WO2022009997A1

WO2022009997A1 - Secondary battery

Info

Publication number: WO2022009997A1
Application number: PCT/JP2021/026538
Authority: WO
Inventors: 昌義谷田; 弘隆前吉
Original assignee: 株式会社村田製作所
Priority date: 2020-07-10
Filing date: 2021-07-08
Publication date: 2022-01-13

Abstract

Provided is a secondary battery that can ensure safety of the secondary battery even when the thickness of a battery can is thin. The secondary battery of the present invention is a secondary battery that uses a square battery can for the exterior case. The square battery can has a pair of facing main surfaces, and a peripheral surface positioned between the pair of main surfaces, and at least one main surface of the pair of main surfaces has a groove positioned on at least one diagonal line of at least one main surface.

Description

Secondary battery

The present invention relates to a secondary battery, and more particularly to a secondary battery using a square battery can in the outer case.

Since the secondary battery is a so-called storage battery, it can be repeatedly charged and discharged, and is used for various purposes. For example, secondary batteries are used in mobile devices such as mobile phones, smartphones and notebook computers.

As a secondary battery, an electrode assembly in which an electrode constituent layer including a positive electrode, a negative electrode and a separator is wound or laminated is impregnated in an electrolytic solution and enclosed in an outer case made of a battery can.

When the temperature of a secondary battery becomes high due to an overcharged state, the electrolytic solution decomposes and gas is generated, which may increase the pressure inside the battery can (hereinafter, also referred to as internal pressure) and cause the battery can to explode. be. On the other hand, by providing a groove for cleavage (hereinafter, also referred to as a cleavage groove) in a part of the battery can, when the internal pressure rises due to the generated gas, the groove is cleaved to discharge the gas. Secondary batteries have been proposed to prevent the battery can from exploding. For example, Patent Document 1 proposes a secondary battery in which a cleavage groove is provided on a side surface of a square battery can.

Japanese Unexamined Patent Publication No. 2013-98027

In the secondary battery of Patent Document 1, a cleavage groove is provided on the side surface of the square battery can so as to intersect diagonally. When the internal pressure rises, a large stress is applied to the diagonal portion of the side surface of the square battery can, so that the opening formed by the cleavage of the cleavage groove can be increased. Hereinafter, unless otherwise specified, a square battery can is referred to as a battery can.

When the thickness of the battery can is large, the strength of the battery can is large, so that the stress when the internal pressure rises tends to be concentrated in the cleavage groove, and the cleavage groove can be opened. However, when the thickness of the battery can becomes thin, for example, according to the findings of the present inventors, when the thickness of the battery can becomes 0.1 mm or less, the deformation of the entire battery can becomes large, so that the cleavage groove is cleaved. There is a problem that a place other than the cleavage groove is cleaved before the opening, or a larger stress is required to cleave the cleavage groove. In such a case, it becomes difficult to ensure the safety of the secondary battery. Further, although it is possible to make the cleavage easier by deepening the groove of the cleavage groove, the thickness of the cleavage groove portion of the battery can becomes thin, and the strength required for normal use cannot be secured, or the battery There is a problem that the processing cost of the can increases.

Therefore, an object of the present invention is to provide a secondary battery capable of ensuring the safety of the secondary battery even if the thickness of the battery can is reduced.

In order to solve the above problems, the secondary battery of the present invention is a secondary battery using a square battery can for the outer case, and the square battery can has a pair of facing main surfaces and the pair of main surfaces. It has a peripheral surface located between the surfaces, and has a groove located on at least one diagonal of the at least one main surface on at least one main surface of the pair of main surfaces. It is characterized by.

According to the present invention, it is possible to provide a secondary battery capable of ensuring the safety of the secondary battery even if the thickness of the battery can is reduced.

It is a schematic perspective view which shows an example of the appearance shape of the secondary battery which concerns on embodiment. It is a simulation result which shows the distribution of the strain generated on the main surface of the battery can of the secondary battery which concerns on Example. It is a simulation result which shows the distribution of the strain generated on the main surface of the battery can of the secondary battery which concerns on a comparative example. This is a simulation result showing the relationship between the internal pressure and the strain generated in the groove in the secondary battery according to the comparative example. It is a simulation result which shows the relationship between the internal pressure and the strain generated in a groove in the case of using the battery can which the thickness is 0.075 mm in the secondary battery of an Example and a comparative example. It is a top view of the secondary battery which concerns on embodiment. In the embodiment, it is a simulation result showing the relationship between the internal pressure and the strain when the L / D is set to 0.1, the length of the groove is fixed, and the position of the start point of the groove is changed. In the embodiment, it is a simulation result showing the relationship between the internal pressure and the strain when the position of the starting point of the groove is fixed and the length of the groove is changed with d / D set to 0.15.

Hereinafter, the secondary battery according to the embodiment of the present invention will be described in more detail. Although the description will be given with reference to the drawings as necessary, the various elements in the drawings are merely schematically and exemplary for the purpose of understanding the present invention, and the appearance or dimensional ratio may differ from the actual ones. ..

The "cross-sectional view" described directly or indirectly herein is based on a hypothetical cross section of a secondary battery cut along the stacking direction of the electrode assembly or electrode constituent layers that make up the secondary battery. ing. Further, the "planar view" used in the present specification is based on a sketch when the object is viewed from above or below along the direction of the thickness.

Further, the "vertical direction" and the "horizontal direction" used directly or indirectly in the present specification correspond to the vertical direction and the horizontal direction in the figure, respectively. Unless otherwise specified, the same sign or symbol shall indicate the same member or part or the same meaning.

Further, the "secondary battery" referred to in the present specification refers to a battery that can be repeatedly charged and discharged. Therefore, the secondary battery according to the present invention is not excessively bound by its name, and may include, for example, a power storage device.

The various numerical ranges referred to herein are intended to include the lower and upper limits themselves, unless specific terms such as "less than" or "more / greater" are used. That is, taking a numerical range such as 1 to 10 as an example, it can be interpreted as including the lower limit value "1" and the upper limit value "10".

FIG. 1 is a schematic perspective view showing an example of the external shape of the secondary battery according to the present embodiment. The secondary battery A uses a square battery can 1 as an outer case, and an electrode assembly in which one or a plurality of electrode constituent layers including a positive electrode, a negative electrode, and a separator are laminated in the square battery can 1 (not). (Illustrated) is housed. The square battery can 1 has a pair of

main surfaces

11 and 12 facing each other and a peripheral surface 13 located between the pair of

main surfaces

11 and 12. The main surface 11 has

corners

111, 112, 113, 114 at the four corners. The main surface 11 has virtual

diagonal lines

115 and 116, and in plan view, the diagonal line 115 extends from one corner 111 through the center 117 of the main surface 11 to the other corner 112. Another diagonal 116 extends from one corner 113 through the center 117 of the main surface 11 to the other corner 114. Further, a groove 118 is formed on the diagonal line 115. Here, the main surface means the surface having the maximum area in the surface of the battery can. The center of the main surface is said to be the point where two diagonal lines intersect. Further, the fact that the groove is located diagonally means that the groove overlaps the diagonal line in the length direction of the groove in a plan view.

When the internal pressure of the battery can rises, the battery can is deformed so that the diagonal becomes a ridge and swells. By providing the grooves on the diagonal line, the deformation becomes larger and the battery can is easily cleaved. Therefore, even when the thickness of the battery can is reduced, it can be easily cleaved at the groove portion.

The above-mentioned effect of the present invention will be described based on the simulation results using the finite element method analysis software. FIG. 2 is a simulation result showing the distribution of strain generated on the main surface of the battery can of the secondary battery according to the embodiment of the present invention, and FIG. 3 is the main surface of the battery can of the secondary battery according to the comparative example. It is a simulation result showing the distribution of the strain generated in. As a comparative example, a battery can described in Patent Document 1 in which a cleavage groove is provided so as to intersect diagonally is used. The thickness of the battery cans used in Examples and Comparative Examples was 0.0075 mm, and the internal pressure was 1 MPa. The lighter the color, the greater the strain, and the darker the color, the smaller the strain. In the embodiment, the stress is concentrated in the groove portion and the strain is large, whereas in the comparative example, the strain is generated in the portion other than the groove, specifically, the diagonal portion, and the stress is dispersed. You can see that. As described above, in the present invention, by providing the grooves diagonally, it is possible to easily cleave the grooves by concentrating the stress on the grooves.

Next, FIG. 4 is a simulation result showing the relationship between the internal pressure and the strain generated in the groove in the secondary battery according to the comparative example, and shows the case where the thickness of the battery can is 0.2 mm and 0.075 mm. ing. When the thickness of the battery can is 0.2 mm, the strain tends to increase as the internal pressure increases. On the other hand, when the thickness of the battery can is 0.075 mm, the strain increases at first and the groove is deformed as the internal pressure increases, but when the internal pressure exceeds a certain level, the strain tends not to increase. It is considered that this is because the stress concentration on the groove portion is relaxed by the start of deformation of the portion other than the groove portion, and the strain of the groove portion is less likely to increase. Therefore, in the comparative example, when the thickness of the battery can is reduced, for example, when the thickness is 0.1 mm or less, a place other than the groove may be cleaved or the groove may be cleaved before the groove is cleaved. There is a problem that a large stress is required.

Next, FIG. 5 is a simulation result showing the relationship between the internal pressure and the strain generated in the groove when a battery can having a thickness of 0.075 mm is used in the secondary batteries of the example and the comparative example. .. In the case of the example, it can be seen that as the internal pressure increases, a larger strain is generated in the groove as compared with the comparative example. From this, it can be seen that in the examples, the grooves are more easily cleaved than in the comparative examples.

Further, FIG. 1 shows an example in which the groove is located on one diagonal line of one main surface, but the present invention is not limited thereto. For example, grooves may be located on each of the two diagonal lines on one main surface. Further, the number of grooves may be one or a plurality, and the plurality of grooves may be located on the same diagonal line, but the predetermined strength required for the battery can can be secured and the processing cost of the battery can can be reduced. From the viewpoint of suppressing the increase, it is preferable that one groove is located diagonally between the center of the main surface and one corner.

Next, the position and length of the groove will be explained more specifically. FIG. 6 is a top view of the battery can for explaining the position and length of the groove. The groove 118 has a start point 118a on one corner 111 side and an end point 118b on the center 117 side. When the distance between one corner 111 and the start point 118a is d and the distance between one corner 111 and the center 117 is D, the d / D is preferably 0 or more and 0.2 or less. .. More preferably, the d / D is 0.05 or more and 0.2 or less. Further, the groove has a length L defined by the distance between the start point 118a and the end point 118b, and the L / D is preferably 0.05 or more and 1 or less. More preferably, the L / D is 0.1 or more and 1 or less.

The position and length of the above groove will be explained based on the simulation results using the finite element method analysis software. FIG. 7 is a simulation result showing the relationship between the internal pressure and the strain when the L / D is set to 0.1, the length of the groove is fixed, and the position of the start point of the groove is changed in the embodiment. In FIG. 7, (1) is when d / D is in the range of 0.1 or more and 0.2 or less, and (2) is when d / D is in the range of 0.15 or more and 0.25 or less (3). ) Shows the result when d / D is in the range of 0.2 or more and 0.3 or less. Further, FIG. 8 is an example of a simulation result showing the relationship between the internal pressure and the strain when the position of the starting point of the groove is fixed and the length of the groove is changed by setting the d / D to 0.15 in the embodiment. .. In FIG. 8, (4) is when the L / D is 0.2, (5) is when the L / D is 0.1, and (6) is when the L / D is 0.05. The results are shown. From FIG. 7, it can be seen that the closer the position of the starting point of the groove is to the corner, the greater the strain. Further, from FIG. 8, it can be seen that the longer the groove length, the greater the strain.

Further, the groove depth t is t from the viewpoint of securing the residual wall thickness for ensuring the strength required for the battery can and from the viewpoint of reducing the processing cost when the thickness of the battery can is T. / T is 0.2 or more and 0.4 or less, preferably 0.3 or more and 0.4 or less.

The cross-sectional shape of the groove in the width direction is not particularly limited, but may be, for example, a V-shape in which the groove width narrows along the depth direction or a U-shape in which the groove width does not change in the depth direction. can.

Further, the groove can be formed by processing the battery can by drawing or the like and then processing by an etching method or a press process or the like.

The battery can used in the present invention is a square battery can. Here, the square battery can is not particularly limited as long as its cross-sectional shape is rectangular, and its appearance includes not only a rectangular parallelepiped shape or a cubic shape but also a flat shape. Further, the battery can may be any as long as it has a can portion having an opening and a sealing portion for sealing the opening. Further, as the battery can, a known battery can made of aluminum alloy or the like can be used. Further, the thickness of the battery can is not particularly limited, but when a battery can having a thickness of 0.1 mm or less is used, a particularly excellent effect can be obtained in that the groove is easily cleaved.

Hereinafter, other members constituting the secondary battery of the present invention will be described.

The secondary battery according to the present invention includes an electrode assembly in which one or more electrode constituent layers including a positive electrode, a negative electrode, and a separator are laminated. In a secondary battery, such an electrode assembly is enclosed in a battery can together with an electrolyte (for example, a non-aqueous electrolyte). The structure of the electrode assembly is not necessarily limited to the planar laminated structure, and for example, an electrode unit (electrode constituent layer) including a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode is wound in a roll shape. It may have a winding structure. Further, for example, the electrode assembly may have a so-called stack-and-folding structure in which a positive electrode, a separator and a negative electrode are laminated on a long film and then folded.

The positive electrode is composed of at least a positive electrode material layer and a positive electrode current collector. In the positive electrode, a positive electrode material layer is provided on at least one surface of the positive electrode current collector, and the positive electrode material layer contains a positive electrode active material as an electrode active material. For example, each of the plurality of positive electrodes in the electrode assembly may be provided with positive electrode material layers on both sides of the positive electrode current collector, or the positive electrode material layer may be provided on only one side of the positive electrode current collector. It may be the one that exists.

The negative electrode is composed of at least a negative electrode material layer and a negative electrode current collector. In the negative electrode, a negative electrode material layer is provided on at least one surface of the negative electrode current collector, and the negative electrode material layer contains a negative electrode active material as an electrode active material. For example, each of the plurality of negative electrodes in the electrode assembly may be provided with a negative electrode material layer on both sides of the negative electrode current collector, or a negative electrode material layer may be provided on only one side of the negative electrode current collector. It may be the one that exists.

The electrode active materials contained in the positive and negative electrodes, that is, the positive electrode active material and the negative electrode active material, are substances that are directly involved in the transfer of electrons in the secondary battery, and are the main substances of the positive and negative electrodes that are responsible for charge / discharge, that is, the battery reaction. be. More specifically, ions are brought to the electrolyte due to the "positive electrode active material contained in the positive electrode material layer" and the "negative electrode active material contained in the negative electrode material layer", and such ions are transferred between the positive electrode and the negative electrode. The electrons are transferred and charged and discharged. The positive electrode material layer and the negative electrode material layer are particularly preferably layers that can occlude and release lithium ions. That is, it is preferable that the secondary battery according to the present invention is a non-aqueous electrolyte secondary battery in which lithium ions move between the positive electrode and the negative electrode via the non-aqueous electrolyte to charge and discharge the battery. .. When lithium ions are involved in charging and discharging, the secondary battery according to the present invention corresponds to a so-called "lithium ion battery", and the positive electrode and the negative electrode have a layer capable of occluding and discharging lithium ions.

When the positive electrode active material of the positive electrode material layer is composed of, for example, granules, a binder may be contained in the positive electrode material layer for more sufficient contact between particles and shape retention. Further, a conductive auxiliary agent may be contained in the positive electrode material layer in order to facilitate the transfer of electrons that promote the battery reaction. Similarly, where the negative electrode active material of the negative electrode material layer is composed of, for example, granules, it may contain a binder for better contact between the particles and shape retention, and transfer of electrons to promote the battery reaction. A conductive auxiliary agent may be contained in the negative electrode material layer in order to facilitate the above. As described above, the positive electrode material layer and the negative electrode material layer can also be referred to as a “positive electrode mixture layer” and a “negative electrode mixture layer”, respectively, because of the form in which a plurality of components are contained.

The positive electrode active material may be a substance that contributes to the occlusion and release of lithium ions. From this point of view, the positive electrode active material may be, for example, a lithium-containing composite oxide. More specifically, the positive electrode active material may be a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese and iron. That is, in the positive electrode material layer of the secondary battery according to the present invention, such a lithium transition metal composite oxide is preferably contained as the positive electrode active material. For example, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium iron phosphate, or a part of the transition metal thereof replaced with another metal. Such a positive electrode active material may be contained as a single species, but may be contained in combination of two or more species.

The binder that can be contained in the positive electrode material layer is not particularly limited, but is not particularly limited, but is limited to polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer and polytetrafluoroethylene. At least one species selected from the group consisting of the above can be mentioned. The conductive auxiliary agent that can be contained in the positive electrode material layer is not particularly limited, but is limited to carbon black such as thermal black, furnace black, channel black, ketjen black and acetylene black, graphite, carbon nanotubes and vapor phase growth. At least one selected from carbon fibers such as carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives can be mentioned.

The thickness dimension of the positive electrode material layer is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness dimension of the positive electrode material layer is the thickness inside the secondary battery, and the average value of the measured values at any 10 points may be adopted.

The negative electrode active material may be a substance that contributes to the occlusion and release of lithium ions. From this point of view, the negative electrode active material is preferably, for example, various carbon materials, oxides, and / or lithium alloys.

Examples of various carbon materials for the negative electrode active material include graphite (natural graphite, artificial graphite), hard carbon, soft carbon, and diamond-like carbon. In particular, graphite has high electron conductivity and excellent adhesion to a negative electrode current collector. As the oxide of the negative electrode active material, at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide and the like can be mentioned. The lithium alloy of the negative electrode active material may be any metal that can be alloyed with lithium, for example, Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, It may be a binary, ternary or higher alloy of a metal such as La and lithium. Such an oxide may be amorphous as its structural form. This is because deterioration due to non-uniformity such as grain boundaries or defects is less likely to occur.

The binder that can be contained in the negative electrode material layer is not particularly limited, but is at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide-based resin, and polyamide-imide-based resin. Can be mentioned. For example, the binder contained in the negative electrode material layer may be styrene-butadiene rubber. The conductive auxiliary agent that can be contained in the negative electrode material layer is not particularly limited, but is limited to carbon black such as thermal black, furnace black, channel black, ketjen black and acetylene black, graphite, carbon nanotubes and vapor phase growth. At least one selected from carbon fibers such as carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives can be mentioned. The negative electrode material layer may contain a component derived from the thickener component (for example, carboxylmethyl cellulose) used at the time of manufacturing the battery.

The thickness dimension of the negative electrode material layer is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness dimension of the negative electrode material layer is the thickness inside the secondary battery, and the average value of the measured values at any 10 points may be adopted.

The positive electrode current collector and the negative electrode current collector used for the positive electrode and the negative electrode are members that contribute to collecting and supplying electrons generated by the electrode active material due to the battery reaction. Such an electrode current collector may be a sheet-shaped metal member. Further, such an electrode current collector may have a porous or perforated form. For example, the current collector may be a metal leaf, a punching metal, a net, an expanded metal, or the like. The positive electrode current collector used for the positive electrode is preferably made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel and the like, and may be, for example, an aluminum foil. On the other hand, the negative electrode current collector used for the negative electrode is preferably made of a metal foil containing at least one selected from the group consisting of copper, stainless steel, nickel and the like, and may be, for example, a copper foil. In addition, "stainless steel" in this specification refers to stainless steel specified in, for example, "JIS G 0203 steel term", and may be chromium or an alloy steel containing chromium and nickel.

The thickness dimensions of the positive electrode current collector and the negative electrode current collector are not particularly limited, but may be 1 μm or more and 100 μm or less, for example, 10 μm or more and 70 μm or less. The thickness dimension of the positive electrode current collector and the negative electrode current collector is the thickness inside the secondary battery, and the average value of the measured values at any 10 points may be adopted.

The separator used for the positive electrode and the negative electrode is a member provided from the viewpoint of preventing a short circuit due to contact between the positive and negative electrodes and retaining the electrolyte. In other words, it can be said that the separator is a member through which ions pass while preventing electronic contact between the positive electrode and the negative electrode. For example, the separator is a porous or microporous insulating member, which has a film morphology due to its small thickness. Although only an example, a microporous film made of polyolefin may be used as a separator. In this respect, the microporous membrane used as the separator may contain, for example, only polyethylene (PE) or polypropylene (PP) as the polyolefin. Furthermore, the separator may be a laminate composed of a "microporous membrane made of PE" and a "microporous membrane made of PP". The surface of the separator may be covered with an inorganic particle coat layer and / or an adhesive layer or the like. The surface of the separator may have adhesiveness. In the present invention, the separator should not be particularly bound by its name, and may be a solid electrolyte, a gel-like electrolyte, and / or an insulating inorganic particle having the same function.

The thickness dimension of the separator is not particularly limited, but may be 1 μm or more and 100 μm or less, for example, 2 μm or more and 20 μm or less. The thickness dimension of the separator is the thickness inside the secondary battery (particularly the thickness between the positive electrode and the negative electrode), and the average value of the measured values at any 10 points may be adopted.

In the secondary battery of the present invention, an electrode assembly composed of an electrode constituent layer including a positive electrode, a negative electrode and a separator is enclosed in a battery can together with an electrolyte. The electrolyte can assist in the movement of metal ions emitted from the electrodes (positive electrode and / or negative electrode). The electrolyte may be a "non-aqueous" electrolyte such as an organic electrolyte and an organic solvent, or it may be a "water-based" electrolyte containing water. When the positive electrode and the negative electrode have a layer capable of occluding and releasing lithium ions, the electrolyte is preferably an "non-aqueous" electrolyte containing an organic electrolyte and / or an organic solvent and the like. That is, it is preferable that the electrolyte is a non-aqueous electrolyte. In the electrolyte, there will be metal ions emitted from the electrodes (positive electrode and / or negative electrode), and therefore the electrolyte will assist in the movement of the metal ions in the battery reaction. The electrolyte may be in the form of a liquid or a gel.

A non-aqueous electrolyte is an electrolyte containing a solvent and a solute. The specific solvent for the non-aqueous electrolyte may be one containing at least carbonate. Such carbonates may be cyclic carbonates and / or chain carbonates. Although not particularly limited, the cyclic carbonates include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC) and vinylene carbonate (VC). be able to. Examples of the chain carbonates include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC) and dipropyl carbonate (DPC). Although only an example, a combination of cyclic carbonates and chain carbonates may be used as the non-aqueous electrolyte, and for example, a mixture of ethylene carbonate and diethyl carbonate may be used. Further, as a specific non-aqueous electrolyte solute, for example, a Li salt such as _{LiPF 6} and / or LiBF _{4 may be used.}

Although the embodiments of the present invention have been described above, they are merely exemplary examples. Therefore, those skilled in the art will easily understand that the present invention is not limited to this, and various aspects are conceivable.

The secondary battery according to the present invention can be used in various fields where storage is expected. The secondary battery according to the present invention is merely an example, but the secondary battery according to the present invention is used in the fields of electricity, information, and communication (for example, mobile phones, smartphones, laptop computers and digital cameras, activity meters, arm computers, etc.) in which mobile devices and the like are used. Electronic paper, wireless earphones, wearable devices, etc. or electrical / electronic equipment fields including small electronic devices such as RFID tags, card-type electronic money, smart watches, etc. or mobile equipment fields), household / small industrial applications (for example, electric tools) , Golf cart, home / nursing / industrial robot field), large industrial use (eg forklift, elevator, bay port crane field), transportation system field (eg hybrid car, electric car, bus, train, Electric assisted bicycles, electric motorcycles and other electric vehicles), power system applications (for example, various power generation, road conditioners, smart grids, general household-installed power storage systems, etc.), medical applications (earphone hearing aids and other medical equipment fields) ), Pharmaceutical applications (fields such as dose management systems), IoT fields, space / deep sea applications (for example, fields such as space explorers and submersible research vessels).

1 Square battery can 11, 12 Main surface 13

Peripheral surface

111, 112, 113, 114

Square

115, 116 Diagonal line 117 Center 118 Groove 118a Start point 118b End point

Claims

It is a secondary battery that uses a square battery can for the outer case.
The square battery can has a pair of facing main surfaces and a peripheral surface located between the pair of main surfaces.
A secondary battery having a groove located on at least one diagonal of the pair of main surfaces on at least one of the main surfaces.
The at least one diagonal extends from one corner of the at least one main surface through the center of the at least one main surface to the other corner in plan view, and the groove extends. The secondary battery according to claim 1, which is located on the diagonal line between the center and the one corner.
The groove has a start point on one corner side and an end point on the center side, the distance between the one corner and the start point is d, and the distance between the one corner and the center is defined as d. The secondary battery according to claim 2, wherein when D is used, d / D is 0 or more and 0.3 or less.
The secondary battery according to claim 3, wherein the groove has a length L defined by a distance between the start point and the end point, and the L / D is 0.05 or more and 1 or less. ..
The secondary battery according to any one of claims 1 to 4, wherein the thickness of the square battery can is 0.1 mm or less.
The one according to any one of claims 1 to 5, wherein the depth t of the groove has a t / T of 0.2 or more and 0.4 ≦, where T is the thickness of the square battery can. Secondary battery.
The secondary battery according to any one of claims 1 to 6, wherein the positive electrode and the negative electrode of the secondary battery include a layer capable of storing and releasing lithium ions.