Non-aqueous electrolyte secondary batteries

Abstract

The present invention provides a non-aqueous electrolyte secondary battery having a low initial resistance and a suppressed increase in resistance during repeated charge and discharge. The non-aqueous electrolyte secondary battery disclosed herein comprises a stacked electrode body and a non-aqueous electrolyte, wherein the stacked electrode body comprises a battery cell formed by stacking a first electrode, a first separator, a second electrode, and a second separator in sequence. The first electrode comprises a first current collector and a first active material layer. The second electrode comprises a second current collector and a second active material layer. An opposing region opposing the second active material layer is formed in the central portion of the first active material layer. A non-opposing region not opposing the second active material layer is formed in the outer peripheral portion of the first active material layer. The non-opposing regions at a pair of opposing ends of the first active material layer each have a through hole. The first separator and the second separator are bent toward the second electrode side outside the non-opposing region having the through hole. The first separator and the second separator are joined in the through hole.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. Background Art

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium secondary batteries have been favorably used as mobile power sources for personal computers and mobile terminals, and as vehicle driving power sources for electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] A typical non-aqueous electrolyte secondary battery has an electrode assembly consisting of a positive electrode and a negative electrode stacked with a separator interposed therebetween. These electrode assemblies are broadly categorized into wound electrode assemblies and laminated electrode assemblies. A laminated electrode assembly has a structure in which positive and negative electrodes are alternately stacked with a separator interposed therebetween.

[0004] One method for manufacturing a stacked electrode assembly includes forming a plurality of single battery cells in which a first electrode, a first separator, a second electrode, and a second separator are sequentially stacked, and then further stacking the plurality of single battery cells (for example, see Patent Document 1). In such a manufacturing method, the separator and the electrode are bonded together with an adhesive to prevent positional displacement between the electrode and the separator. For example, Patent Document 1 describes that in order to bond the separator to the electrode with an adhesive, the adhesive is applied to both surfaces of the first separator, and the adhesive is applied only to the surface of the second separator that faces the second electrode.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6093369 Summary of the Invention

[0008] However, in the prior art, it is difficult for the non-aqueous electrolyte (especially charge carriers (for example, lithium ions, etc.)) to move in the portion of the separator coated with the adhesive, which leads to an increase in resistance. In addition, when the non-aqueous electrolyte secondary battery is repeatedly charged and discharged, the active material repeatedly expands and contracts. When the active material expands, the confining pressure (restraint pressure) increases, and the non-aqueous electrolyte is squeezed out of the stacked electrode body. In the prior art, it is difficult for the non-aqueous electrolyte to flow in the portion of the separator coated with the adhesive, so the squeezed non-aqueous electrolyte is difficult to return to the stacked electrode body, resulting in an increase in resistance.

[0009] Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having low initial resistance and in which resistance increase during repeated charge and discharge is suppressed.

[0010] The non-aqueous electrolyte secondary battery disclosed herein comprises a stacked electrode body and a non-aqueous electrolyte, wherein the stacked electrode body includes a battery cell formed by stacking a first electrode, a first separator, a second electrode, and a second separator in this order. The first electrode comprises a first current collector and a first active material layer. The second electrode comprises a second current collector and a second active material layer. The first active material layer and the second active material layer are opposed to each other. 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. An opposing region opposing the second active material layer is formed in the central portion of the first active material layer. A non-opposing region not opposing the second active material layer is formed in the outer peripheral portion of the first active material layer. The non-opposing regions located at a pair of opposing end portions of the first active material layer each have a through hole. 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. The portion where the first separator and the second separator are stacked covers the opening of the through hole located on the surface of the first active material layer that is opposite to the second active material layer. The first separator and the second separator are bent toward the second electrode outside the non-opposing region having the through hole so as to cover the opening of the through hole located on the surface of the first active material layer that is opposite to the surface that is opposite to the second active material layer. In the through hole, the portion where the first separator and the second separator are stacked is joined to the bent portion of the first separator and the second separator. According to this structure, a non-aqueous electrolyte secondary battery is provided that has a low initial resistance and suppresses the increase in resistance during repeated charge and discharge.

[0011] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the ends of the curved portions of the first and second separators are positioned outward of the stacked portion of the first and second active material layers. This configuration prevents the curved portions of the first and second separators of one battery cell from overlapping the second electrode of another battery cell when the battery cells are stacked. This reduces the likelihood of deformation in the stacked structure of the stacked electrode assembly, and allows the inter-electrode distance between the first electrode of one battery cell and the second electrode of another battery cell to be kept small and constant.

[0012] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the first electrode is a negative electrode, and the second electrode is a positive electrode. With this configuration, the main surface area of the negative electrode active material layer is larger than the main surface area of the positive electrode active material layer, thereby significantly suppressing the formation of metals from ions (e.g., lithium ions) that function as charge carriers.

[0013] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the stacked electrode assembly comprises a stacked body and a single negative electrode. The stacked body is formed by stacking multiple battery cells, with the outermost layers comprising a positive electrode and a negative electrode. The single negative electrode is stacked on the outermost positive electrode of the stacked body. This configuration allows the lithium in the outermost positive electrode to be used for charging and discharging, thereby increasing the battery cell capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a cross-sectional view schematically showing the internal structure of a lithium-ion secondary battery according to one embodiment of the present invention.

[0015] Figure 2 This is a perspective view schematically showing a battery cell included in a stacked electrode assembly of a lithium-ion secondary battery according to one embodiment of the present invention.

[0016] Figure 3 This is an exploded perspective view schematically showing a battery cell included in a stacked electrode assembly of a lithium-ion secondary battery according to one embodiment of the present invention.

[0017] Figure 4 This is a cross-sectional view schematically showing a battery cell included in a stacked electrode assembly of a lithium-ion secondary battery according to one embodiment of the present invention.

[0018] Figure 5 This is a schematic diagram schematically showing a negative electrode of a battery cell included in a stacked electrode assembly of a lithium-ion secondary battery according to one embodiment of the present invention.

[0019] Explanation of symbols

[0020] 10 battery cells

[0021] 20 stacked electrode body

[0022] 30 battery housing

[0023] 36 Safety Valve

[0024] 42 Positive terminal

[0025] 42a Positive electrode collector plate

[0026] 44 Negative terminal

[0027] 44a Negative electrode collector plate

[0028] 50 positive electrode

[0029] 52 positive electrode collector

[0030] 52a Positive electrode active material layer non-formed portion

[0031] 53 missing part

[0032] 54 positive electrode active material layer

[0033] 60 negative electrode

[0034] 62 negative electrode collector

[0035] 62a Negative electrode active material layer non-formed portion

[0036] 64 Negative electrode active material layer

[0037] 64a Opposing area

[0038] 64b Non-opposed area

[0039] 71 1st spacer

[0040] 72 2nd spacer

[0041] 73 joint

[0042] 74 laminated part

[0043] 75 bend

[0044] 76 joint

[0045] 80 bonding part

[0046] 82 Non-aqueous electrolyte flow path

[0047] 100 lithium-ion secondary batteries DETAILED DESCRIPTION

[0048] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that matters not mentioned in this specification and matters required for the implementation of the present invention can be grasped as design matters for those skilled in the art based on the prior art in this field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in this field. In addition, in the following drawings, components and parts that play the same role are marked with the same symbols for description. In addition, the dimensional relationships (length, width, thickness, etc.) of each figure do not reflect the actual dimensional relationships.

[0049] The following describes this embodiment in detail using a lithium-ion secondary battery as an example. It should be noted that the term "secondary battery" in this specification refers to an electrical storage device that can be repeatedly charged and discharged, and is a term that includes storage cells and electrical double-layer capacitors. Furthermore, the term "lithium secondary battery" in this specification refers to a secondary battery that uses lithium ions as charge carriers and achieves charge and discharge through the movement of charge associated with the lithium ions between the positive and negative electrodes.

[0050] Figure 1Schematically shows the internal structure of the lithium-ion secondary battery 100 of this embodiment. Figure 1 The lithium ion secondary battery 100 shown includes a stacked electrode assembly 20, a non-aqueous electrolyte (not shown), and a rectangular battery case 30 for housing these. The battery case 30 is sealed, so the lithium ion secondary battery 100 is a sealed battery.

[0051] like Figure 1 As shown, the battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, as well as a thin-walled safety valve 36 designed to release the internal pressure of the battery case 30 when it rises above a predetermined level. In addition, the battery case 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 electrode collector plate 42a. The negative terminal 44 is electrically connected to the negative electrode collector plate 44a.

[0052] The battery case 30 is made of a metal material such as aluminum due to its light weight and high thermal conductivity. However, the material of the battery case 30 is not limited to this and may also be made of resin. Alternatively, the battery case 30 may be a laminated case using a laminate film.

[0053] Figures 2-4 Schematically shows the battery cell 10 included in the stacked electrode body 20 . Figure 2 is a perspective view of the battery unit 10, Figure 3 This is an exploded perspective view of the battery unit 10 decomposed into its components. Figure 4 It is along Figure 2 A-A cross-sectional view of the line. Therefore, Figure 4 It is a cross-sectional view taken along the width direction of the positive electrode 50 and the negative electrode 60 and along the stacking direction of the positive electrode 50 and the negative electrode 60 . Figure 2 In the following figures, the X direction is the length direction of the positive electrode 50 and the negative electrode 60 included in the stacked electrode body 20, the Y direction is the width direction of the positive electrode 50 and the negative electrode 60 included in the stacked electrode body 20, and the Z direction is the stacking direction of the positive electrode 50 and the negative electrode 60.

[0054] The stacked electrode assembly 20 includes at least one battery cell 10 as shown in the figure. Typically, the stacked electrode assembly 20 includes a plurality of battery cells 10. The number of battery cells 10 included in the stacked electrode assembly 20 is not particularly limited and can be the same as the number of battery cells included in stacked electrode assemblies used in conventional lithium-ion secondary batteries, for example, 1 to 150, preferably 20 to 100.

[0055] like Figures 2-4 ,in particular Figure 3As shown, the battery cell 10 includes 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 battery cell 10, the negative electrode 60, the separator 71, the positive electrode 50, and the separator 72 are stacked in this order.

[0056] The positive electrode 50 includes a positive electrode current collector 52 and a positive electrode active material layer 54 provided on the positive electrode current collector 52. Figure 3 As shown, in this embodiment, positive electrode active material layers 54 are provided on both sides of the positive electrode current collector 52. However, the positive electrode active material layer 54 may be provided on only one side of the positive electrode current collector 52. A positive electrode active material layer-free portion 52a is provided at one end of the positive electrode 50, where the positive electrode active material layer 54 is not formed and the positive electrode current collector 52 is exposed. An insulating tape or an insulating coating containing alumina, boehmite, or the like may be formed on a portion of the positive electrode active material layer-free portion 52a.

[0057] The negative electrode 60 includes a negative electrode current collector 62 and a negative electrode active material layer 64 provided on the negative electrode current collector 62. Figure 3 As shown, in this embodiment, negative electrode active material layers 64 are provided on both sides of the negative electrode current collector 62. However, the negative electrode active material layer 64 may be provided on only one side of the negative electrode current collector 62. A negative electrode active material layer non-formed portion 62a is provided at one end of the negative electrode 60 where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed.

[0058] like Figures 1 to 3 As shown, the positive electrode active material layer non-forming portion 52a and the negative electrode active material layer non-forming portion 62a protrude in opposite directions from the stacked portion of the positive electrode active material layer 54 and the negative electrode active material layer 64. The positive electrode active material layer non-forming portion 52a and the negative electrode active material layer non-forming portion 62a function as collector tabs, respectively. The shapes of the positive electrode active material layer non-forming portion 52a and the negative electrode active material layer non-forming portion 62a are not limited to the shapes shown in the figure, and can be processed into a predetermined shape by cutting, etc. The protruding directions of the positive electrode active material layer non-forming portion 52a and the negative electrode active material layer non-forming portion 62a are not limited to the protruding directions shown in the figure. The positive electrode active material layer non-forming portion 52a and the negative electrode active material layer non-forming portion 62a can be set to positions and shapes that do not overlap with each other and protrude in the same direction.

[0059] In the stacked electrode body 20, as Figure 1 As shown, the positive electrode active material layer non-forming portions 52a of the plurality of battery cells 10 are combined and electrically connected to the positive electrode current collector plate 42a. Figure 1As shown, the negative electrode active material layer non-forming portions 62a of the plurality of battery cells 10 are put together and electrically joined to the negative electrode current collector plate 44a. This joining can be performed by, for example, ultrasonic welding, resistance welding, laser welding, or the like.

[0060] The positive electrode current collector 52 can be a sheet or foil made of a highly conductive metal (e.g., aluminum, nickel, titanium, or stainless steel), preferably aluminum foil. The thickness of the positive electrode current collector 52 is not particularly limited, but is, for example, 5 μm to 35 μm, preferably 7 μm to 20 μm.

[0061] The positive electrode active material layer 54 contains at least a positive electrode active material. Examples of the positive electrode active material include lithium nickel cobalt manganese composite oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc.), lithium nickel composite oxides (e.g., LiNiO2, etc.), lithium cobalt composite oxides (e.g., LiCoO2, etc.), lithium nickel manganese composite oxides (e.g., LiNi 0.5 Mn 1.5 The positive electrode active material layer 54 may further contain a conductive material, a binder, and the like. Conductive materials include, for example, carbon black such as acetylene black (AB) and other carbon materials (such as graphite). Binders include, for example, polyvinylidene fluoride (PVDF). The thickness of the positive electrode active material layer 54 is not particularly limited, but is, for example, 20 μm to 300 μm.

[0062] The negative electrode current collector 62 can be made of a sheet or foil of a highly conductive metal (e.g., copper, nickel, titanium, stainless steel, etc.), preferably copper foil. The thickness of the negative electrode current collector 62 is, for example, 5 μm to 35 μm, preferably 7 μm to 20 μm.

[0063] The negative electrode active material layer 64 contains at least a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, hard carbon, and soft carbon. The negative electrode active material layer 64 may further contain a binder, a thickener, and the like. As a binder, for example, styrene butadiene rubber (SBR) can be used. As a thickener, for example, carboxymethyl cellulose (CMC) 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.

[0064] As separators 71 and 72, various porous sheets similar to separators that have been used in lithium-ion secondary batteries can be used. Examples thereof include porous resin sheets made of polyolefins such as polyethylene (PE) and polypropylene (PP). The porous resin sheet can be a single-layer structure or a multilayer structure with two or more layers (for example, a three-layer structure with PP layers laminated on both sides of a PE layer). Separators 71 and 72 can have a heat-resistant layer (HRL). The thickness of separators 71 and 72 is not particularly limited, and for example, is 10 μm to 40 μm.

[0065] In this embodiment, the main surface area of the negative electrode active material layer 64 of the negative electrode 60 is larger than the main surface area of the positive electrode active material layer 54 of the positive electrode 50. In this case, the precipitation of lithium ions as metallic lithium can be highly suppressed. It should be noted that the main surface of the active material layer refers to the surface with the largest area among the surfaces constituting the active material layer. Therefore, in this embodiment, the main surface of the negative electrode active material layer 64 is the surface in contact with the negative electrode collector 62 and the surface opposite thereto. In addition, the main surface of the positive electrode active material layer 54 is the surface in contact with the positive electrode collector 52 and the surface opposite thereto. On the other hand, from the perspective of insulation and the perspective of enabling bonding in the through-hole 66 described later, the main surface areas of the separator 71 and the separator 72 are respectively larger than the main surface areas of the negative electrode active material layer 64 of the negative electrode 60 and the main surface areas of the positive electrode active material layer 54 of the positive electrode 50. It should be noted that the main surface of the separator refers to the surface with the largest area among the surfaces constituting the separator.

[0066] The positive electrode 50 is sandwiched between the separator 71 and the separator 72. The positive electrode active material layer 54 of the positive electrode 50 is not bonded to the separator 71 and the separator 72. Therefore, in this embodiment, there is no adhesive that hinders the movement of the non-aqueous electrolyte to and from the positive electrode active material layer 54, so the non-aqueous electrolyte can move easily.

[0067] In this embodiment, the positive electrode 50 does not need to be bonded to the separator 71 and the separator 72, but the positive electrode 50 may be bonded to the separator 71 and the separator 72 at a location other than the positive electrode active material layer 54. Examples of the location other than the positive electrode active material layer 54 include the positive electrode active material layer-unformed portion 52a of the positive electrode 50. Figure 2In the illustrated example, a bonding portion 80 is provided that bonds the portion 52a of the positive electrode 50 where the positive electrode active material layer is not formed to the separator 72 via an adhesive. Furthermore, although not shown, the portion 52a of the positive electrode 50 where the positive electrode active material layer is not formed is also bonded to the separator 71. By bonding the positive electrode 50 to the separator 71 and the separator 72 in locations other than the positive electrode active material layer 54, positional displacement between the positive electrode 50 and the separator 71 and the separator 72 can be suppressed during fabrication and stacking of the battery cell 10. As the adhesive, for example, well-known adhesives such as hot melt adhesives, ultraviolet curing adhesives, and thermosetting adhesives can be used.

[0068] In addition, the separator 71 and the separator 72 may be joined at other locations on the outside of the positive electrode 50 in addition to the joint 76 described later. In the example shown in the figure, a joint 73 between the separator 71 and the separator 72 is provided on the outside of the end portion of the positive electrode 50 on the opposite side of the end portion where the positive electrode active material layer is not formed 52a. The joint 73 is formed, for example, by ultrasonic welding or the like. By providing the joint 73 between the separator 71 and the separator 72 on the outside of the positive electrode 50, it is possible to suppress positional deviation of the positive electrode 50, the separator 71, and the separator 72 when manufacturing the battery cell 10 and stacking the battery cells 10. In particular, as shown in the example shown in the figure, when the positive electrode active material layer non-forming portion 52a of the positive electrode 50 has an adhesive portion 80 and the joint 73 is provided on the outside of the end portion of the positive electrode 50 on the opposite side of the positive electrode active material layer non-forming portion 52a, the above-mentioned positional deviation can be highly suppressed.

[0069] Figure 5 The negative electrode 60 is schematically shown in FIG. Figures 3 to 5 As shown, the positive electrode 50 and the negative electrode 60 are stacked in such a manner that the positive electrode active material layer 54 and the negative electrode active material layer 64 face each other. Figure 4 and Figure 5 As shown, an opposing region 64 a facing the positive electrode active material layer 54 is formed in the center of the negative electrode active material layer 64 . Furthermore, a non-opposing region 64 b not facing the positive electrode active material layer 54 is formed in the outer periphery of the negative electrode active material layer 64 .

[0070] like Figures 3 to 5 As shown, in the Y direction, non-opposing regions 64b1 located at a pair of opposing ends of the negative electrode active material layer 64 each have a through-hole 66. In the illustrated example, the non-opposing regions 64b1 located at the pair of opposing ends of the negative electrode active material layer 64 are located at a pair of opposing ends in a direction perpendicular to the protrusion direction of the negative electrode active material layer non-formed portion 62a of the negative electrode 60. Therefore, in the illustrated example, the non-opposing regions 64b1 located at the pair of opposing ends of the negative electrode active material layer 64 are ends of the negative electrode active material layer 64 that do not have the negative electrode active material layer non-formed portion 62a.

[0071] The shape and size of through-hole 66 are not particularly limited as long as the spacer 71 and spacer 72 can be joined within through-hole 66, as described later. For example, when joining through-hole 66 by ultrasonic welding, the through-hole 66 should be sized to accommodate the horn of the ultrasonic welding apparatus. While the opening of through-hole 66 is square in the illustrated example, it may also be circular, elliptical, or other shapes.

[0072] The number of through holes 66 is not particularly limited. In the example shown in the figure, two through holes 66 are formed in each of the non-opposing regions 64b1 located at a pair of end portions of the negative electrode active material layer 64, but it is sufficient to form at least one through hole 66. Preferably, one to three through holes 66 are formed in each of the non-opposing regions 64b1 located at a pair of end portions of the negative electrode active material layer 64. The positions of the through holes 66 are not particularly limited. As shown in the example shown in the figure, when the through holes 66 are provided at both ends of the non-opposing regions 64b1 located at a pair of end portions of the negative electrode active material layer 64 or in the vicinity thereof, it is advantageous because the negative electrode 60 and the separator 71 and the separator 72 can be stably integrated.

[0073] like Figure 4 As shown, a portion (laminated portion) 74 where the separators 71 and 72 are laminated covers the opening of the through-hole 66 located on the surface of the negative electrode active material layer 64 facing the positive electrode active material layer 54 .

[0074] In addition, if Figure 4 As shown, separators 71 and 72 are bent toward negative electrode 60 outside non-opposing region 64b1 having through-hole 66, forming bent portion 75. Separators 71 and 72 cover the openings of the through-holes on the surface of negative electrode active material layer 64 that is opposite to the surface facing positive electrode active material layer 54.

[0075] In the through-hole 66 , the laminated portion 74 of the spacer 71 and the spacer 72 is bonded to the bent portion 75 to form a bonded portion 76 .

[0076] With this configuration, the positive electrode 50 can be sandwiched and fixed by the separator 71 and the separator 72, while the negative electrode 60 can be fixed by the separator 71 and the separator 72. Therefore, without using a binder for the positive electrode active material layer 54 and the negative electrode active material layer 64, the battery cell 10 can be constructed in which the positive electrode 50, the negative electrode 60, the separator 71, and the separator 72 are integrated.

[0077] As a result, in the areas that mainly participate in charging and discharging, namely the positive electrode active material layer 54 and the negative electrode active material layer 64, it is possible to prevent the movement of ions (i.e., lithium ions in this embodiment) that serve as charge carriers from being hindered by the adhesive. As a result, compared with the prior art in which the separator and the active material layer are bonded to the entire surface, the initial resistance can be reduced. Moreover, the uniformity of the resistance in the surface direction of the positive electrode active material layer 54 and the negative electrode active material layer 64 is also excellent. In addition, when the lithium ion secondary battery 100 is repeatedly charged and discharged, the non-aqueous electrolyte is squeezed out of the stacked electrode body 20 due to the expansion of the positive electrode active material layer 54 and the negative electrode active material layer 64, but in the lithium ion secondary battery 100, the non-aqueous electrolyte that has flowed out can be prevented from being hindered by the adhesive from returning to the stacked electrode body 20. As a result, compared with the prior art in which the separator and the active material layer are bonded to the entire surface, the resistance increase during repeated charging and discharging can be suppressed. Furthermore, when manufacturing the lithium-ion secondary battery 100 , the time required for the non-aqueous electrolyte to permeate into the electrode body can be shortened.

[0078] Furthermore, the integration of the battery cells 10 can suppress positional shifts among the positive electrode 50, negative electrode 60, separator 71, and separator 72 during stacking of the battery cells 10. Furthermore, the integration of the battery cells 10 reduces the number of stacking steps compared to stacking the components one by one. Consequently, stacking of the battery cells 10 can be accelerated during the manufacture of the stacked electrode assembly 20 of the lithium-ion secondary battery 100.

[0079] The method for joining the laminated portion 74 and the curved portion 75 is not particularly limited. They can be bonded using an adhesive or the like. However, in this joined portion, the separator comprises four layers (two layers of separator 71 + two layers of separator 72). Ultrasonic welding is advantageous as a joining method because it is easy to simultaneously join these four layers.

[0080] In the illustrated example, the end 75a of the curved portion 75 of the separators 71 and 72 is located outside the stacked portion of the negative electrode active material layer 64 and the positive electrode active material layer 54. That is, the end 75a of the curved portion 75 is located outside the end of the positive electrode 50 in the Y direction. In this case, when the battery cells 10 are stacked, the curved portion 75 of the separators 71 and 72 of one battery cell 10 does not overlap with the positive electrode 50 of another battery cell 10. This reduces the stacking structure of the stacked electrode assembly 20 from being easily deformed. Furthermore, the inter-electrode distance between the negative electrode 60 of one battery cell 10 and the positive electrode 50 of another battery cell 10 can be kept small and constant.

[0081] In the illustrated example, the separators 71 and 72 are bent while being in contact with the side surfaces of the negative electrode active material layer 64 . However, the separators 71 and 72 do not need to be in contact with the side surfaces of the negative electrode active material layer 64 .

[0082] The battery cell 10 can be manufactured, for example, as follows. First, a positive electrode 50, a negative electrode 60, a separator 71, and a separator 72 are prepared. Specifically, the positive electrode 50 is manufactured using conventional methods, with positive electrode active material layers 54 provided on both sides of the positive electrode current collector 52. Meanwhile, the negative electrode 60 is manufactured using conventional methods, with negative electrode active material layers 64 provided on both sides of the negative electrode current collector 62. Two separators without adhesive layers are prepared as separators 71 and 72.

[0083] Through holes 66 are formed in the regions to be non-opposed regions 64b1 at the pair of end portions of the negative electrode active material layer 64 of the negative electrode 60. The through holes 66 can be formed by a known method such as laser processing, punching, or drilling.

[0084] The positive electrode 50 is sandwiched between separators 71 and 72. At this time, as needed, the positive electrode active material layer non-forming portion 52a of the positive electrode 50 is bonded to the separators 71 and 72 by adhesion or the like. Furthermore, as needed, the separators 71 and 72 are bonded to the outside of the positive electrode 50 by ultrasonic welding or the like.

[0085] Next, the negative electrode 60 is stacked thereon so that the positive electrode active material layer 54 and the negative electrode active material layer 64 face each other at their central portions with the separator 71 interposed therebetween. At this time, the portion (stacked portion) 74 where the separator 71 and the separator 72 are stacked covers the opening of the through-hole 66 located on the surface of the negative electrode material layer 64 facing the positive electrode active material layer 54.

[0086] Next, the two separators are bent toward the negative electrode outside the non-opposing region 64b1 of the negative electrode active material layer 64 where the through-holes 66 are formed. At this time, the bent portion (bent portion) 75 is bent so as to cover the openings of the through-holes on the surface of the negative electrode active material layer opposite to the surface facing the positive electrode active material layer.

[0087] The laminated portion 74 and the bent portion 75 of the separator 71 and the separator 72 are joined by ultrasonic welding or the like in the through-hole 66. This provides the battery cell 10 in which the positive electrode 50, the negative electrode 60, the separator 71, and the separator 72 are integrated.

[0088] Next, the stacked electrode assembly 20 will be described. When the stacked electrode assembly 20 is constructed by stacking multiple battery cells 10, adjacent battery cells 10 may or may not be bonded. When two adjacent battery cells 10 are bonded, the negative electrode 60 of one battery cell 10 is bonded to the separator 72 of the other battery cell 10. This has the advantage of less likely misalignment between the battery cells 10.

[0089] When two adjacent battery cells 10 are bonded together, the negative electrode 60 of one battery cell 10 faces the positive electrode 50 of the other battery cell 10. Specifically, the negative electrode active material layer 64 of the negative electrode 60 of one battery cell 10 faces the positive electrode active material layer 54 of the other battery cell 10. In this case, the negative electrode active material layer 64 of the negative electrode 60 of one battery cell 10 preferably has a central region that faces the positive electrode active material layer 54 of the other battery cell 10, and a peripheral region that does not face the positive electrode active material layer 54 of the other battery cell 10. Furthermore, the adhesive (e.g., a hot melt adhesive, a UV-curable adhesive, a thermosetting adhesive, etc.) used to bond the two adjacent battery cells 10 is preferably disposed not in the facing region of the negative electrode active material layer 64, but in a region outside the facing region (particularly the non-facing region). Furthermore, it is preferred to form a non-aqueous electrolyte flow path in at least a portion of the non-opposing region without applying an adhesive. This prevents positional shifting between battery cells and improves the permeability of the non-aqueous electrolyte into the stacked electrode assembly 20 during manufacturing. Furthermore, the uniformity of the resistance across the electrode surface is improved.

[0090] When the stacked electrode body 20 is composed of a stack of multiple battery cells 10, the stacked electrode body 20 is specifically composed of a stack of multiple battery cells 10 stacked such that the negative electrode 60 of one battery cell 10 faces the positive electrode 50 of the other battery cell 10 in two adjacent battery cells 10. In this stack, one outermost layer is the positive electrode 50, and the other outermost layer is the negative electrode 60. In addition to this stack, the stacked electrode body 20 also includes a single negative electrode, which can be stacked on the outermost positive electrode 50 of the stack. In this case, the lithium in the outermost positive electrode 50 can be used for charging and discharging, which can increase the battery cell capacity.

[0091] Next, the non-aqueous electrolyte is described. The non-aqueous electrolyte can use the same non-aqueous electrolyte as that used in known lithium-ion secondary batteries. Typically, the non-aqueous electrolyte contains a non-aqueous solvent and a supporting salt (i.e., an electrolyte salt). As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones used in non-aqueous electrolytes of known lithium-ion secondary batteries can be used without particular limitation, among which carbonates are preferred. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC). The non-aqueous solvent can be used alone or in combination of two or more. As the supporting salt, for example, lithium salts such as LiPF6, LiBF4, and LiClO4 (preferably LiPF6) can be preferably used. The concentration of the supporting salt is preferably 0.7 mol / L to 1.3 mol / L.

[0092] The non-aqueous electrolyte may further contain components other than the above components, for example, gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); thickeners; and various additives such as film-forming agents, unless the effects of the present invention are significantly impaired.

[0093] The lithium-ion secondary battery 100 has a low initial resistance and suppresses resistance increases during repeated charge and discharge. In other words, the lithium-ion secondary battery 100 has excellent resistance characteristics. Furthermore, during manufacture of the lithium-ion secondary battery 100, the nonaqueous electrolyte has excellent permeability into the stacked electrode assembly 20.

[0094] The lithium-ion secondary battery 100 can be used for various applications. Preferred applications include driving power supplies in vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). In addition, the lithium-ion secondary battery 100 can be used as a storage battery for small power storage devices. The lithium-ion secondary battery 100 is typically used in the form of a battery pack formed by connecting multiple batteries in series and / or in parallel.

[0095] While the present embodiment has been described above using a lithium-ion secondary battery as an example, the technology disclosed herein also relates to the junction structure within the battery cell 10 and is therefore applicable to non-aqueous electrolyte secondary batteries that utilize charge carriers other than lithium ions.

[0096] In this embodiment, the first electrode having a larger main surface area 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 may be used as the positive electrode, and the second electrode may be used as the negative electrode.

[0097] Hereinafter, examples according to the present invention will be described in detail, but the present invention is not intended to be limited to the embodiments shown in these examples.

[0098] <Production of lithium-ion secondary batteries for evaluation>

[0099] [Example 1]

[0100] A 13 μm thick aluminum foil was prepared with a LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode is provided with a positive electrode active material layer of O2. The main surface size of the positive electrode active material layer is 300mm×100mm, and the thickness of the positive electrode active material layer is 135μm. In addition, a negative electrode is provided with a negative electrode active material layer containing natural graphite on both sides of a copper foil with a thickness of 8μm. The main surface size of the negative electrode active material layer is 302mm×102mm, and the thickness of the negative electrode active material layer is 170μm. Figure 3 The aluminum foil shown in the figure is exposed in the non-formed portion of the positive electrode active material layer, and the negative electrode is provided with Figure 3 The copper foil shown has exposed areas where the negative electrode active material layer is not formed.

[0101] Two single-layer polypropylene porous films were prepared as separators. The main surface of the separators had a size of 306 mm x 104 mm, a thickness of 20 μm, and an air permeability of 170 sec / 100 mL.

[0102] like Figure 3 and Figure 4 As shown, through-holes are formed in the edge of the negative electrode active material layer in a region that does not face the positive electrode active material layer (a region referred to as the non-facing region). Specifically, through-holes are formed by laser processing near the ends of a pair of end regions perpendicular to the direction in which the non-forming portion of the negative electrode active material layer protrudes, i.e., the end regions that serve as the non-facing region.

[0103] The positive electrode was sandwiched between two separators and stacked on the negative electrode so that the center of the positive electrode active material layer was aligned with the center of the negative electrode active material layer. Next, the two separators were bent toward the negative electrode outside the non-opposing areas where the through-holes were formed.

[0104] The four layers of separators located above the through-holes were welded together by ultrasonic welding. This produced a battery cell. Ninety of these battery cells were fabricated and stacked to form a laminated electrode assembly.

[0105] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a supporting salt at a concentration of 1.1 mol / L in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3.

[0106] The tab leads were ultrasonically bonded to the stacked electrode assembly and housed in an aluminum laminate case. The laminate case was injected with the aforementioned non-aqueous electrolyte and then vacuum-sealed. After 24 hours, a pressure of 2 MPa was applied to the case and the battery was charged (pre-charged) to 2.75 V at a constant current of 0.2 C. A portion of the laminate case was cut under vacuum, degassed, and resealed.

[0107] A pressure of 1 MPa was applied thereto, and constant current charging was performed at a current value of 0.3 C to 4.25 V. Thereafter, constant voltage charging was performed at a voltage of 4.25 V with a cutoff current value of 1.5 A to prepare a lithium ion secondary battery for evaluation with an SOC of 100%.

[0108] [Reference Example 1]

[0109] The same positive electrode and negative electrode as in Example 1 were prepared. In addition, two separators as in Example 1 (i.e., single-layer polypropylene porous membranes; main surface dimensions: 306 mm x 104 mm, thickness: 20 μm, air permeability: 170 sec / 100 mL) were prepared.

[0110] The positive electrode was sandwiched between two separators. These were stacked with the negative electrode, with the center of the positive electrode active material layer aligned with the center of the negative electrode active material layer, and no through-holes were formed in non-opposing areas of the negative electrode active material layer. Thus, a battery cell was obtained. 90 of these battery cells were prepared and stacked to obtain a stacked electrode body. Using this stacked electrode body, a lithium-ion secondary battery for evaluation was prepared in the same manner as in Example 1.

[0111] [Comparative Example 1]

[0112] The same positive and negative electrodes as in Example 1 were prepared. Separately, two polypropylene porous membranes with adhesive layers containing aluminum oxide and polyvinylidene fluoride on both surfaces were prepared as separators. The main surface dimensions of the separators were 306 mm × 104 mm, the thickness was 20 μm (adhesive layer 2 μm + substrate 16 μm + adhesive layer 2 μm), and the air permeability was 170 sec / 100 mL.

[0113] The positive electrode is clamped between two separators. They are overlapped with the negative electrode so that the center of the positive electrode active material layer is aligned with the center of the negative electrode active material layer, and no through-holes are formed in the non-opposing areas of the negative electrode active material layer of the negative electrode. The obtained stack is pressurized at 90°C and 0.5 MPa for 1 minute to bond the two separators to the positive electrode and the one separator to the negative electrode to form a battery cell. 90 of these battery cells are made and stacked to obtain a stacked electrode body. Using this stacked electrode body, a lithium-ion secondary battery for evaluation is made in the same manner as in Example 1.

[0114] [Comparative Example 2]

[0115] The same positive and negative electrodes as in Example 1 were prepared. Separately, two polypropylene porous membranes each having an adhesive layer containing aluminum oxide and polyvinylidene fluoride on one side were prepared as separators. The main surface dimensions of the separators were 306 mm × 104 mm, the thickness was 20 μm (18 μm substrate + 2 μm adhesive layer), and the air permeability was 170 sec / 100 mL.

[0116] The positive electrode is clamped between two separators so that the adhesive layer of the separator is opposite to the positive electrode. They are overlapped with the negative electrode so that the center of the positive electrode active material layer is aligned with the center of the negative electrode active material layer, and no through-holes are formed in the non-opposing area of the negative electrode active material layer of the negative electrode. The obtained stack is pressurized at 90°C and 0.5 MPa for 1 minute to bond the two separators to the positive electrode to form a battery cell. 90 of these battery cells are made and 90 battery cells are overlapped to obtain a stacked electrode body. Using this stacked electrode body, a lithium-ion secondary battery for evaluation is made in the same manner as in Example 1.

[0117] <Evaluation of Initial Resistance Characteristics>

[0118] Each evaluation lithium-ion secondary battery was subjected to a pressure of 1 MPa at 25°C, adjusting the battery to a SOC of 50%. A constant-current discharge at 2C was then performed for 10 seconds. The voltage change during this discharge was determined, and the initial resistance value was calculated from the voltage change and the current value. The results are shown in Table 1.

[0119] <Evaluation of resistance characteristics after charge and discharge cycles>

[0120] A pressure of 1 MPa was applied to each evaluation lithium-ion secondary battery at 25°C. One cycle consisted 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. This cycle was repeated 100 times. The relaxation time between charge and discharge cycles was set to 10 minutes. The resistance value was then determined in the same manner as the initial resistance. The results are shown in Table 1.

[0121] [Table 1]

[0122] Table 1

[0123]

[0124] Comparison of Reference Example 1 with Comparative Examples 1 and 2 shows that bonding the separator to the electrode deteriorates the resistance characteristics. In particular, comparison of Comparative Examples 1 and 2 shows that increasing the amount of adhesive further deteriorates the resistance characteristics.

[0125] However, Example 1, in which a through-hole was provided in a region of the negative electrode active material layer that did not face the positive electrode active material layer, the separator was bent to surround the end of the negative electrode, and the separator was bonded in the through-hole, exhibited resistance characteristics equivalent to those of Reference Example 1. Therefore, in Example 1, although the positive electrode and the separator were bonded and fixed, a lithium-ion secondary battery was obtained that had a low initial resistance and suppressed resistance increase during repeated charge and discharge.

[0126] Therefore, it can be seen from the above that according to the non-aqueous electrolyte secondary battery disclosed herein, the initial resistance is low and the increase in resistance during repeated charge and discharge is suppressed.

[0127] While specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technology described in the claims encompasses various modifications and variations of the specific examples described above.

Claims

1. A non-aqueous electrolyte secondary battery comprising a laminated electrode body and a non-aqueous electrolyte, wherein the laminated electrode body includes a battery cell formed by laminating a first electrode, a first separator, a second electrode, and a second separator in this order, The first electrode includes 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 active material layer and the second active material layer are opposed to each other, The main surface area of the first active material layer of the first electrode is larger than the main surface area of the second active material layer of the second electrode. A facing region facing the second active material layer is formed in the center of the first active material layer. A non-opposing region that does not oppose the second active material layer is formed on the outer peripheral edge of the first active material layer. The non-opposing regions located at a pair of opposing end portions of the first active material layer each have a through hole. The main surface area of the first separator and the main surface area of the second separator are respectively larger than the main surface area of the first active material layer of the first electrode and the main surface area of the second active material layer of the second electrode. The first active material layer and the second active material layer are not bonded to the separator, In each of the pair of opposing end portions, a portion where the first separator and the second separator are stacked covers an opening of the through hole located on a surface of the first active material layer that faces the second active material layer. At each of the pair of opposing end portions, the first separator and the second separator are bent toward the first electrode outside a non-opposing region having the through-hole so as to cover an opening of the through-hole on a surface of the first active material layer opposite to a surface opposing the second active material layer. In the through-holes at the pair of opposing end portions, the stacked portions of the first and second spacers are joined to the bent portions of the first and second spacers.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein Ends of the bent portions of the first separator and the second separator are positioned outside a stacked portion of the first active material layer and the second active material layer.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein The first electrode is a negative electrode, and the second electrode is a positive electrode.

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein The stacked electrode body includes a stacked body and a single negative electrode, wherein the stacked body is a stacked body in which a plurality of the battery cells are stacked and the outermost layers are the positive electrode and the negative electrode. The single negative electrode is stacked on the positive electrode on the outermost layer of the stacked body via the first separator or the second separator.

5. The non-aqueous electrolyte secondary battery according to claim 3, wherein The stacked electrode body includes a stacked body and a single negative electrode, wherein the stacked body is a stacked body in which a plurality of the battery cells are stacked and the outermost layers are the positive electrode and the negative electrode. The single negative electrode is stacked on the positive electrode on the outermost layer of the stacked body via the first separator or the second separator.

Images