Manufacturing method of non-aqueous electrolyte secondary battery

Abstract

This method achieves cost reductions through the use of dry air and suppresses the occurrence of defective batteries with internal short circuits. [Solution] The manufacturing method disclosed herein includes a construction step S10 for constructing a battery assembly in which copper-containing electrodes are housed in a case, an injection step S20 for injecting a non-aqueous electrolyte into the case, an initial charging step S40 for charging the battery assembly, and a sealing step S50 for sealing the case. In this manufacturing method, the atmosphere around the battery assembly is maintained as a dry air atmosphere during the first period T1 until the start of the injection step S20, and the oxygen concentration inside the case is controlled to 10% or less during the second period T2 from the start of the injection step S20 until the start of the initial charging step S40.

Description

[Technical Field]

[0001] The technology disclosed herein relates to a method for manufacturing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, secondary batteries such as lithium-ion batteries have been used in various fields, including electric vehicles and mobile devices. One example of such a secondary battery is the non-aqueous electrolyte secondary battery, which uses a non-aqueous electrolyte as the electrolyte. A manufacturing method for this non-aqueous electrolyte secondary battery includes, for example, a construction step of constructing a battery assembly in which electrodes are housed in a case, an injection step of pouring a non-aqueous electrolyte into the case, an initial charging step of charging the battery assembly, and a sealing step of sealing the case. In conventional manufacturing methods, each of the above steps was carried out in the presence of an inert gas (such as nitrogen gas) to prevent moisture from entering the case. However, in recent years, in order to reduce energy costs, it has been considered to carry out each of the steps from the construction step to the sealing step in a dry air atmosphere. An example of such a manufacturing method using dry air is disclosed in Japanese Patent No. 7265580. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 7265580 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, when the above construction and sealing processes were carried out in a dry air atmosphere, the number of defective batteries with minute internal short circuits increased. In other words, while the manufacturing method using dry air can reduce energy costs, it has the problem of reducing yield due to an increase in defective batteries. The technology disclosed herein was developed to solve this problem. [Means for solving the problem]

[0005] The inventors analyzed a defective battery that had developed an internal short circuit due to the use of dry air and discovered that metallic copper was deposited inside the electrode body (between the positive and negative electrodes). Based on this discovery, the inventors hypothesized the mechanism of internal short circuit occurrence when using dry air as follows: First, the electrode body of a typical secondary battery (for example, the negative electrode core) contains copper. On the other hand, dry air is a gas from which moisture has been removed from the atmosphere, and therefore contains a high concentration (about 20%) of oxygen. In this case, since the copper potential of an uncharged electrode body is high, oxidation of the copper is accelerated when exposed to a high concentration of oxygen. When the oxidizing copper comes into contact with a non-aqueous electrolyte, a large amount of copper dissolves in the non-aqueous electrolyte. The dissolved copper then precipitates from the non-aqueous electrolyte in the form of metallic copper after manufacturing. When metallic copper precipitates between the positive and negative electrodes, an internal short circuit occurs due to damage to the separator. As described above, when the three elements of "uncharged electrodes," "high concentration of oxygen," and "the presence of a non-aqueous electrolyte" coincide during the manufacturing of secondary batteries, the dissolution of copper into the non-aqueous electrolyte is promoted, making internal short circuits more likely to occur in the secondary batteries after manufacturing.

[0006] The method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein is based on the above-mentioned findings. This manufacturing method includes a construction step of constructing a battery assembly in which copper-containing electrodes are housed in a case, an injection step of pouring a non-aqueous electrolyte into the case, an initial charging step of charging the battery assembly, and a sealing step of sealing the case. In this manufacturing method, the atmosphere around the battery assembly is maintained as a dry air atmosphere during the first period until the start of the injection step, and the oxygen concentration inside the case is controlled to 10% or less during the second period from the start of the injection step to the start of the initial charging step.

[0007] First, in the manufacturing method disclosed herein, dry air is used in the first period before the start of the electrolyte injection process. This contributes to cost reduction, which is the purpose of using dry air. Also, since the non-aqueous electrolyte is not injected during this first period, copper dissolution does not occur even when dry air is used. Next, in this manufacturing method, the oxygen concentration inside the case is controlled to 10% or less during the second period from the start of the electrolyte injection process to the start of the initial charging process. This suppresses the oxidation of copper during electrolyte injection, thereby suppressing the dissolution of copper into the non-aqueous electrolyte. After the start of the initial charging process, the potential of copper decreases due to charging, so the dissolution of copper into the non-aqueous electrolyte is suppressed regardless of the ambient oxygen concentration. As described above, in the manufacturing method disclosed herein, one of the three elements, "uncharged electrode body," "high concentration of oxygen," and "presence of non-aqueous electrolyte," is missing in each process from the construction process to the sealing process. This makes it possible to reduce energy costs by using dry air and suppress the occurrence of defective batteries with internal short circuits. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic partial cross-sectional view showing the internal structure of a non-aqueous electrolyte secondary battery. [Figure 2] Figure 2 is a flowchart illustrating a method for manufacturing a non-aqueous electrolyte secondary battery according to one embodiment. [Figure 3] Figure 3 is a schematic partial cross-sectional view showing the battery assembly. [Figure 4] Figure 4 is a schematic partial cross-sectional view showing the battery assembly housed in the chamber. [Figure 5] Figure 5 is a schematic partial cross-sectional view showing the liquid injection step in a manufacturing method according to one embodiment. [Modes for carrying out the invention]

[0009] Hereinafter, one embodiment of the technology disclosed herein will be described in detail with reference to the drawings. Matters other than those specifically mentioned herein but necessary for implementing the technology disclosed herein can be understood as design matters for those skilled in the art based on the prior art. The technology disclosed herein can be implemented based on the content disclosed herein and common technical knowledge in the art.

[0010] Furthermore, in the following drawings, the same reference numeral is used to denote components and parts that perform the same function. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. Also, the symbol X in each drawing indicates the "width direction," and the symbol Z indicates the "height direction." However, these directions are defined for the convenience of explanation and are not intended to limit the installation configuration of non-aqueous electrolyte secondary batteries during use or manufacturing.

[0011] In this specification, "non-aqueous electrolyte secondary battery" refers to any energy storage device that can repeatedly charge and discharge by the movement of a charge carrier between a positive electrode and a negative electrode via a non-aqueous electrolyte. A typical example of such a non-aqueous electrolyte secondary battery is a lithium-ion secondary battery. This lithium-ion secondary battery uses lithium (Li) ions as the electrolyte ions (charge carriers) and is a secondary battery that charges and discharges by the movement of lithium ions between a positive electrode and a negative electrode. In the embodiments described below, a lithium-ion secondary battery is used as the non-aqueous electrolyte secondary battery, but the technology disclosed herein is not limited to lithium-ion secondary batteries and can be applied to other non-aqueous electrolyte secondary batteries (e.g., sodium-ion batteries). In other words, the manufacturing method disclosed herein is not limited to a method for manufacturing a specific type of battery, but can be broadly applied to the manufacture of all non-aqueous electrolyte secondary batteries containing copper in the electrode body.

[0012] 1.Non-aqueous electrolyte secondary battery First, an example of a non-aqueous electrolyte secondary battery to be manufactured by the manufacturing method disclosed herein will be described. FIG. 1 is a partial cross-sectional view schematically showing the internal structure of the non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery 1 shown in FIG. 1 includes a case 10, an electrode body 20, and a non-aqueous electrolyte 30. Hereinafter, each member will be specifically described.

[0013] (1) Case The case 10 is a housing that houses the electrode body 20 and the non-aqueous electrolyte 30. The case 10 shown in FIG. 1 has a flat box-shaped outer shape. The electrode body 20 and the non-aqueous electrolyte 30 are housed in the internal space 10a of this case 10. And the case 10 includes a case main body 14 having an opening on the upper surface, and a plate-shaped lid body 12 that closes the opening. The case main body 14 and the lid body 12 are joined by laser welding or the like. A metal material (such as aluminum, SUS steel, etc.) excellent in rigidity is used for this case 10.

[0014] Also, a pair of electrode terminals 40 are attached to the case 10 (lid body 12). Each electrode terminal 40 is a conductive member extending in the height direction Z. The lower end portion 40a of this electrode terminal 40 is connected to the electrode body 20 inside the case 10. On the other hand, the upper end portion 40b of the electrode terminal 40 is exposed outside the case 10. Further, the non-aqueous electrolyte secondary battery 1 shown in FIG. 1 is provided with a liquid injection port 18 penetrating the case 10 (lid body 12). Although it will be described in detail later, the non-aqueous electrolyte 30 is injected into the case 10 through this liquid injection port 18. And the liquid injection port 18 after injection is sealed by a sealing member 19. Note that the detailed structure regarding these cases can adopt a conventionally known structure without particular limitation, and does not limit the technology disclosed herein. For example, a gas discharge valve 16 may be provided in the case 10 (lid body 12).

[0015] (2) Electrode body The electrode body 20 is housed inside the case 10. Although detailed illustration is omitted, the electrode body 20 is a power generation element in which a positive electrode and a negative electrode are opposed via a separator. For example, the electrode body 20 shown in FIG. 1 is a wound electrode body obtained by winding a laminate in which a long strip-shaped positive electrode, a separator, and a negative electrode are stacked. The positive electrode of this electrode body 20 includes a positive electrode core 21 which is a foil-shaped conductive member, and a positive electrode active material layer (not shown) provided on the surface of the positive electrode core 21. On the other hand, the negative electrode includes a negative electrode core 23 which is a foil-shaped conductive member, and a negative electrode active material layer (not shown) provided on the surface of the negative electrode core 23. As shown in FIG. 1, a core portion 22 in which the positive electrode active material layer and the negative electrode active material layer face each other is formed at the center portion in the width direction X of the electrode body 20. This core portion 22 is the main place where charge and discharge reactions occur. Further, a positive electrode connection portion 24 where the positive electrode core 21 is exposed is formed at one side edge portion in the width direction X of the electrode body 20. Furthermore, a negative electrode connection portion 26 where the negative electrode core 23 is exposed is formed at the other side edge portion. The positive electrode connection portion 24 and the negative electrode connection portion 26 are connected to the electrode terminal 40.

[0016] Here, as described above, the manufacturing method disclosed herein aims to suppress the dissolution of copper from the electrode body 20 into the non-aqueous electrolyte 30. That is, the manufacturing method disclosed herein assumes that the electrode body 20 contains copper. For example, in a lithium ion secondary battery, copper or a copper alloy may be used as the material of the negative electrode core 23. Further, copper may be used not only for the negative electrode core 23 but also for the electrode terminal 40 on the negative electrode side. The manufacturing method disclosed herein is for preventing the dissolution of copper from these copper members into the non-aqueous electrolyte 30. The electrode body 20 is not particularly limited except that it has components containing copper. That is, the material of the electrode body 20 can be any conventionally known material without particular limitation.

[0017] (3) Non-aqueous electrolyte The non-aqueous electrolyte 30 is housed inside the case 10 together with the electrode body 20. Most of the non-aqueous electrolyte 30 permeates into the inside of the electrode body 20 (between the positive and negative electrodes). In addition, a portion of the non-aqueous electrolyte 30 may exist outside the electrode body 20 (between the electrode body 20 and the case 10) as excess electrolyte 32. This allows for the supply of excess electrolyte 32 into the electrode body 20 when the amount of non-aqueous electrolyte 30 inside the electrode body 20 becomes insufficient.

[0018] The non-aqueous electrolyte 30 is a liquid obtained by dissolving a support salt in a non-aqueous solvent. The components of this non-aqueous electrolyte 30 can be conventionally known without particular limitation and do not limit the technology disclosed herein. For example, carbonate-based solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be used as the non-aqueous solvent. In addition, depending on the type of secondary battery, lithium salts, sodium salts, magnesium salts, etc., can be used as the support salt. For example, fluorine-containing lithium salts such as LiPF6 and LiBF4, or LiClO4 can be used as lithium salts.

[0019] 2. Manufacturing method of non-aqueous electrolyte secondary battery Next, an embodiment of the method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein will be described. Figure 2 is a flowchart illustrating the method for manufacturing a non-aqueous electrolyte secondary battery according to this embodiment. As shown in Figure 2, the manufacturing method according to this embodiment comprises a construction step S10, an electrolyte injection step S20, an initial charging step S40, and a sealing step S50. Furthermore, in the manufacturing method according to this embodiment, an impregnation step S30 is performed between the electrolyte injection step S20 and the initial charging step S40. Each step will be described below.

[0020] (1) Construction process S10 Figure 3 is a schematic partial cross-sectional view of the battery assembly. As shown in Figure 3, in this process, a battery assembly 100 is constructed in which an electrode body 20 containing copper is housed in a case 10. An example of the procedure for constructing this battery assembly 100 is as follows: First, an electrode body 20 containing copper (for example, an electrode body 20 having a copper negative electrode core 23) is prepared. Next, a cover body 12 to which a pair of electrode terminals 40 are attached is prepared. Then, one electrode terminal 40 is connected to the positive electrode connection portion 24 of the electrode body 20. Also, the other electrode terminal 40 is connected to the negative electrode connection portion 26 of the electrode body 20. Next, the electrode body 20 is inserted into the internal space 10a through the opening on the top surface of the case body 14, and then the opening on the top surface is closed with the cover body 12. Then, the contact interface between the cover body 12 and the case body 14 is joined by laser welding or the like. This allows the battery assembly 100 in which the electrode body 20 is housed in the case 10 to be constructed.

[0021] In this embodiment of the manufacturing method, the atmosphere surrounding the battery assembly 100 is maintained as a dry air atmosphere during the first period T1 (see Figure 2) until the start of the liquid injection process S20. This prevents the occurrence of defective products due to moisture contamination inside the case 10. For example, in this embodiment, the construction of the battery assembly 100 described above is carried out in a dry air chamber 200 (see Figure 4). This chamber 200 includes a housing 210 that houses the battery assembly 100, a gas supply pipe 220 that supplies gas into the housing 210, and a gas discharge pipe 230 that sucks out the gas inside the housing 210. In the first period T1 of this manufacturing method, dry air is supplied into the housing 210 from the gas supply pipe 220. This makes it possible to maintain a dry air atmosphere inside the housing 210 of the chamber 200.

[0022] In this specification, "dry air" refers to a gas whose dew point is adjusted to -15°C or lower (preferably -20°C or lower, more preferably -30°C or lower, even more preferably -40°C or lower, and particularly preferably -60°C or lower). Since such dry air can be produced simply by heating the atmosphere, the energy cost required for its production is low. In this specification, "dry air" contains an amount of oxygen similar to that of normal atmosphere. Specifically, the oxygen concentration of the dry air in this specification is 15% to 25% (preferably 17.5% to 22.5%, for example, around 20%). In addition, this dry air may contain gases other than oxygen, such as nitrogen, argon, and carbon dioxide.

[0023] (2) Liquid injection process S20 Figure 5 is a schematic partial cross-sectional view showing the liquid injection process in the manufacturing method according to this embodiment. As shown in Figure 5, in this process, a non-aqueous electrolyte 30 is injected into the case 10. For example, the injection of the non-aqueous electrolyte 30 is carried out according to the following procedure. First, a nozzle 240 is inserted into the injection port 18 and a depressurization process is performed by suctioning the inside of the case 10. This creates a negative pressure inside the case 10, including the inside of the electrode body 20 (between the positive and negative electrodes). Then, with the nozzle 240 still attached to the injection port 18, the non-aqueous electrolyte 30 is injected into the case 10 from the nozzle 240. This causes the non-aqueous electrolyte 30 to penetrate into the inside of the electrode body 20, which is under negative pressure. As a result, the penetration time of the non-aqueous electrolyte 30 can be significantly reduced. Note that this process only requires that the non-aqueous electrolyte 30 be injected into the inside of the case 10, and the specific procedure is not particularly limited. For example, if the electrode body 20 can easily penetrate the non-aqueous electrolyte 30, the non-aqueous electrolyte may be injected without performing a reduced pressure treatment.

[0024] In the manufacturing method according to this embodiment, the oxygen concentration inside the case 10 during the second period T2 (see Figure 2), from the start of the liquid injection process S20 to the start of the initial charging process S40, is controlled to 10% or less (preferably 5% or less, more preferably 1% or less, even more preferably 0.5% or less, and particularly preferably 0%). Specifically, in the second period T2 in this embodiment, low-oxygen gas is supplied into the housing 210 from the gas supply pipe 220. Then, after the gas in the chamber 200, including the case 10 of the battery assembly 100, has been replaced with low-oxygen gas, the injection of the non-aqueous electrolyte 30 is started. This suppresses the oxidation of copper during the injection of the non-aqueous electrolyte 30, and thus suppresses the dissolution of copper into the non-aqueous electrolyte 30.

[0025] In this specification, "low-oxygen gas" refers to a gas whose oxygen concentration is controlled to 10% or less (preferably 5% or less, more preferably 1% or less, even more preferably 0.5% or less, and especially preferably 0%). An example of such low-oxygen gas is dry air whose oxygen concentration has been reduced by gas replacement or other methods. Other examples of low-oxygen gases include non-oxidizing gases (gases with an oxygen concentration of 0%) such as nitrogen and noble gases (helium, argon, etc.). In particular, non-oxidizing gases rapidly reduce the oxygen concentration in case 10, so the time from the start of supplying the low-oxygen gas to the start of injecting the non-aqueous electrolyte 30 (gas replacement time) can be significantly shortened.

[0026] The gas replacement time at the start of the second period T2 is adjusted as appropriate, taking into account the volume of case 10, the composition of the hypoxic gas, the amount of hypoxic gas supplied, etc. Therefore, the gas replacement time is set to the time necessary to reduce the oxygen concentration in case 10 to 10% or less, and is not limited to a specific time. For example, when implementing the manufacturing method disclosed herein, it is preferable to conduct preliminary tests according to the actual manufacturing conditions and investigate the appropriate gas replacement time in advance.

[0027] (3) Impregnation process Next, in the manufacturing method according to this embodiment, an impregnation step S30 is performed between the liquid injection step S20 and the initial charging step S40 to impregnate the inside of the electrode body 20 with a non-aqueous electrolyte 30. In this impregnation step S30, the battery assembly 100, after the non-aqueous electrolyte 30 has been injected into the case 10, is left to stand in the chamber 200 for a predetermined time. This allows the non-aqueous electrolyte 30 to properly penetrate the inside of the electrode body 20. For example, if the electrode body 20 is a wound electrode body, the standing time in the impregnation step S30 can be set within the range of 5 hours to 60 hours (preferably 10 hours to 50 hours, more preferably 24 hours to 48 hours).

[0028] In the manufacturing method according to this embodiment, the low-oxygen atmosphere created in the liquid injection step S20 is maintained in the impregnation step S30. This makes it possible to more effectively suppress internal short circuits after manufacturing caused by copper dissolution. Specifically, the standing time in the impregnation step S30 can range from several hours to tens of hours. If the three elements of "uncharged electrode body," "high concentration of oxygen," and "injection of non-aqueous electrolyte" are present for such a long period of time, there is a risk that a large amount of copper will dissolve into the non-aqueous electrolyte 30. In contrast, by maintaining a low-oxygen atmosphere in the impregnation step S30, the amount of copper dissolved into the non-aqueous electrolyte 30 can be significantly reduced.

[0029] (4) Initial charging process S40 In this step, the battery assembly 100 is charged. Specifically, the electrodes of an external charging device are connected to each of the electrode terminals 40 of the battery assembly 100, and charging is performed until a predetermined target voltage is reached between the positive and negative electrode terminals. At this time, it is preferable to charge the battery assembly 100 until its State of Charge (SOC) reaches 5% or more, and more preferably until it reaches 10% or more. In this step, the State of Charge (SOC) of the battery assembly 100 is preferably 50% or less, preferably 40% or less, and more preferably 30% or less. If the non-aqueous electrolyte 30 contains additives, it is preferable to charge at least up to the decomposition potential of the additives. The target voltage may be set to approximately 3V or more, typically 3.5V or more, or for example, 4V or more, if the negative electrode active material is a carbon material. The charging rate may be, for example, around 0.1C to 2C. Charging may be performed once, or it may be repeated two or more times, for example, with a discharge in between. This process may be carried out at room temperature (for example, around 25°C ± 10°C or 25°C ± 5°C) or at a high temperature (for example, around 45°C). Charging at a high temperature can accelerate film formation.

[0030] As described above, in the manufacturing method disclosed herein, the oxygen concentration in case 10 is maintained at 10% or less until the start of the initial charging process S40. In other words, the oxygen concentration in case 10 after the start of the initial charging process S40 is not particularly limited. After the start of the initial charging process S40, the potential of copper decreases due to the charging of the electrode body 20, so the dissolution of copper into the non-aqueous electrolyte 30 is suppressed regardless of the oxygen concentration of the manufacturing environment. For this reason, if a low-oxygen atmosphere can be maintained until the start of the initial charging process S40, internal short circuits after manufacturing caused by copper dissolution can be sufficiently suppressed.

[0031] In the manufacturing method according to this embodiment, the atmosphere surrounding the battery assembly 100 during the third period T3 after the start of the initial charging process S40 is returned to a dry air atmosphere. Specifically, when the battery assembly 100 is started, the gas supplied from the gas supply pipe 220 into the housing 210 is switched from low-oxygen gas to dry air. As described above, once the initial charging process S40 is started, the potential of the copper decreases due to the charging of the electrode body 20, so even if a high concentration of oxygen is supplied, the dissolution of copper can be suppressed. Furthermore, by using dry air when low-oxygen gas is no longer needed, the energy cost in the manufacturing process can be significantly reduced.

[0032] Furthermore, the initial charging process S40 is preferably started within 15 minutes (more preferably within 10 minutes, even more preferably within 5 minutes, and particularly preferably within 1 minute) of the cessation of the supply of low-oxygen gas. This allows charging of the electrode body 20 to begin before the oxygen concentration inside case 10 rises. As a result, exposure of the high-potential copper before charging to oxygen is prevented, thus more preferably suppressing the dissolution of copper into the non-aqueous electrolyte 30.

[0033] (5) Sealing process S50 In this process, the case 10 is sealed. This produces the non-aqueous electrolyte secondary battery 1 shown in Figure 1. Specifically, after the liquid injection port 18 is sealed with a sealing member 19, the case 10 and the sealing member 19 are welded together. This makes it possible to produce a non-aqueous electrolyte secondary battery 1 in which the electrode body 20 and the non-aqueous electrolyte 30 are housed inside the case 10. Furthermore, since no gas flows into the case 10 after sealing, the non-aqueous electrolyte secondary battery 1 can be moved to an atmospheric environment outside the chamber 200.

[0034] (6) Summary The manufacturing method for the non-aqueous electrolyte secondary battery 1 according to this embodiment has been described above. This manufacturing method makes it possible to reduce costs by using dry air and to suppress the occurrence of defective batteries with internal short circuits. The details will be described below with reference to Table 1.

[0035] [Table 1]

[0036] As shown in Table 1 above, in the manufacturing method according to this embodiment, the first period T1 until the start of the liquid injection process S20 is maintained in a dry air atmosphere. This contributes to achieving cost reduction, which is the purpose of using dry air. Here, in the first period T1, since the non-aqueous electrolyte 30 is not injected into the case 10, dissolution of copper into the non-aqueous electrolyte 30 cannot occur. Next, in this embodiment, the oxygen concentration in the second period T2 from the start of the liquid injection process S20 to the start of the initial charging process S40 is reduced to 10% or less. This prevents the non-aqueous electrolyte 30 from coming into contact with the copper during oxidation, and thus suppresses the dissolution of copper into the non-aqueous electrolyte 30. After the start of the initial charging process S40, the potential of the copper decreases due to the charging of the electrode body 20, so the dissolution of copper into the non-aqueous electrolyte 30 is suppressed regardless of the oxygen concentration of the manufacturing environment. In other words, as shown in Table 1, in the manufacturing method according to this embodiment, one of the three elements—"uncharged electrode body," "high concentration of oxygen," and "presence of non-aqueous electrolyte"—is missing in each step from the construction step S10 to the sealing step S50. This prevents internal short circuits after manufacturing caused by copper dissolution. As described above, the manufacturing method according to this embodiment can prevent internal short circuits while minimizing the amount of low-oxygen gas used, thus achieving both cost reduction and a reduction in defective batteries.

[0037] Furthermore, the manufacturing method according to this embodiment is particularly suitable for the manufacture of a large-capacity non-aqueous electrolyte secondary battery 1. As described above, using low-oxygen gas in all steps from the construction step S10 to the sealing step S50 increases the energy cost in the manufacture of the non-aqueous electrolyte secondary battery 1. This cost increase due to the supply of low-oxygen gas is particularly significant in the manufacture of a large-capacity non-aqueous electrolyte secondary battery 1. In contrast, the manufacturing method according to this embodiment can minimize the amount of low-oxygen gas used, thus greatly contributing to reducing the manufacturing cost of a large-capacity non-aqueous electrolyte secondary battery 1. In this specification, "large-capacity non-aqueous electrolyte secondary battery" refers to a battery with an internal volume of 650 cm³ in the case 10. 3(More preferably 700cm) 3 More preferably, 750 cm 3 In particular, 800 cm is preferred. 3 The above refers to the non-aqueous electrolyte secondary battery 1. On the other hand, the upper limit of the internal volume of case 10 is not particularly limited, up to 1500 cm³. 3 The following is also acceptable: 1300cm 3 The following is also acceptable: 1200cm 3 The following is also acceptable: 1000cm 3 The following is also acceptable:

[0038] 3. Other Embodiments The above describes one embodiment of the manufacturing method disclosed herein. However, the manufacturing method disclosed herein is not limited to the embodiment described above, but encompasses various embodiments. Other embodiments of the manufacturing method disclosed herein will be described below.

[0039] For example, in the above manufacturing method, the manufacturing atmosphere in the third period T3 after the start of the initial charging process S40 is returned to dry air. However, the atmosphere in the third period T3 is not limited to the technology disclosed herein. For example, maintaining a low-oxygen atmosphere after the third period T3 can more reliably suppress the dissolution of copper into the non-aqueous electrolyte 30 due to oxidation. In other words, the third period T3 may be a dry air atmosphere from the viewpoint of cost reduction, or a low-oxygen atmosphere from the viewpoint of preventing internal short circuits. In this regard, it is preferable to adjust as appropriate considering the balance between manufacturing costs and the amount of defective batteries generated.

[0040] Furthermore, in the manufacturing method according to the above embodiment, the impregnation step S30 is performed between the liquid injection step S20 and the initial charging step S40. However, the impregnation step S30 is not an essential step in the manufacturing method disclosed herein. For example, the manufacturing method disclosed herein can also be used to manufacture a non-aqueous electrolyte secondary battery having a stacked electrode body made of multiple electrode sheets stacked on top of each other. In this stacked electrode body, the penetration of the non-aqueous electrolyte into the electrode body is very easy, so the impregnation step S30 can be omitted.

[0041] In addition, the manufacturing method according to the above embodiment performs a construction step S10 of constructing the battery assembly 100 in a dry air atmosphere. However, dry air only needs to be supplied before the liquid injection step S20 is started, and is not limited to the above-described embodiment. For example, after constructing the battery assembly 100 in an air atmosphere, the battery assembly 100 may be held in a dry air atmosphere for a certain period. As a result, moisture in the case 10 can be removed, and performance degradation due to moisture intrusion can be prevented. Further, in the manufacturing method according to the above embodiment, the battery assembly 100 is constructed in the chamber 200 maintained in a dry air atmosphere. However, instead of inside the chamber 200, the entire manufacturing environment may be a dry air atmosphere, and the battery assembly 100 may be constructed outside the chamber 200.

[0042] In addition, the manufacturing method disclosed herein may include steps other than the construction step S10 to the sealing step S50 shown in FIG. 2. For example, a drying step of heating the battery assembly 100 to dry the electrode body 20 may be performed between the construction step S10 and the liquid injection step S20. As a result, performance degradation due to moisture intrusion can be surely prevented in a short time. Note that the atmosphere in the drying step may be a dry air atmosphere or a low oxygen atmosphere. However, by performing the drying step in a dry air atmosphere, the energy cost in the manufacture of the non-aqueous electrolyte secondary battery can be more suitably reduced.

[0043] [Test Example] Hereinafter, test examples related to the technology disclosed herein will be described, but the following test examples are not intended to limit the technology disclosed herein.

[0044] 1. Fabrication of Evaluation Batteries (1) Sample 1 First, a wound electrode body obtained by winding a long strip-shaped positive electrode, negative electrode, and separator was fabricated. Specifically, the positive electrode was fabricated by applying a positive electrode active material layer on the surface of an aluminum positive electrode core. Note that the positive electrode active material includes lithium nickel cobalt manganese composite oxide (Li 1-x Ni 1 / 3 Co1 / 3 Mn 1 / 3 O2 was used. Next, the negative electrode was fabricated by coating the surface of a copper negative electrode core with a negative electrode active material layer. Graphite was used as the negative electrode active material. A porous polyolefin sheet was used as the separator.

[0045] Next, a battery assembly was constructed by housing the wound electrode body inside an aluminum case. This battery assembly was constructed in a dry air atmosphere. The dry air used in this test was atmospheric air (oxygen concentration: 20%) with a dew point controlled to -40°C or lower. In this test, the battery assembly underwent pre-drying by heating it at 105°C for 240 minutes in a dry air atmosphere, and vacuum drying by heating the battery assembly at 105°C for 240 minutes in a vacuum atmosphere.

[0046] Next, in Sample 1, an electrolyte injection process was performed in which the electrolyte was poured into the case while the chamber was in a dry air atmosphere. The non-aqueous electrolyte used here was a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 30:40:30, in which a supporting salt (LiPF6) was dissolved at a concentration of 1.1 mol / L. After the electrolyte injection, an impregnation process was performed in which the battery assembly was left to stand for 48 hours.

[0047] Next, in Sample 1, the initial charging process was performed while maintaining a dry air atmosphere inside the chamber. In this initial charging process, constant current constant voltage (CCCV) charging was performed at 0.2C until the battery voltage reached 3.6V. After that, in Sample 1, the sealing process was performed to seal the liquid injection port of the case while maintaining a dry air atmosphere inside the chamber. As described above, all processes in Sample 1 were performed in a dry air atmosphere.

[0048] (2) Sample 2 In Sample 2, the test battery was prepared using the same procedure as Sample 1, except that the atmosphere during the initial charging process was changed to a low-oxygen atmosphere (nitrogen atmosphere). In the initial charging process of Sample 2, charging was started while supplying nitrogen 5 minutes after the supply of dry air was stopped.

[0049] (3) Sample 3 In Sample 3, the test battery was prepared using the same procedure as Sample 1, except that the atmosphere before starting the liquid injection process was changed to a low-oxygen atmosphere (nitrogen atmosphere). In the initial charging process of Sample 3, charging was started while supplying dry air 20 minutes after the nitrogen gas supply was stopped.

[0050] (4) Sample 4 In Sample 4, the test battery was prepared using the same procedure as Sample 3, except that initial charging was started while supplying dry air 5 minutes after the nitrogen gas supply was stopped.

[0051] (5) Sample 5 In Sample 5, the test battery was prepared using the same procedure as Sample 3, except that the initial charging process was started while supplying dry air 15 minutes after the nitrogen gas supply was stopped.

[0052] 2. Evaluation Test (1) Oxygen concentration inside the case In this evaluation, the oxygen concentration inside the case was measured when initial charging began. Specifically, a battery assembly with the case open was placed in a gas bag filled with argon gas. The oxygen concentration of the gas collected inside the gas bag was then measured using a gas chromatograph as the "oxygen concentration inside the case." The measurement results are shown in Table 2.

[0053] (2) Dissolution of copper In this evaluation, the presence or absence of copper dissolution was assessed by disassembling the battery after the sealing process and observing the discoloration of the separator. Specifically, to prevent discoloration due to exposure to air, the battery was disassembled in a glove box filled with an inert gas (argon or nitrogen). The wound electrode body was then disassembled and the color of the separator was visually checked. If a portion of the white separator had turned brown, it was evaluated that copper dissolution from the negative electrode core into the non-aqueous electrolyte had occurred. The measurement results are shown in Table 2.

[0054] [Table 2]

[0055] As shown in Table 2, in samples 4 and 5, the oxygen concentration inside the case was maintained at 10% or less until the start of the initial charging process. Furthermore, in samples 4 and 5, no discoloration of the separator due to copper dissolution occurred. From this, it can be concluded that controlling the oxygen concentration inside the case to 10% or less during the second period from the start of the liquid injection process to the start of the initial charging process effectively suppresses internal short circuits after manufacturing caused by copper dissolution.

[0056] The technologies disclosed herein have been described in detail above, but these are merely illustrative examples and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. In other words, the technologies disclosed herein encompass the forms described in the following sections.

[0057] <Item 1> A construction process for building a battery assembly in which an electrode body containing copper is housed in a case, The injection step involves pouring a non-aqueous electrolyte into the aforementioned case, An initial charging step for charging the aforementioned battery assembly, A sealing step for sealing the aforementioned case and Includes, During the first period until the start of the liquid injection process, the atmosphere surrounding the battery assembly is maintained as a dry air atmosphere. A method for manufacturing a non-aqueous electrolyte secondary battery, characterized by controlling the oxygen concentration inside the case to 10% or less during the second period from the start of the liquid injection step to the start of the initial charging step.

[0058] <Item 2> A method for manufacturing a non-aqueous electrolyte secondary battery according to item 1, wherein the atmosphere surrounding the battery assembly during the third period after the start of the initial charging process is returned to a dry air atmosphere.

[0059] <Item 3> A method for manufacturing a non-aqueous electrolyte secondary battery according to item 1 or 2, wherein an impregnation step is performed between the liquid injection step and the initial charging step to impregnate the inside of the electrode body with the non-aqueous electrolyte.

[0060] <Item 4> A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of items 1 to 3, wherein during the second period, a low-oxygen gas with an oxygen concentration of 10% or less is supplied inside the case.

[0061] <Item 5> The method for manufacturing a non-aqueous electrolyte secondary battery as described in item 4, wherein the low-oxygen gas is nitrogen or a noble gas.

[0062] <Item 6> A method for manufacturing a non-aqueous electrolyte secondary battery according to item 4 or 5, wherein the initial charging process is started within 15 minutes of the cessation of the supply of the hypoxic gas.

[0063] <Item 7> The internal volume of the aforementioned case is 650 cm³. 3 The method for manufacturing a non-aqueous electrolyte secondary battery described in any one of items 1 to 6. [Explanation of symbols]

[0064] 1 Non-aqueous electrolyte secondary battery 10 cases 20 Electrode body 30 Electrolyte 30 Nonaqueous electrolyte 40 electrode terminal 100 battery assembly 200 chambers 210 cabinets 220 Gas supply pipe 230 Gas exhaust pipe 240 nozzles S10 construction process S20 Liquid injection process S30 Impregnation process S40 initial charging process S50 Sealing process T1 Period 1 T2 Second Period T3 Third Period

Claims

1. A construction process for building a battery assembly in which an electrode body containing copper is housed in a case, The injection step involves pouring a non-aqueous electrolyte into the aforementioned case, An initial charging step for charging the aforementioned battery assembly, A sealing step for sealing the aforementioned case and Includes, During the first period until the start of the liquid injection process, the atmosphere surrounding the battery assembly is maintained as a dry air atmosphere. A method for manufacturing a non-aqueous electrolyte secondary battery, characterized by controlling the oxygen concentration inside the case to 10% or less during the second period from the start of the liquid injection step to the start of the initial charging step.

2. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein the atmosphere surrounding the battery assembly during the third period after the start of the initial charging process is returned to a dry air atmosphere.

3. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein an impregnation step is performed between the liquid injection step and the initial charging step to impregnate the inside of the electrode body with the non-aqueous electrolyte.

4. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein during the second period, a low-oxygen gas with an oxygen concentration of 10% or less is supplied inside the case.

5. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 4, wherein the low-oxygen gas is nitrogen or a noble gas.

6. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 4 or 5, wherein the initial charging step is started within 15 minutes of the cessation of the supply of the low-oxygen gas.

7. The internal volume of the aforementioned case is 650 cm³. ３ The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1.

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