Secondary batteries

Abstract

This invention provides a secondary battery that suppresses an increase in internal resistance while maintaining the durability of the separator sheet. [Solution] The secondary battery comprises a wound electrode body 20 formed by winding a laminate including a first electrode plate 60, a second electrode plate 70, and a separator around a winding axis. The active material layer 62 of the first electrode plate 60 has a lower density than the active material layer 72 of the second electrode plate 70. The separator includes two separator sheets 81, 82 that sandwich the first electrode plate 60. At the first side edge 20A in the winding axis direction X of the wound electrode body 20, the separator sheets 81, 82 include first excess length portions 81A, 82A that protrude outward from the active material layer 62 in the winding axis direction X. The first excess length portions 81A, 82A include first end edges 83A, 84A that are in non-fixed contact with the first exposed portion 61A of the current collector foil 61. The first retaining space S1 is partitioned by the first excess length portions 81A, 82A, the current collector foil 61, and the active material layer 62.

Description

Technical Field

[0001] This disclosure relates to secondary batteries.

Background Art

[0002] A secondary battery such as a lithium secondary battery containing a non-aqueous electrolyte is composed of an electrode body formed by laminating a positive electrode plate including a positive electrode active material layer, a negative electrode plate including a negative electrode active material layer, and a separator interposed between the positive electrode plate and the negative electrode plate. The active materials in the positive electrode active material layer and the negative electrode active material layer expand and contract during charge and discharge. Due to the expansion of this active material, the non-aqueous electrolyte in the positive electrode active material layer and the negative electrode active material layer flows out of the electrode body structure. As a result, liquid depletion of the non-aqueous electrolyte and a bias in the salt concentration distribution occur in the electrode body, increasing the internal resistance of the secondary battery. In particular, when high-rate (high current) charge and discharge of the secondary battery are repeated, the internal resistance of the secondary battery increases significantly, causing the secondary battery to deteriorate (i.e., high-rate deterioration occurs).

[0003] In Patent Document 1, a bag-shaped separator for housing the negative electrode plate has been proposed so that the non-aqueous electrolyte does not easily flow out of the electrode body structure. Since the movement of the non-aqueous electrolyte is suppressed by the bag-shaped separator, an increase in the internal resistance in the secondary battery is suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the method for manufacturing a bag-shaped separator described in Patent Document 1, first, one separator is folded over, and the overlapping ends are welded together at the fastening portion. Next, with the negative electrode plate housed in the separator, the end of the separator that overlaps with the current collector of the negative electrode plate is welded to the current collector. This seals the bag-shaped separator. Special equipment is required to perform such partial welding. Furthermore, the heat of welding melts the separator, which may cause the separator's pores to become clogged or the separator to tear. This can lead to a decrease in the separator's durability. [Means for solving the problem]

[0006] A secondary battery according to one aspect of the present disclosure comprises a wound electrode body formed by winding a laminate containing a first electrode plate, a second electrode plate having a polarity different from that of the first electrode plate, and a separator interposed between the first and second electrode plates, around a winding axis, and a battery case for housing the wound electrode body and a non-aqueous electrolyte, wherein each of the first and second electrode plates includes a current collector foil and an active material layer formed on the current collector foil, the active material layer of the first electrode plate having a lower density than the active material layer of the second electrode plate, and the separator is made of two separators laminated with the first electrode plate sandwiched between them. The separator sheet comprises a first side edge in the winding axis direction of the wound electrode body, the current collector foil of the first electrode plate includes a first exposed portion in which the current collector foil is exposed without the active material layer being formed, each of the two separator sheets includes a first excess length portion that protrudes outward from the active material layer of the first electrode plate in the winding axis direction, the first excess length portions of the two separator sheets include a first end edge that is in non-fixed contact with the first exposed portion, and the first excess length portions of the two separator sheets, the current collector foil of the first electrode plate, and the active material layer define a first holding space.

[0007] In the secondary battery described above, the first edges of the two separator sheets may have curved surfaces that are curved toward each other. In the secondary battery described above, the curved surfaces of the two separator sheets may extend over the entire first excess length portion of the separator sheets.

[0008] In the above-described secondary battery, the first excess length portion of the two separator sheets may have an S-shaped cross-section including a tip portion that is curved inward and convexly toward the inside of the two separator sheets and a base portion that is curved outward and convexly toward the outside of the two separator sheets.

[0009] In the above-described secondary battery, the first excess length portion of the two separator sheets may have a semicircular cross-section that is convex outward in the winding axis direction. In the secondary battery described above, each of the two separator sheets includes an intermediate resin layer, an inner resin layer positioned on the side of the first electrode plate facing the current collector foil relative to the intermediate resin layer, and an outer resin layer positioned on the opposite side of the intermediate resin layer from the inner resin layer, wherein the inner resin layer may have less rigidity than the outer resin layer.

[0010] In the above-described secondary battery, the inner resin layer may have a larger porosity, a smaller density, or a thinner thickness than the outer resin layer. In the above-described secondary battery, each of the two separator sheets may include an intermediate resin layer, an inner resin layer positioned on the side of the first electrode plate facing the current collector foil relative to the intermediate resin layer, an outer resin layer positioned on the opposite side of the intermediate resin layer from the inner resin layer, and a heat-resistant layer formed on the outer resin layer.

[0011] In the secondary battery described above, the wound electrode body has a winding start end and a winding end located in a direction perpendicular to the winding axis direction, and the two separator sheets may not be in contact with each other at the winding start end and the winding end of the wound electrode body.

[0012] In the secondary battery described above, at the second side edge of the wound electrode body opposite to the first side edge in the winding axis direction, the current collector foil of the first electrode plate includes a second exposed portion where the current collector foil is exposed without the active material layer being formed, each of the two separator sheets includes a second excess length portion that protrudes outward from the active material layer of the first electrode plate in the winding axis direction, and the two separator sheets include a second end edge that is in non-fixed contact with the second exposed portion, and the second retaining space may be defined by the second excess length portions of the two separator sheets and the current collector foil and active material layer of the first electrode plate.

[0013] In the secondary battery described above, the total volume of the first holding space and the second holding space may be set to be greater than or equal to the void volume of the active material layer of the first electrode plate, which decreases when the secondary battery is charged within a preset operating SOC range.

[0014] In the secondary battery described above, at the second side edge of the wound electrode body opposite to the first side edge in the winding axis direction, each of the two separator sheets includes a second excess length portion that protrudes outward from the active material layer of the first electrode plate in the winding axis direction, and the second excess length portions of the two separator sheets include second end edges that are in non-fixed contact with each other, and the second holding space may be defined by the second excess length portions of the two separator sheets and the active material layer of the first electrode plate. [Effects of the Invention]

[0015] According to the secondary battery of this disclosure, it is possible to suppress an increase in internal resistance while maintaining the durability of the separator sheet. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a perspective view showing the structure of a secondary battery according to this embodiment. [Figure 2] Figure 2 is a schematic diagram showing the structure of the wound electrode body of a secondary battery. [Figure 3]FIG. 3 is a schematic partial cross-sectional view taken along line III-III of FIG. 2. [Figure 4] FIG. 4 is an enlarged cross-sectional view for explaining the multilayer separator sheet. [Figure 5] FIG. 5 is a perspective view showing a laminate in which a separator sheet and a negative electrode plate are laminated. [Figure 6] FIG. 6 is a cross-sectional view of the laminate of FIG. 5. [Figure 7] FIG. 7 is a schematic partial cross-sectional view of the wound body. [Figure 8] FIG. 8 is a partial cross-sectional view for explaining the negative electrode plate and the separator sheet in a wound electrode body of another example. [Figure 9] FIG. 9 is a partial cross-sectional view for explaining the negative electrode plate and the separator sheet in a wound electrode body of another example.

MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, the secondary battery 10 according to the present disclosure will be described with reference to the accompanying drawings. In order to simplify and clarify the description, the components shown in the drawings are not necessarily drawn to a certain scale. The accompanying drawings are merely illustrative of the embodiments of the present disclosure and should not be regarded as limiting the present disclosure. Throughout the drawings, the same reference numerals and descriptions do not necessarily denote the same, but indicate similar components.

[0018] The secondary battery 10 is a secondary battery such as a lithium-ion secondary battery containing a non-aqueous electrolyte 50 described later. In the present embodiment, the secondary battery 10 is a lithium-ion secondary battery and is a battery cell. For example, a battery pack is formed by enclosing a plurality of combined battery cells in a resin or metal case. The battery cell or the battery pack can be used as a power source for electric vehicles, hybrid vehicles, ships, trains, airplanes, etc. Further, the battery cell or the battery pack can also be used in a stationary power storage system or the like.

[0019] [Schematic Configuration of Battery] Figure 1 is a perspective view showing the structure of a secondary battery 10 according to this embodiment. The general configuration of the secondary battery 10 will be described with reference to Figure 1. The secondary battery 10 comprises a wound electrode body 20, a battery case 30 housing the wound electrode body 20, a negative electrode external terminal 41 and a positive electrode external terminal 42 exposed to the outside of the battery case 30, a negative electrode conductive member 41A and a positive electrode conductive member 42A that electrically connect the wound electrode body 20 to the negative electrode external terminal 41 and the positive electrode external terminal 42 inside the battery case 30, and a non-aqueous electrolyte 50 impregnated into the wound electrode body 20.

[0020] [Wound electrode body] Figure 2 is a schematic diagram showing the structure of the wound electrode body 20 of the secondary battery 10. As shown in Figure 2, the wound electrode body 20 is constructed by winding a laminate containing a long sheet-shaped negative electrode plate 60, a long sheet-shaped positive electrode plate 70, and a long sheet-shaped separator 80 (81, 82) interposed between the negative electrode plate 60 and the positive electrode plate 70, around a winding axis WL. In this embodiment, the wound electrode body 20 is shaped to be flat. In the wound electrode body 20, the positive electrode plate 70 is wound inward from the negative electrode plate 60. The wound electrode body 20 is covered by a bag-shaped insulating holder (not shown) made of insulating film inside the battery case 30.

[0021] In the drawing (for example, Figure 1), the X direction of the mutually orthogonal XYZ axes represents the width direction of the secondary battery 10 and the winding axis direction of the wound electrode body 20. The Y direction of the XYZ axis represents the thickness direction of the secondary battery 10. The Z direction of the XYZ axis represents the height direction of the secondary battery 10.

[0022] [negative electrode plate] As shown in Figure 2, the negative electrode plate 60 includes a long sheet-shaped negative electrode current collector foil 61 made of a metal material such as copper, and a negative electrode active material layer 62 formed on both sides of the negative electrode current collector foil 61 along the longitudinal direction of the negative electrode current collector foil 61. The negative electrode active material layer 62 includes, for example, a negative electrode active material, a binder, a conductive agent, etc. For example, as the negative electrode active material, any material capable of intercalating and releasing lithium ions and usable in lithium-ion secondary batteries can be used without particular limitation. Examples of negative electrode active materials include carbon materials such as natural graphite, artificial graphite, hard carbon, and soft carbon, and Li4Ti5O 12 Lithium transition metal composite oxides, lithium transition metal composite nitrides, etc., can be used individually or in combination. In this embodiment, the negative electrode active material layer 62 has a porosity of 30% or more and less than 60%. Here, the "porosity" of the negative electrode active material layer 62 refers to the ratio of the volume of voids not filled with negative electrode active material, binder, conductive material, etc., to the total volume of the negative electrode active material layer 62. The porosity is measured, for example, by an immersion method in which a porous sample is immersed in a liquid with good wettability and the voids are saturated with the liquid. The method for measuring the porosity P may be a method of measurement by direct observation with an electron microscope, or by using a mercury intrusion method, etc.

[0023] The negative electrode current collector foil 61 of the negative electrode plate 60 includes a first exposed portion 61A where the negative electrode current collector foil 61 is exposed without a negative electrode active material layer 62 being formed at a first side edge 20A in the winding axis direction X of the wound electrode body 20, and a second exposed portion 61B where the negative electrode current collector foil 61 is exposed without a negative electrode active material layer 62 being formed at a second side edge 20B on the opposite side of the winding axis direction X of the wound electrode body 20. The first exposed portion 61A is divided into a strip along the first side edge 60A in the winding axis direction X of the negative electrode plate 60, and the second exposed portion 61B is divided into a strip along the second side edge 60B in the winding axis direction X of the negative electrode plate 60. The thickness of the negative electrode current collector foil 61 is, for example, 3 μm or more and 50 μm or less.

[0024] [Positive plate] The positive electrode plate 70 includes a long sheet-shaped positive electrode current collector foil 71 made of a metal material such as aluminum or an aluminum alloy, and a positive electrode active material layer 72 formed on both sides of the positive electrode current collector foil 71 along the longitudinal direction of the positive electrode current collector foil 71. The positive electrode active material layer 72 includes a positive electrode active material, a binder, and a conductive agent. As the positive electrode active material, any material capable of intercalating and releasing lithium ions and usable in lithium-ion secondary batteries can be used without particular limitation. Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel cobalt aluminate (NCA), lithium nickel cobalt manganese oxide (NCM), etc., which can be used alone or in combination. In addition, other metal elements may be added to the positive electrode active material. The positive electrode current collector foil 71 of the positive electrode plate 70 includes an exposed portion 71B at the second side edge 20B in the winding axis direction X of the wound electrode body 20, where the positive electrode active material layer 72 is not formed and the positive electrode current collector foil 71 is exposed. That is, the exposed portion 71B is divided into a strip along the side edge 70B in the winding axis direction X of the positive electrode plate 70. The thickness of the positive electrode current collector foil 71 is, for example, 10 μm or more and 50 μm or less.

[0025] [Exposed portions of the negative electrode current collector foil and the positive electrode current collector foil] As shown in Figure 2, at the first side edge 20A in the winding axis direction X of the wound electrode body 20, the first exposed portion 61A of the negative electrode plate 60 protrudes outward from the positive electrode plate 70 in the winding axis direction X. A group of negative electrode tabs is formed by bundling together multiple stacked portions (tabs) of the first exposed portion 61A of the negative electrode plate 60. The group of negative electrode tabs is electrically connected to the negative electrode external terminal 41 via the negative electrode conductive member 41A.

[0026] Furthermore, at the second side edge 20B in the winding axis direction X of the wound electrode body 20, the exposed portion 71B of the positive electrode plate 70 protrudes outward from the negative electrode plate 60 in the winding axis direction X. A group of positive electrode tabs is formed by bundling together multiple stacked portions (tabs) of the exposed portion 71B of the positive electrode plate 70. The group of positive electrode tabs is electrically connected to the positive electrode external terminal 42 via the positive electrode conductive member 42A.

[0027] [Separator] Figure 3 is a schematic partial cross-sectional view taken along line III-III in Figure 2. As shown in Figures 2 and 3, the separator 80 includes two long, sheet-like separator sheets 81 and 82 that are laminated with the negative electrode plate 60 sandwiched in between. The laminate of the wound electrode body 20 is constructed by laminating the separator sheet 81, the negative electrode plate 60, the separator sheet 82, and the positive electrode plate 70 in this order. Hereinafter, "inside of separator sheets 81 and 82" refers to the inside of the separator sheets 81 and 82 that sandwich the negative electrode plate 60, and the side of the separator sheets 81 and 82 that faces the negative electrode plate 60. Also, "outside of separator sheets 81 and 82" refers to the outside of the separator sheets 81 and 82 that sandwich the negative electrode plate 60, and the side of the separator sheets 81 and 82 that is opposite to the negative electrode plate 60.

[0028] The separator sheets 81 and 82 are porous resin sheets that hold the non-aqueous electrolyte 50. The negative electrode plate 60 and the separator sheets 81 and 82 are overlapped so that their longitudinal directions are aligned. In the wound electrode body 20, the separator sheets 81 and 82 are interposed between the negative electrode plate 60 and the positive electrode plate 70. The separator sheets 81 and 82 maintain the distance between the negative electrode plate 60 and the positive electrode plate 70 to prevent contact short circuits and also hold the non-aqueous electrolyte 50.

[0029] In this embodiment, the negative electrode active material layer 62 has a lower density than the positive electrode active material layer 72. When the active materials of the negative electrode active material layer 62 and the positive electrode active material layer 72 expand, the negative electrode active material layer 62 discharges a larger amount of non-aqueous electrolyte 50 than the positive electrode active material layer 72. For this reason, in this embodiment, the separator sheets 81 and 82 surround the negative electrode active material layer 62 at both side edges 20A and 20B in the winding axis direction X of the wound electrode body 20, efficiently suppressing the outflow of non-aqueous electrolyte 50 from the wound electrode body 20. In this embodiment, the negative electrode plate 60 corresponds to the first electrode plate, and the positive electrode plate 70 corresponds to the second electrode plate having a different polarity from the first electrode plate. In other examples where the positive electrode active material layer 72 has a lower density than the negative electrode active material layer 62, the separator sheets 81, 82 may surround the positive electrode active material layer 72 at both side edges 20A, 20B in the winding axis direction X of the wound electrode body 20.

[0030] As shown in Figure 3, in the winding axis direction X, the length of each separator sheet 81 and 82 is longer than the length of the negative electrode active material layer 62. Therefore, at both side edges 20A and 20B in the winding axis direction X of the wound electrode body 20, the separator sheet 81 has a first excess length portion 81A and a second excess length portion 81B that protrude outward from the first and second side edges 62A and 62B of the negative electrode active material layer 62, respectively, in the winding axis direction X. Similarly, at both side edges 20A and 20B in the winding axis direction X of the wound electrode body 20, the separator sheet 82 has a first excess length portion 82A and a second excess length portion 82B that protrude outward from the first and second side edges 62A and 62B of the negative electrode active material layer 62, respectively, in the winding axis direction X. In this embodiment, the first and second excess portions 81A to 82B are located on the first and second exposed portions 61A and 61B of the negative electrode current collector foil 61.

[0031] The first excess portions 81A and 82A of the separator sheets 81 and 82 include first end edges 83A and 84A in the winding axis direction X that are in non-fixed contact with the first exposed portion 61A. Here, "non-fixed contact" also means "non-integral contact," and it means that the first end edges 83A and 84A simply contact the first exposed portion 61A of the negative electrode current collector foil 61 without using welding or adhesive. As a result, the first end edges 83A and 84A sandwich the first exposed portion 61A, and the separator sheets 81 and 82 can surround the negative electrode active material layer 62 at the first side edge 20A in the winding axis direction X of the wound electrode body 20.

[0032] Furthermore, the separator sheets 81 and 82 are in contact with the first exposed portion 61A without being welded. This reduces the possibility of the separator sheets 81 and 82 becoming clogged or torn at the contact points.

[0033] Furthermore, when the negative electrode active material layer 62 expands and contracts, the first edges 83A and 84A can slide on the first exposed portion 61A in accordance with the expansion and contraction of the negative electrode active material layer 62. This reduces the load on the contact portions of the separator sheets 81 and 82. This improves the durability of the separator sheets 81 and 82.

[0034] Furthermore, the first retaining space S1 is partitioned by the first excess length portions 81A and 82A of the separator sheets 81 and 82, the first exposed portion 61A, and the negative electrode active material layer 62. As a result, the non-aqueous electrolyte 50 discharged from the negative electrode active material layer 62 can be retained by the first retaining space S1. In this embodiment, since the first edges 83A and 84A sandwich the first exposed portion 61A, the non-aqueous electrolyte 50 is less likely to leak to the outside of the separator sheets 81 and 82. The retained non-aqueous electrolyte 50 is re-impregnated by the negative electrode active material layer 62 when the active material of the negative electrode active material layer 62 shrinks. Therefore, it is possible to reduce the depletion of the non-aqueous electrolyte 50 and the uneven distribution of salt concentration in the wound electrode body 20, thereby suppressing an increase in the internal resistance of the secondary battery 10.

[0035] Furthermore, the second excess portions 81B and 82B of the separator sheets 81 and 82 include second end edges 83B and 84B in the winding axis direction X that are in non-fixed contact with the second exposed portion 61B. The second retaining space S2 is partitioned by the second excess portions 81B and 82B of the separator sheets 81 and 82, the second exposed portion 61B, and the negative electrode active material layer 62. As a result, the non-aqueous electrolyte 50 discharged from the negative electrode active material layer 62 is retained by the first retaining space S1 and the second retaining space S2 on both sides in the winding axis direction X, further suppressing the increase in the internal resistance of the secondary battery 10. The total volume of the first retaining space S1 and the second retaining space S2 can be set to be greater than or equal to the volume of air gaps in the negative electrode active material layer 62 that decreases when the secondary battery 10 is charged within a preset SOC (State of Charge) range, such as 0% to 100% or 25% to 75%. The decrease in the void volume of the negative electrode active material layer 62 when the secondary battery 10 is charged within a preset operating SOC range can be determined, for example, by measuring the amount of non-aqueous electrolyte 50 discharged from the negative electrode active material layer 62 when the secondary battery 10 is actually charged within a preset operating SOC range in an experiment. This ensures that the first retention space S1 and the second retention space S2 can hold the maximum amount of non-aqueous electrolyte 50 discharged from the negative electrode active material layer 62.

[0036] Furthermore, as shown in Figure 2, the wound electrode body 20 has a winding start end and a winding end 20C located in a direction Z perpendicular to the winding axis direction X. When the active material expands, the amount of non-aqueous electrolyte 50 discharged from the winding start end and winding end 20C is extremely small and has little effect on the increase in internal resistance. For this reason, in this embodiment, the separator sheets 81 and 82 are left open at the winding start end and winding end 20C of the wound electrode body 20. This makes it possible to suppress the increase in the internal resistance of the secondary battery 10 with a simple configuration. In other examples, the separator sheets 81 and 82 may surround the negative electrode active material layer 62 at the winding start end and winding end 20C of the wound electrode body 20.

[0037] The first edges 83A and 84A of the separator sheets 81 and 82 have curved surfaces that curve toward each other, and the second edges 83B and 84B of the separator sheets 81 and 82 may have curved surfaces that curve toward each other. In other words, these curved surfaces are curved to contact the first and second exposed portions 61A and 61B. Here, the “curved surfaces” are the inner and outer surfaces of the first and second edges 83A to 84B, corresponding to the inner and outer surfaces located on the inside and outside of the separator sheets 81 and 82. In this embodiment, the first edges 83A and 84A of the separator sheets 81 and 82 have curved surfaces that are convex toward the first exposed portion 61A (i.e., to form a convex curve). The second edges 83B and 84B of the separator sheets 81 and 82 have curved surfaces that are convex toward the second exposed portion 61B (i.e., to form a convex curve). The curved surface is in non-fixed contact with the first and second exposed portions 61A and 61B. The first and second edges 83A to 84B of the separator sheets 81 and 82 can contact the first exposed portion 61A and the second exposed portion 61B over a larger area. This allows the non-aqueous electrolyte 50 to be stably held in the first and second holding spaces S1 and S2. Furthermore, this curved surface facilitates the sliding of the first and second edges 83A to 84B of the separator sheets 81 and 82 over the first and second exposed portions 61A and 61B.

[0038] The first excess portions 81A and 82A of the separator sheets 81 and 82 extend from the first end edges 83A and 84A of the separator sheet 81 (first excess portions 81A and 82A) to the first side edge 62A in the winding axis direction X of the negative electrode active material layer 62. The second excess portions 81B and 82B of the separator sheets 81 and 82 extend from the second end edges 83B and 84B of the separator sheet 81 (second excess portions 81B and 82B) to the second side edge 62B in the winding axis direction X of the negative electrode active material layer 62. The entirety of these first and second excess portions 81A to 82B has a curved surface. That is, the entirety of the first and second excess portions 81A to 82B is curved. As a result, the first and second edges 83A to 84B of the separator sheets 81 and 82 can make stronger contact with the first exposed portion 61A and the second exposed portion 61B against the first exposed portion 61A and the second exposed portion 61B. Hereinafter, these overall curved first and second excess portions 81A to 82B may be referred to as the first and second curved excess portions.

[0039] The first and second excess portions 81A to 82B of the separator sheets 81 and 82 may have an S-shaped cross-section including a tip portion that curves convexly inward toward the separator sheets 81 and 82 and a base portion that curves convexly outward toward the separator sheets 81 and 82. In this embodiment, the first curved excess portions 81A and 82A have an S-shaped cross-section including a tip portion that is positioned near the first edge 83A and 84A and curves convexly toward the first exposed portion 61A, and a base portion that is positioned near the negative electrode active material layer 62 and curves convexly toward the opposite side of the first exposed portion 61A. The second curved excess portions 81B and 82B have an S-shaped cross-section including a tip portion that is positioned near the second edge 83B and 84B and curves convexly toward the second exposed portion 61B, and a base portion that is positioned near the negative electrode active material layer 62 and curves convexly toward the opposite side of the second exposed portion 61B.

[0040] These first and second curved excess portions 81A to 82B can be formed by thermal shrinking the separator sheets 81 and 82. In this embodiment, as will be described later, the first and second curved excess portions 81A to 82B are formed by heating the separator sheets 81 and 82 using the heat (thermal history) of heating and drying in the drying process of the manufacturing process of the secondary battery 10. For this reason, each of the separator sheets 81 and 82 uses a multilayer separator sheet containing multiple (three in this embodiment) resin layers, as will be described later. The multiple resin layers are stacked in the thickness direction of the separator sheets 81 and 82. Figure 4 is an enlarged cross-sectional view illustrating the multilayer separator sheet. As shown in Figure 4, each of the separator sheets 81 and 82 includes an intermediate resin layer 85 and an inner resin layer 86 and an outer resin layer 87 that sandwich the intermediate resin layer 85. The inner resin layer 86 is located inside the separator sheets 81 and 82. Furthermore, the outer resin layer 87 is positioned on the outside of the separator sheets 81 and 82.

[0041] In this embodiment, the intermediate resin layer 85 has a lower thermal shrinkage temperature than the inner resin layer 86 and the outer resin layer 87. In one example, the intermediate resin layer 85 may have higher thermal shrinkage than the inner resin layer 86 and the outer resin layer 87. The inner resin layer 86 has weaker rigidity or strength than the outer resin layer 87 in order to curve the separator sheets 81 and 82 inward. The intermediate resin layer 85 includes, for example, polyethylene (PE). The inner resin layer 86 and the outer resin layer 87 include, for example, polypropylene (PP).

[0042] In this embodiment, the amount of thermal shrinkage of the intermediate resin layer 85 is greater than the amount of thermal shrinkage of the inner resin layer 86 and the outer resin layer 87. During the drying process, the intermediate resin layer 85 shrinks with a greater amount of thermal shrinkage than the inner resin layer 86 and the outer resin layer 87, or only the intermediate resin layer 85 shrinks. As will be described later, due to the thermal shrinkage mainly of the intermediate resin layer 85, the first and second excess portions 81A to 82B of the separator sheets 81 and 82 are curved inward. This difference in thermal shrinkage between the intermediate resin layer 85 and the inner resin layer 86 and the outer resin layer 87 is achieved by appropriately adjusting the physical properties of the resin layers 85, 86, and 87, as well as the heating temperature in the drying process. The heating temperature in the drying process is set, for example, to 60°C or higher and 130°C or lower.

[0043] Therefore, when the separator sheets 81 and 82 are heated during the drying process, the intermediate resin layer 85 shrinks, while the inner resin layer 86 and outer resin layer 87 attempt to maintain their current dimensions and shape without shrinking. However, because the inner resin layer 86 has weaker rigidity or strength than the outer resin layer 87, the first and second excess portions 81A to 82B of the separator sheets 81 and 82 curve or curl toward the inner resin layer 86, that is, toward the first and second exposed portions 61A and 61B, due to the shrinkage of the intermediate resin layer 85. This curving or curling causes the first and second edges 83A to 84B of the separator sheets 81 and 82 to move closer to (or toward each other) the first and second exposed portions 61A and 61B, and the entirety of the first and second excess portions 81A to 82B curves convexly toward the opposite side of the first exposed portion 61A (towards the outside of the separator sheets 81 and 82).

[0044] In other examples, the multilayer separator sheet may be configured such that the inner resin layer 86 shrinks with a greater amount of thermal shrinkage than the intermediate resin layer 85 and the outer resin layer 87, or that only the inner resin layer 86 shrinks, in order to curve the first and second excess portions 81A to 82B of the separator sheets 81 and 82 inward. That is, the first and second excess portions 81A to 82B may be curved inward mainly by the thermal shrinkage of the inner resin layer 86 located inside the separator sheets 81 and 82. In this case, the intermediate resin layer 85 may be omitted, meaning that the multilayer separator sheet may consist of two or more separator sheets.

[0045] The multilayer separator sheet is not limited to the multilayer separator sheet exemplified, and can be appropriately configured so that the first and second excess portions 81A to 82B of the separator sheets 81 and 82 are curved inward by thermal shrinkage.

[0046] The intermediate resin layer 85, the inner resin layer 86, and the outer resin layer 87 according to this embodiment can be configured in combinations of characteristics and dimensions as shown in Examples 1 to 4 of Table 1.

[0047] [Table 1] In the multilayer separator sheets of Examples 1 to 4, the intermediate resin layer 85 contains polyethylene, and the inner resin layer 86 and outer resin layer 87 contain polypropylene. The intermediate resin layer 85 has general physical properties used in lithium-ion secondary batteries.

[0048] First, let's describe the first example of a multilayer separator sheet. The inner resin layer 86 has a larger porosity than the outer resin layer 87. The inner resin layer 86 and the outer resin layer 87 are similar in other physical properties. Also, there are no additional layers.

[0049] Next, a second example of a multilayer separator sheet will be described. The inner resin layer 86 has a lower density than the outer resin layer 87. The inner resin layer 86 and the outer resin layer 87 are similar in other physical properties. Also, there are no additional layers.

[0050] Next, a third example of a multilayer separator sheet will be described. The inner resin layer 86 has a smaller thickness than the outer resin layer 87. The inner resin layer 86 and the outer resin layer 87 are similar in other physical properties. Also, there are no additional layers.

[0051] Next, a fourth example of a multilayer separator sheet will be described. The inner resin layer 86 and the outer resin layer 87 have similar physical properties and dimensions. An additional layer is laminated on the outer resin layer 87. For example, the additional layer is a heat-resistant layer (HRL) and contains alumina as its material. The additional layer is laminated on at least one of the inner and outer surfaces of the outer resin layer 87.

[0052] In other words, the inner resin layer 86 has weaker rigidity or strength than the outer resin layer 87, and therefore has a larger porosity, a smaller density, a thinner thickness, and additional layers laminated on top of the outer resin layer 87. In other examples, the inner resin layer 86 and the outer resin layer 87 may consist of multiple layers, and the inner resin layer 86 may have a different number of layers than the outer resin layer 87. In this case, the inner resin layer 86 and the outer resin layer 87, as a whole, have the physical properties such as porosity, density, and thickness described above, so that the inner resin layer 86 can have weaker rigidity or strength than the outer resin layer 87.

[0053] In this case, the degree to which the multilayer separator sheet bends or curls depends on the amount of thermal shrinkage of the intermediate resin layer 85, that is, the physical properties of the intermediate resin layer 85 and the temperature of the drying process. [Nonaqueous electrolyte] The non-aqueous electrolyte 50 is impregnated into the wound electrode body 20. The non-aqueous electrolyte 50 is, for example, a composition obtained by dissolving a lithium salt in an organic solvent. Examples of lithium salts that can be used include LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. Examples of organic solvents that can be used include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butanesultone; or phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One or more of these can be mixed and used as the non-aqueous electrolyte 50. However, the composition of the non-aqueous electrolyte 50 is not limited to these.

[0054] [Battery case] The battery case 30 is made of a metal material such as aluminum, aluminum alloy, and stainless steel. As shown in Figure 1, the battery case 30 includes a case body 31 and a sealing plate 32. In this embodiment, the battery case 30 has a flattened rectangular box shape (square). In other examples, the battery case 30 may have any shape, such as a cylinder. The case body 31 has an internal space for housing the wound electrode body 20 and the non-aqueous electrolyte 50. The case body 31 includes a bottom wall 33 which is a plate member and a peripheral wall 34 which extends upward from the outer peripheral edge of the bottom wall 33. The peripheral wall 34 has a cylindrical shape that encloses the internal space. In this embodiment, to match the square battery case 30, the bottom wall 33 has a rectangular shape in plan view, and the peripheral wall 34 has a rectangular cylindrical shape.

[0055] Furthermore, the surface of the case body 31 facing the bottom wall 33 is open. The peripheral wall 34 is located at the end opposite to the bottom wall 33 and includes an open end that demarcates the opening of the case body 31. The opening of the case body 31 communicates with the internal space of the case body 31. The wound electrode body 20 is inserted into the internal space of the case body 31 through the opening of the case body 31.

[0056] The sealing plate 32 seals the opening of the case body 31. For example, the outer edge of the sealing plate 32 is joined to the opening end of the case body 31 by laser welding or the like. In this embodiment, to match the rectangular battery case 30, the sealing plate 32 is a rectangular plate member. The sealing plate 32 includes a gas discharge valve 36 that releases gas from the internal space in accordance with the pressure of the internal space, and an injection port 37 used for injecting a non-aqueous electrolyte 50.

[0057] [Manufacturing method for secondary battery 10] The manufacturing method for the secondary battery 10 comprises a source preparation process, an electrode body manufacturing process, a terminal welding process, a case insertion process, a sealing process, a drying process, a liquid injection and sealing process, and an activation process.

[0058] First, in the source process, the battery components, namely the negative electrode plate 60, positive electrode plate 70, separator sheets 81 and 82, and non-aqueous electrolyte 50, are manufactured. Figure 5 is a perspective view showing a laminate formed by stacking separator sheets 81, 82 and a negative electrode plate 60. Figure 6 is a cross-sectional view of the laminate in Figure 5. In the laminates of Figures 5 and 6, the positive electrode plate 70 is not shown for ease of understanding. In the electrode manufacturing process, the separator sheet 81, negative electrode plate 60, separator sheet 82, and positive electrode plate 70 are stacked (laminated) in this order so that their longitudinal directions are aligned. The separator sheets 81 and 82 are oriented in opposite directions to each other so that the inner resin layer 86 is adjacent to the negative electrode active material layer 62. This makes it possible to manufacture a long laminate containing the negative electrode plate 60, the positive electrode plate 70, and the separator sheets 81 and 82.

[0059] As shown in Figures 5 and 6, the excess portions 81A to 82B of the separator sheets 81 and 82 protrude outward from the first and second side edges 62A and 62B of the negative electrode active material layer 62 in the width direction corresponding to the winding axis direction X, respectively. Before the drying process, the excess portions 81A to 82B of the separator sheets 81 and 82 extend horizontally or nearly horizontally and do not come into contact with the first and second exposed portions 61A and 61B of the negative electrode plate 60. In Figures 5 and 6, the excess portions 81A to 82B of the separator sheets 81 and 82 are shown horizontally, but in reality, the excess portions 81A to 82B of the separator sheets 81 and 82 may be slightly bent due to gravity or other factors, or may be slightly curled even before the drying process.

[0060] Next, as shown in Figure 7, this laminate is wound longitudinally around the winding axis WL to form a wound body. This wound body is then flattened using a press. This completes the production of the wound electrode body 20.

[0061] In the terminal welding process, the negative electrode conductive member 41A is welded to the group of negative electrode tabs of the wound electrode body 20. Similarly, the positive electrode conductive member 42A is welded to the group of positive electrode tabs of the wound electrode body 20. In the case insertion process, an insulating holder (not shown) is attached to the wound electrode body 20, and the wound electrode body 20 is inserted into the case body 31.

[0062] In the sealing welding process, the case body 31 that houses the wound electrode body 20 and the sealing plate 32 are joined together airtightly by laser welding. In the drying process, the secondary battery 10 is heated to dry the wound electrode body 20. This removes moisture contained in the wound electrode body 20. As for the drying method, conventionally known methods of heat drying can be appropriately adopted. Furthermore, conventionally known drying ovens can be used without any particular limitations. In this embodiment, in the drying process, the heat (thermal history) of the heat drying is used to form the excess curved portions 81A to 82B of the separator sheets 81 and 82. In other examples, the excess curved portions 81A to 82B may be formed in a process other than the drying process, for example, in the electrode body manufacturing process, by separately heating the separator sheets 81 and 82, such as the laminate or wound electrode body 20.

[0063] The heating temperature and heating time required to form the curved excess portions 81A to 82B vary depending on conditions such as the thermal shrinkage temperature and material of the separator sheets 81 and 82, and the difference between the inner resin layer 86 and the outer resin layer 87. Therefore, the heating temperature and heating time in the drying process are appropriately controlled according to these conditions to form the curved excess portions 81A to 82B. As the heating temperature and heating time in the drying process, for example, general heating temperatures and heating times applied to lithium-ion secondary batteries are used. In this embodiment, the heating temperature in the drying process is, for example, 60°C to 130°C. The heating temperature may be constant or changed during the drying process. Such heating temperatures and heating times can be appropriately adjusted according to the structure and equipment capacity of the drying oven, etc., so that the curved excess portions 81A to 82B are formed.

[0064] During the drying process, when the separator sheets 81 and 82 are heated, the intermediate resin layer 85 shrinks, while the inner resin layer 86 and outer resin layer 87 attempt to maintain their current dimensions and shape without shrinking. However, because the inner resin layer 86 has weaker rigidity or strength than the outer resin layer 87, the separator sheets 81 and 82 curve or curl toward the inner resin layer 86 due to the shrinkage of the intermediate resin layer 85, that is, toward the first and second exposed portions 61A and 61B. As shown by the dashed line in Figure 6, as the excess portions 81A to 82B curve or curl toward the first and second exposed portions 61A and 61B from a horizontal position, the edges 83A to 84B of the excess portions 81A to 82B approach the first and second exposed portions 61A and 61B and come into contact with them. In this case, the inner surfaces of the edges 83A to 84B come into contact with the first and second exposed portions 61A and 61B. As the intermediate resin layer 85 shrinks further, the contacted first and second exposed portions 61A and 61B prevent the excess portions 81A to 82B from bending or curling further. Therefore, as shown in Figure 3, the tip portion of the excess portions 81A to 82B that is in contact with the first and second exposed portions 61A and 61B, closer to the edges 83A to 84B, curves convexly toward the first and second exposed portions 61A and 61B. That is, the excess portions 81A to 82B have an S-shaped cross-section, including a tip portion located closer to the edges 83A to 84B and curving convexly toward the first and second exposed portions 61A and 61B, and a base portion located closer to the negative electrode active material layer 62 and curving convexly toward the opposite side of the first and second exposed portions 61A and 61B. This creates the curved excess portions 81A to 82B. Note that the parts of the separator sheets 81 and 82 other than the respective excess portions 81A to 82B are adjacent to the negative electrode active material layer 62, and therefore their shape does not change. In addition, the secondary battery 10 is generally designed so that the temperature of the separator sheets 81 and 82 does not rise to a temperature that deforms the curved excess portions 81A to 82B when the secondary battery 10 is in use. For this reason, the shape of the curved excess portions 81A to 82B can be maintained when the secondary battery 10 is in use.

[0065] Next, referring to Figure 6, the method for setting the lengths Y1 and Y2 of the excess portions 82A and 82B in the width direction X of the separator sheet 82 before heat shrinkage will be explained. For the sake of explanation, Figure 6 shows the wound electrode body 20 before the drying process and illustrates several parameters used in the setting method, but these parameters should be the values ​​for the wound electrode body 20 after the drying process.

[0066] Here, the negative electrode active material layer 62 closer to the separator sheet 82 (upper side in Figure 6) is defined as the upper negative electrode active material layer 62U, the first holding space S1 and the second holding space S2 closer to the separator sheet 82 (upper side in Figure 6) are defined as the first upper holding space S1U and the second upper holding space S2U, the porosity of the upper negative electrode active material layer 62U is set to 50%, the usable SOC range of the secondary battery 10 is set to 0-100%, and the rate of change C of the void volume of the upper negative electrode active material layer 62U when the secondary battery 10 is charged from SOC 0% to 100% is set to Δ5%.

[0067] The maximum amount of electrolyte Dmax discharged from the upper negative electrode active material layer 62U when the secondary battery 10 is charged from SOC 0% to 100% is A × H × L (Pmax - Pmin) [mm²]. 3 Here, "A" is the width [mm] of the upper negative electrode active material layer 62U, "H" is the thickness [mm] of the upper negative electrode active material layer 62U, "L" (see Figure 5) is the length [mm] of the upper negative electrode active material layer 62U, "Pmax" is the maximum porosity [%] (approximately 50% here) in the operating SOC range of the secondary battery 10, and "Pmin" is the minimum porosity [%] in the operating SOC range of the secondary battery 10.

[0068] The volume V1 of the first upper holding space S1U is B1 × H × L / 2 [mm²] 3 The volume V2 of the second upper holding space S2U is B2 × H × L / 2 [mm²]. 3Here, "B1" is the distance from the point of contact between the edge 84A of the excess curved portion 82A after thermal shrinkage in the winding axis direction X and the first exposed portion 61A to the first side edge 62A of the negative electrode active material layer 62, and "B2" is the distance from the point of contact between the edge 84B of the excess curved portion 82B after thermal shrinkage in the winding axis direction X and the second exposed portion 61B to the second side edge 62B of the negative electrode active material layer 62.

[0069] Preferably, the maximum amount of electrolyte Dmax discharged from the upper negative electrode active material layer 62U, the volume V1 of the first upper holding space S1U, and the volume V2 of the second upper holding space S2U have the relationship Dmax ≤ V1 + V2.

[0070] In this embodiment, the negative electrode active material layer 62 as a whole has a uniform amount of non-aqueous electrolyte 50 discharged from the cross-section of the wound electrode body 20. For example, the density and thickness of the negative electrode active material layer 62, as well as the load on the negative electrode active material layer 62, are the same throughout the negative electrode active material layer 62. In this case, Dmax / 2 ≤ V1 and Dmax / 2 ≤ V2 can be defined. Also, if B1 = B2 = B, then A × H × L (Pmax - Pmin) ≤ B × H × L can be defined.

[0071] Furthermore, using the thermal shrinkage rate (porous volume change rate, Δ5% in this embodiment) C of the separator sheet 82 due to the thermal history in the drying process, the lengths Y1 and Y2 of the excess portions 82A and 82B in the width direction X of the separator sheet 82 before thermal shrinkage can be defined by the following formula.

[0072]

number

[0073] Next, in the liquid injection and sealing process, the non-aqueous electrolyte 50 is injected through the injection port 37, and the injection port 37 is sealed airtight. In the activation process, the secondary battery 10 undergoes an initial charging process and aging.

[0074] This allows for the manufacture of a secondary battery 10. [Effects and Effects] Next, the effects and advantages of this embodiment will be described.

[0075] (1) The first excess length portions 81A and 82A of the separator sheets 81 and 82 include first end edges 83A and 84A in the winding axis direction X that are in non-fixed contact with the first exposed portion 61A. This reduces the possibility of the separator sheets 81 and 82 becoming crushed or torn at the contact portion of the separator sheets 81 and 82. In addition, the first retaining space S1 is partitioned by the first excess length portions 81A and 82A of the separator sheets 81 and 82, the first exposed portion 61A, and the negative electrode active material layer 62. This allows the non-aqueous electrolyte 50 discharged from the negative electrode active material layer 62 to be retained by the first retaining space S1. Therefore, the secondary battery 10 can suppress an increase in internal resistance while maintaining the durability of the separator sheets 81 and 82.

[0076] (2) When the negative electrode active material layer 62 expands and contracts, the first edges 83A and 84A are slidable on the first exposed portion 61A in accordance with the expansion and contraction of the negative electrode active material layer 62. This reduces the load on the contact portions of the separator sheets 81 and 82 and improves the durability of the separator sheets 81 and 82.

[0077] (3) The first edges 83A and 84A of the separator sheets 81 and 82 have curved surfaces that curve toward each other. This allows the first edges 83A and 84A of the separator sheets 81 and 82 to contact the first exposed portion 61A over a larger area. Therefore, the non-aqueous electrolyte 50 can be stably held in the first holding space S1.

[0078] (4) The entirety of the first excess portions 81A and 82A has a curved surface. This allows the first end edges 83A and 84A of the separator sheets 81 and 82 to contact the first exposed portion 61A more strongly than the first exposed portion 61A.

[0079] (5) The first excess portions 81A and 82A have an S-shaped cross-section. This allows the first edges 83A and 84A of the separator sheets 81 and 82 to contact the first exposed portion 61A more strongly than the first exposed portion 61A.

[0080] (6) The first excess portions 81A and 82A have a semicircular cross-section. This allows the first edges 83A and 84A of the separator sheets 81 and 82 to contact the first exposed portion 61A more strongly than the first exposed portion 61A.

[0081] (7) Multilayer separator sheets are used as separator sheets 81 and 82. The inner resin layer 86 has lower rigidity or strength than the outer resin layer 87. As a result, the first and second curved excess portions 81A to 82B can be formed by heating the separator sheets 81 and 82.

[0082] (8) The inner resin layer 86 has a larger porosity, a lower density, or a thinner thickness than the outer resin layer 87. As a result, the inner resin layer 86 can have weaker rigidity or strength than the outer resin layer 87.

[0083] (9) The inner resin layer 86 has an additional layer laminated on the outer resin layer 87. This allows the inner resin layer 86 to have less rigidity or strength than the outer resin layer 87.

[0084] (10) The separator sheets 81 and 82 are released at the winding start end and winding end end 20C of the wound electrode body 20. This makes it possible to suppress the increase in the internal resistance of the secondary battery 10 with a simple configuration.

[0085] (11) The second excess portions 81B and 82B of the separator sheets 81 and 82 include second end edges 83B and 84B in the winding axis direction X that are in non-fixed contact with the second exposed portion 61B. Furthermore, the second retaining space S2 is partitioned by the second excess portions 81B and 82B of the separator sheets 81 and 82, the second exposed portion 61B, and the negative electrode active material layer 62. As a result, the non-aqueous electrolyte 50 discharged from the negative electrode active material layer 62 is retained by the first retaining space S1 and the second retaining space S2 on both sides in the winding axis direction X, thereby further suppressing the increase in the internal resistance of the secondary battery 10.

[0086] (12) The total volume of the first holding space S1 and the second holding space S2 is set to be greater than or equal to the volume of voids in the negative electrode active material layer 62 that decreases when the secondary battery 10 is charged within a preset operating SOC range. As a result, the first holding space S1 and the second holding space S2 can hold the maximum amount of non-aqueous electrolyte 50 discharged from the negative electrode active material layer 62.

[0087] [Another example] The present invention can be implemented as follows, notwithstanding the above embodiments. Figure 8 is a partial cross-sectional view illustrating the negative electrode plate 60 and separator sheets 81, 82 in an alternative example of a wound electrode body 120. In this embodiment, at the second side edge 20B in the winding axis direction X of the wound electrode body 20, the negative electrode current collector foil 61 includes a second exposed portion 61B, and the second end edges 83B, 84B of the separator sheets 81, 82 are in non-fixed contact with the second exposed portion 61B. As shown in Figure 8, at the second side edge 20B in the winding axis direction X of the wound electrode body 20, the negative electrode current collector foil 61 does not include a second exposed portion 61B and does not need to protrude outward from the negative electrode active material layer 62. The first exposed portion 61A is necessary for electrical connection to the negative electrode external terminal 41 via the negative electrode conductive member 41A, but the second exposed portion 61B may be omitted. In this case, the second edges 83B and 84B of the separator sheets 81 and 82 are in non-fixed contact with each other. The second holding space S2 is not divided into two spaces by the second exposed portion 61B, but is a single space. Even in this case, the curved excess portions 81B and 82B are formed in the same manner as in this embodiment, and the secondary battery 10 can achieve the same effects as in this embodiment.

[0088] Figure 9 is a partial cross-sectional view illustrating the negative electrode plate 60 and separator sheets 81 and 82 in an alternative example of a wound electrode body 220. In this embodiment, during the drying process, the inner surfaces of the first and second edges 83A to 84B come into contact with the first and second exposed portions 61A and 61B, after which excess portions 81A to 82B having an S-shaped cross-section are formed. As shown in Figure 9, at the second side edge 20B in the winding axis direction X of the wound electrode body 20, the length Y2 of the excess portions 81B and 82B of the separator sheet 82 before heat shrinkage may be made relatively short to form excess portions 81B and 82B having a semicircular cross-section. Even in this case, the second edges 83B and 84B have curved surfaces that curve toward each other. Specifically, when the separator sheets 81 and 82 are heated during the drying process, the excess portions 81B and 82B curve or curl toward each other from a horizontal state. Because the length Y2 of the excess portions 81B and 82B is relatively short, the inner surfaces of the second edges 83B and 84B do not come into contact with each other, and the excess portions 81B and 82B further curve or curl, causing the outer surfaces of the second edges 83B and 84B to come into contact with each other. The entirety of the excess portions 81B and 82B has a semicircular cross-section that is convex outward in the winding axis direction X. The length Y2 of the excess portions 81B and 82B can be set so that the inner surfaces of the second edges 83B and 84B do not come into contact with each other. Even in this case, the secondary battery 10 can achieve the same effects as in this embodiment.

[0089] In another example shown in Figure 9, excess portions 81B and 82B having a semicircular cross-section were formed on the second side edge 20B in the winding axis direction X of the wound electrode body 20. However, excess portions 81A to 82B having a semicircular cross-section may be formed on at least one of the first side edge 20A and the second side edge 20B in the winding axis direction X of the wound electrode body 20. When excess portions 81A and 82A having a semicircular cross-section are formed on the first side edge 20A in the winding axis direction X of the wound electrode body 20, the outer surfaces of the first end edges 83A and 84A come into contact with each other via the first exposed portion 61A. In other words, the outer surfaces of the first end edges 83A and 84A come into non-fixed contact with the first exposed portion 61A.

[0090] In the alternative example shown in Figure 9, the negative electrode current collector foil 61 does not include the second exposed portion 61B, and the outer surfaces of the second edges 83B and 84B are in non-fixed contact with each other. However, the negative electrode current collector foil 61 may include the second exposed portion 61B. In this case, the outer surfaces of the second edges 83B and 84B are in contact with each other via the second exposed portion 61B. In other words, the outer surfaces of the second edges 83B and 84B are in non-fixed contact with the second exposed portion 61B.

[0091] The numerical limitations in the above embodiments are illustrative and do not limit this disclosure. Those skilled in the art can optimize them as appropriate depending on the configuration and manufacturing conditions of the secondary battery 10. It goes without saying that this disclosure can be implemented by those skilled in the art by adding, deleting, or modifying its configuration, as long as it does not deviate from the scope of the claims. [Explanation of symbols]

[0092] S1...first holding space S2…Second holding space WL…winding shaft X…Winding axis direction 10…Secondary battery 20,120,220...Wound electrode body 20A...First side edge 20B…Second side edge 20C...End of winding 30...Battery case 50...Nonaqueous electrolyte 60…First electrode plate (negative electrode plate) 61...Current collector foil (negative electrode current collector foil) 61A…1st exposed part 61B…Second exposed part 62...Active material layer (negative electrode active material layer) 70...Second electrode plate (positive electrode plate) 80... Separator 81... Separator sheet 81A…1st extra length part 81B…Second extra length part 82... Separator sheet 82A…1st extra length part 82B…Second extra length part 83A,84A…1st end 83B, 84B…Second Ending 85…Intermediate resin layer 86…Inner resin layer 87…Outer resin layer

Claims

1. A wound electrode body is formed by winding a laminate containing a first electrode plate, a second electrode plate having a polarity different from that of the first electrode plate, and a separator interposed between the first electrode plate and the second electrode plate, around a winding axis. The battery comprises the aforementioned wound electrode body and a battery case for housing a non-aqueous electrolyte, Each of the first electrode plate and the second electrode plate includes a current collector foil and an active material layer formed on the current collector foil, wherein the active material layer of the first electrode plate has a lower density than the active material layer of the second electrode plate. The separator includes two separator sheets stacked with the first electrode plate sandwiched in between, At the first side edge in the winding axis direction of the winding electrode body, The current collector foil of the first electrode plate includes a first exposed portion in which the current collector foil is exposed without the formation of the active material layer. Each of the two separator sheets includes a first excess length portion that protrudes outward from the active material layer of the first electrode plate in the winding axis direction, The first excess length portion of the two separator sheets includes a first end edge that is in non-fixed contact with the first exposed portion. A secondary battery in which the first holding space is partitioned by the first excess length portion of the two separator sheets and the current collector foil and active material layer of the first electrode plate.

2. The secondary battery according to claim 1, wherein the first edges of the two separator sheets have curved surfaces that curve toward each other.

3. The secondary battery according to claim 2, wherein the curved surfaces of the two separator sheets extend over the entire first excess length portion of the separator sheets.

4. The secondary battery according to claim 3, wherein the first excess length portion of the two separator sheets has an S-shaped cross-section including a tip portion that is curved inward and convexly toward the inside of the two separator sheets and a base portion that is curved outward and convexly toward the outside of the two separator sheets.

5. The secondary battery according to claim 3, wherein the first excess length portion of the two separator sheets has a semicircular cross-section that is convex outward in the winding axis direction.

6. Each of the two separator sheets is It includes an intermediate resin layer, an inner resin layer positioned on the side of the first electrode plate facing the current collector foil relative to the intermediate resin layer, and an outer resin layer positioned on the opposite side of the intermediate resin layer from the inner resin layer, The secondary battery according to claim 3, wherein the inner resin layer has less rigidity than the outer resin layer.

7. The inner resin layer is The secondary battery according to claim 6, having a larger porosity than the outer resin layer, a smaller density than the outer resin layer, or a thinner thickness than the outer resin layer.

8. Each of the two separator sheets is A secondary battery according to claim 3, comprising: an intermediate resin layer; an inner resin layer disposed on the side of the first electrode plate facing the current collector foil relative to the intermediate resin layer; an outer resin layer disposed on the opposite side of the intermediate resin layer from the inner resin layer; and a heat-resistant layer formed on the outer resin layer.

9. The wound electrode body has a winding start end and a winding end located in a direction perpendicular to the winding axis direction, The secondary battery according to claim 1, wherein the two separator sheets are not in contact and are open at the winding start end and winding end end of the wound electrode body.

10. At the second side edge of the wound electrode body opposite to the first side edge in the winding axis direction, The current collector foil of the first electrode plate includes a second exposed portion in which the current collector foil is exposed without the formation of the active material layer. Each of the two separator sheets includes a second excess length portion that protrudes outward from the active material layer of the first electrode plate in the winding axis direction. The two separator sheets include a second edge that is in non-fixed contact with the second exposed portion. The secondary battery according to any one of claims 1 to 9, wherein the second holding space is partitioned by the second excess length portion of the two separator sheets and the current collector foil and active material layer of the first electrode plate.

11. The secondary battery according to claim 10, wherein the total volume of the first holding space and the second holding space is set to be greater than or equal to the void volume of the active material layer of the first electrode plate that decreases when the secondary battery is charged within a preset operating SOC range.

12. At the second side edge of the wound electrode body opposite to the first side edge in the winding axis direction, Each of the two separator sheets includes a second excess length portion that protrudes outward from the active material layer of the first electrode plate in the winding axis direction. The second excess length portion of the two separator sheets includes a second end edge that is in non-fixed contact with each other. The secondary battery according to any one of claims 1 to 9, wherein the second holding space is partitioned by the second excess length portion of the two separator sheets and the active material layer of the first electrode plate.

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