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

Abstract

In an electrode body (10) of a lithium ion secondary battery, winding is performed around a winding axis, and the electrode body (10) is formed in a flat shape. In a cross section of the electrode body (10) orthogonal to the winding axis, a flat portion (F) is provided which is flatly pressed in a planar shape, and a pair of curved portions (R) are formed by bending both ends thereof in a semicircular cylindrical shape. A combined resistance of a reaction resistance due to an inter-electrode distance and a solution resistance due to a permeability of a separator from a center (C) of the curved portion (R) to a position (D) of an outer surface of the curved portion (R) in a length direction is set to be equal to a combined resistance of a reaction resistance due to an inter-electrode distance and a solution resistance due to a permeability of a separator from a straight line connecting the center (C) of the curved portion (R) to a position (B) of an outer surface of the flat portion (F) in a thickness direction. In the electrode body (10), there is no unevenness of resistance, and deposition of metal (Li) due to unevenness of current density is suppressed.

Description

Technical Field

[0001] This invention relates to a method for manufacturing non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries. More specifically, it relates to a method for manufacturing non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries in which metals are less likely to deposit. Background Technology

[0002] In recent years, non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, have been used as power sources for electric vehicles and other applications. Therefore, they are constructed by connecting a large number of cell units in series or parallel to supply high voltage / high current. Consequently, wound-type batteries, which are formed by winding electrode plates, are used to compactly stack a large number of cell units. Furthermore, to improve cooling efficiency and ensure the electrode plates are tightly sealed together, cell units using flat, wound electrode bodies are becoming increasingly common.

[0003] Such a flat electrode body has a flat portion formed by a pressing process, and a curved portion for folding back at the end of the flat portion. In such an electrode body, since the flat portion and the curved portion have different structures, various problems arise due to the differences in structure.

[0004] For example, the non-aqueous electrolyte secondary battery disclosed in Japanese Patent Application Publication No. 2020-57458 has the following configuration. The negative electrode composite material layer includes a first region located in the flat portion of the electrode body and a second region located in a pair of curved portions. The ratio (B / A) of the filling density (B) of the second region to the filling density (A) of the first region is 0.75 or more and 0.95 or less. Furthermore, in a cross-section perpendicular to the axial center of the electrode body, the ratio (SB / SA) of the cross-sectional area of ​​the pair of curved portions to the cross-sectional area (SA) of the flat portion is 0.28 or more and 0.32 or less.

[0005] With this configuration, the capacity retention and output are high, and it is not easy to cause lithium deposition on the negative electrode surface.

[0006] Furthermore, in the invention described in Japanese Patent Application Publication No. 2018-32575, the thickness from the inner bending vertex V to the outer bending vertex P in the cross-section of the wound electrode body is defined as the center thickness D of the bent R portion. The thickness from the inner bending vertex V along the R / F portion boundary line W to the outer surface S of the wound electrode body is defined as the boundary thickness B of the bent R portion. In this case, the D / B ratio is assumed to be 1.01 or more and 1.07 or less.

[0007] This configuration enables high capacity retention and suppression of resistance rise, resulting in high durability. Summary of the Invention

[0008] However, when only the density of the flat and curved portions is changed, as in Japanese Patent Application Publication No. 2020-57458, or the thickness of the flat and curved portions is changed, as in Japanese Patent Application Publication No. 2018-32575, problems arise such as the inhomogeneity of current density in the electrode body and the inability to sufficiently suppress the deposition of metallic lithium.

[0009] The problem to be solved by the non-aqueous electrolyte secondary battery and the manufacturing method of the non-aqueous electrolyte secondary battery disclosed herein is to suppress the precipitation of metallic lithium.

[0010] This disclosure discloses a method for manufacturing a non-aqueous electrolyte secondary battery, comprising an electrode body, a non-aqueous electrolyte, and a cuboid battery casing housing the electrode body and the non-aqueous electrolyte. The method is characterized by comprising the following steps: a lamination step, wherein a positive electrode comprising a positive electrode substrate and a positive electrode composite material layer and a negative electrode comprising a negative electrode substrate and a negative electrode composite material layer are laminated together with a separator made of porous resin to form an electrode body; and a winding step, wherein the laminated electrode body is wound around a winding axis. The process involves a central winding process; a flat pressing process, in which the electrode body, after being wound in the above winding process, is pressed from a direction orthogonal to the winding axis to form a planar flat portion F and a pair of semi-cylindrical curved portions R formed at both ends of the flat portion F; and a recovery process, in which the elastic deformation in the above flat pressing process is restored, wherein the width direction is defined as the direction parallel to the winding axis of the electrode body, the thickness direction is defined as the direction orthogonal to the winding axis of the electrode body and orthogonal to the surface of the flat portion F, and the direction orthogonal to the width direction and the thickness direction are defined as... When the point located at the central axis of the semi-cylindrical curved portion R is taken as the center C of the curved portion R along the length direction, the portion spanning from the center C of the curved portion R to the outer surface of the curved portion R along the length direction at the completion of the restoration process is taken as portion D; the portion spanning from the straight line connecting the centers C of the pair of curved portions R to the outer surface of the flat portion F along the thickness direction at the completion of the restoration process is taken as portion B; and the portion spanning from one outer surface of the flat portion F along the thickness direction of the electrode body at the completion of the restoration process is taken as portion B. When the distance from one surface to the other outer surface is taken as the thickness dimension B′, the lamination thickness when the above-mentioned electrode body is completed is taken as the electrode body lamination thickness E, and the distance from one outer surface to the other outer surface of the above-mentioned flat portion F in the thickness direction when the above-mentioned electrode body is completed is taken as the thickness dimension B″, the thickness of part D / thickness of part B, the air permeability of part D / air permeability of part B, the thickness dimension B′ / (2×electrode body lamination thickness E), and the thickness dimension B′ / thickness dimension B″ are respectively adjusted to a number of preset ranges.

[0011] In the above-described method for manufacturing a non-aqueous electrolyte secondary battery, the ranges of the thickness of part D / thickness of part B, the air permeability of part D / air permeability of part B, the thickness dimension B′ / (2×electrode body layer thickness E), and the thickness dimension B′ / thickness dimension B″ are set such that the combined resistance Rdc of part D caused by the inter-electrode distance and the solution resistance Rd2 caused by the air permeability of the separator is equal to the combined resistance Rbc of part B caused by the inter-electrode distance and the solution resistance Rb2 caused by the air permeability of the separator.

[0012] In the above-mentioned manufacturing method of non-aqueous electrolyte secondary battery, the range of the thickness of part D / thickness of part B can be set to 1.01 ≤ thickness of part D / thickness of part B ≤ 1.10, the range of the air permeability of part D / air permeability of part B can be set to 0.90 ≤ air permeability of part D / air permeability of part B ≤ 0.99, the range of the thickness dimension B′ / (2×electrode body layer thickness E) can be set to 0.98 ≤ B′ / 2E ≤ 1.00, and the range of the thickness dimension B′ / thickness dimension B″ can be set to 0.88 ≤ B′ / B″ ≤ 0.98.

[0013] The above-mentioned non-aqueous electrolyte secondary batteries can be appropriately applied when they are lithium-ion secondary batteries.

[0014] Furthermore, other aspects of the non-aqueous electrolyte secondary battery disclosed herein include an electrode body, a non-aqueous electrolyte, and a cuboid battery case housing the electrode body and the non-aqueous electrolyte. The non-aqueous electrolyte secondary battery is characterized in that, in the electrode body, a positive electrode comprising a positive electrode substrate and a positive electrode composite material layer, and a negative electrode comprising a negative electrode substrate and a negative electrode composite material layer, are separated by a separator layer made of porous resin, and are wound around a winding axis to form a flat shape. The electrode body has a flat, flat portion F pressed flat in a cross-section orthogonal to the winding axis, and a pair of semi-cylindrical curved portions R formed by bending towards both ends of the flat portion F. The width direction is parallel to the axis of winding the electrode body, and the width direction is orthogonal to the winding axis of the electrode body and perpendicular to the flat portion. When the direction orthogonal to the surface of F is taken as the thickness direction, the direction orthogonal to the width and thickness directions is taken as the length direction, and the point located at the central axis of the semi-cylindrical curved portion R is taken as the center C of the curved portion R, when the portion spanning from the center C of the curved portion R to the outer surface of the curved portion R in the length direction is taken as portion D, and the portion spanning from the straight line connecting the centers C of the pair of curved portions to the outer surface of the flat portion F in the thickness direction is taken as portion B, the combined resistance Rdc of the reaction resistance Rd1 caused by the inter-electrode distance and the solution resistance Rd2 caused by the permeability of the spacer in portion D is set to be equal to the combined resistance Rbc of the reaction resistance Rb1 caused by the inter-electrode distance and the solution resistance Rb2 caused by the permeability of the spacer in portion B.

[0015] The above-mentioned non-aqueous electrolyte secondary batteries can be appropriately applied when they are lithium-ion secondary batteries.

[0016] The effects of the invention

[0017] The manufacturing method of the non-aqueous electrolyte secondary battery according to the present invention can suppress the deposition of metallic lithium. Attached Figure Description

[0018] Figure 1 This is a 3D view of lithium-ion secondary battery 1.

[0019] Figure 2 This is a schematic diagram showing the structure of the laminated body of the electrode body 10 of the lithium-ion secondary battery 1.

[0020] Figure 3 This is a perspective view showing the end of the wound electrode body 10 on the negative electrode side in the width direction.

[0021] Figure 4 This is a schematic diagram showing the flat portion F and the curved portion R as viewed from the width direction W.

[0022] Figure 5This is a diagram showing the portions of the current collector 10 at various dimensions as viewed from the width direction W.

[0023] Figure 6 This is a flowchart illustrating the manufacturing process of the lithium-ion secondary battery 1 according to this embodiment.

[0024] Figure 7(a) is a schematic diagram of the electrode body after the winding process (S3) is completed, (b) is a schematic diagram of the electrode body in the flat pressing process (S4) is completed, and (c) is a schematic diagram of the electrode body in the recovery process (S5).

[0025] Figure 8 This is a table showing the "D / B ratio", "B part (part B) / D part (part D) air permeability ratio", and "B′(B″) / (2×electrode body layer thickness E) ratio" in the recovery process (S5) shortly after the winding process (S3) and the flat pressing process (S4).

[0026] Figure 9 This is a table showing the results of Experiment Example 1.

[0027] Figure 10 This is a table showing the results of Experiment Example 2.

[0028] Figure 11 This is a table showing the results of Experiment Example 3. Detailed Implementation

[0029] Reference Figures 1-11 The manufacturing method of the non-aqueous electrolyte secondary battery of the present invention will be described using the manufacturing method of lithium-ion secondary battery 1 as an example.

[0030] (Summary of this implementation method)

[0031] <Principle of this implementation method>

[0032] This embodiment can effectively suppress the precipitation of metallic Li in lithium-ion secondary batteries. In lithium-ion secondary battery 1, one of the reasons for Li precipitation can be cited as... Figure 4 The uneven current density between the positive electrode 100 and the negative electrode 110 in the electrode body 10 shown. As described above, in the lithium-ion secondary battery 1 for automotive use, a wound-type battery formed by winding the electrode plates is used. In addition, in order to improve compactness and cooling efficiency, flat wound-type cell batteries are often used.

[0033] Such a flat electrode has a flat portion F formed by a flattening process, and a bent portion R for folding back at the end of the flat portion F. In such an electrode, because the flat portion F and the bent portion R have different structures, the resistance values ​​will be different due to the difference in structure, which can easily lead to uneven current density.

[0034] However, simply changing the density of the flat portion F and the curved portion R, as in Japanese Patent Application Publication No. 2020-57458, or changing the thickness of the flat portion F and the curved portion R, as in Japanese Patent Application Publication No. 2018-32575, cannot sufficiently suppress the deposition of metallic lithium. Therefore, the inventors aim to fundamentally make the combined resistance of the flat portion F and the combined resistance of the curved portion R uniform.

[0035] According to the inventor's analysis, reactive resistance is one of the many factors determining the combined resistance of the flat portion F and the combined resistance of the curved portion R. Reactive resistance varies with the inter-electrode distance. Through the flattening pressing process, the inter-electrode distance of the flat portion F is closer than that of the curved portion R, thus reducing the reactive resistance caused by the inter-electrode distance of the flat portion F. In the flat, wound lithium-ion secondary battery 1, due to this flattening pressing process, the difference in reactive resistance is not easily zero. Furthermore, even if the reactive resistances depending on the inter-electrode distance are equal, the combined resistance of the negative electrode plate 100 and the positive electrode plate 110 is not zero.

[0036] Therefore, as another factor determining the combined resistance of the flat portion F and the curved portion R, the inventors focused on the solution resistance. Furthermore, they considered that even with the same electrolyte, the solution resistance is affected by the permeability of the spacer 120. The spacer 120 is a porous resin sheet with fine openings, and the resistance between the electrodes varies depending on the inner diameter of these openings. Low permeability increases the solution resistance, while high permeability decreases it. However, the flat, wound electrode body 10 uses a continuous strip-shaped spacer 120, thus the flat portion F and the curved portion R have different permeabilities.

[0037] Therefore, the inventors have developed the following configuration: by using a strip spacer 120 of uniform material while changing the air permeability of the flat portion F and the curved portion R, the solution resistance is adjusted so that the combined resistance of the flat portion F is equal to the combined resistance of the curved portion R.

[0038] Specifically, the inventors discovered that when the separator 120 is temporarily pressed, its air permeability changes even after its thickness is restored. This led to the discovery of a method for manufacturing a lithium-ion secondary battery 1 in which the flat portion F and the curved portion R have different air permeabilities.

[0039] <Basic Structure of a Lithium-ion Secondary Battery>

[0040] First, a brief description will be given of the structure of the lithium-ion secondary battery 1, which is the premise of this embodiment.

[0041] Figure 1 This is a 3D diagram of lithium-ion secondary battery 1. (See diagram below.) Figure 1As shown, the lithium-ion secondary battery 1 is configured as a single-cell battery. The lithium-ion secondary battery 1 has a rectangular battery case 11 with an opening on its upper side. The battery case 11 has a cover 12 that seals the battery case 11. The electrode body 10 is housed inside the battery case 11. A non-aqueous electrolyte 17 is injected into the battery case 11 through an injection hole (not shown). The battery case 11 and the cover 12 are made of a metal such as aluminum alloy. In the lithium-ion secondary battery, a sealed battery cell is formed by mounting the cover 12 to the battery case 11. Furthermore, the lithium-ion secondary battery has a negative external terminal 14 and a positive external terminal 16 on the cover 12 for charging and discharging electricity.

[0042] <Electrode 10>

[0043] Figure 2 This is a schematic diagram showing the structure of the laminated electrode body 10 of the lithium-ion secondary battery 1. (See diagram below.) Figure 2 As shown, the electrode body 10 of the lithium-ion secondary battery 1 includes a negative electrode plate 100, a positive electrode plate 110, and a separator 120. The negative electrode plate 100 has a negative electrode composite material layer 102 on both sides of the negative electrode substrate 101. The positive electrode plate 110 has a positive electrode composite material layer 112 on both sides of the positive electrode substrate 111. The negative electrode plate 100 and the positive electrode plate 110 are overlapped and laminated with the separator 120 in between to form a laminate. This laminate is wound along the length direction with a winding axis as the center and shaped into a flat shape to form the electrode body 10.

[0044] The negative electrode connection portion 103 functions as a current collector for drawing electricity from the negative electrode composite material layer 102 of the negative electrode plate 100. The positive electrode connection portion 113 functions as a current collector for drawing electricity from the positive electrode composite material layer 112 of the positive electrode plate 110.

[0045] <End configuration of electrode 10>

[0046] Figure 3 This is a perspective view showing the negative electrode side end of the wound electrode body 10 in the width direction. The electrode body 10 is wound around the portion supporting the center CC with the winding axis AX as the center. Figure 6 Next, from the thickness direction T, which is orthogonal to the width direction W, a flattening process is performed using a pair of opposing presses 2 (see Figure 7(b)). Figure 6 S4) The shape is designed to be flattened at the ends when viewed from the width direction W, such as a flattened shape like a racing track. Then, as... Figure 1 As shown, the flat electrode 10 is housed in the battery casing 11, as... Figure 2As shown, the negative current collector 13 is welded to the negative connection portion 103. The positive current collector 15 is welded to the positive connection portion 113. Methods for welding the connection portion to the current collector include, for example, ultrasonic welding, resistance welding, and electric welding. Then, the negative external terminal 14 is connected to the negative current collector 13 through the cover 12, and the positive external terminal 16 is connected to the positive current collector 15.

[0047] Here, the direction of the electrode body 10 parallel to the winding axis AX is referred to as the "width direction W". Furthermore, the direction of the electrode body 10 orthogonal to the winding axis AX and to the surface of the flat portion F is referred to as the "thickness direction T". Additionally, the direction orthogonal to both the width direction W and the thickness direction T is referred to as the "length direction L".

[0048] <F flat section and R curved section>

[0049] Figure 4 This is a schematic diagram showing the flat portion F and the curved portion R of the electrode body 10 as viewed from the width direction W. The central portion of the flattened electrode body 10 is straight, and the planar "flat portion F" is formed by the negative electrode plate 100, the positive electrode plate 110 and the spacer 120.

[0050] In addition, at the upper and lower ends of the flat portion F, the electrode body 10, which is composed of a laminated negative electrode plate 100, a positive electrode plate 110, and a separator 120, is bent into a semi-cylindrical shape to form a bent portion R.

[0051] The curved section R, when viewed from the width direction W, is approximately a concentric semicircle. That is, the laminated negative electrode plate 100, positive electrode plate 110, and separator 120 of the curved section R, when viewed from the width direction W, are approximately concentric semicircles. The position of the center of these semicircles is designated as "center C". This center C can be imagined as a continuous straight line along the width direction W. Alternatively, "center C" can also be described as the midpoint of the boundary line between the flat section F and the curved section R in the length direction L.

[0052] <Dimensions of current collector 10>

[0053] Figure 5 This is a diagram showing the various dimensions of the current collector 10 as viewed from the width direction W. (See diagram below.) Figure 5 As shown, the portion spanning the bending portion R from the center C to the outer surface of the bending portion R in the length direction L when the restoration process (see Figure 7: S5) is completed is designated as portion D.

[0054] Furthermore, the portion spanning the straight line from the center C connecting the pair of curved portions R to the outer surface of the flat portion F in the thickness direction when the restoration process (S5) is completed is designated as portion B. Here, regarding the restoration process (S5), although the details are described below, the electrode body 10, which was deformed in the flat pressing process (S4), is restored by repulsion based on elastic force, thus constituting a dimensionally stable state as a product.

[0055] Furthermore, the distance from one outer surface to the other outer surface of the flat portion F in the thickness direction T of the electrode body 10 at the time of completion of the restoration process (S5) is taken as the thickness dimension B′. That is, the thickness dimension B′ is approximately twice the length of the portion B.

[0056] The thickness of the electrode body 10 at the completion of the winding process (S3), i.e., the thickness of the laminate at the completion of the winding process (S3) of the electrode body 10 (laminar thickness), is defined as the electrode body lamination thickness E (see Figure 7(a)). Here, although the details are described below, the lamination process (S2) is a process of laminating the negative electrode plate 100 and the positive electrode plate 110 with the separator 120 in between. In addition, the winding process (S3) is a process of further laminating the laminated strip-shaped negative electrode plate 100, positive electrode plate 110, and separator 120 (laminar body) into a ring shape by winding the portion supporting the center CC with the winding axis AX as the center. The thickness at the completion of the winding process (S3) is the original thickness of the negative electrode plate 100, positive electrode plate 110, and separator 120 before the flat pressing process (S4) when no force is applied. That is, the thickness of the laminated negative electrode plate 100, positive electrode plate 110, and separator 120 when the winding process (S3) is completed is the original thickness of the negative electrode plate 100, positive electrode plate 110, and separator 120 before the flat pressing process (S4) when no force is applied.

[0057] The distance from one outer surface of the flat portion F in the thickness direction of the electrode body 10 to the other outer surface when the flat pressing process (S4) of the electrode body 10 is completed is taken as the thickness dimension B″ (see Figure 7(b)).

[0058] <Negative electrode plate 100>

[0059] A negative electrode plate 100 is formed by forming negative electrode composite material layers 102 on both sides of a negative electrode substrate 101. In this embodiment, the negative electrode substrate 101 is made of Cu foil. The negative electrode substrate 101 forms the basis of the aggregate for the negative electrode composite material layer 102 and functions as a current collector that collects electricity from the negative electrode composite material layer 102. The negative electrode plate 100 forms the negative electrode composite material layer 102 on a metal-made negative electrode substrate 101. In the first embodiment, the negative electrode active material is a material capable of intercalating / deintercalating lithium ions, and a powdered carbon material composed of graphite (black lead) or the like is used.

[0060] The negative electrode plate 100 is manufactured, for example, by mixing the negative electrode active material, solvent and binder (adhesive), coating the mixed negative electrode composite material onto the negative electrode substrate 101 and drying it.

[0061] <Positive Plate 110>

[0062] A positive electrode plate 110 is formed by forming positive electrode composite material layers 112 on both sides of a positive electrode substrate 111. In an embodiment, the positive electrode substrate 111 is made of Al foil or Al alloy foil. The positive electrode substrate 111 forms the basis of the aggregate of the positive electrode composite material layer 112 and has the function of a current collector that collects electricity from the positive electrode composite material layer 112.

[0063] In the positive electrode plate 110, a positive electrode composite material layer 112 is formed on the surface of the positive electrode substrate 111. The positive electrode composite material layer 112 has a positive electrode active material. The positive electrode active material is a material capable of lithium intercalation / deintercalation, and can be, for example, lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), etc. Alternatively, a material formed by mixing LiCoO2, LiMn2O4, and LiNiO2 in any proportion can also be used.

[0064] In addition, the positive electrode composite layer 112 contains a conductive material. As a conductive material, carbon black such as acetylene black (AB) and Ketjen black, or graphite (lead black) can be used.

[0065] The positive electrode plate 110 is manufactured, for example, by mixing positive electrode active material, conductive material, solvent and binder (adhesive), coating the mixed positive electrode composite material onto positive electrode substrate 111 and drying it.

[0066] <Separator 120>

[0067] The separator 120 is a nonwoven fabric such as polypropylene used to hold the non-aqueous electrolyte 17 between the negative electrode plate 100 and the positive electrode plate 110. Alternatively, the separator 120 can be a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or a lithium-ion or ion-conductive polymer electrolyte membrane, used alone or in combination. When the electrode body 10 is immersed in the non-aqueous electrolyte 17, the non-aqueous electrolyte permeates from the ends of the separator 120 toward the center.

[0068] <Mechanical properties of spacer 120>

[0069] The spacer 120 is constructed as a whole as a porous structure, with a relatively coarse skeleton portion and a relatively fine 3D mesh-like portion formed on the skeleton portion. Furthermore, during the flattening pressing process (S4), when the spacer 120 is compressed, due to the elasticity of the resin in the spacer 120, the spacer 120 undergoes elastic deformation, causing the porous portion to be flattened. At this time, even when the same force is applied, the relatively fine 3D mesh-like portion formed on the skeleton portion undergoes greater deformation compared to the relatively coarse skeleton portion. When the spacer 120 is in a free state without applied force from its uncompressed state, its thickness is approximately restored under elastic restoring force. At this time, the relatively fine 3D mesh-like portion, which has undergone greater deformation, exhibits plastic deformation exceeding its yield point. In contrast, the relatively coarse skeleton portion is less prone to plastic deformation and approximately returns to its original shape under elastic restoring force.

[0070] <Air permeability of spacer 120 [μm / (Pa·s)]>

[0071] Here, "air permeability" refers to the numerical value indicating the ease with which air passes through paper, nonwoven fabrics, and filters. Air permeability is determined using a Gurley air permeability tester based on the Gurley method, as specified in JIS P 8117 (Test Method for Air Permeability of Paper and Paperboard). The Gurley test method is applicable to paper and paperboard with ISO air permeability of 0.1 μm / (Pa·s) to 100 μm / (Pa·s) or air resistance of 1.4 s to 1300 s. Air is compressed by the vertical weight of an inner cylinder floating in a liquid, and this air passes through a test piece as the inner cylinder slowly descends. The time required for a certain volume of air to pass through is measured, and this value is used to calculate the ISO air permeability.

[0072] In the Gurley test, the number of seconds it takes for a certain volume of air to pass through a certain area of ​​paper under a given pressure difference is called the Gurley seconds, which is used as the air permeability (JIS terminology is "air resistance," conventionally denoted as "air permeability"). Alternatively, the Wang Yan test machine method can be used instead of the Gurley test for measurement.

[0073] In the spacer 120, the relatively fine 3D mesh-like portion present before the flattening pressing process (S4) undergoes plastic deformation with a deformation greater than the yield point after the flattening pressing process (S4), resulting in a smaller void diameter compared to before the flattening pressing process (S4). That is, the "air permeability" of the spacer 120 changes before and after the flattening pressing process (S4). As mentioned above, the overall dimensions do not change significantly before and after the flattening pressing process (S4) due to the restoring force of the skeleton portion. However, even if the overall dimensions are restored, the voids in the spacer 120 are flattened and reduced, correspondingly decreasing the air permeability of the spacer 120. That is, the non-aqueous electrolyte 17 is not easily replaceable.

[0074] That is, by managing the "air permeability" of the septum 120, the "solution resistance" can be managed.

[0075] <Non-aqueous electrolyte 17>

[0076] A non-aqueous electrolyte is a composition containing a supporting salt in a non-aqueous solvent. Here, ethylene carbonate (EC) can be used as the non-aqueous solvent. Alternatively, the non-aqueous solvent can be one or more materials selected from the group consisting of propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Furthermore, the supporting salt can be LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc. Additionally, the supporting salt can also be one or more lithium compounds (lithium salts) selected from these.

[0077] <Manufacturing process of lithium-ion secondary battery 1>

[0078] Figure 6 This is a flowchart illustrating the manufacturing process of the lithium-ion secondary battery 1 according to this embodiment. (Refer to...) Figure 6 The manufacturing process of the lithium-ion secondary battery according to this embodiment will be described in summary.

[0079] <Initial Process (Source Project) (S1)>

[0080] In this embodiment, an initial process (S1) is performed first. This initial process is the manufacturing process of the battery elements of a lithium-ion secondary battery. Specifically, it is the process of manufacturing the negative electrode plate 100, the positive electrode plate 110, and the separator 120, which constitute the battery elements of a lithium-ion secondary battery.

[0081] <Lamination Process (S2)>

[0082] In the initial process (S1), the negative electrode plate 100, the positive electrode plate 110 and the separator 120 are fabricated respectively, and then the lamination process (S2) is performed.

[0083] like Figure 2 As shown, in the lamination process, the negative electrode plate 100, separator 120, positive electrode plate 110, and separator 120 are sequentially laminated. At this time, the negative electrode composite material layer 101 and the positive electrode composite material layer 111 are arranged facing each other with the separator 120 in between. Furthermore, at one end in the width direction W, the negative electrode connection portion 103 is arranged to protrude from the separator 120. At the other end, the positive electrode connection portion 113 is arranged to protrude from the separator 120.

[0084] <Winding process (S3)>

[0085] In the lamination process (S2), the electrode plate 10, which is formed by sequentially laminating the negative electrode plate 100, the separator 120, the positive electrode plate 110, and the separator 120, undergoes a winding process (S2). In the winding process (S2), the laminated electrode plate 10 is wound around the core material with the winding axis AX in the width direction W as the center, using the portion of the core material supporting the center CC.

[0086] Figure 7(a) is a schematic diagram showing the electrode body 10 after the winding process (S3) is completed. As shown in Figure 7(a), the wound electrode body 10 forms a flat portion F such as a racing track, and curved portions R formed at both ends thereon.

[0087] <Flattening process (S4)>

[0088] Figure 7(b) is a schematic diagram showing the electrode body 10 in the flattening pressing process (S4). As shown in Figure 7(b), in the winding process (S3), the electrode body 10 is wound, forming a flat portion F and curved portions R at both ends when viewed from the width direction W. In this electrode body 10, the flat portion F is squeezed and compressed from the thickness direction T by a press 2 having a pressing surface 2a composed of a pair of opposing planes. On the other hand, the curved portions R are basically not deformed in the flattening pressing process (S4).

[0089] <Restoration Process (S5)>

[0090] Figure 7(c) is a schematic diagram showing the electrode body 10 in the restoration process (S5). The electrode body 10, which is extruded by the press 2 in the flattening process (S4), is roughly restored to its original shape in the restoration process (S5) by the action of elastic rebound force. It should be noted that in the restoration process (S5), the electrode body 10 is simply placed in a free state without any active processing. The placement time varies depending on the material and structure, but in this embodiment it is approximately a few seconds.

[0091] Terminal soldering (S6)

[0092] like Figure 2 As shown, the electrode body 10, after being shaped by the flat pressing process (S4), forms a negative electrode connection portion 103 with the negative electrode substrate 101 exposed at one end, and a positive electrode connection portion 113 with the positive electrode substrate 111 exposed at the other end.

[0093] After that, as Figure 3 As shown, in terminal welding (S6), the negative current collector 13 is welded to the negative connection part 103 to make an electrical / mechanical connection.

[0094] In addition, such as Figure 1 As shown, the positive current collector 15 is also welded to the positive connection part 113 for electrical / mechanical connection.

[0095] <Shell Insertion (S7)>

[0096] After that, as Figure 1 As shown, the electrode body 10, which is wound into a flat shape, and the positive current collector 15 and the negative current collector 13 welded thereon are inserted into the battery case 11 by means of a case insertion (S7).

[0097] <Sealing Welding (S8)>

[0098] In the sealing welding (S8) process, the battery casing 11 and the cover 12 are sealed by laser welding or the like. At this stage, the non-aqueous electrolyte has not yet been injected, and the injection port of the cover 12 is open.

[0099] <Battery Cell Drying (S9)>

[0100] In the battery cell drying (S9) process, the moisture and other substances remaining in the battery case are heated and dried thoroughly.

[0101] <Injection / Sealing (S10)>

[0102] In the electrolyte injection / sealing (S10) process, non-aqueous electrolyte 17 is injected through the injection port. After injection, the injection port is sealed. This completes the assembly of the cell unit.

[0103] <Activation (S11)>

[0104] After the cell assembly is completed, an activation (S11) process is performed to form an SEI (Solid Electrolyte Interphase) coating. Here, initial charging and aging are carried out to chemically stabilize / activate the cell.

[0105] <Inspection (S12)>

[0106] Next, in the inspection (S12) process, the battery cell voltage, internal resistance, self-discharge, etc., are checked, and batteries that exhibit specific performance become products. The inspected automotive lithium-ion secondary battery cells are stacked in groups of 6 to 12 to form battery modules. These battery modules are then further housed in a container, and control devices, various sensors, etc., are installed to form a battery pack for vehicles.

[0107] <Management of the size / permeability of electrode body 10>

[0108] Next, the management of the size and permeability of the electrode body 10 in the manufacturing process of the lithium-ion secondary battery 1 described above will be explained.

[0109] The purpose of dimensional management in this embodiment is to adjust the solution resistance by changing the air permeability of the flat part F and the curved part R, so that the combined resistance of the flat part F is equal to the combined resistance of the curved part R.

[0110] Figure 8 This table shows the "D / B ratio", "B section / D section air permeability ratio", and "B′ / (2×electrode body layer thickness E) ratio" after the winding process (S3), shortly after the flat pressing process (S4), and after the recovery process (S5).

[0111] <Adjustments after winding process (S3)>

[0112] As shown in Figure 7(a), after the winding process (S3) is completed, the thickness of the outer surface of the flat portion F in the thickness T direction from the center C of the line connecting the pair of curved portions R to the electrode body 10 is defined as the "electrode body lamination thickness E". During this stage, the spacer 120 is not subjected to compressive forces such as pressing, and its original thickness from the initial manufacturing process can be maintained; the flat portion F and the curved portion R have fixed thicknesses. Furthermore, the porous structure of the spacer 120 also maintains the original manufacturing space, preserving the air permeability of the main body. Therefore, the "B′ / (2×electrode body lamination thickness E) ratio" is 1.00.

[0113] Furthermore, regarding the "air permeability [μm / (Pa·s)]", since the spacer 120 maintains its original manufacturing structure, this air permeability is fixed in the flat portion F and the curved portion R. Therefore, the "air permeability ratio of portion B (part B) / portion D (part D)" is 1.00.

[0114] <Dimensions shortly after the flat pressing process (S4) is completed>

[0115] Next, in the flattening pressing process (S4) shown in Figure 7(b), the electrode body 10 is compressed using the opposing pressing surface 2a of the press 2, and the distance from one outer surface of the flat portion F to the other outer surface of the electrode body 10 in the thickness direction T is taken as the "thickness dimension B″". At this time, the original thickness of the electrode body 10, "2 × electrode body layer thickness E", is compressed and reduced to "thickness dimension B″". Specifically, the "B″ / (2 × electrode body layer thickness E) ratio" is compressed to 0.88 to 0.98.

[0116] On the other hand, the portion D from the center C of the bend R to the outer surface of the bend R along its length is not compressed. Therefore, as Figure 8 As shown, the "D / B ratio" is 1.03 to 1.25.

[0117] It should be noted that for the electrode body 10 compressed in the flattening pressing process (S4), the compressed dimensions change in the subsequent recovery process (S5). Regarding the "thickness dimension B" that becomes part of the flattening pressing process (S4), its size itself is not important; what is important is its influence on the subsequent air permeability [μm / (Pa·s)]. That is, through the flattening pressing process (S4), the fine openings of the spacer 120 are flattened, exceeding the yield point and undergoing plastic deformation. Therefore, the air permeability [μm / (Pa·s)] decreases. By controlling this "thickness dimension B", the air permeability of part B can be managed. Specifically, as... Figure 8 As shown, the air permeability ratio of "B part (section B) / D part (section D)" is approximately 0.90 to 0.99.

[0118] <Dimensions after restoration process (S5)>

[0119] After the flattening process (S4), the electrode body 10 is in a free state, and a restoration process (S5) is performed. In the restoration process (S5), the length D from the center C of the curved portion R to the outer surface of the curved portion R in the length direction remains unchanged. On the other hand, the distance B″ from one outer surface of the flat portion F to the other outer surface in the thickness direction T of the electrode body 10 becomes the distance B′ from one outer surface of the flat portion F to the other outer surface in the thickness direction T of the electrode body 10. Regarding the thickness of the electrode body 10, the D / B ratio = D / (B′ / 2) is 1.01 to 1.10.

[0120] In addition, since the skeleton part of the spacer 120 will almost return to its original size under the action of elastic rebound force during the restoration process (S5), the ratio of "B′ / (2×electrode body layer thickness E)" is 0.98 to 1.00.

[0121] Furthermore, in the flattening pressing process (S4), the fine openings of the spacer 120 are flattened beyond the yield point, resulting in plastic deformation. Therefore, even when it becomes free in the recovery process (S5), and even after the recovery process (S4) is completed, the "air permeability ratio of part B (section B) / part D (section D)" remains unchanged compared to shortly after the flattening pressing process (S4). Therefore, the air permeability [μm / (Pa·s)] of section B remains unchanged, and the "air permeability ratio of part B (section B) / part D (section D)" is 0.90 to 0.99.

[0122] <Synthetic resistance Rdc and synthetic resistance Rbc>

[0123] The combined resistances Rdc and Rbc are derived, for example, by the following method: First, the reaction resistance Rb1 caused by the inter-electrode distance at site B and the reaction resistance Rd1 caused by the inter-electrode distance at site D are calculated. Next, the solution resistance Rd2 caused by the permeability at site D and the solution resistance Rb2 caused by the permeability at site B are calculated. Then, the combined resistance Rdc of site D is calculated using the formula: combined resistance Rdc = reaction resistance Rd1 + solution resistance Rd2. And the combined resistance Rbc of site B is calculated using the formula: combined resistance Rbc = reaction resistance Rb1 + solution resistance Rb2. The combined resistances Rdc of site D and Rbc of site B are then compared. If the difference between Rdc and Rbc is less than a set threshold, it can be determined that the non-uniformity of the current density is within a range where the precipitation of metallic Li is unlikely.

[0124] <Determination of Reaction Resistance and Solution Resistance>

[0125] In a lithium-ion secondary battery 1, the reaction resistance and solution resistance can be determined by alternating current impedance spectroscopy. Alternating current impedance spectroscopy is a method of observing the impedance spectrum by applying an alternating voltage to the electrode system of the secondary battery with small amplitude and gradually changing the frequency.

[0126] A lithium-ion secondary battery 1 can be represented by an equivalent circuit. That is, it can be represented as a parallel circuit consisting of the solution resistance and the charge migration resistance connected in series with the solution resistance, which is the double-layer reactive resistance. The structure with a non-aqueous electrolyte between the electrodes is conceived as a double layer, functioning as a capacitor. Therefore, the AC resistance of the double layer becomes a resistive component equivalent to dielectric loss due to polarization delay of the dielectric in the low-frequency region, and a resistive component equivalent to the skin effect or proximity effect of the electrodes in the high-frequency region. It is equivalent to the reactive resistance. Thus, the impedance changes with frequency. Theoretically, under DC, the double layer is not energized, and the resistance becomes zero as the frequency of the AC voltage increases. Therefore, at high frequencies (e.g., above 100 Hz), the combined resistance of the circuit is equal to the solution resistance, and as the frequency increases (100 MHz to 100 Hz), it becomes the solution resistance, the charge migration resistance, and the combined resistance of the double layer. Furthermore, at low frequencies (below 100 MHz), the combined resistance of the circuit becomes the sum of the solution resistance and the charge migration resistance.

[0127] According to the AC impedance method, although the explanation is omitted, the reaction resistances Rb1 and Rd1 caused by the interelectrode distance and the solution resistances Rd2 and Rb2 caused by the permeability can be determined by using Nyquist plots (not shown) with real numbers on the horizontal axis and imaginary numbers on the vertical axis.

[0128] According to the Nyquist plot, the electrode reaction rate, electrolyte conductivity, and double-layer capacity of a secondary battery can be determined based on impedance and phase difference. In the Nyquist plot, the vertical axis represents the imaginary value of resistance, Zimg [Ω], and the horizontal axis represents Zreal [Ω]. An AC voltage is applied to the electrode system of secondary battery 1 by changing the frequency in stages with small amplitudes from a high frequency. Thus, an arc-shaped graph with a center on the horizontal axis extends upward from the zero-crossing point Px, which is offset to the right along the horizontal axis from the origin Po in the lower left. Furthermore, a linear graph extends outward in the radial direction from a specific point in the upper right. "Solution resistance (electron movement resistance)" is represented by the distance from the origin Po to the zero-crossing point Px, that is, by the real value of the resistance at the zero-crossing point Px, Zreal [Ω]. Regarding "solution resistance (electron movement resistance)," the resistance of the electrolyte, electrodes, current collectors, etc., when electrons move at high frequencies above 100 Hz can be analyzed.

[0129] Regarding "reaction resistance," at intermediate frequencies (0.1Hz to 100Hz), the chemical reaction at the electrodes can be used to analyze the "reaction resistance Pct," which is the resistance to the movement of generated charges (ions). It is represented by an arc-shaped diagram with a center on the horizontal axis starting from the zero crossover Px; if the electrode performance deteriorates, it becomes an arc with a large radius.

[0130] (Experimental example of this implementation method)

[0131] The lithium-ion secondary battery 1 and manufacturing method of this embodiment have the above-described configuration. Here, experimental examples of this embodiment will be described. Experimental Examples 1 to 3 are examples of experiments conducted by changing the numerical settings in the above-described manufacturing method of the lithium-ion secondary battery 1.

[0132] <Experimental Example 1: D / B Ratio and Li Precipitation Resistance>

[0133] Figure 9 This is a table showing the results of Experiment Example 1. Figure 9 The results show the determination of Li precipitation resistance when the "permeability ratio of part B (section B) / part D (section D)" is fixed at 0.95, the "B′ (B″) / (2 × electrode body layer thickness E) ratio" is fixed at 0.99, and the "D / B ratio" is varied in the range of 1.00 to a maximum of 1.11. "〇" indicates the case where the Li precipitation resistance is desired as a product, and "×" indicates the case where the Li precipitation resistance is undesirable as a product.

[0134] like Figure 8 As shown, when the D / B ratio is 1.00, the inter-electrode distance of the flat portion F is equal to that of the curved portion R. That is, the reaction resistance Rb1 caused by the inter-electrode distance in portion B is equal to that caused by the inter-electrode distance in portion D. On the other hand, the permeability of the septum 120 is different in the flat portion F and the curved portion R. That is, the solution resistance Rd2 caused by the permeability in portion D is different from that caused by the permeability in portion B. Therefore, the combined resistance Rdc in portion D is different from that in portion B, resulting in non-uniform current density between the negative electrode plate 100 and the positive electrode plate 110, and reducing the Li deposition resistance.

[0135] On the other hand, when the D / B ratio is 1.01 to 1.10, the inter-electrode distance of the flat portion F is different from that of the curved portion R. That is, the reaction resistance Rb1 caused by the inter-electrode distance in portion B is different from that in portion D. Furthermore, the permeability of the septum 120 is also different in the flat portion F and the curved portion R. That is, the solution resistance Rd2 caused by the permeability in portion D is different from that in portion B. Within this range, the difference between the reaction resistance Rd1 and the reaction resistance Rb1 and the difference between the solution resistance Rd2 and the solution resistance Rb2 cancel each other out. Therefore, the difference between the combined resistance Rdc in portion D and the combined resistance Rbc in portion B is within an acceptable range, there is no non-uniformity in the current density between the negative electrode plate 100 and the positive electrode plate 110, and the Li deposition resistance is improved.

[0136] Furthermore, when the D / B ratio is 1.11, the inter-electrode distance in the flat portion F differs from that in the curved portion R. That is, the reaction resistance Rb1 caused by the inter-electrode distance in portion B differs from that in portion D. On the other hand, the permeability of the septum 120 also differs between the flat portion F and the curved portion R. That is, the solution resistance Rd2 caused by the permeability in portion D differs from that in portion B. Within this range, the difference between the reaction resistance Rd1 and the reaction resistance Rb1 is too large to be offset by the difference between the solution resistance Rd2 and the solution resistance Rb2. Therefore, the difference between the combined resistance Rdc in portion D and the combined resistance Rbc in portion B is outside the acceptable range, resulting in uneven current density between the negative electrode plate 100 and the positive electrode plate 110, and deterioration of Li precipitation resistance.

[0137] Based on the above results, the permeability ratio of part B (section B) to part D (section D) was fixed at 0.95, and the ratio of B′ (B″) to (2 × electrode body thickness E) was fixed at 0.99. On the other hand, the D / B ratio was varied within a range of 1.00 to a maximum of 1.11. In this case, when the D / B ratio was 1.00, Li precipitation resistance decreased. Furthermore, when the D / B ratio was between 1.01 and 1.10, Li precipitation resistance was good. Moreover, when the D / B ratio was 1.11, Li precipitation resistance deteriorated again.

[0138] Therefore, it can be seen that the "D / B ratio" should be appropriately set relative to the values ​​of "permeability ratio of part B (section B) / part D (section D)" and "B′(B″) / (2 × electrode body thickness E) ratio". Thus, by keeping the combined resistance Rdc of section D and the combined resistance Rbc of section B within an acceptable range, the Li precipitation resistance can be improved.

[0139] <Experimental Example 2: Air permeability ratio of section B / D and Li precipitation resistance>

[0140] Figure 10 This is a table showing the results of Experiment Example 2. Figure 10 The results of measuring Li precipitation resistance are shown with the "D / B ratio" fixed at 1.05, the "B′(B″) / (2×electrode body layer thickness E) ratio" fixed at 0.99, and the "air permeability ratio of part B (section B) / part D (section D)" varying from 0.88 to a maximum of 1.00. "〇" indicates the desired Li precipitation resistance as a product, and "×" indicates the undesirable Li precipitation resistance as a product.

[0141] Assuming a permeability ratio of B / D of 0.88, the D / B ratio is fixed at 1.05. Consequently, the interelectrode distance in section D (bent section R) is greater than that in section B (flat section F). That is, the reaction resistance Rd1 of section D (bent section R) is greater than the reaction resistance Rb1 of section B (flat section F). With a permeability ratio of B / D of 0.88, the solution resistance Rd2 of section D (bent section R) is less than the solution resistance Rb2 of section B (flat section F). In this case, Li precipitation resistance decreases. Therefore, with a permeability ratio of B / D of 0.88, the difference between solution resistance Rd2 and solution resistance Rb2 is excessively large compared to the difference between reaction resistance Rd1 and reaction resistance Rb1. As a result, the difference between the combined resistance Rdc of section D and the combined resistance Rbc of section B is outside the acceptable range, and Li precipitation resistance can be considered to be reduced.

[0142] Next, assuming the permeability ratio of section B to section D is 0.90 to 0.99, the difference between reaction resistance Rd1 and reaction resistance Rb1, and the difference between solution resistance Rd2 and solution resistance Rb2, can be balanced. As a result, the difference between the synthesis resistance Rdc of section D and the synthesis resistance Rbc of section B is within an acceptable range, which can be considered as an improvement in Li precipitation resistance.

[0143] Furthermore, assuming the permeability ratio of section B to section D is 1.00, the solution resistance Rd2 and solution resistance Rb2 are equal, making it impossible to eliminate the difference between the reaction resistance Rd1 and reaction resistance Rb1, which are prerequisites for this. Therefore, the difference between the synthesis resistance Rdc of section D and the synthesis resistance Rbc of section B is outside the acceptable range, which can be considered as a decrease in Li precipitation resistance.

[0144] Therefore, relative to the values ​​of "D / B ratio" and "B′(B″) / (2×electrode body layer thickness E) ratio", the "permeability ratio of part B (section B) / section D (section D)" should be appropriately set. In this way, the difference between reaction resistance Rd1 and reaction resistance Rb1 and the difference between solution resistance Rd2 and solution resistance Rb2 can be balanced, thereby keeping the difference between the synthesis resistance Rdc of section D and the synthesis resistance Rbc of section B within an acceptable range, which can improve the resistance to Li precipitation.

[0145] <Experimental Example 3: B′ / 2E Ratio and Li Precipitation Resistance>

[0146] Figure 11 A table showing the results of Experiment Example 3. Figure 11The results show the determination of Li precipitation resistance when the "D / B ratio" is fixed at 1.05, the "permeability ratio of part B (section B) / part D (section D)" is fixed at 0.95, and the "B′(B″) / (2×electrode body layer thickness E) ratio" is varied in the range of 0.97 to a maximum of 1.01. "〇" indicates the desired Li precipitation resistance as a product, and "×" indicates the undesirable Li precipitation resistance as a product.

[0147] like Figure 11 As shown, when the "B′ / 2E ratio" is set to 0.97, even after the restoration process (S5) is completed, the thickness of the spacer 120 of the electrode body 10, which has been compressed by the flat pressing process (S4), is not fully restored. That is, as a result, the inter-electrode distance of the flat portion F is maintained at a reduced value. The shortened inter-electrode distance results in the reaction resistance Rb1 of part B in the flat portion F being much smaller than the reaction resistance Rd1 of part D in the curved portion R. On the other hand, since the "air permeability ratio of part B (part B) / part D (part D)" is fixed at 0.95, the solution resistance Rb2 of part B (part B) is greater than the solution resistance Rd2 of part D (part D). In this case, if the difference between the reaction resistance Rd1 and the reaction resistance Rb1 is compared with the difference between the solution resistance Rd2 and the solution resistance Rb2, the difference between the reaction resistance Rd1 and the reaction resistance Rb1 is even greater. Therefore, the difference between the combined resistance Rdc of part D and the combined resistance Rbc of part B is outside the allowable range, and the Li precipitation resistance is reduced.

[0148] Next, with the "B′ / 2E ratio" set to 0.98 to 1.00, after the restoration process (S5) is completed, the thickness of the spacer 120 of the electrode body 10, which has been compressed by the flat pressing process (S4), is fully restored. That is, as a result, the inter-electrode distance of the flat portion F is restored to its state before the flat pressing process (S4). The result of this inter-electrode distance restoration is that the reaction resistance Rb1 of part B in the flat portion F is slightly less than the reaction resistance Rd1 of part D in the curved portion R. On the other hand, since the "air permeability ratio of part B (part B) / part D (part D)" is fixed at 0.95, the solution resistance Rb2 of part B (part B) is greater than the solution resistance Rd2 of part D (part D). In this case, if the difference between the reaction resistance Rd1 and the reaction resistance Rb1 is compared with the difference between the solution resistance Rd2 and the solution resistance Rb2, the difference between the reaction resistance Rd1 and the reaction resistance Rb1 is balanced. Therefore, the difference between the combined resistance Rdc of part D and the combined resistance Rbc of part B is within the allowable range, and the Li precipitation resistance is improved.

[0149] Furthermore, assuming the "B′ / 2E ratio" is 1.01, after the restoration process (S5), the thickness of the spacer 120 of the electrode body 10, which has been compressed by the flattening pressing process (S4), is in an over-restored state. That is, as a result, the inter-electrode distance of the flat portion F becomes greater than before the flattening pressing process (S4). The increased inter-electrode distance results in the reaction resistance Rb1 of part B of the flat portion F being greater than the reaction resistance Rd1 of part D of the curved portion R. On the other hand, since the "air permeability ratio of part B (part B) / part D (part D)" is fixed at 0.95, the solution resistance Rb2 of part B (part B) is greater than the solution resistance Rd2 of part D (part D). In this case, when comparing the difference between reaction resistance Rd1 and reaction resistance Rb1 and the difference between solution resistance Rd2 and solution resistance Rb2, the difference between reaction resistance Rd1 and reaction resistance Rb1 is smaller. Therefore, the difference between the combined resistance Rdc of part D and the combined resistance Rbc of part B increases and falls outside the allowable range, resulting in a deterioration of Li precipitation resistance.

[0150] Therefore, compared to a fixed "D / B ratio" and "permeability ratio of part B (section B) / part D (section D)," appropriately setting the "B′(B″) / (2×electrode body layer thickness E) ratio" will ensure that the difference between the combined resistance Rdc of section D and the combined resistance Rbc of section B is within an acceptable range, thereby improving Li precipitation resistance.

[0151] <Summary of Experiments 1-3>

[0152] From the above experimental examples 1 to 3, it can be deduced that the following conditions can improve the tolerance of Li precipitation.

[0153] First, the range of "thickness of part D / thickness of part B" is set to 1.01 ≤ thickness of part D / thickness of part B ≤ 1.10. Additionally, the range of "air permeability of part D / air permeability of part B" is set to 0.90 ≤ air permeability of part D / air permeability of part B ≤ 0.99. Furthermore, the range of "thickness dimension B′ / (2 × electrode body layer thickness E)" is set to 0.98 ≤ B′ / 2E ≤ 1.00. Additionally, the range of "thickness dimension B′ / thickness dimension B″" is set to 0.88 ≤ B′ / B″ ≤ 0.98. By setting these parameters, the lithium-ion secondary battery 1 of this embodiment can achieve good Li deposition resistance.

[0154] (The function of this implementation method)

[0155] The lithium-ion secondary battery and its manufacturing method according to this embodiment have the following effects. In the negative electrode plate 100 in the electrode body 10 and the positive electrode plate 110 opposite therein, the difference in reaction resistance Rd1 and Rb1 caused by the distance between the electrode plates is generated in the flat portion F and the curved portion R by a flat pressing process (S4).

[0156] Therefore, in order to eliminate the difference in reaction resistance, the permeability is changed by compressing the spacer 120 to a specific size B″ using a flat pressing process (S4). If the permeability changes, the solution resistance changes. Furthermore, a difference in solution resistance Rd2 and Rb2 arises between the flat portion F and the curved portion R. Through this difference in solution resistance Rd2 and Rb2, the difference in reaction resistance Rd1 and Rb1 is canceled out, thus eliminating the difference in combined resistance Rdc and Rbc. Therefore, the difference in current density caused by the difference in combined resistance Rdc and Rbc between the flat portion F and the curved portion R can be eliminated. As a result, the precipitation of metallic Li caused by non-uniform current density can be effectively suppressed.

[0157] (Effects of this implementation method)

[0158] (1) The lithium-ion secondary battery and its manufacturing method according to this embodiment can suppress the precipitation of metallic lithium.

[0159] (2) Since the combined resistance of the flat part F is the same as that of the curved part R, the deposition of metallic lithium can be effectively suppressed.

[0160] (3) Since the combined resistance of the flat part F and the combined resistance of the curved part R are analyzed and controlled separately as reaction resistance and solution resistance, the combined resistance of the flat part F and the combined resistance of the curved part R can be made to be exactly the same.

[0161] (4) Since the reaction resistance and solution resistance are measured by AC impedance method, their respective resistances can be accurately determined.

[0162] (5) Since the solution resistance is controlled by adjusting the opening diameter of the septum 120, it can be adjusted to any value.

[0163] (6) The opening diameter of the partition 120 can be adjusted by the extrusion pressure in the flat pressing process (S4).

[0164] (7) The opening diameter of the partition 120, which is adjusted by the extrusion pressure in the flat pressing process (S4), can be managed by air permeability.

[0165] (8) In the lithium-ion secondary battery manufacturing method of this embodiment, it can be implemented directly through general manufacturing processes by means of numerical management alone. Therefore, no special equipment or special processes are required.

[0166] (9) In particular, in the manufacturing of the negative electrode plate 100, positive electrode plate 110 and separator 120 of the electrode body 10, no special processing or treatment is required, and the conventional negative electrode plate 100, positive electrode plate 110 and separator 120 can be used directly.

[0167] (10) In the manufacturing method of lithium-ion secondary battery of this embodiment, since it can be properly implemented by numerical management, it does not require skilled personnel and can be objectively controlled.

[0168] (11) Therefore, high-quality lithium-ion secondary batteries can be manufactured without reducing production efficiency.

[0169] (12) Furthermore, since no special materials, special equipment, fixtures, etc. are required, the manufacturing method of the lithium-ion secondary battery 1 of this embodiment can be implemented without incurring additional costs.

[0170] (Other examples)

[0171] The lithium-ion secondary battery 1 of this embodiment is an example of the non-aqueous electrolyte secondary battery of the present invention, and is not limited to the shape of the plate-shaped automotive lithium-ion secondary battery 1 shown in the figure. Furthermore, it is not limited to automotive applications.

[0172] The numerical ranges shown are examples of preferred embodiments in this implementation, and the present invention is not limited to these numerical limitations.

[0173] • In addition, Experimental Examples 1 to 3 are experiments conducted in conventionally common lithium-ion secondary batteries, and the results can be widely applied, but the present invention is not limited thereto.

[0174] Regarding the location B for measuring the thickness of the flat portion F, since the surface of the flat portion F is approximately flat, location B is defined as the area spanning the straight line from the center C connecting the pair of curved portions R to the outer surface of the flat portion F in the thickness direction after the restoration process (S5) is completed. However, since the flat portion F is approximately flat, the measurement can be performed, for example, at the center of the flat portion F. In short, as long as the measurement location is fixed to objectively control dimensional changes, there are no limitations on the measurement location.

[0175] The AC impedance method is illustrated in the determination of reaction resistance and solution resistance, but there are no limitations on the method as long as the reaction resistance and solution resistance can be accurately obtained.

[0176] · Figure 6The flowchart shown is for illustrative purposes only. Those skilled in the art can add to, remove from, or modify the process, and can change the order of implementation.

[0177] The present invention may, of course, be implemented by those skilled in the art by adding, removing or modifying its components without departing from the scope of the claims.

Claims

1. A method for manufacturing a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery comprising an electrode body, a non-aqueous electrolyte, and a cuboid battery casing housing the electrode body and the non-aqueous electrolyte, the method for manufacturing the non-aqueous electrolyte secondary battery being characterized by comprising the following steps: The lamination process involves laminating a positive electrode containing a positive electrode substrate and a positive electrode composite material layer with a negative electrode containing a negative electrode substrate and a negative electrode composite material layer, separated by a separator made of porous resin, to form an electrode body. The winding process involves winding the laminated electrode body around a winding shaft. In the flattening pressing process, the electrode body, after being wound in the winding process, is pressed from a direction orthogonal to the winding axis to form a planar flat portion F and a pair of semi-cylindrical curved portions R formed at both ends of the flat portion F; and The recovery process restores the elastic deformation that occurred during the flattening and pressing process. When the direction parallel to the winding axis of the electrode body is taken as the width direction, the direction orthogonal to the winding axis of the electrode body and orthogonal to the surface of the flat portion F is taken as the thickness direction, the direction orthogonal to both the width direction and the thickness direction is taken as the length direction, and the point located on the central axis of the curved portion R formed as a semi-cylindrical shape is taken as the center C of the curved portion R, When the restoration process is completed, the portion spanning from the center C of the bent portion R to the outer surface of the bent portion R in the length direction is designated as portion D. The portion spanning the center C of the pair of curved portions R at the completion of the restoration process and extending to the outer surface of the flat portion F in the thickness direction is designated as portion B. The distance from one outer surface of the flat portion F to the other outer surface in the thickness direction of the electrode body when the restoration process is completed is taken as the thickness dimension B′. The layer thickness at the completion of the winding process of the electrode body is defined as the electrode body layer thickness E. When the pressing process of the electrode body is completed, the distance from one outer surface of the flat portion F to the other outer surface in the thickness direction of the electrode body is taken as the thickness dimension B″. The range of the thickness of part D / the thickness of part B is set as follows: 1.01 ≤ Thickness of part D / Thickness of part B ≤ 1.10 The range of air permeability of part B / air permeability of part D is set as follows: 0.90 ≤ air permeability of part B / air permeability of part D ≤ 0.99 The range of the thickness dimension B′ / (2×electrode body layer thickness E) is set as follows: 0.98≤B′ / 2E≤1.00 The range of the thickness dimension B″ / thickness dimension B′ is set as follows: 0.88≤B″ / B′≤0.98 Furthermore, the combined resistance Rdc of the reaction resistance Rd1 caused by the inter-electrode distance and the solution resistance Rd2 caused by the permeability of the septum in the part D is set to be equal to the combined resistance Rbc of the reaction resistance Rb1 caused by the inter-electrode distance and the solution resistance Rb2 caused by the permeability of the septum in the part B.

2. The method for manufacturing a non-aqueous electrolyte secondary battery as described in claim 1, characterized in that, The non-aqueous electrolyte secondary battery is a lithium-ion secondary battery.

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