Non-aqueous electrolyte secondary battery

Abstract

The present application provides a non-aqueous electrolyte secondary battery which has a small initial resistance and inhibits an increase in resistance during repeated charge and discharge. The non-aqueous electrolyte secondary battery disclosed herein has a stacked electrode body including a single cell unit in which a first electrode, a first separator, a second electrode, and a second separator are stacked. The first electrode has a first current collector and a first active material layer. The second electrode has a second current collector and a second active material layer. The first separator and the second separator have a larger area of a main surface than the first active material layer and the second active material layer. The second electrode has a second active material layer non-formed portion in which the second active material layer is not formed and the second current collector is exposed. The second active material layer non-formed portion has a defect. The first separator and the second separator are not bonded to the second active material layer of the second electrode, and the first separator and the second separator are welded at the defect of the second active material layer non-formed portion.

Description

TECHNICAL FIELD

[0001] The present application relates to a nonaqueous electrolyte secondary battery. BACKGROUND

[0002] In recent years, nonaqueous electrolyte secondary batteries such as lithium secondary batteries are suitably used for portable power sources such as personal computers, portable terminals, and the like, or for vehicle drive power sources such as electric vehicles (BEV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and the like.

[0003] A general nonaqueous electrolyte secondary battery has an electrode body in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween. The electrode body is roughly classified into a wound electrode body and a laminated electrode body. The laminated electrode body has a structure in which a positive electrode and a negative electrode are alternately laminated with a separator interposed therebetween.

[0004] As one of the manufacturing methods of the laminated electrode body, a method can be exemplified in which a plurality of unit cells in which a first electrode, a first separator, a second electrode, and a second separator are sequentially laminated are formed, and the plurality of unit cells are further laminated (for example, refer to Patent Literature 1). In such a manufacturing method, in order to prevent positional deviation of the electrodes and the separators, the separators and the electrodes are adhered with an adhesive. For example, in Patent Literature 1, it is described that, in order to adhere the separators and the electrodes with the adhesive, the adhesive is applied to both surfaces of the first separator, and the adhesive is applied to only the surface of the second separator which faces the second electrode.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent No. 6093369

[0008] However, in the prior art, in the portion of the separator to which the adhesive is applied, the nonaqueous electrolyte (particularly, a charge carrier such as lithium ions and the like) is difficult to move, and thus this becomes a cause of resistance reduction. In addition, when the nonaqueous electrolyte secondary battery is repeatedly charged and discharged, the active material is repeatedly expanded and contracted. When the active material is expanded, the constraint pressure rises, and the nonaqueous electrolyte is squeezed out from the laminated electrode body. In the prior art, since the nonaqueous electrolyte is difficult to flow in the portion of the separator to which the adhesive is applied, the nonaqueous electrolyte which is squeezed out is difficult to return to the laminated electrode body, and as a result, an increase in resistance is caused. SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] Therefore, an object of the present application is to provide a nonaqueous electrolyte secondary battery which has a small initial resistance and in which an increase in resistance at the time of repeated charge and discharge is suppressed.

[0011] The nonaqueous electrolyte secondary battery disclosed herein has a laminated electrode body and a nonaqueous electrolyte, the laminated electrode body including a single cell unit in which a first electrode, a first separator, a second electrode, and a second separator are sequentially laminated. The first electrode has a first current collector and a first active material layer. The second electrode has a second current collector and a second active material layer. The area of the main surface of the first separator and the area of the main surface of the second separator are larger than the area of the main surface of the first active material layer of the first electrode and the area of the main surface of the second active material layer of the second electrode. A second active material layer non-formed portion in which the second active material layer is not formed and the second current collector is exposed is provided in the second electrode. The second active material layer non-formed portion has a defect portion in which the second current collector is removed from one main surface to the opposite main surface. The first separator and the second separator are not bonded to the second active material layer of the second electrode, and the first separator and the second separator are welded at the defect portion of the second active material layer non-formed portion. According to such a configuration, a nonaqueous electrolyte secondary battery having a small initial resistance and in which an increase in resistance during repeated charge and discharge is suppressed is provided.

[0012] In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the defect portion is a through hole. According to such a structure, the first electrode is easily fixed to the first separator and the second separator by welding at one location. Furthermore, the position of the defect portion is not limited, and the strength of the second active material layer non-formed portion is easily improved.

[0013] In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the first active material layer faces the second active material layer. The area of the main surface of the first active material layer of the first electrode is larger than the area of the main surface of the second active material layer of the second electrode. A facing region facing the second active material layer is formed in the central portion of the first active material layer. A non-facing region not facing the second active material layer is formed in the outer peripheral portion of the first active material layer. The first separator and the first electrode are bonded by a first bonding agent. The first bonding agent bonding the first electrode and the first separator is not disposed in the facing region of the first active material layer and is disposed in a region other than the facing region. According to such a structure, the initial resistance can be further reduced, and an increase in resistance during repeated charge and discharge can be further suppressed.

[0014] At this time, in the case where the first electrode is a negative electrode and the second electrode is a positive electrode, since the area of the main surface of the negative active material layer is larger than the area of the main surface of the positive active material layer, the situation in which ions (for example, lithium ions and the like) functioning as charge carriers are deposited as metal can be highly suppressed.

[0015] In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the thickness of the first adhesive is smaller than the thickness of the second electrode. According to such a structure, concentration of stress to the portion where the first adhesive is provided can be avoided when the single cell units are stacked.

[0016] In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the stacked electrode body includes a stack in which a plurality of the single cell units are stacked and the outermost layer is a positive electrode and a negative electrode, and a single negative electrode. The single negative electrode is stacked on the positive electrode of the outermost layer of the stack. According to such a configuration, lithium of the outermost positive electrode can be used for charge and discharge, and the single cell capacity can be increased. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a cross-sectional view schematically showing the internal configuration of a lithium ion secondary battery of one embodiment of the present application.

[0018] Figure 2 is an exploded perspective view schematically showing a single cell unit included in a stacked electrode body of a lithium ion secondary battery of one embodiment of the present application.

[0019] Figure 3 is a perspective view for schematically showing an example of the stacked configuration of a positive electrode and a separator in a single cell unit included in a stacked electrode body of a lithium ion secondary battery of one embodiment of the present application.

[0020] Figure 4 is a perspective view for schematically showing a modification example of the stacked configuration of a positive electrode and a separator in a single cell unit included in a stacked electrode body of a lithium ion secondary battery of one embodiment of the present application.

[0021] Figure 5 is a perspective view for schematically showing another modification example of the stacked configuration of a positive electrode and a separator in a single cell unit included in a stacked electrode body of a lithium ion secondary battery of one embodiment of the present application.

[0022] Figure 6 is a cross-sectional view schematically showing a single cell unit included in a stacked electrode body of a lithium ion secondary battery of one embodiment of the present application.

[0023] Figure 7 is a schematic view of a negative electrode of a single cell unit included in a stacked electrode body of a lithium ion secondary battery of one embodiment of the present application.

[0024] BRIEF DESCRIPTION OF DRAWINGS

[0025] 10 single cell unit

[0026] 20 stacked electrode body

[0027] 30 battery case

[0028] 36 safety valve

[0029] 42 positive terminal

[0030] 42a positive current collecting plate

[0031] 44 negative terminal

[0032] 44a negative current collecting plate

[0033] 50 positive electrode

[0034] 52 positive electrode current collector

[0035] 52a positive active material layer non-forming portion

[0036] 53 defective portion

[0037] 54 positive active material layer

[0038] 60 negative electrode

[0039] 62 negative electrode current collector

[0040] 62a negative active material layer non-forming portion

[0041] 64 negative active material layer

[0042] 64a facing region

[0043] 64b non-facing region

[0044] 71 first separator

[0045] 72 second separator

[0046] 73 first fused portion

[0047] 80 first adhesive

[0048] 82 non-aqueous electrolyte solution flow path

[0049] 100 lithium ion secondary battery DETAILED DESCRIPTION

[0050] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that any aspects of the present invention not mentioned in this specification but necessary for its implementation can be understood by those skilled in the art based on prior art. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components and parts that perform the same function are labeled with the same reference numerals. Additionally, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships.

[0051] The following describes this embodiment in detail using a lithium-ion secondary battery as an example. Furthermore, in this specification, "secondary battery" refers to an energy storage device capable of repeated charging and discharging, and is a term that includes energy storage elements such as batteries and double-layer capacitors. Additionally, in this specification, "lithium-ion secondary battery" refers to a secondary battery that utilizes lithium ions as charge carriers and achieves charging and discharging through the movement of lithium ions' charge between the positive and negative electrodes.

[0052] Figure 1 The internal structure of the lithium-ion secondary battery 100 of this embodiment is schematically shown. Figure 1 The lithium-ion secondary battery 100 shown includes a stacked electrode body 20, a non-aqueous electrolyte (not shown), and a square battery casing 30 that houses them. The battery casing 30 is sealed, therefore the lithium-ion secondary battery 100 is a sealed battery.

[0053] like Figure 1 As shown, the battery casing 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin-walled safety valve 36 configured to release the internal pressure if the internal pressure of the battery casing 30 rises above a predetermined level. Additionally, the battery casing 30 is provided with an injection port (not shown) for injecting a non-aqueous electrolyte. The positive terminal 42 is electrically connected to the positive current collector 42a. The negative terminal 44 is electrically connected to the negative current collector 44a.

[0054] Because the battery casing 30 is made of a lightweight material with high thermal conductivity, it is made of metal materials such as aluminum. However, the material of the battery casing 30 is not limited to this; it can also be made of resin. Additionally, the battery casing 30 can also be a laminated casing using a laminated film, etc.

[0055] Figure 2 The single cell unit 10 included in the stacked electrode body 20 is shown schematically. Figure 2 It is an exploded 3D diagram. Figure 2 In the figures below, the X direction is the direction of the long side of the positive electrode 50 and negative electrode 60 included in the stacked electrode body 20, the Y direction is the direction of the width of the positive electrode 50 and negative electrode 60 included in the stacked electrode body 20, and the Z direction is the stacking direction of the positive electrode 50 and negative electrode 60.

[0056] The stacked electrode body 20 has at least one single cell unit 10 as illustrated. Typically, the stacked electrode body 20 has a plurality of single cell units 10. The number of single cell units 10 that the stacked electrode body 20 has is not particularly limited and can be the same as the number of single cell units that a stacked electrode body used in a conventional lithium-ion secondary battery has, for example, 1 or more and 150 or less, and preferably 20 or more and 100 or less.

[0057] As illustrated in FIG. 1, the single cell unit 10 has a negative electrode 60 as a first electrode, a separator 71 as a first separator, a positive electrode 50 as a second electrode, and a separator 72 as a second separator. In the single cell unit 10, the negative electrode 60, the separator 71, the positive electrode 50, and the separator 72 are stacked in this order. Figure 2

[0058] The positive electrode 50 has a positive electrode current collector 52 and a positive electrode active material layer 54 provided on the positive electrode current collector 52. The negative electrode 60 has a negative electrode current collector 62 and a negative electrode active material layer 64 provided on the negative electrode current collector 62. The positive electrode 50 and the negative electrode 60 are stacked in such a manner that the positive electrode active material layer 54 faces the negative electrode active material layer 64.

[0059] In the present embodiment, the area of the main surface of the negative electrode active material layer 64 of the negative electrode 60 is larger than the area of the main surface of the positive electrode active material layer 54 of the positive electrode 50. At this time, the situation in which lithium ions are deposited as metallic lithium can be highly suppressed. Alternatively, the area of the main surface of the negative electrode active material layer 64 of the negative electrode 60 can be the same as the area of the main surface of the positive electrode active material layer 54 of the positive electrode 50. In addition, the main surface of the active material layer refers to the surface having the largest area among the surfaces constituting the active material layer. Thus, in the present embodiment, the main surface of the negative electrode active material layer 64 refers to the surface in contact with the negative electrode current collector 62 and the surface facing the surface. In addition, the main surface of the positive electrode active material layer 54 refers to the surface in contact with the positive electrode current collector 52 and the surface facing the surface. On the other hand, from the viewpoint of insulation, the areas of the main surfaces of the separators 71 and 72 are each larger than the area of the main surface of the negative electrode active material layer 64 of the negative electrode 60 and the area of the main surface of the positive electrode active material layer 54 of the positive electrode 50. In addition, the main surface of the separator refers to the surface having the largest area among the surfaces constituting the separator.

[0060] The positive electrode 50 will be described in detail. Figure 3 The stacked configuration of the positive electrode and the separator is schematically illustrated. As illustrated in FIG. 2, the positive electrode 50 has the positive electrode current collector 52 and the positive electrode active material layer 54 provided on the positive electrode current collector 52. The positive electrode active material layer 54 has a plurality of positive electrode active material particles 55. The positive electrode active material particles 55 are dispersed in the positive electrode active material layer 54. The positive electrode active material particles 55 are in contact with each other and the positive electrode current collector 52. The positive electrode active material layer 54 has a plurality of positive electrode active material particles 55. The positive electrode active material particles 55 are dispersed in the positive electrode active material layer 54. The positive electrode active material particles 55 are in contact with each other and the positive electrode current collector 52. Figure 2 ​As shown, in this embodiment, a positive electrode active material layer 54 is provided on both sides of the positive electrode current collector 52. However, it is also possible to provide a positive electrode active material layer 54 only on one side of the positive electrode current collector 52. At one end of the positive electrode 50, a portion of the positive electrode current collector 52 is provided where the positive electrode active material layer 54 is not formed, i.e., a portion where the positive electrode active material layer is not formed 54, i.e., a portion 52a where the positive electrode active material layer is not formed.

[0061] like Figure 2 and Figure 3 As shown, the non-forming portion 52a of the positive electrode active material layer has a defect 53 formed by removing the positive electrode current collector 52 from one main surface to the opposite main surface. In the example shown, the defect 53 is a through hole. In this case, the positive electrode 50 can be easily fixed to the separator 71 and separator 72 by one welding point. However, the shape of the defect 53 is not limited to a through hole; the defect 53 can also be a notch or the like.

[0062] Separators 71 and 72 are not bonded to the positive electrode active material layer 54 of the positive electrode 50. On the other hand, as... Figure 3 As shown, diaphragms 71 and 72 are welded at the defect (in this case, the through hole) 53 using welding methods such as ultrasonic welding or laser welding to form a first welded portion 73. When bonding the non-forming portion of the positive electrode active material layer to the diaphragm using an adhesive, it typically becomes a bonding between dissimilar materials such as metal (the non-forming portion of the positive electrode active material layer) and resin (diaphragm), thus limiting the type of adhesive material and requiring strict management of bonding conditions. However, as in this embodiment, when diaphragms 71 and 72 are welded together, bonding can be easily performed, which is advantageous in terms of ease of process management and cost.

[0063] Here, the larger the size of the defect 53, the weaker the strength of the non-formed portion 52a of the positive electrode active material layer. When the defect 53 is a through hole, the positive electrode current collector 52 can be removed only in the area required for welding at the non-formed portion 52a of the positive electrode active material layer. Therefore, it also has the advantage of easily improving the strength of the non-formed portion 52a of the positive electrode active material layer without limiting the location of the defect 53.

[0064] In the example shown, the through hole 53 is a square hole, but its shape is not particularly limited. The shape of the through hole 53 can be appropriately determined according to the shape of the area where the diaphragm 71 and diaphragm 72 are welded (i.e., the first welded portion 73). The through hole 53 can also be a circular, elliptical, or other shape. In the example shown, there is one through hole 53. However, there can also be multiple through holes 53 (e.g., two or three).

[0065] The size of the through hole 53 is not particularly limited. The size of the through hole 53 can be appropriately determined based on the size of the first welded portion 73. From the viewpoint of high strength of the non-forming portion 52a of the positive electrode active material layer, the radial area of ​​the through hole 53 is preferably 1.05 times or more and 2 times or less the area in the face direction of the first welded portion 73.

[0066] In the example diagram, the through hole 53 is located in a direction orthogonal to the protruding direction of the non-forming portion 52a of the positive electrode active material layer. Figure 2 and Figure 3 The central portion (in the Y direction) is near the positive electrode active material layer 54. However, the location of the defect 53 is not particularly limited.

[0067] The position of the first welded portion 73 is not particularly limited as long as it is within the range of the through hole 53. Furthermore, in the example shown, there is only one first welded portion 73. However, there can also be multiple first welded portions 73 (e.g., two or three).

[0068] As in this embodiment, by providing a defect 53 in the non-formed portion 52a of the positive electrode active material layer, and by not bonding the separator 71 and separator 72 to the positive electrode active material layer 54, and by fusing the separator 71 and separator 72 at the defect 53, the movement of the positive electrode 50 is restricted. This prevents the movement of charge-carrying ions (i.e., lithium ions in this embodiment) from being hindered by the adhesive in the positive electrode active material layer 54, a region highly relevant to the charging and discharging of the positive electrode 50. As a result, the initial resistance is reduced compared to the prior art where the separator is bonded to the active material layer across the entire surface. Furthermore, the uniformity of resistance in the surface direction of the positive electrode 50 is also excellent. Additionally, during repeated charging and discharging of the lithium-ion secondary battery 100, non-aqueous electrolyte is squeezed out of the stacked electrode body 20 due to the expansion of the active material layer. However, in the lithium-ion secondary battery 100, the outflowing non-aqueous electrolyte is prevented from returning to the stacked electrode body 20 by the adhesive. As a result, compared to existing technologies that bond the separator to the active material layer across the entire surface, the resistance increase during repeated charge and discharge cycles can be suppressed. Furthermore, in manufacturing the lithium-ion secondary battery 100, the time required for the non-aqueous electrolyte to penetrate into the electrode body can be shortened.

[0069] On the other hand, as in this embodiment, a second welded portion 74 may be formed on the outer side of the end of the positive electrode 50 facing the non-formed portion 52a of the positive electrode active material layer by welding the diaphragm 71 and the diaphragm 72 together.

[0070] The position of the second fused portion 74 is not particularly limited as long as it is located at an outer side portion of the end portion of the positive electrode 50 facing the positive electrode active material layer non-forming portion 52a. In the illustrated example, the number of the second fused portion 74 is one. However, the number of the second fused portion 74 can also be plural (for example, two or three).

[0071] Thus, in the single cell unit 10, by sandwiching the positive electrode 50 with the separators 71 and 72, and fusing the separators 71 and 72 at the through hole 53 of the positive electrode active material layer non-forming portion 52a and the outer side portion of the end portion of the positive electrode facing the positive electrode active material layer non-forming portion 52a, it is possible to fix the positive electrode using the frictional force of the first fused portion 73 and the second fused portion 74, the separators 71 and 72, and the positive electrode 50. Therefore, it is possible to suppress the positional displacement of the positive electrode 50 and the separators 71 and 72.

[0072] In particular, in a case where one first fused portion 73 is provided at the central portion in the width direction (i.e., the Y direction of the drawing) of the positive electrode 50 on the positive electrode active material layer non-forming portion 52a side, and one second fused portion 74 is provided at the outer side of the end portion facing the positive electrode active material layer non-forming portion 52a and the central portion in the width direction of the positive electrode 50, as in the illustrated example, it is possible to suppress the positional displacement of them with a total of two such small number of fused portions.

[0073] It is also possible, as in the illustrated example, for the separators 71 and 72 to be fused also at the outer side of the end portion in the width direction (i.e., the Y direction of the drawing) of the positive electrode 50. In the illustrated example, a third fused portion 75 and a fourth fused portion 76 are formed at the outer side of the end portion in the width direction of the positive electrode 50. According to such a structure, it is possible to further suppress the positional displacement of the positive electrode 50.

[0074] Figure 4 A modification related to the configuration of these engagement portions is shown. In the example shown in FIG. 6, in addition to the first fused portion 73 formed at the through hole 53, a fused portion 75' and a fused portion 76' are formed at both outer sides of the end portion in the width direction (i.e., the Y direction of the drawing) of the positive electrode 50 in a manner sandwiching the positive electrode 50. The fused portion 75' and the fused portion 76' are formed at the end portion on the side opposite to the positive electrode active material layer non-forming portion 52a. According to such a structure, it is possible to highly suppress the positional displacement caused by the rotation of the positive electrode 50 with a total of three such small number of fused portions. Figure 4

[0075] Another modification related to the configuration of these engagement portions is shown. In the example shown in FIG. 7, in addition to the first fused portion 73 formed at the through hole 53, a fused portion 75' and a fused portion 76' are formed at both outer sides of the end portion in the width direction (i.e., the Y direction of the drawing) of the positive electrode 50 in a manner sandwiching the positive electrode 50. The fused portion 75' and the fused portion 76' are formed at the end portion on the side opposite to the positive electrode active material layer non-forming portion 52a. According to such a structure, it is possible to highly suppress the positional displacement caused by the rotation of the positive electrode 50 with a total of three such small number of fused portions. Figure 5 Figure 5 ​In the illustrated example, a first fusion portion 73" is formed at the through-hole 53". The through-hole 53" and the first fusion portion 73" are formed at a position close to the first corner portion 54a of the positive electrode active material layer 54. Further, a fusion portion 74" and a fusion portion 76" are formed so as to sandwich a second corner portion 54b opposite the first corner portion of the positive electrode active material layer 54. According to such a structure, the positional displacement caused by the rotation of the positive electrode 50 can be highly suppressed with a small number of three such fusion portions in total.

[0076] In the illustrated example, each fusion portion is rectangular, but the shape of each fusion portion is not particularly limited. The shape of each fusion portion can be square, circular, elliptical, or the like.

[0077] The negative electrode 60 will be described in detail. As Figure 2 illustrated, in the present embodiment, the negative electrode active material layer 64 is provided on both surfaces of the negative electrode current collector 62. However, the negative electrode active material layer 64 can be provided on only one surface of the negative electrode current collector 62. A portion of one end portion of the negative electrode 60 in which the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed, that is, a negative electrode active material layer non-formed portion 62a is provided.

[0078] As Figure 1 and Figure 2 illustrated, the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a protrude in directions opposite to each other from the laminated portion of the positive electrode active material layer 54 and the negative electrode active material layer 64. The positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a function as current collector tabs, respectively. The shapes of the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a are not limited to the illustrated shapes, and can be processed into predetermined shapes by cutting or the like. The protruding directions of the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a are not limited to the illustrated directions. The positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a can also be provided at positions and in shapes that do not overlap each other and protrude in the same direction. In the illustrated example, the positive electrode active material layer non-formed portion 52a and the negative electrode active material layer non-formed portion 62a are provided at end portions in the longitudinal direction (the X direction of the drawing) of the electrode, but can be provided at end portions in the width direction (the Y direction of the drawing) of the electrode.

[0079] In the laminated electrode body 20, the positive electrode active material layer non-formed portions 52a of the plurality of single cell units 10 are gathered, as Figure 1 illustrated, and electrically joined to the positive electrode current collector plate 42a. The negative electrode active material layer non-formed portions 62a of the plurality of single cell units 10 are gathered, as Figure 1The positive electrode current collector 52 is electrically connected to the positive electrode lead 42a. The connection is made, for example, by ultrasonic welding, resistance welding, laser welding, or the like.

[0080] As the positive electrode current collector 52, a sheet-like or foil-like member composed of a metal having good electrical conductivity (for example, aluminum, nickel, titanium, stainless steel) can be used, and an aluminum foil or the like is preferably used. The thickness of the positive electrode current collector 52 is not particularly limited, and is, for example, 5 μm to 35 μm, and is preferably 7 μm to 20 μm.

[0081] The positive electrode active material layer 54 contains at least a positive electrode active material. As the positive electrode active material, for example, lithium nickel cobalt manganese composite oxide (for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, or the like), lithium nickel composite oxide (for example, LiNiO2, or the like), lithium cobalt composite oxide (for example, LiCoO2, or the like), lithium nickel manganese composite oxide (for example, LiNi 0.5 Mn 1.5 O4, or the like), lithium transition metal composite oxide, or the like. The positive electrode active material layer 54 can further contain a conductive material, a binder, or the like. As the conductive material, for example, carbon black such as acetylene black (AB) or other carbon material (graphite, or the like) can be used. As the binder, for example, polyvinylidene fluoride (PVDF), or the like can be used. The thickness of the positive electrode active material layer 54 is not particularly limited, and is, for example, 20 μm to 300 μm.

[0082] As the negative electrode current collector 62, a sheet-like or foil-like member composed of a metal having good electrical conductivity (for example, copper, nickel, titanium, stainless steel, or the like) can be used, and a copper foil is preferably used. The thickness of the negative electrode current collector 62 is, for example, 5 μm to 35 μm, and is preferably 7 μm to 20 μm.

[0083] The negative electrode active material layer 64 contains at least a negative electrode active material. As the negative electrode active material, for example, carbon material such as graphite, hard carbon, soft carbon, or the like can be listed. The negative electrode active material layer 64 can further contain a binder, a tackifier, or the like. As the binder, for example, styrene butadiene rubber (SBR), or the like can be used. As the tackifier, for example, carboxymethyl cellulose (CMC), or the like can be used. The thickness of the negative electrode active material layer 64 is not particularly limited, and is, for example, 20 μm to 300 μm.

[0084] As the separators 71 and 72, various porous sheets similar to those used in the conventional lithium-ion secondary batteries can be used, and as examples thereof, polyolefin-based porous resin sheets such as polyethylene (PE) and polypropylene (PP) can be listed. The porous resin sheets can be of a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which a PP layer is stacked on both sides of a PE layer). The separators 71 and 72 can also have a heat-resistant layer (HRL). The thickness of the separators 71 and 72 is not particularly limited, and is, for example, 10 μm to 40 μm.

[0085] Figure 6 A cross-sectional view of the single cell unit 10 is shown. Figure 6 is a cross-sectional view along the width direction of the single cell unit 10 (i.e., the Y direction of Figure 2 ). Figure 7 The negative electrode 60 included in the single cell unit 10 is shown. Figure 7 is a view along the direction of the main surface of the negative electrode 60. As Figure 6 and Figure 7 shown, the facing region 64a facing the positive electrode active material layer 54 is formed in the central portion of the negative electrode active material layer 64. In addition, the non-facing region 64b not facing the positive electrode active material layer 54 is formed in the outer peripheral portion of the negative electrode active material layer 64.

[0086] In the present embodiment, for example, as Figure 6 and Figure 7 shown, the separator 71 and the negative electrode 60 are adhered by the first adhesive 80. The first adhesive 80 adhering the separator 71 and the negative electrode 60 is not disposed in the facing region 64a of the negative electrode active material layer 64, but is disposed in a region other than the facing region 64a. Typically, the first adhesive 80 is disposed in either or both of the negative electrode active material layer non-formed portion 62a and the non-facing region 64b of the negative electrode active material layer 64.

[0087] The first adhesive 80 functions to suppress positional displacement of the negative electrode 60 and the separator 71. In addition, since the first adhesive 80 is not disposed in the facing region 64a of the negative electrode active material layer 64 but is disposed in a region other than the facing region 64a, in the region of the negative electrode active material layer 64 that is greatly involved in charge and discharge of the negative electrode 60, i.e., in the negative electrode active material layer 64, it is possible to prevent the movement of ions that are charge carriers, i.e., lithium ions in the present embodiment, from being hindered by the adhesive. Thus, compared to the related art, it is possible to further reduce the initial resistance. Furthermore, the uniformity of the resistance in the surface direction of the negative electrode 60 is also excellent. Moreover, it is possible to further suppress the increase in resistance when the lithium ion secondary battery 100 is repeatedly charged and discharged. In addition, compared to the related art, the amount of adhesive required is less, which is advantageous in terms of cost and the like. Furthermore, the layers of the single cell unit 10 are fixed by adhesion, welding, and the like, and electrode displacement is suppressed, so the workability is good and it is possible to stack the layers at high speed.

[0088] In the illustrated example, the first adhesive 80 is disposed in the non-facing region 64b of the outer peripheral edge portion of the negative electrode active material layer 64. However, in the present embodiment, as long as the first adhesive 80 is disposed in a region other than the facing region 64a of the negative electrode active material layer 64 of the negative electrode 60 and adheres the negative electrode 60 and the separator 71, the disposition of the first adhesive 80 is not particularly limited. It is also possible to dispose the first adhesive 80 in the negative electrode active material layer non-formed portion 62a and adhere the separator 71. It is also possible to dispose the first adhesive 80 in both the non-facing region 64b of the negative electrode active material layer 64 and the negative electrode active material layer non-formed portion 62a and adhere the separator 71. Furthermore, in the present embodiment, the disposition of the first adhesive 80 is not limited to the above. For example, it is also possible to dispose the first adhesive 80 in the facing region 64a of the negative electrode active material layer 64 and adhere the separator 71. Figure 2 In the present embodiment, the illustration of the first adhesive 80 is omitted.

[0089] As the first adhesive 80, for example, a hot melt adhesive, an ultraviolet-curable adhesive, a thermally-curable adhesive, or the like can be used.

[0090] In the example illustrated in FIG. 1, the first adhesive 80 is disposed in the non-facing region 64b of the negative electrode active material layer 64. However, the disposition of the first adhesive 80 is not limited to this. For example, it is also possible to dispose the first adhesive 80 in the facing region 64a of the negative electrode active material layer 64 and adhere the separator 71. Figure 7 In the example illustrated in FIG. 1, the first adhesive 80 is not disposed in at least a portion of the non-facing region 64b of the negative electrode active material layer 64. However, the disposition of the first adhesive 80 is not limited to this. It is also possible to dispose the first adhesive 80 in all of the non-facing region 64b of the negative electrode active material layer 64 without gaps.

[0091] In the example illustrated in FIG. 1, the first adhesive 80 has a rectangular cross-sectional shape, but the shape of the first adhesive 80 is not particularly limited. The first adhesive 80 can also have a circular or elliptical cross-sectional shape. Figure 7 In the example illustrated in FIG. 1, the first adhesive 80 has a rectangular cross-sectional shape, but the shape of the first adhesive 80 is not particularly limited. The first adhesive 80 can also have a circular or elliptical cross-sectional shape.

[0092] Figure 7 ​In the illustrated example, a portion in which the first adhesive 80 is not disposed exists between the first adhesive 80 and the first adhesive 80. In this portion, the nonaqueous electrolyte solution is able to flow. Therefore, in the illustrated example, a path (nonaqueous electrolyte solution flow path) 82 through which the nonaqueous electrolyte solution flows is formed in the portion in which the first adhesive 80 is not disposed. By thus providing the nonaqueous electrolyte solution flow path 82 in the non-facing region 64b of the negative electrode active material layer 64, the time required for the nonaqueous electrolyte solution to permeate into the electrode body can be greatly shortened when the nonaqueous electrolyte secondary battery is manufactured.

[0093] In the case where the nonaqueous electrolyte solution flow path 82 is provided, the disposition of the first adhesive 80 in the non-facing region 64b of the negative electrode active material layer 64 and the disposition of the nonaqueous electrolyte solution flow path 82 in the non-facing region 64b of the negative electrode active material layer 64 are not particularly limited. In the case where the nonaqueous electrolyte solution flow path 82 is provided, the first adhesive 80 can be disposed in the non-facing region 64b of the negative electrode active material layer 64. Figure 7 In the illustrated example, the shape of the major surface of the negative electrode active material layer 64 is rectangular. Therefore, as Figure 7 As illustrated, the non-facing region 64b is a rectangular frame-shaped region composed of two short sides and two long sides. The first adhesive 80 can be disposed in a portion of any one side of the rectangular frame-shaped non-facing region 64b.

[0094] Here, the distance from the portion of the negative electrode active material layer 64 on the long side to the center of the negative electrode active material layer 64 is short. Therefore, in the case where the nonaqueous electrolyte solution flow path 82 is formed in at least the portion on the long side of the non-facing region 64b, there is an advantage that the nonaqueous electrolyte solution is easily caused to permeate to the center of the negative electrode active material layer 64.

[0095] The nonaqueous electrolyte solution flow path 82 is preferably disposed in a portion of two or more sides of the rectangular frame-shaped non-facing region 64b, is preferably disposed in a portion of three or more sides, and is preferably disposed in a portion of all four sides.

[0096] In the illustrated example, one nonaqueous electrolyte solution flow path 82 is formed in the portion on the short side of the non-facing region 64b, and two nonaqueous electrolyte solution flow paths 82 are formed in the portion on the long side of the non-facing region 64b. However, the number of nonaqueous electrolyte solution flow paths 82 disposed in one side of the non-facing region 64b is not particularly limited. The number of nonaqueous electrolyte solution flow paths 82 can be one or more.

[0097] As Figure 7 As illustrated, the non-facing region 64b is a rectangular frame-shaped region, and therefore the first adhesive 80 is disposed along the sides of the major surface of the negative electrode active material layer 64. The size of the nonaqueous electrolyte solution flow path 82 is not particularly limited as long as the nonaqueous electrolyte solution is able to flow. The total of the sizes of the nonaqueous electrolyte solution flow path 82 in the direction of the sides of the major surface of the negative electrode active material layer 64 (for example, the total of the lengths of the nonaqueous electrolyte solution flow path 82 in the direction of the sides of the major surface of the negative electrode active material layer 64) is not particularly limited.Figure 7 the length W1 and the length W2 in the long side direction) is 10% or more of the length L of the long side. In the case where the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64 (for example, the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64 in the case where the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64), the length of the edge of the main surface of the negative electrode active material layer 64 is the length of the edge of the main surface of the negative electrode active material layer 64 in the case where the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64. Figure 7 In the case where the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64 (for example, the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64 in the case where the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64), the length of the edge of the main surface of the negative electrode active material layer 64 is the length of the edge of the main surface of the negative electrode active material layer 64 in the case where the length W1 and the length W2 in the long side direction are the total of the lengths of the edges of the main surface of the negative electrode active material layer 64.

[0098] In addition, as shown in FIG. 6, the thickness of the first adhesive 80 (i.e., the size of the first adhesive 80 in the stacking direction of the positive electrode 50 and the negative electrode 60) disposed in the non-facing region 64b of the negative electrode active material layer 64 can be made smaller than the thickness of the positive electrode 50 (i.e., the size of the positive electrode 50 in the stacking direction of the positive electrode 50 and the negative electrode 60). Figure 6

[0099] In the case where the thickness of the first adhesive 80 is larger than the thickness of the positive electrode 50, a portion of the first adhesive 80 protrudes in the single cell unit 10. Therefore, in the stacked electrode body 20 in which such single cell units 10 are stacked, in the case where pressure is applied in the stacking direction thereof, the pressure is concentrated on the first adhesive 80. When the pressure is concentrated, adverse situations such as deformation of the negative electrode 60, breakage of the negative electrode active material layer 64, and the like can occur. Therefore, in the case where the thickness of the first adhesive 80 is smaller than the thickness of the positive electrode 50, a portion of the first adhesive 80 does not protrude in the single cell unit 10, and thus adverse situations caused by such concentration of pressure can be suppressed.

[0100] The single cell unit 10 can be produced, for example, as follows. First, the positive electrode 50, the negative electrode 60, the separator 71, and the separator 72 are prepared. Next, the separator 71, the positive electrode 50, and the separator 72 are stacked, and the separator 71 and the separator 72 are fused. Next, the first adhesive 80 is applied to the non-facing region 64b of the negative electrode active material layer 64 of the negative electrode 60, and is adhered to the separator 71.

[0101] ​Specifically, the positive electrode 50 in which the positive electrode active material layer 54 is provided on both surfaces of the positive electrode current collector 52 is produced according to a conventional method. On the other hand, the negative electrode 60 in which the negative electrode active material layer 64 is provided on both surfaces of the negative electrode current collector 62 is produced according to a conventional method. Further, the positive electrode active material layer non-formed portion 52a in which the positive electrode active material layer 54 of the positive electrode current collector 52 is exposed is provided in the positive electrode 50, and the defective portion 53 is provided in the positive electrode active material layer non-formed portion 52a by punching or the like. A positive electrode current collector 52 having the defective portion 53 in advance can also be used. The negative electrode active material layer non-formed portion 62a in which the negative electrode current collector 62 is exposed is provided in the negative electrode 60. Two separators not having an adhesive layer are prepared as the separator 71 and the separator 72.

[0102] The separators 71 and 72 are stacked in a manner in which the positive electrode 50 is sandwiched by the separators 71 and 72. The area of the main surface of the separator 71 and the area of the main surface of the separator 72 are larger than the area of the main surface of the positive electrode active material layer 54, and thus the defective portion 53 can be covered with the separators 71 and 72. At the defective portion 53, the separators 71 and 72 are fused by heat fusion, ultrasonic fusion, laser fusion, or the like. At this time, the fusion of the separators 71 and 72 is performed in addition to the defective portion 53, as necessary.

[0103] The first adhesive 80 is applied to the non-facing region 64b of the negative electrode active material layer 64 on one side of the negative electrode 60. The method of application is not particularly limited, but since the non-facing region 64b of the negative electrode active material layer 64 is very small, it is advantageous to perform the application of the first adhesive 80 using a piezoelectric type jet dispenser or the like.

[0104] The separator 71 and the negative electrode active material layer 64 to which the first adhesive 80 is applied are overlapped in a manner in which the central portions of the positive electrode active material layer 54 and the negative electrode active material layer 64 face each other, and are bonded. The bonding is appropriately performed in accordance with the type of the first adhesive 80. For example, in the case where the first adhesive 80 is a heat-fusible adhesive, the heat-fusible adhesive is cooled and solidified. For example, in the case where the first adhesive 80 is an ultraviolet-curable adhesive, ultraviolet rays are irradiated and the adhesive is cured. For example, in the case where the first adhesive 80 is a thermally-curable adhesive, the adhesive is heated and cured.

[0105] In the single cell unit 10, the negative electrode 60 is bonded to the separator 71, and the positive electrode 50 is fixed between the fused separators 71 and 72, and thus they are integrated. By using such a single cell unit 10, in the case where the stacked electrode body 20 is configured by stacking a plurality of single cell units 10, high-speed stacking at the time of producing the stacked electrode body 20 can be achieved.

[0106] In the case where the stacked electrode body 20 is configured by stacking a plurality of single cell units 10, the two adjacent single cell units 10 can be bonded or can not be bonded. In the case where the two adjacent single cell units 10 are bonded, the negative electrode 60 of one single cell unit 10 is bonded to the separator 72 of the other single cell unit 10. In this case, it is advantageous that displacement between the single cell units 10 is less likely to occur.

[0107] In the case where the two adjacent single cell units 10 are bonded, the negative electrode 60 of one single cell unit 10 faces the positive electrode 50 of the other single cell unit 10. That is, the negative electrode active material layer 64 of the negative electrode 60 of one single cell unit 10 faces the positive electrode active material layer 54 of the other single cell unit 10. At this time, it is preferable that the negative electrode 60 of one single cell unit 10 is bonded to the separator 72 of the other single cell unit 10 in the same manner as the bonding of the negative electrode 60 to the separator 71 in the single cell unit 10.

[0108] Specifically, it is preferable that the negative electrode active material layer 64 of the negative electrode 60 of one single cell unit 10 is formed with a facing region facing the positive electrode active material layer 54 of the other single cell unit 10 at a central portion thereof, and is formed with a non-facing region not facing the positive electrode active material layer 54 of the other single cell unit 10 at a peripheral edge portion thereof. Further, in the same manner as described above, it is preferable that the second bonding agent bonding the two adjacent single cell units 10 is not disposed in the facing region 64a of the negative electrode active material layer 64, and is disposed in a region other than the facing region 64a (particularly, the non-facing region 64b), and in at least a part of the non-facing region 64b, the second bonding agent is not disposed, and a path through which the non-aqueous electrolyte solution flows is formed. At this time, displacement between the single cell units is suppressed, and the impregnation of the non-aqueous electrolyte solution into the stacked electrode body 20 at the time of production is more excellent. In addition, uniformity of the resistance in the surface direction of the electrode is more excellent.

[0109] As examples of the second bonding agent, the same bonding agents as exemplified as the first bonding agent can be listed. The second bonding agent can be the same as or different from the bonding agent used as the first bonding agent.

[0110] In a case where the laminated electrode body 20 is configured from a laminate of a plurality of single cell units 10, specifically, the laminated electrode body 20 is configured from a laminate in which a plurality of single cell units 10 are laminated in a manner that the negative electrode 60 of one of the adjacent two single cell units 10 faces the positive electrode 50 of the other single cell unit 10. In this laminate, the outermost layer of one is the positive electrode 50, and the outermost layer of the other is the negative electrode 60. It can also be that the laminated electrode body 20 contains a single negative electrode in addition to this laminate, and the single negative electrode is laminated on the positive electrode 50 of the outermost layer of the laminate. At this time, lithium of the positive electrode 50 of the outermost layer can be used for charge and discharge, and the single cell capacity can be improved.

[0111] The non-aqueous electrolyte solution can use the same non-aqueous electrolyte solution as the known lithium ion secondary battery. Typically, the non-aqueous electrolyte solution contains a non-aqueous solvent and a supporting salt (i.e., an electrolyte salt). As the non-aqueous solvent, various carbonates, ethers, esters, nitriles, sulfones, lactones, and the like organic solvents used in the non-aqueous electrolyte solution of the known lithium ion secondary battery can be used without particular limitation, of which carbonates are preferred. As examples of carbonates, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), and the like can be exemplified. The non-aqueous solvent can be used alone in one kind or in two or more kinds in an appropriate combination. As the supporting salt, for example, lithium salts such as LiPF6, LiBF4, LiClO4, and the like (preferably LiPF6) can be preferably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0112] The non-aqueous electrolyte solution can contain components other than the above-described components as long as the effects of the present application are not significantly impaired, such as a gas generating agent such as biphenyl (BP), cyclohexylbenzene (CHB), and the like, various additives such as a tackifier, and the like.

[0113] The lithium ion secondary battery 100 has a small initial resistance, and also suppresses an increase in resistance at the time of repeated charge and discharge. That is, the lithium ion secondary battery 100 has excellent resistance characteristics. In addition, the lithium ion secondary battery 100 has excellent impregnability of the non-aqueous electrolyte solution into the laminated electrode body 20 at the time of manufacture.

[0114] The lithium-ion secondary battery 100 can be used for various uses. As a preferred use, a power source for driving a vehicle such as an electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like can be cited. In addition, the lithium-ion secondary battery 100 can be used as a storage battery for a small-sized power storage device or the like. The lithium-ion secondary battery 100 can typically be used in the form of a battery pack in which a plurality of cells are connected in series and / or in parallel.

[0115] In the above, the present embodiment has been described taking a lithium-ion secondary battery as an example. However, the technology disclosed herein relates to the joining structure within a single cell 10, and thus can be understood to be applicable also to a nonaqueous electrolyte secondary battery that uses ions other than lithium ions as charge carriers.

[0116] In the present embodiment, the first electrode having a large area of the main surface of the active material layer is used as the negative electrode, and the second electrode is used as the positive electrode. However, in the technology disclosed herein, the first electrode can also be used as the positive electrode, and the second electrode can be used as the negative electrode.

[0117] Hereinafter, an embodiment related to the present application will be described in detail, but the present application is not intended to be limited to the content shown in the embodiment.

[0118] <Manufacture of Evaluation Lithium-ion Secondary Battery>

[0119] (Example 1)

[0120] A positive electrode having a positive electrode active material layer containing LiNi0.5Co0.2Mn0.3O2 on both surfaces of an aluminum foil having a thickness of 13 μm was prepared. The positive electrode active material layer had a main surface with a size of 300 mm x 100 mm, and the thickness of the positive electrode active material layer was 135 μm. In addition, a negative electrode having a negative electrode active material layer containing natural graphite on both surfaces of a copper foil having a thickness of 8 μm was prepared. The negative electrode active material layer had a main surface with a size of 302 mm x 102 mm, and the thickness of the negative electrode active material layer was 170 μm. A positive electrode active material layer non-formed portion in which the aluminum foil was exposed was provided in the positive electrode, and a negative electrode active material layer non-formed portion in which the copper foil was exposed was provided in the negative electrode. 0.8 Co 0.1 Mn 0.1 O2 on both surfaces of an aluminum foil having a thickness of 13 μm was prepared. The positive electrode active material layer had a main surface with a size of 300 mm x 100 mm, and the thickness of the positive electrode active material layer was 135 μm. In addition, a negative electrode having a negative electrode active material layer containing natural graphite on both surfaces of a copper foil having a thickness of 8 μm was prepared. The negative electrode active material layer had a main surface with a size of 302 mm x 102 mm, and the thickness of the negative electrode active material layer was 170 μm. A positive electrode active material layer non-formed portion in which the aluminum foil was exposed was provided in the positive electrode, and a negative electrode active material layer non-formed portion in which the copper foil was exposed was provided in the negative electrode.

[0121] Two pieces of a single-layered polypropylene porous film were prepared as separators. The separators had a main surface with a size of 306 mm x 104 mm, a thickness of 20 μm, and a gas permeability of 170 seconds / 100 mL.

[0122] The positive electrode active material layer non-formed portion (i.e., the exposed aluminum foil) of the positive electrode was coated with a 10-μm-thick layer of a positive electrode coating solution containing 10 parts by weight of a binder and 90 parts by weight of a conductive agent. Figure 2 and Figure 3At the location shown, namely the central part in the width direction and adjacent to the positive electrode active material layer, a rectangular through-hole is formed by punching. The positive electrode is held between two diaphragms. Figure 3 The two membranes are fused together by ultrasonic welding at the locations shown, namely the through hole of the non-formed part of the positive electrode active material layer and the outer part of the positive electrode end facing the non-formed part of the positive electrode active material layer.

[0123] Apply hot melt adhesive "Hybon ZH234-1" (manufactured by Hitachi Chemical Co., Ltd.) to the main surface of the negative electrode active material layer, in areas not facing the positive electrode active material layer. Apply as tiny dots (φ0.5mm) to six locations. The application points are the four corners of the area not facing the positive electrode active material layer and the center of the two long sides of that area.

[0124] The separator holding the positive electrode is overlapped with the negative electrode, and then bonded using a hot-melt adhesive at 0.5 MPa for 1 minute at 90°C to create a single cell unit. Ninety such single cell units are then fabricated and overlapped to obtain a stacked electrode body.

[0125] A non-aqueous electrolyte was prepared by dissolving LiPF6, used as a supporting salt, in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3 at a concentration of 1.1 mol / L.

[0126] The tab leads are ultrasonically bonded to the laminated electrode body, which is then housed in an aluminum laminated housing. After injecting the aforementioned non-aqueous electrolyte into the laminated housing, it is vacuum-sealed. After 24 hours, a pressure of 2 MPa is applied, and it is pre-charged to 2.75 V using a constant current at 0.2 C. A portion of the laminated housing is then cut under vacuum to vent the air, and the housing is resealed.

[0127] A pressure of 1 MPa was applied, and the battery was charged to 4.25V with a constant current of 0.3C. Then, it was charged with a constant voltage of 1.5A with a cutoff current of 4.25V to produce a lithium-ion secondary battery with a state of 100% SOC for evaluation.

[0128] Reference Example 1

[0129] Prepare the same positive and negative electrodes as in Example 1. In addition, prepare two diaphragms identical to those in Example 1 (i.e., single-layer polypropylene porous membranes; main surface dimensions are 306mm × 104mm, thickness is 20μm, and air permeability is 170 seconds / 100mL).

[0130] The positive electrode is held between two separators. The separators holding the positive electrode are then overlapped with the negative electrode to fabricate a single-cell unit. Ninety such single-cell units are fabricated, and these 90 units are overlapped to obtain a stacked electrode body. Using this stacked electrode body, an evaluation lithium-ion secondary battery is fabricated in the same manner as in Example 1.

[0131] [Comparative Example 1]

[0132] Prepare the same positive and negative electrodes as in Example 1. Additionally, prepare two porous polypropylene membranes with adhesive layers containing alumina and polyvinylidene fluoride on both sides as separators. The main surface dimensions of the separator are 306 mm × 104 mm, the separator thickness is 20 μm (2 μm adhesive layer + 16 μm substrate + 2 μm adhesive layer), and the air permeability is 170 seconds / 100 mL.

[0133] The positive electrode is held between two separators. The separators holding the positive electrode are overlapped with the negative electrode, and pressure is applied at 0.5 MPa for 1 minute at 90°C to bond the two separators to the positive electrode and the one separator to the negative electrode, thus fabricating a single-cell unit. Ninety such single-cell units are fabricated, and the 90 single-cell units are overlapped to obtain a stacked electrode body. Using this stacked electrode body, an evaluation lithium-ion secondary battery is fabricated in the same manner as in Example 1.

[0134] (Comparative Example 2)

[0135] Prepare the same positive and negative electrodes as in Example 1. Additionally, prepare two porous polypropylene membranes with an adhesive layer containing alumina and polyvinylidene fluoride on one side as separators. The main surface dimensions of the separator are 306 mm × 104 mm, the separator thickness is 20 μm (18 μm substrate + 2 μm adhesive layer), and the air permeability is 170 seconds / 100 mL.

[0136] The positive electrode is held between two separators with the adhesive layer of the separator facing each other. The separator holding the positive electrode is then overlapped with the negative electrode, and pressure is applied at 0.5 MPa for 1 minute at 90°C to bond the two separators to the positive electrode, thus fabricating a single-cell unit. Ninety such single-cell units are fabricated, and these 90 units are overlapped to obtain a stacked electrode body. Using this stacked electrode body, an evaluation lithium-ion secondary battery is fabricated in the same manner as in Example 1.

[0137] <Evaluation of Initial Resistance Characteristics>

[0138] At a temperature of 25°C, a pressure of 1 MPa was applied to each evaluation lithium-ion secondary battery to adjust it to a state of 50% SOC. Then, a constant current discharge of 2C was performed for 10 seconds. The voltage change was calculated, and the initial resistance value was calculated based on the voltage change and the current value. The results are shown in Table 1.

[0139] <Evaluation of resistance characteristics after charge-discharge cycles>

[0140] At a temperature of 25°C, a pressure of 1 MPa was applied to each evaluation lithium-ion secondary battery. For each battery, 100 charge-discharge cycles were performed, with one cycle consisting of charging at a constant current of 1C from 2.5V to 4.25V and discharging at a constant current of 1C from 4.25V to 2.5V. A 10-minute buffer time was set between charge-discharge cycles. The resistance value was then calculated in the same manner as the initial resistance. The results are shown in Table 1.

[0141] [Table 1]

[0142] Table 1

[0143]

[0144] A comparison of Reference Example 1 with Comparative Examples 1 and 2 shows that bonding the diaphragm to the electrode deteriorates the resistance characteristics. In particular, a comparison with Comparative Examples 1 and 2 shows that if more adhesive is used, the resistance characteristics deteriorate further.

[0145] However, in Example 1, where a defect was provided in the non-formed portion of the positive electrode active material layer, and the two separators were not bonded to the positive electrode active material layer but instead fused at the defect, the same resistance characteristics as in Reference Example 1 were observed. Therefore, it can be seen that in Example 1, although the positive electrode and separator were fused and fixed, a lithium-ion secondary battery with low initial resistance and suppressed resistance increase during repeated charge and discharge was obtained.

[0146] Therefore, as can be seen from the above, the non-aqueous electrolyte secondary battery disclosed herein has a low initial resistance and suppresses the increase in resistance during repeated charging and discharging.

[0147] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes technologies obtained by various modifications and alterations to the specific examples described above.

Claims

1. A nonaqueous electrolyte secondary battery comprising a laminated electrode body and a nonaqueous electrolyte, the laminated electrode body including a single cell unit in which a first electrode, a first separator, a second electrode, and a second separator are sequentially laminated, wherein the first electrode has a first current collector and a first active material layer, the second electrode has a second current collector and a second active material layer, an area of a main surface of the first separator and an area of a main surface of the second separator are larger than an area of a main surface of the first active material layer of the first electrode and an area of a main surface of the second active material layer of the second electrode, a second active material layer non-forming portion in which the second active material layer is not formed and the second current collector is exposed is provided in the second electrode, the second active material layer non-forming portion has a defect portion in which the second current collector is removed from one main surface to an opposite main surface, the first separator and the second separator are not bonded to the second active material layer of the second electrode, the first separator and the second separator are welded at the defect portion of the second active material layer non-forming portion, the defect portion is formed at a position close to a first corner portion of the second active material layer, two welding portions are formed by welding the first separator and the second separator so as to sandwich a second corner portion opposite the first corner portion of the second active material layer, the first active material layer faces the second active material layer, an area of a main surface of the first active material layer of the first electrode is larger than an area of a main surface of the second active material layer of the second electrode, a facing region facing the second active material layer is formed in a central portion of the first active material layer, a non-facing region not facing the second active material layer is formed in an outer peripheral portion of the first active material layer, the first separator and the first electrode are bonded by a first bonding agent, the first bonding agent bonding the first electrode and the first separator is not disposed in the facing region of the first active material layer and is disposed in the non-facing region, the non-facing region is a rectangular frame-shaped region constituted by two short sides and two long sides, a path for the nonaqueous electrolyte to flow is formed in at least a portion of the non-facing region in which the first bonding agent is not disposed, and the path for the nonaqueous electrolyte to flow is disposed in a portion of all four sides of the rectangular frame-shaped non-facing region.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the defect portion is a through-hole.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode is a negative electrode and the second electrode is a positive electrode.

4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a thickness of the first bonding agent is smaller than a thickness of the second electrode.

5. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the laminated electrode body includes a laminate in which a plurality of the single cell units are laminated and outermost layers are a positive electrode and a negative electrode, and a single negative electrode. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The negative electrode of the single body is stacked on the positive electrode of the outermost layer of the laminate.

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