Manufacturing method for non-aqueous secondary batteries

Abstract

The present invention provides a method for manufacturing a non-aqueous secondary battery that forms a gap between the outermost negative electrode and the outermost separator of the wound body. [Solution] The method for manufacturing a non-aqueous secondary battery includes a winding step of producing a wound body (electrode body 20) by winding a positive electrode sheet, a negative electrode sheet, and a separator; a pre-compression step of forming a concave curved surface CA with a concave center in the radial direction by compressing the radial center of the wound body (electrode body 20) from both the upper and lower directions; and a compression step of compressing the concave curved surface CA of the pre-compressed wound body (electrode body 20) from both the upper and lower directions with a press head 50. The axial cross section of the pre-compressed wound body (electrode body 20) has a concave curved surface CA formed at the top and bottom, and a convex curved surface CB formed between the concave curved surfaces CA. The axial cross section of the press head 50 has a curve with a radius of curvature larger than the radius of curvature of the curve connecting the central point PA located at the radial center of the concave curved surface CA and the inflection points PB and PC between the concave curved surface CA and the convex curved surface CB.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a non-aqueous secondary battery.

Background Art

[0002] In the method for manufacturing a non-aqueous secondary battery described in Patent Document 1, a winding step of obtaining a cylindrical electrode body by winding a strip-shaped positive electrode, negative electrode, and separator in a stacked state in the thickness direction, and applying a predetermined force to the side surface of the cylindrical electrode body to form a flat electrode body, and a loosening process of loosening the outermost peripheral side of the electrode body by applying a force that loosens in the direction opposite to the winding direction of the electrode body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the method for manufacturing a non-aqueous secondary battery described in Patent Document 1, in order to perform a loosening process for loosening the outermost peripheral side of the electrode body, a gap is also formed between the positive electrode and the negative electrode. As a result, a difference in the distance between the positive electrode and the negative electrode occurs, and there is a risk that the lithium precipitation resistance deteriorates.

Means for Solving the Problems

[0005] A method for manufacturing a non-aqueous secondary battery that solves the above problems is a method for manufacturing a non-aqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte, comprising: a winding step of making a wound body by winding the positive electrode sheet, the negative electrode sheet, and the separator such that a separator is located between the positive electrode sheet and the negative electrode sheet and outside thereof; a pre-compression step of compressing the radial center of the wound body from both above and below to form a concave curved surface in which the radial center is recessed; and a compression step of compressing the pre-compressed concave curved surface of the wound body from both above and below with a press head, wherein the pre-compressed wound body has, in an axial cross-section, the concave curved surface formed vertically and a convex curved surface formed between the concave curved surfaces, and the contact surface of the press head has, in an axial cross-section, a curve with a radius of curvature larger than the radius of curvature of the curve connecting the central point located at the radial center of the concave curved surface and the inflection point of the concave curved surface and the convex curved surface.

[0006] According to the above configuration, when the curved surface of a pre-compressed winding is compressed by a press head having a curve with a radius of curvature larger than the radius of curvature of the curve connecting the central point located at the radial center of the concave surface of the winding body and the inflection point between the concave surface and the convex surface, only the outermost separator in contact with the press head is stretched. As a result, a gap can be formed between the outermost negative electrode and the outermost separator of the winding body while maintaining the distance between the positive and negative electrodes. Therefore, the amount of non-aqueous electrolyte held by the gap increases, improving high-rate performance and suppressing minute short circuits caused by lithium ion consumption at the outermost negative electrode.

[0007] Regarding the manufacturing method of the non-aqueous secondary battery described above, it is preferable that the radial length of the press head is greater than or equal to the length of the straight line connecting the inflection points located at both ends of the concave curved surface. In the above method for manufacturing a non-aqueous secondary battery, it is preferable that the radius of curvature of the axial cross-section of the contact surface of the press head is 1 to 2.2 times the radius of curvature of the curve connecting the inflection points.

[0008] In the above method for manufacturing a non-aqueous secondary battery, it is preferable that the static friction coefficient of the press head with respect to the separator is 0.8 or higher. [Effects of the Invention]

[0009] According to the present invention, a gap can be formed between the outermost negative electrode and the outermost separator of the wound body. [Brief explanation of the drawing]

[0010] [Figure 1] This is a perspective view showing the schematic configuration of a cell battery according to one embodiment. [Figure 2] This is a diagram showing a portion of the electrode body of the same embodiment unfolded. [Figure 3] This is a flowchart showing the method for manufacturing the electrode body according to the same embodiment. [Figure 4] This figure shows the winding process of the electrode body in the same embodiment. [Figure 5] This figure shows the electrode body extraction process in the same embodiment. [Figure 6] This figure shows the preliminary compression process of the electrode body in the same embodiment. [Figure 7] This figure shows the compression process of the electrode body in the same embodiment. [Figure 8] This is an enlarged view of the dashed line portion of the electrode body in the same embodiment shown in Figure 7. [Figure 9] This figure shows a cross-section of the electrode body in the same embodiment. [Figure 10] This figure shows a cross-section of the electrode body of the same embodiment, specifically the 10-10 section in Figure 9. [Figure 11] This is a cross-sectional view illustrating a minute short circuit in a secondary battery where no gap is formed between the outermost negative electrode and the outermost separator. [Figure 12] This table shows examples and comparative examples of non-aqueous secondary batteries. [Modes for carrying out the invention]

[0011] [This Circumstance] Hereinafter, an embodiment of a method for manufacturing a non-aqueous secondary battery will be described with reference to FIGS. 1 to 10. A lithium-ion secondary battery will be described as an example of the non-aqueous secondary battery.

[0012] [Lithium-ion secondary battery 10] As shown in FIG. 1, the lithium-ion secondary battery 10 is a cell battery that is enclosed in a resin or metal case in a state combined with a plurality of lithium-ion secondary batteries 10 to form a battery pack. The battery pack is used in a hybrid vehicle or an electric vehicle.

[0013] The lithium-ion secondary battery 10 includes a battery case 11 and a lid 12. The battery case 11 has a rectangular parallelepiped shape with an opening on the upper side. The lid 12 seals the opening of the battery case 11. The battery case 11 and the lid 12 are made of a metal such as aluminum or an aluminum alloy. The lithium-ion secondary battery 10 forms a sealed battery cell by attaching the lid 12 to the battery case 11.

[0014] Two positive electrode external terminals 13A and a negative electrode external terminal 13B are provided on the lid 12. The positive electrode external terminal 13A and the negative electrode external terminal 13B are used for charging and discharging electric power. Inside the battery case 11, an electrode body 20 is accommodated. The positive electrode current collector portion 20A, which is the end portion on the positive electrode side of the electrode body 20, is electrically connected to the positive electrode external terminal 13A via the positive electrode current collector member 14A. The negative electrode current collector portion 20B, which is the end portion on the negative electrode side of the electrode body 20, is electrically connected to the negative electrode external terminal 13B via the negative electrode current collector member 14B. Also, a non-aqueous electrolyte is injected into the battery case 11 through a liquid injection hole (not shown). Note that the shapes of the positive electrode external terminal 13A and the negative electrode external terminal 13B are not limited to the shapes shown in FIG. 1 and may be any shape.

[0015] [Electrode body 20] As shown in FIG. 2, the electrode body 20 is a flat wound body obtained by winding a laminate in which a long positive electrode sheet 21 and a negative electrode sheet 24 are laminated via a separator 27. The positive electrode sheet 21, the negative electrode sheet 24, and the separator 27 are laminated such that the longitudinal direction of each coincides with the longitudinal direction D1. The laminate before winding is laminated in the order of the positive electrode sheet 21, the separator 27, the negative electrode sheet 24, and the separator 27. The positive electrode sheet 21 and the negative electrode sheet 24 are electrode sheets.

[0016] [Positive electrode sheet 21] The positive electrode sheet 21 includes a positive electrode current collector 22 and a positive electrode composite layer 23. The positive electrode current collector 22 is a foil-shaped positive electrode base material formed in a long shape. The positive electrode composite layer 23 is provided on each of the two opposite surfaces of the positive electrode current collector 22. The positive electrode current collector 22 includes a positive electrode side uncoated portion 22A where the positive electrode current collector 22 is exposed without the formation of the positive electrode composite layer 23 at one end in the width direction D2.

[0017] The positive electrode current collector 22 is made of a metal foil composed of aluminum or an alloy mainly composed of aluminum. The positive electrode current collector 22 functions as a current collector in the positive electrode. The positive electrode side uncoated portion 22A provided in the positive electrode current collector 22 forms a positive electrode side current collecting portion 20A by the opposing surfaces being pressed against each other in the state of the wound body.

[0018] The positive electrode composite layer 23 is a cured body of a liquid positive electrode composite paste. The positive electrode composite paste contains a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. The positive electrode composite layer 23 is formed by drying the positive electrode composite paste and vaporizing the positive electrode solvent. Therefore, the positive electrode composite layer 23 contains a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0019] The positive electrode active material is a lithium-containing composite oxide capable of intercalating and releasing lithium ions, which are charge carriers in the lithium-ion secondary battery 10. The lithium-containing composite oxide is an oxide containing lithium and other metallic elements other than lithium. The other metallic elements other than lithium are, for example, at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained as iron phosphate in the lithium-containing composite oxide.

[0020] For example, lithium-containing composite oxides include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), and lithium manganate (LiMn2O4). Another example is lithium-containing composite oxide, a ternary lithium-containing composite oxide containing nickel, cobalt, and manganese, which is lithium nickel-cobalt-manganate (LiNiCoMnO2). Yet another example is lithium iron phosphate (LiFePO4).

[0021] The positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent. Examples of positive electrode conductive materials include carbon black such as acetylene black and Ketjenblack, carbon fibers such as carbon nanotubes and carbon nanofibers, and graphite. The positive electrode binder is an example of a resin component contained in the positive electrode paste. Examples of positive electrode binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and styrene-butadiene rubber (SBR).

[0022] The positive electrode sheet 21 may have an insulating layer at the boundary between the uncoated portion 22A on the positive electrode side and the positive electrode composite layer 23. The insulating layer contains an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0023] [Negative electrode sheet 24] The negative electrode sheet 24 comprises a negative electrode current collector 25 and a negative electrode composite layer 26. The negative electrode current collector 25 is a foil-shaped negative electrode substrate formed in an elongated shape. The negative electrode composite layer 26 is provided on each of two opposing surfaces of the negative electrode current collector 25. The negative electrode current collector 25 has a negative electrode side unpainted portion 25A at one end in the width direction D2, which is located opposite the positive electrode side unpainted portion 22A, where the negative electrode composite layer 26 is not formed and the negative electrode current collector 25 is exposed.

[0024] The negative electrode current collector 25 is made of metal foil composed of copper or an alloy mainly composed of copper. The negative electrode current collector 25 functions as a current collector at the negative electrode. In the wound state, the unpainted negative electrode side portion 25A has opposing surfaces pressed against each other to form the negative electrode side current collector portion 20B.

[0025] The negative electrode composite layer 26 is a cured body of a liquid negative electrode composite paste. The negative electrode composite paste contains a negative electrode active material, a lithium salt, a negative electrode solvent, a negative electrode thickener, and a negative electrode binder. The negative electrode composite layer 26 is formed when the negative electrode composite paste dries and the negative electrode solvent vaporizes. Therefore, the negative electrode composite layer 26 contains the negative electrode active material, a lithium salt, and further, as additives, a negative electrode thickener and a negative electrode binder. The negative electrode composite layer 26 may further contain additives such as a conductive material.

[0026] The negative electrode active material is a material capable of intercalating and releasing lithium ions. Examples of negative electrode active materials include carbon materials such as graphite, poorly graphitizable carbon, and easily graphitizable carbon. The negative electrode solvent is, for example, water. The lithium salt can be one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, and LiBOB (lithium bisoxalate borate). In this embodiment, LiBOB is used as the lithium salt. As an example of a negative electrode thickener, CMC (carboxymethylcellulose) can be used as a thickener containing a sodium salt. The negative electrode binder can be the same as that used for the positive electrode binder. As an example of a negative electrode binder, SAR (styrene-acrylic acid copolymer) can be used as a binder containing a sodium salt.

[0027] [Separator 27] The separator 27 prevents contact between the positive electrode sheet 21 and the negative electrode sheet 24, and holds the non-aqueous electrolyte between the positive electrode sheet 21 and the negative electrode sheet 24. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte penetrates from the ends in the width direction D2 of the separator 27 toward the center.

[0028] The separator 27 is a nonwoven fabric made of polypropylene or the like. As the separator 27, for example, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, and ion-conductive polymer electrolyte membranes can be used.

[0029] [Nonaqueous electrolyte] A non-aqueous electrolyte is a composition containing a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc., can be used. In this embodiment, ethylene carbonate is used as the non-aqueous solvent. As the supporting salt, one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc., can be used.

[0030] [Manufacturing method] Next, the manufacturing method of the lithium-ion secondary battery 10 will be described with reference to Figures 3 to 10. The manufacturing method of the lithium-ion secondary battery 10 includes a winding step, a extraction step, a pre-compression step, a compression step, a terminal welding step, a liquid injection and sealing step, and an activation step.

[0031] [Winding process] In the winding process of step S1 in Figure 3, a wound body is produced by winding the positive electrode sheet 21, the negative electrode sheet 24, and the separator 27. As shown in Figure 4, in the winding process, the wound body is produced by winding it onto a roll 30. The separator 27 is located between and outside the positive electrode sheet 21 and the negative electrode sheet 24. The wound body becomes the electrode body 20.

[0032] [Sampling process] Next, in step S2 of Figure 3, the winding body (electrode body 20) wound onto the roll 30 is removed from the roll 30. As shown in Figure 5, the electrode body 20 becomes hollow.

[0033] [Pre-compression process] Next, in the preliminary compression step S3 in Figure 3, as shown in Figure 6, the center of the spiral body (electrode body 20) in the radial direction (direction of the left and right arrows in the figure) is compressed from both directions by the chuck 40. The chuck 40 compresses from both directions along the center line L passing through the center of the spiral body (electrode body 20), thereby forming a concave curved surface CA on the spiral body (electrode body 20) with a concave center in the radial direction. The preliminary compressed spiral body (electrode body 20) has, in its axial cross-section, concave curved surfaces CA formed vertically and a convex curved surface CB formed between the concave curved surfaces CA.

[0034] [Compression process] Next, in the compression step S4 in Figure 3, as shown in Figure 7, the center of the concave curved surface CA of the wound body (electrode body 20) is compressed from both above and below by the press head 50. The press head 50 has a symmetrical shape on the center line L passing through the center of the wound body (electrode body 20). The contact surface of the press head 50 has a curve with a radius of curvature that is larger than the radius of curvature of the curve connecting the central point PA, located in the radial center of the concave curved surface CA, and the inflection points PB and PC between the concave curved surface CA and the convex curved surface CB in the axial cross-section. The radial length WP of the press head 50 is greater than or equal to the length WR of the straight line connecting the inflection points PB and PC located at both ends of the concave curved surface CA. It is desirable that the radius of curvature of the axial cross-section of the contact surface of the press head 50 be between 1 and 2.2 times the radius of curvature of the curve connecting the inflection points PB and PC of the wound body (electrode body 20). Specifically, the radius of curvature of the curve connecting the inflection points PB and PC of the wound body (electrode body 20) is 35 mm. The radius of curvature of the press head 50 is preferably between 35 mm and 75 mm. The static friction coefficient of the press head 50 with respect to the separator 27 is preferably 0.8 or higher.

[0035] As shown in Figure 8, the press head 50 compresses the wound body (electrode body 20) in the vertical direction indicated by the dashed line in Figure 8. The press head 50 first makes contact at the inflection point PB(PC). Therefore, the compressive force P is divided into a first compressive force P1 perpendicular to the tangent to the inflection point PB(PC) and a second compressive force P2 horizontal to the tangent to the inflection point PB(PC). As a result, the outermost separator 27 of the wound body (electrode body 20) that the press head 50 contacts is stretched by the second compressive force P2 in the direction horizontal to the tangent to the inflection point PB(PC).

[0036] As shown in Figure 9, when the electrode body 20 is compressed by the press head 50, the outermost separator 27 is stretched, and a gap S is formed between the outermost separator 27 and the outermost negative electrode sheet 24. At this time, the distance between the positive electrode sheet 21 and the negative electrode sheet 24 does not change, and only the outermost separator 27 is stretched.

[0037] [Terminal welding process] Next, in the terminal welding process of step S5 in Figure 3, the positive electrode external terminal 13A is joined to the positive electrode side current collector portion 20A, which is the positive electrode end in the axial direction of the electrode body 20, via the positive electrode side current collector member 14A. The negative electrode external terminal 13B is joined to the negative electrode side current collector portion 20B, which is the negative electrode end in the axial direction of the electrode body 20, via the negative electrode side current collector member 14B. These are then inserted into the battery case 11, and the cover 12 is attached, for example, by laser welding, to close the opening of the battery case 11.

[0038] [Liquid injection / sealing process] Next, in the liquid injection and sealing process of step S6 in Figure 3, a non-aqueous electrolyte is injected through an inlet (not shown) formed in the lid 12, and a cap (not shown) is attached to the inlet, for example by laser welding, to seal it.

[0039] As shown in Figure 10, when the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the edges of the separator 27 towards the center. A large amount of non-aqueous electrolyte is present in the gap S between the outermost negative electrode sheet 24 and the outermost separator 27. In other words, the amount of non-aqueous electrolyte held by the gap S increases. As a result, the high-rate performance of the lithium-ion secondary battery 10 is improved.

[0040] [Activation process] Next, in the activation process of step S7 in Figure 3, the lithium-ion secondary battery 10 is initially charged, stored at a high temperature for a certain period of time, and subjected to a high-temperature aging treatment to dissolve metallic foreign matter and stabilize the SEI (Solid Electrolyte Interphase) coating.

[0041] Incidentally, when a high-temperature aging treatment is performed on a lithium-ion secondary battery in which oxygen contained in the space inside the battery case 11 is easily brought into contact with the negative electrode composite layer 26 of the outermost negative electrode sheet 24, a minute short circuit may occur. The mechanism of such a minute short circuit will be explained with reference to Figure 11. The lithium-ion secondary battery shown in Figure 11 is the same as the lithium-ion secondary battery 10 of this embodiment, except that there is no gap formed between the outermost separator 27 and the outermost negative electrode sheet 24.

[0042] As shown in Figure 11, in the lithium-ion secondary battery, the separator 27 constitutes the outer surface of the outermost wound body (electrode body 20), and the negative electrode sheet 24 is arranged on the inner layer side of the outermost separator 27. Therefore, the region constituting the outermost edge of the positive electrode sheet 21 contributes to the battery reaction of the lithium-ion secondary battery, thus enabling a high energy density. On the other hand, if oxygen contained in the space inside the battery case 11 permeates through the separator 27, it is easily brought into contact with the outermost negative electrode composite layer 26.

[0043] In high-temperature aging treatment, lithium-ion secondary batteries with a high State of Charge (SOC) (e.g., 3.97V) are used. In lithium-ion secondary batteries with a high SOC, in the inner negative electrode composite layer 26 that constitutes the outermost periphery of the negative electrode sheet 24, a large number of lithium ions are present in the region facing the positive electrode composite layer 23. On the other hand, it is thought that there are almost no lithium ions in the region not facing the positive electrode composite layer 23. Furthermore, it is thought that there are almost no lithium ions in the outer negative electrode composite layer 26 that constitutes the outermost periphery.

[0044] As shown in Figure 11, when a lithium-ion secondary battery with a high SOC is subjected to high-temperature aging treatment, lithium ions 60 move from the positive electrode composite layer 23, which constitutes the outermost periphery of the positive electrode sheet 21, to the outermost periphery of the negative electrode sheet 24.

[0045] At the outermost periphery, in the negative electrode composite layer 26 on the inner layer side, due to the difference in lithium ion concentration, lithium ions 60 present in the region facing the positive electrode composite layer 23 move to the non-facing region that does not face the positive electrode composite layer 23 (arrow DA direction).

[0046] Lithium ions 60 that have moved to the non-facing region of the inner negative electrode composite layer 26 move to the outermost negative electrode composite layer 26 via the non-aqueous electrolyte, passing along the side of the negative electrode sheet 24 (arrow DB direction), due to the difference in lithium ion concentration.

[0047] The outermost negative electrode composite layer 26 comes into contact with oxygen in the battery case 11 when oxygen contained in the battery case 11 permeates through the separator 27. As a result, lithium ions 60 that have moved to the outermost negative electrode composite layer 26 react with oxygen, forming a film 61 on the surface of the negative electrode composite layer 26. In other words, lithium ions 60 that have moved to the outermost negative electrode composite layer 26 are consumed by reacting with oxygen. Consequently, in the inner negative electrode composite layer 26, the movement of lithium ions 60 to the non-opposing region is accelerated due to the consumption of lithium ions 60 by the formation of the film 61.

[0048] As lithium ions 60 move in this manner, the potential of the area adjacent to the non-opposing area in the opposing region of the inner layer negative electrode composite material layer 26 rises locally. Furthermore, due to local potential equalization, the potential of the area adjacent to the non-opposing area of ​​the negative electrode composite material layer 26 also rises in the opposing region of the outermost layer positive electrode composite material layer 23. In other words, the outermost periphery of the positive electrode sheet 21 becomes locally overvoltage (for example, 4.3V or higher).

[0049] When an overvoltage occurs in the positive electrode sheet 21, the crystalline structure of the positive electrode composite layer 23 collapses, making it easier for the metal component 62 contained in the positive electrode composite layer 23 to dissolve into the non-aqueous electrolyte. The metal component 62 dissolved in the non-aqueous electrolyte tends to precipitate on the surface of the opposing portion of the negative electrode composite layer 26 on the inner layer side. As a result, metal deposits 63 that electrically connect the positive electrode sheet 21 and the negative electrode sheet 24 are formed on the surface of the negative electrode composite layer 26 on the inner layer side. Consequently, a minute short circuit occurs.

[0050] In this embodiment, a gap S is formed between the outermost separator 27 and the outermost negative electrode sheet 24. Therefore, the consumption of lithium ions in the outermost negative electrode sheet 24 is suppressed, and minute short circuits due to the dissolution of the positive electrode can be suppressed.

[0051] [Effects of this embodiment] Next, the effects of this embodiment will be described. (1) When the curved surface of the pre-compressed wound body (electrode body 20) is compressed by a press head 50 having a curve with a radius of curvature larger than the radius of curvature of the curve connecting the central point PA located at the radial center of the concave curved surface CA of the wound body (electrode body 20) and the inflection points PB and PC between the concave curved surface CA and the convex curved surface CB, only the outermost separator 27 in contact with the press head 50 is stretched. As a result, a gap S can be formed between the outermost negative electrode sheet 24 and the outermost separator 27 of the wound body (electrode body 20) while maintaining the distance between the positive electrode and the negative electrode. Therefore, the amount of non-aqueous electrolyte held by the gap S increases, improving high-rate performance and suppressing minute short circuits caused by lithium ion consumption at the outermost negative electrode.

[0052] (2) The radial length WP of the press head 50 is greater than or equal to the length WR of the straight line connecting the inflection points PB and PC of the wound body (electrode body 20). Therefore, the press head 50 can always come into contact with the inflection points PB and PC of the wound body (electrode body 20), stretching the outermost separator 27 while compressing the wound body (electrode body 20).

[0053] (3) The radius of curvature of the axial cross-section of the contact surface of the press head 50 is between 1 and 2.2 times the radius of curvature of the curve connecting the inflection points PB and PC of the wound body (electrode body 20). Therefore, the outermost separator 27 of the wound body (electrode body 20) that is in contact with the press head 50 can be stretched further.

[0054] (4) The static friction coefficient between the press head 50 and the separator is 0.8 or higher. Therefore, the outermost separator 27 of the wound body (electrode body 20) that is in contact with the press head 50 can be stretched further.

[0055] [Other embodiments] The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0056] In the above embodiment, the radial length WP of the press head 50 was set to be greater than or equal to the length WR of the straight line connecting the inflection points PB and PC. However, the radial length WP of the press head 50 may be shorter than the length WR of the straight line connecting the inflection points PB and PC. Even with such a configuration, the contact portion of the outermost separator 27 that comes into contact with the press head 50 will be stretched.

[0057] The lithium-ion secondary battery 10 may be installed in automated transport machines, special vehicles for cargo handling, electric vehicles, hybrid vehicles, etc., as well as in computers and other electronic devices, or it may constitute a system other than those mentioned above. For example, it may be installed in mobile objects such as ships and aircraft, or it may be part of a power supply system that supplies electricity from a power plant to buildings and homes where the secondary battery is installed via a substation or the like.

[0058] [Examples] Next, with reference to Figure 12, examples and comparative examples of lithium-ion secondary batteries 10 will be described. Note that these examples and comparative examples do not limit the manufacturing method of non-aqueous secondary batteries.

[0059] In the following, as shown in Figure 12, lithium-ion secondary batteries 10 of examples and comparative examples were prepared by changing the combination of the radius of curvature of the press head 50 and the static friction coefficient between the press head 50 and the separator 27. The radius of curvature of the press head 50 is the ratio to the radius of curvature of the curve connecting the inflection points PB and PC of the wound body (electrode body 20). Then, for each example and comparative example, the positive electrode deposition on the negative electrode sheet 24 and the high-rate performance were evaluated.

[0060] [Comparative Example 1] The radius of curvature of the press head 50 was set to 5.7 times, and the coefficient of static friction between the press head 50 and the separator 27 was set to 0.6. If the radius of curvature of the winding body (electrode body 20) is, for example, 35 [mm], then the radius of curvature of the press head 50 is 200 [mm].

[0061] [Comparative Example 2] The radius of curvature of the press head 50 was set to 5.7 times, and the coefficient of static friction between the press head 50 and the separator 27 was set to 0.8. If the radius of curvature of the wound body (electrode body 20) is, for example, 35 [mm], then the radius of curvature of the press head 50 is 200 [mm].

[0062] [Comparative Example 3] The radius of curvature of the press head 50 was set to 1.7 times, and the coefficient of static friction between the press head 50 and the separator 27 was set to 0.6. If the radius of curvature of the winding body (electrode body 20) is, for example, 35 [mm], then the radius of curvature of the press head 50 is 60 [mm].

[0063] [Comparative Example 4] The radius of curvature of the press head 50 was set to 0.9 times, and the coefficient of static friction between the press head 50 and the separator 27 was set to 0.8. If the radius of curvature of the winding body (electrode body 20) is, for example, 35 [mm], then the radius of curvature of the press head 50 is 30 [mm].

[0064] [Example 1] The radius of curvature of the press head 50 was set to 1.7 times, and the coefficient of static friction between the press head 50 and the separator 27 was set to 0.8. If the radius of curvature of the winding body (electrode body 20) is, for example, 35 [mm], then the radius of curvature of the press head 50 is 60 [mm].

[0065] [Example 2] The radius of curvature of the press head 50 was set to 1.4 times, and the coefficient of static friction between the press head 50 and the separator 27 was set to 0.9. If the radius of curvature of the winding body (electrode body 20) is, for example, 35 [mm], then the radius of curvature of the press head 50 is 50 [mm].

[0066] [evaluation] For each of the above examples and comparative examples, the deposition of positive electrode on the negative electrode sheet 24 and the high-rate performance were evaluated. High-rate performance is the reciprocal of the increase rate [%] of the internal resistance (DC-IR) after performing a charge-discharge cycle test in which charge and discharge are repeated for a predetermined time at a high current (tens of amperes or more), and is an indexed value with Comparative Example 1 set to 100%.

[0067] In Example 1, where the press head 50, having a radius of curvature of 1.7 times and a static friction coefficient with the separator 27 of 0.8, was compressed, there was no positive electrode deposition on the negative electrode sheet 24, and the high-rate performance was 105. Therefore, since the radius of curvature of the press head 50 is between 1 and 2.2 times, and the static friction coefficient with the separator 27 is 0.8 or higher, the desired effect can be obtained.

[0068] In Example 2, which was compressed with a press head 50 having a radius of curvature of 1.4 times and a static friction coefficient with the separator 27 of 0.9, there was no positive electrode deposition on the negative electrode sheet 24, and the high-rate performance was 110. Therefore, since the radius of curvature of the press head 50 is between 1 and 2.2 times, and the static friction coefficient with the separator 27 is 0.8 or higher, the desired effect can be obtained.

[0069] Comparative Example 1, compressed by a press head 50 with a radius of curvature of 5.7 times and a static friction coefficient with the separator 27 of 0.6, exhibits significant positive electrode deposition on the negative electrode sheet 24 and a high-rate performance of 100. Therefore, if the static friction coefficient is less than 0.8 and the radius of curvature of the press head 50 is greater than 2.2 times, positive electrode deposition on the negative electrode sheet 24 cannot be suppressed.

[0070] Comparative Example 2, compressed with a press head 50 having a radius of curvature of 5.7 times and a static friction coefficient with the separator 27 of 0.8, exhibits significant positive electrode deposition on the negative electrode sheet 24, resulting in a high-rate performance of 100. Therefore, increasing the radius of curvature of the press head 50 beyond 2.2 times makes it impossible to suppress positive electrode deposition on the negative electrode sheet 24.

[0071] Comparative Example 3, compressed with a press head 50 having a radius of curvature of 1.7 times and a static friction coefficient with the separator 27 of 0.6, exhibits small positive electrode deposition on the negative electrode sheet 24 and a high-rate performance of 100. Therefore, while setting the static friction coefficient to less than 0.8 can reduce positive electrode deposition on the negative electrode sheet 24, it cannot completely suppress it.

[0072] Comparative Example 4, compressed with a press head 50 having a radius of curvature of 0.9 times and a static friction coefficient with the separator 27 of 0.8, exhibits significant positive electrode deposition on the negative electrode sheet 24 and a high-rate performance of 100. Therefore, if the radius of curvature of the press head 50 is less than 1 times, positive electrode deposition on the negative electrode sheet 24 cannot be suppressed.

[0073] Examples 1 and 2, in which the radius of curvature of the press head 50 is between 1 and 2.2 times, and the static friction coefficient with the separator 27 is 0.8 or higher, show no positive electrode deposition on the negative electrode sheet 24 and exhibit good high-rate performance. Excellent results were obtained in Examples 1 and 2. [Explanation of Symbols]

[0074] L…Center line P... Compression force PA…center point PB…Inflection point PC…Inflection point P1...First compression force P2...Second compression force S... Gap WP... Radial length of the press head WR…The length of the straight line between the inflection points of the coiled body. 10…Lithium-ion rechargeable battery 11…Battery case 12... Lid 13A…Positive external terminal 13B…Negative external terminal 14A... Positive electrode current collector 14B... Negative electrode current collector 20...Electrode body 20A... Positive electrode current collector 20B... Negative electrode current collector 21…Positive electrode sheet 22...Positive electrode current collector 22A...Unpainted area on the positive electrode side 23…Positive electrode composite layer 24... Negative electrode sheet 25...Negative electrode current collector 25A...Unpainted area on the negative electrode side 26…Negative electrode composite material layer 27... Separator 30... rolls 40... Chuck 50…Press head

Claims

1. A method for manufacturing a non-aqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte, A winding step to produce a winding body by winding the positive electrode sheet, the negative electrode sheet, and the separator such that a separator is positioned between the positive electrode sheet and the negative electrode sheet and outside thereof, A preliminary compression step is performed to form a concave curved surface in which the radial center of the coiled body is recessed by compressing it from both the upper and lower directions, The process includes a compression step in which the concave curved surface of the pre-compressed coiled body is compressed from both above and below using a press head, The pre-compressed coiled body has, in its axial cross-section, the concave curved surfaces formed vertically and the convex curved surface formed between the concave curved surfaces, The contact surface of the press head has a curve with a radius of curvature greater than the radius of curvature of the curve connecting the central point located at the radial center of the concave surface and the inflection point of the concave surface and the convex surface in the axial cross-section. A method for manufacturing a non-aqueous secondary battery.

2. The radial length of the press head is greater than or equal to the length of the straight line connecting the inflection points located at both ends of the concave surface. A method for manufacturing a non-aqueous secondary battery according to claim 1.

3. The radius of curvature of the axial cross-section of the contact surface of the press head is between 1 and 2.2 times the radius of curvature of the curve connecting the inflection points. A method for manufacturing a non-aqueous secondary battery according to claim 1 or 2.

4. The press head has a static friction coefficient of 0.8 or higher with respect to the separator. A method for manufacturing a non-aqueous secondary battery according to claim 3.

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