Electrode body for secondary battery
By employing a combination structure of outer and inner separators in the secondary battery, and utilizing high-melting-point adhesive resin to form an end overlap with increased thickness during cutting, the problem of end bending of the separator is solved, thereby improving the uniformity and durability of the electrode body.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SANYO ELECTRIC CO LTD
- Filing Date
- 2021-02-08
- Publication Date
- 2026-05-29
AI Technical Summary
In existing technologies, the ends of the separators in secondary batteries are prone to bending, resulting in uneven electrode thickness and affecting performance and durability.
The structure employs a combination of outer and inner separators, wherein the thickness of the outer and inner separators at the overlapping portion at the end is greater than the sum of the thicknesses of the opposite portions of the electrodes, and they are fused together during cutting using a high-melting-point adhesive resin to form an end overlap with increased thickness.
It effectively prevents bending at the ends of the separator, ensures the uniformity of electrode thickness and rigidity, and improves battery performance and durability.
Smart Images
Figure CN115298877B_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to electrode bodies for secondary batteries. Background Technology
[0002] In high-capacity secondary batteries, in order to improve the filling efficiency, production cycle and quality of the electrode body including the positive electrode, negative electrode and separator, it is considered to use a separator with an adhesive resin having a melting point higher than that of the substrate coated on at least one side.
[0003] Patent Document 1 describes the following: In an electrode body for a secondary battery, one of the positive and negative electrodes is held between two separators. The ends of the two separators at the end of their winding are overlapped and joined by heat fusion to form a joint. This prevents contact between the positive and negative electrodes caused by bending of the ends of the separators.
[0004] Existing technical documents
[0005] Patent documents
[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-129366 Summary of the Invention
[0007] Even when the ends of the two separators are overlapped and thermally fused together to form a joint, as described in Patent Document 1, it is possible that only the corners of the ends including the joint are bent inwards and stacked on top of the other parts of the electrode body. In this case, since the thickness of a part of the electrode body locally increases, uneven stress occurs when pressure is applied to the electrode body from the outside, thus leaving room for improvement in performance and durability.
[0008] An electrode body for a secondary battery, as one aspect of this disclosure, includes: a positive electrode and a negative electrode; an outer separator and an inner separator disposed on the inner side of the outer separator, the outer separator and the inner separator having a functional layer on at least one side, the functional layer having an adhesive resin with a melting point higher than that of the separator substrate, the outer electrode of the positive electrode and the negative electrode disposed on the outer side being held by the outer separator and the inner separator, wherein the outer separator and the inner separator have: two electrode opposing portions that are opposite to and overlap the outermost layer of the outer electrode; and end overlapping portions disposed at the ends of the outer separator and the inner separator, the thickness of the end overlapping portions being greater than the sum of the thicknesses of the two electrode opposing portions.
[0009] According to the electrode body for secondary batteries disclosed herein, when the separator is wound or overlapped to form the electrode body, bending can be prevented only at the corners of the ends of the separator. Attached Figure Description
[0010] Figure 1 This is a diagram showing a cross-section of the outer casing of a non-aqueous electrolyte secondary battery in one embodiment.
[0011] Figure 2 yes Figure 1 A cross-sectional view of the electrode body for a secondary battery.
[0012] Figure 3 yes Figure 2 Enlarged view of part B.
[0013] Figure 4 This is a perspective view showing the state in which the outer and inner separators of the electrode body for the secondary battery in the comparative example are bent.
[0014] Figure 5 Another example of the embodiment is the electrode body for a secondary battery. Figure 3 The corresponding diagram. Detailed Implementation
[0015] The following describes in detail an electrode body for a secondary battery as an example of an embodiment. Specific dimensional ratios, etc., should be determined with reference to the following description. In this specification, the use of the phrase "approximately the same" means, in the case of cases where the parts are substantially the same, not only identical but also substantially identical. Furthermore, the term "end" refers to the edge of the object and its vicinity. Additionally, the shapes, materials, quantities, and values described below are illustrative examples and can be varied depending on the specifications of the electrode body for a secondary battery. Hereinafter, the same reference numerals will be used to label the same structures, and descriptions will follow.
[0016] The secondary battery, including the electrode body described below, is a square secondary battery used as a drive power source for electric vehicles or hybrid vehicles.
[0017] The following uses Figures 1 to 3 A secondary battery as an example of an embodiment will be described. Hereinafter, the case where the secondary battery 10 is a non-aqueous electrolyte secondary battery will be described, but the secondary battery of this disclosure can also be applied to other secondary batteries. Figure 1 This is a diagram showing the outer casing 12 cut across the secondary battery 10. Figure 2 yes Figure 1 A cross-sectional view of electrode body 20 for secondary batteries. Figure 3 yes Figure 2 A magnified view of part B. Figure 1 In the description, for convenience, the sealing plate 14 side of the outer shell 12 is described as the top and the side opposite to the sealing plate 14 is described as the bottom.
[0018] The secondary battery 10 includes an outer casing 12 as the housing and secondary battery electrode bodies 20 disposed inside the outer casing 12. Hereinafter, the secondary battery electrode body 20 will be referred to as electrode body 20. A non-aqueous electrolyte, equivalent to a non-aqueous electrolyte, is contained inside the outer casing 12. The non-aqueous electrolyte is, for example, an electrolyte containing lithium salt, which has lithium-ion conductivity.
[0019] like Figure 2 As shown, the electrode body 20 is wound along the length direction of the secondary battery 10. Figure 1 left and right directions Figure 2 The winding structure extending from the front and back of the paper is a flat wound electrode body obtained by winding the positive electrode 22 and the negative electrode 26 with spacers 30 and 31 in between. The electrode body 20 is, for example, a strip-shaped positive electrode 22, a strip-shaped inner spacer 30, a strip-shaped negative electrode 26, and a strip-shaped outer spacer 31 are wound in a stacked state, with the outer spacer 31 arranged at the outermost periphery.
[0020] like Figure 1 As shown, the metal outer casing 12 is box-shaped with an opening at the top, and the secondary battery 10 has a sealing plate 14 that closes the opening. The outer casing 12 and the sealing plate 14 can be made of aluminum or an aluminum alloy. On the sealing plate 14, the positive terminal 15 extends from one end in the length direction (… Figure 1 The right end of the negative terminal 16 protrudes from the other end along its length. Figure 1 The left end of the electrode body 20 protrudes. The positive terminal 15 and the negative terminal 16, inserted into the two through holes formed in the sealing plate 14, are fixed and mounted to the sealing plate 14 by means of resin gaskets. The winding axis of the electrode body 20 is parallel to the length direction of the sealing plate 14. Figure 1 The electrodes 20 and the outer casing 12 are parallel (in the left and right directions). Alternatively, insulation between the electrodes 20 and the outer casing 12 can be achieved by providing an insulating sheet that is bent in a box shape on the inner side of the outer casing 12.
[0021] The positive electrode 22 is a positive electrode in which a positive electrode active material mixture layer containing a positive electrode active material is formed on both sides of a positive electrode core, for example, made of aluminum foil. Preferably, in addition to containing the positive electrode active material, the positive electrode active material mixture layer also contains a binder material and a conductive material. One end of the positive electrode 22 in the width direction, before being wound, has a positive electrode core exposed portion 23.
[0022] As the positive electrode active material, a lithium transition metal oxide capable of lithium-ion insertion and extraction can be used. The metallic element constituting the lithium transition metal oxide is, for example, at least one selected from cobalt (Co), nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), tin (Sn), antimony (Sb), tungsten (W), lead (Pb), and bismuth (Bi). Among the aforementioned metallic elements, it is preferable to include at least one selected from Co, Ni, Mn, and Al.
[0023] Examples of carbon materials that can be used as conductive materials include carbon black, acetylene black, Ketjen black, and graphite. These carbon materials can be used alone or in combination of two or more.
[0024] Examples of suitable adhesives include fluoropolymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefins. Additionally, these resins can be used in combination with carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc. These resins can be used alone or in combination of two or more.
[0025] The negative electrode 26 is a negative electrode in which a negative electrode active material mixture layer containing a negative electrode active material is formed on both sides of a negative electrode core, for example, made of copper foil. Preferably, the negative electrode active material mixture layer also contains a binder material in addition to the negative electrode active material. One end of the negative electrode 26 in the width direction, before winding, has a negative electrode core exposed portion 27.
[0026] As negative electrode active materials, examples include substances that allow for the reversible insertion and extraction of lithium ions. Specifically, these include carbon materials such as natural graphite and artificial graphite, metals such as silicon (Si) and tin (Sn) alloyed with lithium, alloys containing metal elements such as Si and Sn, and composite oxides. These substances can be used alone or in combination of two or more.
[0027] As a binder, similar to the case of cathode 22, fluoropolymers, PAN, polyimide, acrylic resins, polyolefins, etc., can be used. When using an aqueous solvent to prepare the slurry, CMC or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc., are preferred.
[0028] like Figure 1 As shown, in electrode body 20, in the direction of extension of the winding axis, i.e., the winding axis direction ( Figure 1 One end on the left and right sides ( Figure 1 The right end of the electrode body 20 has a wound positive electrode core exposed portion 23. At the other end in the winding axis direction of the electrode body 20... Figure 1 The left end of the electrode is provided with a wound negative electrode core exposed portion 27.
[0029] like Figure 2 As shown, the inner separator 30 is arranged in a wound state between the positive electrode 22 and the negative electrode 26 to electrically isolate the positive electrode 22 and the negative electrode 26.
[0030] Additionally, in the electrode body 20, on one side of the outermost outermost separator 31 located at the end of the winding end, an insulating tape 60 is attached to the outer periphery of the electrode body 20 in such a way that the winding end is fixed to the outer periphery of the electrode body 20. Figure 1 ).
[0031] Furthermore, a positive current collector 40 is electrically connected to the exposed portion 23 of the wound positive electrode core. Thus, the positive current collector 40 is electrically connected to the positive electrode 22. The positive current collector 40 is located on the side opposite to the thickness direction of the electrode body 20. Figure 1 The positive electrode receiving member 48 (on the surface of the paper) is integrally connected with the positive electrode core exposed portion 23, sandwiching it together. The positive electrode current collector 40 is electrically connected to the lower end of the positive electrode terminal 15, which passes through the first insulating member 61 disposed on the inner side of the sealing plate 14 in the vertical direction.
[0032] A negative electrode current collector 50 is electrically connected to the exposed portion 27 of the wound negative electrode core. Thus, the negative electrode current collector 50 is electrically connected to the negative electrode 26. The negative electrode current collector 50 is located on the side opposite to the thickness direction of the electrode body 20. Figure 1 The negative electrode receiving member 58 (on the surface of the paper) is integrally connected with the exposed negative electrode core 27, sandwiching it between them. The negative electrode current collector 50 is electrically connected to the lower end of the negative electrode terminal 16, which passes through the second insulating member 62 disposed on the inner side of the sealing plate 14 in the vertical direction.
[0033] In the outer casing 12, the opening is closed by welding a sealing plate 14 to the opening end. Next, using... Figure 2 , Figure 3 The electrode body 20 is described in detail. The electrode body 20 includes: an outer separator 31 and an inner separator 30 disposed inside the outer separator 31, as well as a positive electrode 22 and a negative electrode 26.
[0034] Each separator 30, 31 may be made of, for example, a porous sheet material with ion permeability and insulation. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the separator may be, for example, a multilayer structure having a separator substrate 32 and a functional layer 34. The separator substrate 32 is a porous layer with a melting point of 120°C to 150°C and is primarily composed of thermoplastic resin, i.e., containing more than 50% thermoplastic resin. The functional layer 34 has an adhesive resin with a melting point higher than that of the separator substrate 32. Specifically, such as... Figure 3 As shown, each separator 30, 31 is formed of a three-layer structure consisting of a separator substrate 32 and two functional layers 34 disposed on both sides of the separator substrate 32. The separator substrate 32 has a function to prevent the positive electrode 22 ( Figure 2 The layer that provides short circuit to the negative electrode 26 and allows ion permeation.
[0035] In each of the separators 30 and 31, the thermoplastic resin constituting the separator substrate 32 is preferably an olefin resin such as polyethylene or polypropylene, or cellulose. The separator may also be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, multilayer separators including polyethylene layers and polypropylene layers can be used.
[0036] The functional layer 34 of each separator 30, 31 is a layer used to impart specific functions to the separators 30, 31, and contains an adhesive resin, and may also be mixed with inorganic particles. The melting point of the adhesive resin is higher than that of the separator substrate 32, for example, a melting point of 170°C or higher. As the adhesive resin, for example, a resin containing any one of the following can be used: fluorinated resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); fluorinated rubbers such as vinylidene fluoride-tetrafluoroethylene copolymers and ethylene-tetrafluoroethylene copolymers; polyimide; polyamide (especially aromatic polyamide); and polyamide-imide.
[0037] When the functional layer 34 contains inorganic particles, the inorganic particles may be, for example, Al₂O₃ (alumina), SiO₂ (silicon dioxide), or Al(OH)O (boehmite). The melting point of the inorganic particles is higher than that of the adhesive resin. The inorganic particles may have, for example, a near-spherical or plate-like shape. By including such inorganic particles, the functional layer 34 can possess heat resistance, shrinkage prevention, and short-circuit prevention functions, among others.
[0038] In the functional layer 34, the mass of the adhesive resin is not particularly limited as long as it exhibits adhesiveness to the positive or negative electrode. For example, for the functional layer 34, when the adhesive resin is mixed with inorganic particles, it is preferable to use a layer containing 10% or more of the adhesive resin by mass, and more preferably a layer containing 25% or more of the adhesive resin by mass.
[0039] Two separators 30 and 31 are disposed on both sides of the negative electrode 26. At the winding end on the outer periphery, the winding end of the two separators 30 and 31 extends from the winding end of the negative electrode 26, and the two separators 30 and 31 are directly opposite each other. The winding end of the two separators 30 and 31 is arranged opposite each other with their respective functional layers 34, and in this state, the two separators 30 and 31 are joined. Thus, the negative electrode 26 is equivalent to the outer electrode disposed on the outside of the positive electrode 22 and the negative electrode 26, which is held by the two separators 30 and 31.
[0040] The outer separator 31 and the inner separator 30 each have two electrode-facing portions 35 that overlap with and are opposite to the outermost layer of the negative electrode 26, separated by the negative electrode 26; and an end overlap portion 36 located at the winding end of the outer separator 31 and the winding end of the inner separator 30. The thickness of each separator 30, 31 at the top tip 37 of the end overlap portion 36 is greater than the thickness of other portions of each separator 30, 31. Therefore, the thickness t3 of the top tip 37 of the end overlap portion 36 is greater than the sum of the thicknesses t1 and t2 of the electrode-facing portions 35 of each separator 30, 31 (t1+t2) (t3>(t1+t2)). Therefore, as will be described later, when the separators 30, 31 overlap during winding to form the electrode body 20, bending at only the corners of the ends of the separators 30, 31 can be prevented.
[0041] Furthermore, the thickness t3 of the tip portion 37 of the end overlap portion 36 is smaller than the sum of the thickness t4 of the negative electrode 26 and the thicknesses t1 and t2 of the electrode opposing portions 35 of each separator 30 and 31 (t1+t2+t4) (t3<(t1+t2+t4)). Therefore, it is possible to prevent the thickness of the electrode body 20 from increasing in a certain area due to the tip portion 37 of the end overlap portion 36, and it is possible to increase the thickness of the tip portion 37 of the end overlap portion 36.
[0042] In the case of manufacturing the electrode body 20 of the embodiment, the positive electrode 22 ( Figure 2The inner separator 30, negative electrode 26, and outer separator 31 are pulled out from the winding body and stacked. The resulting stack is then wound up using a spool to form the electrode body 20. At this time, the positive electrode 22, inner separator 30, negative electrode 26, and outer separator 31 are cut by the cutting section at the moment they have been wound to their respective predetermined lengths. Furthermore, when cutting the two separators 30 and 31, the cutting section used to cut them is heated so that its heating temperature is higher than the melting point of the adhesive resin constituting the functional layer 34. This melts the adhesive resin during cutting, fusing the cut ends of the two separators 30 and 31 together. Furthermore, by heating the cut ends of the two separators 30 and 31, the thickness of the cut ends is increased, thereby making the thickness t3 of the top end portion 37 in the overlapping portion 36 of the ends of the two separators 30 and 31 greater than the sum of the thicknesses (t1+t2) of the electrode opposing portions 35 of each separator 30 and 31 (t3>(t1+t2)).
[0043] According to the electrode body 20 described above, the thickness t3 of the tip portion 37 in the end overlap portion 36 of the outer separator 31 and the inner separator 30 is greater than the sum of the thicknesses (t1+t2) of the electrode-facing portions 35 of each separator 30, 31. This increases the stiffness of the tip portion, thus preventing bending only at the corners of the ends of the separators 30, 31 during overlapping, such as when the separators 30, 31 are wound to form the electrode body 20. In particular, when the electrode body 20 is a wound structure as in the embodiment, stress in the direction of inward bending is easily applied to the separators 30, 31, making corner bending prone to occur at the winding end. However, by making the thickness t3 of the tip portion in the end overlap portion 35 greater than the sum of the thicknesses (t1+t2) of the electrode-facing portions 35 of each separator 30, 31 as described above, this bending can be prevented. Therefore, the effect of preventing bending becomes significant.
[0044] on the other hand, Figure 4 This is a perspective view showing the state in which the outer separator 31 and the inner separator 30 are bent in the electrode body 20a of the comparative example. In the comparative example, with Figures 1-3 Similarly, the negative electrode 26 is clamped using the outer separator 31 and its inner separator 30, so that the top ends of the two separators 30 and 31 overlap. Furthermore, each separator 30 and 31... Figures 1-3 The embodiment similarly includes a separator substrate 32 and two functional layers 34 disposed on both sides of the separator substrate 32, but unlike the embodiment described above, the thickness t3 of the top portion of the overlapping end of the two separators 30, 31 is equal to or less than the sum of the thicknesses (t1+t2) of the opposing electrode portions of each separator 30, 31. In such a comparative example, such as Figure 4As shown, when the separators 30 and 31 are wound to form the electrode body 20, the stiffness of the ends of the separators 30 and 31 is relatively small, so only at the corners of those ends ( Figure 4 The portion enclosed by the dashed line C) bent. Figures 1-3 The implementation method can prevent such adverse situations.
[0045] Figure 5 In another embodiment, the electrode body is in conjunction with Figure 3 The corresponding diagram. In the structure of this example, with Figures 1-3 The structure differs from that of the previous example. The end overlap portion 36a, located at the ends of the two separators 30 and 31, is formed by folding the winding ends of the two separators 30 and 31 outwards in an overlapping state in a U-shape and then further overlapping them. Therefore, by not making the thickness of the winding ends of each separator 30 and 31 greater than the thickness of each electrode-facing portion 35 before forming the end overlap portion 36a, the thickness t3a of the tip portion 37a of the end overlap portion 36a is greater than the sum of the thicknesses (t1+t2) of the electrode-facing portions 35 of each separator 30 and 31, which are the two electrode-facing portions. According to the structure of this example, it is also similar to... Figures 1-3 Similarly, when the separators 30 and 31 are overlapped during winding to form the electrode body 20, bending can be prevented only at the corners of the ends of the separators 30 and 31.
[0046] In this case, also with Figures 1-3 Similarly, preferably, the thickness t3a of the tip portion 37a of the end overlap portion 36a is smaller than the sum of the thickness t4 of the negative electrode 26 and the thicknesses t1 and t2 of the electrode-facing portions 35 of each separator 30 and 31 (t1+t2+t4) (t3a<(t1+t2+t4)). This prevents the electrode body thickness from increasing in a certain area due to the tip portion 37a of the end overlap portion 36a, and allows the thickness of the tip portion 37a of the end overlap portion 36a to increase. In this example, other structures and functions are similar. Figures 1-3 The structures are the same.
[0047] In addition, as another example of the implementation, each separator can be formed of ultraviolet-curable resin or thermosetting resin, and ultraviolet light or heat can be irradiated or heated at the winding end, thereby making the thickness of the top part of the end overlap greater than the sum of the thicknesses of the electrode opposite parts of each separator.
[0048] Furthermore, in the above embodiments, the case where the negative electrode 26 is the outer electrode has been described. However, in a structure where the positive electrode 22 is the outer electrode and the outermost layer of the positive electrode 22 is held by the outer and inner separators, the thickness of the top part of the end overlap can be greater than the sum of the thicknesses of the electrode-opposite parts of each separator.
[0049] In addition, in the above embodiments, both the outer and inner partitions are configured to have functional layers on both sides of the partition substrate. However, each partition may also adopt the following structure: it is configured to have a functional layer on only one side of the partition substrate, and the outer and inner partitions are overlapped with the functional layer located on the inner side.
[0050] The present disclosure will be further illustrated below by way of examples, but the present disclosure is not limited to these examples. The electrode body of Comparative Example 1 will also be described below.
[0051] <Example 1>
[0052] In the case of LiNi 0.5 Co 0.2 Mn 0.3 O2, the positive electrode active material, polyvinylidene fluoride (PVdF), and carbon, the conductive material, were mixed in a mass ratio of 92:4:4 and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. This slurry was then coated onto aluminum foil, which served as the positive electrode core, and subsequently dried and rolled to produce the positive electrode plate.
[0053] A negative electrode slurry was prepared by mixing natural graphite as the negative electrode active material and styrene-butadiene rubber and carboxymethyl cellulose as binders in a mass ratio of 96:2:2, and then dispersing the mixture in water. This slurry was then coated onto copper foil, which serves as the negative electrode core, and subsequently dried and rolled to produce the negative electrode plate.
[0054] Using a positive electrode plate, a negative electrode plate, and a separator, the separator is cut through the separator cutting section at a temperature of 170°C to manufacture the electrode body of Example 1. The separator is a separator substrate and a component with functional layers disposed on both sides of the separator substrate. The separator substrate is made of polyethylene, and the functional layer is a layer made of polyvinylidene fluoride (PVDF) and Al2O3 (alumina).
[0055] <Example 2>
[0056] During the manufacture of the electrode body, each separator is cut through the separator cutting section at a temperature of 200°C. The structure otherwise is the same as the electrode body of Example 1.
[0057] <Comparative Example 1>
[0058] During the manufacture of the electrode body, each separator is cut through the separator cutting section at a temperature of 150°C. The structure otherwise is the same as the electrode body of Example 1.
[0059] <Thickness Measurement>
[0060] The insulating tape of the electrode body in Example 1 was removed, the electrode body was unwound, and the thickness of the two separators on the opposite part of the electrode and the thickness of the top end of the overlapping part without the insulating tape were measured. Thickness measurements were performed using a TECLOCK PG-02J constant-pressure thickness measuring machine with a measuring contact diameter of 5 mm. When measuring the thickness of the top end of the overlapping part, the measuring contact was brought into contact with the top end of the overlapping part by approximately 0.5 mm to 1 mm. The same measurements were performed in Example 2 and Comparative Example 1. Ten samples were collected for each example and Comparative Example 1.
[0061] <Bending of the separator>
[0062] Will Figure 4 The state shown in the diagram is defined as the separator bending.
[0063] Table 1 summarizes the sum of the thicknesses (t1+t2) of the two separators at the electrode-opposing portions of Examples 1, 2, and Comparative Example 1, the thickness (t3) of the separator at the top of the end-overlapping portion, and the number of separator bending incidents. Table 1 shows the average thickness of the separators at the electrode-opposing portions as the sum of the thicknesses (t1+t2) of the two separators at the electrode-opposing portions. Table 1 also shows the average thickness (t3) of the separator at the top of the end-overlapping portion. It can be evaluated that the fewer the number of separator bending incidents, the better the separator bending is prevented.
[0064] [Table 1]
[0065]
[0066] As shown in Table 1, in Examples 1 and 2, the bending of the separator can be significantly reduced. Therefore, it can be said that in an electrode body where the thickness of the separator at the top of the overlapping end portion is thicker than the sum of the thicknesses of the two separators at the opposite electrode portion, bending of the separator can be prevented. On the other hand, a considerable amount of separator bending occurred in Comparative Example 1. Therefore, in Comparative Example 1, there is room for improvement in terms of preventing separator bending.
[0067] Explanation of reference numerals in the attached figures
[0068] 10. Secondary battery; 12. Outer casing; 14. Sealing plate; 15. Positive terminal; 16. Negative terminal; 20, 20a. Electrode body (electrode body) for secondary battery; 22. Positive electrode; 23. Exposed part of positive electrode core; 26. Negative electrode; 27. Exposed part of negative electrode core; 30. Inner separator; 31. Outer separator; 32. Separator substrate; 34. Functional layer; 35. Electrode opposite part; 36, 36a. End overlap part; 37, 37a. Top part; 40. Positive current collector; 48. Positive electrode receiving member; 50. Negative current collector; 58. Negative electrode receiving member; 60. Insulating tape; 61. First insulating member; 62. Second insulating member.
Claims
1. An electrode body for a secondary battery, comprising: A positive electrode and a negative electrode; and an outer separator and an inner separator disposed on the inner side of the outer separator, the outer separator and the inner separator having a functional layer on at least one side, the functional layer having an adhesive resin having a melting point higher than the melting point of the separator substrate, wherein the outer electrode of the positive electrode and the negative electrode disposed on the outer side is sandwiched between the outer separator and the inner separator, wherein... The outer separator and the inner separator each have: two opposing electrode portions that are opposite to and overlap the outermost layer of the outer electrode; and end overlapping portions located at the ends of the outer separator and the inner separator. The thickness of the top end of the overlapping portion is greater than the sum of the thicknesses of the two opposing portions of the electrodes. The ends of the outer partition and the inner partition are joined by welding. The end of the outer separator on the winding end side is fixed to the outer periphery of the electrode body using an insulating tape.
2. The electrode body for a secondary battery according to claim 1, wherein, The thickness of the top end of the overlapping portion is smaller than the sum of the thickness of the outer electrode and the thickness of the opposing portions of the two electrodes.
3. The electrode body for a secondary battery according to claim 1 or 2, wherein, The functional layer contains inorganic particles.
4. The electrode body for a secondary battery according to claim 1 or 2, wherein, The adhesive resin includes any one of fluorinated resin, fluorinated rubber, polyimide, polyamide, and polyamide-imide.
5. The electrode body for a secondary battery according to claim 1 or 2, wherein, The adhesive resin in the functional layer accounts for more than 10% by mass.
6. The electrode body for a secondary battery according to claim 1 or 2, wherein, The electrode body for the secondary battery is a wound structure in which the positive electrode, the negative electrode, the outer separator, and the inner separator are wound in a stacked state.