JP7306069B2 - battery - Google Patents

Description

The present invention relates to batteries.

BACKGROUND ART In recent years, batteries having a wound structure in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a strip-shaped separator interposed therebetween are widely used. Patent Document 1 discloses a double-sided formation portion in which an active material layer is formed on both sides of a current collector and a single-sided formation portion in which an active material layer is formed only on one side of the current collector. is provided at the end of the electrode on the winding outer peripheral side.

JP 2004-146222 A

However, in the battery described in Patent Document 1, there is a problem that the negative electrode active material tends to fall off at the boundary between the single-sided formation portion and the double-sided formation portion provided at the end portion on the winding outer peripheral side.

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery capable of suppressing the occurrence of a short circuit caused by falling off of a negative electrode active material.

In order to solve the above problems, the present invention
a negative electrode current collector having a first surface and a second surface;
a first negative electrode active material layer formed on the first surface;
a wound negative electrode having a second negative electrode active material layer formed on the second surface;
and an insulating member provided on the negative electrode,
A single - sided formation portion in which only the first negative electrode active material layer of the first negative electrode active material layer and the second negative electrode active material layer is formed is provided at the end portion of the negative electrode on the winding outer peripheral side,
The insulating member is a battery that covers the boundary between the single-sided formation portion and the second negative electrode active material layer.

According to the present invention, it is possible to suppress the occurrence of a short circuit due to falling off of the negative electrode active material.

1 is an exploded perspective view showing an example of the configuration of a non-aqueous electrolyte secondary battery according to a first embodiment of the invention; FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1; FIG. It is the schematic for demonstrating a winding process. 4 is an enlarged view of a region R shown in FIG. 3; FIG. It is a block diagram which shows an example of a structure of the electronic device which concerns on the 2nd Embodiment of this invention.

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

<1 First Embodiment>
[Battery configuration]
First, an example of the configuration of a non-aqueous electrolyte secondary battery (hereinafter simply referred to as "battery") according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. The battery has a flat shape as shown in FIG. The battery includes a flat wound electrode body 20 to which a positive electrode lead (positive electrode tab) 31 and a negative electrode lead (negative electrode tab) 32 are attached, an electrolytic solution (not shown) as an electrolyte, and these electrodes. A body 20 and a case 10 containing an electrolytic solution are provided. The battery has a rectangular shape when viewed from above in a direction perpendicular to its main surface.

(Case)
The case 10 is a rectangular parallelepiped thin battery can, and is made of metal. For example, iron (Fe) plated with nickel (Ni) can be used as the metal. When a metal case is used, the case itself can also serve as a terminal of the battery by connecting to either the positive electrode or the negative electrode, which facilitates miniaturization of the battery. The case 10 includes a housing portion 11 and a lid portion 12 . The accommodation portion 11 accommodates the electrode assembly 20 . The housing portion 11 includes a main surface portion 11A and a wall portion 11B provided along the periphery of the main surface portion 11A. The main surface portion 11A covers the main surface of the electrode body 20, and the wall portion 11B covers the side surfaces and end surfaces of the electrode body 20. As shown in FIG. A positive electrode terminal 13 is provided in a portion of the wall portion 11B that faces one end face of the electrode body 20 (the end face from which the positive electrode lead 31 and the negative electrode lead 32 are taken out). The positive lead 31 is connected to the positive terminal 13 . The negative lead 32 is connected to the inner surface of the case 10 . The lid portion 12 covers the opening of the housing portion 11 . The top portion of the wall portion 11B of the housing portion 11 and the peripheral edge portion of the lid portion 12 are joined by welding, an adhesive, or the like.

(positive lead, negative lead)
The positive lead 31 and the negative lead 32 are led out from one end surface of the electrode assembly 20 . The positive electrode lead 31 and the negative electrode lead 32 are each made of a metal material such as Al, Cu, Ni, or stainless steel, and each have a thin plate shape.

Sealants (adhesive films) 31A and 32A are inserted between the case 10 and the positive electrode lead 31 and between the case 10 and the negative electrode lead 32, respectively, to prevent outside air from entering. The sealants 31A and 32A are made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, such as polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

(electrode body)
As shown in FIG. 2, the electrode body 20 has a pair of opposing flat portions 20A and a pair of opposing curved portions 20B provided between the pair of flat portions 20A. The electrode body 20 includes a strip-shaped positive electrode 21, a strip-shaped negative electrode 22, two strip-shaped separators 23A and 23B, insulating members 25B1 and 25B2 provided on the positive electrode 21, and the negative electrode 22. and insulating members 26B1 and 26B2. Separators 23A and 23B are alternately provided between positive electrode 21 and negative electrode 22 . The electrode body 20 has a configuration in which a positive electrode 21 and a negative electrode 22 are laminated with a separator 23A or a separator 23B interposed therebetween and wound in the longitudinal direction so as to form a flat spiral shape. The electrode assembly 20 is wound such that the positive electrode 21 is the innermost electrode and the negative electrode 22 is the outermost electrode. A negative electrode 22 , which is the outermost electrode, is fixed by a winding stop tape 24 . The positive electrode 21, the negative electrode 22, and the separators 23A and 23B are impregnated with an electrolytic solution.

(positive electrode)
The positive electrode 21 includes a positive electrode current collector 21A having an inner surface (first surface) 21S1 and an outer surface (second surface) 21S2, and a positive electrode active material layer 21B1 provided on the inner surface 21S1 of the positive electrode current collector 21A. and a positive electrode active material layer 21B2 provided on the outer surface 21S2 of the positive electrode current collector 21A. As used herein, the term “inner surface” means the surface located on the winding center side, and the term “outer surface” means the surface located on the side opposite to the winding center. The thickness of the positive electrode current collector 21A is, for example, 3 μm or more and 20 μm or less. The thickness of the positive electrode active material layers 21B1 and 21B2 is, for example, 30 μm or more and 100 μm or less.

The positive electrode active material layer 21B1 is not provided on the inner surface 21S1 of the winding outer peripheral end of the positive electrode 21 (hereinafter simply referred to as the “outer peripheral end”), and the inner surface 21S1 of the positive electrode current collector 21A is exposed. A positive electrode current collector exposed portion 21D1 is provided. The outer surface 21S2 of the outer peripheral edge of the positive electrode 21 is not provided with the positive electrode active material layer 21B2, and is provided with a positive electrode current collector exposed portion 21D2 where the outer surface 21S2 of the positive electrode current collector 21A is exposed. A positive electrode lead 31 is connected to a portion of the positive electrode current collector exposed portion 21D2 that corresponds to the flat portion 20A. The length of the positive electrode current collector exposed portion 21D1 in the winding direction is, for example, substantially the same as the length of the positive electrode current collector exposed portion 21D2 in the winding direction.

The positive electrode current collector 21A is made of, for example, metal foil such as aluminum foil, nickel foil, or stainless steel foil. The positive electrode active material layers 21B1 and 21B2 contain a positive electrode active material capable of intercalating and deintercalating lithium. The positive electrode active material layers 21B and 21B2 may further contain at least one of a binder and a conductive agent, if necessary.

(Positive electrode active material)
As the positive electrode active material, for example, lithium-containing compounds such as lithium oxides, lithium phosphorous oxides, lithium sulfides, and intercalation compounds containing lithium are suitable, and two or more of these may be mixed and used. A lithium-containing compound containing lithium, a transition metal element, and oxygen is preferable for increasing the energy density. Examples of such lithium-containing compounds include lithium composite oxides having a layered rock salt structure and lithium composite phosphates having an olivine structure. The lithium-containing compound more preferably contains at least one selected from the group consisting of Co, Ni, Mn and Fe as a transition metal element. Examples of such lithium-containing compounds include LiNi _0.50 Co _0.20 Mn _0.30 O ₂ , LiCoO ₂ , LiNiO ₂ , LiNiaCo _1-a O ₂ (0<a<1), LiMn ₂ O ₄ and LiFePO ₄ . .

As the positive electrode active material capable of intercalating and deintercalating lithium, in addition to these, inorganic compounds not containing lithium such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS can also be used. can.

The positive electrode active material capable of intercalating and deintercalating lithium may be one other than those described above. Moreover, two or more 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 polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, styrene-butadiene rubber, carboxymethylcellulose, and copolymers mainly composed of one of these resin materials. Seeds can be used.

(Conductive agent)
As the conductive 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. Note that the conductive agent may be any material as long as it has conductivity, and is not limited to a carbon material. For example, a metal material, a conductive polymer material, or the like may be used as the conductive agent. Moreover, the shape of the conductive agent may be, for example, granular, scale-like, hollow, needle-like, or cylindrical, but is not particularly limited to these shapes.

(negative electrode)
The negative electrode 22 includes a negative electrode current collector 22A having an inner surface (first surface) 22S1 and an outer surface (second surface) 22S2, and a negative electrode active material layer 22B1 provided on the inner surface 22S1 of the negative electrode current collector 22A. and a negative electrode active material layer 22B2 provided on the outer surface 22S2 of the negative electrode current collector 22A. The thickness of the negative electrode current collector 22A is, for example, 3 μm or more and 20 μm or less. The thickness of the negative electrode active material layers 22B1 and 22B2 is, for example, 30 μm or more and 100 μm or less.

The inner surface 22S1 of the outer peripheral edge of the negative electrode 22 is not provided with the negative electrode active material layer 22B1, and is provided with a negative electrode current collector exposed portion 22D1 where the inner surface 22S1 of the positive electrode current collector 21A is exposed. The outer surface 22S2 of the outer peripheral edge of the negative electrode 22 is not provided with the negative electrode active material layer 22B2, and is provided with a negative electrode current collector exposed portion 22D2 where the outer surface 22S2 of the negative electrode current collector 22A is exposed. A negative electrode lead 32 is connected to a portion of the negative electrode current collector exposed portion 22D1 that corresponds to the flat portion 20A. The positive electrode lead 31 and the negative electrode lead 32 are provided on the same flat portion 20A side.

The length of the negative electrode current collector exposed portion 22D1 in the winding direction is longer than the length of the negative electrode current collector exposed portion 22D2 in the winding direction by about one turn. That is, at the outer peripheral edge of the negative electrode 22, of the negative electrode active material layer 22B1 and the negative electrode active material layer 22B2, only the negative electrode active material layer 22B1 is formed on the negative electrode current collector 22A. For example, it is provided for about one round.

At the outermost periphery of the negative electrode 22, a portion where both the inner side surface 22S1 and the outer side surface 22S2 of the negative electrode current collector 22A are exposed (that is, the negative electrode current collector exposed portion 22D1 and the negative electrode current collector exposed portion 22D2 are formed on both surfaces of the positive electrode 21). provided portion) is provided over, for example, about one round. As a result, the negative electrode current collector exposed portion 22D2 and the inner surface of the case 10 are brought into electrical contact. Therefore, it is possible to electrically connect between the negative electrode 22 and the case 10 and further reduce the resistance.

The negative electrode current collector 22A is made of, for example, metal foil such as copper foil, nickel foil, or stainless steel foil. The negative electrode active material layers 22B1 and 22B2 contain a negative electrode active material capable of intercalating and deintercalating lithium. The negative electrode active material layers 22B1 and 22B2 may further contain at least one of a binder and a conductive agent, if necessary.

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

(binder)
As the binder, the same binder as that used for the positive electrode active material layers 21B1 and 21B2 can be used.

(Conductive agent)
As the conductive agent, the same material as that used for the positive electrode active material layers 21B1 and 21B2 can be used.

(separator)
The separators 23A and 23B separate the positive electrode 21 and the negative electrode 22 from each other and allow lithium ions to pass therethrough while preventing current short circuit due to contact between the two electrodes. The separators 23A and 23B are made of, for example, polytetrafluoroethylene, polyolefin resin (polypropylene (PP) or polyethylene (PE), etc.), acrylic resin, styrene resin, polyester resin, nylon resin, or a blend of these resins. and may have a structure in which two or more of these porous films are laminated.

Among them, a polyolefin porous film is preferable because it has an excellent short-circuit prevention effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material for the separators 23A and 23B because it can obtain a shutdown effect within the range of 100° C. or more and 160° C. or less and has excellent electrochemical stability. Among them, low-density polyethylene, high-density polyethylene, and linear polyethylene are suitably used because they have suitable melting temperatures and are readily available. In addition, a material obtained by copolymerizing or blending a chemically stable resin 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 the mass ratio [wt%] of PP and PE is PP:PE=60:40 to 75:25. Alternatively, from a cost point of view, a single layer substrate of 100 wt% PP or 100 wt% PE can be used. The method for producing the separators 23A and 23B may be wet or dry.

A nonwoven fabric may be used as the separators 23A and 23B. Aramid fibers, glass fibers, polyolefin fibers, polyethylene terephthalate (PET) fibers, nylon fibers, or the like can be used as fibers constituting the nonwoven fabric. Moreover, it is good also as a nonwoven fabric by mixing these 2 or more types of fiber.

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

As the organic solvent, a cyclic carbonate such as ethylene carbonate or propylene carbonate can be used, and it is preferable to use one of ethylene carbonate and propylene carbonate, particularly a mixture of both. This is because the cycle characteristics can be further improved.

As the organic solvent, in addition to these cyclic carbonates, it is preferable to use a mixture of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and methylpropyl carbonate. This is because high ionic conductivity can be obtained.

The organic solvent also preferably contains 2,4-difluoroanisole or vinylene carbonate. This is because 2,4-difluoroanisole can further improve the discharge capacity, and vinylene carbonate can further improve the cycle characteristics. Therefore, it is preferable to use a mixture of these because the discharge capacity and the cycle characteristics can be further improved.

In addition to these, organic solvents include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3 -dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropyronitrile, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N- dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethylsulfoxide, trimethyl phosphate and the like.

Compounds obtained by substituting fluorine for at least part of the hydrogen in these organic solvents may improve the reversibility of the electrode reaction, depending on the type of electrode to be combined with, and are thus preferable in some cases.

Examples of electrolyte salts include lithium salts, which may be used singly or in combination of two or more. Lithium salts include _LiPF6 , _{LiBF4 , LiAsF6, LiClO4, LiB(C6H5)4 , LiCH3SO3 , LiCF3SO3 , LiN ( SO2CF3 ) 2 ,} LiC( _{SO2CF 3} ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, lithium difluoro[oxolato-O,O']borate, lithium bisoxalate borate, or LiBr. Among them, LiPF ₆ is preferable because it can obtain high ionic conductivity and can further improve cycle characteristics.

(insulating member)
Each of the insulating members 25B1, 25B2, 26B1, and 26B2 has, for example, a rectangular film shape and has an adhesive surface on one side. More specifically, the insulating members 25B1, 25B2, 26B1, 26B2 include a base material and an adhesive layer provided on the base material. In this specification, pressure sensitive adhesion is defined as a type of adhesion. According to this definition, the adhesive layer is considered a type of adhesive layer. Also, the film is defined as including a sheet. For example, insulating tapes are used as the insulating members 25B1, 25B2, 26B1, and 26B2. Examples of materials for the insulating members 25B1, 25B2, 26B1, and 26B2 include polyethylene terephthalate (PET), polyimide (PI), polyethylene (PE), polypropylene (PP), and the like.

(Insulating member provided on positive electrode)
The insulating member 25B1 covers the step portion at the boundary between the positive electrode current collector exposed portion 21D1 and the positive electrode active material layer 21B1 and the positive electrode current collector exposed portion 21D1. The insulating member 25B2 covers the step portion at the boundary between the positive electrode current collector exposed portion 21D2 and the positive electrode active material layer 21B2 and the positive electrode current collector exposed portion 21D2. The insulating member 25B2 also covers the positive electrode lead 31 together with the positive electrode current collector exposed portion 21D2. The boundary between the positive electrode current collector exposed portion 21D1 and the positive electrode active material layer 21B1 and the boundary between the positive electrode current collector exposed portion 21D2 and the positive electrode active material layer 21B2 are formed parallel to the winding axis direction of the electrode body 20. there is

The insulating member 25B1 is provided in a region where the positive electrode current collector exposed portion 21D1 and the negative electrode active material layer 22B2 face each other and in a region where the positive electrode current collector exposed portion 21D1 and the negative electrode current collector exposed portion 22D2 face each other. The insulating member 25B2 is provided in a region where the positive electrode current collector exposed portion 21D2 and the negative electrode active material layer 22B1 face each other and in a region where the positive electrode current collector exposed portion 21D2 and the negative electrode current collector exposed portion 22D1 face each other.

In the positive electrode 21, the outer peripheral edge of the positive electrode current collector exposed portion 21D1 is not covered with the insulating member 25B1 and is exposed, and the outer peripheral edge of the positive electrode current collector exposed portion 21D2 is insulated. It has a positive electrode current collector exposed portion 21D4 that is exposed without being covered by the member 25B2.

(Insulating member provided on the negative electrode)
The insulating member 26B1 covers the portion of the negative electrode current collector exposed portion 22D1 where the negative electrode lead 32 is provided and the portion facing the positive electrode current collector exposed portion 21D4. The insulating member 26B1 may cover substantially the entire portion of the negative electrode current collector exposed portion 22D1 corresponding to one flat portion 20A.

The insulating member 26B2 includes a stepped portion at the boundary 22P between the negative electrode current collector exposed portion 22D2 and the negative electrode active material layer 22B2 (that is, the boundary 22P between the single-sided active material layer forming portion and the negative electrode active material layer 22B2) and the negative electrode current collector. It covers the exposed body portion 22D2. A boundary 22P between the negative electrode current collector exposed portion 22D2 and the negative electrode active material layer 22B2 is formed parallel to the winding axis direction of the electrode body 20. As shown in FIG. The insulating member 26B2 preferably also covers a portion of the negative electrode current collector exposed portion 22D2 that faces the positive electrode current collector exposed portion 21D3. The positive electrode current collector exposed portion 21D3 is positioned closer to the winding outer peripheral side of the electrode body 20 than the boundary 22P, and the negative electrode lead 32 is positioned closer to the winding outer peripheral side of the electrode body 20 than the positive electrode current collector exposed portion 21D3. there is The positive electrode current collector exposed portion 21D3 is located, for example, in the flat portion 20A opposite to the flat portion 20A where the boundary 22P is provided.

The area density of the winding outer peripheral side end portion of the negative electrode active material layer 22B2 provided on the outer peripheral surface 22S2 of the negative electrode 22 is higher than the area density of the portion other than the end portion. Here, "area density" means mass density [g/cm ³ ] per unit area.

In the step of applying the negative electrode mixture slurry, swells are formed at the ends of the negative electrode active material layer 22B2 in the longitudinal direction. When such a raised portion is compression-molded by a roll press or the like, as described above, the area density of the end of the negative electrode active material layer 22B2 on the winding outer peripheral side is the area density of the portion other than the end. higher than In addition, since a large load is likely to be applied to such a raised portion during compression molding using a roll press machine or the like, peeling is likely to occur on the back surface of the raised portion. Therefore, as described above, in the configuration in which the boundary 22P between the negative electrode current collector exposed portion 22D2 and the negative electrode active material layer 22B2 is covered with the insulating member 26B2, the area density of the end portion on the winding outer peripheral side of the negative electrode active material layer 22B2 is , it is particularly effective to be applied to a battery having a higher areal density than the portion other than the end.

The tip of the insulating member 26B2 on the winding outer peripheral side is located within the range of the negative electrode current collector exposed portion 22D2, which exceeds the region facing the positive electrode current collector exposed portion 21D3 and is closer to the winding center side than the negative electrode lead 32. preferably. If the end of the insulating member 26B2 on the winding outer peripheral side exceeds the region facing the positive electrode current collector exposed portion 21D3, contact between the positive electrode current collector exposed portion 21D3 and the negative electrode current collector exposed portion 22D2 is suppressed. can be done. On the other hand, if the tip of the insulating member 26B2 on the winding outer peripheral side is closer to the winding center than the negative electrode lead 32, it is possible to prevent the rigidity of the outer peripheral side end portion of the negative electrode 22 from becoming too high due to the insulating member 26B2. . Therefore, since the negative electrode 22 can be easily collapsed in the “negative electrode end bending step”, in the “separator cutting step” that follows the “negative electrode end bending step”, the negative electrode 22 along with the separators 23A and 23B can be easily bent. You can prevent it from being cut. The details of the “negative electrode end portion bending step” and the “separator cutting step” will be described later.

The thickness of the insulating member 26B2 is preferably 9 μm or more and 25 μm or less. When the thickness of the insulating member 26B2 is 9 μm or more, bending of the negative electrode 22 starting from the boundary 22P between the negative electrode current collector exposed portion 22D2 and the negative electrode active material layer 22B2 in the “step of bending the negative electrode end portion” is effectively prevented. can be suppressed to Therefore, it is possible to effectively prevent the negative electrode active material from falling off from the portion of the negative electrode active material layer 22B1 located on the back surface side of the boundary 22P. Therefore, it is possible to effectively suppress the occurrence of a micro-short due to the dropping of the negative electrode active material. On the other hand, when the thickness of the insulating member 26B2 is 25 μm or less, it is possible to prevent the insulating member 26B2 from becoming excessively thick. Therefore, in the "separator cutting process" which is a process after the "negative electrode end bending process", it is possible to prevent the negative electrode 22 from being cut together with the separators 23A and 23B.

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

(Manufacturing process of positive electrode)
The positive electrode 21 is produced as follows. First, for example, a positive electrode active material, a binder, and a conductive 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) to form a paste. to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector 21A, the solvent is dried, and the positive electrode active material layers 21B1 and 21B2 are formed by compression molding using a roll press machine or the like to obtain the positive electrode 21. At this time, the application position of the positive electrode mixture slurry is adjusted so that the positive electrode current collector exposed portions 21D1 and 21D2 are formed at one end of the positive electrode 21 .

Next, the positive electrode lead 31 is attached to the positive electrode current collector exposed portion 21D2 provided at one end of the positive electrode 21 by welding. Next, insulating members 25B1 and 25B2 are attached to the positive electrode current collector exposed portions 21D1 and 21D2 provided at one end of the positive electrode 21, respectively.

(Manufacturing process of negative electrode)
The negative electrode 22 is produced 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 pasty negative electrode mixture slurry. do. Next, this negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 22A, the solvent is dried, and the negative electrode active material layers 22B1 and 22B2 are formed by compression molding using a roll press machine or the like to obtain the negative electrode 22. At this time, the application position of the negative electrode mixture slurry is adjusted so that the negative electrode current collector exposed portions 22D1 and 22D2 are formed at one end of the negative electrode 22 .

Next, the negative electrode lead 32 is attached to the negative electrode current collector exposed portion 22D1 provided at one end of the negative electrode 22 by welding. Next, insulating members 26B1 and 26B2 are attached to the positive electrode current collector exposed portions 21D1 and 21D2 provided at the other end of the negative electrode 22, respectively.

(Winding process)
As shown in FIG. 3, the electrode body 20 is manufactured by winding the positive electrode 21, the negative electrode 22, and the separators 23A and 23B with a winding core 41 to a prescribed length. The positive electrode 21 and the negative electrode 22 are cut to predetermined lengths in advance.

(Bending process of negative electrode end)
Using a jig (not shown), the outer peripheral edge of the negative electrode 22 is tilted in the direction indicated by the arrow 43 (downward). As shown in FIG. 4, the outer edge of the negative electrode 22 that is laid down in this way includes the boundary 22P between the negative electrode current collector exposed portion 22D2 and the negative electrode active material layer 22B2. Since the insulating member 26B2 covers the boundary 22P, the rigidity of the negative electrode 22 at the boundary 22P can be increased, and the bending of the outer peripheral end of the negative electrode 22 starting from the boundary 22P can be suppressed. Therefore, it is possible to prevent the negative electrode active material from falling off from the portion of the negative electrode active material layer 22B1 located on the back surface side of the boundary 22P. Therefore, it is possible to suppress the occurrence of a minute short circuit caused by falling off of the negative electrode active material. It should be noted that the outer peripheral edge of the negative electrode 22 may be laid down by means other than a jig.

Since the negative electrode lead 32 is attached to the outer peripheral edge of the negative electrode 22 in advance, the negative electrode lead 32 can function as a weight when the outer peripheral edge of the negative electrode 22 is tilted. Therefore, the outer edge of the negative electrode 22 can be easily laid down. Therefore, it is possible to prevent the negative electrode 22 from being cut together with the separators 23A and 23B in the "separator cutting process" that follows the "negative electrode end bending process".

(Separator cutting process)
After the separators 23A and 23B are supported above the electrode body 20 by a supporting member (not shown), the separators 23A and 23B are cut by the cutter 42. FIG. After cutting, the outer edge of the negative electrode 22 , which is the outermost electrode, is fixed with a winding stop tape 24 . Thereby, the electrode body 20 is obtained.

In the state after winding shown in FIG. 3, the negative electrode 22 is attracted to the separator 23A by static electricity. If the separators 23A and 23B are cut in this state, the negative electrode 22 is also cut together with the separators 23A and 23B, and the length of the negative electrode 22 may become shorter than the prescribed length. By cutting the separators 23A and 23B after laying down the outer peripheral edge of the negative electrode 22 as described above, it is possible to prevent the negative electrode 22 from being cut together with the separators 23A and 23B.

(sealing process)
The electrode body 20 is sealed with the case 10 as follows. First, the electrode body 20 and the electrolytic solution are accommodated in the accommodating portion 11 . Subsequently, the positive lead 31 is connected to the positive terminal 13 installed on the case 10 , and the negative lead 32 is connected to the inner surface of the case 10 . Next, the opening of the housing portion 11 is covered with the lid portion 12, and the periphery portions of the housing portion 11 and the lid portion 12 are joined by welding or an adhesive. A battery is thus obtained.

[effect]
In the battery according to the first embodiment, at the outer peripheral edge of the negative electrode 22, the insulating member 26B2 forms the boundary 22P between the negative electrode active material layer 22B2 and the negative electrode current collector exposed portion 22D2 (that is, the single-sided active material layer forming portion and the negative electrode). It covers the boundary 22P) between the active material layers 22B2. As a result, the rigidity of the negative electrode 22 at the boundary 22P can be increased, and bending of the negative electrode 22 starting from the boundary 22P can be suppressed in the “step of bending the negative electrode end portion”. Therefore, it is possible to prevent the negative electrode active material from falling off from the portion of the negative electrode active material layer 22B1 located on the back surface side of the boundary 22P. Therefore, it is possible to suppress the occurrence of a minute short circuit caused by falling off of the negative electrode active material.

A portion of the negative electrode active material layer 22B1 located on the back side of the boundary 22P is particularly susceptible to damage during compression molding of the negative electrode 22 . Therefore, the effect of covering the boundary 22P with the insulating member 26B2 is remarkably exhibited in a battery manufactured by compression-molding the negative electrode 22 using a roll press machine or the like. However, even in a battery in which the negative electrode 22 is not compression-molded by a roll press machine or the like, the above effect is exhibited.

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

An example of the configuration of the electronic device 100 according to the second embodiment of the present invention will be described below with reference to FIG. The electronic device 100 includes an electronic circuit 110 of an electronic device body and a battery pack 120 . The battery pack 120 is electrically connected to the electronic circuit 110 via a positive terminal 123a and a negative terminal 123b. Electronic device 100 may have a configuration in which battery pack 120 is detachable.

Examples of the electronic device 100 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), EL (Electro Luminescence ) displays, electronic paper, etc.), imaging devices (e.g., digital still cameras, digital video cameras, etc.), audio devices (e.g., portable audio players), game devices, cordless phone slaves, e-books, electronic dictionaries, radios, headphones, navigation Systems, memory cards, pacemakers, hearing aids, electric tools, electric shavers, refrigerators, air conditioners, televisions, stereos, water heaters, microwave ovens, dishwashers, washing machines, dryers, lighting equipment, toys, medical equipment, robots, road conditioners Alternatively, a traffic signal or the like may be used, but the present invention is not limited to these.

(electronic circuit)
The electronic circuit 110 includes, for example, a CPU (Central Processing Unit), a peripheral logic section, an interface section, a storage section, and the like, and controls the entire electronic device 100 .

(battery pack)
The battery pack 120 includes an assembled battery 121 and a charge/discharge circuit 122 . Battery pack 120 may further include an exterior material (not shown) that accommodates assembled battery 121 and charging/discharging circuit 122 as necessary.

The assembled battery 121 is configured by connecting a plurality of secondary batteries 121a in series and/or in parallel. The plurality of secondary batteries 121a are connected, for example, in n parallel and m series (n and m are positive integers). Note that FIG. 7 shows an example in which six secondary batteries 121a are connected in two parallel three series (2P3S). As the secondary battery 121a, the battery according to the above-described first embodiment is used.

Here, a case where the battery pack 120 includes an assembled battery 121 configured by a plurality of secondary batteries 121a will be described. may be adopted.

The charging/discharging circuit 122 is a control unit that controls charging/discharging of the assembled battery 121 . Specifically, during charging, the charging/discharging circuit 122 controls charging of the assembled battery 121 . On the other hand, during discharging (that is, when electronic device 100 is in use), charging/discharging circuit 122 controls discharging to electronic device 100 .

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

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited only to these examples.

[Examples 1 to 5]
(Manufacturing process of positive electrode)
A positive electrode was produced as follows. First, a positive electrode mixture was prepared by mixing 91 parts by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder. After that, by dispersing it in N-methyl-2-pyrrolidone, a pasty positive electrode mixture slurry was obtained.

Next, a strip-shaped aluminum foil with a thickness of 19 μm is prepared as a positive electrode current collector, and the positive electrode mixture slurry is applied to both sides of this aluminum foil, dried, and then compression-molded with a roll press to form a positive electrode active material layer. A positive electrode was obtained by forming At this time, the application position of the positive electrode mixture slurry was adjusted so that the positive electrode current collector exposed portion was formed on both sides of one end of the positive electrode. Next, of the positive electrode current collector exposed portions formed on both sides of one end of the positive electrode, the positive electrode lead made of aluminum is welded to the positive electrode current collector exposed portion which becomes the outer surface of the outer peripheral side end after winding. and installed. Next, an insulating tape was attached to each exposed portion of the positive electrode current collector formed on both sides of one end of the positive electrode (see FIG. 2).

(Manufacturing process of negative electrode)
A negative electrode was produced as follows. First, 97 parts by mass of artificial graphite powder as a negative electrode active material and 3 parts by mass of polyvinylidene fluoride as a binder are mixed to form a negative electrode mixture, and then dispersed in N-methyl-2-pyrrolidone to obtain a paste. A negative electrode mixture slurry was obtained.

Next, a strip-shaped copper foil with a thickness of 6 μm is prepared as a negative electrode current collector, and the negative electrode mixture slurry is applied to both sides of the copper foil, dried, and then compression-molded with a roll press to form a negative electrode active material layer. By forming, a negative electrode was obtained. At this time, the application position of the negative electrode mixture slurry was adjusted so that the negative electrode current collector exposed portion was formed on both sides of one end of the negative electrode. Next, of the negative electrode current collector exposed portions formed on both sides of one end of the negative electrode, a nickel negative electrode lead is welded to the negative electrode current collector exposed portion that becomes the inner surface of the outer peripheral end after winding. and installed. Next, an insulating tape was attached to each exposed part of the negative electrode current collector formed on both sides of one end of the negative electrode (see FIG. 2). At this time, the position at which the insulating tape was attached was adjusted so that the insulating tape covered the boundary between the negative electrode active material layer and the exposed portion of the current collector on the outer surface of the outer peripheral edge of the negative electrode. As the insulating tape, as shown in Table 1, those having different thicknesses Tt were used in Examples 1 to 5. It should be noted that the thickness Tt of the insulating tape in Table 1 was measured using a negative electrode taken out by disassembling the battery after manufacturing the battery.

(Preparation step of electrolytic solution)
An electrolyte was prepared as follows. First, ethylene carbonate (EC) and propylene carbonate (PC) were mixed in a mass ratio of EC:PC=1:1 to prepare a mixed solvent. Next, an electrolyte solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt in this mixed solvent so as to have a concentration of 1.0 mol/kg.

(Battery manufacturing process)
A battery was produced as follows (see FIGS. 3 and 4). First, a positive electrode, a negative electrode, and two separators were wound around a winding core to obtain a wound electrode body having a flat shape. A microporous polyethylene film with a thickness of 25 μm was used as the separator. Subsequently, the outer edge of the negative electrode was laid down with a jig. Next, after the separator was supported above the electrode assembly by the supporting member, the separator was cut by a cutter. After that, the outer peripheral edge of the negative electrode, which is the outermost peripheral electrode, was fixed with a winding stop tape. An electrode body was thus obtained. Next, the metal can was sealed by housing the electrode assembly and the electrolytic solution in the housing of the metal can, covering the opening of the housing with the lid, and joining the housing and the peripheral edges of the lid. Thus, the target battery was obtained.

[Comparative Example 1]
The insulating tape is attached so that the insulating tape does not cover the boundary between the negative electrode active material layer and the current collector exposed portion on the outer surface of the outer peripheral edge of the negative electrode, and is positioned on the winding outer peripheral side of this boundary after winding. A battery was obtained in the same manner as in Example 1, except that the alignment position was adjusted.

(Occurrence rate of short circuit voltage abnormality)
The rate of occurrence of short system voltage anomalies was evaluated as follows. After winding the electrode body, while pressing the electrode body, 100 kV was temporarily applied and the resistance was measured to determine the occurrence of short circuit. The ratio of the total number of short-circuited electrode bodies to the number of manufactured electrode bodies was defined as the rate of occurrence of short-circuit system voltage anomalies. The number of electrode bodies manufactured was 100.

(Occurrence rate of defective winding)
The occurrence rate of defective winding was evaluated as follows. In the process of producing a wound electrode body using a winding machine, it was confirmed whether or not the winding of the negative electrode could not be completed and the negative electrode would be cut by the cutter and the machine would stop. The ratio of the total number of electrode bodies for which the apparatus was stopped to the number of products manufactured in the above process was defined as the occurrence rate of defective winding. The number of electrode bodies manufactured was 100.

表１中における“境界”とは、負極の外周側端部の外側面における負極活物質層と集電体露出部の境界を意味する。 Table 1 shows the configurations and evaluation results of the batteries of Examples 1 to 5 and Comparative Example 1.

"Boundary" in Table 1 means the boundary between the negative electrode active material layer and the current collector exposed portion on the outer surface of the outer peripheral edge of the negative electrode.

Table 1 shows the following.
In the batteries of Examples 1 to 5, in which the insulating tape covers the boundary between the negative electrode active material layer and the negative electrode current collector exposed portion, the insulating tape does not cover the boundary between the negative electrode active material layer and the negative electrode current collector exposed portion. Compared with the battery of Example 1, the rate of occurrence of short-circuit system voltage abnormality can be reduced.
In batteries 1 to 3 and 5 in which the thickness of the insulating tape is set to 25 μm or less, the occurrence rate of defective winding can be reduced to 0%.
In batteries 1 to 4 in which the thickness of the insulating tape is 9 μm or more, the rate of occurrence of short circuit voltage abnormality can be reduced to 0%.

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

For example, the configurations, methods, steps, shapes, materials, numerical values, etc., given in the above-described embodiments and examples are merely examples, and different configurations, methods, steps, shapes, materials, numerical values, etc., may be used if necessary. may be used. Also, the configurations, methods, steps, shapes, materials, numerical values, etc. of the above-described embodiments and examples can be combined with each other without departing from the gist of the present invention.

Further, the chemical formulas of the compounds and the like exemplified in the above-described embodiments are representative ones, and the common names of the same compounds are not limited to the described valence numbers. Further, in the numerical ranges described stepwise in the above embodiments, the upper limit or lower limit of the numerical range at one stage may be replaced with the upper limit or lower limit of the numerical range at another stage. In addition, the materials exemplified in the above embodiments can be used singly or in combination of two or more unless otherwise specified.

Also, in the above-described embodiment, the case where the present invention is applied to the negative electrode 22 has been described, but the present invention may be applied to the positive electrode 21 . That is, the configurations of the positive electrode 21 and the negative electrode 22 may be interchanged in the first embodiment described above.

REFERENCE SIGNS LIST 10 case 11 accommodating portion 11A main surface portion 11B wall portion 12 lid portion 20 electrode body 20A flat portion 20B curved portion 21 positive electrode 21A positive electrode current collector 21B1, 21B2 positive electrode active material layer 22 negative electrode 22A negative electrode current collector 22B1, 2B2 negative electrode active material Layers 23A, 23B Separator 24 Winding stop tape 25B1, 25B2, 26B1, 26B2 Insulating member 21D1, 21D2, 21D3, 21D4 Positive electrode current collector exposed part 22D1, 22D2 Negative electrode current collector exposed part 21S1, 22S1 Inside surface 21S2, 22S2 Outside surface 31 positive electrode lead 32 negative electrode lead 41 winding core 42 cutter 100 electronic device 120 battery pack

Claims (4)

a negative electrode current collector having a first surface and a second surface;
a first negative electrode active material layer formed on the first surface;
a wound negative electrode having a second negative electrode active material layer formed on the second surface;
and an insulating member provided on the negative electrode,
A single-sided formation portion in which only the first negative electrode active material layer of the first negative electrode active material layer and the second negative electrode active material layer is formed is formed at the end portion of the negative electrode on the winding outer peripheral side. provided,
The battery, wherein the insulating member covers a boundary between the single-sided forming portion and the second negative electrode active material layer. 2. The battery according to claim 1, wherein the insulating member has a thickness of 9 [mu]m or more and 25 [mu]m or less. 3. The battery according to claim 1, wherein the negative electrode further comprises a negative electrode tab provided at the end of the negative electrode on the winding outer peripheral side. 2. The battery according to claim 1, wherein the area density of the end of the second negative electrode active material layer on the winding outer peripheral side is higher than the area density of the portion other than the end.

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