG. 1 is a perspective view showing the outline of the external configuration of a lithium-ion secondary battery 1 according to the present embodiment. [Figure 4] 2 is a schematic diagram showing the configuration of a wound electrode body 12. FIG. [Diagram 5] FIG. 1 is a block diagram of a device for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery. [Figure 6] 4 is a flowchart showing an example of a method for manufacturing the lithium-ion secondary battery 1 of the present embodiment. [Figure 7] 1 is a flowchart showing an example of a procedure for a method of manufacturing a negative electrode plate in a source process. [Figure 8] 1 is a graph showing the relationship between the average diameter (d50) D [μm], the specific surface area BET [m2 / g] and the coating amount Ac [g]. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a manufacturing method and manufacturing apparatus for a lithium ion secondary battery according to the present invention will be described by way of one embodiment of a manufacturing method for a lithium ion secondary battery 1 with reference to FIGS. (Principle of this embodiment) As mentioned in the Background Art, the specific surface area [m2 It has been proposed to control the irreversible capacity IC [mAh] by adjusting the amount of charge / g of the battery or the amount of amorphous carbon coating [g]. However, this is difficult to control because it involves multiple factors and changes over time.

[0019] <Relationship between coating amount Ac [g] and irreversible capacity IC [mAh]> FIG. 1 is a graph showing the relationship between the coating amount Ac [g] and the irreversible capacity IC [mAh]. The horizontal axis is the coating amount Ac [g] of the amorphous graphite coating NC of the graphite particle GP. The vertical axis is the irreversible capacity IC C The graph shows the irreversible capacity [mAh] based on the coating amount Ac [g] and the irreversible capacity IC [mAh] [mAh]. When the relationship between the coating amount Ac [g] and the irreversible capacity IC [mAh] was measured and plotted, and multiple regression analysis was performed, it was found that there was a strong correlation with a coefficient of determination R2 = 0.94. This relationship is shown in graph L1. In this embodiment, as a result of measuring the coating amount Ac [g], for example, if the coating amount Ac [g] is Ac1 [g], the irreversible capacity IC C In other words, if the amount of coating Ac [g] is known, the irreversible capacity IC [mAh] derived from the coating NC can be determined.

[0020] <Negative plate specific surface area BET[m 2 / g] and irreversible capacity IC [mAh]> Figure 2 shows the specific surface area of ​​the negative plate BET [m 2 / g] and irreversible capacity IC [mAh]. The horizontal axis shows the relationship between the specific surface area BET [m 2 / g] is indicated.

[0021] Here, the specific surface area BET [m 2 / g] is expressed as the area per unit mass. There are various methods for specific surface area analysis, including the adsorption method, the moist heat method, and the reaction method. The adsorption method involves adsorbing molecules with a known adsorption area onto the surface of powder particles at the temperature of liquid nitrogen, and determining the specific surface area of ​​the sample from the amount of adsorption. There are two types of adsorption methods: the BET method and the Langmuir method, but the most commonly used method for specific surface area analysis is the BET method, which uses low-temperature and low-humidity physical adsorption of an inert gas.

[0022] In this embodiment, a method for determining the specific surface area of ​​a powder is used by the BET method (Berunauer Emmett and Teller's method, a gas adsorption method). Specifically, for example, the negative electrode was cut into a strip of 1 cm x 20 cm, and this was used as the sample. The BET specific surface area measurement device used was Quantasorb manufactured by Quanta Chrome, and nitrogen gas was used as the adsorption gas. A bulk solid cell was used as the sample cell, and the negative electrode sample was rolled up and set in this cell.

[0023] The vertical axis is the irreversible capacitance IC derived from the coating NC C The irreversible capacity [mAh] based on the specific surface area BET [m 2 When the relationship between the specific surface area BET [m / g] and the irreversible capacity IC [mAh] was measured and plotted, and multiple regression analysis was performed, and it was found that there was a strong correlation with a coefficient of determination R2 = 0.80. This relationship is shown in graph L2. In this embodiment, 2 / g], for example, the specific surface area BET [m 2 / g] is BET1[m 2 / g], then the specific surface area BET [m 2 / g]. A [mAh] is approximately 4.0 [mAh]. In other words, the specific surface area BET [m 2 / g], the specific surface area BET [m 2 The irreversible capacity IC [mAh] derived from the capacity [mAh / g] can be determined.

[0024] <Irreversible capacitance IC due to coating amount C [mAh] and specific surface area-derived irreversible capacity IC A [m 2 / g] relationship> As mentioned above, the irreversible capacity [mAh] is a function of the amount of coating Ac [g] and the specific surface area BET [m 2 / g]. Here, the inventors of the present invention have determined the irreversible capacity IC C [mAh] and specific surface area-derived irreversible capacity IC A [m 2 / g], it was confirmed that the irreversible capacity [mAh] of the entire cell battery is the sum of these.

[0025] As a result, the irreversible capacity IC C [Ah] and specific surface area-derived irreversible capacity IC A [Ah] and the total irreversible capacity IC T It was found that the cell battery capacity Cc [Ah] can be estimated based on [Ah].

[0026] Here, the cell battery capacity Cc [Ah], the design capacity Cc S When [Ah] is used, Cell battery capacity Cc=Cc S -I C T …(Formula 1) Experiments have demonstrated that the cell battery capacity Cc [Ah] can be predicted using this method.

[0027] <Determining the quality of a cell battery based on the cell battery capacity Cc [Ah]> The cell battery capacity Cc [Ah] calculated by the above formula (1) is set to a threshold value Th C [Ah]. If the cell battery capacity Cc [Ah] exceeds the threshold value ThC [Ah], the test is considered to be passed. C If it falls below [Ah], it is considered a failure.

[0028] <When the cell battery capacity Cc [Ah] falls below the threshold ThC [Ah]> When the cell battery capacity Cc [Ah] falls below the threshold ThC [Ah], it is necessary to restore the cell battery capacity Cc [Ah]. Here, as described above, in the lithium ion secondary battery 1, after the assembly of the battery is completed, the initial charging is performed to form the SEI. After that, an aging process is performed to eliminate micro-short circuits caused by fine metal powder mixed inside the lithium ion secondary battery 1. In the aging process, for example, in an aging process for about 20 [hours] in a high-temperature environment of a voltage of 4.0 [V] and a temperature of 60 [°C], the lithium ions in the facing portion are diffused to the non-facing portion, and fine metal foreign matter mixed inside the electrode body 12 that causes self-discharge is dissolved. At this time, the lithium ions are consumed along with the decomposition of the non-aqueous electrolyte 13 on the surface of the negative electrode plate 2. Then, the cell battery capacity Cc [Ah] decreases over time.

[0029] Therefore, in this embodiment, the time of this aging process is adjusted so that the cell battery capacity Cc [Ah] ultimately reaches the target value by adjusting the time of this aging process.

[0030] A plurality of cell batteries of the lithium ion secondary battery 1 are stacked and controlled as a battery module. In this case, it is desirable that the cell battery capacities Cc [Ah] constituting the battery module are equal. For this reason, it is preferable to regulate the upper and lower limits of the cell battery capacity Cc [Ah]. In this embodiment, the lower limit threshold value Th C Not only [Ah] but also the upper threshold Th C´ [Ah] can also be set. In this case, the cell battery capacity Cc [Ah] is set to the threshold value Th C ≦Cc≦threshold Th C´ In addition, the cell battery capacity Cc [Ah] is within the upper threshold Th C´ If the cell battery capacity Cc[Ah] is exceeded, the aging process time is extended to deliberately reduce the cell battery capacity Cc[Ah].

[0031] <Effects of this embodiment> In the method for producing the lithium ion secondary battery 1 according to the present embodiment, the specific surface area-derived irreversible capacity IC A [Ah] and irreversible capacity IC derived from the coating amount C [Ah] and total irreversible capacity IC T For this reason, the coating NC of the graphite particles GP having the coating NC of amorphous carbon, which is the raw material, may vary, and the specific surface area BET [m 2 / g], the exact total irreversible capacity IC T [Ah] can be estimated.

[0032] Next, this total irreversible capacity IC T [Ah], the cell battery capacity Cc [Ah] is estimated. Then, the threshold value Th C [Ah], the quality of the cell battery is judged. Based on this quality judgment, the time of the aging process can be adjusted to equalize the completed cell battery capacity Cc [Ah]. Then, by constructing a battery module using cell batteries with equalized cell battery capacity Cc [Ah], a high-performance, long-life battery module can be constructed.

[0033] The method for manufacturing the lithium ion secondary battery 1 of this embodiment will be described in detail below. (Configuration of this embodiment) First, an example of the configuration of this embodiment will be described.

[0034] <Configuration of lithium-ion secondary battery 1> 3 is a perspective view showing the outline of the external configuration of the lithium ion secondary battery 1 of this embodiment. First, the configuration of the lithium ion secondary battery 1 of this embodiment, which is an example of the present invention, will be described.

[0035] As shown in FIG. 3, the lithium ion secondary battery 1 is configured as a cell battery. The lithium ion secondary battery 1 includes a battery case 11 in the shape of a plate-like rectangular parallelepiped having an opening on the upper side. An electrode body 12 is accommodated inside the battery case 11. A nonaqueous electrolyte 13 is filled into the battery case 11 through a liquid inlet. The battery case 11 is made of a metal such as an aluminum alloy, and forms a battery container sealed by a lid. The lithium ion secondary battery 1 also includes 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 a positive electrode current collector terminal 16 inside the battery case 11 via the lid. The negative electrode external terminal 15 is electrically connected to a 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 a positive electrode current collector part 33 (see FIG. 4) of the electrode body 12. Moreover, the negative electrode current collector terminal 17 is electrically connected to the negative electrode current collector portion 23 of the electrode body 12 (see FIG. 4).

[0036] <Electrode body 12> FIG. 4 is a schematic diagram showing the configuration of the wound electrode body 12. The electrode body 12 is formed by stacking a large number of negative electrode plates 2 and positive electrode plates 3 with separators 4 arranged between them. The stacked negative electrode plates 2, positive electrode plates 3, and separators 4 are wound to form a flat shape. The negative electrode plates 2 have a negative electrode composite layer 22 formed on a negative electrode current collector 21 made of copper foil as a base material. A negative electrode current collector 23 is provided on one end side of a width direction W (winding axis direction) perpendicular to the winding direction (winding direction L). The negative electrode current collector 23 is configured such that the negative electrode composite layer 22 is not formed and the negative electrode current collector 21 is exposed.

[0037] In the positive electrode plate 3, a positive electrode composite layer 32 is formed on a positive electrode collector 31 made of aluminum foil as a base material. As shown in Fig. 4, a positive electrode collector 33 is provided on the other end side (opposite to the negative electrode collector 23) in a width direction W (winding axis direction) perpendicular to the winding direction (winding direction L) of the positive electrode collector 31. The positive electrode collector 33 does not have the positive electrode composite layer 32 formed thereon, and the metal of the positive electrode collector 31 is exposed.

[0038] <Layer structure of electrode body 12> As shown in FIG. 4, the basic configuration of an electrode assembly 12 of a lithium ion secondary battery 1 includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4.

[0039] The negative electrode plate 2 includes a negative electrode mixture layer 22 on both sides of a negative electrode current collector 21 serving as a negative electrode base material. One end of the negative electrode current collector 21 serves as a negative electrode current collector 23 where the metal is exposed. The positive electrode plate 3 includes a positive electrode mixture layer 32 on both sides of a positive electrode current collector 31 serving as a positive electrode base material. The other end of the positive electrode current collector 31 forms a positive electrode current collecting portion 33 where the metal is exposed.

[0040] The negative electrode plate 2 and the positive electrode plate 3 are stacked with a separator 4 interposed therebetween to form a laminate. As shown in Fig. 4, this laminate is wound in the longitudinal direction around the winding axis to form a wound-type electrode body 12 that is shaped into a flat shape as shown in Fig. 4.

[0041] <Nonaqueous electrolyte 13> The non-aqueous electrolyte 13 of the lithium ion secondary battery 1 of this embodiment shown in FIG. 3 is a composition in which a lithium salt is dissolved in an organic solvent. As the lithium salt, LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. can be used. As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain 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 ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used. As the non-aqueous electrolyte 13, one or more of these can be mixed and used. The composition of the non-aqueous electrolyte 13 is not limited to this.

[0042] <Components of electrode body 12> Next, the negative electrode plate 2, the positive electrode plate 3, and the separator 4, which are the components that make up the electrode assembly 12, will be described.

[0043] <Negative electrode plate 2> As shown in Fig. 4, negative electrode mixture layers 22 are formed on both sides of negative electrode current collector 21, which is a negative electrode base material, to form negative electrode plate 2. In a source process (Fig. 6: S1), negative electrode mixture layer 22 is formed by applying a negative electrode mixture paste to negative electrode current collector 21. After that, negative electrode plate 2 is completed through a drying process, a pressing process, and a cutting process.

[0044] <Negative electrode current collector 21> In this embodiment, the negative electrode current collector 21 is made of Cu foil. The negative electrode current collector 21 serves as a base for the aggregate of the negative electrode mixture layer 22, and also functions as a current collecting member that collects electricity from the negative electrode mixture layer 22. One end of the negative electrode current collector 21 serves as a negative electrode current collecting part 23 where the negative electrode mixture layer 22 is not formed and the metal surface is exposed. 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 collecting part 23, and the negative electrode current collecting terminal 17.

[0045] <Negative electrode composite layer 22> The negative electrode mixture layer 22 is made of a negative electrode active material as a raw material, a binder (binding material) as a secondary material, an additive, etc. The raw material and the secondary material are kneaded with an organic solvent, etc. to generate a negative electrode mixture paste. This negative electrode mixture paste is applied to the negative electrode current collector 21. The applied negative electrode mixture paste is dried and pressed to be shaped, thereby completing the negative electrode plate 2.

[0046] <Negative electrode active material> In this embodiment, the negative electrode active material is powdered graphite particles GP made of graphite having a layered structure, and lithium ions Li + It is a material that can absorb and release energy.

[0047] <Amorphous carbon coating NC> A non-crystalline (amorphous) carbon coating NC is formed on the surface of the graphite particles GP. This amorphous carbon coating NC can reduce the reaction resistance between the graphite particles GP and the non-aqueous electrolyte 13. On the other hand, the amorphous carbon coating NC itself can insert lithium ions, but lithium ions that do not release are generated, increasing the irreversible capacity IC [Ah]. For this reason, if the coating amount Ac [g] of the coating NC is too large, the irreversible capacity increases.

[0048] Generally, the graphite particles GP of the negative electrode active material are delivered as the raw material for the negative electrode composite paste with the amorphous carbon coating NC already formed. In this case, the thickness and the amount of the amorphous carbon coating NC may be specified in advance in the specifications of the raw material. In this case, the coating amount Ac [g] can be calculated based on the specifications. However, there are also cases where such specifications are not clear. In such cases, it is necessary to estimate the coating amount Ac [g]. For this reason, the average diameter (d 50 In this application, the average diameter (d 50 )D [μm] is the median diameter (d 50 )

[0049] <Specific surface area BET[m 2 / g]> This amorphous carbon coating NC is hard but brittle. It can be crushed or broken during mixing of the negative electrode composite paste, or by the shaping press after coating and drying, resulting in a loss of specific surface area [m 2 / g] increases.

[0050] Specific surface area BET[m 2 / g] is expressed as the area per unit mass. There are various methods for specific surface area analysis, including the adsorption method, the moist heat method, and the reaction method. The adsorption method involves adsorbing molecules with a known adsorption area onto the surface of powder particles at the temperature of liquid nitrogen, and determining the specific surface area of ​​the sample from the amount of adsorption. There are two types of adsorption methods: the BET method and the Langmuir method, but the most commonly used method for specific surface area analysis is the BET method, which uses low-temperature and low-humidity physical adsorption of an inert gas.

[0051] In this embodiment, the specific surface area of ​​the powder is determined by the BET method (Berunauer Emmett and Teller's method, gas adsorption method). Quantasorb manufactured by Quantachrome is used as the BET specific surface area measurement device, and nitrogen gas is used as the adsorption gas.

[0052] <Positive electrode plate 3> As shown in Fig. 4, the positive electrode plate 3 is composed of a positive electrode current collector 31, which is a positive electrode base material, and a positive electrode composite layer 32 applied thereto. The positive electrode composite layer 32 is formed by applying a positive electrode composite paste to the positive electrode current collector 31 in a source process (Fig. 7: S1). The positive electrode plate 3 is then completed through a drying process, a pressing process, and a cutting process. The method of manufacturing the positive electrode plate 3 of this embodiment is performed during the manufacturing process of this positive electrode plate 3, and will be described in detail later.

[0053] <Positive electrode current collector 31> A positive electrode mixture layer 32 is formed on both sides of a positive electrode current collector 31, which is a positive electrode base material, to form a positive electrode plate 3. In this embodiment, the positive electrode current collector 31 is made of an Al foil. The positive electrode current collector 31 serves as a base for the aggregate of the positive electrode mixture layer 32, and also functions as a current collecting member that collects electricity from the positive electrode mixture layer 32.

[0054] First, the positive electrode base material constituting the positive electrode current collector 31 is exemplified as an Al foil, but may be made of a conductive material made of a metal having good conductivity. As a material having good conductivity, for example, in addition to Al foil, a material containing an Al alloy may be used. The configuration of the positive electrode current collector 31 is not limited to this.

[0055] <Positive electrode mixture layer 32> Positive electrode mixture layer 32 is formed by applying a positive electrode mixture paste to positive electrode current collector 31 and drying it. Positive electrode mixture layer 32 contains additives such as a conductive assistant, a binder, and a dispersant in addition to positive electrode active material particles.

[0056] <Composition of positive electrode active material> The positive electrode active material particles contain a lithium transition metal oxide having a layered crystal structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn. The positive electrode active material of this embodiment is exemplified by a ternary system called NCM having a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0057] The positive electrode active material of the present embodiment is not limited to a lithium transition metal oxide containing all of Ni, Co, and Mn, and may also be a composition containing, for example, Al in addition to these.

[0058] <Separator 4> The separator 4 is a highly insulating nonwoven fabric made of polypropylene or the like, which is a porous resin for holding the nonaqueous electrolyte 13 between the negative electrode plate 2 and the positive electrode plate 3. As the separator 4, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, and a porous polyvinyl chloride membrane, or a lithium ion or ion conductive polymer electrolyte membrane can be used alone or in combination.

[0059] <Manufacturing Control Device 50 for Lithium-ion Secondary Battery 1> 5 is a block diagram of a manufacturing control device 50 for the lithium-ion secondary battery 1 that accurately estimates the irreversible capacity of the negative electrode of the lithium-ion secondary battery 1 to suppress variation in the initial capacity of the battery cells. The manufacturing control device 50 for the lithium-ion secondary battery 1 constitutes a part of the manufacturing equipment for the lithium-ion secondary battery 1 together with other devices (not shown). The manufacturing control device 50 for the lithium-ion secondary battery 1 includes a measurement circuit and a cell battery capacity control device 70.

[0060] <Measurement circuit> 5, the measurement circuit for measuring the negative electrode capacity [Ah] of the lithium-ion secondary battery 1 includes the lithium-ion secondary battery 1, and a measurement charge / discharge device 60 for supplying a direct current and an alternating current between the terminals of the lithium-ion secondary battery 1. The measurement circuit also includes a voltage meter 61 for measuring the voltage [V] between the terminals of the lithium-ion secondary battery 1, and a current meter 62 for measuring the current flowing between the measurement charge / discharge device 60 and the lithium-ion secondary battery 1.

[0061] <Measurement charging / discharging device 60> The measurement charging / discharging device 60 can charge a predetermined amount of direct current to the lithium ion secondary battery 1, and can discharge a predetermined amount of direct current from the lithium ion secondary battery 1. In other words, the measurement charging / discharging device 60 can estimate and adjust the SOC [%] of the lithium ion secondary battery 1 from the measured current [A] and voltage [V].

[0062] A temperature measuring device 63 that measures the temperature of the lithium ion secondary battery 1 is attached to the lithium ion secondary battery 1. The temperature measuring device 63 outputs a temperature signal corresponding to the measured temperature of the lithium ion secondary battery 1 to the cell battery capacity control device 70. Although not described in detail here, necessary temperature corrections and the like can be performed.

[0063] <Cell battery capacity control device 70> The cell battery capacity control device 70 measures and controls the cell battery capacity Cc [Ah] of the lithium ion secondary battery 1. The procedure for controlling the cell battery capacity Cc [Ah] of the lithium ion secondary battery 1 will be described in detail later with reference to a flowchart.

[0064] The cell battery capacity control device 70 includes a processing unit 80 and a memory unit 90. <Processing section 80> The processing unit 80 is configured with a computer equipped with a CPU, ROM, and RAM. The processing unit 80 is responsible for the overall control of the cell battery capacity control device 70 of the lithium ion secondary battery 1. The processing unit 80 also performs the following functions according to a program stored in the storage unit 90.

[0065] <SOC adjustment unit 81> The SOC adjustment unit 81 estimates the SOC [%] of the lithium-ion secondary battery 1 based on the voltage signal input from the voltage measuring device 61 and the current signal input from the current measuring device 62. Further, the SOC adjustment unit 81 adjusts the lithium-ion secondary battery 1 to a predetermined SOC [%] by giving an instruction of charge and discharge of current to the charge and discharge device 60 for measurement.

[0066] <Coating amount estimation unit 84> The coating amount estimation unit 84 estimates the coating amount Ac [g] of amorphous carbon which is a raw material of the negative electrode active material of the lithium-ion secondary battery 1. In order to obtain the coating amount Ac [g], first, the specific surface area BET [m 2 / g] of the graphite particles GP and the average diameter (d 50 ) D [μm] of the graphite particles GP are obtained.

[0067] Here, the coating amount Ac [g] is measured for the specific surface area BET [m 2 / g] of the graphite particles GP by the BET method. On the other hand, the average diameter (d 50 ) D [μm] of the graphite particles GP is obtained. The coating amount Ac [g] is proportional to the surface area [m 2 of the graphite particles GP. Therefore, the coating amount Ac [g] can be approximately expressed by a function using the average diameter (d 50 ) D [μm] of the graphite particles GP and the specific surface area BET [m 2 / g] of the graphite particles GP as variables. Therefore, the coating amount Ac [g] is estimated using the relationship of the following (Equation 2).

[0068] Coating amount Ac [g] = F (average diameter (d 50 ) D [μm], specific surface area BET [m 2 / g])... (Equation 2) <Threshold setting unit 85> In the determination step (S18) within the specified amount, the threshold setting unit 85 determines the quality of the cell battery as a step of determining good or bad, based on the cell battery capacity Cc [Ah] calculated in the cell battery capacity Cc calculation step (S17). The threshold Th CThe cell battery capacity Cc [Ah] calculated by (Equation 1) is a threshold value Th C Compared to [Ah].

[0069] <Good / bad judgement unit 86> The quality determining unit 86 performs a quality determining process as a quality determining means. In this embodiment, the quality determining unit 86 determines the quality of the lithium ion secondary battery 1 based only on the specific capacity difference ΔSC [mAh / g] and a threshold value Th. The threshold value Th may indicate only a lower limit for determining whether the battery is a quality product or not, or may indicate a range.

[0070] <Storage section 90> The memory unit 90 is a storage medium such as an HDD or SSD, and stores data such as a reference specific capacity 91 and a judgment threshold value 92, such as the threshold value Th of the difference ΔSC, which are necessary for processing by the processing unit 80, as well as other programs and data required by the processing unit 80.

[0071] <Method of Manufacturing Lithium-Ion Secondary Battery 1> FIG. 6 is a flow chart showing an example of a method for manufacturing the lithium ion secondary battery 1 of this embodiment. The method for manufacturing the lithium ion secondary battery 1 of this embodiment will be briefly described below. In the lithium ion secondary battery 1, which is a cell battery, first, in the source step (S1), the negative electrode plate 2, the positive electrode plate 3, and the separator 4, which are power generating elements, are prepared. After the negative electrode plate 2, the positive electrode plate 3, and the separator 4 are prepared in the source step (S1), the negative electrode plate 2 and the positive electrode plate 3 are stacked and integrated with each other via the separator 4 in the stacking step (S2). The stack thus prepared is wound in the winding step (S3) in the winding direction L as shown in FIG. 4. The stack wound in the winding step (S3) is roughly plate-shaped. Such a wound body is pressed from the thickness direction T by the pressing surfaces of the opposing presses in the wound body pressing step (S4). In the wound body pressing step (S4), the electrode body 12 is pressed until it has a specified thickness [mm] in order to fit the electrode body 12 into the battery case 11 shown in FIG. 1 without any gaps.

[0072] After the thickness of the electrode body 12 is adjusted in the wound body pressing process (S4), an assembly process (S5) is performed. In the assembly process (S5), as shown in FIG. 1, a negative electrode current collector terminal 17 and a positive electrode current collector terminal 16 are attached to the electrode body 12, and further, a negative electrode external terminal 15 and a positive electrode external terminal 14 are attached via a lid. Then, the electrode body 12 is housed in a battery case 11. Then, the lid is welded to the battery case 11 to seal the opening. At this stage, the liquid injection port of the lid is open, so the cell is heated in a cell drying process (S6) to dry the inside of the cell. After the inside of the cell is dried in the cell drying process (S6), nonaqueous electrolyte 13 is injected in a liquid injection / sealing process (S7), and the liquid injection port is sealed and hermetically sealed. This completes the assembly of the lithium ion secondary battery 1.

[0073] Then, in the activation step (S8), an SEI film is formed by initial charging, and in the aging step, the battery is stored at high temperature for a long period of time to eliminate micro-short circuits. Once this activation process (S8) is complete, an inspection process (S9) is carried out to check the battery capacity, internal resistance, self-discharge, OCV, etc., and those that pass are shipped as products.

[0074] <Method of Manufacturing Negative Electrode Plate 2> 7 is a flow chart showing an example of the procedure of the source step (S1) in the method for manufacturing the negative electrode plate 2. The procedure of the method for manufacturing the negative electrode plate 2 will be described with reference to FIG.

[0075] <Material delivery process (S10)> In the material delivery step (S10), the negative electrode active material, which is the main raw material of the negative electrode composite paste, and the secondary materials, such as the binder, conductive additive, additive, organic solvent, etc., are delivered. Among these, in the step of obtaining the coating amount, if the thickness and amount of addition of the amorphous carbon coating NC are specified in advance in the raw material specifications, the numerical value can be obtained as the coating amount Ac [g].

[0076] <Negative plate manufacturing process (S11)> In the negative electrode plate manufacturing process (S11), the negative electrode plate 2 is manufactured from the delivered materials as a step for manufacturing the negative electrode plate. Here, the negative electrode active material, which is the main raw material of the negative electrode mixture paste, and the secondary materials such as the binder, conductive aid, additive, and organic solvent are first blended and kneaded in a kneading process. After kneading to produce the negative electrode mixture paste, a predetermined basis weight [g / m2] is applied to the negative electrode current collector 21 made of copper foil. 2 The paste is then coated uniformly with a die nozzle so that the paste is uniformly coated with the negative electrode current collector 21. After that, the organic solvent is evaporated by hot air in the drying process, and the negative electrode composite paste coated on the negative electrode current collector 21 is solidified. After the drying process is completed, the surface is shaped flat in the shaping press process, and the negative electrode current collector 21 is compressed with a roller press until it has a predetermined thickness [μm]. The negative electrode plate 2 is then cut to the specified dimensions, and the negative electrode plate 2 is completed.

[0077] In the above kneading and shaping press processes, the glassy amorphous carbon coating NC is crushed, new surface is generated, and the specific surface area [m 2 / g] increases. <Negative plate specific surface area BET measurement process (S12)> In the negative plate specific surface area BET measurement process (S12), as a step of measuring the specific surface area, the specific surface area BET [m 2 / g] is measured by the BET method.

[0078] <Irreversible capacitance IC derived from specific surface area A Prediction (S13) Irreversible capacitance IC derived from specific surface area A In prediction (S13), the specific surface area BET [m 2 / g] based on the specific surface area-derived irreversible capacity IC A Here, we predict the specific surface area BET [m 2 / g] and irreversible capacity IC [mAh], the specific surface area-derived irreversible capacity IC A Predict.

[0079] <Step of determining whether the coating amount Ac is known or unknown (S14)> In the step (S14) of determining whether the coating amount Ac is known or unknown, if the coating amount Ac can be acquired in the material delivery step (S10), it is determined that the coating amount Ac is known (S14: YES). On the other hand, if the coating amount Ac cannot be acquired in the material delivery step (S10), it is determined that the coating amount Ac is unknown (S14: NO).

[0080] <Coating Amount Ac Prediction Step (S15)> In the coating amount Ac prediction step (S15), if the coating amount Ac[g] cannot be obtained and is determined to be unknown in the step (S14) of determining whether the coating amount Ac[g] is known or unknown, the following procedure is performed. First, in the step of obtaining the coating amount, the coating amount Ac[g] of amorphous carbon, which is the raw material of the negative electrode active material of the lithium-ion secondary battery 1, is obtained. In order to obtain the coating amount Ac[g], the specific surface area BET[m 2 / g] and the average diameter of the graphite particles (d 50 )D [μm] is obtained.

[0081] Here, the amount of coating Ac [g] is the specific surface area BET [m 2 / g] is measured by the BET method. On the other hand, the average diameter of the graphite particles (d 50 )D [μm] is obtained. The amount of coating Ac [g] is the surface area of ​​the graphite particle GP [m 2 ]. Therefore, the coating amount Ac [g] is proportional to the average diameter of the graphite particles GP (d 50 )D [μm], specific surface area of ​​graphite particles BET [m 2 / g] as a variable. Therefore, the coating amount Ac [g] is estimated using the relationship in Equation 2 below.

[0082] Coating amount Ac[g]=F(average diameter(d 50 )D[μm], specific surface area BET[m 2 / g])…(Formula 2) Here, FIG. 8 shows the average diameter (d 50 )D[μm], specific surface area BET[m 2 Graphs L3, L4, and L5 show the relationship between the amount of carbon dioxide per unit area [g] and the coating amount Ac [g].

[0083] As can be seen, the average diameter (d 50 )D[μm], specific surface area BET[m 2 / g] is a straight line of a linear function with graph a: slope and b: intercept. The slope a and intercept b are determined by measurements on the same type of lithium-ion secondary battery 1. The slope a is a common constant. The intercept b is also a constant, but the intercept itself changes depending on the amount of coating Ac [g]. Here, graph L3 is the graph with the largest amount of coating Ac [g]. Graph L4 is the graph with a medium amount of coating Ac [g]. And graph L5 is the graph with the smallest amount of coating Ac [g]. The reason for this is that the graphite particles GP are an aggregate of many small particles, their surfaces are uneven, and the specific surface area [m 2 / g] is relatively large. On the other hand, the amorphous coating NC is glassy and has few irregularities. As shown in FIG. 8, for example, at point P2 where the coating amount Ac [g] is relatively small, the specific surface area [m 2 On the other hand, at point P8 where the amount of coating Ac [g] is relatively large, the surface shape of the original graphite particle GP is evened out and the specific surface area [m 2 / g] is relatively small. For this reason, graphs L3, L4, and L5 have different intercepts.

[0084] In this embodiment, from such measurement results, Specific surface area BET[m 2 / g]=a×average diameter(d 50 )D[μm]+Coating amount Ac[g]+b…(Formula 3) Therefore, the coating weight Ac [g] can be calculated from the following (Equation 4).

[0085] Coating amount Ac[g]=Specific surface area BET[m 2 / g]-a×average diameter(d 50 )D[μm]-b…(Formula 4) Here, the specific surface area BET [m 2 / g] and the average diameter (d 50 )D [μm] is a known measured value. The slope a and intercept b are also known by measurement. For example, the average diameter (d50 )D [μm] is D1, and the specific surface area BET [m 2 / g] is BET1, the coordinates of point P5 on the graph are shown. Then, the only graph that passes through these coordinates is L4. Then, in this case, it can be seen that the coating amount Ac [g] is medium.

[0086] The same average diameter (d 50 )D [μm], the specific surface area BET [m 2 / g] is large, the amount of coating Ac [g] is small. On the other hand, the average diameter (d 50 )D [μm], the specific surface area BET [m 2 It can be seen that when [A / g] is small, the coating amount Ac [g] is large.

[0087] In the coating amount Ac prediction step (S15), the coating amount Ac [g] is estimated according to the above-mentioned procedure. <Irreversible capacitance IC due to coating amount C Prediction process (S16) Irreversible capacitance IC derived from coating amount C In the prediction step (S16), as a step of predicting the irreversible capacity derived from the coating amount, the coating amount-derived irreversible capacity IC C The prediction is performed based on the coating amount Ac [g] obtained as a known value in the material delivery step (S10) or the coating amount Ac [g] estimated in the coating amount Ac prediction step (S15). C The prediction is based on the relationship between the amount of coating Ac [g] and the irreversible capacity IC [mAh] as shown in Figure 1.

[0088] <Cell battery capacity Cc calculation process (S17)> In the cell battery capacity Cc calculation step (S17), the total irreversible capacity IC T [mAh] is estimated. Here, the irreversible capacity IC derived from the specific surface area is used. A The irreversible capacity IC derived from the specific surface area predicted in prediction (S13) A [mAh] and irreversible capacity IC derived from the coating amount CThe irreversible capacity IC derived from the coating amount predicted in the prediction step (S16) C [mAh] Add them all together. This sum is the total irreversible capacity IC T [mAh].

[0089] In addition, the cell battery capacity Cc calculation step (S17) is a step of predicting the cell battery capacity, and calculates the cell battery capacity Cc [Ah]. The calculation of the cell battery capacity Cc [Ah] is as follows.

[0090] Cell battery capacity Cc [Ah], design capacity Cc S When [Ah] is used, Cell battery capacity Cc=Cc S -I C T …(Formula 1) The cell battery capacity Cc [Ah] is predicted using this.

[0091] <Step of determining whether the amount is within the specified amount (S18)> In the step of determining whether the battery is within the specified amount (S18), the quality of the cell battery is determined based on the cell battery capacity Cc [Ah] calculated in the step of calculating the cell battery capacity Cc (S17). The cell battery capacity Cc [Ah] calculated by the above (Equation 1) is compared with a threshold value Th that is set in advance by measuring the same type of lithium ion secondary battery 1. C If the cell battery capacity Cc [Ah] exceeds the threshold value ThC [Ah], the test is considered to be passed (S18: YES). C If it falls below [Ah], it is considered a failure (S18: NO).

[0092] <Normal aging process (S19)> If the cell battery capacity Cc [Ah] exceeds the threshold value ThC [Ah] and is deemed to be acceptable (S18: YES), the aging process is carried out as usual.

[0093] <Aging time adjustment step (S20)> In the aging time adjustment step (S20), the aging time is adjusted as a step of adjusting the aging time.

[0094] Cell battery capacity Cc [Ah] is threshold Th C If the cell capacity Cc [Ah] is below the threshold value Th (S18: NO), the aging time adjustment step (S20) is performed. In this case, the aging time is shortened compared to the normal aging step (S19) because the cell capacity Cc [Ah] is significantly reduced. The shortened time is determined by the relationship between the cell capacity Cc [Ah] and the threshold value Th C It is shortened according to the difference in [Ah].

[0095] In addition, the aging process time is adjusted by adjusting the cell battery capacity Cc [Ah] and the threshold value Th C If the difference in [Ah] cannot be corrected, the cell battery will be rejected as not being adjustable. (Action of this embodiment) In the method for estimating the irreversible capacity of the negative electrode of the lithium ion secondary battery 1 according to the present embodiment, the specific surface area-derived irreversible capacity IC A In the prediction (S13), as a step of predicting the irreversible capacity derived from the specific surface area, the specific surface area BET [m 2 / g] based on the specific surface area-derived irreversible capacity IC A Predict.

[0096] In addition, the irreversible capacity IC C In the prediction step (S16), as a step of predicting the irreversible capacity derived from the coating amount, the coating amount-derived irreversible capacity IC C Predict. In the cell battery capacity Cc calculation step (S17), the total irreversible capacity IC T [mAh] is estimated. Here, the irreversible capacity IC derived from the specific surface area is used. A The irreversible capacity IC derived from the specific surface area predicted in prediction (S13) A [mAh] and irreversible capacity IC derived from the coating amount C The irreversible capacity IC derived from the coating amount predicted in the prediction step (S16) C [mAh] Add them all together. This sum is the total irreversible capacity IC T [mAh].

[0097] In addition, the cell battery capacity Cc calculation step (S17) is a step for predicting the cell battery capacity, and the cell battery capacity Cc=Cc S -I C T ...Calculate the cell battery capacity Cc [Ah] using (Equation 1).

[0098] In the step of determining whether the battery is within the specified amount (S18), the quality of the cell battery is determined based on the cell battery capacity Cc [Ah] calculated in the step of calculating the cell battery capacity Cc (S17). The cell battery capacity Cc [Ah] calculated by the above (Equation 1) is compared with a threshold value Th that is set in advance by measuring the same type of lithium ion secondary battery 1. C If the cell battery capacity Cc [Ah] exceeds the threshold value ThC [Ah], the test is considered to be passed (S18: YES). C If it falls below [Ah], it is deemed to have failed (S18: NO).

[0099] If the cell battery capacity Cc [Ah] exceeds the threshold value ThC [Ah] and is deemed to be acceptable (S18: YES), the aging process is carried out as usual. In the aging time adjustment step (S20), the aging time is adjusted as a step of adjusting the aging time.

[0100] Cell battery capacity Cc [Ah] is threshold Th C If the cell capacity Cc [Ah] falls below the threshold value Th (S18: NO), the aging time is adjusted (S20). In this case, the aging time is shortened compared to the normal aging process (S19) because the cell capacity Cc [Ah] is significantly reduced. The shortened time is determined by the relationship between the cell capacity Cc [Ah] and the threshold value Th C It is shortened according to the difference in [Ah].

[0101] In addition, the aging process time is adjusted by adjusting the cell battery capacity Cc [Ah] and the threshold value Th C If the difference in [Ah] cannot be corrected, the cell battery will be rejected as not being adjustable. The method for estimating the irreversible capacity of the negative electrode of the lithium ion secondary battery 1 according to the present embodiment provides the above-mentioned functions.

[0102] (Effects of this embodiment) (1) According to the method for estimating the irreversible capacity of the negative electrode of the lithium ion secondary battery 1 and the method for manufacturing the lithium ion secondary battery 1 of the present embodiment, it is possible to accurately estimate the irreversible capacity of the negative electrode and suppress variation in the initial capacity of the battery cells.

[0103] (2) Irreversible capacitance IC derived from specific surface area A [Ah] and irreversible capacity IC derived from the coating amount C [Ah] and the total irreversible capacity IC T [Ah] is calculated, and the cell battery capacity Cc [Ah] is calculated from this. This makes it possible to calculate the total irreversible capacity IC T This has the effect of making it possible to calculate [Ah].

[0104] (3) The specific surface area BET [m 2 / g] and the average diameter (d 50 )D [μm] of the graphite particles GP, the coating amount Ac [g] is obtained. Therefore, even if the coating amount Ac [g] of the graphite particles GP is unknown, the specific surface area BET [m 2 / g] and the average diameter (d 50 )D [μm].

[0105] (4) Total irreversible capacitance IC T The cell battery capacity Cc [Ah] is predicted based on the current [mAh]. This has the effect of making it possible to more accurately predict the cell battery capacity Cc [Ah].

[0106] (5) Total irreversible capacitance IC T [Ah], cell battery capacity Cc [Ah], design capacity Cc S [Ah], cell battery capacity Cc = CcS -I C T ...The cell battery capacity Cc [Ah] is predicted by (Equation 1). This has the effect of making it possible to easily predict the cell battery capacity Cc [Ah].

[0107] (6) Based on the cell battery capacity Cc [Ah] predicted in the cell battery capacity prediction step, a preset threshold value Th of the cell battery capacity Cc [Ah] is set. C By comparing it with [Ah], it is possible to determine whether the cell battery is good or bad. Therefore, it is easy to determine whether the cell battery is degraded or not.

[0108] (7) Even if a product is judged to be defective in a normal aging process, it can be made usable as a non-defective product by adjusting the aging process time.

[0109] (Another example) In the manufacturing method including the method for estimating the irreversible capacity of the negative electrode of the lithium ion secondary battery 1 of this embodiment, if the cell battery capacity Cc [Ah] does not reach a specified amount, the retention time of the aging process is adjusted to prevent the cell battery capacity Cc [Ah] from decreasing. However, it is not limited to the retention time, and it can also be adjusted by other conditions such as the retention temperature [°C] and SOC [%].

[0110] Although the lithium ion secondary battery 1 of this embodiment is exemplified as a battery cell constituting a battery pack for driving a hybrid vehicle, the lithium ion secondary battery 1 may be used as a single cell. In addition, the application may be for use as a stationary battery or as a power source for portable devices.

[0111] The lithium ion secondary battery 1 of this embodiment is illustrated as having a flat, thin, rectangular battery case 11, but the shape is not limited thereto and may be cylindrical or the like. The numerical values ​​and numerical ranges in this embodiment are optimized for the lithium ion secondary battery 1 in this embodiment, and can be optimized as appropriate by a person skilled in the art in accordance with the characteristics of the target battery.

[0112] The flowcharts shown in FIGS. 6 and 7 are an example of a manufacturing method including a method for estimating the irreversible capacity of the negative electrode of the lithium-ion secondary battery 1 of this embodiment, and a person skilled in the art may add or delete steps, change the order, or modify the steps.

[0113] In addition, those skilled in the art may add, delete, or modify the configuration without departing from the scope of the claims. [Explanation of symbols]

[0114] 1...Lithium-ion secondary battery (cell battery) 11…Battery case 12...Electrode body 13...Nonaqueous electrolyte 14…Positive external terminal 15...Negative external terminal 16…Positive current collecting terminal 17...Negative current collecting terminal 2...Negative electrode plate 21...Negative electrode current collector 21a...Metal foil 22...Negative electrode composite material layer 22a...Negative electrode active material 23...Negative electrode current collector 3…Positive electrode plate 31...Positive electrode current collector 32...Positive electrode mixture layer 33…Positive electrode current collector 4…Separator 50...Production control device 61...Voltage measuring instrument 62…Current measuring device 63…Temperature measuring device 70...Cell battery capacity control device 80... Processing section 81...SOC adjustment section 82...Reference specific capacity calculation section 83…Actual capacity measurement section 84...Coating amount estimation section 85...Threshold setting section 86…Good / bad judgment section 90...Storage section 91…Reference specific capacity 92…Decision threshold GP: Graphite particles NC...(amorphous) coating Ac[g]: Amount of coating (of amorphous carbon) Cc [Ah]…cell battery capacity Cc S [Ah]…(cell battery capacity) design capacity Th C [Ah]...(cell battery capacity) threshold BET[m 2 / g] Specific surface area IC [mAh]: Irreversible capacity I C C [mAh]…Irreversible capacity derived from coating amount I C A [m 2 / g]…Irreversible capacity derived from specific surface area D [μm]…(Graphite particle GP) average diameter (d 50 )

Claims

1. A step of acquiring a coating amount Ac [g] of the amorphous carbon coating NC in graphite particles GP having an amorphous carbon coating NC, which is a negative electrode active material serving as a raw material for a negative electrode plate of a lithium ion secondary battery; The coating amount Ac [g] obtained in the step of obtaining the coating amount is used to calculate the coating amount-derived irreversible capacity IC derived from the coating NC of the amorphous carbon. Ｃ A step of predicting the irreversible capacity derived from the coating amount [Ah]; A step of producing a negative electrode plate by using the graphite particles GP having the amorphous carbon coating NC as a raw material, kneading them with a secondary material to produce a negative electrode composite paste, and coating the produced negative electrode composite paste on a negative electrode current collector to produce the negative electrode plate; The specific surface area BET [m ２ / g]; and The specific surface area BET [m ２ / g] Ａ A step of predicting the specific surface area-derived irreversible capacity [Ah]; The film amount-derived irreversible capacity IC predicted in the film amount-derived irreversible capacity prediction step Ｃ [Ah] and the specific surface area-derived irreversible capacity IC predicted in the specific surface area-derived irreversible capacity prediction step Ａ From [Ah], the total irreversible capacity IC Ｔ A step of estimating the total irreversible capacity [Ah]; A method for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery, comprising:

2. In the step of obtaining the coating amount, The specific surface area BET [m ２ / g] and the average diameter of the graphite particles GP (d ５０ 2. The method for estimating the irreversible capacity of the negative electrode of a lithium ion secondary battery according to claim 1, further comprising the step of: acquiring a coating amount Ac [g] of the graphite particles GP based on the coating amount D [μm] of the graphite particles GP.

3. In addition to the method for estimating the irreversible capacity of a negative electrode of a lithium ion secondary battery according to claim 1, The total irreversible capacity IC estimated by the total irreversible capacity estimation step Ｔ A step of predicting the cell battery capacity Cc [Ah] based on the cell battery capacity Cc [Ah]; The method for producing a lithium ion secondary battery further comprises:

4. In the step of predicting the cell battery capacity, The film amount-derived irreversible capacity IC predicted in the film amount-derived irreversible capacity prediction step Ｃ [Ah] and the specific surface area-derived irreversible capacity IC predicted in the specific surface area-derived irreversible capacity prediction step Ａ The total irreversible capacity IC Ｔ Based on [Ah], Cell battery capacity Cc [Ah], design capacity Cc Ｓ When [Ah], Cell battery capacity Cc = Cc Ｓ -IC Ｔ ...(Formula 1) 4. The method for manufacturing a lithium ion secondary battery according to claim 3, further comprising the steps of: predicting a cell battery capacity Cc [Ah] by:

5. Based on the cell battery capacity Cc [Ah] predicted in the cell battery capacity prediction step, a preset threshold value Th of the cell battery capacity Cc [Ah] is set. Ｃ 4. The method for manufacturing a lithium ion secondary battery according to claim 3, further comprising a step of determining whether the cell battery is good or bad by comparing the capacity of the cell with the capacity of the battery [Ah].

6. In the step of determining whether or not the battery is defective, if the battery cell capacity Cc [Ah] is insufficient, the aging time to be performed thereafter is adjusted to the design capacity Cc [Ah] that targets the battery cell capacity Cc [Ah]. Ｓ [Ah]. The method for producing a lithium ion secondary battery according to claim 5 .

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