Electrode body for secondary battery

Abstract

This electrode body for secondary batteries comprises: a positive electrode; a negative electrode; an outer separator which has a functional layer on at least one surface, said functional layer comprising an adhesive resin that has a higher melting point than a separator base material; and an inner separator which is arranged inside the outer separator. An outer electrode, which is either the positive electrode or the negative electrode arranged on the outer side, is sandwiched between the outer separator and the inner separator. The outer separator and the inner separator have: two electrode facing parts that face the outermost layers of the outer electrode, while overlapping with each other, with the outer electrode being interposed therebetween; and a terminal overlapping part that is provided at respective ends of the outer separator and the inner separator. The thickness of the front end of the terminal overlapping part is larger than the sum of the thicknesses of the two electrode facing parts.

Description

Technical Field

[0001] The present disclosure relates to an electrode body for a secondary battery.

Background Art

[0002] In a high-capacity secondary battery, in order to improve the filling efficiency, production tact, and quality of an electrode body including a positive electrode, a negative electrode, and a separator, it is conceivable to use, as the separator, a material in which an adhesive resin having a melting point higher than that of the base material is coated on at least one side.

[0003] Patent Document 1 describes that in an electrode body for a secondary battery, one of the positive electrode and the negative electrode is sandwiched between two separators, and the end portions on the winding end side of the two separators are overlapped and joined by heat fusion to form a joint portion. Thereby, it is said that contact between the positive and negative electrodes due to bending of the end portion of the separator can be prevented.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Even when the end portions of two separators are overlapped and heat-fused to form a joint portion as in the configuration described in Patent Document 1, only the corner portion of the end portion including the joint portion may be bent inward or the like and laminated on other portions of the electrode body. In this case, when pressure is applied to the electrode body from the outside due to a locally increased thickness of a part of the electrode body, stress non-uniformity occurs, and there is room for improvement in terms of improving performance and durability.

[0006] An electrode body for a secondary battery according to one aspect of the present disclosure includes a positive electrode and a negative electrode, an outer separator having a functional layer with an adhesive resin having a melting point higher than that of a separator base material on at least one side, and an inner separator disposed inside the outer separator. Among the positive electrode and the negative electrode, an outer electrode disposed on the outside is a secondary battery electrode body sandwiched between the outer separator and the inner separator. The outer separator and the inner separator have two electrode facing portions that overlap with each other through the outer electrode facing the outermost layer of the outer electrode, and an end overlapping portion provided at the ends of the outer separator and the inner separator. The thickness of the end overlapping portion is larger than the sum of the thicknesses of the two electrode facing portions.

[0007] According to the electrode body for a secondary battery according to the present disclosure, it is possible to prevent bending only at the corners of the ends of the separator when the separator is overlapped, such as when the separator is wound around the electrode body.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0009] Hereinafter, an electrode body for a secondary battery, which is an example of an embodiment, will be described in detail. Specific dimensional ratios and the like should be determined in consideration of the following description. In this specification, the description of "substantially ~" is intended to include, by way of example of substantially the same, not only exactly the same but also those recognized as substantially the same. Also, the term "end portion" means the end of the object and its vicinity. Further, the shapes, materials, numbers, numerical values, etc. described below are examples for explanation and can be changed according to the specifications of the electrode body for a secondary battery. In the following, the same components will be described with the same reference numerals.

[0010] The secondary battery configured to include the electrode body for a secondary battery described below is, for example, a rectangular secondary battery used as a drive power source for an electric vehicle or a hybrid vehicle.

[0011] Hereinafter, with reference to FIGS. 1 to 3, a secondary battery which is 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 the present disclosure can also be applied to other secondary batteries. FIG. 1 is a view showing the exterior body 12 of the secondary battery 10 in cross section. FIG. 2 is a cross-sectional view taken along line A-A of the electrode body 20 for a secondary battery in FIG. 1. FIG. 3 is an enlarged view of part B in FIG. 2. In the description of FIG. 1, for convenience, the side of the sealing plate 14 of the exterior body 12 is taken as the top, and the side opposite to the sealing plate 14 is taken as the bottom for description.

[0012] The secondary battery 10 includes an exterior body 12 as a case and an electrode body 20 for a secondary battery disposed inside the exterior body 12. Hereinafter, the electrode body 20 for a secondary battery will be referred to as the electrode body 20. Inside the exterior body 12, a non-aqueous electrolyte solution corresponding to a non-aqueous electrolyte is stored. The non-aqueous electrolyte solution is, for example, an electrolyte solution containing a lithium salt and has lithium ion conductivity.

[0013] As shown in FIG. 2, the electrode body 20 has a winding structure in which the winding axis extends in the longitudinal direction of the secondary battery 10 (the left - right direction in FIG. 1, the front - back direction of the paper surface in FIG. 2), and is a flat wound electrode body in which the positive electrode 22 and the negative electrode 26 are wound with separators 30 and 31 interposed therebetween. The electrode body 20 is wound, for example, in a state where a long positive electrode 22, a long inner separator 30, a long negative electrode 26, and a long outer separator 31 are laminated, and the outer separator 31 is arranged on the outermost periphery.

[0014] As shown in FIG. 1, the metal exterior body 12 is box - shaped with an opening at the upper end, and the secondary battery 10 includes a sealing plate 14 that closes this opening. The exterior body 12 and the sealing plate 14 can be made of aluminum or an aluminum alloy. On the sealing plate 14, the positive electrode terminal 15 protrudes from one end in the longitudinal direction (the right - end in FIG. 1), and the negative electrode terminal 16 protrudes from the other end in the longitudinal direction (the left - end in FIG. 1). The positive electrode terminal 15 and the negative electrode terminal 16 are fixed and attached to the sealing plate 14 via a resin gasket while being inserted into two through - holes formed in the sealing plate 14. The winding axis of the electrode body 20 is parallel to the longitudinal direction of the sealing plate 14 (the left - right direction in FIG. 1). An insulating sheet bent into a box shape may be provided inside the exterior body 12 to insulate the electrode body 20 from the exterior body 12.

[0015] The positive electrode 22 is formed by forming a positive electrode active material mixture layer containing a positive electrode active material on both surfaces of a positive electrode core made of, for example, an aluminum foil. The positive electrode active material mixture layer preferably contains a binder and a conductive material in addition to the positive electrode active material. The positive electrode 22 has a positive electrode core exposed portion 23 at one end in the width direction in the state before winding.

[0016] As the positive electrode active material, a lithium transition metal oxide capable of inserting and extracting lithium ions can be used. The metal 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 these, it is preferable to contain at least one selected from Co, Ni, Mn, and Al.

[0017] Examples of the conductive material include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more.

[0018] Examples of the binder include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. Further, these resins may be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. These may be used alone or in combination of two or more.

[0019] The negative electrode 26 is formed by forming a negative electrode active material mixture layer containing a negative electrode active material on both surfaces of a negative electrode core made of, for example, a copper foil. The negative electrode active material mixture layer preferably contains a binder in addition to the negative electrode active material. The negative electrode 26 has a negative electrode core exposed portion 27 at one end in the width direction in the state before winding.

[0020] Examples of the negative electrode active material include those that can reversibly occlude and release lithium ions, etc. Specifically, carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as silicon (Si) and tin (Sn), or alloys containing metal elements such as Si and Sn, complex oxides, etc. can be used. These can be used alone or in combination of two or more types.

[0021] As the binder, fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc. can be used in the same manner as in the case of the positive electrode 22. When preparing the composite material slurry using an aqueous solvent, it is preferable to use CMC or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc.

[0022] As shown in FIG. 1, in the electrode body 20, at one end (the right end in FIG. 1) in the winding axis direction (the left-right direction in FIG. 1) which is the direction in which the winding axis extends, an exposed portion 23 of the wound positive electrode core is arranged. At the other end (the left end in FIG. 1) of the electrode body 20 in the winding axis direction, an exposed portion 27 of the wound negative electrode core is arranged.

[0023] As shown in FIG. 2, the inner separator 30 is arranged between the positive electrode 22 and the negative electrode 26 in a wound state, and electrically isolates the positive electrode 22 and the negative electrode 26.

[0024] Also, in the electrode body 20, an insulating tape 60 (FIG. 1) is adhered to the end on the winding end side of the outermost separator 31 arranged on the outermost periphery so as to fix this winding end side end to the outer peripheral portion of the electrode body 20 on one side surface in the thickness direction of the electrode body 20.

[0025] Furthermore, a positive electrode current collector 40 is electrically connected to the exposed portion 23 of the wound positive electrode core. As a result, the positive electrode current collector 40 is electrically connected to the positive electrode 22. The positive electrode current collector 40 is integrally connected with the positive electrode receiving member 48 disposed on the side opposite to the thickness direction of the electrode body 20 (the front side of the paper surface in FIG. 1) with the exposed portion 23 of the positive electrode core interposed therebetween. The positive electrode current collector 40 is electrically connected to the lower end portion of the positive electrode terminal 15 that vertically penetrates the first insulating member 61 disposed on the inner surface of the sealing plate 14.

[0026] A negative electrode current collector 50 is electrically connected to the exposed portion 27 of the wound negative electrode core. As a result, the negative electrode current collector 50 is electrically connected to the negative electrode 26. The negative electrode current collector 50 is integrally connected with the negative electrode receiving member 58 disposed on the side opposite to the thickness direction of the electrode body 20 (the front side of the paper surface in FIG. 1) with the exposed portion 27 of the negative electrode core interposed therebetween. The negative electrode current collector 50 is electrically connected to the lower end portion of the negative electrode terminal 16 that vertically penetrates the second insulating member 62 disposed on the inner surface of the sealing plate 14.

[0027] The opening of the exterior body 12 is closed by welding the sealing plate 14 to the opening end portion. Next, the electrode body 20 will be described in detail with reference to FIGS. 2 and 3. The electrode body 20 includes an outer separator 31 and an inner separator 30 disposed inside the outer separator 31, a positive electrode 22, and a negative electrode 26.

[0028] For each of the separators 30 and 31, for example, a porous sheet having ion permeability and insulation properties is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric. As the material of the separator, for example, it is a separator base material 32 having a melting point of 120 to 150°C and mainly composed of a thermoplastic resin, that is, a porous layer containing 50% or more of the thermoplastic resin, and a functional layer 34 having an adhesive resin with a melting point higher than that of the separator base material 32. Specifically, as shown in FIG. 3, each of the separators 30 and 31 is formed in a three-layer structure of a separator base material 32 and two functional layers 34 disposed on both sides thereof. The separator base material 32 is a layer having a function of preventing short circuit between the positive electrode 22 (FIG. 2) and the negative electrode 26 and allowing ions to permeate.

[0029] In each of the separators 30 and 31, the thermoplastic resin constituting the separator base material 32 is preferably an olefin resin such as polyethylene or polypropylene, or cellulose. The separator may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Also, a multilayer separator including a polyethylene layer and a polypropylene layer can be used.

[0030] The functional layer 34 of each of the separators 30 and 31 is a layer for imparting a specific function to the separators 30 and 31, contains an adhesive resin, and may be mixed with inorganic particles. The adhesive resin has a melting point higher than that of the separator base material 32, for example, a melting point of 170°C or higher. As the adhesive resin, for example, a fluorine-containing resin such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), a fluorine-containing rubber such as a vinylidene fluoride-tetrafluoroethylene copolymer or an ethylene-tetrafluoroethylene copolymer, a polyimide, a polyamide (especially aramid), and a polyamideimide, any one of which is used.

[0031] When the functional layer 34 contains inorganic particles, the inorganic particles are, for example, Al2O3 (alumina), SiO2 (silica), or Al(OH)O (boehmite). The melting point of the inorganic particles is higher than that of the adhesive resin. The inorganic particles have, for example, a shape close to a spherical shape or a plate shape. By including such inorganic particles in the functional layer 34, the functional layer 34 can be provided with a heat resistance function, a shrinkage prevention function, a short circuit prevention function, and the like.

[0032] In the functional layer 34, the mass of the adhesive resin is not particularly limited as long as it exhibits adhesiveness to the positive electrode or the negative electrode. For example, when the adhesive resin is mixed with inorganic particles in the functional layer 34, those containing preferably 10% and more preferably 25% or more of the adhesive resin by mass ratio are used.

[0033] Two separator sheets 30 and 31 are arranged on both sides of the negative electrode 26. At the winding end portion on the outer peripheral side, the winding end of the two separator sheets 30 and 31 extends from the winding end of the negative electrode 26, and the two separator sheets 30 and 31 face each other directly. The winding ends of the two separator sheets 30 and 31 are arranged such that their respective functional layers 34 face each other, and in this state, the two separator sheets 30 and 31 are joined. Thereby, the negative electrode 26 corresponds to the outer electrode disposed on the outside among the positive electrode 22 and the negative electrode 26, and is sandwiched between the two separator sheets 30 and 31.

[0034] The outer separator 31 and the inner separator 30 have two electrode facing portions 35 that face the outermost layer of the negative electrode 26 and overlap via the negative electrode 26, and an end overlapping portion 36 provided at the winding end portion of the outer separator 31 and the inner separator 30. The thickness of each separator 30, 31 at the tip portion 37 of the end overlapping portion 36 is larger than the thickness of the other portions of each separator 30, 31. Thereby, the thickness t3 of the tip portion 37 of the end overlapping portion 36 is larger than the sum (t1 + t2) of the thicknesses t1, t2 of the electrode facing portions 35 of each separator 30, 31 which are the two electrode facing portions 35 (t3 > (t1 + t2)). For this reason, as will be described later, when overlapping such as when winding the separators 30 and 31 around the electrode body 20, bending only at the corner portions of the ends of the separators 30 and 31 can be prevented.

[0035] Furthermore, the thickness t3 of the tip portion 37 of the end overlapping portion 36 is smaller than the sum (t1 + t2 + t4) of the thickness t4 of the negative electrode 26 and the thicknesses t1, t2 of the electrode facing portions 35 of each separator 30, 31 (t3 < (t1 + t2 + t4)). Thereby, while preventing the thickness of the electrode body 20 from increasing partially due to the tip portion 37 of the end overlapping portion 36, the thickness of the tip portion 37 of the end overlapping portion 36 can be increased.

[0036] When manufacturing the electrode body 20 of the embodiment, the positive electrode 22 (Fig. 2), the inner separator 30, the negative electrode 26, and the outer separator 31 are laminated while being pulled out from the winding body, and the laminated product is wound around a winding shaft to form the electrode body 20. At that time, the positive electrode 22, the inner separator 30, the negative electrode 26, and the outer separator 31 are cut by a cutting portion when each predetermined length is wound. Further, when cutting the two separators 30 and 31, the cutting portions for cutting the two separators 30 and 31 are heated, and the heating temperature of the cutting portion is made higher than the melting point of the adhesive resin constituting the functional layer 34. Thereby, the adhesive resin is melted at the time of cutting, and the cut ends of the two separators 30 and 31 are fused together. Furthermore, by increasing the thickness of the cut ends of the two separators 30 and 31 by heating the cut ends, the thickness t3 of the tip portion 37 at the end overlapping portion 36 of the two separators 30 and 31 can be made larger than the sum of the thicknesses (t1 + t2) of the electrode facing portions 35 of the respective separators 30 and 31 (t3 > (t1 + t2)).

[0037] According to the above electrode body 20, the thickness t3 of the tip portion 37 at the end overlapping portion 36 of the outer separator 31 and the inner separator 30 is larger than the sum of the thicknesses (t1 + t2) of the electrode facing portions 35 of the respective separators 30 and 31. Thereby, since the rigidity of the above tip portion can be increased, when overlapping such as when winding the separators 30 and 31 around the electrode body 20, bending only at the corner portions of the ends of the separators 30 and 31 can be prevented. In particular, when the electrode body 20 has a wound structure as in the embodiment, stress in the direction of bending inward on the inner peripheral side is likely to be applied to the separators 30 and 31, so that bending at the corner portions is likely to occur at the end portion after winding. However, by making the thickness t3 of the tip portion at the end overlapping portion 35 larger than the sum of the thicknesses (t1 + t2) of the electrode facing portions 35 of the respective separators 30 and 31 as described above, the above bending can be prevented. Thereby, the effect of preventing bending becomes remarkable.

[0038] On the one hand, FIG. 4 is a perspective view showing a state in which bending has occurred in the outer separator 31 and the inner separator 30 in the electrode body 20a of the comparative example. In the comparative example, similar to the configurations of FIGS. 1 to 3, the negative electrode 26 is sandwiched between the outer separator 31 and the inner separator 30 inside it, and the tip portions of the two separators 30 and 31 are overlapped. Further, each of the separators 30 and 31 includes a separator base material 32 and two functional layers 34 disposed on both sides thereof, similar to the embodiments of FIGS. 1 to 3. However, different from the above embodiments, the thickness t3 of the tip portion at the end overlapping portion of the two separators 30 and 31 is equal to or smaller than the sum (t1 + t2) of the thicknesses of the electrode facing portions of each of the separators 30 and 31. In such a comparative example, as shown in FIG. 4, when the separators 30 and 31 are wound around the electrode body 20, since the rigidity of the end portions of the separators 30 and 31 is small, bending occurs only at the corner portions of this end portion (the portion surrounded by the dashed-dotted line C in FIG. 4). According to the embodiments of FIGS. 1 to 3, such inconveniences can be prevented.

[0039] FIG. 5 is a view corresponding to FIG. 3 in the electrode body of another example of the embodiment. In the configuration of this example, different from the configurations of FIGS. 1 to 3, the end overlapping portion 36a provided at the ends of the two separators 30 and 31 is formed by folding back the end portions of the two separators 30 and 31 that are wound up and overlapped outward in a U shape and then further overlapping them. Thereby, before the formation of the end overlapping portion 36a, without making the thickness of the end portion of each of the separators 30 and 31 that is wound up larger than the thickness of each electrode facing portion 35, the thickness t3a of the tip portion 37a of the end overlapping portion 36a is made larger than the sum (t1 + t2) of the thicknesses of the electrode facing portions 35 of each of the two separators 30 and 31 that are the electrode facing portions. Also according to the configuration of this example, similar to the configurations of FIGS. 1 to 3, when overlapping such as when the separators 30 and 31 are wound around the electrode body 20, bending only at the corner portions of the ends of the separators 30 and 31 can be prevented.

[0040] Also in this example, similar to the configurations of FIGS. 1 to 3, the thickness t3a of the tip portion 37a of the end overlapping portion 36a is preferably smaller than the sum (t1 + t2 + t4) of the thickness t4 of the negative electrode 26 and the thicknesses t1 and t2 of the electrode facing portions 35 of the separators 30 and 31 (t3a < (t1 + t2 + t4)). Thereby, while preventing the thickness of the electrode body from being partially increased by the tip portion 37a of the end overlapping portion 36a, the thickness of the tip portion 37a of the end overlapping portion 36a can be increased. In this example, the other configurations and operations are the same as those of the configurations of FIGS. 1 to 3.

[0041] Note that, as another example of the embodiment, each separator may be formed of an ultraviolet curable resin or a thermosetting resin, and the thickness of the tip portion of the end overlapping portion may be made larger than the sum of the thicknesses of the electrode facing portions of the separators by irradiating ultraviolet rays or applying heat to the end overlapping portion after winding.

[0042] Also, in each of the above embodiments, the case where the negative electrode 26 is the outer electrode has been described. However, in a configuration in which the positive electrode 22 is the outer electrode and the outermost layer of the positive electrode 22 is sandwiched between the outer separator and the inner separator, the thickness of the tip portion in the end overlapping portion may be made larger than the sum of the thicknesses of the electrode facing portions of the separators.

[0043] Also, in each of the above embodiments, each of the outer separator and the inner separator has a functional layer on both sides of the separator substrate. However, each separator may have a functional layer on only one side of the separator substrate, and the outer separator and the inner separator may be stacked with the functional layers facing inward.

[0044] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples. Hereinafter, the electrode body of Comparative Example 1 will also be described.

[0045] <Example 1> LiNi as the positive electrode active material 0.5 Co 0.2 Mn 0.3O2, polyvinylidene fluoride (PVdF) as a binder, and carbon as a conductive material were mixed at a mass ratio of 92:4:4, and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode composite slurry. After coating this slurry on an aluminum foil as a positive electrode core, it was dried and rolled to produce a positive electrode plate.

[0046] Natural graphite as a negative electrode active material, styrene-butadiene rubber and carboxymethyl cellulose as binders were mixed at a mass ratio of 96:2:2, and then dispersed in water to prepare a negative electrode composite slurry. After coating this slurry on a copper foil as a negative electrode core, it was dried and rolled to produce a negative electrode plate.

[0047] Using a positive electrode plate, a negative electrode plate, and a separator composed of a separator substrate made of polyethylene and layers of polyvinylidene fluoride (PVDF) and Al2O3 (aluminum oxide) as functional layers disposed on both sides of the separator substrate, each separator was cut by the separator cutting part at a temperature of 170°C at the separator cutting part to produce the electrode body of Example 1.

[0048] <Example 2> During the production of the electrode body, each separator was cut by the separator cutting part at a temperature of 200°C at the separator cutting part. Other configurations are the same as those of the electrode body of Example 1.

[0049] <Comparative Example 1> During the production of the electrode body, each separator was cut by the separator cutting part at a temperature of 150°C at the separator cutting part. Other configurations are the same as those of the electrode body of Example 1.

[0050] <Thickness Measurement> The insulating tape of the electrode body of Example 1 was removed, the electrode body was unwound, and the thickness of the two separators at the electrode facing portion and the thickness of the tip portion of the end overlapping portion where the insulating tape was not applied were measured. For the thickness measurement, a constant pressure thickness measuring machine PG-02J manufactured by TECLOCK with a measuring probe diameter of 5 mm was used. When measuring the thickness of the tip portion of the end overlapping portion, the measurement was performed so that the measuring probe hit the tip portion of the end overlapping portion by about 0.5 to 1 mm. The same measurement was performed in Example 2 and Comparative Example 1. The number of samples for each of the examples and Comparative Example 1 was 10.

[0051] <Separator bend> The state shown in Fig. 4 was defined as a separator bend.

[0052] The sum of the thicknesses of the two separators (t1 + t2) at the electrode facing portion, the thickness of the separator (t3) at the tip portion of the end overlapping portion, and the number of occurrences of separator bends in Examples 1 and 2 and Comparative Example 1 were summarized in Table 1. The average separator thickness at the electrode facing portion in Table 1 indicates the sum of the thicknesses of the two separators (t1 + t2) at the electrode facing portion as an average value. The average separator thickness at the tip portion in Table 1 indicates the thickness of the separator (t3) at the tip portion of the end overlapping portion as an average value. The fewer the number of occurrences of separator bends, the more it can be evaluated that separator bending is prevented.

[0053]

Table 1

[0054] As can be seen from Table 1, in Examples 1 and 2, separator bending is significantly reduced. Therefore, it can be said that separator bending is prevented in the electrode body in which the thickness of the separator at the tip portion of the end overlapping portion is thicker than the sum of the thicknesses of the two separators at the electrode facing portion. On the other hand, in Comparative Example 1, a considerably large number of separator bends occurred. Therefore, there is room for improvement in terms of preventing separator bending in Comparative Example 1.

Explanation of symbols

[0055] 10 Secondary battery 12 Outer package 14 Sealing plate 15 Positive terminal 16 Negative terminal 20, 20a Electrode body for secondary battery (electrode body) 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 base material 34 Functional layer 35 Electrode facing part 36, 36a End overlapping part 37, 37a Tip part 40 Positive current collector 48 Positive receiving member 50 Negative current collector 58 Negative receiving member 60 Insulating tape 61 First insulating member 62 Second insulating member

Claims

1. A secondary battery electrode body including a positive electrode and a negative electrode, an outer separator having a functional layer with an adhesive resin having a melting point higher than that of the separator substrate on at least one side, and an inner separator disposed inside the outer separator, wherein, among the positive electrode and the negative electrode, an outer electrode disposed on the outside is wound in a state sandwiched between the outer separator and the inner separator, the outer separator and the inner separator have two electrode facing portions that overlap with each other via the outer electrode facing the outermost layer of the outer electrode, and an end overlapping portion provided at the end of the winding side of the outer separator and the inner separator and consisting only of the outer separator and the inner separator, the thickness of the tip of the end overlapping portion is larger than the sum of the thicknesses of the two electrode facing portions, A secondary battery electrode body.

2. The thickness of the tip of the end overlapping portion is smaller than the sum of the thickness of the outer electrode and the thicknesses of the two electrode facing portions, The secondary battery electrode body according to Claim 1.

3. The functional layer contains inorganic particles, The secondary battery electrode body according to Claim 1 or Claim 2.

4. The adhesive resin contains any one of a fluorine-containing resin, a fluorine-containing rubber, a polyimide, a polyamide, and a polyamideimide, The secondary battery electrode body according to any one of Claims 1 to 3.

5. The mass ratio of the adhesive resin in the functional layer is 10% or more, The secondary battery electrode body according to any one of Claims 1 to 4.

6. It has a winding structure in which the positive electrode, the negative electrode, the outer separator, and the inner separator are wound in a laminated state, The secondary battery electrode body according to any one of Claims 1 to 5.

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