Non-aqueous electrolyte secondary battery and method for manufacturing non-aqueous electrolyte secondary battery

Abstract

The present invention provides a non-aqueous electrolyte secondary battery having a wound electrode body, and a method for manufacturing the non-aqueous electrolyte secondary battery. The manufacturing method is a method for manufacturing a non-aqueous electrolyte secondary battery comprising a flat wound electrode body having a positive electrode plate and a negative electrode plate, a non-aqueous electrolyte, and a battery case. The negative electrode plate comprises a negative electrode core and a negative electrode active material layer formed on the negative electrode core. The length of the negative electrode active material layer in the winding axis direction of the wound electrode body is at least 20 cm. The manufacturing method comprises the following steps: an assembly step (S1) of housing the wound electrode body and the non-aqueous electrolyte in a battery case to construct a secondary battery assembly; a first step (S2) of initially charging the secondary battery assembly; and a second step (S3) of, after the first step, lowering the temperature of the wound electrode body to 50°C or lower and maintaining this temperature for at least 72 hours.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the non-aqueous electrolyte secondary battery. Background Art

[0002] Currently, secondary batteries such as lithium-ion batteries are widely used in various fields, including vehicles and portable devices. A typical example of such a secondary battery is a non-aqueous electrolyte secondary battery, which comprises an electrode assembly having a positive electrode plate and a negative electrode plate; a non-aqueous electrolyte; and a battery case that houses the electrode assembly and the non-aqueous electrolyte.

[0003] In the manufacture of non-aqueous electrolyte secondary batteries, the secondary battery assembly in which the electrode body and the non-aqueous electrolyte are housed in the battery case is usually initially charged. By performing the initial charge, a so-called SEI film can be formed on the surface of the negative electrode plate. On the other hand, during the initial charge, gas from the components contained in the secondary battery assembly may be generated in the electrode body. Such gas generation in the electrode body may become the main cause of uneven charging in the electrode body. Therefore, it is required to develop a technology for suppressing the generation of uneven charging caused by the above-mentioned gas generation. Here, as an example of the prior art related to gas generation in the electrode body, Patent Document 1 can be cited. In the manufacturing method of the secondary battery disclosed in this document, it is proposed to erect the secondary battery precursor in a manner having an opening at the uppermost position in the vertical direction, and perform initial charging while allowing the generated gas to escape from the opening. It is recorded that according to the above-mentioned manufacturing method, uneven charging caused by bubbles can be more fully prevented in the secondary battery precursor.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2019 / 044560 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] In addition, as an example of the above-mentioned electrode body, a flat-shaped wound electrode body formed by winding a strip-shaped positive plate and a strip-shaped negative plate with a strip-shaped separator can be cited. In addition, with the popularity of secondary batteries in recent years, non-aqueous electrolyte secondary batteries are required to be further high-energy. In order to meet this requirement, the inventors considered, for example, increasing the formation width of the electrode active material layer in the positive plate and the negative plate (that is, the length in the winding axis direction of the wound electrode body). However, the inventors newly learned that when a wound electrode body with a large formation width of the electrode active material layer is initially charged and aged at high temperature, a black area that is darker than other areas except the part of the area may be formed in a part of the wound electrode body. In addition, the inventors found that the resistance of the black area is higher than the resistance of other areas. Therefore, in a non-aqueous electrolyte secondary battery having a wound electrode body with a black area, its battery characteristics (such as capacity retention rate, etc.) may become lower. Moreover, the inventors conducted in-depth research and found that due to the generation of gas during initial charging, a part of the negative electrode active material layer where a high-quality SEI coating is not formed is produced. If high-temperature aging is directly performed in this state, a non-high-quality coating (i.e., the above-mentioned black area) will be formed in this part.

[0009] The present invention has been made to solve this problem, and an object of the present invention is to provide a technique for suppressing the formation of a black region in a wound electrode body in a non-aqueous electrolyte secondary battery including the wound electrode body.

[0010] Means for solving problems

[0011] The manufacturing method disclosed herein is a method for manufacturing a non-aqueous electrolyte secondary battery, comprising: a flat wound electrode body formed by winding a strip-shaped positive electrode plate and a strip-shaped negative electrode plate with a strip-shaped separator interposed therebetween; a non-aqueous electrolyte; and a battery case that houses the wound electrode body and the non-aqueous electrolyte. The negative electrode plate comprises a negative electrode core and a negative electrode active material layer formed on the negative electrode core. The length of the negative electrode active material layer in the winding axis direction of the wound electrode body is at least 20 cm. The manufacturing method comprises the following steps: an assembly step of housing the wound electrode body and the non-aqueous electrolyte in the battery case to construct a secondary battery assembly; a first step of initially charging the secondary battery assembly; and a second step of, after the first step, maintaining the temperature of the wound electrode body at 50°C or below for at least 72 hours.

[0012] In the manufacturing method described above, after the initial charge in the first step, the secondary battery assembly is left in a predetermined, non-high-temperature state for a predetermined period of time in the second step. This allows the gas generated within the wound electrode body during the initial charge to be fully released outside the wound electrode body, allowing the formation of a high-quality coating in areas where the gas had previously prevented the formation of a high-quality coating. Consequently, the formation of black areas in the wound electrode body, as described above, can be suppressed.

[0013] In a preferred embodiment of the disclosed manufacturing method, the second step is performed while the secondary battery assembly is constrained in the thickness direction of the wound electrode body. Performing the second step while the secondary battery assembly is constrained facilitates gas release into the exterior of the wound electrode body during this step. This further enhances the effect of suppressing the formation of the black region.

[0014] The manufacturing method disclosed herein enables the production of a non-aqueous electrolyte secondary battery having the following structure. In this non-aqueous electrolyte secondary battery, the battery case comprises an outer casing having an opening and a bottom facing the opening, and a sealing plate for sealing the opening. The wound electrode assembly is disposed within the outer casing with the winding axis parallel to the bottom.

[0015] According to the technology disclosed herein, a non-aqueous electrolyte secondary battery is provided, comprising: a flat wound electrode body formed by winding a strip-shaped positive electrode plate and a strip-shaped negative electrode plate with a strip-shaped separator interposed therebetween; a non-aqueous electrolyte; and a battery case for housing the wound electrode body and the non-aqueous electrolyte. The negative electrode plate comprises a negative electrode core and a negative electrode active material layer formed on the negative electrode core. The length of the negative electrode active material layer in the winding axis direction of the wound electrode body is at least 20 cm. In the winding start end region of the negative electrode plate, the ratio of the average plate resistance Rave in the end region to the maximum plate resistance Rmax in the region (Rmax / Rave) is 2.7 or less. In a non-aqueous electrolyte secondary battery with this structure, a local increase in resistance is suppressed in the winding start end region of the negative electrode plate. Consequently, a decrease in battery performance is suppressed in this non-aqueous electrolyte secondary battery.

[0016] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the battery case comprises an outer casing comprising an opening and a bottom facing the opening, and a sealing plate for sealing the opening. The outer casing comprises a pair of facing large-area side walls and a pair of facing small-area side walls, wherein the small-area side walls have an area smaller than that of the large-area side walls. The distance between the pair of large-area side walls is at least 3 cm. A plurality of the wound electrode bodies are housed in the outer casing. As described above, in the non-aqueous electrolyte secondary battery disclosed herein, the reduction in battery performance is suppressed. Therefore, by providing a plurality of wound electrode bodies, energy can be obtained more efficiently from the non-aqueous electrolyte secondary battery.

[0017] One embodiment of the non-aqueous electrolyte secondary battery disclosed herein comprises: a positive electrode current collector and a negative electrode current collector electrically connected to the wound electrode body; a positive electrode tab group comprising a plurality of tabs protruding from one end of the wound electrode body in the direction of the winding axis; and a negative electrode tab group comprising a plurality of tabs protruding from the other end of the wound electrode body in the direction of the winding axis. The positive electrode current collector is connected to the positive electrode tab group, and the negative electrode current collector is connected to the negative electrode tab group. The effects of the technology disclosed herein can be appropriately exhibited in a non-aqueous electrolyte secondary battery having the above-described structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a perspective view schematically showing a non-aqueous electrolyte secondary battery manufactured by the manufacturing method of the first embodiment.

[0019] Figure 2 It is along Figure 1 Schematic cross-sectional view of line II-II.

[0020] Figure 3 This is a perspective view schematically showing a wound electrode body used in the production method of the first embodiment.

[0021] Figure 4 This is a schematic diagram showing the structure of a wound electrode body used in the production method of the first embodiment.

[0022] Figure 5 Schematic diagram illustrating the state of the negative electrode active material layer after initial charge.

[0023] Figure 6 This is a plan view illustrating the winding start end region of the negative electrode plate used in the manufacturing method of the first embodiment.

[0024] Figure 7 It is a process diagram of the method for manufacturing the non-aqueous electrolyte secondary battery in the first embodiment.

[0025] Figure 8This is a perspective view of the restraining body in the manufacturing method of the first embodiment.

[0026] Figure 9 It is a schematic diagram explaining the effects of the manufacturing method of the first embodiment.

[0027] Figure 10 This is a perspective view of a restraining body in the manufacturing method of the second embodiment.

[0028] Figure 11 It is a top view of the restraining body in the manufacturing method of the third embodiment. DETAILED DESCRIPTION

[0029] Below, with reference to the accompanying drawings, several preferred embodiments of the technology disclosed herein are described. In addition, matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention (for example, the general structure and manufacturing process of secondary batteries that are not characterized by the technology disclosed herein) can be understood as design matters made by those skilled in the art based on the existing technology in this field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the technical common sense in this field.

[0030] In this specification, the term "secondary battery" refers to a whole range of electrical storage devices that can be repeatedly charged and discharged. This term encompasses so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and capacitors (physical batteries) such as electric double-layer capacitors. In this specification, "active material" refers to a material that can reversibly store and release charge carriers (e.g., lithium ions).

[0031] In the figures referenced in this specification, the reference symbol X represents the "depth direction", the reference symbol Y represents the "width direction", and the reference symbol Z represents the "height direction". In addition, F in the depth direction X represents "front", and Rr represents "back". L in the width direction Y represents "left", and R represents "right". Moreover, U in the height direction Z represents "up", and D represents "down". However, these are directions for convenience of explanation only and do not impose any restrictions on the arrangement of the secondary battery. In addition, in this specification, the expression "A to B" indicating a numerical range includes the meaning of "above A and below B", and also includes the meaning of "greater than A and less than B".

[0032] <First embodiment>

[0033] Figure 1 、 2 An example of a non-aqueous electrolyte secondary battery manufactured using the manufacturing method disclosed herein is shown. The non-aqueous electrolyte secondary battery 100 includes a wound electrode body 20, a non-aqueous electrolyte (not shown), and a battery case 10 that houses the wound electrode body and the non-aqueous electrolyte. The non-aqueous electrolyte secondary battery 100 is a lithium-ion secondary battery.

[0034] The non-aqueous electrolyte may contain a non-aqueous solvent and a supporting salt. As the non-aqueous solvent, organic solvents such as various carbonates used in general lithium-ion secondary batteries can be used without particular limitation. As specific examples, chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be cited; cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), methyl ethylene carbonate, and ethyl ethylene carbonate; fluorinated chain carbonates such as methyl-2,2,2-trifluoroethyl carbonate (MTFEC); fluorinated cyclic carbonates such as monofluoroethylene carbonate (FEC) and bisfluoroethylene carbonate (DFEC). Such non-aqueous solvents can be used alone or in combination of two or more.

[0035] As supporting salts, LiPF6, LiBF4 and the like can be cited. The concentration of the supporting salt in the non-aqueous electrolyte can be set in the range of 0.7 mol / L to 1.3 mol / L. The non-aqueous electrolyte may contain, as components other than the above-mentioned components, oxalic acid complexes containing boron (B) atoms and / or phosphorus (P) atoms (such as lithium bis(oxalato)borate (LiBOB)), vinylene carbonate (VC), lithium difluorophosphate and other film-forming agents; gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB). In addition, as long as the effect of the technology disclosed herein is not significantly impaired, conventionally known additives such as thickeners and dispersants may be included.

[0036] From the viewpoint of preferably realizing the effect of the technology disclosed herein, above-mentioned nonaqueous solvent is preferably cyclic carbonate.Wherein, can preferably use ethylene carbonate (EC).In addition, from the same viewpoint, above-mentioned film forming agent is preferably vinylene carbonate (VC).

[0037] The battery case 10 includes an outer body 12 having an opening and a sealing plate (lid) 14 that seals the opening. The battery case 10 is integrated and hermetically sealed (sealed) by joining the sealing plate 14 to the periphery of the opening of the outer body 12. The outer body 12 is a square outer body with a bottom and a square tube shape, including the above-mentioned opening, a rectangular bottom 12a facing the opening, a pair of large-area side walls 12b rising from the long sides of the bottom 12a, and a pair of small-area side walls 12c rising from the short sides of the bottom 12a. The small-area side wall 12c has an area smaller than that of the large-area side wall 12b. The sealing plate 14 is provided with a liquid injection hole 15 for non-aqueous electrolyte, a gas discharge valve 17, a positive terminal 30, and a negative terminal 40. The liquid injection hole 15 is sealed by a sealing member 16. The positive terminal 30 and the negative terminal 40 are electrically connected to the wound electrode body 20 housed in the battery case 10. The battery case 10 is made of, for example, metal. Examples of the metal material constituting the battery case 10 include aluminum, aluminum alloys, iron, and iron alloys.

[0038] The dimensions of the battery case 10 are not particularly limited. As described later, in several embodiments, when multiple wound electrode assemblies 20 are housed within the exterior body 12, the distance between the pair of large-area side walls 12b can be appropriately set based on the number and size of the housed wound electrode assemblies 20. For example, this distance can be at least 3 cm, more than 3 cm, more than 4 cm, or more than 5 cm. Furthermore, this distance can be, for example, less than 10 cm, less than 8 cm, or less than 6 cm.

[0039] The wound electrode body 20 is a power generation element of the non-aqueous electrolyte secondary battery 100 and includes a positive electrode plate, a negative electrode plate, and a separator. Figure 2 As shown, in the battery case 10 (exterior body 12), a plurality of (for example, 2 or more, 3 or more, or 4 or more, in a state arranged in the depth direction X) batteries are housed. Figure 2 (3 in the figure) wound electrode bodies 20. Figures 1 to 4 As shown, the wound electrode body 20 is arranged inside the outer body 12 with the winding axis WL parallel to the bottom 12a. The wound electrode body 20 is housed in the battery case 10 in the state of being housed in the electrode body holder 70. In addition, the constituent materials of the various components (positive electrode plate, negative electrode plate, separator, etc.) constituting the wound electrode body 20 can be used without particular limitation. Materials that can be used in general non-aqueous electrolyte secondary batteries can be used. Since the technology disclosed herein is not limited, detailed descriptions are sometimes omitted.

[0040] The length L1 of the wound electrode body 20 in the direction of the winding axis WL is at least 20 cm, and can be set to, for example, 20 cm or more, or 30 cm or more. Alternatively, the length L1 can be, for example, 60 cm or less, 50 cm or less, or 40 cm or less. The length L1 does not include the length of the positive electrode tab 22t or the length of the negative electrode tab 24t, which will be described later.

[0041] like Figure 4 As shown, the wound electrode body 20 includes a positive electrode plate 22 and a negative electrode plate 24. The wound electrode body 20 is a flat wound electrode body formed by winding a long strip-shaped positive electrode plate 22 and a long strip-shaped negative electrode plate 24 with a long strip-shaped separator 26 interposed therebetween around a winding axis WL perpendicular to the longitudinal direction. Figure 3 As shown, the wound electrode body 20 has a pair of flat portions 20 a and a pair of end portions 20 b in the width direction Y. The end portions 20 b are stacked surfaces of the positive electrode plate 22 , the negative electrode plate 24 , and the separator 26 and are open to the outside of the wound electrode body 20 .

[0042] The positive electrode plate 22 comprises a long strip-shaped positive electrode core 22c (e.g., aluminum foil or aluminum alloy foil) and a positive electrode active material layer 22a fixed to at least one surface (preferably both surfaces) of the positive electrode core 22c. Although not particularly limited, a positive electrode protective layer 22p may be provided on one side edge of the positive electrode plate 22 in the width direction Y as needed. At one end ( Figure 4 A plurality of positive electrode tabs 22t are provided at the left end portion of the positive electrode. The plurality of positive electrode tabs 22t are respectively oriented to one side in the width direction Y ( Figure 4 on the left side of the

[0043] The plurality of positive electrode tabs 22t are spaced apart (intermittently) along the longitudinal direction of the positive electrode plate 22. The positive electrode tab 22t is a part of the positive electrode core 22c, which is the part of the positive electrode core 22c where the positive electrode active material layer 22a and the positive electrode protective layer 22p are not formed (core exposed part). The plurality of positive electrode tabs 22t are spaced apart (intermittently) along the longitudinal direction of the positive electrode plate 22. Figure 4 The positive electrode tab group 23 is stacked with a plurality of positive electrode tabs 22t. A positive electrode current collector 50 (see FIG. 2 ) is joined to the positive electrode tab group 23. Figures 2-4 ).

[0044] The dimensions of the positive electrode plate 22 can be set to achieve the aforementioned length L1 of the wound electrode body 20. The length of the positive electrode plate 22 in the direction of the winding axis WL can be set, for example, to 20 cm or greater, or 30 cm or greater. Alternatively, this length can be, for example, 60 cm or less, 50 cm or less, or 40 cm or less. The aforementioned length does not include the length of the positive electrode tab 22t.

[0045] The negative electrode plate 24 includes a long strip-shaped negative electrode core 24c (e.g., copper foil or copper alloy foil) and a negative electrode active material layer 24a fixed on at least one surface (preferably both surfaces) of the negative electrode core 24c. Figure 4 A plurality of negative electrode tabs 24t are provided on the right end portion of the negative electrode. The plurality of negative electrode tabs 24t face one side in the width direction Y ( Figure 4 The plurality of negative electrode tabs 24t are arranged at intervals (intermittently) along the longitudinal direction of the negative electrode plate 24. The negative electrode tab 24t is a part of the negative electrode core 24c, which is the part of the negative electrode core 24c where the negative electrode active material layer 24a is not formed (the exposed part of the core). The plurality of negative electrode tabs 24t are arranged at one end in the width direction Y ( Figure 4 The negative electrode tab group 25 is stacked to form a plurality of negative electrode tabs 24t. A negative electrode current collector 60 (see FIG. 2 ) is joined to the negative electrode tab group 25. Figures 2-4 ).

[0046] The dimensions of the negative electrode plate 24 can be set to achieve the aforementioned length L1 of the wound electrode body 20. The length of the negative electrode plate 24 in the direction of the winding axis WL (e.g., the length of the negative electrode active material layer 24a) is at least 20 cm, and can be set, for example, to 20 cm or more, or 30 cm or more. Alternatively, this length can be, for example, 60 cm or less, 50 cm or less, or 40 cm or less. The aforementioned length does not include the length of the negative electrode tab 24t.

[0047] In addition, when the secondary battery assembly is initially charged, the negative electrode active material decomposes the organic matter (such as non-aqueous electrolyte components, additives such as film forming agents, etc.) in contact at a predetermined potential or above. Such decomposition products are deposited on the surface of the negative electrode active material layer as an SEI film. The SEI film does not have electronic conductivity, but it is not a completely continuous film, so it allows the passage of ions. Therefore, the SEI film can stabilize and / or passivate the surface of the active material, inhibiting excessive decomposition of non-aqueous electrolyte components, etc. On the other hand, through initial charging, gases from components contained in the secondary battery assembly (such as water, constituent components of the non-aqueous electrolyte, etc.) may be generated inside the electrode body. The gas generated in the electrode body is released from the open surface of the electrode body to the outside of the electrode body. Here, if the electrode body is a structure such as a wound electrode body 20, the above-mentioned gas is only released from the open surface of the wound electrode body 20, that is, the end 20b, so a part of the generated gas is likely to remain in the electrode body.

[0048] The present inventors speculate the following mechanism regarding the formation of black areas due to gas generation during initial charging. Figure 5 As shown, a coating 3 (SEI coating) is formed on the surface of the negative electrode active material layer 24a after initial charge. In addition, gas G exists between the negative electrode active material layer 24a and the separator 26. Charging reaction is difficult to occur in the portion where gas G exists, thereby hindering the formation of coating 3. Gas G is released to the outside of the wound electrode body 20 through subsequent high-temperature aging, etc. In the portion where gas G is removed, the formation of coating 3 is insufficient, so that, for example, the non-aqueous electrolyte components and the negative electrode active material react rapidly under the action of high temperature. As a result, a non-high-quality coating (black area) having properties different from those of coating 3 is formed. The resistance of the black area is higher than that of other areas. Therefore, due to the formation of the black area, uneven charging may occur in the wound electrode body 20, which reduces the battery performance of the non-aqueous electrolyte secondary battery.

[0049] Furthermore, according to the research of the present inventors, it is known that the black region is easily formed in the winding start end region of the negative electrode plate 24 (specifically, on the negative electrode active material layer 24a). In particular, it is known that the black region is more frequently formed in the portion of this region that overlaps with the central portion 201 of the wound electrode body 20 (see Figure 3 ).like Figure 6As shown, the winding start end region 240 refers to the region of length L3 from the winding start end 241 of the negative electrode plate 24 toward the other end 242 in the longitudinal direction of the negative electrode plate 24. The ratio (L3 / L4) of the length L4 of the longitudinal direction of the negative electrode plate 24 to the length L3 of the winding start end region 240 in the same direction can be, for example, 1 / 10 or more, 1 / 8 or more, or 1 / 5 or less, or 1 / 2 or less, or 1 / 3 or less, or 1 / 4 or less. In addition, Figure 6 In the embodiment, the number of negative electrode tabs 24t formed in the winding start end region 240 does not impose any limitation on the setting of the winding start end region.

[0050] The central portion 201 refers to the region including the centerline C in the width direction Y of the flat portion 20a of the wound electrode body 20. The ratio of the length L2 of the central portion 201 to the length L1 (L2 / L1) in the same direction can be, for example, 1 / 6 or greater, 1 / 4 or greater, or 1 / 2 or less, or 1 / 3 or less. "Including the centerline C" means that the central portion 201 only includes the centerline C. For example, the distance between the centerline of the central portion 201 and the centerline C is 1 / 4 L2 or less.

[0051] Furthermore, the present inventors have conducted intensive research and have found that the formation of the above-mentioned black area can be suppressed by manufacturing a non-aqueous electrolyte secondary battery using the technology disclosed herein. Figure 7 As shown, the manufacturing method has at least an assembly step S1, a first step S2, and a second step S3. In the assembly step S1, the wound electrode body and the non-aqueous electrolyte are housed in a battery case to construct a secondary battery assembly. First, the wound electrode body 20 is made using the above-mentioned materials by a conventionally known method. Next, the positive electrode collector 50 is installed on the positive electrode tab group 23 of the wound electrode body 20, and the negative electrode collector 60 is installed on the negative electrode tab group 25, and a combination of the wound electrode body and the electrode collector (first combination) is prepared (refer to Figure 3 ) In this embodiment, three first combined objects are prepared.

[0052] Next, the three first assemblies and the sealing plate 14 are integrated to prepare a second assembly. Specifically, for example, the positive electrode terminal 30, previously attached to the sealing plate 14, is joined to the positive electrode current collector 50 of the first assembly. Similarly, the negative electrode terminal 40, previously attached to the lid 14, is joined to the negative electrode current collector 60 of the first assembly. Examples of joining methods include ultrasonic bonding, resistance welding, and laser welding.

[0053] Next, the second composite is housed in the outer body 12. Specifically, for example, three wound electrode bodies 20 are housed in an electrode body holder 70, which is made by bending an insulating resin sheet (for example, made of polyolefins such as polyethylene (PE)) into a bag or box shape. Then, the wound electrode body 20 covered by the electrode body holder 70 is inserted into the outer body 12. In this state, the sealing plate 14 is overlapped with the opening of the outer body 12, and the outer body 12 and the sealing plate 14 are welded to seal the outer body 12. Then, the non-aqueous electrolyte is injected into the battery case 10 through the injection hole 15 by a conventionally known method. The injected non-aqueous electrolyte is impregnated into the wound electrode body 20. In this way, a secondary battery assembly is constructed in which the wound electrode body 20 and the non-aqueous electrolyte are housed in the battery case 10.

[0054] In the first step S2, the secondary battery assembly is initially charged. In this step, the secondary battery assembly obtained in the assembly step S1 is initially charged using a known charge-discharge mechanism. This step enables the formation of a high-quality coating. In this step, the secondary battery assembly is charged so that its depth of charge (hereinafter referred to as "SOC") reaches the desired depth of charge. The depth of charge is preferably 5% or greater, more preferably 10% or greater. On the other hand, the depth of charge is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. The temperature conditions for the initial charge are preferably 45°C or less, more preferably 15°C to 35°C, and even more preferably 20°C to 30°C. The charging rate for the initial charge is not particularly limited and can be set appropriately, for example, 1C or less. Furthermore, although not particularly limited, to release gases generated during this step, the first step S2 is preferably performed with the liquid injection port 15 open (i.e., with the battery case 10 open).

[0055] Although not particularly limited, from the perspective of gas movement / diffusion within the wound electrode body 20 and gas release to the outside of the wound electrode body 20, the secondary battery assembly may be constrained after the first step S2. The second step S3 is preferably performed with the secondary battery assembly constrained. Figure 8 As shown, the secondary battery assembly 101 can be formed in the depth direction X of the battery case 10 (ie, the thickness direction of the wound electrode body 20 (see FIG. Figure 3 Specifically, a pair of restraining fixtures 80 can be arranged to be aligned with a pair of large-area side walls 12b (see Figure 1 )’s overall orientation.

[0056] As described above, a constraint body 180 consisting of a secondary battery assembly 101 and a pair of constraint clamps 80 is constructed. Then, for example, by bridging the two ends of the constraint body 180 in the depth direction X (i.e., a pair of constraint clamps 80) with a constraint belt, a predetermined constraint pressure can be applied to the secondary battery assembly 101. The above-mentioned constraint pressure is not particularly limited, and is, for example, 1 kN or more, preferably 3 kN to 15 kN, and more preferably 6 kN to 10 kN. Alternatively, the above-mentioned constraint pressure can be applied to each secondary battery assembly 101 by arranging a plurality of constraint bodies 180 in the depth direction X and bridging the constraint bodies at both ends with a constraint belt. In this case, from the viewpoint of uniformly applying constraint pressure to each secondary battery assembly 101, an elastic body such as a spring can be arranged between the constraint bodies 180 and the constraint bodies 180.

[0057] In the second step S3, after the first step S2, the temperature of the wound electrode body 20 is set to 50°C or lower, and this state is maintained for at least 72 hours. The details will be described later, but by performing this step, the gas generated in the first step S2 can be fully released to the outside of the wound electrode body 20. The charge depth of the secondary battery assembly in the second step S3 is preferably 25% or lower, more preferably 20% or lower. The above-mentioned charge depth is preferably 5% or higher, more preferably 10% or higher. The above-mentioned charge depth is preferably 10% to 15%, for example. In addition, in order to achieve an appropriate charge depth in this step, the secondary battery assembly after the first step S2 may be discharged or not discharged.

[0058] The temperature conditions in the second step S3 can be appropriately set within the above range. The above temperature conditions are preferably 45°C or less, more preferably 40°C or less. Alternatively, the above temperature conditions are, for example, 0°C or more, preferably 5°C or more, more preferably 10°C or more, and even more preferably 15°C or more. Furthermore, after the first step S2, if the temperature of the secondary battery assembly exceeds 50°C, it is preferred that the temperature be maintained for no more than 120 seconds.

[0059] The maintenance time (storage time) of the secondary battery assembly in the second step S3 can be appropriately set within the above range. The above maintenance time is, for example, more than 72 hours, preferably more than 144 hours, and can also be set to more than 200 hours. The upper limit of the above maintenance time is not particularly limited, but from the perspective of efficiently obtaining the effect of the technology disclosed herein, it can be set to, for example, less than 336 hours or less than 300 hours. In several embodiments, without constraining the secondary battery assembly, from the perspective of better obtaining the effect of the technology disclosed herein, it is preferred that the above maintenance time be set to more than 144 hours.

[0060] The manufacturing method may further include a third step S4 and a fourth step S5. In the third step S4, after the second step S3, the secondary battery assembly is charged. In this step, the charging and discharging mechanism is used to charge so that the depth of charge of the secondary battery assembly after the second step S3 is within the desired range. The above-mentioned depth of charge is preferably 5% or more, preferably 10% or more, and more preferably 15% or more. On the other hand, the above-mentioned depth of charge is preferably 50% or less, and more preferably 40% or less. In addition, the temperature condition for initial charging is preferably 45°C or less, more preferably 15°C to 35°C, and more preferably 20°C to 30°C. The charging rate for the above-mentioned charging is not particularly limited and can be set appropriately, for example, it can be set to 1C or less. In addition, when the secondary battery assembly is constrained as described above, the constraint can be released at the beginning of this step.

[0061] In the fourth step S5, the secondary battery assembly after the third step S4 is aged at high temperature. High temperature aging is a process in which the secondary battery assembly is kept in a high temperature environment while maintaining the charged state. Here, the secondary battery assembly after the third step S4 is placed in a high temperature environment while maintaining its charge depth unchanged, and high temperature aging is started. The temperature in high temperature aging is not particularly limited, for example, it can be higher than 50°C, can be above 55°C, can be below 80°C, or can be below 70°C. As described above, by implementing the manufacturing method disclosed herein, a non-aqueous electrolyte secondary battery in a usable state can be manufactured.

[0062] Reference Figure 5 、 9 , the inventor's investigation into the mechanism for achieving the effect of the technology disclosed herein is described. However, it is not intended to limit the mechanism of the above-mentioned effect to the following case. If, after the initial charge, in the second step S3, the secondary battery assembly is maintained in a non-high temperature state of 50°C or less for at least 72 hours, during this period, the gas G generated in the initial charge of the first step S2 moves from between the separator 26 and the negative electrode active material layer 24a and is soon released to the outside of the wound electrode body. Then, in a non-high temperature state, the non-aqueous electrolyte component that serves as a donor of the coating component reacts with the negative electrode active material and decomposes, and in the portion where the gas G is present but no high-quality coating is formed (high-quality coating non-formed portion) (refer to Figure 5 ) additionally forms a high-quality coating 3a (refer to Figure 9 ). Therefore, even if the secondary battery assembly is placed in a high temperature state in the fourth step S5, the non-aqueous electrolyte component and the negative electrode active material can be suppressed from reacting rapidly under the action of high temperature. Thus, the formation of a poor quality coating (black area) on the negative electrode plate is suppressed.

[0063] By implementing the manufacturing method disclosed herein, a non-aqueous electrolyte secondary battery in which the formation of black areas is suppressed can be provided. The effect of suppressing the formation of black areas can be evaluated, for example, by disassembling the wound electrode body after high-temperature aging and visually observing the negative plate. In addition, the above-mentioned effect can be evaluated by measuring the average plate resistance Rave and the maximum plate resistance Rmax of the above-mentioned winding starting end area in the negative plate and calculating their ratio (Rmax / Rave). When the ratio (Rmax / Rave) is 2.7 or less (preferably 2.5 or less, more preferably 2.0 or less, and further preferably 1.5 or less), it can be evaluated to have the above-mentioned effect. Although not particularly limited, the lower limit of the ratio (Rmax / Rave) can be approximately 1.0. An example of a method for calculating the average plate resistance Rave and the maximum plate resistance Rmax is described in the following embodiment.

[0064] Alternatively, the above-mentioned effect can be evaluated by measuring the area of ​​the black area formed in the above-mentioned winding starting end area. For example, first, use a commercially available image acquisition device (such as a camera, etc.) to acquire an image of the above-mentioned winding starting end area. Then, use commercially available image analysis software to measure the area of ​​the black area. Then, calculate the ratio (%) of the area of ​​the black area formed when the area of ​​the above-mentioned winding starting end area is set to 100%. The judgment standard for the formation of the black area is, for example, by comparing the image data of the electrode surface before and after the charge and discharge (both after cleaning with electrolyte) using binarization, and judging based on whether a discolored portion is confirmed locally. In addition, when the local resistance value increases relative to the corresponding portion extracted at the same time, the same discoloration is judged as a black area. When the above-mentioned ratio is, for example, less than 3.0% (preferably less than 1.0%, more preferably less than 0.5%), it can be evaluated as having the above-mentioned effect.

[0065] Alternatively, the winding starting end area can be divided into 1 cm × 1 cm sections, and the number of black area-forming sections can be counted for evaluation. For example, the image analysis software described above can be used to determine the presence or absence of black areas in each section. Then, the number of black area-forming sections is counted, and the ratio (number of black area-forming sections / total number of sections) is calculated. If this ratio is, for example, 0.3 or less (preferably 0.2 or less, more preferably 0.1 or less), it can be evaluated as having the above-mentioned effect. In addition, the criteria for judging the formation of black areas in this evaluation method are as described above.

[0066] [Test Example]

[0067] Hereinafter, test examples related to the present invention will be described. However, the contents of the test examples described below are not intended to limit the present invention.

[0068] -Assembly process-

[0069] Lithium nickel cobalt manganese composite oxide (NCM) as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and acetylene black (AB) as a conductive material were weighed in a mass ratio of NCM:PVdF:AB=98:1:1 and mixed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of a long strip of positive electrode core (aluminum foil, thickness 18μm) and dried. It was cut into a specified size and rolled by a roller press to obtain a positive electrode plate with a positive electrode active material layer on both sides of the positive electrode core. In addition, the density of the positive electrode active material layer is 3.4g / cm 3 The thickness of each side is 110 μm. The length of the positive electrode plate is 72 mm in the longitudinal direction and 242 mm in the width direction.

[0070] Graphite powder (C) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were weighed in a mass ratio of C:SBR:CMC=98:1:1 and mixed in water to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides of a long strip of negative electrode core (copper foil, 12μm) and dried. It was cut into a specified size and rolled by a roller press to obtain a negative electrode plate having a negative electrode active material layer on both sides of the negative electrode core. In addition, the density of the negative electrode active material layer is 1.4g / cm 3 The thickness of each side is 200 μm. The length of the positive electrode plate is 80 mm in the longitudinal direction and 252 mm in the width direction.

[0071] Next, the positive electrode plate and the negative electrode plate prepared above are stacked facing each other with a separator (separator) interposed therebetween. By winding them in the sheet length direction, a sheet as shown in FIG. Figure 4 The wound electrode body shown. Furthermore, the separator comprises a substrate composed of a porous layer made of polyolefin and a heat-resistant layer comprising aluminum oxide and a resin binder. The substrate has a thickness of 16 μm, and the heat-resistant layer has a thickness of 4 μm. Furthermore, the heat-resistant layer is formed on the surface facing the positive electrode plate. The separator has a longitudinal length of 82 mm and a width of 260 mm.

[0072] The dimensional relationship of the wound electrode body produced as described above is as follows:

[0073] W: 8mm;

[0074] L1: 260mm; and

[0075] H:82mm.

[0076] In addition, the reference numerals are as follows Figure 3 Specifically, W is the thickness of the wound electrode body 20 , L1 is the width of the wound electrode body 20 , and H is the height of the wound electrode body 20 .

[0077] Next, the wound electrode body is connected to the lid of the battery case via the positive electrode collector and the negative electrode collector. Insert it into the case body, and weld the case body and the lid. Next, inject a non-aqueous electrolyte from the injection hole of the battery case (sealing plate). The non-aqueous electrolyte is a non-aqueous electrolyte obtained by dissolving LiPF6 as a supporting salt at a concentration of 1 mol / L and dissolving vinylene carbonate (VC) as an additive (film forming agent) at a concentration of 0.3 wt% in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC=30:40:30 (25°C, 1atm). In this way, a secondary battery assembly for testing was constructed.

[0078] (Example 1)

[0079] -First process-

[0080] After the nonaqueous electrolyte was injected into the battery case as described above, initial charging was performed at 25°C, a nitrogen atmosphere, and 1 atm with the liquid injection hole of the sealing plate open (unsealed). During this initial charge, charging was performed at a current of 0.3 C until the SOC reached 15% of the specified capacity of the test secondary battery assembly.

[0081] - Second process -

[0082] The test secondary battery assembly was left standing at 25° C., a nitrogen atmosphere, and an atmosphere of 1 atm for 72 hours with the liquid injection hole of the sealing plate open (not sealed).

[0083] -The third process-

[0084] Next, the liquid injection hole of the sealing plate was sealed with a sealing member to hermetically seal the battery case, and then charging was performed at a current of 0.5 C until the SOC reached 35% relative to the specified capacity of the test secondary battery assembly.

[0085] -Fourth process-

[0086] Next, the test secondary battery assembly was placed in an environment of 60° C. for 15 hours. In this manner, a test secondary battery of Example 1 was prepared.

[0087] (Examples 2, 3)

[0088] Each of the first to fourth steps was performed in the same manner as in Example 1, except that the standing time in the second step was set to the period described in the corresponding column of Table 1, to prepare a test secondary battery for each example.

[0089] (Examples 4~6)

[0090] After the first step, the test secondary battery assembly was restrained. Specifically, Figure 8 The pair of restraining plates shown restrain the test secondary battery assembly from both sides in the thickness direction. The restraining pressure at this time is 6 kN. In the second step, the test secondary battery assembly is placed for the period described in the corresponding column of Table 1. After the second step, the restraints on the test secondary battery assembly are released. Otherwise, the same procedures as in Example 1 are followed for each step from Step 1 to Step 4 to prepare the test secondary battery for each example.

[0091] (Example 7)

[0092] After the first step, the second step was not performed. Otherwise, the third and fourth steps were performed in the same manner as in Example 1 to prepare a secondary battery for testing in this example. In Table 1, a "-" in the "Second Step" column indicates that the step was not performed.

[0093] <Evaluation of Black Area Formation>

[0094] The test secondary batteries of Examples 1 to 7 prepared as described above were discharged at a current of 0.5C until the depth of charge reached 0% relative to the specified capacity of the test secondary battery. Next, the test secondary batteries of each example were disassembled, the negative plates were cleaned with a cleaning solution (dimethyl carbonate (DMC), 100 vol%), and dried. For the dried negative plates, the presence or absence of blackened areas was visually confirmed. For the disassembled negative plates, the half-circle portion of the winding was set to 1T (turn). The number of turns in which the formation of black areas was visually observed in the entire 35T of the negative plate is shown in the "Black area (in the entire 35T of the negative plate)" column of Table 1. In addition, in the corresponding column of Table 1, "0" means that the formation of black areas was not observed.

[0095] <Measurement of Negative Plate Resistance>

[0096] For the negative plate whose presence or absence of black areas has been confirmed as described above, the resistance value of the plate surface is measured by AC impedance measurement. Then, the resistance value (Ω) is calculated by fitting the equivalent circuit to the obtained Cole-Cole diagram (Nyquist diagram). The measurement is carried out by a two-terminal method using an electrochemical impedance device (Solartron Metrology, Solartron1250E). First, the winding starting end area in the negative plate (here, an area of ​​a specified length from the winding starting end in the negative plate toward the other end in the longitudinal direction of the negative plate) is cut off and used as a measurement sample. The measurement sample is divided into 1 cm × 1 cm areas, and the resistance value of each area is calculated using the above-mentioned measurement device. The average value of the resistance value of each area obtained in this way is calculated to obtain the average plate resistance Rave. In addition, the maximum value of the resistance value of each area obtained is set to the maximum plate resistance Rmax. Then, the ratio (Rmax / Rave) is calculated. The results are shown in the corresponding columns of Table 1.

[0097] <Determination of Capacity Retention Rate>

[0098] For the test secondary battery after the above-mentioned fourth step, discharge at a current of 0.5C until the battery voltage reaches 3.0V. Then, charge at a current of 0.5C until the battery voltage reaches 4.1V. Then, discharge at a current of 0.5C until the battery voltage reaches 3.0V. The capacity of the test secondary battery at this time is defined as the initial capacity. For the test secondary battery after the initial capacity measurement, charge and discharge between 3.0V and 4.1V are performed at a current of 0.3C for 500 cycles. The battery capacity after the 500 cycles is obtained, and this value is used as the capacity after endurance. Then, using the above-mentioned initial capacity and the above-mentioned capacity after endurance, based on the following formula (1):

[0099] Capacity retention rate (%) = capacity after endurance / initial capacity × 100 (1)

[0100] The capacity retention rate (%) during the cycle test was calculated. The results are shown in the corresponding columns of Table 1.

[0101]

Table 1

[0102]

[0103] As shown in Table 1, if Examples 1 to 6 are compared with Example 7, it is confirmed that the formation of black areas in the negative plate can be suppressed by placing the battery for at least 72 hours in the second step after the initial charge in the first step. In addition, it was confirmed that the ratio (Rmax / Rave) was 2.7 or less by the implementation of the second step, which suppressed the generation of resistance unevenness in the negative plate. Furthermore, it was confirmed that the reduction in battery performance (here, capacity retention rate) was suppressed by the implementation of the second step. If the results of Examples 1 to 3 are compared with the results of Examples 4 to 6, it is confirmed that the effect of suppressing the formation of black areas can be improved by implementing the second step in a state where the secondary battery assembly is constrained. Furthermore, it was confirmed that the effect of suppressing the formation of black areas can be further improved by extending the placement time in the second step.

[0104] <Second embodiment>

[0105] In the first embodiment described above, Figure 8 As shown, a pair of restraint jigs 80 are arranged to be aligned with a pair of large-area side walls 12b (see Figure 1 However, it is sufficient to apply a predetermined restraining pressure to at least the central portion 201 of the wound electrode body 20. As long as this structure can be achieved, the shape and size of the restraining fixture are not limited. Figure 10 As shown, the secondary battery assembly 101 can be clamped by a pair of restraining clamps 82 so that the secondary battery assembly 101 can be clamped in the depth direction X of the battery case 10 (ie, the thickness direction of the wound electrode body 20 (see FIG. Figure 3 )) A predetermined restraining pressure is applied to the central portion 201 of the wound electrode body 20. In this manner, the restraining body 280 composed of the secondary battery assembly 101 and the pair of restraining jigs 82 is constructed.

[0106] When the restraining jig 82 is used, a predetermined restraining pressure is applied to the central portion 201 of the wound electrode body 20, but no restraining pressure is applied to the end portions 202 and 203. By selectively applying restraining pressure to the central portion 201, the release of gas from the central portion 201 can be promoted. The manufacturing method of the second embodiment can be the same as the manufacturing method of the first embodiment, except for the use of the restraining jig 82.

[0107] <Third embodiment>

[0108] Or, as another example, it is also possible to use Figure 11 The restraining fixture 83 shown. Figure 11 As shown, a pair of restraining jigs 83 can be used to tighten the battery case 10 in the depth direction X (ie, the thickness direction of the wound electrode body 20 (see FIG. Figure 3The secondary battery assembly 101 is clamped on the secondary battery assembly 101. In this way, the restraining body 380 composed of the secondary battery assembly 101 and the pair of restraining jigs 83 is constructed.

[0109] Here, the restraining fixture 83 has a flat wide surface 83a and a curved surface 83b facing the wide surface 83a. The curved surface 83b faces the large-area side wall 12b of the battery case 10 and is curved toward the large-area side wall 12b. The restraining portion 831 of the curved surface 83b, which includes a bending vertex 83t, contacts the large-area side wall 12b. Here, the position of the bending vertex 83t and the length of the restraining portion 831 in the width direction Y are not particularly limited and can be appropriately set so as to apply a predetermined restraining pressure to the central portion 201 of the wound electrode body 20 through restraint. The other portions of the curved surface 83b, except for the restraining portion 831, do not contact the large-area side wall 12b.

[0110] When the restraining jig 83 is used, a predetermined restraining pressure is applied to the central portion 201 of the wound electrode body 20, but no restraining pressure is applied to the end portions 202 and 203. By selectively applying restraining pressure to the central portion 201, the release of gas from the central portion 201 can be promoted. The manufacturing method of the third embodiment can be similar to the manufacturing method of the first embodiment, except for the use of the restraining jig 83.

[0111] While specific examples of the technology disclosed herein have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology disclosed herein includes various modifications and variations of the specific examples described above.

[0112] Description of Reference Numerals

[0113] 10 Battery housing

[0114] 12 outer body

[0115] 14 Sealing plate (cover)

[0116] 15 injection hole

[0117] 16 Sealing component

[0118] 17 Gas exhaust valve

[0119] 20 wound electrode body

[0120] 22 positive plate

[0121] 23. Positive electrode tab assembly

[0122] 24 negative plate

[0123] 25 negative electrode tab assembly

[0124] 26 Spacers

[0125] 30 Positive terminal

[0126] 40 Negative terminal

[0127] 50 positive electrode collector

[0128] 60 negative electrode collector

[0129] 70 Electrode body holder

[0130] 80, 82, 83 Constraint fixtures

[0131] 100 Non-aqueous electrolyte secondary battery

[0132] 101 Secondary battery assembly

[0133] 180, 280, 380 constraints.

Claims

1. A method for manufacturing a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery comprising: A flat wound electrode body formed by winding a strip-shaped positive electrode plate and a strip-shaped negative electrode plate with a strip-shaped separator interposed therebetween; non-aqueous electrolyte; as well as a battery case for housing the wound electrode body and the non-aqueous electrolyte, in, The negative electrode plate comprises a negative electrode core and a negative electrode active material layer formed on the negative electrode core. The length of the negative electrode active material layer in the winding axis direction of the wound electrode body is at least 20 cm, The method for manufacturing the non-aqueous electrolyte secondary battery comprises the following steps: an assembling step of housing the wound electrode body and the non-aqueous electrolyte in the battery case to construct a secondary battery assembly; The first step is to initially charge the secondary battery assembly so that the depth of charge is 50% or less; and In the second step, after the first step, the temperature of the wound electrode body is lowered to 50° C. or lower, and the secondary battery assembly is maintained at a state where the depth of charge is lower than 50% for at least 72 hours.

2. The manufacturing method according to claim 1, wherein The second step is performed in a state where the secondary battery assembly is restrained in the thickness direction of the wound electrode body.

3. The manufacturing method according to claim 1 or 2, wherein: The battery case includes an outer casing having an opening and a bottom facing the opening, and a sealing plate for sealing the opening. The wound electrode body is arranged in the exterior body with the winding axis being parallel to the bottom portion.

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