Secondary battery

Abstract

To provide a secondary battery having an appropriate Young's modulus both during winding and during charging.SOLUTION: A lithium ion secondary battery includes an electrode assembly 20 in which a positive electrode plate 21, a first separator 27, a negative electrode plate 24, and a second separator 28 are stacked in this order and then wound. The Young's modulus of the low load region of the separators 27 and 28 is set higher than the Young's modulus of the high load region.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] The following Patent Document 1 describes a secondary battery having an electrode assembly in which positive and negative plates are stacked and wound with a separator between them. In this secondary battery, the separator is made of two or more layers of porous resin with different elastic moduli in the thickness direction. This is intended to suppress deterioration of the secondary battery caused by expansion and contraction of the positive and negative plates due to charging and discharging of the secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-4873 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the elastic modulus appropriate for dealing with the expansion and contraction of the negative electrode plate and the like accompanying charge and discharge as described above is not necessarily the elastic modulus appropriate for the process in which the positive electrode plate and the negative electrode plate are stacked with the separator interposed therebetween and then wound up. If the elastic modulus is excessively low during winding, wrinkles will occur in the electrode body. [Means for solving the problem]

[0005] Means for solving the above problems and their effects will be described below. 1. A secondary battery having an electrode assembly in which a positive electrode plate and a negative electrode plate are stacked and wound with a separator between them, wherein when the expansion coefficient of the negative electrode plate is A [%,] the Young's modulus in the tensile direction of the separator is 1.0 [GPa] or more when the coefficient is 0 [MPa] or more and less than 10 [MPa], and is 3.0 / A [GPa] or less when the coefficient is 10 [MPa] or more and 50 [MPa] or less.

[0006] In the process of stacking the positive and negative plates with the separator interposed therebetween and then winding them, tension is applied to the separator. If the separator has a low Young's modulus, the separator may shift relative to the negative or positive plate, or wrinkles may occur in the separator. On the other hand, during charging control of the secondary battery, the negative plate expands in the thickness direction. In order for the separator to follow the expansion and contraction of the negative plate, it is desirable to lower the Young's modulus of the separator.

[0007] The load applied to the separator is greater when the secondary battery is charged than when the separator is wound. If the Young's modulus is equal in the pair of load regions, it is difficult to set an appropriate Young's modulus for both winding and charging.

[0008] Therefore, in the above configuration, the Young's modulus is set separately when the load is 0 MPa or more and less than 10 MPa, and when the load is 10 MPa or more and 50 MPa or less. In particular, the Young's modulus when the load is 10 MPa or more and 50 MPa or less is set so as to have a negative correlation with the magnitude of the expansion coefficient of the negative electrode. This allows the Young's modulus to be set appropriately for both winding and charging.

[0009] 2. A secondary battery as described in claim 1, wherein the separator has a multi-layer structure, the Young's modulus of the surface layer separator is higher than the Young's modulus of the intermediate layer separator, the surface layer separator is a separator that constitutes the surface layer of the separator, and the intermediate layer separator is a separator sandwiched between two of the surface layer separators.

[0010] When a load is applied to the separator, the surface layer separator deforms before the intermediate layer separator. Therefore, in the low load region, the Young's modulus of the separator is dominated by the Young's modulus of the surface layer separator. Therefore, in the above configuration, the Young's modulus of the surface layer separator is set high. In addition, by lowering the Young's modulus of the intermediate layer separator, the Young's modulus can be reduced in the high load region.

[0011] 3. The secondary battery according to the above item 2, wherein the thickness of the intermediate separator layer is greater than the thickness of the surface separator layer. In the above-described configuration, by making the thickness of the intermediate separator layer, which has a low Young's modulus, thicker than the thickness of the surface separator layer, it is possible to sufficiently reduce the Young's modulus of the separator.

[0012] 4. A secondary battery as described in claim 1, wherein the separator has a multilayer structure including a high Young's modulus separator layer and a low Young's modulus separator layer, the Young's modulus of the high Young's modulus separator layer is higher than that of the low Young's modulus separator layer, and the thickness of the low Young's modulus separator layer is thicker than that of the high Young's modulus separator layer.

[0013] In the above-described configuration, by making the thickness of the low Young's modulus separator layer thicker than the thickness of the high Young's modulus separator layer, the Young's modulus of the separator can be sufficiently reduced. 5. The secondary battery according to claim 2 or 3, wherein the surface layer separator and the intermediate layer separator are made of different materials.

[0014] In the above-described configuration, the Young's modulus of the surface layer separator and the Young's modulus of the intermediate layer separator can be adjusted to be different from each other by selecting the materials. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of a lithium ion secondary battery. [Diagram 2] FIG. 2 is a perspective view showing the electrode body in an expanded state. [Diagram 3] FIG. 3 is a cross-sectional view showing a cross-sectional configuration of a separator. [Figure 4] FIG. 4 is a diagram showing the characteristics of the separator according to the embodiment. [Diagram 5] FIG. 5 is a diagram showing an example and a comparative example according to this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment will be described with reference to the drawings. [Lithium-ion secondary battery] As shown in FIG. 1, a lithium ion secondary battery 10, which is an example of a secondary battery, includes a case 11 and an electrode assembly 20. The case 11 has a flat, bottomed, rectangular outer shape with an opening on the upper side. The case 11 contains the electrode assembly 20 and a non-aqueous electrolyte. The case 11 includes a pair of side walls 11A disposed opposite each other. The lid 12 closes the opening of the case 11. By attaching the lid 12, the case 11 forms a sealed rectangular parallelepiped battery container.

[0017] The lid 12 is provided with a positive external terminal 13A and a negative external terminal 13B. The positive electrode side current collector 20A, which is the end of the electrode body 20 on the positive electrode side, is electrically connected to the positive electrode external terminal 13A via a positive electrode side current collector 14A. The negative electrode side current collector 20B, which is the end of the electrode body 20 on the negative electrode side, is electrically connected to the negative electrode external terminal 13B via a negative electrode side current collector 14B. The lid 12 is provided with an injection port 15 for injecting a nonaqueous electrolyte. The shapes of the external terminals 13A and 13B are not limited to those shown in FIG. 1 and may be any shape.

[0018] The lithium ion secondary battery 10 is used, for example, in the state of an assembled battery configured by arranging a plurality of the lithium ion secondary batteries 10. In the state of the assembled battery, for example, the lithium ion secondary batteries 10 are arranged in a predetermined arrangement direction so that the side walls 11A of adjacent lithium ion secondary batteries 10 face each other, and a restraining load is applied to sandwich the plurality of lithium ion secondary batteries 10 in the arrangement direction. This allows the plurality of lithium ion secondary batteries 10 to be held integrally.

[0019] [Electrode body 20] As shown in FIG. 2, the electrode body 20 is a flat wound body formed by winding a laminate in which a positive electrode plate 21 and a negative electrode plate 24 are stacked with a first separator 27 and a second separator 28 interposed therebetween. As an example, the laminate is stacked in the order of the positive electrode plate 21, the first separator 27, the negative electrode plate 24, and the second separator 28. The positive electrode plate 21, the negative electrode plate 24, and the separators 27 and 28 are stacked so that their respective longitudinal directions coincide with the longitudinal direction D1. The electrode body 20 has a structure in which the positive electrode plate 21 and the negative electrode plate 24 stacked with the separators 27 and 28 sandwiched therebetween are wound around a winding axis L1 extending along the width direction D2 of the band shape.

[0020] The electrode body 20 comprises a flat portion 31, an upper curved portion 32, and a lower curved portion 33. The flat portion 31 comprises a pair of flat surfaces 31S facing in opposite directions. The upper curved portion 32 is located at the upper portion of the flat portion 31. The upper curved portion 32 has a shape that bulges upward from the upper end of the flat portion 31. The lower curved portion 33 is located at the lower portion of the flat portion 31. The lower curved portion 33 has a shape that bulges downward from the lower end of the flat portion 31. The upper curved portion 32 and the lower curved portion 33 are each an example of a curved portion that the electrode body 20 comprises.

[0021] The electrode body 20 is housed in the case 11 with the winding axis L1 extending parallel to the bottom surface of the case 11 so that the upper curved portion 32 is located on the lid body 12 side and the lower curved portion 33 is located on the bottom surface side of the case 11. Furthermore, when the electrode body 20 is housed in the case 11, each of the flat surfaces 31S of the flat portion 31 faces the side wall 11A of the case 11.

[0022] The electrode body 20 is stacked in a stacking direction such that the separators 27, 28 are disposed between the positive electrode plate 21 and the negative electrode plate 24. The stacking direction is a direction perpendicular to a plane including the longitudinal direction D1 and the width direction D2.

[0023] [Positive plate 21] The positive electrode plate 21 includes a positive electrode substrate 22 and a positive electrode mixture layer 23. The positive electrode substrate 22 is formed of a foil-like metal made of aluminum or an aluminum alloy. The positive electrode mixture layer 23 is provided on each of two surfaces of the positive electrode substrate 22 that face in opposite directions. The positive electrode substrate 22 includes a positive electrode-side uncoated portion 22A at one end in the width direction D2 where the positive electrode mixture layer 23 is not formed and the positive electrode substrate 22 is exposed. In the positive electrode substrate 22, the positive electrode-side uncoated portion 22A includes opposing portions that are pressed against each other in a wound body state to form a positive electrode-side current collecting portion 20A.

[0024] The positive electrode mixture layer 23 includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode mixture paste, which is a precursor of the positive electrode mixture layer 23, further includes a positive electrode solvent. An example of the positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent.

[0025] The positive electrode active material contains a lithium transition metal oxide which is a charge carrier in the lithium ion secondary battery 10. The lithium transition metal oxide has a layered crystal structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn. A suitable example of the lithium transition metal oxide is a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0026] The positive electrode active material may additionally contain one or more elements in addition to the above-mentioned predetermined transition metal elements (i.e., at least one of Ni, Co, and Mn). The additional element may include any element belonging to Group 1 (alkali metals such as sodium) of the periodic table. The additional element may include any element belonging to Group 2 (alkaline earth metals such as magnesium and calcium). The additional element may include any element belonging to Group 4 (transition metals such as titanium and zirconium). The additional element may include any element belonging to Group 6 (transition metals such as chromium and tungsten). The additional element may include any element belonging to Group 8 (transition metals such as iron). The additional element may include any element belonging to Group 13 (metalloid element boron, or metals such as aluminum). The additional element may include any element belonging to Group 17 (halogens such as fluorine).

[0027] The positive electrode conductive agent is, for example, carbon black such as acetylene black (AB) or Ketjen black, carbon fiber such as carbon nanotube (CNT) or carbon nanofiber, or graphite. The positive electrode binder is, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and styrene butadiene rubber (SBR).

[0028] The positive electrode plate 21 may have an insulating layer at the boundary between the positive electrode uncoated portion 22A and the positive electrode mixture layer 23. The insulating layer includes an inorganic component having insulating properties and a resin component functioning as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0029] [Negative plate 24] The negative electrode plate 24 includes a negative electrode substrate 25 and a negative electrode mixture layer 26. The negative electrode substrate 25 is formed of a foil-like metal made of copper or a copper alloy. The negative electrode mixture layer 26 is provided on each of two surfaces of the negative electrode substrate 25 that face in opposite directions. The negative electrode substrate 25 includes a negative electrode side uncoated portion 25A in which the negative electrode mixture layer 26 is not formed and the negative electrode substrate 25 is exposed at an end portion located opposite the positive electrode side uncoated portion 22A in the width direction D2. In the negative electrode side uncoated portion 25A, facing portions are pressed against each other in a wound body state to form the negative electrode side current collecting portion 20B.

[0030] The negative electrode mixture layer 26 includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder. The negative electrode mixture paste, which is a precursor of the negative electrode mixture layer 26, further includes a negative electrode solvent. An example of the negative electrode solvent is water. The negative electrode active material is a material capable of absorbing and releasing lithium ions. The negative electrode active material absorbs lithium ions during charging and releases lithium ions during discharging. The negative electrode active material is, for example, a carbon material such as graphite, non-graphitizable carbon, easily graphitizable carbon, or carbon nanotubes. The negative electrode active material may be a composite particle in which graphite particles are coated with an amorphous carbon layer. The particle size (median diameter D50) of the negative electrode active material is, for example, 5 μm or more and 10 μm or less.

[0031] The negative electrode conductive agent may be formed of, for example, the same material as the positive electrode conductive agent. The negative electrode thickener is, for example, carboxymethyl cellulose (CMC). CMC also functions as a dispersant for dispersing the negative electrode active material in the negative electrode mixture paste. The negative electrode binder is, for example, at least one selected from the group consisting of PVDF, PVA, and SBR.

[0032] [Nonaqueous electrolyte] The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent is, for example, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, one or more lithium compounds selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc.

[0033] A film-forming agent is added to the non-aqueous electrolyte. The film-forming agent is, for example, lithium bis(oxalato)borate (LiBOB). For example, LiBOB is added to the non-aqueous electrolyte so that the concentration of LiBOB in the non-aqueous electrolyte is 0.001 to 0.1 [mol / L].

[0034] [First separator 27 and second separator 28] The first separator 27 and the second separator 28 prevent contact between the positive electrode plate 21 and the negative electrode plate 24, and also hold a nonaqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 24. When the electrode body 20 is immersed in the nonaqueous electrolyte, the nonaqueous electrolyte permeates from the ends of the separators 27, 28 toward the center.

[0035] The first separator 27 and the second separator 28 have a multi-layer structure. FIG. 3 shows a schematic cross-sectional structure of the separators 27 and . As shown in FIG. 3, the separators 27 and 28 have a laminated structure in which the intermediate layer separators 27b and 28b are sandwiched between two surface layer separators 27a and 28a. The surface layer separators 27a and 28a are made of polypropylene, for example. The intermediate layer separators 27b and 28b are made of polyethylene, for example. Here, the thickness of the intermediate layer separators 27b and 28b is greater than that of the surface layer separators 27a and 28a. However, FIG. 3 merely shows this difference in thickness in a schematic manner. In addition, the Young's modulus in the tensile direction of the surface layer separators 27a and 28a is higher than that of the intermediate layer separators 27b and 28b. The tensile direction is the longitudinal direction D1 in FIG. 2.

[0036] The electrode body 20 is formed by stacking the first separator 27, the negative electrode plate 24, the second separator 28, and the positive electrode plate 21 in this order, and then winding them around a winding core to form a wound body. The winding core is then pulled out from the wound body. The first separator 27 is a member that comes into contact with the winding core.

[0037] "Actions and Effects of the Present Embodiment" FIG. 4 shows the relationship between stress and strain in the first separator 27 and the second separator 28. As shown in FIG.

[0038] As shown by the solid line in FIG. 4, the Young's modulus, which is the ratio of the change in stress to the change in strain, of the first separator 27 and the second separator 28 is lower in the high load region A2 than in the low load region A1. Here, the low load region A1 is a region of 0 or more and less than 10 [MPa]. The load in the low load region A1 is the load applied to the first separator 27 and the second separator 28 when the electrode body 20 shown in FIG. 2 is wound. The high load region A2 is a region of 10 [MPa] or more and 50 [MPa] or less. The load in the high load region A2 is the load applied to the first separator 27 and the second separator 28 by the charging process of the lithium ion secondary battery 10. In addition, a comparative example is shown by a dashed line in FIG. 4.

[0039] In this embodiment, by lowering the Young's modulus in the high load region A2, the first separator 27 and the second separator 28 can follow the deformation of the negative electrode plate 24 due to the expansion and contraction of the negative electrode plate 24 accompanying the charging and discharging of the lithium ion secondary battery 10. If the first separator 27 and the second separator 28 cannot follow the deformation of the negative electrode plate 24, the distance between the positive electrode plate 21 and the negative electrode plate 24 increases, and the resistance to lithium precipitation decreases. In contrast, if the first separator 27 and the second separator 28 can be made to follow the deformation of the negative electrode plate 24, the resistance to lithium precipitation can be improved.

[0040] On the other hand, in the step of winding the electrode body 20, the electrode body 20 is wound around the winding core while tension is applied to the electrode body 20 in the longitudinal direction D1. Next, the winding core is pulled out from the wound electrode body 20. When the winding core is pulled out, if the Young's modulus is low, the first separator 27 and the second separator 28 may shift relative to the negative electrode plate 24 or the positive electrode plate 21, or wrinkles may occur in the first separator 27 and the second separator 28. Therefore, in this embodiment, the Young's modulus is increased in the load of the low load region A1, which is the load applied to the first separator 27 and the second separator 28 during winding. This suppresses the occurrence of wrinkles.

[0041] FIG. 5 shows various settings and characteristics in Example 1 and Example 2 in this embodiment and Comparative Example 1 to Comparative Example 4. The negative electrode expansion rate is, for example, the amount of change in thickness of the negative electrode plate 24 when the state of charge (SOC) is increased from 10% to 90% by charging the lithium ion secondary battery 10. The state of charge indicates the ratio of the actual charge amount to the fully charged charge amount. The thickness may be measured using, for example, a CT or a confocal microscope. The Young's modulus of the low load region A1 is, for example, calculated based on the amount of change in strain when the stress is changed from 0 MPa to 10 MPa. The Young's modulus of the high load region A2 is, for example, calculated based on the amount of change in strain when the stress is changed from 10 MPa to 50 MPa.

[0042] In FIG. 5, "low load Young's modulus" indicates the Young's modulus of the first separator 27 and the second separator 28 in the low load region A1. Also, "high load Young's modulus" indicates the Young's modulus of the first separator 27 and the second separator 28 in the high load region A2. In Comparative Examples 1, 3, and 4, the Young's modulus is high in the high load region A2, so the deposition limit current is reduced. In Comparative Example 2, the Young's modulus is low, so there is no problem with the deposition limit current, but wrinkles are generated. This is because the Young's modulus is low in the low load region A1.

[0043] In Examples 1 and 2, by increasing the Young's modulus in the low load region A1 and decreasing the Young's modulus in the high load region A2, it is possible to achieve a favorable balance between increasing the deposition limit current and suppressing the occurrence of wrinkles. Incidentally, Example 1 and Comparative Example 4 are examples in which the Young's modulus is equal, but there is a difference in the negative electrode expansion coefficient A. That is, since the negative electrode expansion coefficient A of Comparative Example 4 is larger than that of Example 1, a larger load is applied during charging of the lithium ion secondary battery 10. Therefore, in Comparative Example 4, it is desirable to lower the Young's modulus in the high load region A2.

[0044] The Young's modulus in the first and second embodiments is set by making the intermediate separator layer 27b as thick as possible and the surface separator layer 27a as thin as possible. That is, when a load is applied to the separators 27 and 28, the surface layer separators 27a and 28a deform before the intermediate layer separators 27b and 28b. Therefore, in the low load region A1, the Young's modulus of the surface layer separators 27a and 28a has a dominant effect on the Young's modulus of the separators 27 and 28. Therefore, the Young's modulus of the surface layer separators 27a and 28a is set high.

[0045] On the other hand, in order to minimize the Young's modulus in the high load region A2, it is desirable to make the separator with a low Young's modulus as thick as possible, so the intermediate separators 27b and 28b are made as thick as possible.

[0046] The Young's modulus may be adjusted by changing the conditions in the manufacturing process in addition to selecting the material and thickness. For example, the stretching ratio may be increased to lower the Young's modulus. The film formation temperature or the temperature in the stretching process may also be adjusted.

[0047] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the above "Means for solving the problem" column is as follows. In the following, the correspondence is shown for each number of the means for solving the problem described in the "Means for solving the problem" column. [1] In Example 1 of FIG. 5, Young's modulus in the high load area A2 corresponds to 0.30 or less, which is 3.0 / A. In Example 2 of FIG. 5, Young's modulus in the high load area A2 corresponds to 0.20 or less, which is 3.0 / A. [2,3,5] The multilayer structure corresponds to the structure illustrated in FIG. 3. [4] The high Young's modulus separator layer corresponds to the surface layer separators 27a, 28a. The low Young's modulus separator layer corresponds to the intermediate layer separators 27b, 28b.

[0048] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0049] "About the negative electrode expansion rate" It is not essential that the negative electrode expansion rate is the amount of change in thickness of the negative electrode plate 24 when the charging rate SOC is increased from 10% to 90%. However, it is preferable that a control device in a control system in which the lithium-ion secondary battery 10 is mounted defines the negative electrode expansion rate according to a lower limit and an upper limit of the charging rate SOC when controlling charging of the lithium-ion secondary battery 10. In other words, it is preferable to define the negative electrode expansion rate according to the amount of change in thickness of the negative electrode plate 24 when the charging rate of the lithium-ion secondary battery 10 is increased from the lower limit to the upper limit.

[0050] "About the surface layer separator" The surface layer separators 27a and 28a do not necessarily have to be made of polypropylene. For example, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or an ion-conductive polymer electrolyte membrane may be used.

[0051] "About the intermediate layer separator" The intermediate separators 27b and 28b do not necessarily have to be porous polyethylene films. For example, they may be made of polypropylene. Alternatively, for example, a porous polymer membrane such as a porous polyolefin membrane or a porous polyvinyl chloride membrane, or an ion-conductive polymer electrolyte membrane may be used.

[0052] "High Young's modulus separator layer" The first separator 27 may have only one surface layer separator 27a as a high Young's modulus separator layer.

[0053] The second separator 28 may have only one surface layer separator 28a as a high Young's modulus separator layer. "About the multi-layer structure of the separator" The separator having a multi-layer structure is not limited to a three-layer structure. The separator having a multi-layer structure may be, for example, two layers, as described above in "High Young's modulus separator layer." The separator having a multi-layer structure may be four or more layers. Here, for example, in the case of a four-layer structure, the thickness of the two intermediate layer separators may be thicker than the thickness of the two surface layer separators. Also, for example, the Young's modulus of the two intermediate layer separators may be lower than the Young's modulus of the two surface layer separators.

[0054] "Young's modulus of separator" The Young's modulus of the low load area A1 and the high load area A2 are not limited to the values ​​exemplified in Examples 1 and 2. It is sufficient that the Young's modulus is 1.0 [GPa] or more in the low load area A1 and 3.0 / A [GPa] or less in the high load area A2. Incidentally, [3.0 / A] in Comparative Example 4 in FIG. 5 is "0.20". Therefore, the Young's modulus of the high load area A2 in Comparative Example 4 does not satisfy the condition of being less than this value.

[0055] "About separators" The ratio of the thickness of the intermediate layer separators 27b, 28b to the thickness of the surface layer separators 27a, 28a is not limited to the ratio exemplified in Examples 1 and 2. The thickness of the intermediate layer separators 27b, 28b is preferably 10 times or more the thickness of the surface layer separators 27a, 28a. Furthermore, the thickness of the intermediate layer separators 27b, 28b is more preferably 15 times or more the thickness of the surface layer separators 27a, 28a.

[0056] The thickness of the intermediate separators 27b, 28b is not necessarily greater than that of the surface separators 27a, 28a. In other words, the above thickness settings are not essential in adjusting the Young's modulus of the high load region A2 and the Young's modulus of the low load region A1 to meet the conditions described in the "Young's modulus of the separator" section above.

[0057] The ratio between the Young's modulus of the intermediate layer separators 27b, 28b and the Young's modulus of the surface layer separators 27a, 28a is not limited to the ratio exemplified in Examples 1 and 2. The Young's modulus of the surface layer separators 27a, 28a is preferably 5 times or more the Young's modulus of the intermediate layer separators 27b, 28b.

[0058] It is not essential that the Young's modulus of the intermediate layer separators 27b, 28b be lower than that of the surface layer separators 27a, 28a. In other words, the magnitude relationship between the Young's modulus of the high load region A2 and the Young's modulus of the low load region A1 is not essential when adjusting the Young's modulus of the high load region A2 and the Young's modulus of the low load region A1 to meet the conditions described in the above section "Young's modulus of the separator."

[0059] It is not essential that the first separator 27 and the second separator 28 have the same structure, dimensions, and material. "Others" Although the lithium ion secondary battery 10 has been exemplified as a nonaqueous secondary battery, the present invention can be applied to any nonaqueous secondary battery in which the negative electrode active material expands during charging. Also, although a graphite-based material has been exemplified as the negative electrode active material, the present invention can also be applied to nonaqueous secondary batteries that use silicon-based negative electrode active materials, since the negative electrode active material expands during charging.

[0060] The secondary battery may be mounted on an automatic transport vehicle, a special vehicle for loading and unloading, an electric vehicle, a hybrid electric vehicle, etc., as well as on a computer or other electronic device. The secondary battery may also be mounted on a moving object such as a ship or an aircraft. The secondary battery may also be a secondary battery that stores electricity supplied from a power plant via a substation or the like to a building or a home. [Explanation of symbols]

[0061] 10...Lithium-ion secondary battery 11. Case 14A…Positive electrode side current collecting member 14B: Negative electrode side current collecting member 20...Electrode body 21…Positive electrode plate 24…Negative electrode plate 27…Separator 27a…Surface layer separator 27b...Intermediate layer separator 28…Separator 28a…Surface layer separator 28b...Intermediate layer separator

Claims

1. A secondary battery including an electrode assembly in which a positive electrode plate and a negative electrode plate are stacked with a separator interposed therebetween and wound, When the expansion coefficient of the negative electrode plate is A [%], A secondary battery in which the separator has a Young's modulus in a tensile direction of 1.0 [GPa] or more when the range is 0 [MPa] or more and less than 10 [MPa], and 3.0 / A [GPa] or less when the range is 10 [MPa] or more and 50 [MPa] or less.

2. The separator has a multi-layer structure, The Young's modulus of the surface layer separator is higher than the Young's modulus of the intermediate layer separator, the surface layer separator is a separator that constitutes a surface layer of the separator, 2. The secondary battery according to claim 1, wherein the intermediate layer separator is a separator sandwiched between two of the surface layer separators.

3. 3. The secondary battery according to claim 2, wherein the intermediate separator layer is thicker than the surface separator layer.

4. the separator has a multi-layer structure including a high Young's modulus separator layer and a low Young's modulus separator layer, the Young's modulus of the high Young's modulus separator layer is higher than the Young's modulus of the low Young's modulus separator layer; 2. The secondary battery in accordance with claim 1, wherein the low Young's modulus separator layer is thicker than the high Young's modulus separator layer.

5. 3. The secondary battery in accordance with claim 2, wherein the surface layer separator and the intermediate layer separator are made of different materials.

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