WO2015046537A1

WO2015046537A1 - Lithium ion secondary battery and method for manufacturing same

Info

Publication number: WO2015046537A1
Application number: PCT/JP2014/075957
Authority: WO
Inventors: 志村　健一
Original assignee: 日本電気株式会社
Priority date: 2013-09-30
Filing date: 2014-09-29
Publication date: 2015-04-02
Also published as: JPWO2015046537A1

Abstract

A lithium ion secondary battery (19), wherein a plurality of positive electrodes (31) and a plurality of negative electrodes (21) are laminated with separators being interposed therebetween, comprises a positive electrode tab (63) which is electrically connected to the plurality of positive electrodes (31) and is led out to the outside of the battery and a negative electrode tab (53) which is electrically connected to the plurality of negative electrodes (21) and is led out to the outside of the battery. The positive electrode (31) has a collector foil exposed portion (33) that is not coated with an active material. The exposed portion (33) is covered with an insulating material, and a portion of the positive electrode tab (63) arranged within the battery is covered with an insulating material.

Description

Lithium ion secondary battery and manufacturing method thereof

The present invention relates to a lithium ion secondary battery with little decomposition of an electrolytic solution and a manufacturing method thereof.

With the rapid market expansion of notebook computers, mobile phones, hybrid cars, etc., energy storage devices such as capacitors and lithium ion secondary batteries are being actively researched. In particular, lithium ion secondary batteries have a higher energy density because they have a higher operating voltage and a larger current capacity than nickel / cadmium batteries and nickel / hydrogen batteries.

Since a lithium ion secondary battery has a high operating voltage, an electrolytic solution using water as a solvent cannot be used because electrolysis occurs. Therefore, those obtained by dissolving like LiPF ₆ and LiBF ₄ in a non-aqueous solvent obtained by mixing a low chain carbonate having a high dielectric constant cyclic carbonate and the viscosity have been used as an electrolyte.

An aluminum alloy foil obtained by adding an additive element to aluminum is used for a positive electrode current collector foil of a lithium ion secondary battery. Hereinafter, it is also simply referred to as an aluminum foil. A natural oxide film (aluminum oxide film) covering the surface of the aluminum foil can prevent corrosion in the electrolytic solution. Furthermore, during the first charge, the surface of the aluminum foil reacts with PF ₆ ⁻ and BF ₄ ^— in the electrolytic solution to form an aluminum fluoride AlF ₃ coating having higher corrosion resistance than aluminum oxide.

Since aluminum oxide is an insulator, it should be insulated between the aluminum foil and the active material layer applied on its surface. However, in practice, sufficient electrical conductivity exists between the aluminum foil and the active material layer, as shown by the fact that the aluminum foil is used as a positive electrode current collector foil of a lithium ion battery. It is considered that a defect exists in the natural oxide film as a reason for showing electrical conductivity while being covered with the natural oxide film. Further, since the natural oxide film of aluminum is as thin as several nanometers, it is considered that a tunnel current flows.

Also, when an aluminum fluoride film is formed on the aluminum oxide by a reaction between aluminum and a supporting salt, it is considered that a current flows using defects in the film as a conductive path.

The non-aqueous solvent has a wider potential window indicating the range in which no oxidation-reduction reaction occurs with the electrode than the aqueous electrolyte solution. However, in a lithium ion battery having a voltage exceeding 4 V, oxidation or reduction reaction on the positive and negative electrode surfaces cannot be ignored. . When the solvent decomposes, problems such as increase in the internal resistance of the battery due to changes in the composition of the solvent and accumulation of decomposition products on the electrode surface and inhibition of Li ion conduction in the electrode stack due to the generated gas occur. . In order to prevent decomposition of the electrolytic solution on the electrode surface, an additive that decomposes during the charging process to form a film on the active material surface of the positive electrode or the negative electrode is effective. Although this film allows Li ions to pass through, it does not have electronic conductivity, so that the decomposition of the electrolyte solution on the surface of the electrode active material can be suppressed. For example, thiophene is an additive that forms a film on the surface of the positive electrode active material. Thiophene is oxidized and polymerized on the surface of the positive electrode active material to form a film. In addition, vinylene carbonate is known as an additive for forming a film on the surface of the negative electrode active material.

However, there are portions where potential is applied inside the battery in addition to the surface of the electrode active material. For example, it is the surface of the current collector foil extending portion for taking out current from the electrode or the surface of a tab for taking out current from the battery. Therefore, even when a film is formed on the surface of the electrode active material by the additive, the electrolytic solution may be decomposed.

Patent Document 1 (Japanese Patent Laid-Open No. 2011-216360) discloses a technique for suppressing the decomposition of the electrolytic solution in the exposed metal portion electrically connected to the electrode. Holding the separator by increasing the Gurley-type air permeability of the separator at the portion located between the positive electrode core exposed portion and the negative electrode plate of the spiral electrode body in which the positive electrode plate and the negative electrode plate are wound via the separator. The amount of the electrolytic solution to be reduced is reduced, and the decomposition of the electrolytic solution due to the potential applied to the exposed portion of the positive electrode core is suppressed.

However, since the method of Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-216360) reduces the amount of the electrolytic solution relative to other places in the battery, the contact between the electrolytic solution and the exposed metal portion is greatly increased. It is difficult to suppress. In addition, since the electrolytic solution continues to be supplied through the separator to the contact portion with the exposed metal portion, there is a problem that the electrolytic solution continues to be decomposed.

Patent Document 2 (Japanese Patent Laid-Open No. 11-007962) describes a technique for preventing corrosion of aluminum by forming a film mainly composed of a fluorine compound on the surface of aluminum electrically connected to the positive electrode. ing. For example, after heating the aluminum foil in fluorine gas and fluorinating the surface, the positive electrode active material is applied. However, if there is no electrical conductivity between the current collector foil and the active material, it will not function as a battery, so the aluminum fluoride disclosed in Patent Document 2 has electronic conductivity. Therefore, even if the aluminum fluoride disclosed in Patent Document 2 is formed in the extending portion of the aluminum current collector foil, electrons are transferred and oxidative decomposition of the electrolytic solution cannot be prevented.

Patent Document 3 (Japanese Patent Laid-Open No. 2001-084993) describes a technique for forming an oxide film on the surface of a tab for taking out current from the inside of the battery to the outside. Patent Document 4 (Japanese Patent No. 4298883) describes a method for producing aluminum hydrate on the surface of an aluminum tab by boiling in hot water or using hot steam.

The techniques of Patent Document 3 and Patent Document 4 form an oxide film or aluminum hydrate at a place where the tab is sandwiched and sealed between the laminate films, and prevents the surface of the tab from being corroded by the electrolytic solution. This is intended to maintain the adhesion between the tab and the laminate. Since the oxide film and the aluminum hydrate are insulative, decomposition of the electrolyte solution can be prevented. However, in the techniques of Patent Document 3 and Patent Document 4, an oxide film or Since aluminum hydrate is not formed, decomposition of the electrolyte in this region cannot be prevented.

Patent Document 5 (Japanese Patent Laid-Open No. 62-61268) and Patent Document 6 (Japanese Patent Laid-Open No. 2013-012468) describe that a portion of a terminal material or tab that is sealed with a laminate outer package is covered with a resin. . These are for increasing the adhesion between the terminal material or tab and the laminate outer package. Since the portion of the terminal material or tab covered with the resin is insulated from the electrolytic solution, the electrolytic solution does not electrolyze. However, since the metal is exposed or only a very thin oxide film on the order of nanometers exists in a portion not covered with resin, electrolysis of the electrolytic solution cannot be prevented.

Patent Document 5 also describes a case where the resin covering the terminal material extends in the battery internal direction. This is to prevent the terminals from coming into contact with electrode plates having different polarities, and does not completely prevent the conductor of the terminal material from coming into contact with the electrolytic solution. Further, in Patent Document 5, the surface of the electrode plate opposite to the surface on which the positive electrode mixture is applied is exposed with metal, and there is a risk of oxidative decomposition of the electrolytic solution.

JP 2011-216360 A JP-A-11-007962 JP2001 / 084993A No. 4298883 JP 62-61268 A JP2013-012468

As described above, none of Patent Documents 1 to 6 can sufficiently electrically insulate the metal surfaces of the electrodes and tabs of the lithium ion battery (particularly, the positive electrode current collector foil and the positive electrode tab) from the electrolytic solution.

Accordingly, an object of the present invention is to suppress the decomposition of the electrolyte solution of the lithium ion secondary battery, and to reduce the gas generation inside the battery and the composition deviation of the electrolyte solvent, and to provide a long-life lithium ion secondary battery and a manufacturing method thereof Is to provide.

The lithium ion secondary battery of the present invention is electrolyzed by subjecting the exposed portion of the positive electrode inside the battery and the surface of the metal electrically connected to the positive electrode to oxidation treatment or coating with an insulating material or an insulating film. It electrically insulates from the liquid and suppresses oxidative decomposition of the electrolytic solution. In addition, the exposed portion of the negative electrode and the surface of the metal electrically connected to the negative electrode are electrically insulated from the electrolytic solution by oxidation treatment or coating with an insulating material or insulating film. Inhibits reductive decomposition.

In order to achieve the above object, a lithium ion secondary battery according to an embodiment of the present invention is provided.
A plurality of positive electrodes and negative electrodes, which are electrodes, are stacked via a separator, and are connected to the plurality of positive electrodes and drawn to the outside of the battery, and are electrically connected to the plurality of negative electrodes and drawn to the outside of the battery. A lithium ion secondary battery having a negative electrode tab,
The positive electrode has an exposed portion of a current collector foil not coated with an active material,
At least a part of the exposed portion is covered with an insulating material, and a portion of the positive electrode tab that is disposed inside the battery is covered with an insulating material.

In the present specification, the phrase “covered with an insulating material” is not necessarily limited to a form in which the entire member is completely covered, but as described later with reference to FIG. Includes a mode in which only the main surface (front surface and back surface) is covered without being insulated. This is because the end surface has a relatively small influence on the oxidative decomposition of the electrolytic solution even if the end surface has a small exposed area with respect to the main surface and is not insulated.

According to the present invention, it is possible to prevent electrolysis of the electrolytic solution on the surface of the metal member electrically connected to the electrode in the lithium ion secondary battery and the accompanying gas generation, so that the lithium ion secondary battery Can improve long-term reliability.

1 is an exploded perspective view schematically showing a lithium ion secondary battery according to an embodiment of the present invention. It is a top view which shows typically the structure of the electrode laminated body in one form of this invention. (A) It is a schematic diagram of the negative electrode in one form of this invention. (B) It is a schematic diagram of the positive electrode in one form of this invention. It is an example of the other shape of an electrode. It is a top view which shows typically the lithium ion secondary battery of other embodiment of this invention. It is a perspective view which shows the shape of an electrode extending | stretching part or an electrode tab typically.

[First embodiment]
<Basic configuration of lithium ion secondary battery>
The structure of the electrode body of the lithium ion secondary battery is roughly classified into a wound type and a laminated type. The present invention can be applied to both, but is preferably applied to a laminated type. As a form of the lithium ion secondary battery to which the present invention can be applied, a laminated laminate type in which the electrode laminate is housed in an exterior body made of a laminate film of a resin film and a metal film is suitable.

Hereinafter, a laminated laminate type secondary battery will be described as an example. First, the overall configuration of the lithium ion secondary battery of the present embodiment will be described with reference to FIGS. 1 to 4, and then each part will be described in detail.

In the following description, the current collector foils of the positive electrode and the negative electrode have “stretched portions” (FIG. 3, details will be described later), and the stretched portions are “exposed portions” where no active material is applied. Although an aspect is demonstrated, this invention is not necessarily limited to this. For example, the active material may be applied to a part of the stretched part, or conversely, the active material may be applied to a part of the area other than the stretched part. Also good. That is, in the present invention, it is only necessary that the “exposed portion” to which the active material is applied is covered with an insulating material. More specifically, it is sufficient that at least a part of the exposed portion is covered with an insulating material.

As illustrated in FIG. 1, the lithium ion secondary battery 1 of the present embodiment includes an electrode stack 10, and a positive electrode tab 63 and a negative electrode tab 53 (hereinafter, positive electrode and negative electrode are not distinguished from each other). And an electrode stack 10 and an exterior body that houses part of the electrode tab together with the electrolyte.

The electrode laminate 10 is obtained by laminating a plurality of positive electrodes and a plurality of negative electrodes with a separator interposed therebetween. Although not limited, the electrode laminated body 10 may be a flat rectangular parallelepiped shape whose outline is a rectangle (rectangle) in a plan view as viewed from above.

As shown in FIG. 3A, the negative electrode 21 is formed in a rectangular shape in a plan view, and a region 22 (active material application surface) on which an active material is applied, and a negative electrode current collector foil extending from the peripheral portion thereof Part 23 (the negative electrode active material is not applied). In this example, the extending portion 23 of the negative electrode is provided at a position on the left side in the left-right direction in FIG.

As shown in FIG. 3B, the positive electrode 31 is formed in a substantially symmetrical shape with the negative electrode 21 as an example. That is, the positive electrode 31 is also formed in a rectangular shape in a plan view, and an active material application surface 32 (active material application surface) 32 and a positive electrode current collector foil extending portion 33 extending from the peripheral portion (the negative electrode active material is applied). Not).

The positive electrode extending portion 33 is formed on the opposite side to the negative electrode extending portion 23 (a position on the right side in the left-right direction in FIG. 1B) so as not to overlap the negative electrode extending portion 23 when the positive electrode and the negative electrode are laminated. ing.

Regarding the laminated structure of the positive electrode and the negative electrode, the negative electrode active material application surface 22 has a larger area than the positive electrode active material application surface 32, and therefore the positive electrode active material application surface 32 is relative to the separator 25 (see FIG. 2). It is good also as a structure accommodated inside the negative electrode active material application surface 22 to do.

In addition, although detailed illustration is abbreviate | omitted in drawing, even if the several positive electrode extending | stretching part and several negative electrode extending | stretching part which extended from each electrical power collector were each gathered together by the conventionally well-known system, respectively. Good. The electrode tab is electrically connected to a part of the extended portion collected in this way. For example, in the state of FIG. 1, the

electrode tabs

53 and 63 may be connected to the lower surface side of the plurality of extending

portions

23 and 33.

Ultrasonic welding may be used for connection between the electrode tab and the extended portion. Part of the

electrode tabs

53 and 63 is configured to protrude from the exterior body. A heat sealing resin 15 (see FIG. 1) may be provided at a portion of the

electrode tabs

53 and 63 sandwiched between the laminate outer bodies.

As shown in FIG. 1, the laminate outer package may be surrounded by two

outer packaging materials

11 and 12 from both sides in the thickness direction. The

exterior materials

11 and 12 may be a laminate film having flexibility, and an electrolytic solution is also included in the exterior body formed by the exterior material.

Of course, the contour shape of the electrode laminate 10 and the active material application surfaces 22 and 32 of each electrode may be any shape such as a square or a polygon other than a rectangle. Various changes can be made to the extending direction of the extending portions 23 and 33 (the extending direction of the electrode tab). In the example of FIG. 1, both electrode tabs are drawn out in the rearward direction of the drawing, but one electrode tab and the other electrode tab may be reversed.

<Negative electrode>
The negative electrode active material in the present embodiment is not particularly limited. For example, the carbon material (a) that can occlude and release lithium ions, the metal (b) that can be alloyed with lithium, and the lithium ions are occluded and released. The metal oxide (c) etc. which can be mentioned.

Examples of the carbon material (a) include graphite, amorphous carbon, carbon nanotube, or a composite thereof. Here, carbon with high crystallinity has high electrical conductivity, and is excellent in adhesiveness and voltage flatness with a negative electrode current collector made of a metal such as copper. On the other hand, since amorphous carbon having low crystallinity has a relatively small volume expansion, it has a high effect of relaxing the volume expansion of the entire negative electrode, and deterioration due to non-uniformity such as crystal grain boundaries and defects hardly occurs.

Examples of the metal (b) include Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, or alloys of two or more thereof. It is done. Moreover, you may use these metals or alloys in mixture of 2 or more types. These metals or alloys may contain one or more non-metallic elements.

Examples of the metal oxide (c) include silicon oxide, aluminum oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, and composites thereof. In this embodiment, it is preferable that tin oxide or silicon oxide is included as a negative electrode active material, and it is more preferable that silicon oxide is included. This is because silicon oxide is relatively stable and hardly causes a reaction with other compounds. In addition, one or more elements selected from nitrogen, boron, and sulfur may be added to the metal oxide (c), for example, 0.1 to 5% by mass. By carrying out like this, the electrical conductivity of a metal oxide (c) can be improved.

The negative electrode current collector is preferably aluminum, nickel, stainless steel, chromium, copper, silver, or an alloy thereof in view of electrochemical stability. Examples of the shape include foil, flat plate, and mesh.

(Insulation of the negative electrode extension)
In the present embodiment, the negative electrode extension 23 (see FIGS. 1 to 3) is preferably covered with an insulating material. In FIG. 2, a state in which the extending portion 23 of the negative electrode is covered with the insulating material 16 is illustrated.

As such a coating with an insulating material,
-Melt application of thermoplastic resin such as polyethylene and polypropylene,
-Application and drying / curing of resin material dissolved in solvent,
-It can be done in one or a combination of resin film or tape sticking.

As illustrated in FIG. 6, the insulating material is preferably formed on the front surface 5a, the back surface 5b, and the cut surfaces (end surfaces) 5c, 5d, and 5e of the negative electrode extending portion. However, since the areas of the front surface 5a and the back surface 5b are larger than the areas of the cut surfaces 5c to 5e, only these both surfaces may be covered. The same applies to the case where an insulating material is formed on the extending portion of the positive electrode and each electrode tab described later.

In this specification, when the extending portion / electrode tab says “the insulating material is covered”, the insulating material is applied only to the front surface 5a and the back surface 5b of the extending portion or the electrode tab. The state in which is formed is also included.

(Insulation of the positive electrode extension)

The material of the positive electrode current collector may be aluminum or an alloy containing aluminum as a main component, and examples thereof include a foil shape, a flat plate shape, and a mesh shape.

The positive electrode 31 may be one that has been cut into a predetermined dimension as shown in FIG. This is because an oxide film (see reference numeral 26 in FIG. 2) is formed on the surface of the extending portion 33, thereby providing insulation. The oxidation treatment may be performed before producing the electrode laminate. As in the case of the extending portion of the negative electrode described above, it is preferably formed on the front surface 5a, the back surface 5b, and the respective cut surfaces (end surfaces) 5c, 5d, and 5e (see FIG. 6). Specifically, it is more preferable that an oxide film is formed by oxidation treatment on aluminum exposed on the cut surface (end surface) of the positive electrode. However, you may make it coat | cover only the front surface 5a and the back surface 5b.

In order to prevent the positive electrode active material from absorbing moisture, oxidation by dry process with oxygen or ozone is preferable to oxidation with hot water or hot steam.

The positive electrode active material has a layered structure such as LiMnO ₂ , LixMn ₂ O ₄ (0 <x <2), Li ₂ MnO ₃ , Li _x Mn _1.5 Ni _0.5 O ₄ (0 <x <2). Lithium manganate or lithium manganate having a spinel structure, LiCoO ₂ , LiNiO ₂ or a part of these transition metals replaced with other metals, LiNi _1/3 Co _1/3 Mn _1/3 O _2, etc. Lithium transition metal oxides whose specific transition metals are less than half, those in which these lithium transition metal oxides have an excess of Li over the stoichiometric composition, those having an olivine structure such as LiFePO ₄ , etc. It is done. Further, these metal oxides were partially substituted with Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, etc. Materials can also be used. A positive electrode active material can be used individually by 1 type or in combination of 2 or more types.

Also, radical materials or the like can be used as the positive electrode active material. A conductive auxiliary material may be added to the coating layer of the positive electrode active material for the purpose of reducing impedance. Examples of the conductive auxiliary material include carbonaceous fine particles such as carbon black and acetylene black.

In addition, the shape of the negative electrode or the positive electrode is not limited to that shown in FIG. 3. For example, it is only necessary that the extending portion of the current collector foil exists. For example, although the extending

portions

23 and 33 are disposed in the vicinity of the side edge in the example of FIG. 3, the extending portion may be disposed at a position slightly shifted inward from the side edge. Moreover, the shape of the extending part of the positive electrode and the extending part of the negative electrode may be different.

Also, the configuration shown in FIG. 4 can be taken. In the case of this configuration, the positive electrode and the negative electrode are laminated via separators so that one current collecting foil extending portion 42 is alternately opposite to the other current collecting foil extending portion 42 without overlapping.

<Separator>
The separator has a role of insulating the positive electrode plate and the negative electrode plate and holding lithium electrolyte and conducting lithium ions between the positive electrode and the negative electrode. Generally, a polyolefin-based microporous film having a thickness of about 15 μm to 25 μm is used. In addition, a cellulose nonwoven fabric and a synthetic fiber nonwoven fabric are used. In the lithium ion secondary battery of the present embodiment, any separator that is used in a normal lithium ion secondary battery can be used without any particular limitation.

<Electrolyte>
As the electrolytic solution used in the present embodiment, a non-aqueous electrolytic solution including a lithium salt and a non-aqueous solvent that dissolves the lithium salt can be used.

As the non-aqueous solvent, an aprotic organic solvent such as carbonate ester (chain or cyclic carbonate), carboxylic acid ester (chain or cyclic carboxylic acid ester), and phosphate ester can be used. Or what substituted some hydrogen atoms of these compounds by the fluorine atom is mentioned.

Examples of carbonate solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC); dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. (EMC), chain carbonates such as dipropyl carbonate (DPC); and propylene carbonate derivatives.

Examples of the carboxylic acid ester solvent include aliphatic carboxylic acid esters such as methyl formate, methyl acetate, and ethyl propionate; and lactones such as γ-butyrolactone.

Among these, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), dipropyl carbonate Carbonate esters (cyclic or chain carbonates) such as (DPC) and those in which some hydrogen atoms of these compounds are substituted with fluorine atoms are preferred.

Examples of the phosphate ester include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, trioctyl phosphate, triphenyl phosphate, and the like.

Other solvents that can be contained in the non-aqueous electrolyte include, for example, ethylene sulfite (ES), propane sultone (PS), butane sultone (BS), dioxathilane-2,2-dioxide (DD), and sulfolene. 3-methylsulfolene, sulfolane (SL), succinic anhydride (SUCAH), propionic anhydride, acetic anhydride, maleic anhydride, diallyl carbonate (DAC), dimethyl 2,5-dioxahexanoate, 2,5 Dimethyl hexane hexanoate, furan, 2,5-dimethylfuran, diphenyl disulfide (DPS), dimethoxyethane (DME), dimethoxymethane (DMM), diethoxyethane (DEE), ethoxymethoxyethane, chloroethylene carbonate , Dimethyl ether, methyl Tyl ether, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl butyl ether, diethyl ether, phenyl methyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), tetrahydropyran (THP), 1,4-dioxane (DIOX), 1,3-dioxolane (DOL), methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, methyl difluoroacetate, methyl propionate, ethyl propionate, propyl propionate, methyl formate , Ethyl formate, ethyl butyrate, isopropyl butyrate, methyl isobutyrate, methyl cyanoacetate, vinyl acetate, diphe Rudisulfide, dimethylsulfide, diethylsulfide, adiponitrile, valeronitrile, glutaronitrile, malononitrile, succinonitrile, pimonitrile, suberonitrile, isobutyronitrile, biphenyl, thiophene, methyl ethyl ketone, fluorobenzene, hexafluorobenzene, carbonate electrolyte, Glyme, ether, acetonitrile, propiononitrile, γ-butyrolactone, γ-valerolactone, dimethyl sulfoxide (DMSO) ionic liquid, aliphatic carboxylic acid esters such as phosphazene, methyl formate, methyl acetate, ethyl propionate, or the like A compound in which a part of hydrogen atoms of a compound is substituted with a fluorine atom.

As the supporting salt in this embodiment, LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN ( CF ₃ SO _{₂₎ 2} normal lithium salt which can be used in lithium ion batteries or the like can be used. The supporting salt can be used alone or in combination of two or more.

<Tab>
(Positive electrode tab)
For the positive electrode tab 63, aluminum or an alloy containing aluminum as a main component can be used. An oxide film is formed on the surface of at least the portion of the positive electrode tab 63 disposed inside the battery. This oxide film may be, for example, a film formed by oxidizing the surface of aluminum.

The oxidation treatment may be performed before the positive electrode tab is connected to the laminate. In addition, since the area | region arrange | positioned outside the exterior body of a positive electrode tab does not contact electrolyte solution, it is not necessary to perform an oxidation process.

The positive electrode tab 63 can be connected to the positive electrode extension portion 33 by ultrasonic welding, but the oxide film on the surface of the positive electrode current collector foil extension portion 33 and the oxide film on the surface of the positive electrode tab 63 are destroyed during ultrasonic welding. Therefore, both members are electrically connected.

On the other hand, in the case of ultrasonic welding, traces of the horn and anvil of the ultrasonic welder remain on the positive electrode extending portion 33 and / or the positive electrode tab 63, but an insulating material is provided so as to cover at least the trace portion. It is also preferable. In this case, the coating with insulating material is:
-Melt application of thermoplastic resin such as polyethylene and polypropylene,
-Application and drying / curing of resin material dissolved in solvent,
-Pasting sheet-like members such as resin films and tapes
Can be done in one or a combination.

Regarding the application of the resin film or tape, such a sheet-like member may be cut to a size that can be applied to one surface of the extending portion of the current collector foil or one surface of the electrode tab. Good. As another aspect, a tape-like member may be wound (or sandwiched) around the welded portion. As still another aspect, the sheet may be sandwiched from above and below by two sheet-like members.

(Negative electrode tab)
The negative electrode tab may be made of copper or nickel. In the present embodiment, the negative electrode tab is not oxidized, but the portion of the metal exposed portion of the negative electrode tab that is disposed inside the battery is covered with an insulating material. Specifically, in this case as well, as described above, coating with an insulating material is performed by applying a thermoplastic resin such as polyethylene or polypropylene, applying and drying / curing a resin material dissolved in a solvent, a sheet such as a resin film or a tape. It can be carried out by one or a combination of pasting of the shaped members.

The covering of the insulating material on the positive electrode tab and the negative electrode tab is also formed on the front surface 5a, the back surface 5b, and the cut surfaces (end surfaces) 5c, 5d, and 5e of the tab, as in the case of the above-described extending portion. Although it is preferable (refer FIG. 6), the form which covers only the front surface 5a and the back surface 5b may be sufficient.

<Exterior body>
The exterior body can be appropriately selected as long as it is stable to the electrolytic solution and has a sufficient water vapor barrier property. For example, in the case of a laminated laminate type secondary battery, it is preferable to use a laminate film made of aluminum and resin for the exterior body. An exterior body may be comprised with a single member and may be comprised combining several members.

[Second Embodiment]
In the second embodiment of the present invention, the oxidation of the positive electrode and the oxidation treatment of the positive electrode tab performed in the first embodiment are not performed. The other positive electrode and negative electrode materials, electrolytic solution, separator, and outer package are the same as those in the first embodiment.

FIG. 5 shows a schematic diagram of the laminate, the negative electrode tab, and the positive electrode tab in the second embodiment. The electrode laminate 10 is produced basically in the same manner as in the first embodiment except that the positive electrode and the positive electrode tab are not oxidized. However, since the oxide film is not formed, the extending portion is entirely covered with the insulating material 16.

The ultrasonic welded positive electrode current collector foil extending portion and the exposed metal portion of the positive electrode tab 63 disposed inside the battery are covered with an insulating material. Insulating the exposed metal part of the positive electrode from the electrolytic solution suppresses oxidative decomposition of the electrolytic solution.

Similarly, the negative electrode current collector foil extending portion and the exposed metal portion of the negative electrode tab 53 disposed inside the battery are also covered with an insulating material. Insulating the metal exposed portion of the negative electrode from the electrolytic solution suppresses reductive decomposition of the electrolytic solution.

As the insulating material, heat, for example, melt coating of plastic polyethylene or polypropylene resin is used. In addition, an insulating and electrolyte-resistant resin can be used.

As described above through the two embodiments, according to one aspect of the present invention, at least a part of the exposed metal portion such as the positive electrode extension portion, the positive electrode tab, the negative electrode extension portion, and the negative electrode tab is an insulating material. Since it is covered, the contact of the metal and electrolyte solution in the part is substantially prevented, As a result, decomposition | disassembly of the electrolyte solution in a battery is suppressed.

Even if only a part of the exposed portion (metal exposed portion) that is not coated with the active material is covered with an insulating material, the electrolytic solution is compared with a configuration in which the exposed portion is not insulated at all. Such an arrangement is also preferable as one embodiment of the present invention. As an example of the aspect “at least a part of the exposed portion is covered”, the area of the exposed portion (when both surfaces of the foil are exposed, the total exposed area of both surfaces. The area of the end surface of the foil is not included). 10) or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more is preferably covered. When both surfaces of the foil are exposed, at least one exposed portion may be entirely covered.

In the above description, the negative electrode extension portion and the portion of the negative electrode tab that are disposed inside the battery are covered with an insulating coating. However, if the nonaqueous electrolyte is strong in reducing resistance and does not undergo reductive decomposition, the negative electrode There is no need for side insulation. By covering the exposed metal portion electrically connected to the positive electrode, oxidative decomposition of the electrolytic solution can be suppressed.

In the above description, the extending

portions

23 and 33 have been described as exposed portions where the active material is not applied, but as described above, the shape of the exposed metal portion does not necessarily match the shape of the extending portion.

The description of each part described above can be made as appropriate as long as it does not depart from the content of the present invention.

(Appendix)
This specification discloses the following invention:
1. A plurality of positive electrodes and negative electrodes, which are electrodes, are stacked via a separator, and are connected to the plurality of positive electrodes and drawn to the outside of the battery, and are electrically connected to the plurality of negative electrodes and drawn to the outside of the battery. A lithium ion secondary battery having a negative electrode tab,
The positive electrode has an exposed portion of a current collector foil not coated with an active material,
A lithium ion secondary battery in which at least a part of the exposed portion is covered with an insulating material, and a portion of the positive electrode tab disposed inside the battery is covered with an insulating material.

2. The negative electrode has an exposed portion of the current collector foil to which no active material is applied,
At least a part of the exposed portion of the negative electrode is covered with an insulating material, and a portion of the negative electrode tab that is disposed inside the battery is covered with an insulating material.
The lithium ion secondary battery described above.

3. The insulating material covering the exposed portion of the positive electrode includes an oxide film of the positive electrode material,
The insulating material covering the positive electrode tab includes an oxide film of the material of the tab;
The lithium ion secondary battery described above.

4). The insulating material covering the exposed portion of the positive electrode;
The insulating material covering the positive electrode tab;
The insulating material covering the exposed portion of the negative electrode; and
The insulating material covering the negative electrode tab;
The lithium ion secondary battery according to claim 2, wherein at least one of comprises an insulating organic polymer material.

5. The lithium ion secondary battery as described above, wherein the organic polymer material is a sheet-like member.

6). The lithium ion secondary battery according to the above, wherein the exposed portion is a stretched portion of the current collector foil.

7). A plurality of negative electrodes and positive electrodes, which are electrodes, are stacked via a separator, are positively connected to the plurality of positive electrodes and drawn out of the battery, and are electrically connected to the plurality of negative electrodes and drawn out of the battery. A method for producing a lithium ion secondary battery having a negative electrode tab,
(A) applying an active material to a part of the positive electrode;
(B) Thereafter, before the step of laminating the electrode and the separator, the positive electrode is exposed to an oxidizing atmosphere to oxidize the exposed portion of the positive electrode where the active material is not applied, and at least a portion thereof is an oxide film. Forming a step;
(C) connecting the exposed portion of the positive electrode and the positive electrode tab;
A method for producing a lithium ion secondary battery.

8). In the step (c), the exposed portion and the positive electrode tab are connected by ultrasonic welding,
further,
(D) The method for producing a lithium ion secondary battery according to the above, which includes a step of coating with an insulating material so as to cover a trace formed by the ultrasonic welding.

9. further,
(E) After connecting the exposed portion and the tab,
The method for producing a lithium ion secondary battery as described above, further comprising a step of covering at least the exposed portion and a portion of the positive electrode tab disposed inside the battery with an insulating material.

The secondary battery according to one embodiment of the present invention can be used for a power storage system. The scale of the power storage system is not limited in any way, but includes a power supply unit having at least one secondary battery, a control device for monitoring and controlling the charge / discharge, and the like. As such a power storage system, for example, a backup power source may be used, and various types such as for large facilities, offices, and homes can be used. As another aspect, a secondary battery can be used for an electric vehicle. The electric vehicle includes a power supply unit having at least one secondary battery, a control device that performs monitoring / control of charge / discharge, and the like.

Next, the present invention will be specifically described with reference to examples.

<Example 1>
<Production of battery>
(Preparation of positive electrode)
As a positive electrode active material, 93% by mass of LiNi _0.5 Mn _1.5 O ₄ powder, which is a spinel-type metal composite oxide and operates at a potential exceeding 4.5 V with respect to metallic lithium, carbon as a conductive assistant 3% by mass of black and 4% by mass of polyvinylidene fluoride as a binder were mixed and dispersed in N-methylpyrrolidone (NMP) to form a slurry. Then, it apply | coated to the aluminum foil (thickness 20 micrometers) as a positive electrode electrical power collector, and was heat-dried. In addition, the slurry is not apply | coated to the location which forms a collector foil extending part.

After applying the active material on both sides of the current collector, the electrode was pressed to produce a thickness of 80 μm after the treatment. Further, this was punched into a shape in which the stretched portion protruded. The active material application portion had a width of 46 mm and a length of 50 mm. The extending part was 20 mm long and 8 mm wide along the long side direction of the active material application part.

After punching into the above shape, the positive electrode was oxidized to form an oxide film on the surface of the stretched portion (including the cut surface). Specifically, the punched positive electrodes were arranged on an alumina sintered plate so that the positive electrode current collector foil extending portion did not overlap with other electrodes, and this was put in a vacuum chamber and the pressure was reduced to 1 hPa. Next, oxygen gas was introduced into the vacuum chamber up to 500 hPa and held for 30 minutes.

When the electrical resistance of the positive electrode current collector foil stretched part before the oxidation treatment was measured by applying a terminal to the surface of one side of the foil by the DC 4-terminal method, the sheet resistance was 5 mΩ / sq. Below, the resistance of the surface oxide film could not be estimated.

This is presumably because current flowed through the current collector foil body because the electric resistance of the oxide film formed on the surface of the current collector extending portion was low. As a result of measuring the resistance of the positive electrode current collector foil after the oxidation treatment, the resistance in the film thickness direction of the surface oxide film is estimated to be 1 × 10 ⁻³ Ωcm ^{2 as} a product of the resistance and the area, and the resistance on the surface There was a layer.

In the present application, the “oxide film” formed on the current collector or the electrode tab refers to one having a resistance value of about 1 × 10 ⁻³ Ωcm ² or more. On the other hand, the resistance value of the natural oxide film is generally about 1 × 10 ⁻⁵ Ωcm ² or less.

(Positive electrode tab)
The tab of the positive electrode was made of aluminum, and the surface was oxidized under the same conditions as the oxidation of the positive electrode. Further, a heat seal resin made of polypropylene was provided near the center of the positive electrode tab, and the exterior body was sealed so as to sandwich the heat seal resin.

(Preparation of negative electrode)
As a negative electrode active material, 95% by mass of artificial graphite powder and 5% by mass of polyvinylidene fluoride as a binder are mixed and dispersed in NMP to form a slurry, which is then applied to a copper foil having a thickness of 10 μm as a negative electrode current collector. And heat dried.

In addition, the slurry is not apply | coated to the location which forms a collector foil extending part. After the active material was applied to both sides of the current collector, the electrode was pressed to produce a thickness of 65 μm after the treatment. Further, this was punched into a shape in which the stretched portion protruded. The active material application portion had a width of 50 mm and a length of 54 mm. The stretched part was formed with a length of 20 mm and a width of 8 mm along the long side direction of the active material application part.

(Negative electrode tab)
A nickel tab was used for the negative electrode tab. The negative electrode tab was provided with a heat sealing resin made of polypropylene.

(Separator)
As the separator, a microporous film made of polypropylene having a thickness of 25 μm was cut into a width of 54 mm and a length of 58 mm.

(Production of electrode laminate)
In the order of negative electrode, separator, positive electrode, separator, and negative electrode, four positive electrodes and five negative electrodes were alternately laminated via separators. Since the negative electrode which becomes the outermost surface of the laminate does not have a positive electrode surface facing the outer side, it is not involved in charge / discharge.

(Production of battery)
A positive electrode tab and a negative electrode tab were joined to the extended portion of the positive electrode and the negative electrode of the electrode laminate by ultrasonic welding, respectively. The traces of the horn and anvil of the ultrasonic welder when the positive electrode extension and the positive electrode tab were ultrasonically welded were covered with polypropylene tape.

The used polypropylene tape does not swell or peel off even when immersed in the electrolyte. The extending portion of the negative electrode and the portion of the negative electrode tab disposed inside the battery were also covered with the polypropylene tape.

As an exterior material, two sheets of a laminate film made of aluminum and resin cut into 80 mm × 90 mm were prepared. These two laminate films were overlapped with the electrode laminate interposed therebetween. At this time, an electrode laminated body is arrange | positioned so that a positive electrode tab and a negative electrode tab may protrude from one of the short sides of a laminate film. The stacked laminate films were thermally welded with a width of 5 mm on the remaining three sides, leaving one of the long sides. The heat welding was performed so as to sandwich the heat sealing resin provided on the tab.

Next, the electrolyte solution was injected into the exterior body of the laminate film using the long side not thermally welded as the injection port. After injecting the electrolytic solution, the injection port was sealed by heat welding in an atmosphere reduced to 2 kPa, thereby completing the battery. The electrolyte used was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3: 7, with 1 mol of LiPF ₆ dissolved per liter of solvent.

(Battery evaluation)
The manufactured battery was charged at a constant current up to 4.8 V at a current corresponding to a 5-hour rate (0.2 ItA), and then charged at a constant voltage of 4.8 V for a total of 10 hours. Next, it was discharged to 3.0 V with a current of 0.2 ItA. The above charging and discharging were performed in an environment of 25 ° C. After the discharge, the battery volume at 25 ° C. was obtained by the Archimedes method from the difference in weight between air and water, and was defined as the volume before the soot discharge test. The charge / discharge test was performed 100 cycles at an environmental temperature of 45 ° C., an upper limit voltage of 4.8 V, a lower limit voltage of 3.0 V, and a charge / discharge rate of 1 ItA. After the test, the volume at 25 ° C. was measured as before the test. An exterior body made of a laminate film sealed under reduced pressure swells when the pressure inside the battery increases due to the gas generated by the decomposition of the electrolyte. Therefore, the degree of decomposition of the electrolyte can be compared from the change in volume of the battery.

<Example 2>
(Production of battery)
In Example 2, a battery was manufactured without oxidizing the positive electrode and the positive electrode tab. After joining the positive electrode tab and the negative electrode tab to the extending portion of the positive electrode and the negative electrode of the electrode laminate by ultrasonic welding, respectively, the positive electrode current collector foil extending portion and the portion disposed inside the battery of the positive electrode tab, The negative electrode current collector foil extending portion and the portion of the negative electrode tab disposed inside the battery were each coated with polypropylene tape. At this time, the polypropylene tape was affixed so that there was no gap with the heat sealing resin of each of the positive electrode tab and the negative electrode tab, and it did not cover the portion sandwiched by heat sealing. Otherwise, an electrode laminate was produced in the same manner as in Example 1.

(Battery evaluation)
The manufactured battery was charged and discharged for the first time under the same conditions as in Example 1, and the volume change due to the cycle test was measured.

<Example 3>
(Production of battery)
A battery was fabricated in the same manner as in Example 1 except that the negative electrode current collector foil stretched portion and the negative electrode tab were not covered with polypropylene tape.

(Battery evaluation)
The manufactured battery was charged and discharged for the first time under the same conditions as in Example 1, and the gas generation amount was estimated by a cycle test.

<Comparative Example 1>
(Production of battery)
As in Example 2, an electrode laminate was produced without oxidizing the positive electrode and the positive electrode tab. The positive electrode current collector foil extension and the positive electrode tab were ultrasonically welded to the negative electrode current collector foil extension and the negative electrode tab, respectively. Further, without covering the positive electrode side and the negative electrode side, the metal part is exposed, and in the same manner as in Example 1, it is housed in an exterior body made of a laminate film and injected with electrolyte and Sealing was performed.

(Comparison of Example and Comparative Example)
Table 1 shows the increase in battery volume in Examples 1 to 3 and Comparative Example 1 by the charge / discharge test. Here, the volume increase amount is an amount obtained by subtracting “battery volume before cycle test” from “battery volume after cycle test”. In Examples 1 to 3, the increase in volume due to the cycle test is small compared to Comparative Example 1, and it can be seen that gas generation due to decomposition of the electrolytic solution is reduced.

The present invention can be used in all industrial fields that require a power source and industrial fields related to the transport, storage and supply of electrical energy. Specifically, power supplies for mobile devices such as mobile phones and laptop computers, electric vehicles such as electric cars, hybrid cars, electric bikes, electric assist bicycles, power supplies for mobile and transport media such as trains, satellites, and submarines, UPS It can be used for backup power sources such as, power storage facilities that store power generated by solar power generation, wind power generation, etc.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Electrode laminated body 11 Exterior material 12 Exterior material 15 Heat sealing resin 16 Insulating material 21 Negative electrode 22 Negative electrode active material application surface 23 Extension part of negative electrode current collection foil 26 Oxide film 31 Positive electrode 32 Positive electrode active material application Surface 33 Extension part of positive electrode current collector foil 41 Electrode active material application surface 42 Electrode extension part 53 Negative electrode tab 63 Positive electrode tab

Claims

A plurality of positive electrodes and negative electrodes, which are electrodes, are stacked via a separator, and are connected to the plurality of positive electrodes and drawn to the outside of the battery, and are electrically connected to the plurality of negative electrodes and drawn to the outside of the battery. A lithium ion secondary battery having a negative electrode tab,
The positive electrode has an exposed portion of a current collector foil not coated with an active material,
A lithium ion secondary battery in which at least a part of the exposed portion is covered with an insulating material, and a portion of the positive electrode tab disposed inside the battery is covered with an insulating material.
The negative electrode has an exposed portion of the current collector foil to which no active material is applied,
At least a part of the exposed portion of the negative electrode is covered with an insulating material, and a portion of the negative electrode tab that is disposed inside the battery is covered with an insulating material.
The lithium ion secondary battery according to claim 1.
The insulating material covering the exposed portion of the positive electrode includes an oxide film of the positive electrode material,
The insulating material covering the positive electrode tab includes an oxide film of the material of the tab;
The lithium ion secondary battery according to claim 1 or 2.
The insulating material covering the exposed portion of the positive electrode;
The insulating material covering the positive electrode tab;
The insulating material covering the exposed portion of the negative electrode; and
The insulating material covering the negative electrode tab;
The lithium ion secondary battery according to claim 2, wherein at least one of comprises an insulating organic polymer material.
The lithium ion secondary battery according to claim 4, wherein the organic polymer material is a sheet-like member.
The lithium ion secondary battery according to any one of claims 1 to 5, wherein the exposed portion is a stretched portion of a current collector foil.
A plurality of negative electrodes and positive electrodes, which are electrodes, are stacked via a separator, are positively connected to the plurality of positive electrodes and drawn out of the battery, and are electrically connected to the plurality of negative electrodes and drawn out of the battery. A method for producing a lithium ion secondary battery having a negative electrode tab,
(A) applying an active material to a part of the positive electrode;
(B) Thereafter, before the step of laminating the electrode and the separator, the positive electrode is exposed to an oxidizing atmosphere to oxidize the exposed portion of the positive electrode where the active material is not applied, and at least a portion thereof is an oxide film. Forming a step;
(C) connecting the exposed portion of the positive electrode and the positive electrode tab;
A method for producing a lithium ion secondary battery.
In the step (c), the exposed portion and the positive electrode tab are connected by ultrasonic welding,
further,
(D) The manufacturing method of the lithium ion secondary battery of Claim 7 which has the process of coat | covering with an insulating material so that the trace produced by the said ultrasonic welding may be covered.
further,
(E) After connecting the exposed portion and the tab,
The method for manufacturing a lithium ion secondary battery according to claim 7, further comprising a step of covering at least the exposed portion and a portion of the positive electrode tab disposed inside the battery with an insulating material.