Secondary battery and battery pack thereof

Abstract

Provided are a rectangular secondary battery in which a shallow deep-drawn battery can and a lid plate are welded and fixed and sealed, and a battery pack thereof, in which when a battery pack is manufactured, the size of a bus bar is not increased or the arrangement of a duct is not hindered, and the stress caused by a constraint load is not concentrated on a weld seam. This secondary battery (1) is provided with a power generation element, a battery can (3), a non-aqueous electrolyte solution, a cover plate (5), and a pair of external terminals (6, 7). The battery can (3) has a square shallow deep drawing shape, and is a metal battery can in which a power generation element is placed down and stored. In addition, the battery can (3) is provided with a flange part (34) around the opening part of the battery can (3). A battery can (3) in which a power generating element is housed is filled with the non-aqueous electrolyte solution. The cover plate (5) is a metal cover plate of which the outer edge part (51a) is welded and fixed to the flange part (34) of the battery can (3) so as to cover the battery can (3). In addition, the cover plate (5) is provided with a protruding part (52) which protrudes more in a planar shape than the outer edge part (51a) in a region closer to the inner side than the outer edge part (51a).

Description

Technical Field

[0001] The present invention relates to a secondary battery and a battery pack comprising a plurality of the secondary batteries connected in series. Background Art

[0002] In the past, the following method was generally used to manufacture secondary batteries: after a power generation element was housed in a cylindrical battery can made of metal with a bottom, a metal cover was pressed into the inner side of the battery can surrounded by the open end, and the pressed-in butt joint was welded by irradiating a laser beam from above the cover.

[0003] However, when the cover plate is press-fitted into the battery can, foreign matter such as burrs may be generated and enter the battery can, or weld particles (sputters) may enter the battery can. These intrusive matters may cause degradation of battery performance.

[0004] Therefore, as a method for manufacturing such a sealed secondary battery, there have been proposed methods of making the outer edge of the cover plate overlap with the open end of the battery can and laser welding the overlapping portion from the side of the cover plate (Patent Document 1); providing a step portion on the inner circumference of the open end of the battery can, placing the cover plate on the step portion, and laser welding the circumferential surface contact portion of the two from above the cover plate (Patent Document 2); or providing the cover plate with a stepped shape, overlapping the large diameter portion of the battery can with the small diameter portion being embedded in the battery can, and laser welding the overlapping portion of the two from the side of the cover plate (Patent Document 3), etc.

[0005] However, no matter which proposal is made, although it is possible to prevent the intrusion of foreign matter accompanying the pressing, since the weld portion is expanded to the inner peripheral side of the battery can, it is impossible to avoid the intrusion of spatter into the battery can, and it is not sufficient as a countermeasure to prevent the degradation of battery performance caused by the intrusion of foreign matter.

[0006] In contrast, Patent Document 4 discloses a sealed battery in which a cover plate is welded and fixed to the open end of a battery can that accommodates a power generation element, wherein an annular flange portion extending outward is provided at the open end of the battery can, the outer edge portion of the cover plate is butted against the flange portion, and the butting portion is laser welded from the upper surface side of the cover plate.

[0007] With this configuration, the welded portion is set at the outer portion of the outer peripheral surface of the battery can, thereby eliminating the risk of spatters caused by welding intruding into the battery can.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 3-93148

[0011] Patent Document 2: Japanese Patent Application Publication No. 2000-231908

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 11-307065

[0013] Patent Document 4: Japanese Patent Application Laid-Open No. 2003-132857 Summary of the invention

[0014] Problem that the invention aims to solve

[0015] However, secondary batteries are currently becoming popular for power storage systems such as electric vehicles or solar power generation. These secondary batteries are mostly square in shape from the perspective of applicability and accommodation to products or systems. However, in the case of a battery can formed into a bottomed cylindrical shape by deep drawing, the shape freedom is low. Therefore, it is difficult to make a square secondary battery thinner.

[0016] On the other hand, if a battery can is formed into a square shape by shallow drawing and a power generating element is laid down and housed at the bottom of the battery can, the secondary battery can also be made square and thin.

[0017] However, when a plurality of secondary batteries having a rectangular battery can by shallow drawing are connected in series to form a battery pack, a new problem arises.

[0018] That is, in the battery pack, a plurality of secondary batteries are arranged in an overlapping manner in a direction perpendicular to the main surface of the largest area of ​​the secondary battery. At this time, a pair of positive and negative external terminals of each secondary battery are separately arranged in the long side direction of the side portion of the secondary battery that becomes the upper surface of the battery pack. In order to connect adjacent secondary batteries in series with each other, one of a pair of external terminals of a secondary battery (for example, a positive terminal) is connected to the other of a pair of external terminals of an adjacent secondary battery (for example, a negative terminal) with a metal member called a bus bar. In addition, a restraining member applies a restraining load to the secondary battery pack in which a plurality of secondary batteries are arranged in an overlapping manner.

[0019] When the secondary batteries are arranged in such a manner that the battery cans and cover plates of each secondary battery are all oriented in the same direction, since the external terminals of the same pole of the battery pack are arranged in a row in the arrangement direction of the secondary batteries, the busbars must be hung obliquely between adjacent secondary batteries and connected in series, resulting in a problem of large busbars. In addition, the busbars hung obliquely between adjacent secondary batteries will hinder the ducts arranged on the upper surface of the battery pack through which smoke, steam, etc. released from the safety valves of the secondary batteries pass.

[0020] In addition, when the secondary batteries are arranged between adjacent secondary batteries in such a manner that the battery cans and the cover plates are in opposite directions, that is, the shallowly drawn bottom surfaces of the battery cans of the adjacent secondary batteries and the cover plates are opposite to each other, since the external terminals of the same pole of the battery pack advance in a zigzag shape relative to the arrangement direction of the secondary batteries, it is also possible not to obliquely hang the busbars between the adjacent secondary batteries and connect them in series. That is, the external terminals are connected by a plurality of busbars parallel to the arrangement direction of the secondary batteries.

[0021] However, in this case, since the cover plates of adjacent secondary batteries are opposite to each other, the flange of the battery can and the butt joint of the cover plate, that is, the welded portion based on laser welding, overlap each other. In order to assemble multiple secondary batteries into a battery pack, a restraining load is applied in the arrangement direction of the secondary batteries by a restraining member, so the restraining load is applied even though the welded portions overlap. As a result, there is a problem that stress is concentrated on the weld of the welded portion and durability is reduced.

[0022] Therefore, the present invention solves this problem and provides a secondary battery and a battery pack thereof. The secondary battery is a square secondary battery in which a shallowly drawn battery can and a cover plate are welded and fixed and sealed. When made into a battery pack, the bus bar will not be enlarged or hinder the pipeline configuration, and the stress caused by the constraint load will not be concentrated on the weld.

[0023] Solutions for solving problems

[0024] Hereinafter, a plurality of aspects will be described as means for solving the problem. These aspects can be arbitrarily combined as needed.

[0025] A secondary battery according to one aspect of the present invention includes a power generation element, a battery can, a nonaqueous electrolyte, a cover plate, and a pair of external terminals.

[0026] The power generating element includes a positive electrode, a negative electrode, and a separator for insulating them in a stacked manner, and is flat.

[0027] The battery can is a square shallowly drawn shape, and is a metal battery can that is laid down to house the power generation element. In addition, the battery can has a flange around its opening. The non-aqueous electrolyte is filled in the battery can that houses the power generation element.

[0028] The cover plate is a metal cover plate whose outer edge is welded and fixed to the flange of the battery can and covers the battery can. In addition, the cover plate has a convex portion protruding in a plane shape from the outer edge in an area inside the outer edge.

[0029] One of the pair of external terminals is arranged on one of the side walls of the battery can and is electrically connected to one of the positive and negative electrodes of the power generation element. The other of the pair of external terminals is arranged on one side of the cover plate on the same side as the side wall on which the one external terminal is arranged and at a position line-symmetrical with the one external terminal in a plan view and is electrically connected to the other of the positive and negative electrodes of the power generation element.

[0030] In addition, a battery pack according to one aspect of the present invention is configured with a plurality of batteries having a positive and negative pair of external terminals as the upper side, with the front and back sides of the main surface alternately replaced in a direction perpendicular to the main surface with the largest area. In addition, the adjacent secondary batteries are connected in series by bus bars. Moreover, a restraining load is applied by a restraining member in the arrangement direction of the secondary batteries.

[0031] In the battery pack having such a configuration, the external terminals are connected by two bus bars parallel to the arrangement direction of the secondary batteries, so the bus bars do not become large or interfere with the arrangement of the ducts.

[0032] In addition, since each secondary battery cover has a convex portion protruding in a planar shape in the inner region than the outer edge portion, the outer edges of adjacent cover plates do not contact each other when the battery pack is manufactured. Therefore, stress caused by the restraint load does not concentrate on the weld.

[0033] Furthermore, the height of the convex portion of the cover plate of the secondary battery may be set to 0.1 to 3 mm.

[0034] Furthermore, the cover plate of the secondary battery may be a metal plate that is shallowly drawn, and the shallowly drawn portion may constitute the convex portion.

[0035] Alternatively, the cover plate of the secondary battery may be a laminate of a metal plate formed of a flat plate and a convex portion forming layer having an area smaller than that of the metal plate, and the convex portion is formed by the thickness of the laminated convex portion forming layer. Furthermore, when the convex portion forming layers are laminated, the convex portion protruding in a planar shape is divided into a plurality of regions when viewed from above, and there are gaps between the convex portions between the plurality of regions.

[0036] Effects of the Invention

[0037] According to the secondary battery and the battery pack of the present invention, when the secondary battery is made into a battery pack, the bus bar does not become larger or hinder the arrangement of the pipes, and the stress caused by the restraint load does not concentrate on the weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 These are front and back perspective views showing an example of the appearance of the lithium ion secondary battery according to the first embodiment of the present invention.

[0039] Figure 2This is an exploded perspective view showing an example of the internal structure of the lithium ion secondary battery according to the first embodiment of the present invention.

[0040] Figure 3 This is a partially enlarged cross-sectional view showing an example of a convex structure in the cover plate of the lithium ion secondary battery according to the first embodiment of the present invention.

[0041] Figure 4 This is a perspective view showing an example of a battery pack using the lithium ion secondary battery according to the first embodiment of the present invention.

[0042] Figure 5 This is a partially enlarged cross-sectional view showing an example of a convex structure in a cover plate of a lithium ion secondary battery according to a second embodiment of the present invention.

[0043] Figure 6 This is a plan view showing an example of various convex portion structures in a cover plate of a lithium ion secondary battery according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0044] In the following embodiments, a case where the present invention is applied to a lithium ion secondary battery as an example of a secondary battery will be described. The secondary battery of the present invention is not limited to a lithium ion secondary battery.

[0045] [First embodiment]

[0046] Hereinafter, a first embodiment of the present invention will be described based on the drawings.

[0047] 1. Structure of secondary battery

[0048] Figure 1 1 is a perspective view showing the front and back of an example of the appearance of a lithium ion secondary battery according to the first embodiment of the present invention. Figure 1 In the figure, (a) is a perspective view when viewed from the battery can side, and (b) is a perspective view when viewed from the cover plate side. Figure 2 1 is an exploded perspective view showing an example of the internal structure of the lithium ion secondary battery according to the first embodiment of the present invention. Figure 2 In order to understand the internal structure of the lithium ion secondary battery, the non-aqueous electrolyte solution of the secondary battery originally filled in the battery can is removed and depicted. Figure 3 This is a partially enlarged cross-sectional view showing an example of a convex structure in the cover plate of the lithium ion secondary battery according to the first embodiment of the present invention.

[0049] like Figure 1 and Figure 2As shown, the lithium-ion secondary battery 1 of the first embodiment has a square flat shape and includes: a power generation element 2, a battery can 3 for accommodating the power generation element 2, a non-aqueous electrolyte (not shown) filled in the battery can 3 for accommodating the power generation element 2, a cover plate 5 covering the battery can 3, and a pair of external terminals (a positive terminal 6 and a negative terminal 7) electrically connected to the positive electrode and the negative electrode of the power generation element 2.

[0050] 1-a. Power generation element

[0051] The power generating element 2 includes a positive electrode, a negative electrode, and a separator for insulating them in a stacked manner, and is flat.

[0052] As such a power generation element 2, for example, there is a stacked type in which a plurality of positive electrodes, negative electrodes and separators are respectively provided, and the positive electrodes, negative electrodes and separators are stacked one by one. In addition, the positive electrodes and negative electrodes are alternately stacked one by one, and the outermost sides thereof are all negative electrodes. In addition, separators are respectively arranged between the positive electrode and the negative electrode and on the outermost side of the power generation element 2. In addition, the main surface of the power generation element 2 is parallel to the electrode surfaces of the positive electrode and the negative electrode.

[0053] In addition, as another example of a stacked type power generation element 2, a plurality of positive electrodes, a plurality of negative electrodes, and a repeatedly folded separator can also be combined to form a structure. Repeated folding refers to a folding method of folding into a zigzag shape. That is, the separator is bent into a zigzag shape by repeated folding, so that it is sandwiched between the positive electrode 11 and the negative electrode 12 that are alternately stacked in a continuous strip-shaped member. In addition, one end side of the separator is also arranged at the outermost side of the power generation element 2. In addition, the main surface of the power generation element 2 is parallel to the electrode surface of the positive electrode and the negative electrode.

[0054] Alternatively, a wound type power generating element 2 may be used in which a laminate sheet including a positive electrode, a negative electrode and two separators is wound multiple times. However, in the present invention, since the power generating element 2 is flat, the winding type power generating element 2 is also flat.

[0055] (1) Positive electrode

[0056] The positive electrode constituting the power generating element 2 has a structure in which positive electrode active material layers are supported on both surfaces of a positive electrode current collector.

[0057] The positive electrode current collector has the function of collecting current from the positive electrode active material layer and is made of, for example, a metal foil such as aluminum, titanium, stainless steel, nickel, iron, or an alloy foil made of an alloy thereof and has a thickness of about 1 μm to about 500 μm.

[0058] The positive electrode active material layer is composed of a positive electrode active material that can absorb and release lithium ions. Examples of the positive electrode active material include oxides containing lithium. Specifically, examples include LiCoO2, LiFeO2, LiMnO2, LiMn2O4, and compounds in which transition metals in these oxides are partially replaced by other metal elements.

[0059] (2) Negative electrode

[0060] The negative electrode constituting the power generating element 2 has a structure in which negative electrode active material layers are supported on both surfaces of a negative electrode current collector.

[0061] The negative electrode current collector has the function of collecting current from the negative electrode active material layer and is made of, for example, metal foil such as copper, nickel, stainless steel, iron, nickel plating, or alloy foil made of alloys thereof and has a thickness of about 1 μm to about 100 μm.

[0062] The negative electrode active material layer is composed of a negative electrode active material that can absorb and release lithium ions. As the negative electrode active material, for example, it is composed of a material that can absorb and release lithium. Specifically, granular (flake-shaped, block-shaped, fibrous, whisker-shaped, spherical, crushed granular, etc.) natural graphite or artificial graphite can be cited. In addition, as the negative electrode active material, artificial graphite obtained by graphitizing mesophase carbon microbeads, mesophase asphalt powder, isotropic asphalt powder, etc. can also be used. In addition, graphite particles with amorphous carbon attached to the surface can also be used. Moreover, lithium transition metal oxides, lithium transition metal nitrides, transition metal oxides, and silicon oxide can also be used. As lithium transition metal oxides, for example, Li4Ti5O 12 Represented by lithium titanate.

[0063] (3) Isolation

[0064] The separator constituting the power generating element 2 is a member having holes for allowing ions to pass therethrough.

[0065] As a separator, it can be a separator with sufficient strength and capable of holding a large amount of non-aqueous electrolyte. From such a point of view, for example, a microporous membrane or non-woven fabric containing polyethylene, polypropylene or ethylene-propylene copolymer is preferred. In addition, for example, a microporous membrane composed of polymers such as polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyether sulfone, polycarbonate, polyamide, polyimide, polyether, cellulose, poly(meth)acrylic acid, and poly(meth)acrylate can also be used. In addition, a multilayer film formed by overlapping these microporous membranes can also be used. As the thickness of the separator, it is preferably 5μm to 100μm. In addition, as the porosity of the separator, it is preferably 30% to 90%.

[0066] (4) Electrode tabs

[0067] like Figure 2 As shown, the power generation element 2 is electrically connected to a pair of external terminals (positive terminal 6 and negative terminal 7) from the positive electrode collector of the positive electrode via the positive electrode tab 21 and from the negative electrode collector of the negative electrode via the negative electrode tab 22. The positive electrode tab 21 and the negative electrode tab 22 protrude from the same end surface of the power generation element 2. The positive electrode tab 21 and the negative electrode tab 22 can be made of the same material as the collector, but can also be made of different materials.

[0068] 1-b. Non-aqueous electrolyte

[0069] The non-aqueous electrolyte (not shown) sealed in the battery can 3 together with the power generation element 2 is not particularly limited. As a solvent, for example, esters such as ethylene carbonate (EC), propylene carbonate, butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and γ-butyrolactone; ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, diethyl ether, dimethoxyethane, diethoxyethane, and methoxyethoxyethane; polar solvents such as dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, and methyl acetate can be used. These solvents can be used alone or two or more can be mixed to form a mixed solvent.

[0070] 1-c.Battery can

[0071] The battery can 3 is a flat square can made of metal. The battery can 3 is formed by shallow drawing a metal plate. The shallow drawing shape of the battery can 3 has a rectangular bottom 31, side walls 32 that stand up on four sides of the bottom 31, an opening 33 formed by the ends of the four side walls 32 on the opposite side to the bottom 31, and a flange 34 that extends around the opening 33. In addition, the bottom 31 of the battery can 3 is parallel to the flange 34.

[0072] The dimensions of the bottom 31, the side wall 32, and the opening 33 of the battery can 3 are such that the flat power generating element 2 can be laid down, that is, can be accommodated in such a manner that the main surface of the power generating element 2 faces the bottom 31. Specifically, the length of the outer surface side of the bottom 31 of the battery can 3 ( Figure 2 The length L1 in the Y direction is 202 mm, and the lateral length of the outer surface side of the bottom 31 is ( Figure 2 The length W1 in the X direction is formed to be 94 mm. The depth of the outer surface of the battery can 3 ( Figure 2 The length T1 in the Z direction is, for example, 4 mm.

[0073] The size of the opening 33 of the battery can 3 is the same as or slightly larger than the size of the bottom 31. In the latter case, the inclination of the inner surface side of the side wall 32 is, for example, about 5°.

[0074] The size of the flange portion 34 of the battery can 3 is sufficient for welding and fixing to the outer edge portion 51a of the cover plate 5 described later. The length of the flange portion 34 in the extension direction ( Figure 2 The width W2 in the X direction and the Y direction is formed to be 3 mm, for example.

[0075] In addition, each numerical value of the size of the battery can 3 shown in this paragraph and the previous paragraph is an example, and the present invention is not limited thereto.

[0076] Shallow drawing is a type of drawing. Drawing is a method of making bottomed containers of various shapes from a thin metal plate without any joints. Generally speaking, the drawing process of making shallow containers such as ashtrays or frying pans is called shallow drawing, and the process of making a container deeper than the opening size of the cylinder (the diameter of a cylinder or the mouth of a square cylinder) is called deep drawing. The shallow drawing process in the present invention is a process of forming a battery can 3 with the main surface of a square flat lithium-ion secondary battery 1 as the bottom.

[0077] The metal plate used for shallow drawing of the battery can 3 can be formed using a metal plate made of iron, stainless steel, aluminum, copper, or the like, for example. The thickness of the metal plate can be set to 0.1 mm to 1 mm, for example.

[0078] In addition, one of the four side walls 32 of the battery can 3 is provided at the center with a safety valve 8 (see FIG. 8 ) which opens when the internal pressure of the battery exceeds a predetermined pressure. Figure 1 , Figure 2 ). The increase in the internal pressure of the battery is caused by excessive heat due to deterioration or overcharging. The safety valve 8 is closed from the outside by a cover, for example, and the cover falls off due to the increase in the internal pressure of the battery, thereby opening. In addition, the safety valve 8 is preferably provided on the side wall portion 32 that becomes the upper side when a plurality of secondary batteries are used as a battery pack.

[0079] In addition, for the reasons described in the section “2. Structure of battery pack” below, the outer surface of the metal battery can 3 is preferably covered with an insulating film (not shown).

[0080] 1-d. Cover

[0081] The cover plate 5 is made of metal, and its outer edge portion 51a is welded and fixed to the flange portion 34 of the battery can 3 to cover the battery can 3. The cover plate 5 and the battery can 3 constitute the outer container of the lithium ion secondary battery 1. Figure 1 and Figure 2As shown, the cover plate 5 is in a rectangular shape covering the opening 33 of the battery can 3, and has a convex portion 52 protruding in a planar shape toward the outer surface side from the outer edge portion 51a in the inner area of ​​the metal plate 51 constituting the cover plate 5. In addition, the bottom 31 of the battery can 3 is parallel to the top surface of the convex portion 52 of the cover plate 5.

[0082] In addition, if Figure 3 As shown, the convex portion 52 of the cover plate 5 in the first embodiment is formed by shallow drawing a flat metal plate. That is, the cover plate 5 is a shallowly drawn metal plate 51, and the shallowly drawn portion forms the convex portion 52 on the outer surface side of the cover plate 5.

[0083] The size of the cover plate 5 is such that the outer edge portion 51 a thereof can overlap with the flange portion 34 of the battery can 3 and be fixed by welding.

[0084] The height of the protrusion 52 of the cover plate 5 ( Figure 1 (b) T2 in the Z direction is 0.1 to 3 mm, preferably 0.1 to 2 mm. If the height of the protrusion 52 is less than 0.1 mm, when the cover plates 5 of adjacent lithium-ion secondary batteries 1 are arranged in an opposing manner to form a battery pack 10, the cover plates 5 contact each other, and stress concentration on the weld of the welding portion between the battery can 3 and the cover plate 5 cannot be avoided. When the height of the protrusion 52 exceeds 3 mm, the problem of interference between the laser used in welding and the side of the protrusion 52 occurs. Of course, it is also possible to consider further tilting the laser irradiation, but this exceeds the range that can be processed with a galvanometer scanner, and productivity is reduced.

[0085] As the metal plate 51 used in the shallow drawing process of the cover plate 5 , a metal plate made of the same material and thickness as those used in the battery can 3 can be used.

[0086] The outer edge portion 51 a of the cover plate 5 and the flange portion 34 of the battery can 3 are fixed by welding using laser or the like.

[0087] In addition, after the opening 33 of the battery can 3 is sealed by the cover plate 5, the non-aqueous electrolyte is injected from the injection hole (not shown). Then, after a sealing member having a diameter substantially the same as that of the injection hole is set at the injection hole, the injection hole is sealed by welding such as laser. The formation location of the injection hole is not particularly limited. The injection hole may be provided at the bottom 31 of the battery can 3 and any one of the four side walls 32, or the injection hole may be provided at the cover plate 5.

[0088] In addition, for the reasons described in the section “2. Structure of battery pack” below, the outer surface of the metal cover plate 5 is preferably further covered with an insulating film (not shown).

[0089] 1-e.External terminal

[0090] The lithium ion secondary battery 1 includes a positive electrode terminal 6 and a negative electrode terminal 7 as a pair of external terminals (see Figure 1 , Figure 2 ), and is electrically connected to the positive electrode and negative electrode (not shown) of the power generating element 2. Figure 2 As shown, in the power generation element 2 housed in the battery can 3, a positive electrode tab 21 for connecting the positive electrode with the positive terminal 6 serving as an external terminal and a negative electrode tab 22 for connecting the negative electrode with the negative terminal 7 serving as an external terminal are provided in a manner protruding from the same end face of the power generation element 2.

[0091] The positive terminal 6 is disposed on one of the side walls 32 of the battery can 3. The positive terminal 6 includes, for example, a thin plate-shaped positive terminal body 61 inserted into the through hole 35 of the side wall 32 of the battery can 3; and an insulating member 62 (see FIG. 1 ) for preventing the positive terminal body 61 from contacting the inner wall of the through hole 35 of the battery can 3. Figure 1 , Figure 2 ). The gap between the positive electrode terminal body 61 and the inner wall of the through hole 35 of the battery can 3 is completely sealed by the insulating member 62 .

[0092] The negative terminal 7 is arranged on one side of the cover plate 5 on the same side as the side wall portion 32 of the battery can 3 on which the positive terminal 6 is arranged. The negative terminal 7 is arranged at a position that is line-symmetrical with the positive terminal 6 when viewed from above. The negative terminal 7 is, for example, a negative terminal punched out from a metal plate as a continuous and integral pattern with the rectangular cover plate 5 (see FIG. 1 ). Figure 1 , Figure 2 ).

[0093] Furthermore, the positive electrode terminal 6 and the negative electrode terminal 7 may not be completely line-symmetrical in a plan view as long as the effects of the present invention described in this specification can be obtained, and some positional deviation is within an allowable range.

[0094] Alternatively, the negative electrode terminal 7 which is a separate body from the rectangular cover plate 5 may be fixed to the cover plate 5 by welding using laser or the like.

[0095] In addition, the positive terminal 6 and the negative terminal 7 can be replaced as long as the positive terminal 6 and the positive electrode of the power generation element 2 and the negative terminal 7 are respectively and correctly electrically connected, and the above connection structure can also be replaced. Moreover, the external terminal of the present invention can appropriately adopt a known external terminal other than the connection structure shown in the first embodiment.

[0096] 2. Battery pack structure

[0097] Figure 4 This is a perspective view showing an example of a battery pack using the lithium ion secondary battery according to the first embodiment of the present invention.

[0098] like Figure 4 As shown, the battery pack 10 using the lithium ion secondary battery 1 of the first embodiment is a battery pack 10 in which a plurality of the above-mentioned lithium ion secondary batteries 1 are arranged in a direction perpendicular to the main surface having the largest area. In addition, the battery pack 10 includes a bus bar 11 that connects adjacent lithium ion secondary batteries 1 in series. Furthermore, the battery pack 10 includes a restraining member (for example, a belt 12) that applies a restraining load in the arrangement direction of the lithium ion secondary batteries 1. Figure 4 In the example shown, there are seven lithium-ion secondary batteries 1 .

[0099] 2-a. Arrangement of secondary batteries

[0100] like Figure 4 As shown, the plurality of lithium-ion secondary batteries 1 constituting the battery pack 10 are arranged so that a pair of positive and negative external terminals (positive electrode terminal 6 and negative electrode terminal 7 ) are on the upper side.

[0101] In addition, if Figure 4 As shown, the plurality of lithium-ion secondary batteries 1 constituting the battery pack 10 are arranged while the front and back sides of the main surfaces are alternately replaced. For example, if the cover plate 5 side is the front (front) side of the lithium-ion secondary battery 1 and the battery can 3 side is the back side, the plurality of lithium-ion secondary batteries 1 in the battery pack 10 are arranged front and back, reverse, front and back, ..., reverse. At this time, since the positive terminal 6 and the negative terminal 7 in each lithium-ion secondary battery 1 are arranged at a linearly symmetrical position when viewed from above (refer to Figure 1 , Figure 2 ), so the external terminals located on the upper side of the battery pack 19 are arranged in two rows in the arrangement direction of the lithium-ion secondary batteries 1. And in one row, the positive and negative are arranged alternately as the positive terminal 6, the negative terminal 7, the positive terminal 6, the negative terminal 7, ..., the positive terminal 6, the negative terminal 7. In addition, in the other row, the positive and negative are arranged alternately as the negative terminal 7, the positive terminal 6, the negative terminal 7, the positive terminal 6, ..., the negative terminal 7, the positive terminal 6. Figure 4 In the example shown, the lithium ion secondary batteries 1 have seven external terminals arranged in each row.

[0102] When a plurality of lithium-ion secondary batteries 1 of the present embodiment are arranged to form a battery pack 10, since the housing formed by welding and fixing the metal battery can 3 and the cover plate 5 has a potential, the lithium-ion secondary batteries 1 need to be insulated from each other. As an insulating means, it is preferred to coat the portion of the metal housing surface of each lithium-ion secondary battery 1 that contacts the adjacent lithium-ion secondary battery 1 with an insulating film (not shown). In addition, as another insulating means, each lithium-ion secondary battery 1 may be housed in an insulating bag, or an insulating plate (not shown) may be sandwiched between the lithium-ion secondary batteries 1.

[0103] 2-b. Busbar

[0104] The bus bar 11 is a metal member that connects adjacent lithium-ion secondary batteries 1 , 1 in series.

[0105] As described above, the external terminals located on the upper side of the battery pack 19 are arranged in two rows in the arrangement direction of the lithium-ion secondary batteries 1. In each row, the negative terminals 7 and the positive terminals 6 are arranged alternately. Figure 4 As shown, the bus bar 11 is not hung obliquely between adjacent lithium-ion secondary batteries 1 , but extends parallel to the arrangement direction of the lithium-ion secondary batteries 1 .

[0106] The battery pack 10 having such a configuration connects external terminals via a plurality of bus bars 11 arranged in two rows in the arrangement direction of the lithium ion secondary batteries 1 . Therefore, the bus bars 11 do not become large or interfere with the arrangement of the ducts.

[0107] As a material of the bus bar 11 , for example, copper, aluminum, steel, nickel, and alloys thereof can be used.

[0108] In addition, Figure 4 In the example of the battery pack 19 shown, the external terminals arranged in two rows in the arrangement direction of the lithium-ion secondary batteries 1 are connected by three bus bars 11 in each row.

[0109] In addition, Figure 4 In the embodiment, a plurality of lithium-ion secondary batteries 1 are sandwiched from both sides by two end plates 13, 13. In addition, battery pack terminals 14, 14 provided on the upper surfaces of the two end plates 13, 13 are electrically connected to the outermost positive terminal 6 and negative terminal 7 of the battery pack 10 through the same metal member as the bus bar 11.

[0110] 2-c. Belt

[0111] The band 12 is a member that constrains the plurality of lithium-ion secondary batteries 1 of the battery pack 10 so that the lithium-ion secondary batteries 1 are not separated from each other.

[0112] exist Figure 4 In the example shown, two parallel bands 12 restrain a plurality of lithium ion secondary batteries 1 from the side surfaces of the battery pack 10 (surfaces other than the upper surface on which the positive electrodes 6 and the negative electrodes 7 of the lithium ion secondary batteries 1 are arranged and the lower surface opposite to the upper surface).

[0113] In the battery pack 10 having such a structure, since the cover plate 5 of each lithium ion secondary battery 1 has a protrusion 52 protruding in a planar shape in the area inside the outer edge 51, the outer edges 51 of the cover plates 5 of adjacent lithium ion secondary batteries 1 do not contact each other. Therefore, the stress caused by the restraint load will not be concentrated on the weld.

[0114] As the belt 12, an iron strip is preferred.

[0115] In addition, in addition to the belt 12, a shaft, a slit structure for press-fitting, or the like may be used as the restraining member.

[0116] [Second embodiment]

[0117] Hereinafter, a second embodiment of the present invention will be described based on the drawings.

[0118] Figure 5 This is a partially enlarged cross-sectional view showing an example of a convex structure in a cover plate of a lithium ion secondary battery according to a second embodiment of the present invention.

[0119] In the lithium ion secondary battery 1 of the first embodiment, the cover plate 5 is a metal plate 51 that is shallowly drawn, and the shallowly drawn portion forms a convex portion 52 on the outer surface side of the cover plate 5 (see Figure 3 ), but the lithium ion secondary battery 1 of the present invention is not limited thereto.

[0120] For example, Figure 5 As shown, the lithium ion secondary battery 1 may be a laminate of a cover plate 5 including a flat metal plate 53 and a convex portion forming layer 54 having a smaller area than the metal plate 53 , and the convex portion 52 may be formed with a thickness corresponding to the laminated convex portion forming layer 54 (second embodiment).

[0121] The size of the metal plate 53 is the same as that of the metal plate 51 of the cover plate 5 of the first embodiment, and is such that the outer edge portion 53a thereof can overlap and be welded to the flange portion 34 of the battery can 3. In addition, since shallow drawing is not performed, the thickness of the metal plate 53 may also be different from that of the metal plate 51 of the cover plate 5 of the first embodiment.

[0122] The convex portion forming layer 54 having a smaller area than the metal plate 53 is stacked as described above to form the convex portion 52 of the cover plate 5. The height of the convex portion 52 of the cover plate 5 of the second embodiment (i.e., the same as or similar to the thickness of the convex portion forming layer 54) is the same as that of the convex portion 52 of the cover plate 5 of the first embodiment.

[0123] The metal plate 53 formed of a flat plate can be formed of materials such as iron, stainless steel, aluminum, copper, etc., similarly to the metal plate 51 of the cover plate 5 of the first embodiment. The thickness of the metal plate 53 formed of a flat plate can be set to, for example, 0.1 to 1 mm, similarly to the metal plate 51 of the cover plate 5 of the first embodiment.

[0124] If the thickness of the metal plates 51 and 53 is less than 0.1 mm, the cover plate 5 of the first and second embodiments does not function as the cover plate 5. If the thickness of the metal plates 51 and 53 exceeds 1 mm, it is difficult to fix the outer edges 51a and 53a to the battery can 3 by laser welding.

[0125] The convex portion forming layer 54 may be made of the same material as the metal plate 53, but it is more preferable to use an insulating material. For example, a resin film or coating made of polyethylene, polypropylene, nylon, ABS, PBT, phenolic resin, polyacetal, vinyl chloride, fluororesin, PAI, PEEK, PEI, PI, etc., an epoxy glass plate, or a ceramic plate may be used.

[0126] In addition, the height of the protrusion 52 formed by stacking the protrusion forming layer 54 can be set to, for example, 0.1 mm to 3 mm. If the height of the protrusion 52 is less than 0.1 mm, when the cover plates 5 of adjacent lithium-ion secondary batteries 1 are arranged in an opposing manner to form a battery pack 10, the cover plates 5 contact each other, and it is inevitable that stress is concentrated on the weld of the welding portion between the battery can 3 and the cover plate 5. When the height of the protrusion 52 exceeds 3 mm, the problem of interference between the laser used in welding and the side of the protrusion 52 occurs. Of course, it is also possible to consider further tilting the laser irradiation, but it will exceed the range that can be processed with a galvanometer scanner, and productivity will be reduced.

[0127] The projection-forming layer 54 may be laminated on the metal plate 53 by bonding with a double-sided tape or adhesive material (not shown), coating, or transfer. When a double-sided tape or adhesive material is used, its thickness is included in the height of the projection 52 .

[0128] In addition, if Figure 6 As shown in (a), the convex portion 52 of the cover plate 5 in this embodiment can protrude uniformly in the inner region of the outer edge portion 53a of the cover plate 5, but it is not limited to this. For example, the convex portion 52 protruding in a planar shape may be divided into a plurality of regions when viewed from above, and there may be gaps 55 between the convex portion forming layers 54 between the plurality of regions. As an example, the convex portion 52 is arranged horizontally in the X direction (refer to Figure 6 (b)) and arranged vertically in the Y direction (refer to Figure 6 (c)) and arranged vertically and horizontally in the XY direction (refer to Figure 6 (d) etc. In addition, in addition to the example shown in the figure, the arrangement direction or the number can also be changed and set appropriately.

[0129] With this configuration, the gap 55 can be used as a passage for cooling air of the battery pack 10 .

[0130] Since the other configurations are the same as those of the first embodiment, description thereof will be omitted.

[0131] Although one embodiment of the present invention has been described above, the present invention is not limited to the embodiment and various modifications can be made without departing from the gist of the invention. For example, the number of components of the secondary battery 1 is not limited to the content described as an example in this specification.

[0132] Description of Reference Numerals

[0133] 1: Secondary battery

[0134] 2: Power generation element

[0135] 21: Positive electrode tab

[0136] 22: Negative electrode tab

[0137] 3: Battery tank

[0138] 31: Bottom

[0139] 32: Side wall

[0140] 33: Opening

[0141] 34: Flange

[0142] 35: Through hole

[0143] 5: Cover

[0144] 51, 53: Metal plate

[0145] 51a, 53a: Outer edge

[0146] 52: convex part

[0147] 54: convex formation layer

[0148] 55: Gap

[0149] 6: Positive terminal

[0150] 7: Negative terminal

[0151] 8: Safety valve

[0152] 10: Battery Pack

[0153] 11: Busbar

[0154] 12: belt

[0155] 13: End plate

[0156] 14: Battery pack terminals.

Claims

1. A secondary battery comprising: A flat power generating element including a positive electrode, a negative electrode, and a separator for insulating the positive electrode from the negative electrode in a stacked manner; A battery can having a square shallow-drawn shape and having a flange portion around the opening of the battery can for laying down and accommodating the power generating element, wherein the battery can is made of metal; A non-aqueous electrolyte filled in the battery can housing the power generation element; a cover plate, the outer edge of the cover plate being welded and fixed to the flange of the battery can to cover the battery can, the cover plate having a convex portion protruding in a plane toward the outer surface side more than the outer edge in an area inside the outer edge, the cover plate being made of metal; an external terminal disposed on one of the side walls of the battery can and electrically connected to one of the positive electrode and the negative electrode of the power generating element; as well as Another external terminal is arranged on one side of the cover plate on the same side as the side wall portion where one of the external terminals is arranged and is line-symmetrical with one of the external terminals when viewed from above, and is electrically connected to the other of the positive and negative electrodes of the power generating element.

2. The secondary battery according to claim 1, wherein The height of the protrusion of the cover plate is 0.1 to 3 mm.

3. The secondary battery according to any one of claim 1 or claim 2, wherein: The cover plate is a metal plate that is shallowly drawn, and the shallowly drawn portion of the metal plate forms the convex portion on the outer surface side of the cover plate.

4. The secondary battery according to any one of claim 1 or claim 2, wherein: The cover plate is a laminate of a metal plate formed of a flat plate and a convex-portion forming layer having an area smaller than that of the metal plate, and the convex portion is formed by a thickness obtained by laminating the convex-portion forming layer.

5. The secondary battery according to claim 4, wherein The convex portion protruding in a planar shape is divided into a plurality of regions in a plan view, and there are gaps between the convex portions between the plurality of regions.

6. A battery pack, wherein: The secondary battery of claim 1 is a battery in which a plurality of positive and negative external terminals are arranged with the front and back surfaces of the main surface being alternately replaced in a direction perpendicular to the main surface having the largest area, Furthermore, adjacent secondary batteries are connected in series by bus bars. A restraining load is applied by a restraining member in an arrangement direction of the secondary batteries.

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