JP2002373660A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery minimized in the deterioration of battery characteristics, accompanied by gas generation by suppressing the generation of gas in initial charging (forming). SOLUTION: In this nonaqueous secondary battery comprising a positive electrode, a negative electrode and an electrolyte, a film of a polymerization product of a multifunctional acrylic ester monomer or oligomer is formed on the surface of the positive electrode and the negative electrode. The thickness of the film is preferably set to 2-10 μm. As the multifunctional acrylic ester monomer or the oligomer, one having three or more polymerizable double bonds in one molecule is preferably used, and dipentaerythritol hexacrylate is particularly preferred.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery, and more particularly, to a non-aqueous secondary battery particularly suitable for packaging with a laminate film.

[0002]

2. Description of the Related Art Non-aqueous rechargeable batteries such as lithium ion rechargeable batteries are small and have high energy densities and are suitable as power sources for portable equipment. Although used as a power source for mobile phones and the like, recently, batteries using a laminate film as an exterior material have attracted attention in order to further reduce the weight and thickness.

The battery packaged with this laminated film includes a battery using a gel polymer electrolyte obtained by gelling an electrolyte solution as a liquid electrolyte with a polymer, and a battery using the electrolyte solution without gelation. In each case, a laminated film using an aluminum foil as a core material is used as an exterior material, and a sheet-like electrode is laminated or wound into an electrode group, which is exteriorly covered with the laminated film to form a battery. Since it is possible and the area can be increased, new applications are expected.

[0004]

However, the battery packaged with this laminated film is advantageous in reducing the weight because the package material is made of a material having a small strength called a laminate film. When a battery occurs, unlike a battery packaged with a metal can, the battery swells even with a small amount of gas generated, the battery thickness deviates from the standard, the electrode loosens due to gas, and the internal resistance increases. was there.

[0005] In the case of a lithium ion secondary battery, when the battery is assembled and formed (initial charge), lithium ions enter between layers of the negative electrode carbon. Ethylene carbonate and propylene carbonate are decomposed by reacting with carbon to form a stable solid electrolyte layer on the carbon surface,
It is generally said that subsequent lithium ions can easily enter the interlayer.

However, when ethylene carbonate or propylene carbonate reacts and decomposes as described above, it is said that decomposition products such as ethylene, propylene, carbon monoxide (CO), and carbon dioxide (CO ₂ ) are generated. And they accumulate as gas inside the battery.

When gas is generated in the battery as described above, the battery swells, and bubbles accumulate between the electrodes to inhibit the reaction, causing a decrease in battery capacity, particularly a decrease in heavy load discharge characteristics, and the swelling itself. In this case, the product value is impaired.

[0008] The generation of gas occurs in a large amount in the formation step, which is the first charge (first charge), due to the above mechanism, and can be almost ignored thereafter. Therefore, the gas generated during the formation (first charge) must be discharged out of the battery. I just need.

However, in order to discharge the generated gas to the outside of the battery, the battery is formed without sealing the battery, and after the formation is completed, the battery is sealed, or the once sealed battery is formed and opened. There is a problem that a very complicated process such as resealing after degassing has to be taken.

The present invention solves the above-mentioned problems in the prior art, suppresses generation of gas during chemical formation, eliminates complicated steps for degassing, increases productivity, An object of the present invention is to provide a non-aqueous secondary battery in which a decrease in battery characteristics due to occurrence is suppressed.

[0011]

According to the present invention, a film of a polymerization product of a polyfunctional acrylic ester monomer or oligomer is formed on the surfaces of a positive electrode and a negative electrode.
An object of the present invention is to solve the above-described problem by suppressing gas generation in a battery during chemical formation, substantially eliminating gas degassing, and suppressing deterioration of battery characteristics due to gas generation.

As described above, in order to form a film of a polymerization product of a polyfunctional acrylic ester monomer or oligomer on the surfaces of the positive electrode and the negative electrode, a double bond which generates a radical in an electrolyte solution which is a liquid electrolyte is formed by one bond. After adding a polyfunctional acrylic ester monomer or oligomer containing two or more molecules in the molecule, assembling the battery using an electrolytic solution to which the polyfunctional acrylic ester monomer or oligomer is added, and then performing a chemical conversion, And forming a film of a polymerization product of a polyfunctional acrylic ester monomer or oligomer on the surface of the negative electrode. The coating prevents, for example, solvent molecules in the electrolytic solution from directly decomposing with the carbon of the negative electrode, and enables stable formation and charge / discharge.

As a result, the generation of gas during chemical formation is reduced, so that a battery can be manufactured without substantially performing degassing, and the productivity during battery manufacturing is improved. The deterioration of the battery performance which has been performed is also suppressed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail in the order of a positive electrode, a negative electrode, an electrolyte, and a polyfunctional acrylic ester monomer or oligomer. First, as the positive electrode active material, various materials can be used without any particular limitation. However, transition metal oxides containing lithium are preferably used because of their high energy density and excellent reversibility. For example, lithium cobalt oxides such as LiCoO ₂ , lithium manganese oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , mixtures thereof, and a part of Ni of LiNiO ₂
Alternatively, those substituted with Mn are preferably used.

For the positive electrode, for example, a conductive auxiliary such as flake graphite, acetylene black or carbon black, or a binder such as polyvinylidene fluoride or polytetrafluoroethylene may be added to the above positive electrode active material, if necessary. , Mixing to prepare a positive electrode mixture, dispersing it in a solvent to form a paste (the binder may be previously dissolved or dispersed in a solvent and then mixed with the positive electrode active material, etc.), and the positive electrode mixture containing Applying paste to a positive electrode current collector made of aluminum foil or the like, drying, forming a positive electrode mixture layer on at least a part of the positive electrode current collector, and, if necessary, passing through a step of pressure molding. Produced by
However, the method for producing the positive electrode is not limited to the method described above, but may be another method. In addition, as the conductive auxiliary agent, a conductive polymer or the like can be used in addition to the above examples, and as the binder, in addition to the above examples, a styrene-butadiene copolymer or the like can be used.

As the negative electrode active material, a carbon-based material capable of doping and undoping lithium ions is used. Specifically, for example, graphite-based materials such as natural graphite and artificial graphite, pyrolytic carbons, coke , Glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads,
Carbon fiber, activated carbon, graphite and the like are preferably used. Among them, when a graphite-based material is used as the negative electrode active material, the effects of the present invention are more remarkably exhibited.

The negative electrode is prepared, for example, by adding the same conductive aid and binder as in the case of the positive electrode to the negative electrode active material, if necessary, mixing to prepare a negative electrode mixture, and dispersing it in a solvent. A paste (the binder may be dissolved or dispersed in a solvent in advance and then mixed with the negative electrode active material, etc.), and the paste containing the negative electrode mixture is converted to a negative electrode current collector made of copper foil, nickel foil, or the like. It is prepared by applying and drying to form a negative electrode mixture layer on at least a part of the negative electrode current collector, and then, if necessary, through a step of pressure molding. However, the method for manufacturing the negative electrode is not limited to the method described above, and may be another method.

The electrolyte constituting the power generating element together with the positive electrode and the negative electrode is usually a non-aqueous liquid electrolyte (hereinafter referred to as "electrolyte") in which an electrolyte salt such as lithium salt is dissolved in an organic solvent, or the above-mentioned electrolyte. A gel polymer electrolyte obtained by gelling with a polymer is used. First, the electrolytic solution will be described. Examples of the solvent for the electrolytic solution include chain carbonates such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate, cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, ethyl acetate, and propion. Methyl acid, γ-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane, 1,3-dioxolan, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether, and the like can be used. In addition, amine-based or imide-based organic solvents,
Sulfur-containing or fluorine-containing organic solvents can also be used. These solvents can be used alone or as a mixture of two or more. Among them, when a mixed solvent of a chain carbonate and a cyclic carbonate is used as a constituent solvent of the electrolytic solution, the effect of the present invention is obtained. Are more remarkably expressed.

When preparing the electrolytic solution, the
The electrolyte salt to be used is, for example, LiClO_Four, LiP
F₆, LiBF_Four, LiAsF₆, LiSbF₆, Li
CF _ThreeSO_Three, LiC_FourF₉SO_Three, LiCF_ThreeC
O_Two, Li_TwoC_TwoF_Four(SO_Three) _Two, LiN (CF_ThreeS
O_Two)_Two, LiC (CF_ThreeSO_Two)_Three, LiC_nF_{2n + 1}
SO_Three(N ≧ 2) alone or in combination of two or more
Used. Especially LiPF ₆And LiC_FourF₉SO_ThreeSuch
Is preferable because of good charge / discharge characteristics. In the electrolyte
Is not particularly limited.
Is at least 0.3 mol / l, especially at least 0.4 mol / l
Is preferable, and 1.7 mol / l or less, especially 1.5 mol / l
mol / l or less is preferred.

The gel polymer electrolyte corresponds to a gel obtained by gelling the above-mentioned electrolytic solution with a gelling agent. For the gelation, for example, a linear polymer such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or the like is used. These copolymers, polyfunctional monomers polymerized by irradiation with actinic rays such as ultraviolet rays, electron beams, visible rays, and far infrared rays (for example, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentane) Tetra- or higher-functional acrylates such as erythritol hydroxypentaacrylate or dipentaerythritol hexa-acrylate and the same tetra- or higher-functional methacrylates as the above acrylates) Polymer is used as a gelling agent.

When a polyfunctional monomer is used as described above, if necessary, as a polymerization initiator, for example, benzoyls, benzoin alkyl ethers, benzophenones, benzoylphenylphosphine oxides,
Acetophenones, thioxanthones, anthraquinones, and the like can be used, and alkylamines, amino esters, and the like can also be used as sensitizers for the polymerization initiator.

In the present invention, a film of a polymerization product of a polyfunctional acrylic ester monomer or oligomer is formed on the surfaces of the positive electrode and the negative electrode as a means for suppressing gas generation. Two polymerizable double bonds in one molecule
Any material having at least two (that is, bifunctional or more crosslinkable) and polymerizable by actinic rays such as ultraviolet rays, electron beams, visible rays, and far-infrared rays or heat can be used.

Specific examples thereof include acrylic ester monomers having two polymerizable double bonds in one molecule (bifunctional crosslinkable acrylic ester monomers) such as 1,3-butanediol acrylate. ,
1,4-butanediol acrylate, 1,6-butanediol acrylate, ethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, ethoxy Bifunctional acrylates such as functionalized bisphenol A diacrylate, novolak diacrylate, and propoxylated neopentyl glycol diacrylate, and the same bifunctional methacrylate as the above acrylate.

In addition, a polymerizable double bond is contained in one molecule.
Examples of the acrylic ester monomer (trifunctional crosslinkable acrylic ester monomer) include tris (2-hydroxyethyl) isocyanurate triacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, and pentaerythritol triacrylate. Examples include trifunctional acrylates such as acrylate, propoxylated trimethylolpropane triacrylate, propoxylated glyceryl triacrylate, and caprolactone-modified trimethylolpropane acrylate, and trifunctional methacrylates similar to the above acrylates.

Examples of acrylic ester monomers having four or more polymerizable double bonds in one molecule (tetrafunctional or more crosslinkable acrylic ester monomers) include, for example, pentaerythritol tetraacrylate, ditrimethylolpropane tetra Examples thereof include tetrafunctional or higher acrylates such as acrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hydroxypentaacrylate, and dipentaerythritol hexaacrylate, and tetrafunctional or higher methacrylate similar to the above acrylate.

With these polyfunctional acrylic ester monomers, it is considered that the more polyfunctional, that is, the more polymerizable double bonds are in one molecule, the greater the effect is. Therefore, it is possible to polymerize in one molecule. Three double bonds
Those containing more than two (i.e., those having three or more functional groups), particularly those containing four or more polymerizable double bonds (i.e., those having four or more functional groups) are preferably used, and in particular, dipentaerythritol hexaacrylate or dipentaerythritol. Hexafunctional acrylates and methacrylates such as pentaerythritol hexamethacrylate are preferably used. In consideration of the solubility in the electrolytic solution and the like, the polyfunctional acrylic ester monomer preferably has a molecular weight of 2000 or less, more preferably 1000 or less. And
As is clear from the above examples, in the present invention, the acrylic ester monomer includes not only acrylate but also methacrylate. As the polyfunctional acrylic ester oligomer, for example, an oligomer of the polyfunctional acrylic ester monomer exemplified above is used.

These polyfunctional acrylic ester monomers or oligomers are used in an amount of 0.1 to 2% by weight based on the electrolytic solution (liquid electrolyte) (ie, based on 100 parts by weight of the electrolytic solution). 0.1 to 2 parts by weight),
It is more preferable to contain 0.5 to 1.5% by weight,
More preferably, the content is 0.7 to 1.5% by weight. However, since the polyfunctional acrylic ester monomer or oligomer contained in the electrolytic solution forms a film of the polymerization product on the surfaces of the positive electrode and the negative electrode after assembling the battery, the content is reduced. It is sufficient that such a content as described above is satisfied when the battery is assembled.

When the content of the polyfunctional acrylic ester monomer or oligomer is in the above-mentioned range, formation of a film of the polymerization product on the surfaces of the positive electrode and the negative electrode without gelling the electrolytic solution is performed. The reaction between the carbon-based material of the negative electrode active material and ethylene carbonate or propylene carbonate, which is a constituent solvent of the electrolytic solution, during the first charge) is suppressed.

By setting the content of the polyfunctional acrylic ester monomer or oligomer to 0.1% by weight or more with respect to the electrolytic solution, the above-mentioned effects can be sufficiently exhibited. By setting the content of the functional acrylic ester monomer or oligomer to 2% by weight or less based on the electrolytic solution, it is possible to suppress a decrease in load characteristics and the like due to too much polyfunctional acrylic ester monomer or oligomer. Also, when a gel polymer electrolyte is used in the construction of the battery,
The polyfunctional acrylic ester monomer or oligomer may be contained in an amount of 0.1 to 2% by weight with respect to the base electrolyte solution.

Many of the above-mentioned polyfunctional acrylic ester monomers or oligomers are known as a material for gelling an electrolytic solution, and dipentaerythritol hexaacrylate is also used as a gelling agent, and the electrolytic solution is cured by an ultraviolet curing method. Is gelled, and the gelled polymer electrolyte is used as an electrolyte of a polymer battery. However, in order to gel the electrolytic solution, a certain amount of gelling agent is required. However, gelation is difficult unless tetrafunctional dipentaerythritol hexaacrylate is used in an amount of 3% by weight or more with respect to the electrolytic solution.

According to the present invention, a film of a polymerization product of a polyfunctional acrylic ester monomer or oligomer is formed on the surfaces of a positive electrode and a negative electrode. As a means for forming the film, a polyfunctional acrylic ester monomer or oligomer is used. The added electrolytic solution is used, and the amount of the added electrolytic solution is very small, not more than a concentration that causes gelation of the electrolytic solution.

In the present invention, the site where the film of the polymerization product of the polyfunctional acrylic ester monomer or oligomer is formed is the surface of the positive electrode and the negative electrode, and the surface is, of course, the reaction surface.

In the present invention, the film of the polymerization product of the polyfunctional acrylic ester monomer or oligomer is formed on both the surface of the positive electrode and the surface of the negative electrode. The effect is particularly remarkable when the thickness is larger than the film formed on the surface of the negative electrode.

The thickness of the film of the polymerization product of the polyfunctional acrylic ester monomer or oligomer formed on the surfaces of the above-mentioned positive electrode and negative electrode is preferably 2 to 10 μm. That is, by setting the thickness of the film of the polymerization product of the polyfunctional acrylic ester monomer or oligomer to 2 μm or more, the effect of suppressing the generation of gas can be sufficiently exerted. By setting the thickness of the film of the polymerization product of the monomer or oligomer to 10 μm or less, it is possible to suppress deterioration of battery characteristics such as load characteristics due to the film and maintain good battery characteristics. In the present invention, the thickness of the film of the polymerization product of the polyfunctional acrylic ester monomer or oligomer may be a film formed of only the polyfunctional acrylic ester monomer or oligomer (that is, not a battery but a polyfunctional acrylic ester). FT-IR (Fourier transform infrared spectroscopy) of the positive electrode and negative electrode after battery disassembly, and a polyfunctional acrylic ester monomer or oligomer polymerization product film formed on aluminum foil or the like using only the ester monomer or oligomer. Device).

In the present invention, as the separator, for example, a microporous resin film, a nonwoven fabric or the like is suitably used. Examples of the microporous resin film include a microporous polyethylene film, a microporous polypropylene film, and a microporous ethylene-propylene copolymer film. Further, as the nonwoven fabric, for example,
Examples include a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, a polyethylene terephthalate nonwoven fabric, and a polybutylene terephthalate nonwoven fabric.

As the exterior material, for example, a three-layer laminated film composed of a nylon film-aluminum foil-modified polyolefin film or a three-layer laminated film composed of a polyester film-aluminum foil-modified polyolefin film is used. Can be

[0037]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples.

Examples 1 to 5 First, the production of the positive electrode and the negative electrode used in Examples 1 to 5 and the preparation of the electrolyte will be described. The thickness of the coating of the polymerization product of the polyfunctional acrylic ester monomer or oligomer formed on the surface of the positive electrode or the negative electrode is different between each of the examples, but the base portions are the same as those of the examples 1 to 5. Are common to both.

Preparation of positive electrode: LiCoO as positive electrode active material
And ₂ 90 parts by weight, and 5 parts by weight of carbon black as a conductive auxiliary agent were uniformly mixed and polyvinylidene fluoride 5 parts by weight of the binder, added to and mixed with further N- methyl-2-pyrrolidone as a diluent Then, a positive electrode mixture-containing paste was prepared. The obtained positive electrode mixture-containing paste is applied to both surfaces of a positive electrode current collector made of aluminum foil, dried to form a positive electrode mixture layer, and then calendered and compressed to form both surfaces of the positive electrode current collector. In this example, four positive electrodes having a positive electrode mixture layer were produced. However, during the production of the positive electrode, the positive electrode mixture-containing paste was not applied to a part of the positive electrode current collector, and an exposed part was left, and the exposed part was used as a lead part. The lead portion of the positive electrode was made longer than that of the others, and was used as a connection portion with the positive terminal as an external terminal.

Preparation of negative electrode: Natural graphite 9 as negative electrode active material
4 parts by weight, 6 parts by weight of polyvinylidene fluoride, and N-methyl-2-pyrrolidone were mixed to prepare a negative electrode mixture-containing paste. The obtained negative electrode mixture-containing paste was applied to a negative electrode current collector made of copper foil, dried to form a negative electrode mixture layer, calendered, and compressed to produce a negative electrode. However, when producing the negative electrode, the paste containing the negative electrode mixture was not applied to a part of the negative electrode current collector, an exposed part was left in part, and the exposed part was used as a lead part. In the production of this negative electrode, three negative electrode mixture layers were formed on both sides of the negative electrode current collector, so-called double-sided negative electrodes, and a negative electrode mixture layer was formed on one surface of the negative electrode current collector, a so-called single-sided negative electrode. Were produced. Further, at the time of producing the above-mentioned negative electrode, the lead portion of one negative electrode was made longer than the others, and was used as a connection portion with the negative electrode terminal as an external terminal.

Preparation of electrolytic solution: LiPF ₆ was added to a mixed solvent of ethylene carbonate, propylene carbonate and diethyl carbonate at a volume ratio of 1: 1: 1 at a ratio of 1.2 mol / L.
1 prepared by dissolution. Then, 0.3 to 2.0% by weight of dipentaerythritol hexaacrylate to this electrolyte (0.3 to 2.0% by weight of dipentaerythritol hexaacrylate to 100 parts by weight of electrolyte).
2.0 parts by weight) to make the electrolyte contain dipentaerythritol hexaacrylate.

As a separator, a microporous polyethylene film was used, and in assembling the battery, four positive electrode-coated positive electrodes each having the positive electrode mixture layer formed on both surfaces of the positive electrode current collector and three double-coated negative electrodes described above were used. And two single-sided coated negative electrodes,
Using the above eight separators, these positive electrodes, negative electrodes, and separators are referred to as negative electrodes (the negative electrodes are single-side coated negative electrodes), separators, positive electrodes,... Negative electrodes, separators, positive electrodes, separators, and negative electrodes (the negative electrodes are also single-side coated negative electrodes). There is a middle 3
Each of the negative electrodes was a double-sided coated negative electrode), in which order, four positive electrodes, five negative electrodes, and eight separators were laminated to form a laminated electrode group.

Then, the lead portions of the four positive electrodes were welded, and the free end side of the longest lead portion was used for connection to the positive terminal as an external terminal. Further, the lead portions of the five negative electrodes were welded, and one of them was welded.
The free end side of the longest lead portion is used for connection to a negative terminal as an external terminal.

Two sheets of a three-layer laminated film composed of a nylon film, an aluminum foil, and a modified polyolefin film were prepared as an exterior material for exteriorly covering the above-mentioned laminated electrode group. The sheet is kept in the shape of a container with a flange), a nickel ribbon is used as the positive electrode terminal, and the aluminum foil of the positive electrode is removed from the aluminum foil of the positive electrode at a position where the laminated electrode group is sealed with the outer material. The longest of the lead portions and the positive electrode terminal made of the nickel ribbon were ultrasonically welded. Further, when a nickel ribbon is used as a negative electrode terminal and the above-mentioned laminated electrode group is packaged with a package, the longest one of the lead portions made of copper foil of the negative electrode and the nickel The negative electrode terminal made of a ribbon was ultrasonically welded, and then, the laminated electrode group was packaged with a package and sealed. The exterior by this exterior material, by arranging the laminated electrode group between two exterior materials, heating the overlapping portion of the peripheral portion, melting the innermost modified polyolefin film and heat-sealing the same. In this heat fusion, the peripheral parts of three sides of the four sides are thermally fused in advance, and a predetermined amount of the above-mentioned electrolyte is injected from the peripheral part of the remaining one side. After the inside was reduced in pressure, the periphery of the remaining one side was heat-sealed. For the above-mentioned reason, the two exterior materials were arranged so that their modified polyolefin films faced each other.

The welding width between the lead portion of the positive electrode and the positive electrode terminal was 2 mm, and the width of the sealing portion of the exterior material was 4 mm. The welding width between the negative electrode lead and the negative electrode terminal is 2 mm.
mm, and the width of the sealing portion of the exterior material is 4 m as described above.
m. And the thickness of the whole battery was 3.0 mm. These batteries were preliminarily formed by charging them at 25 ° C. and 0.05 C for 1 hour, and then at 0.2 C for 8 hours.
It was formed by charging under the condition of a constant current of 4.2 V and a constant voltage.

Here, the structure of the stacked non-aqueous secondary battery of Embodiment 1 among the stacked non-aqueous secondary batteries of Embodiments 1 to 5 will be described with reference to FIG. However, as described above, the laminated nonaqueous secondary batteries of Examples 1 to 5 had a thickness of the coating film of the polymerization product of dipentaerythritol hexaacrylate formed on the surfaces of the positive electrode and the negative electrode. Are different from each other in the basic structure, and a film of a polymerization product of dipentaerythritol hexaacrylate is formed on the surfaces of the positive electrode and the negative electrode by the above-mentioned chemical conversion. 1 schematically shows a laminated nonaqueous secondary battery of No. 1; since a coating film of a polymerization product of dipentaerythritol hexaacrylate is much thinner than other members, FIG. Illustration is omitted.

As shown in FIG. 1, the laminated nonaqueous secondary battery of Example 1 comprises a laminated electrode group using four positive electrodes 1, five negative electrodes 2, and eight separators 3. A battery is formed by externally sealing the laminated electrode group with a packaging material 4 composed of a three-layer laminated film of a nylon film-aluminum foil-modified polyolefin film. However, as described above, the coating film of the polymerization product of dipentaerythritol hexaacrylate formed on the surfaces of the positive electrode 1 and the negative electrode 2 is not shown in FIG. Reference numeral 1a denotes a lead portion of the positive electrode 1. The free end side of the longest one of these lead portions 1a is connected to one end of the positive electrode terminal 5 by welding. It is arranged in the part 4a. Reference numeral 2a denotes a lead portion of the negative electrode 2, and the free end side of the longest one of the lead portions 2a is connected to the negative electrode terminal 6.
Is connected by welding to the other end, and the connection portion is disposed in the sealing portion 4 a of the exterior material 4. Here, the stacked electrode group will be described in further detail. First, a negative electrode 2 (this negative electrode 2 is a single-sided coated negative electrode) is arranged in the lowermost layer,
Separator 3, positive electrode 1, separator 3, negative electrode 2, separator 3, positive electrode 1, separator 3, negative electrode 2, separator 3, positive electrode 1, separator 3, negative electrode 2, separator 3, positive electrode 1, and separator 3 are disposed thereon. Further, a negative electrode 2 (the negative electrode 2 is a single-sided coated negative electrode) is disposed thereon. Each of the three intermediate negative electrodes 2 is a double-sided coated negative electrode, and the single-sided coated negative electrodes on both sides are arranged such that their negative electrode mixture layers face the separator 3.

Comparative Example 1 The procedure of Example 1 was repeated, except that dipentaerythritol hexaacrylate was not added to the electrolytic solution, and a film of a polymerization product of dipentaerythritol hexaacrylate was not formed on the surface of the positive electrode or the negative electrode. A stacked non-aqueous secondary battery was produced and was formed in the same manner as in Example 1.

The amounts of gas generated and the load characteristics of the batteries of Examples 1 to 5 and Comparative Example 1 after formation (initial charge) were measured. Table 1 shows the results.

The amount of gas generated was evaluated based on the swelling of the battery. In other words, the evaluation was made based on the thickness (3.0 mm) of the battery before formation and the thickness of the battery after formation. The load characteristics are
Ratio (%) of discharge capacity when discharging to 3.0 V at a current density of 2 C to discharge capacity when discharging to 3.0 V at a current density of 0.2 C at 25 ° C. [(discharge capacity at 2 C) {Discharge capacity at 0.2 C) × 100].

Table 1 shows the load characteristics, the battery swelling, and the thickness of the coating film of the polymerization product of dipentaerythritol hexaacrylate formed on the surfaces of the positive electrode and the negative electrode. The thickness of the coating of the polymerization product of dipentaerythritol hexaacrylate formed on the surface of the positive electrode is simplified and indicated as “positive electrode film thickness”, and the thickness of the dipentaerythritol hexaacrylate formed on the surface of the negative electrode is also indicated. The thickness of the film of the polymerization product is simplified and indicated as “negative electrode coating thickness”. The film thickness of the polymerized product of these dipentaerythritol hexaacrylates was determined by FT-IR analysis of a film formed by polymerizing separately on an aluminum foil using only dipentaerythritol hexaacrylate and a positive electrode or a negative electrode after battery decomposition. It was determined from the strength value at the time.

[0052]

[Table 1]

As shown in Table 1, in Examples 1 to 3, there was no battery swelling, and in Examples 4 and 5, battery swelling was slight. , Stayed in a range that could not be determined.

As is apparent from the comparison between Examples 1 to 5 and Comparative Example 1, the formation of a film of a polymerization product of dipentaerythritol hexaacrylate on the surfaces of the positive electrode and the negative electrode makes it possible to form a gas by chemical conversion. It was evident that the occurrence of odor was suppressed.

As described above, in the fourth and fifth embodiments.
Although the battery swelling of the battery may be practically acceptable, in the case of a laminate type battery, even a slight swelling may reduce the appearance of the battery.
Therefore, the thickness of the dipentaerythritol hexaacrylate film is preferably 2 μm or more, and 3 μm or more.
The above is more preferable.

On the other hand, when looking at the load characteristics, the coating film of the polymerized product of dipentaerythritol hexaacrylate lowers the load characteristics. Therefore, when the thickness of the coating film is large, it is difficult to use it under heavy load. The thickness is 1
0 μm or less is preferable, and 8 μm or less is more preferable.

In the above embodiments and the like, a case where a laminate film is used as an exterior material has been described. However, the present invention is not limited to this case, and a material other than a laminate film such as a metal can is used as an exterior material. You may.

[0058]

As described above, according to the present invention, it is possible to provide a non-aqueous secondary battery in which the generation of gas during chemical formation is suppressed, and the deterioration of battery characteristics due to gas generation is small.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a stacked nonaqueous secondary battery of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Lead part 2 Negative electrode 2a Lead part 3 Separator 4 Exterior material 4a Seal part 5 Positive terminal 6 Negative terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (6)

[Claims] 1. A non-aqueous secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein a film of a polymerization product of a polyfunctional acrylic ester monomer or oligomer is formed on surfaces of the positive electrode and the negative electrode. Non-aqueous secondary battery. 2. The method according to claim 1, wherein the thickness of the coating formed on the surfaces of the positive electrode and the negative electrode is 2 to 10 μm.
The non-aqueous secondary battery according to the above. 3. The non-aqueous secondary battery according to claim 1, wherein a film formed on the surface of the positive electrode is thicker than a film formed on the surface of the negative electrode. 4. The non-aqueous secondary battery according to claim 1, wherein the polyfunctional acrylic ester monomer or oligomer has three or more polymerizable double bonds in one molecule. 5. The polyfunctional acrylic ester monomer,
The non-aqueous secondary battery according to claim 1, wherein the battery is dipentaerythritol hexaacrylate. 6. The method according to claim 1, wherein the polyfunctional acrylic ester monomer or oligomer is contained in the liquid electrolyte at the time of assembling the battery and is polymerized at the time of the first charge to form a film of a polymerization product on the surfaces of the positive electrode and the negative electrode. The non-aqueous secondary battery according to claim 1, wherein: