Lithium ion secondary battery and method for manufacturing lithium ion secondary battery

Abstract

The present invention provides a lithium-ion secondary battery and a method for manufacturing such a lithium-ion secondary battery. The lithium-ion secondary battery is a high-capacity, compact battery having a smaller positive-negative electrode capacity ratio (RC) than a positive-negative electrode capacity ratio (RC), and suppresses an increase in battery resistance even in a low SOC region. The lithium-ion secondary battery (1) comprises a positive electrode (30) and a negative electrode (40), wherein a positive-negative electrode capacity ratio (RC) of the positive electrode capacity of the positive electrode to the negative electrode capacity of the negative electrode is 1.02 to 1.40, and the negative electrode irreversible capacity (CNn) of the negative electrode (40) is greater than the positive electrode irreversible capacity (CPn) of the positive electrode (30) (CPn < CNn).

Description

Technical Field

[0001] The present invention relates to a lithium ion secondary battery and a method for manufacturing a lithium ion secondary battery Background Art

[0002] There is a trend toward high-output lithium-ion secondary batteries (hereinafter also referred to as batteries) for hybrid vehicles (HVs). However, batteries used in electric vehicles (EVs) and plug-in hybrid vehicles (PHVs) are also required to have high capacity and compact size over a wide SOC range (e.g., from less than SOC 10% to more than SOC 95%).

[0003] However, when manufacturing a battery, after manufacturing an uncharged battery, an initial charge is performed, and then, the battery is completed by performing high-temperature aging. If such an initial charge is performed, the SEI (Solid Electrolyte Interphase) generated by the decomposition of the electrolyte components contained in the electrolyte in the positive and negative electrodes is accumulated, and irreversible capacity is generated respectively. Moreover, the irreversible capacity generated in the positive and negative electrodes due to the initial charge is usually proportional to the size of the positive electrode capacity and the negative electrode capacity. It should be noted that as a prior art related to the initial charge, Patent Document 1 (with reference to the claims of Patent Document 1, etc.) can be cited.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 011 / 024250 Summary of the Invention

[0007] However, in order to achieve higher capacity and more compact batteries for applications such as EVs, it is considered to reduce the amount of negative electrode reserves. This is done by reducing the negative electrode capacity (CN) relative to the positive electrode capacity (CP) compared to high-power batteries for hybrid vehicles (HVs). For example, the positive-to-negative electrode capacity ratio (RC = CN / CP) is set to approximately RC = 1.2, for example, RC = 1.02 to 1.40. In this way, when the negative electrode capacity (CN) is reduced without reducing the positive electrode capacity (CP) (when the positive-to-negative electrode capacity ratio (RC) is close to 1), the irreversible capacity generated at the positive electrode remains unchanged, but the irreversible capacity of the negative electrode decreases.

[0008] Therefore, the irreversible capacity of the negative electrode may become smaller than that of the positive electrode. In this case, for example, when the battery is discharged in a low SOC range (e.g., below SOC 20% but greater than SOC 0%) to reduce the battery voltage, the positive electrode potential drops significantly before the negative electrode potential rises, resulting in an undesirable increase in battery resistance (DC-IR). When a large amount of Li ions are filled into the positive electrode active material through discharge, the Li ions become difficult to move within the positive electrode active material, the positive electrode potential drops, and the battery resistance increases.

[0009] The present invention is completed in view of the above-mentioned problems, and its purpose is to provide a high-capacity, compact battery with a small positive-to-negative electrode capacity ratio (RC), a lithium-ion secondary battery that suppresses the increase in battery resistance even in the low SOC region, and a method for manufacturing such a lithium-ion secondary battery.

[0010] (1) One embodiment of the present invention for solving the above-mentioned problems is a lithium-ion secondary battery having a positive electrode and a negative electrode, wherein the positive-to-negative electrode capacity ratio (RC) of the positive electrode capacity of the positive electrode to the negative electrode capacity of the negative electrode is 1.02 to 1.40, and the negative electrode irreversible capacity (CNn) of the negative electrode is greater than the positive electrode irreversible capacity (CPn) of the positive electrode (CPn<CNn).

[0011] The battery described above has a positive-to-negative electrode capacity ratio (RC) of 1.02 to 1.40, and the negative electrode irreversible capacity (CNn) is greater than the positive electrode irreversible capacity (CPn), as described above. That is, it is a high-capacity, compact battery with a small positive-to-negative electrode capacity ratio (RC), and unlike the matters described in the above-mentioned subject, the negative electrode irreversible capacity (CNn) is greater than the positive electrode irreversible capacity (CPn). Therefore, when the battery is discharged in a low SOC region to reduce the battery voltage, the negative electrode potential rises significantly and the battery voltage decreases before the positive electrode potential decreases. Therefore, it is possible to prevent the use of regions where the positive electrode potential is significantly reduced, and to suppress the increase in battery resistance in regions with low SOC.

[0012] It should be noted that the positive-to-negative electrode capacity ratio (RC) is the ratio of the positive electrode capacity (CP) to the negative electrode capacity (CN) (RC = CN / CP). In order to prevent the precipitation of Li metal at the negative electrode, the negative electrode active material layer needs to include a range opposite the positive electrode active material layer, must be wider than the positive electrode active material layer, must make the negative electrode capacity per unit area greater than the positive electrode capacity per unit area, and, considering the assembly accuracy (positioning accuracy, etc.) as an electrode body, the lower limit of the positive-to-negative electrode capacity ratio (RC) is set to 1.02. On the other hand, the upper limit of the positive-to-negative electrode capacity ratio (RC) (RC = 1.40) is: when performing initial charging, etc., without performing the first initial charging process and the first high-temperature aging process described later to increase the negative electrode irreversible capacity (CNn), the negative electrode irreversible capacity (CNn) is less than the upper limit value in the range of the positive-to-negative electrode capacity ratio (RC) of the positive electrode irreversible capacity (CPn).

[0013] (2) Another embodiment of the present invention for solving the above-mentioned problems is a method for manufacturing a lithium-ion secondary battery, wherein the lithium-ion secondary battery has a positive electrode and a negative electrode, a positive-to-negative electrode capacity ratio (RC) of the positive electrode capacity of the positive electrode to the negative electrode capacity of the negative electrode is 1.02 to 1.40, and the negative electrode irreversible capacity (CNn) of the negative electrode is greater than the positive electrode irreversible capacity (CPn) of the positive electrode (CPn < CNn). The method for manufacturing the lithium-ion secondary battery comprises the following steps: a first initial charging step, charging an uncharged battery having the positive-to-negative electrode capacity ratio (RC) of 1.02 to 1.40 to a first SOC within a first SOC range of 2 to 13% at a first charging battery temperature within a first battery temperature range of 20 to 25°C; a first high-temperature aging step, charging the battery to the first SOC within the first SOC range of 2 to 13%; The above-mentioned lithium ion secondary battery with a SOC of 0.0547 W / m is placed at a first aging ambient temperature in the range of 60 to 65°C with the positive and negative terminals open during a first aging period in the range of 5 to 25 hours; a second initial charging process, after the above-mentioned first high-temperature aging process, charging the above-mentioned lithium ion secondary battery to a second SOC in the range of 13 to 91% higher than the above-mentioned first SOC at a second charging battery temperature in the range of 20 to 25°C; a second high-temperature aging process, placing the above-mentioned lithium ion secondary battery charged to the above-mentioned second SOC at a second aging ambient temperature in the range of 60 to 75°C with the positive and negative terminals open during a second aging period in the range of 6 to 30 hours.

[0014] In this manufacturing method, a battery that has been charged to a low first SOC in a first initial charging step is placed in a high-temperature first aging environment in a first high-temperature aging step. Then, in a second initial charging step, the battery is charged to a second SOC higher than the first SOC and then placed in a high-temperature second aging environment in a second aging step. This method, after temporarily charging to a low first SOC and undergoing high-temperature aging, and then charging to a higher second SOC and undergoing high-temperature aging, increases the negative irreversible capacity (CNn) generated by the negative electrode plate compared to conventional methods that perform initial charging at a higher SOC and then high-temperature aging without employing the first initial charging and first high-temperature aging steps. This allows for a battery in which the negative irreversible capacity (CNn) is greater than the positive irreversible capacity (CPn) despite a positive-to-negative capacity ratio (RC) of 1.02 to 1.40.

[0015] This makes it possible to manufacture a high-capacity, compact battery having positive and negative electrode capacities smaller than RC, and a lithium-ion secondary battery in which an increase in battery resistance is suppressed even in a low SOC region.

[0016] It should be noted that if the battery is fully acclimatized to the temperature between the first high-temperature aging step and the second initial charging step, before the second initial charging step, the second initial charging step can be performed under conditions where the battery voltage is stable and uniform, which is more preferable. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a longitudinal cross-sectional view of the battery according to the embodiment.

[0018] Figure 2 In the figure, the solid line is a flow chart of the battery manufacturing process of an embodiment including two initial charging steps and two high-temperature aging steps, and the dotted line is a flow chart of the conventional battery manufacturing process including a single initial charging step and high-temperature aging step.

[0019] Figure 3 The characteristics of the battery according to the embodiment are shown. The upper graph shows the relationship between the charge amount (capacity), the electrode potential, and the battery voltage. The lower graph shows the relationship between the charge amount (capacity) and the battery resistance.

[0020] Figure 4 This is a diagram showing the relationship between the SOC in the first initial charging step, the first aging period in the first high-temperature aging step, and the battery resistance.

[0021] Figure 5 The diagram shows the characteristics of a battery that has a small positive-negative electrode capacity ratio but has undergone conventional initial charging and high-temperature aging. The upper part is a graph showing the relationship between the charging charge (capacity) and the potential, and the lower part is a graph showing the relationship between the charging charge (capacity) and the battery resistance.

[0022] Explanation of symbols

[0023] 1. 1J (fully charged) battery

[0024] TB battery temperature

[0025] 30 positive plate

[0026] 40 negative plate

[0027] 50 Isolators

[0028] CP (positive plate) positive electrode capacity

[0029] CN (negative plate) negative electrode capacity

[0030] RC positive and negative electrode capacity ratio

[0031] CPn, CPna Positive electrode irreversible capacity

[0032] CNn, CNna negative electrode irreversible capacity

[0033] PE positive electrode potential

[0034] NE negative electrode potential

[0035] VB battery voltage

[0036] VB1, VB1a SOC0% battery voltage

[0037] VB2 SOC100% battery voltage

[0038] S3 First initial charging process

[0039] TA1 First battery temperature range

[0040] TB1 Battery temperature during first charge

[0041] SA1 First SOC range

[0042] SC1 First SOC

[0043] S4 First high temperature aging process

[0044] EA1 First Period Range

[0045] EP1 First aging period

[0046] TD1 First ambient temperature range

[0047] TE1 First aging environment temperature

[0048] S6 Second initial charging process

[0049] TA2 Second battery temperature range

[0050] TB2 Battery temperature during the second charge

[0051] SA2 Second SOC range

[0052] SC2 Second SOC

[0053] S7 Second high temperature aging process

[0054] EA2 Second period range

[0055] EP2 Second aging period

[0056] TD2 Second ambient temperature range

[0057] TE2 Second aging environment temperature

[0058] S9 inspection process

[0059] TB3 Check battery temperature

[0060] Rb Battery resistance (DC-IR)

[0061] SJ3 initial charging process

[0062] TBJ Battery temperature during charging

[0063] SCJ Initial Charge SOC

[0064] SJ4 high temperature aging process

[0065] EPJ aging period

[0066] TEJ aging ambient temperature

[0067] SJ5 cooling process DETAILED DESCRIPTION

[0068] Hereinafter, embodiments and reference modes of the present invention will be described with reference to the accompanying drawings. Figure 1 A longitudinal cross-sectional view of a lithium-ion secondary battery (hereinafter also referred to simply as a "battery") 1 according to this embodiment and a reference battery 1J is shown. Batteries 1 and 1J are composed of a rectangular box-shaped battery case 10, a flat wound electrode assembly 20 and an electrolyte 15 housed therein, and a positive terminal member 60 and a negative terminal member 70 supported by the battery case 10.

[0069] The electrode body 20 is formed by winding a strip-shaped positive electrode plate 30 and a strip-shaped negative electrode plate 40 through a pair of strip-shaped separators 50. In this embodiment, as the positive electrode active material contained in the positive electrode active material layer of the positive electrode plate 30, a lithium transition metal composite oxide, specifically lithium nickel cobalt manganese oxide, is used. In addition, as the negative electrode active material contained in the negative electrode active material layer of the negative electrode plate 40, a carbon material, specifically graphite, is used. Here, the positive electrode capacity of the positive electrode plate 30 is CP (Ah), and the negative electrode capacity of the negative electrode plate 40 is CN (Ah) (refer to Figure 3 、 Figure 5 ).

[0070] It should be noted that, as described above, the negative active material layer (not shown) of the negative electrode plate 40 and the positive active material layer (not shown) of the positive electrode plate 30 are arranged opposite each other via a separator. However, these layers must be arranged so that the negative active material layer is wider than the positive active material layer and that the negative active material layer includes a region opposing the positive active material layer (i.e., the negative active material layer is positioned opposite any portion of the positive active material layer), and must be wider than the positive active material layer. Furthermore, the negative electrode capacity per unit area of ​​the negative active material layer must be greater than the positive electrode capacity per unit area of ​​the positive active material layer. This is to prevent Li metal precipitation on the negative electrode plate 40 during charging of the batteries 1 and 1J. In addition, as the electrode body 20, if the assembly requirements (positioning accuracy, etc.) of the positive electrode plate 30 and the negative electrode plate 40 via the separator are also considered, the negative electrode capacity CN of the negative electrode plate 40 needs to be slightly larger than the positive electrode capacity CP of the positive electrode plate 30, and the positive-to-negative electrode capacity ratio RC (=CN / PC) needs to be set to at least RC=1.02 or above.

[0071] On the other hand, if the negative electrode capacity CN of the negative electrode plate 40 is sufficiently greater than the positive electrode capacity CP of the positive electrode plate 30, as in high-output batteries, the negative electrode irreversible capacity CNn can be made greater than the positive electrode irreversible capacity CPn without performing the first initial charging step S3 and the first high-temperature aging step S4, described later. Taking this into account, the upper limit of the positive-to-negative electrode capacity ratio RC of the present application is given as the upper limit value within the range of the positive-to-negative electrode capacity ratio RC where the negative electrode irreversible capacity CNn is less than the positive electrode irreversible capacity CPn, without performing the first initial charging step S3 and the first high-temperature aging step S4, which increase the negative electrode irreversible capacity CNn. This is approximately RC = 1.40.

[0072] In the batteries 1 and 1J of the present embodiment and the reference embodiment, the positive and negative electrode capacity ratio RC is RC=CN / CP=1.38.

[0073] It should be noted that as the electrolyte 15, a non-aqueous electrolyte containing a lithium salt as a supporting salt in an organic solvent is used. As the supporting salt used in the electrolyte 15, for example, lithium salts such as LiPF6, LiBF4, LiClO4, LiAsF6, Li(CF3SO2)2N, and LiCF3SO3 can be exemplified. The above-mentioned supporting salts can be used alone or in combination of two or more. As a particularly preferred example, LiPF6 can be cited, and LiPF6 is also used in this embodiment. In addition, the electrolyte 15 is preferably prepared so that the concentration of the supporting salt is, for example, in the range of 0.7 to 1.3 mol / L.

[0074] In addition, as the non-aqueous solvent used in the electrolyte 15, an organic solvent commonly used in lithium-ion secondary batteries can be appropriately selected and used. Particularly preferred non-aqueous solvents include carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC). These organic solvents can be used alone or in combination of two or more. For example, a solution of EC, DMC, and EMC mixed in a volume ratio of approximately 2 to 5:2 to 5:2 to 5 can be used.

[0075] In addition, about 0.1 to 1% by mass of one selected from carboxylic anhydrides such as maleic anhydride and succinic anhydride and dicarboxylic acids such as oxalic acid and malonic acid may be added alone or in combination of two or more. In addition, about 0.1 to 1% by mass of one selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfite, and fluoroethylene carbonate may be added alone or in combination of two or more.

[0076] (Reference method)

[0077] Here, using the uncharged battery 1X with a smaller positive and negative electrode capacity ratio RC (RC=1.38), before explaining each step of manufacturing the battery 1 of this embodiment using the manufacturing method of this embodiment, as a reference, Figure 2 、 Figure 5 The following describes a process of manufacturing a battery 1J using the uncharged battery 1X described above without performing the first initial charging step S3 and the first high-temperature aging step S4 of the embodiment described later and the characteristics of the manufactured battery 1J.

[0078] First, in the "assembly step" S1, an uncharged battery 1X is assembled using a known method (see Figure 1Next, in the "stacking load application step" S2, a plurality (10 in the reference embodiment) of assembled batteries 1X (batteries 1J described later) are stacked and constrained by applying a predetermined first load BL1 (BL1 = 9 kN in the reference embodiment) using a restraining jig (not shown). While the first load BL1 is applied to the plurality of batteries 1J (batteries 1X) in this manner, steps SJ3 to SJ5, indicated by dashed lines, and the inspection step S9 are performed on each battery 1J.

[0079] After the stacking load application step S2, in the reference method, enter Figure 2 In the "initial charging step" SJ3 indicated by the dotted line, after setting the battery temperature TB of battery 1X to the charging battery temperature TBJ (TBJ = 20.0°C in the reference method), charging is performed until the initial charge SOC reaches SCJ (SCJ = 91% in the reference method). Specifically, a charging and discharging device (not shown) is connected to the two terminal members 60 and 70 of battery 1X, which is restrained by the restraint jig, and initial charging is performed on battery 1J (battery 1X) using constant current constant voltage (CCCV) charging until the battery voltage VB of battery 1X reaches a predetermined value (VB = 3.97V, corresponding to SCJ = 91% in the reference method).

[0080] Next, in Figure 2 In the "high temperature aging process" SJ4 indicated by the dotted line, the following high temperature aging is performed: the battery 1J that has been initially charged to the initial charge SOC (SCJ = 91%) in the initial charging process SJ3 is placed at an aging ambient temperature TEJ (TEJ = 63°C in this reference method) for the entire aging period EPJ (EPJ = 20 hrs in this reference method) with the positive terminal component 60 and the negative terminal component 70 open. It is believed that if high temperature aging is performed at such a high SOC, the formation of SEI occurs on the surface of the negative plate 40 of the battery 1J, resulting in a negative electrode irreversible capacity CNna. In addition, it is believed that in the positive plate 30, the fluorine-containing supporting salt (LiPF6, etc.) that forms the electrolyte 15 reacts with moisture to produce hydrofluoric acid, destroying the crystal structure of the positive electrode active material, thereby causing a decrease in the positive electrode capacity, thereby producing a positive electrode irreversible capacity CPna (reference Figure 5 ).

[0081] Then, in Figure 2In the "cooling and placing process" SJ5 indicated by the dotted line in FIG, the battery 1J is forcibly cooled by a fan in a cooling room (not shown) at a cooling ambient temperature TCJ (TCJ = 20°C in this reference embodiment) for a cooling period CPJ (CPJ = 20 minutes in this embodiment). Then, the battery 1J is transferred to a placing room (not shown) set to an ambient temperature TKJ (TKJ = 20.0°C in this reference embodiment) and placed for a placing period HPJ (HPJ = 30 minutes in this reference embodiment). The battery temperature TB of the battery 1J is set to a third battery temperature TB3 (TB3 = 20.0°C in this reference embodiment) which is the same as the ambient temperature TKJ (refer to FIG. Figure 2 ).

[0082] Then, similarly to the embodiment described later, in the "inspection process" S9, various inspections (details omitted) such as a self-discharge inspection to check the size of self-discharge and a capacity inspection to check the size of the capacity of the battery 1 are performed on the battery 1 with the third battery temperature TB3 = 20.0°C, leaving the good battery 1J.

[0083] In this way, a battery 1J manufactured by a conventional method was obtained, in which the positive and negative electrode capacity ratio RC=CN / CP=1.38 was obtained.

[0084] It should be noted that the positive electrode irreversible capacity CPna and negative electrode irreversible capacity CNna generated by battery 1J are roughly proportional to the positive electrode capacity CP of the positive electrode plate 30 and the negative electrode capacity CN of the negative electrode plate 40 of battery 1J (battery 1X), respectively. Specifically, for battery 1J (battery 1X), when the initial charge step SJ3 and high-temperature aging step SJ4 are performed as described above, the positive electrode irreversible capacity CPna is approximately 3% of the positive electrode capacity CP, and the negative electrode irreversible capacity CNna is approximately 2% of the negative electrode capacity CN.

[0085] Therefore, if battery 1J (battery 1X) is different from the above and is a battery in which the negative electrode capacity CN of the negative electrode plate 40 is sufficiently large compared to the positive electrode capacity CP of the positive electrode plate 30 (specifically, when the positive-negative electrode capacity ratio RC = CN / CP > 1.5), the negative electrode irreversible capacity is greater than the positive electrode irreversible capacity.

[0086] In such a battery in which the irreversible capacity of the negative electrode is greater than the irreversible capacity of the positive electrode, for example, when discharging is carried out and the SOC is gradually reduced to a low state such as below SOC10%, the negative electrode potential NE rises significantly before the positive electrode potential PE drops significantly, and the battery voltage VB given by the difference between the positive electrode potential PE and the negative electrode potential NE drops (for example, in this reference method, it is close to VB1=3.0V corresponding to SOC0%). Therefore, if the battery in the range where the positive electrode potential PE drops significantly (becoming a range below SOC0%) is not used, the battery resistance Rb will not rise too much in the low SOC area.

[0087] In contrast, in battery 1J (battery 1X), as described above, the negative electrode capacity CN of the negative electrode plate 40 is not much larger than the positive electrode capacity CP of the positive electrode plate 30 (positive-negative electrode capacity ratio RC = CN / CP ≤ 1.40). Specifically, the positive-negative electrode capacity ratio RC = CN / CP = 1.38. Therefore, the positive electrode irreversible capacity CPna and the negative electrode irreversible capacity CNna generated after the initial charging step SJ2 and the high-temperature aging step SJ3 are as follows: Figure 5 As shown in the upper graph, the negative electrode irreversible capacity CNna is smaller than the positive electrode irreversible capacity CPna (CPna>CNna).

[0088] In the battery 1J of the present reference embodiment in which the negative electrode irreversible capacity CNna is smaller than the positive electrode irreversible capacity CPna, contrary to the above, for example, when the discharge progresses to a low SOC state such as SOC 10% or less, before the negative electrode potential NE rises significantly along the double-dashed chain line ( Figure 5 The positive electrode potential PE decreases significantly along the dotted line, and the battery voltage VB decreases, approaching VB1a = 3.0 V corresponding to SOC 0%. Therefore, in this battery 1J, the positive electrode potential PE decreases significantly in the low SOC region, as shown in FIG. Figure 5 As shown in the lower graph of , in the low SOC region, the battery resistance Rb tends to increase.

[0089] It should be explained that Figure 5 The range in which the positive electrode potential PE is greatly reduced, indicated by the dotted line in the upper part of the figure, is that when a large amount of Li ions are filled into the positive electrode active material by discharge, it is difficult for Li ions to move in the positive electrode active material, the positive electrode potential is reduced, and the battery resistance Rb increases.

[0090] (Implementation Method)

[0091] Next, a method for manufacturing the battery 1 of this embodiment will be described (see Figure 2 ). As in the reference method, first, in the "assembly step" S1, the uncharged battery 1X is assembled using a known method (see Figure 1 ), in the "stacking load application step" S2, multiple (10 in this embodiment) assembled batteries 1X (hereinafter referred to as batteries 1) are stacked and restrained by applying a predetermined first load BL1 (in this embodiment, BL1 = 9 kN) using a restraining jig. With the first load BL1 applied to the batteries 1 (battery 1X), each battery 1 undergoes the first initial charging step S3 (shown by the solid line) through the inspection step S9 (hereinafter referred to).

[0092] First, in a "first initial charging step" S3, after the battery temperature TB of the battery 1X is set to a first charging battery temperature TB1 within a first battery temperature range TA1 of 20 to 25°C (TB1 = 20.0°C in this embodiment), charging is performed until the first SOC reaches SC1 within a first SOC range SA1 of 2 to 13% (SC1 = 10% in this embodiment). Specifically, a charging and discharging device (not shown) is connected to the two terminal members 60 and 70 of the battery 1X, which is restrained by the restraint jig, and the battery 1 (battery 1X) is charged using constant current constant voltage (CCCV) charging until the battery voltage VB of the battery 1X reaches a predetermined value (VB = 3.44V, corresponding to SC1 = 10% in this embodiment).

[0093] Next, in the "first high-temperature aging step" S4, the following first high-temperature aging is performed: the battery 1, which has been initially charged to a first SOC (SC1 = 10%) in the first initial charging step S3, is placed in a first aging environment temperature TE1 (TE1 = 63°C in this embodiment) within a first ambient temperature range TD1 of 60 to 65°C for a first aging period EP1 (EP1 = 20 hours in this embodiment) within a first period EA1 of 5 to 25 hours, with the positive terminal member 60 and the negative terminal member 70 open. It is believed that high-temperature aging at such a low SOC selectively promotes SEI formation in the battery 1, particularly in the negative electrode plate 40, increasing the negative electrode irreversible capacity CNn.

[0094] Next, in the "first cooling and placing step" S5, the battery 1 is forcibly cooled by a fan in a cooling room (not shown) at a first cooling ambient temperature TC1 (TC1 = 20°C in this embodiment) for a first cooling period CP1 (CP1 = 20 minutes in this embodiment). Furthermore, the battery 1 is transferred to a placing room (not shown) set to a first ambient temperature TK1 (TK1 = 20.0°C in this embodiment) and placed for a first placing period HP1 (HP1 = 30 minutes in this embodiment), and the battery temperature TB of the battery 1 is set to a second charging battery temperature TB2 (TB2 = 20.0°C in this embodiment) which is the same as the first ambient temperature TK1 (see FIG. 1 ). Figure 2 ) In this way, the temperature of the battery is fully adapted before the second initial charging step S6 described later, so that the second initial charging step S6 can be performed under the condition that the voltage of the battery is stable and uniform.

[0095] Next, in the "second initial charging step" S6, each battery at a second charging battery temperature TB2 (TB2 = 20.0°C in the present embodiment) within a second battery temperature range TA2 of 20-25°C is charged until the second SOC reaches SC2 (SC2 = 91% in the present embodiment) within a second SOC range SA2 of 13-91%. Specifically, as in the first initial charging step S3, a charging and discharging device (not shown) is connected to the two terminal members 60 and 70 of the battery 1 restrained by the restraining fixture, and the battery 1 is initially charged using constant current constant voltage (CCCV) charging until the battery voltage VB of the battery 1 reaches a predetermined value (VB = 3.97V, corresponding to SC2 = 91% in the present embodiment).

[0096] Next, in the "second high-temperature aging step" S7, the following second high-temperature aging is performed: the battery 1, which has been initially charged to the second SOC (SC2 = 91%) in the second initial charging step S6, is placed in a second aging environment temperature TE2 (TE2 = 63°C in the present embodiment) within a second ambient temperature range TD2 of 60 to 75°C for a second aging period EP2 (EP2 = 20 hours in the present embodiment) within a second period EA2 of 6 to 30 hours, with the positive terminal member 60 and the negative terminal member 70 open. It is believed that this second high-temperature aging process causes SEI formation in both the positive electrode plate 30 and the negative electrode plate 40 of the battery 1, increasing the positive electrode irreversible capacity CPn and further increasing the negative electrode irreversible capacity CNn already generated in the first initial charging step S3 and the first high-temperature aging step S4.

[0097] Next, in the "second cooling and placement step" S8, the battery 1 is forcibly cooled by a fan in a cooling chamber (not shown) at a second cooling ambient temperature TC2 (in this embodiment, TC2 = 20°C) for a second cooling period CP2 (in this embodiment, CP2 = 20 minutes). Furthermore, the battery 1 is transferred to a placement chamber (not shown) set to a second ambient temperature TK2 (in this embodiment, TK2 = 20.0°C) and placed for a second placement period HP2 (in this embodiment, HP2 = 30 minutes). The battery temperature TB of the battery 1 is set to a third battery temperature TB3 (in this embodiment, TB3 = 20.0°C) which is the same as the second ambient temperature TK2 (see FIG. 1 ). Figure 2 ).

[0098] It should be noted that, for ease of comparison, it can be understood by comparing with the reference method that the contents of the second initial charging process S6 to the second cooling and placement process S8 performed on the battery 1 in this embodiment are the same as the contents of the initial charging process SJ2 to the cooling and placement process SJ4 performed on the battery 1J in the reference method.

[0099] Then, in the "inspection process" S9, the battery 1 set to the third battery temperature TB3 = 20.0°C is subjected to various inspections (details omitted) such as a self-discharge inspection to inspect the size of self-discharge and a capacity inspection to inspect the size of the capacity of the battery 1, and good batteries 1 are retained.

[0100] In this way, the battery 1 is manufactured.

[0101] Reference Figure 3 The characteristics of battery 1 according to this embodiment will now be described. Similar to battery 1J described above, battery 1 according to this embodiment has a negative electrode capacity CN of negative electrode plate 40 that is not significantly greater than the positive electrode capacity CP of positive electrode plate 30 (positive-to-negative electrode capacity ratio RC = CN / CP ≤ 1.40). Specifically, the positive-to-negative electrode capacity ratio RC = CN / CP = 1.38.

[0102] However, with battery 1J ( Figure 5 Reference) is different, the battery 1 has increased the negative electrode irreversible capacity after the first initial charging step S3 and the first high temperature aging step S4, so as Figure 3 As shown in the upper part of the figure, the negative electrode irreversible capacity CNn is greater than the positive electrode irreversible capacity CPn (CPn<CNn).

[0103] Therefore, in the battery 1 of this embodiment, in contrast to the battery 1J, when the discharge progresses and the SOC reaches a low state such as 10% or less, the positive electrode potential PE decreases significantly along the dotted line ( Figure 3 The negative electrode potential NE rises significantly along the double-dashed line, and the difference between the two, that is, the battery voltage VB, decreases and approaches VB1 = 3.0 V corresponding to SOC 0%. Therefore, in the low SOC region, the range where the positive electrode potential PE drops significantly is not used, such as Figure 3 As shown in the figure below, Figure 5 The lower graph is easier to understand, as it shows that even in the low SOC region, the region where the battery resistance Rb increases significantly is not used. In other words, a high-capacity, compact battery 1 with a small positive and negative electrode capacity ratio RC can be obtained, while also suppressing the increase in battery resistance Rb in the low SOC region.

[0104] Next, the relationship between the first SOC value SC1 in the first initial charging step S3 and the length of the first aging period EP1 in the first high-temperature aging step S4 and the battery resistance Rb at SOC 21% was investigated. Figure 4 ) for research.

[0105] First, for the battery 1 that is the same as the above-mentioned embodiment, but does not perform the first initial charging step S3, the first high-temperature aging step S4, and the first cooling and placing step S5, and performs the second initial charging steps S6 to S9 after the stacking load application step S2 (the same as the battery 1J that performs the initial charging steps SJ3 to S9 after the stacking load application step S2), the battery resistance Rb (DC-IR) measured at the battery temperature TB = 25°C and the battery voltage VB set to VB = 3.50V corresponding to SOC 21% is taken as Figure 4 Note that this example corresponds to the battery resistance Rb in the first aging period EP1=0.

[0106] In the first initial charge step S3, the first SOC is set to SC1 = 10% (corresponding to VB = 3.18V), and the first aging period EP1 in the first high-temperature aging step S4 is varied over three periods: 5, 10, and 20 hrs. This is indicated in the figure as "SOC 10% aging." Conversely, in the first initial charge step S3, the first SOC is set to SC1 = 20% (corresponding to VB = 3.49V), and the first aging period EP1 in the first high-temperature aging step S4 is varied over three periods: 5, 10, and 20 hrs. This is indicated in the figure as "SOC 20% aging."

[0107] In addition, the battery resistance Rb is obtained by the DC-IR measurement method. Specifically, the test battery 1 is set to a battery temperature TB = 25 ° C, and then the battery 1 is connected to the charger and discharger, and the battery 1 is charged or discharged by constant current constant voltage (CCCV) so that the battery 1 is in a charged state of SOC = 21%. That is, the battery voltage VB is set to VB = 3.50V, which is equivalent to SOC21%. Then, constant current discharge (CC discharge) is performed at a current value I of a specified discharge rate (30C in this example), and the battery voltage drop ΔV generated by the battery from 0.1 seconds to 10 seconds after the start of discharge is obtained. In addition, the battery resistance Rb is obtained using the battery resistance Rb = ΔV / I.

[0108] The voltage drop occurring during the period from the start of discharge to 0.1 seconds is not considered because the voltage drop occurring immediately after the start of current flow includes the influence of the DC resistance of the battery 1 and is therefore excluded.

[0109] Depend on Figure 4It is easy to understand that in the case of aging at 20% SOC connected by the dotted line, that is, when the first SOC is set to a slightly higher value of SC1 = 20% in the first initial charging step S3, the battery resistance Rb hardly changes even when the first aging period EP1 is changed. This shows that if the first SOC value SC1 in the first initial charging step S3 is set too high, such as SC1 = 20%, it will be difficult to selectively form SEI on the negative electrode plate 40 (negative electrode active material layer) during the first initial charging step S3 and the first high-temperature aging step S4.

[0110] On the other hand, in the case of SOC 10% aging indicated by the solid line, that is, when the first SOC magnitude SC1 is set to a relatively low SC1 = 10% in the first initial charging step S3 , the battery resistance Rb decreases as the first aging period EP1 increases.

[0111] Based on these results, it can be said that the first SOC in the first initial charging step S3 is preferably less than 20%. In addition, from the perspective of the ease of SEI formation in the negative electrode plate 40, it is preferably selected from the range of SC1 = 13% or less. More preferably, as Figure 4 As shown in the figure, it can be seen that if SC1 is set to 10% or less, a good battery resistance Rb can be obtained. It should be noted that, from the perspective of supplying an amount of Li ions capable of forming SEI to the negative electrode active material layer (negative electrode active material particles) of the negative electrode plate, the first SOC in the first initial charging step S3 is preferably selected from a range of at least SC1 = 2%, and preferably set to 5% or more.

[0112] In addition, according to Figure 4 It can be seen that the length of the first aging period EP1 in the first high temperature aging step S4 is preferably EP1 = 5 hours or more, and more preferably EP1 = 10 hours or more. On the other hand, if the length of the first aging period EP1 is too long, the productivity of the process is reduced, so it is preferably set to EP1 = 25 hours or less, and further, as shown in FIG. Figure 4 As shown, it is preferable to set EP1 to 20 hours or less.

[0113] In addition, in the implementation and Figure 4 In the investigation shown, the first aging environment temperature TE1 in the first high-temperature aging step S4 was set to TE1 = 63°C. However, to achieve the effect of the first high-temperature aging step S4 (formation of SEI in the negative electrode), it is preferably set to TE1 = 60°C or higher. On the other hand, considering the degradation of the positive electrode due to excessively high temperatures, it is preferably set to TE1 = 65°C or lower. In other words, the first environment temperature range TD1 is preferably set to TD1 = 60-65°C.

[0114] Furthermore, the second SOC value SC2 in the second initial charging step S6 is preferably set within a second SOC range SA2 that is 13% to 91% higher than the range selected as the first SOC in the first initial charging step S3, and more preferably selected from a range of SC2 = 60% or greater. On the other hand, if the second SOC value SC2 is too large, the positive electrode active material, which contains less Li, will experience crystal collapse and deteriorate more easily during the second high-temperature aging step S7. Therefore, the second SOC value SC2 is preferably set to SC2 = 91% or less.

[0115] In addition, the second aging period EP2 and the second aging environment temperature TE2 in the second high-temperature aging process S7 can be considered in the same way as the existing high-temperature aging conditions. However, if the characteristics of the battery 1 after the second high-temperature aging process S7 and the dissolution of foreign matter that may be contained in the electrode body 20 are taken into consideration, it is preferred that the second aging period EP2 be selected from the range of 6 to 30 hours (second period range EA2) and the second aging environment temperature TE2 be selected from the range of 60 to 75°C (second environment temperature range TD2).

[0116] on the other hand, Figure 3 、 Figure 5 The upper graph of and the magnitudes of the positive electrode irreversible capacities CPna and CPn, and the negative electrode irreversible capacities CNna and CNn of the reference battery 1J and the battery 1 according to the embodiment are obtained as follows.

[0117] In the assembly step S1, the battery 1X is assembled (see Figure 1 ), a reference electrode (not shown) made of Li metal foil is placed so as to be immersed in the electrolyte 15. Furthermore, a lead wire connected to the reference electrode is extended to the outside, thereby assembling a battery 1X with a reference electrode. Subsequently, the same steps as those for manufacturing the aforementioned battery 1J or battery 1 are performed (S2, SJ3 to S9, or S2 to S9).

[0118] Then, CCCV charging was performed at a constant current of 1 / 3C until the battery voltage VB2 corresponding to SOC=100% reached 4.1V. Then, CC discharge was performed at a constant current of 1 / 3C until the battery voltage VB=0V.

[0119] During each step and CCCV charge and CC discharge, the positive electrode potential PE generated between the reference electrode and the positive electrode (positive terminal component 60), the negative electrode potential NE generated between the reference electrode and the negative electrode (negative terminal component 70), and the battery voltage VB generated between the positive electrode (positive terminal component 60) and the negative electrode (negative terminal component 70) are obtained. Figure 3 、 Figure 5 The upper part of the picture.

[0120] When the battery voltage VB becomes 0V by CC discharge, the positive electrode potential PE and the negative electrode potential NE are Figure 3 、 Figure 5 The path indicated by the dotted line or the double-dashed line in the upper diagram does not return to the initial state of the charge level = 0. Figure 3 、 Figure 5 As shown in the upper portion of the figure, the charge capacity corresponding to the lower charge capacity endpoint (the left end point in the figure) of the upper dashed line representing the path of the positive electrode potential PE is defined as the positive electrode irreversible capacity CPna, CPn of the battery 1J or the battery 1. Similarly, the charge capacity corresponding to the lower charge capacity endpoint (the left end point in the figure) of the lower two-dot chain line representing the path of the negative electrode potential NE is defined as the negative electrode irreversible capacity CNna, CNn of the battery 1J or the battery 1.

[0121] Furthermore, for the battery 1J or the battery 1 manufactured through the above-mentioned steps, the battery resistance Rb at each charge level (each SOC) is obtained by the above-mentioned DC-IR measurement method. Figure 3 、 Figure 5 The lower part of the picture.

[0122] As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change suitably and apply within the range which does not deviate from the summary.

Claims

1. A method for manufacturing a lithium-ion secondary battery, wherein the lithium-ion secondary battery has a positive electrode and a negative electrode, The negative electrode active material layer and the positive electrode active material layer are arranged opposite to each other via a separator, and are arranged such that: the negative electrode active material layer is wider than the positive electrode active material layer, the negative electrode active material layer includes a range opposite to the positive electrode active material layer, and a positive-to-negative electrode capacity ratio RC of the positive electrode capacity to the negative electrode capacity of the negative electrode is 1.02 to 1.

40. The negative electrode irreversible capacity CNn of the negative electrode is greater than the positive electrode irreversible capacity CPn of the positive electrode, that is, CPn<CNn; The method for manufacturing the lithium-ion secondary battery comprises the following steps: In a first initial charging step, the uncharged battery having a positive-to-negative electrode capacity ratio RC of 1.02 to 1.40 is charged to a first SOC within a first SOC range of 2 to 13% at a first charging battery temperature within a first battery temperature range of 20 to 25° C.; In the first high-temperature aging step, the lithium-ion secondary battery charged to the first SOC is placed in a first aging environment temperature within a first aging period ranging from 60° C. to 65° C. with the positive and negative terminals open for a first aging period ranging from 5 to 25 hours. a second initial charging step, after the first high-temperature aging step, charging the lithium-ion secondary battery to a second SOC within a second SOC range that is 13 to 91% higher than the first SOC at a second battery temperature during charging within a second battery temperature range of 20 to 25° C.; In the second high-temperature aging step, the lithium-ion secondary battery charged to the second SOC is placed in a second aging environment temperature ranging from 60 to 75° C. for a second aging period ranging from 6 to 30 hours with the positive and negative terminals open.

Images