WO2022138243A1

WO2022138243A1 - Battery

Info

Publication number: WO2022138243A1
Application number: PCT/JP2021/045590
Authority: WO
Inventors: 雄大平野
Original assignee: 株式会社村田製作所
Priority date: 2020-12-24
Filing date: 2021-12-10
Publication date: 2022-06-30

Abstract

Provided is a battery which enables improvement of safety against impact.　This battery comprises a wound-type battery element, and a film-shaped exterior material for accommodating the battery element. The battery element comprises a long positive electrode, a long negative electrode, and a long separator. The positive electrode, the negative electrode, and the separator are wound in the longitudinal direction, and both long sides of the positive electrode are provided on the inner side of both long sides of the negative electrode. The negative electrode comprises: a negative electrode current collector; a first negative electrode active material layer provided on the inner surface of the negative electrode current collector; and a second negative electrode active material layer provided on the outer surface of the negative electrode current collector. An end portion on the side of one of the long sides of the negative electrode is bent toward the inner surface side of the negative electrode. The thickness ratio (A1/B1) between the end surface thickness A1 of the second negative electrode active material layer on the side of the one of the long sides of the negative electrode and the end surface thickness B1 of the first negative electrode active material layer on the one side of the the one of the long sides of the negative electrode is 1.1-2.0. The exterior material has an accommodation part for accommodating the battery element, and has a difference between the width of the negative electrode and the width of the accommodation part in the negative-electrode width direction of 1.3 mm or less.

Description

battery

The present invention relates to a battery.

Conventionally, a film exterior battery in which a battery element is housed in a film-shaped exterior material has been widely used. In the film exterior battery, various studies have been made on the configuration of the battery element in order to improve the battery characteristics.

For example, in Patent Document 1, in a lithium ion secondary battery in which a laminated battery element is housed in an aluminum laminated film, the positive electrode sheet and the negative electrode sheet have at least one bent portion in a cross section in the stacking direction of the battery element. Therefore, it is disclosed that the leakage of the electrolytic solution from the aluminum laminated film can be suppressed even when affected by the vibration.

Japanese Unexamined Patent Publication No. 2009-129722

In recent years, film exterior batteries have been used in various electronic devices such as mobile phones, and therefore it is desired to improve the safety against impacts such as dropping. In the above Patent Document 1, this is the case. No safety technology is disclosed.

An object of the present invention is to provide a battery capable of improving safety against impact.

In order to solve the above-mentioned problems, the present invention
With a winding type battery element
It is equipped with a film-like exterior material that houses the battery element.
The battery element includes a long positive electrode, a long negative electrode, and a long separator. The positive electrode, the negative electrode, and the separator are wound in the longitudinal direction, and both long sides of the positive electrode are formed. Provided inside both long sides of the negative electrode,
The negative electrode includes a negative electrode current collector, a first negative electrode active material layer provided on the inner surface of the negative electrode current collector, and a second negative electrode active material layer provided on the outer surface of the negative electrode current collector. ,
One end on the long side of the negative electrode is bent toward the inner side surface of the negative electrode,
Thickness ratio (A ₁ /) of the end face thickness A ₁ of the second negative electrode active material layer on one long side of the negative electrode and the end face thickness B ₁ of the first negative electrode active material layer on one long side of the negative electrode. B ₁ ) is 1.1 or more and 2.0 or less,
The exterior material is a battery having an accommodating portion for accommodating a battery element, and the difference between the width of the negative electrode and the width of the accommodating portion in the width direction of the negative electrode is 1.3 mm or less.

According to the present invention, the safety of the battery against impact can be improved.

It is an exploded perspective view which shows an example of the structure of the film exterior battery which concerns on 1st Embodiment of this invention. It is sectional drawing along the line II-II of FIG. It is a figure which shows an example of the cross section in the width direction of a positive electrode, a negative electrode, and a separator. It is a block diagram which shows an example of the structure of the electronic device which concerns on 2nd Embodiment of this invention.

Embodiments of the present invention will be described in the following order.
1 First embodiment (example of film exterior battery)
2 Second embodiment (example of electronic device)

<1 First Embodiment>
[Battery configuration]
FIG. 1 is an exploded perspective view showing an example of the configuration of a film exterior battery (hereinafter, simply referred to as “battery”) according to the first embodiment of the present invention. The battery includes a winding type battery element 20 having a flat shape, and a film-shaped exterior material 10 accommodating the battery element 20. Here, it is assumed that the flat battery element 20 also includes a square battery element 20. A positive electrode lead 11 and a negative electrode lead 12 are attached to the battery element 20. When the battery is viewed in a plan view from a direction perpendicular to its main surface, the battery has a rectangular shape.

(Positive and negative electrode leads)
The positive electrode lead 11 and the negative electrode lead 12 are led out in the same direction from one short side of the battery. Hereinafter, the short side of the battery element 20 from which the positive electrode lead 11 and the negative electrode lead 12 are derived is referred to as a top side, and the short side opposite to the short side is referred to as a bottom side. The positive electrode lead 11 and the negative electrode lead 12 have, for example, a thin plate shape or a mesh shape. The positive electrode lead 11 and the negative electrode lead 12 are made of a metal material such as aluminum (Al), copper (Cu), nickel (Ni), or stainless steel (SUS).

An adhesion film 13 for suppressing the intrusion of outside air is inserted between the exterior material 10 and the positive electrode lead 11 and between the exterior material 10 and the negative electrode lead 12, respectively. The adhesion film 13 is made of a material having adhesion to the positive electrode lead 11 and the negative electrode lead 12, for example, a polyolefin resin such as polyethylene (PE), polypropylene (PP), modified polyethylene or modified polypropylene.

(Exterior material)
The exterior material 10 has a rectangular shape, and is folded back so that its sides overlap each other from the central portion in the longitudinal direction thereof. A notch or the like may be provided in advance in the central portion to be the folded portion. The battery element 20 is sandwiched between the folded exterior materials 10. Seal portions are formed on the top side and the two long side sides (both sides) of the circumference of the folded exterior material 10. The exterior material 10 has an accommodating portion 10A for accommodating the battery element 20 on one of the surfaces to be overlapped. The accommodating portion 10A is a recess provided on one of the surfaces to be overlapped, and is formed by, for example, deep drawing.

The exterior material 10 is made of, for example, a flexible rectangular laminated film. The exterior material 10 has a metal layer, a first resin layer provided on one surface (first surface) of the metal layer, and a second surface provided on the other surface (second surface) of the metal layer. It is provided with a resin layer of. If necessary, the exterior material 10 may further include an adhesive layer between the metal layer and the first resin layer, and at least one of the metal layer and the second resin layer. Of both sides of the exterior material 10, the surface on the first resin layer side is the outer surface, and the surface on the second resin layer side is the inner surface for accommodating the battery element 20.

The metal layer is a barrier layer that suppresses the ingress of moisture and plays a role of protecting the battery element 20 that is a stored object. The metal layer may be a metal leaf and may include, for example, aluminum or an aluminum alloy.

The first resin layer is a surface protective layer having a function of protecting the surface of the exterior material 10. The first resin layer contains, for example, at least one of nylon (Ny), polyethylene terephthalate (PET) and polyethylene naphthalate (PEN).

The second resin layer is a heat-sealing resin layer for sealing the peripheral edges of the inner side surfaces of the folded exterior material 10 by heat-sealing. The second resin layer contains, for example, at least one of polypropylene and polyethylene.

The exterior material 10 may be made of a laminated film having another structure, for example, a polymer film such as polypropylene or a metal film, instead of the above-mentioned laminated film. Alternatively, it may be composed of a laminated film in which an aluminum film is used as a core material and a polymer film is laminated on one side or both sides thereof.

Further, the exterior material 10 may further include a colored layer from the viewpoint of the beauty of appearance, and at least one of the first resin layer and the second resin layer contains a coloring material. You may. When the exterior material 10 further includes an adhesive layer between the metal layer and the first resin layer, and at least one of the metal layer and the second resin layer, the adhesive layer provides a coloring material. It may be included.

(Battery element)
FIG. 2 is a cross-sectional view taken along the line II-II of the battery element 20 shown in FIG. The battery element 20 includes a long positive electrode 21, a long negative electrode 22, and a long separator 23, and the separator 23 is sandwiched between the positive electrode 21 and the negative electrode 22. The positive electrode 21, the negative electrode 22, and the separator 23 are wound in the longitudinal direction so as to be flat and spiral. A space is provided on the innermost circumference of the battery element 20. A folded portion of the exterior material 10 is provided on one long side of the negative electrode 22 (that is, the bottom side of the negative electrode 22), and the exterior material 10 is provided on the other long side of the negative electrode 22 (that is, the top side of the negative electrode 22). A seal portion is provided.

FIG. 3 is a diagram showing an example of a cross section of the positive electrode 21, the negative electrode 22, and the separator 23 in the width direction. In the width direction 22D of the positive electrode 21 and the negative electrode 22, both long sides of the positive electrode 21 are provided inside both long sides of the negative electrode 22. As a result, it is possible to suppress the precipitation of lithium on the end portion on the long side of the negative electrode 22, so that the safety of the battery can be improved.

In the width direction 22D of the negative electrode 22 and the separator 23, both long sides of the negative electrode 22 are provided inside both long sides of the separator 23. As a result, since the separator 23 is interposed between the negative electrode 22 and the end on the long side of the positive electrode 21, it is possible to prevent the negative electrode 22 from coming into contact with the end on the long side of the positive electrode 21. Therefore, the risk of a short circuit between the positive electrode 21 and the negative electrode 22 can be reduced, and the safety of the battery can be improved.

The outermost peripheral portion of the battery element 20 is protected by a protective tape 24. An electrolytic solution as an electrolyte is injected into the exterior material 10 and impregnated into the positive electrode 21, the negative electrode 22, and the separator 23.

Hereinafter, the positive electrode 21, the negative electrode 22, the separator 23, and the electrolytic solution constituting the battery will be sequentially described.

(Positive electrode)
The positive electrode 21 is, for example, a positive electrode current collector 21A, a first positive electrode active material layer 21B ₁ provided on the inner surface of the positive electrode current collector 21A, and a second positive electrode current collector 21A provided on the outer surface of the positive electrode current collector 21A. The positive electrode active material layer 21B ₂ of the above is provided. In the present specification, the "inner surface" means a surface located on the winding center side of the battery element 20, and the "outer surface" means a surface located on the opposite side of the winding center of the battery element 20. Means. Hereinafter, when the first positive electrode active material layer 21B ₁ and the second positive electrode active material layer 21B ₂ are collectively referred to, they are referred to as a positive electrode active material layer 21B. The positive electrode active material layer 21B is provided up to both ends in the width direction of the positive electrode current collector 21A.

The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode current collector 21A may have a plate shape or a mesh shape. The positive electrode lead 11 may be configured by extending a part of the peripheral edge of the positive electrode current collector 21A. The positive electrode active material layer 21B contains one or more positive electrode active materials capable of occluding and releasing lithium. The positive electrode active material layer 21B may further contain at least one selected from the group consisting of a binder and a conductive auxiliary agent, if necessary.

(Positive electrode active material)
As the positive electrode active material capable of storing and releasing lithium, for example, a lithium-containing compound such as a lithium oxide, a lithium phosphorus oxide, a lithium sulfide or an interlayer compound containing lithium is suitable, and these two types are suitable. The above may be mixed and used. In order to increase the energy density, a lithium-containing compound containing lithium, a transition metal element and oxygen is preferable. Examples of such a lithium-containing compound include a lithium composite oxide having a layered rock salt type structure represented by the formula (A), a lithium composite phosphate having an olivine type structure represented by the formula (B), and the like. Can be mentioned. As the lithium-containing compound, it is more preferable that the transition metal element contains at least one selected from the group consisting of Co, Ni, Mn and Fe. Examples of such a lithium-containing compound include a lithium composite oxide having a layered rock salt type structure represented by the formula (C), the formula (D) or the formula (E), and a spinel type represented by the formula (F). Examples thereof include a lithium composite oxide having a structure, a lithium composite phosphate having an olivine-type structure represented by the formula (G), and specifically, LiNi _0.50 Co _0.20 Mn _0.30 O. ₂ , LiCoO ₂ , LiNiO ₂ , LiNi _a Co _1-a O ₂ (0 <a <1), LiMn ₂ O ₄ or LiFePO ₄ and the like.

Li _p Ni _(1-q-r) Mn _q M1 _r O _(2-y) X _z ... (A)
(However, in the formula (A), M1 represents at least one of the elements selected from Group 2 to Group 15 excluding Ni and Mn. X is from the group consisting of Group 16 elements and Group 17 elements other than oxygen. Indicates at least one selected. P, q, y, z are 0 ≦ p ≦ 1.5, 0 ≦ q ≦ 1.0, 0 ≦ r ≦ 1.0, −0.10 ≦ y ≦ 0. .20, a value within the range of 0 ≦ z ≦ 0.2.)

Li _a M2 _b PO ₄ ... (B)
(However, in the formula (B), M2 represents at least one of the elements selected from groups 2 to 15. a and b are 0 ≦ a ≦ 2.0 and 0.5 ≦ b ≦ 2.0. It is a value within the range of.)

Li _f Mn _(1-g-h) Ni _g M3 _h O _(2-j) F _k ... (C)
(However, in the formula (C), M3 was selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W. Represents at least one species. F, g, h, j and k are 0.8 ≦ f ≦ 1.2, 0 <g <0.5, 0 ≦ h ≦ 0.5, g + h <1, −0. The value is in the range of 1 ≦ j ≦ 0.2 and 0 ≦ k ≦ 0.1. The composition of lithium differs depending on the state of charge and discharge, and the value of f represents the value in the state of complete discharge. )

Li _m Ni _(1-n) M4 _n O _(2-p) F _q ... (D)
(However, in the formula (D), M4 was selected from the group consisting of Co, Mn, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ca, Sr and W. Represents at least one species. M, n, p and q are 0.8 ≦ m ≦ 1.2, 0.005 ≦ n ≦ 0.5, −0.1 ≦ p ≦ 0.2, 0 ≦ q ≦ The value is in the range of 0.1. The composition of lithium differs depending on the state of charge and discharge, and the value of m represents the value in the state of complete discharge.)

Li _r Co _(1-s) M5 _s O _(2-t) _Fu ... (E)
(However, in the formula (E), M5 was selected from the group consisting of Ni, Mn, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ca, Sr and W. Represents at least one species. r, s, t and u are 0.8 ≦ r ≦ 1.2, 0 ≦ s <0.5, −0.1 ≦ t ≦ 0.2, 0 ≦ u ≦ 0. It is a value within the range of 1. The composition of lithium differs depending on the state of charge and discharge, and the value of r represents the value in the state of complete discharge.)

Li _v Mn _2-w M6 _w O _x F _y ... (F)
(However, in the formula (F), M6 was selected from the group consisting of Co, Ni, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ca, Sr and W. Represents at least one type. V, w, x and y are 0.9 ≦ v ≦ 1.1, 0 ≦ w ≦ 0.6, 3.7 ≦ x ≦ 4.1, 0 ≦ y ≦ 0.1. The composition of lithium differs depending on the state of charge and discharge, and the value of v represents the value in the state of complete discharge.)

Li _z M7PO ₄ ... (G)
(However, in the formula (G), M7 is selected from the group consisting of Co, Mg, Fe, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr. Z represents a value within the range of 0.9 ≦ z ≦ 1.1. The composition of lithium differs depending on the state of charge and discharge, and the value of z is a value in the state of complete discharge. Represents.)

In addition to these, lithium-free inorganic compounds such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS can be used as the positive electrode active material capable of occluding and releasing lithium. can.

The positive electrode active material capable of occluding and releasing lithium may be other than the above. Further, two or more kinds of the positive electrode active materials exemplified above may be mixed in any combination.

(Binder)
As the binder, for example, at least one selected from the group consisting of resin materials such as polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, styrene butadiene rubber and carboxymethyl cellulose, and copolymers mainly composed of these resin materials. Seeds are used.

(Conductive aid)
As the conductive auxiliary agent, for example, at least one carbon material selected from the group consisting of graphite, carbon fiber, carbon black, acetylene black, ketjen black, carbon nanotubes, graphene and the like can be used. The conductive auxiliary agent may be any material having conductivity, and is not limited to the carbon material. For example, a metal material, a conductive polymer material, or the like may be used as the conductive auxiliary agent. The shape of the conductive auxiliary agent includes, for example, granules, scales, hollows, needles, cylinders, and the like, but is not particularly limited to these shapes.

(Negative electrode)
The negative electrode 22 is, for example, a negative electrode current collector 22A, a first negative electrode active material layer 22B ₁ provided on the inner surface of the negative electrode current collector 22A, and a second negative electrode current collector 22A provided on the inner surface of the negative electrode current collector 22A. The negative electrode active material layer 22B ₂ of the above is provided. Hereinafter, when the first negative electrode active material layer 22B ₁ and the second negative electrode active material layer 22B ₂ are collectively referred to, they are referred to as a negative electrode active material layer 22B. The negative electrode active material layer 22B is provided up to both ends of the negative electrode current collector 22A in the width direction 22D.

The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The negative electrode current collector 22A may have a plate shape or a mesh shape. The negative electrode lead 12 may be configured by extending a part of the peripheral edge of the negative electrode current collector 22A. The negative electrode active material layer 22B contains one or more negative electrode active materials capable of occluding and releasing lithium, and a binder. The negative electrode active material layer 22B may further contain at least one selected from the group consisting of a thickener and a conductive auxiliary agent, if necessary.

In this battery, the electrochemical equivalent of the negative electrode 22 or the negative electrode active material is larger than the electrochemical equivalent of the positive electrode 21, and theoretically, lithium metal does not precipitate on the negative electrode 22 during charging. It is preferable to have.

(Negative electrode active material)
Examples of the negative electrode active material include non-graphitizable carbon, easily graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, calcined organic polymer compounds, carbon fibers, and carbon materials such as activated carbon. Can be mentioned. Among these, cokes include pitch coke, needle coke, petroleum coke and the like. An organic polymer compound calcined body is a carbonized product obtained by calcining a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and a part of it is graphitizable carbon or graphitizable carbon. Some are classified as. These carbon materials are preferable because the change in the crystal structure that occurs during charging / discharging is very small, a high charging / discharging capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a large electrochemical equivalent and can obtain a high energy density. Further, graphitizable carbon is preferable because excellent cycle characteristics can be obtained. Furthermore, those having a low charge / discharge potential, specifically those having a charge / discharge potential close to that of lithium metal, are preferable because high energy density of the battery can be easily realized.

Further, as another negative electrode active material capable of increasing the capacity, a material containing at least one selected from the group consisting of a metal element and a metalloid element as a constituent element (for example, an alloy, a compound or a mixture) can be mentioned. .. This is because a high energy density can be obtained by using such a material. In particular, when used together with a carbon material, high energy density can be obtained and excellent cycle characteristics can be obtained, which is more preferable. In the present invention, the alloy includes not only an alloy composed of two or more kinds of metal elements but also an alloy containing one or more kinds of metal elements and one or more kinds of metalloid elements. It may also contain non-metal elements. Some of the structures are solid solutions, eutectics (eutectic mixtures), intermetallic compounds, or two or more of them coexist.

Examples of such a negative electrode active material include a metal element or a metalloid element capable of forming an alloy with lithium. Specific examples thereof include Mg, B, Al, Ti, Ga, In, Si, Ge, Sn, Pb, Bi, Cd, Ag, Zn, Hf, Zr, Y, Pd or Pt. These may be crystalline or amorphous.

The negative electrode active material preferably contains a metal element or a metalloid element of Group 4B in the short periodic table as a constituent element, and more preferably contains at least one of Si and Sn as a constituent element. This is because Si and Sn have a large ability to occlude and release lithium, and a high energy density can be obtained. Examples of such a negative electrode active material include a simple substance of Si, an alloy or a compound, a simple substance of Sn, an alloy or a compound, and a material having at least one or more of them.

As the alloy of Si, for example, as the second constituent element other than Si, Sn, Ni, Cu, Fe, Co, Mn, Zn, In, Ag, Ti, Ge, Bi, Sb, Nb, Mo, Al, Examples include those containing at least one selected from the group consisting of P, Ga and Cr. As the alloy of Sn, for example, as the second constituent element other than Sn, Si, Ni, Cu, Fe, Co, Mn, Zn, In, Ag, Ti, Ge, Bi, Sb, Nb, Mo, Al, Examples include those containing at least one selected from the group consisting of P, Ga and Cr.

Examples of the Sn compound or Si compound include those containing O or C as a constituent element. These compounds may contain the second constituent element described above.

Among them, the Sn-based negative electrode active material preferably contains Co, Sn, and C as constituent elements and has a low crystallinity or an amorphous structure.

Other negative electrode active materials include, for example, metal oxides or polymer compounds capable of occluding and releasing lithium. Examples of the metal oxide include lithium titanium oxide containing Li and Ti such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ), iron oxide, ruthenium oxide, molybdenum oxide and the like. Examples of the polymer compound include polyacetylene, polyaniline, polypyrrole and the like.

(Binder)
As the binder, the same as that of the positive electrode active material layer 21B can be exemplified.

(Conductive aid)
As the conductive auxiliary agent, the same as the positive electrode active material layer 21B can be exemplified.

(Bottom end of negative electrode)
As shown in FIG. 3, the bottom side end portion of the negative electrode 22 (that is, the one long side end portion of the negative electrode 22) is bent toward the inner side surface side of the negative electrode 22. Since the bottom side end is bent in this way, the direction in which the bottom side end of the negative electrode 22 bends when an impact is applied to the battery is defined as the space provided on the innermost circumference of the battery element 20. Can be constrained in direction. As a result, when an impact is applied to the battery, it is possible to prevent the bottom end of the negative electrode 22 from being deformed so that the positive electrode 21 and the bottom end of the negative electrode 22 come into contact with each other. The risk of short circuit between 21 and the negative electrode 22 can be reduced. Therefore, it is possible to improve the safety of the battery against impact due to dropping or the like. The bending of the bottom side end portion of the negative electrode 22 may be bending or bending.

Thickness ratio of the end face thickness A1 of the second negative electrode active material layer 22B ₂ on the bottom side of the negative electrode 22 to the end face thickness B ₁ of the _first negative electrode active material layer 22B ₁ on the bottom side of the negative electrode 22 (A ₁ / B ₁ ) is 1.1 or more and 2.0 or less. When the thickness ratio (A ₁ / B ₁ ) is less than 1.1, the strengths of the first negative electrode active material layer 22B ₁ and the second negative electrode active material layer 22B ₂ approach each other, so that a shock is applied to the battery. At that time, the negative electrode 22 is less likely to be deformed in a predetermined direction, and the safety of the battery against impact is lowered. On the other hand, when the thickness ratio (A ₁ / B ₁ ) exceeds 2.0, the difference in thickness change due to expansion and contraction of the first negative electrode active material layer 22B ₁ and the second negative electrode active material layer 22B ₂ during charging and discharging. Will increase. This increases the risk of damage to the negative electrode current collector 22A at the bent portion of the bottom end, and reduces the safety of the battery against impact.

The end face thickness A1 of the _second negative electrode active material layer 22B ₂ on the bottom side of the negative electrode 22 is preferably 50 μm or more and 90 μm or less. The end face thickness B ₁ of the first negative electrode active material layer 22B ₁ on the bottom side of the negative electrode 22 is preferably 30 μm or more and 80 μm or less.

The end face thickness A ₁ , the end face thickness B ₁ and the thickness ratio (A ₁ / B ₁ ) are measured as follows. First, after discharging the battery to 3.0 V, the battery is disassembled and the negative electrode 22 is taken out. Next, after the negative electrode 22 is dried, the innermost peripheral portion of the negative electrode 22 is cut out to prepare a measurement sample. Next, the measurement sample is processed by Ar ion milling processing (CP processing) to form a smooth cross section parallel to both the width direction 22D and the thickness direction of the negative electrode 22. Next, using a scanning electron microscope (SEM), the portion of the above-mentioned forming cross section corresponding to the bottom end portion of the negative electrode 22 is observed, and an SEM image (secondary electron image) is obtained. .. The observation conditions of the SEM image are as follows.
Equipment: JSM-7401F manufactured by JEOL Ltd.
Irradiation voltage: 0.5kV
Magnification: 2000 times Next, from the acquired SEM image, the end face thickness B ₁ of the first negative electrode active material layer 22B ₁ and the end face thickness A ₁ of the second negative electrode active material layer 22B ₂ are obtained. Next, the thickness ratio (A ₁ / B ₁ ) is calculated using the obtained end face thickness B ₁ and end face thickness A ₁ .

(Top side end of negative electrode)
The top side end portion of the negative electrode 22 (that is, the other long side end portion of the negative electrode 22) may or may not be bent toward the outer side surface side or the inner side surface side of the negative electrode 22. As shown in FIG. 3, it is preferable that the negative electrode 22 is bent toward the outer surface side. Since the top end of the negative electrode 22 is bent toward the outer surface side of the negative electrode 22, the contact between the electrode terminal provided on the innermost peripheral portion and the electrode (contact between the positive electrode lead 11 and the negative electrode 22 and / or Since the contact between the negative electrode lead 12 and the positive electrode 21) can be suppressed, the safety of the battery against impact can be further improved. The bending of the top side end portion of the negative electrode 22 may be bending or bending.

As described above, at the top side end portion of the negative electrode 22, unlike the bottom side end portion of the negative electrode 22, the direction of bending the end portion is not limited to the inner side surface side of the negative electrode 22. This is due to the following reasons. That is, since the sealing portion of the exterior material 10 is formed along the end surface of the battery element 20 on the top side, the restraint of the battery element 20 by the exterior material 10 is stronger on the top side of the battery than on the bottom side of the battery. , It is difficult to form an extra space between the top side end surface of the battery element 20 and the exterior material 10. Therefore, even when an impact is applied to the battery due to dropping or the like, the top side end portion of the negative electrode 22 is less likely to be deformed than the bottom side end portion of the negative electrode 22.

Thickness ratio of the end face thickness A ₂ of the second negative electrode active material layer 22B ₂ on the top side of the negative electrode 22 to the end face thickness B ₂ of the first negative electrode active material layer 22B ₁ on the top side of the negative electrode 22 (A ₂ / B ₂ ) is preferably 0.5 or more and 0.9 or less. When the thickness ratio (A ₂ / B ₂ ) is 0.5 or more, the difference in thickness change due to expansion and contraction of the first negative electrode active material layer 22B ₁ and the second negative electrode active material layer 22B ₂ during charging and discharging It is possible to suppress an excessive increase. As a result, the risk of damage to the negative electrode current collector 22A at the bent portion on the top side end can be reduced, so that the safety of the battery against impact can be further improved. On the other hand, when the thickness ratio (A ₂ / B ₂ ) is 0.9 or less, the strength of the first negative electrode active material layer 22B ₁ and the second negative electrode active material layer 22B ₂ are different, so that the battery is impacted. Is added, the negative electrode 22 is likely to be deformed in a predetermined direction, so that the safety of the battery against impact can be further improved.

The end face thickness A ₂ of the second negative electrode active material layer 22B ₂ on the top side of the negative electrode 22 is preferably 30 μm or more and 80 μm or less. The end face thickness B ₂ of the first negative electrode active material layer 22B ₁ on the top side of the negative electrode 22 is preferably 50 μm or more and 90 μm or less.

In the above-mentioned measurement method of the end face thickness A ₂ , the end face thickness B ₂ and the thickness ratio (A ₂ / B ₂ ), an SEM image is obtained by observing the portion corresponding to the top side end portion of the negative electrode 22 in the formed cross section of the sample. Except for the above, the method for measuring the end face thickness A ₁ , the end face thickness B ₁ and the thickness ratio (A ₁ / B ₁ ) is the same.

(Regulations regarding the width of the negative electrode and the housing)
The difference ΔWA _A between the width W ₂₁ of the negative electrode 22 and the width W ₁₀ of the accommodating portion 10A in the width direction 22D of the negative electrode 22 is 1.3 mm or less. When _ΔWA exceeds 1.3 mm, the surplus space between the bottom side end surface of the battery element 20 and the exterior material 10 and the surplus space between the top side end surface of the battery element 20 and the exterior material 10 become large. Therefore, when an impact such as a drop is applied to the battery, the movement (displacement, slippage, etc.) of the battery element 20 in the accommodating portion 10A cannot be suppressed. Further, since the restraint of the bottom side end portion of the battery element 20 by the exterior material 10 is weakened, the shape of the bottom side end portion of the negative electrode 22 is likely to change with charging and discharging. Therefore, there is a possibility that the bending of the bottom side end portion (the bending toward the inner side surface side of the negative electrode 22), which is advantageous against an impact such as dropping, cannot be maintained. Therefore, the safety of the battery against impact is reduced.

Further, when ΔWA _A exceeds 1.3 mm, the restraint of the top side end portion of the battery element 20 by the exterior material 10 is weakened. Therefore, when the top side end portion is bent toward the outer surface side of the negative electrode 22, the top side end portion is bent (bending toward the outer surface side of the negative electrode 22), which is advantageous against impacts such as dropping. May not be maintained.

The width W ₁₀ of the accommodating portion 10A means the width of the internal space of the accommodating portion 10A measured in the width direction 22D of the negative electrode 22 at the position of the depth 1/2 of the accommodating portion 10A.

(Regulations regarding the width of the negative electrode and the positive electrode)
The difference _ΔWB between the width W ₂₂ of the negative electrode 22 and the width W ₂₁ of the positive electrode 21 is preferably 1.2 mm or more and 1.8 mm or less. When _ΔWB is 1.2 mm or more, the positive electrode in the width direction is positive even if the deviation that occurs between the positive electrode 21 and the negative electrode 22 during winding and the deviation that occurs between the positive electrode 21 and the negative electrode 22 when the battery is dropped are taken into consideration. Since the risk that the positional relationship between the 21 and the negative electrode 22 is reversed can be reduced, the safety of the battery against impact can be further improved. On the other hand, when _ΔWB is 1.8 mm or less, deformation of the negative electrode 22 when an impact is applied can be suppressed, so that the safety of the battery against an impact can be further improved.

(Regulations regarding the width of the negative electrode and separator)
The difference _ΔWC between the width W ₂₃ of the separator 23 and the width W ₂₂ of the negative electrode 22 is 3.0 mm or more and 4.0 mm or less. When _ΔWC is 3.0 mm or more, even if the deviation generated between the separator 23 and the negative electrode 22 during winding and the deviation generated between the separator 23 and the negative electrode 22 when the battery is dropped are taken into consideration, the separator 23 and the negative electrode 22 are taken into consideration. Since the clearance between 22 can be maintained, the safety of the battery against impact can be further improved. On the other hand, when _ΔWC is 4.0 mm or less, it is possible to prevent the separator 23 from being caught during the heat sealing of the laminated film in the assembly process and to prevent the electrolytic solution from leaking, so that the safety of the battery against impact is further improved. Can be improved.

(Separator)
The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is made of, for example, polytetrafluoroethylene, a polyolefin resin (polypropylene (PP) or polyethylene (PE), etc.), an acrylic resin, a styrene resin, a polyester resin or a nylon resin, or a resin blended with these resins. It is composed of a quality film, and may have a structure in which two or more of these porous films are laminated.

Among them, the porous film made of polyolefin is preferable because it has an excellent short-circuit prevention effect and can improve the safety of the battery by the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because it can obtain a shutdown effect in the range of 100 ° C. or higher and 160 ° C. or lower and is also excellent in electrochemical stability. Among them, low-density polyethylene, high-density polyethylene or linear polyethylene are preferably used because they have an appropriate melting temperature and are easily available. In addition, a material obtained by copolymerizing or blending a resin having chemical stability with polyethylene or polypropylene can be used. Alternatively, the porous membrane may have a structure of three or more layers in which a polypropylene layer, a polyethylene layer, and a polypropylene layer are sequentially laminated. For example, it is desirable to have a three-layer structure of PP / PE / PP and have a mass ratio [mass%] of PP to PE of PP: PE = 60: 40 to 75:25. Alternatively, from the viewpoint of cost, a single-layer base material containing 100% by mass of PP or 100% by mass of PE can be used. The method for producing the separator 23 may be wet or dry.

A non-woven fabric may be used as the separator 23. As the fiber constituting the non-woven fabric, at least one selected from the group consisting of aramid fiber, glass fiber, polyolefin fiber, polyethylene terephthalate (PET) fiber, nylon fiber and the like can be used.

The separator 23 may have a structure including a base material and a surface layer provided on one side or both sides of the base material. The surface layer contains inorganic particles having an insulating property and a resin material that binds the inorganic particles to the surface of the base material and also binds the inorganic particles to each other. This resin material may have, for example, a three-dimensional network structure in which fibrils are formed and a plurality of fibrils are connected. In this case, the inorganic particles may be supported on the resin material having this three-dimensional network structure. Further, the resin material may bind the surface of the base material or the inorganic particles to each other without forming fibril. In this case, higher binding properties can be obtained. By providing the surface layer on one side or both sides of the base material as described above, the oxidation resistance, heat resistance, mechanical strength and the like of the separator 23 can be improved.

(Electrolytic solution)
The electrolytic solution is a so-called non-aqueous electrolytic solution, and contains a non-aqueous solvent (organic solvent) and an electrolyte salt dissolved in the non-aqueous solvent. The electrolytic solution may contain known additives in order to improve the battery characteristics. The battery may be provided with an electrolyte layer containing an electrolytic solution and a polymer compound serving as a retainer for holding the electrolytic solution, instead of the electrolytic solution. In this case, the electrolyte layer may be in the form of a gel.

It is preferable that the non-aqueous solvent further contains at least one cyclic carbonate ester from the viewpoint of improving the cycle characteristics. As the cyclic carbonate ester, it is preferable to use at least one selected from the group consisting of ethylene carbonate (EC) and propylene carbonate (PC), and it is particularly preferable to contain both ethylene carbonate and propylene carbonate.

It is preferable that the non-aqueous solvent further contains at least one chain-like carbonic acid ester from the viewpoint of improving ionic conductivity. As the chain carbonic acid ester, it is preferable to use at least one selected from the group consisting of diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate and the like.

The non-aqueous solvent may contain at least one selected from the group consisting of 2,4-difluoroanisole, vinylene carbonate and the like. This is because 2,4-difluoroanisole can further improve the discharge capacity, and vinylene carbonate can further improve the cycle characteristics.

In addition to these, non-aqueous solvents include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methylnitrile, 1,3-dioxolane, 4-methyl-1,3. -Dioxolane, Methyl acetate, Methyl propionate, acetonitrile, Glutaronitrile, Adiponitrile, Acetonitrile, 3-methoxypropyronitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N- It may contain at least one selected from the group consisting of dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethylsulfoxide, trimethyl phosphate and the like.

As the electrolyte salt, for example, at least one lithium salt is used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO). ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, difluoro [oxorat-O, O'] lithium borate, lithium bisoxalate borate, LiBr and the like can be mentioned at least one selected from the group. Among them, LiPF ₆ is preferable because it can obtain high ionic conductivity and further improve the cycle characteristics.

[Battery operation]
In the battery having the above-described configuration, when charging is performed, for example, lithium ions are released from the positive electrode active material layer 21B and stored in the negative electrode active material layer 22B via the electrolytic solution. Further, when the electric discharge is performed, for example, lithium ions are released from the negative electrode active material layer 22B and are occluded in the positive electrode active material layer 21B via the electrolytic solution.

[Battery manufacturing method]
Next, an example of a method for manufacturing a battery according to the first embodiment of the present invention will be described.

(Process for manufacturing positive electrode)
The positive electrode 21 is manufactured as follows. First, for example, a positive electrode active material, a binder, and a conductive auxiliary agent are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) and pasted. A positive electrode mixture slurry is prepared. Next, this positive electrode mixture slurry is applied to the first surface and the second surface of the positive electrode current collector 21A, respectively, the solvent is dried, and the first positive electrode active material layer is compression-molded by a roll press machine or the like. 21B ₁ and a second positive electrode active material layer 21B ₂ are formed to obtain a long positive electrode 21. The obtained positive electrode 21 may be slit to a predetermined width.

(Negative electrode manufacturing process)
The negative electrode 22 is manufactured as follows. First, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a paste-like negative electrode mixture slurry. do. Next, this negative electrode mixture slurry is applied to the first surface and the second surface of the negative electrode current collector 22A, respectively, the solvent is dried, and the first negative electrode active material layer is compression-molded by a roll press machine or the like. The 22B ₁ and the second negative electrode active material layer 22B ₂ are formed to obtain a long negative electrode 22. The obtained negative electrode 22 may be slit to a predetermined width.

Next, for example, by applying an external force to one long side end of the negative electrode 22 using a metal plate, one long side end of the negative electrode 22 is placed on the first surface side of the negative electrode 22. bend. Next, if necessary, for example, by using a metal plate and applying an external force to the other long side end of the negative electrode 22, the other long side end is applied to the second surface side of the negative electrode 22. Bend the part. The end of one long side of the negative electrode 22 is the bottom side of the finished battery, and the end of the other long side of the negative electrode 22 is the top side of the finished battery. Further, the first surface of the negative electrode 22 is the inner surface of the finished battery, and the second surface of the negative electrode 22 is the outer surface of the finished battery.

(Battery element manufacturing process)
The winding type battery element 20 is manufactured as follows. First, the positive electrode lead 11 is attached to one end of the positive electrode current collector 21A by welding, and the negative electrode lead 12 is attached to one end of the negative electrode current collector 22A by welding. Next, the positive electrode 21 and the negative electrode 22 are wound around the flat winding core via the separator 23, wound many times in the longitudinal direction, and then the protective tape 24 is adhered to the outermost peripheral portion to adhere the battery element 20. To get.

(Sealing process)
The battery element 20 is sealed with the exterior material 10 as follows. First, the battery element 20 is accommodated in the accommodating portion 10A, the battery element 20 is sandwiched between the exterior materials 10, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and the battery element 20 is accommodated inside the exterior material 10. .. At that time, the adhesion film 13 is inserted between the positive electrode lead 11 and the negative electrode lead 12 and the exterior material 10. The adhesion film 13 may be attached to the positive electrode lead 11 and the negative electrode lead 12 in advance. Next, the electrolytic solution is injected into the exterior material 10 from one side of the unfused, and then one side of the unfused is heat-fused and sealed in a vacuum atmosphere. As a result, the batteries shown in FIGS. 1 and 2 can be obtained.

[Action effect]
As described above, in the battery according to the first embodiment, the bottom side end portion of the negative electrode 22 is bent toward the inner side surface side of the negative electrode 22 (that is, the innermost peripheral side of the battery element 30). Since the bottom side end is bent in this way, the direction in which the bottom side end of the negative electrode 22 bends when an impact is applied to the battery is defined as the space provided on the innermost circumference of the battery element 20. Can be constrained in direction. As a result, when an impact is applied to the battery, the bottom side end portion of the negative electrode 22 is prevented from being deformed so that the positive electrode 21 and the bottom side end portion of the negative electrode 22 come into contact with each other, and the positive electrode 21 and the negative electrode 22 are prevented from being deformed. The risk of short circuit can be reduced. Therefore, it is possible to improve the safety of the battery against impact due to dropping or the like.

Further, the difference _ΔWA between the width W ₂₁ of the negative electrode 22 and the width W ₁₀ of the accommodating portion 10A in the width direction 22D of the negative electrode 22 is 1.3 mm or less. As a result, the surplus space between the bottom end surface of the battery element 20 and the exterior material 10 and the surplus space between the top end surface of the battery element 20 and the exterior material 10 are reduced, and an impact such as a drop is applied to the battery. When added, the movement (displacement, slippage, etc.) of the battery element 20 can be suppressed in the accommodating portion 10A. Further, since the surplus space between the bottom side end surface of the battery element 20 and the exterior material 10 becomes smaller, the restraint of the bottom side end portion of the battery element 20 by the exterior material 10 is strengthened, so that the negative electrode 22 is charged and discharged. It is possible to suppress the change in the shape of the bottom side end portion. Therefore, it is possible to maintain the bending of the bottom side end portion (the bending toward the inner side surface side of the negative electrode 22), which is advantageous for impacts such as dropping.

<2 Second Embodiment>
In the second embodiment, the electronic device including the battery according to the first embodiment described above will be described.

FIG. 4 shows an example of the configuration of the electronic device 400 according to the second embodiment of the present invention. The electronic device 400 includes an electronic circuit 401 of the main body of the electronic device and a battery pack 300. The battery pack 300 is electrically connected to the electronic circuit 401 via the positive electrode terminal 331a and the negative electrode terminal 331b. The electronic device 400 may have a structure in which the battery pack 300 can be attached and detached.

Examples of the electronic device 400 include a notebook personal computer, a tablet computer, a mobile phone (for example, a smartphone), a personal digital assistant (PDA), a display device (LCD (Liquid Crystal Display), and an EL (Electro Luminescence). ) Display, electronic paper, etc.), image pickup device (for example, digital still camera, digital video camera, etc.), audio equipment (for example, portable audio player), game equipment, cordless phone handset, electronic book, electronic dictionary, radio, headphones, navigation Systems, memory cards, pacemakers, hearing aids, power tools, electric shavers, refrigerators, air conditioners, TVs, stereos, water heaters, microwave ovens, dishwashers, washing machines, dryers, lighting equipment, toys, medical equipment or robots, etc. However, it is not limited to this.

(Electronic circuit)
The electronic circuit 401 includes, for example, a CPU (Central Processing Unit), a peripheral logic unit, an interface unit, a storage unit, and the like, and controls the entire electronic device 400.

(Battery pack)
The battery pack 300 includes an assembled battery 301 and a charge / discharge circuit 302. The battery pack 300 may further include an exterior material (not shown) that houses the assembled battery 301 and the charge / discharge circuit 302, if necessary.

The assembled battery 301 is configured by connecting a plurality of secondary batteries 301a in series and / or in parallel. The plurality of secondary batteries 301a are connected, for example, in n parallel m series (n and m are positive integers). Note that FIG. 4 shows an example in which six secondary batteries 301a are connected in two parallels and three series (2P3S). As the secondary battery 301a, the battery according to the first embodiment described above is used.

Here, a case where the battery pack 300 includes an assembled battery 301 composed of a plurality of secondary batteries 301a will be described, but the battery pack 300 includes one secondary battery 301a instead of the assembled battery 301. It may be adopted.

The charge / discharge circuit 302 is a control unit that controls the charge / discharge of the assembled battery 301. Specifically, at the time of charging, the charging / discharging circuit 302 controls the charging of the assembled battery 301. On the other hand, at the time of discharging (that is, when the electronic device 400 is used), the charge / discharge circuit 302 controls the discharge to the electronic device 400.

As the exterior material, for example, a case made of a metal, a polymer resin, a composite material thereof, or the like can be used. Examples of the composite material include a laminate in which a metal layer and a polymer resin layer are laminated.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

In the following examples and comparative examples, the end face thicknesses A ₁ , B ₁ , A ₂ , B ₂ of the finished battery and the thickness ratios A ₁ / B ₁ and A ₂ / B ₂ of the finished battery are included in the first embodiment. It was obtained by the measurement method described above.

[Examples 1 to 3, Comparative Examples 1 and 2]
(Process for manufacturing positive electrode)
The positive electrode was prepared as follows. First, 97 parts by mass of lithium cobalt composite oxide as a positive electrode active material, 1 part by mass of carbon black as a conductive agent, and 2 parts by mass of polyvinylidene fluoride (PVdF) as a binder are mixed to prepare a positive electrode mixture. By dispersing it in N-methyl-2-pyrrolidone, a paste-like positive electrode mixture slurry was obtained. Next, the positive electrode mixture slurry is applied to the first surface and the second surface of the strip-shaped aluminum foil (positive electrode current collector) having a thickness of 10 μm, dried, and then compression-molded by a roll press machine. As a result, a first positive electrode active material layer and a second positive electrode active material layer were formed on the first surface and the second surface of the aluminum foil, respectively. Next, a strip-shaped positive electrode was obtained by slitting (cutting) the obtained laminate to a predetermined width.

(Negative electrode manufacturing process)
The negative electrode was prepared as follows. First, 96% by mass of artificial graphite powder as a negative electrode active material and 4% by mass of polyvinylidene fluoride (PVdF) as a binder are mixed to prepare a negative electrode mixture, and then this negative electrode mixture is used as an organic solvent (N-methyl-). 2-Pyrrolidone: NMP) was dispersed to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to the first surface and the second surface of the strip-shaped copper foil (negative electrode current collector) having a thickness of 10 μm, dried, and then compression-molded by a roll press machine. As a result, a first negative electrode active material layer and a second negative electrode active material layer were formed on the first surface and the second surface of the copper foil, respectively. Here, the first surface of the copper foil is the surface that becomes the inner surface after the negative electrode is wound, and the second surface of the copper foil is the surface that becomes the outer surface after the negative electrode is wound. Next, a strip-shaped negative electrode was obtained by slitting (cutting) the obtained laminate to a predetermined width.

Next, by applying an external force to the ends on both long sides of the negative electrode using a metal plate, the ends on both long sides were bent. At this time, on both long sides, the bottom end of the negative electrode is bent toward the inner side surface of the negative electrode in the finished battery, and the top end of the negative electrode is bent toward the outer side of the negative electrode in the finished battery. The bending direction of the end was set. In addition, in order to ensure that the end face thicknesses A ₁ , B ₁ , A ₂ , and B ₂ of the finished battery and the thickness ratios A ₁ / B ₁ and A ₂ / B ₂ of the finished battery are the values shown in Table 1. The thickness of the negative electrode active material layer was adjusted by changing the coating machine gap at the time of applying the negative electrode mixture slurry.

(Preparation process of electrolytic solution)
The electrolyte was prepared as follows. First, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC: PC: DEC = 15: 15: 70 to prepare a mixed solvent. Subsequently, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was dissolved in this mixed solvent so as to be 1 mol / l to prepare an electrolytic solution.

(Battery manufacturing process)
The battery was made as follows. First, an aluminum positive electrode lead was welded to the positive electrode current collector, and a copper negative electrode lead was welded to the negative electrode current collector. Subsequently, the positive electrode and the negative electrode are brought into close contact with each other via a microporous polyethylene film, then wound in the longitudinal direction, and a protective tape is attached to the outermost peripheral portion to form a flat wound battery. The element was manufactured.

Next, after forming an accommodating portion in the exterior material by deep drawing, the battery element is accommodated in the accommodating portion, the battery element is loaded between the exterior materials, and the three sides of the exterior material are heat-sealed. , One side has an opening without heat fusion. As the exterior material, a moisture-proof aluminum laminated film in which a nylon film having a thickness of 25 μm, an aluminum foil having a thickness of 40 μm, and a polypropylene film having a thickness of 30 μm were laminated in order from the outermost layer was used. Then, the electrolytic solution was injected through the opening of the exterior material, and the remaining one side of the exterior material was heat-sealed under reduced pressure to seal the battery element. As a result, the target battery was obtained.

By adjusting the slit width of the laminate in the positive electrode manufacturing step and the negative electrode manufacturing step and adjusting the width of the separator prepared in the battery manufacturing step, both long sides of the positive electrode become both long sides of the negative electrode. It is provided on the inside so that both long sides of the negative electrode are provided inside both long sides of the separator. Further, ΔW _A = 0.9 mm, ΔW _B = 1.5 mm, and _ΔWC = 3.5 mm. In addition, ΔW _A , ΔWB _B and _ΔWC are as follows.
ΔWA _A : Difference between the width W ₂₁ of the negative electrode and the width W ₁₀ of the accommodating portion in the width direction of the negative electrode (see FIGS. 1 and 3).
_ΔWB : Difference between the negative electrode width W ₂₂ and the positive electrode width W ₂₁ (see FIG. 3).
_ΔWC : Difference between the width W ₂₃ of the separator and the width W ₂₂ of the negative electrode (see FIG. 3).

[Comparative Example 3]
In the process of manufacturing the negative electrode, a battery was obtained in the same manner as in Example 2 except that no external force was applied to the end on the long side of one of the negative electrodes and the end on the long side of one was flattened. One long side of the negative electrode is the bottom side of the completed battery.

[Comparative Example 4]
In the process of manufacturing the negative electrode, both lengths are such that the bottom end of the negative electrode is bent toward the outer side of the negative electrode in the finished battery, and the top end of the negative electrode is bent toward the outer side of the negative electrode in the finished battery. A battery was obtained in the same manner as in Example 2 except that the bending direction of the end portion on the side side was set.

[Examples 4 and 5, Comparative Examples 5 and 6]
The slit width of the laminate was adjusted in the positive electrode manufacturing step and the negative electrode manufacturing step so that ΔWA _A , ΔWB _B , and _ΔWC were the values shown in Table 3, and the width of the separator prepared in the battery manufacturing step was adjusted. A battery was obtained in the same manner as in Example 2 except that the adjustment was made.

[Examples 6 to 10]
The thickness of the negative electrode active material layer is adjusted by changing the coating machine gap at the time of applying the negative electrode mixture slurry so that the thickness ratio A ₂ / B ₂ of the completed battery becomes the value shown in Table 4, and the other A battery was obtained in the same manner as in Example 2 except that the external force applied to the end portion on the long side of the above was adjusted. The other long side of the negative electrode is the top side of the completed battery.

[Example 11]
In the process of manufacturing the negative electrode, a battery was obtained in the same manner as in Example 2 except that no external force was applied to the other end on the long side of the negative electrode and the other end on the long side was flattened.

[Examples 12 to 16]
The slit width of the laminate was adjusted in the positive electrode manufacturing step and the negative electrode manufacturing step so that ΔWA _A , ΔWB _B , and _ΔWC were the values shown in Table 5, and the width of the separator prepared in the battery manufacturing step was adjusted. A battery was obtained in the same manner as in Example 2 except that the adjustment was made.

[Examples 17 to 21]
The slit width of the laminate was adjusted in the positive electrode manufacturing step and the negative electrode manufacturing step so that ΔWA _A , ΔWB _B , and _ΔWC were the values shown in Table 6, and the width of the separator prepared in the battery manufacturing step was adjusted. A battery was obtained in the same manner as in Example 2 except that the adjustment was made.

(Fall safety)
The drop safety of the battery obtained as described above was evaluated as follows. The drop test was conducted with the device mounted on a jig simulating the state of being incorporated in a consumer electronic device. The battery weight was about 30 g and the jig was about 150 g. The battery attached to the jig was dropped onto a flat plate from a height of 1.5 m. The OCV (Open Circuit Voltage) was measured each time it was dropped, and the presence or absence of smoke and ignition was confirmed. It was defined that the drop safety test was passed when OCV reduction and smoke ignition did not occur after 20 drop tests. The above test was performed on 100 batteries, and the pass ratio of the batteries that passed the above test ([(the number of batteries that passed the above test) / (the number of batteries that passed the above test)] × 100 [%]) was calculated. I asked.

Table 1 shows the configurations and evaluation results of the batteries of Examples 1 to 3 and Comparative Examples 1 and 2.

Table 2 shows the configurations and evaluation results of the batteries of Example 2, Comparative Examples 3 and 4.

Table 3 shows the configurations and evaluation results of the batteries of Examples 2, 4, 5, and Comparative Examples 5, 6.

Table 4 shows the configurations and evaluation results of the batteries of Examples 2 and 6 to 11.

Table 5 shows the configurations and evaluation results of the batteries of Examples 12 to 16.

Table 6 shows the configurations and evaluation results of the batteries of Examples 17 to 21.

The following can be seen from Tables 1 to 3. When the bottom end of the negative electrode is bent toward the inner side surface of the negative electrode, the thickness ratio A ₁ / B ₁ is 1.1 or more and 2.0 or less, and _ΔWA is 1.3 mm or less, the drop safety is improved. Can be improved.

The following can be seen from Table 4. Among the batteries in which the top side end of the negative electrode is bent toward the inner side surface of the negative electrode, the battery in which the top side end of the negative electrode is bent toward the outer side of the negative electrode and the battery in which the top side end of the negative electrode is not bent. It is possible to improve the drop safety as compared with (see Examples 2, 10 and 11).
In a battery in which the top end of the negative electrode is bent toward the inner side surface of the negative electrode, the thickness ratio A ₂ / B ₂ is preferably 0.5 or more and 0.9 or less from the viewpoint of improving drop safety (from the viewpoint of improving drop safety). See Examples 2 and 6-9).

The following can be seen from Table 5. From the viewpoint of improving drop safety, it is preferable that _ΔWB is 1.2 mm or more and 1.8 mm or less.

The following can be seen from Table 6. From the viewpoint of improving drop safety, it is preferable that _ΔWC is 3.0 mm or more and 4.0 mm or less.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible.

For example, the configurations, methods, processes, shapes, materials, numerical values, etc. given in the above-described embodiments are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, etc. may be used as necessary. May be good.

The configurations, methods, processes, shapes, materials, numerical values, etc. of the above-described embodiments can be combined with each other as long as they do not deviate from the gist of the present invention.

In the numerical range described stepwise in the above embodiment, the upper limit value or the lower limit value of the numerical range of one stage may be replaced with the upper limit value or the lower limit value of the numerical range of another stage.

Unless otherwise specified, the materials exemplified in the above-described embodiments can be used alone or in combination of two or more.

10 Exterior material 10A Accommodating part 11 Positive electrode lead 12 Negative electrode lead 13 Adhesive film 20 Battery element 21 Positive electrode 21A Positive electrode current collector 21B ₁ First positive electrode active material layer 21B ₂ Second positive electrode active material layer 22 Negative electrode 22A Negative electrode current collector 22B ₁ First negative electrode active material layer 22B ₂ Second negative electrode active material layer 23 Separator 24 Protective tape 300 Battery pack 400 Electronic equipment

Claims

With a winding type battery element
A film-like exterior material for accommodating the battery element is provided.
The battery element includes a long positive electrode, a long negative electrode, and a long separator, and the positive electrode, the negative electrode, and the separator are wound in the longitudinal direction and of the positive electrode. Both long sides are provided inside both long sides of the negative electrode.
The negative electrode has a negative electrode current collector, a first negative electrode active material layer provided on the inner surface of the negative electrode current collector, and a second negative electrode active material layer provided on the outer surface of the negative electrode current collector. And with
One end of the negative electrode on the long side is bent toward the inner side surface of the negative electrode.
The thickness ratio between the end face thickness A1 of the second negative electrode active material layer on one long side of the negative electrode and the end face thickness B1 of the first negative electrode active material layer on one long side of the negative electrode. (A 1 / B 1 ) is 1.1 or more and 2.0 or less.
The exterior material has an accommodating portion for accommodating the battery element, and the difference between the width of the negative electrode and the width of the accommodating portion in the width direction of the negative electrode is 1.3 mm or less.
The battery according to claim 1, wherein the exterior material has a folded-back portion provided on one long side of the negative electrode and a sealing portion provided on the other long side of the negative electrode.
The other long side end of the negative electrode is bent toward the outer surface side of the negative electrode.
The thickness ratio between the end face thickness A 2 of the second negative electrode active material layer on the other long side of the negative electrode and the end face thickness B 2 of the first negative electrode active material layer on the other long side of the negative electrode. The battery according to claim 2, wherein (A 2 / B 2 ) is 0.5 or more and 0.9 or less.
The battery according to any one of claims 1 to 3, wherein the difference between the width of the negative electrode and the width of the positive electrode is 1.2 mm or more and 1.8 mm or less.
Both long sides of the negative electrode are provided inside both long sides of the separator.
The battery according to any one of claims 1 to 4, wherein the difference between the width of the separator and the width of the negative electrode is 3.0 mm or more and 4.0 mm or less.