JPH11219728A - Polymer battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer battery with excellent cycle property and high productivity by improving compatibility with a monomer-containing mixed solution of a core material of an electrolytic sheet in gel state (that is, a mixed solution of an electrolytic solution and low molecular weight liquid-phase monomer becoming electrolytic solution holding material of the electrolytic sheet in gel state by polymerization) without deteriorating the cycle property. SOLUTION: In this polymer battery comprising a sheet-like positive electrode 1, sheet-like negative electrode 2, and a gel electrolytic substance sheet, a porous polyolefin sheet surface-treated in gas phase is used as the core material of the gel electrolytic sheet 3. Plasma treatment, corona discharge treatment, sputtering etching, electron beam radiation, ultraviolet radiation, radioactive ray radiation, etc., are preferably employed for the method of gas phase surface treatment of the porous polyolefin sheet 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer battery, and more particularly, to an improvement in a gel electrolyte sheet.

[0002]

2. Description of the Related Art Hitherto, as a gel electrolyte sheet of a polymer lithium ion secondary battery, a porous sheet using a matrix material such as polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, etc. is impregnated with an electrolyte. Have been used exclusively [for example, Tsuchida et al., “Industrial Materials”, 30
(4), 109 ('82)]. Among them, polyvinylidene fluoride has the advantages of excellent thermal stability and low water absorption, and its research has been particularly actively conducted in recent years [for example, Toriyama et al., "The 37th Battery Abstracts of Symposiums at Debates, "238 ('96). However, when polyvinylidene fluoride is used, a solution containing polyvinylidene fluoride, which is a starting material for producing a gel electrolyte sheet, has a high viscosity, so that a dedicated apparatus is required for producing the gel electrolyte sheet.

[0003] Therefore, it has been proposed to prepare a gel electrolyte sheet from a lower viscosity solution. One example is the production of a gel electrolyte sheet by simultaneous gelation of an acrylate low molecular weight liquid monomer and an electrolytic solution (for example, US Pat. No. 5,609,974). The electrolyte sheet is very soft,
There was a problem that handling was difficult and it was not suitable for mass production.

Therefore, it has been proposed to reinforce the gel electrolyte sheet by using a nonwoven fabric as a core material of the gel electrolyte sheet (for example, US Pat.
603,982). However, even in this case, the nonwoven fabric was not optimized for the intended use, and thus was not sufficiently satisfactory.

For example, when a non-hydrophilic polyolefin fiber non-woven fabric is used as a core material of a gel electrolyte sheet, a low molecular weight acrylate monomer of acrylate which is polymerized and becomes an electrolyte holding material of the gel electrolyte sheet is used as an electrolyte. It is difficult to be impregnated at normal pressure due to poor compatibility with the mixed solution with the liquid (hereinafter simply referred to as "monomer-containing mixed solution"), and requires a complicated operation of impregnation under reduced pressure. It is difficult to completely eliminate the entrapped air bubbles, and therefore, the productivity is low, and the battery using the gel electrolyte sheet has a problem that sufficient performance cannot be obtained.

For this reason, it has been proposed to use a polyolefin fiber nonwoven fabric hydrophilically treated with a surfactant as a core material of a gel electrolyte sheet. However, when a polyolefin fiber nonwoven fabric hydrophilically treated with this surfactant is used, Although familiar with the above-mentioned monomer-containing mixed solution, the impregnation time is shortened, but when a battery is manufactured using the obtained gel electrolyte sheet and charged and discharged, the surfactant is detached from the nonwoven fabric and decomposed. Therefore, there is a problem that the cycle life of the battery is shortened.

Also, when a nonwoven fabric of polyester fiber or polyamide fiber having better wettability of the fiber itself with the monomer-containing mixed solution than the polyolefin fiber is used as the core material of the gel electrolyte sheet, the polyolefin fiber not subjected to hydrophilic treatment is not used. Although the impregnation time is shorter than in the case of using a non-woven fabric and the inclusion of bubbles is reduced, there is a problem that the fibers themselves are poor in oxidation resistance, so that they are decomposed by charging and discharging, causing deterioration in cycle characteristics. Also, because these polyester fibers and polyamide fibers are not sufficiently compatible with the monomer-containing mixed solution as it is,
For industrial use, they can be hydrophilically treated with a surfactant,
There was also the problem that vacuum impregnation had to be employed.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and adapts the core material of the gel electrolyte sheet to the monomer-containing mixed solution without deteriorating the cycle characteristics. And to provide a polymer battery with high productivity and excellent cycle characteristics.

[0009]

The present invention has solved the above-mentioned problems by subjecting a porous polyolefin sheet such as a nonwoven fabric of a polyolefin fiber to a gas phase surface treatment and using it as a core material of a gel electrolyte sheet. It is.

That is, by subjecting a porous polyolefin sheet to a gas phase surface treatment, its surface is oxidized,
Since a lyophilic group such as a COOH group is generated, compatibility with the monomer-containing mixed solution (that is, a mixed solution of a low-molecular-weight liquid monomer and an electrolytic solution that is polymerized and becomes an electrolyte retaining material for a gel electrolyte sheet) is improved. As a result, the rate of impregnation of the monomer-containing mixed solution into the core material is increased, the productivity is improved, and bubbles are hardly trapped in the obtained gel electrolyte sheet.

Further, CO generated by the gas phase surface treatment is used.
A lyophilic group such as an OH group is stable even when the battery is charged and discharged, and does not cause a large decrease in cycle characteristics.The parent polyolefin is also extremely stable against charge and discharge, and the cycle characteristics are reduced. Not cause.

As described above, the productivity of the gel electrolyte sheet is improved, and as a result, the productivity of the polymer battery is improved, and a polymer battery having excellent cycle characteristics can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, examples of a porous polyolefin sheet used as a core material of a gel electrolyte sheet and serving as a matrix of a porous polyolefin sheet subjected to a gas phase surface treatment include a polyolefin fiber nonwoven fabric and a polyolefin fiber woven fabric. , Polyolefin powder fusion products, polyolefin foams, and the like. Examples of the polyolefin fiber of the polyolefin fiber nonwoven fabric or the polyolefin fiber woven fabric include polyethylene fiber, polypropylene fiber, a mixed fiber of polyethylene fiber and polypropylene fiber, a composite fiber in which polypropylene is coated with polyethylene around polypropylene, and polypropylene and polyethylene in parallel. For example, a laid composite fiber is used.

[0014] Examples of the gas phase surface treatment of these porous polyolefin sheets include plasma treatment, corona discharge treatment, sputter etching, electron beam irradiation, ultraviolet irradiation, and radiation irradiation.

In the gel electrolyte sheet, examples of the polymer compound serving as an electrolyte retaining material include polyacrylate, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, and the like.
Examples include polyethylene oxide.

The electrolytic solution constituting the gel electrolyte sheet together with the vapor-phase surface-treated porous polyolefin sheet or the electrolyte retaining material serving as the core material can be the same as the conventional electrolyte solution. The negative electrode and the like can be the same as the conventional one.

[0017]

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

Example 1 First, a gel electrolyte sheet, a positive electrode and a negative electrode were prepared as follows.
Was manufactured as shown in FIG.

Gel Electrolyte Sheet A nonwoven polyolefin fiber having a basis weight of 25 g / m ² and a thickness of 70 μm was set in a plasma processing apparatus, and was temporarily set to 1.3 mP.
After reducing the pressure to a, oxygen gas was supplied at a flow rate of 10 cc / min, adjusted to 1.3 Pa, and the frequency was 13.56 MHz.
And the product of the high-frequency output density and the processing time is 10 W · sec /
Plasma treatment was performed so as to obtain cm ² . The polyolefin fiber nonwoven fabric subjected to the gas phase surface treatment by the plasma treatment is hereinafter referred to as “plasma-treated polyolefin fiber nonwoven fabric”. The polyolefin fibers constituting the polyolefin nonwoven fabric which is the base material of the plasma-treated polyolefin fiber nonwoven fabric are composite fibers in which polypropylene is coated with polyethylene around polypropylene.

Separately, after mixing 50 parts by weight of 2-ethoxyethyl acrylate, 13 parts by weight of triethylene glycol dimethacrylate and 33 parts by weight of ethylene glycol ethyl carbonate methacrylate, 5 parts by weight of benzoyl peroxide and 1.22 M LiP
580 parts by weight of an EC / PC (50/50) solution containing F ₆ was added and mixed to prepare a mixed solution in which benzoyl peroxide was completely dissolved.

Next, the above-mentioned plasma-treated polyolefin nonwoven fabric was immersed in the mixed solution, immersed for 20 seconds, taken out, sandwiched between two glass plates having a gap of 75 μm, and heated at 75 ° C. for 30 minutes. A gel electrolyte sheet was obtained. The size of this gel electrolyte sheet is 7
4 mm x 42 mm, ionic conductivity 1.2 x 10
^-3 S / cm.

The EC / PC (50/50) containing 1.22 M LiPF ₆ used in the preparation of the above mixed solution was used.
50) The solution refers to a mixed solvent of ethylene carbonate and propylene carbonate having a volume ratio of 50:50 and LiPF
₆ is a solution in which 1.22 mol / l is dissolved, and is generally called an electrolytic solution. In addition, the obtained gel electrolyte sheet is made of a monomer such as 2-ethoxyethyl acrylate, triethylene glycol dimethacrylate, ethylene glycol ethylene carbonate methacrylate, benzoyl peroxide, etc. Is mixed, and the monomer component is polymerized by heating and gelled while containing a solvent component and the like.

Positive electrode After dry-mixing 40 parts by weight of LiCoO ₂ powder as an active material, 8 parts by weight of flake graphite powder as a conductive additive and 5 parts by weight of polyvinylidene fluoride powder as a binder, 1.22 M of LiPF was further mixed. EC / PC, including ₆ (50 /
50) 25 parts by weight of the solution was added and mixed to obtain an active material-containing paste.

This active material-containing paste is applied to a 25 μm-thick aluminum foil serving as a base material to a thickness of 75 μm, and then heated at 120 ° C. for 20 minutes to form an active material-containing layer. A positive electrode was produced. The dimensions of the active material-applied portion of the positive electrode (meaning the size of the active material-containing layer formed by applying the active material-containing paste to the substrate and heating) were 72 mm × 40 mm.

After dry-mixing 40 parts by weight of spherical graphite powder as the negative electrode active material, 4 parts by weight of flaky graphite powder as the conductive additive, and 5 parts by weight of polyvinylidene fluoride powder as the binder,
37 parts by weight of an EC / PC (50/50) solution containing 2M LiPF ₆ were added and mixed to obtain an active material-containing paste.

The paste containing the active material is coated with a thickness of 25 μm.
After coating to a thickness of 75 μm on a copper foil of
The anode was formed into a sheet by heating for minutes to form an active material-containing layer. The dimensions of the active material coated portion of the negative electrode were 72 mm × 40 mm.

After the gel electrolyte sheet, the sheet-shaped positive electrode, and the sheet-shaped negative electrode produced as described above are laminated so that the active material coated portions of the positive electrode and the negative electrode face each other with the gel electrolyte sheet interposed therebetween. While allowing the ends of the positive and negative electrode leads to be drawn out to the outside as the positive and negative terminals of the battery, the polyester film is used as the outer layer, and the aluminum film is used as the intermediate layer,
The modified polyolefin film was covered with an outer package composed of a three-layer laminate film having an inner layer surface to produce a polymer battery having a schematic structure shown in FIG.

Here, the battery shown in FIG. 1 will be described. A gel electrolyte sheet 3 is disposed between a sheet-like positive electrode 1 and a sheet-like negative electrode 2 to form a laminate. Film-Aluminum film-
The positive electrode terminal 5 and the negative electrode terminal 6 are covered with an exterior body 4 made of a three-layer laminate film of a modified polyolefin film, and are drawn out of the exterior body 4 from ends of the positive electrode 1 and the negative electrode 2.

Comparative Example 1 The same polyolefin fiber nonwoven fabric as in Example 1 was used as a core material except that plasma treatment was not performed, and the polyolefin nonwoven fabric was immersed in the same monomer-containing mixed solution as in Example 1 to obtain a gel electrolyte. An attempt was made to produce a sheet, but no air bubbles escaped, and a gel electrolyte sheet could not be produced.

Comparative Example 2 As in Comparative Example 1, a non-plasma-treated non-woven fabric was used as a core, and the polyolefin non-woven fabric was immersed in the same monomer-containing mixed solution as in Example 1 and impregnated under reduced pressure. A gel electrolyte sheet was produced in the same manner as in Example 1. The ion conductivity of this gel electrolyte sheet was 8.2 × 10 ⁻⁴ S / cm. And
A polymer battery was produced in the same manner as in Example 1 except that this gel electrolyte sheet was used.

Comparative Example 3 A nonwoven fabric of polyethylene terephthalate fiber having a basis weight of 25 g / m ² and a thickness of 70 μm was used as a core material, and this polyethylene terephthalate fiber nonwoven fabric was immersed in the same monomer-containing mixed solution as in Example 1 and impregnated under reduced pressure. Thereafter, a gel electrolyte sheet was produced in the same manner as in Example 1. The ion conductivity of this gel electrolyte sheet is 1.0 × 10 ^−3.
S / cm. Then, a polymer battery was produced in the same manner as in Example 1 except that this gel electrolyte sheet was used.

Table 1 shows the discharge capacities at 20 ° C. and 8 mA discharge, the discharge capacities at 20 ° C. and 80 mA discharge, and the results of the cycle test of the batteries of Example 1 and Comparative Examples 2-3 prepared as described above. Show. In the cycle test, each battery was charged at a constant current of 20 mA, and after the voltage reached 4.2 V, the battery was charged at a low voltage. After a total of 3 hours, the battery was charged at 20 mA.
The cycle of discharging to 2.75 V was repeated, and the number of cycles until the discharge capacity became 80% or less of the initial discharge capacity was examined. The results are shown in Table 1 as the cycle life. The reason for not examining the battery characteristics of Comparative Example 1 is that a gel electrolyte sheet could not be produced in Comparative Example 1 as described above.

[0033]

[Table 1]

As shown in Table 1, in Example 1, the discharge capacity was large, the cycle life was long, and the cycle characteristics were excellent. On the other hand, in Comparative Example 2, the 80 mA discharge capacity (discharge capacity at 80 mA discharge) was smaller than in Example 1, and the cycle life was shorter. The reason for this is that in Example 1, the affinity between the plasma-treated polyolefin fiber nonwoven fabric of the core material and the monomer-containing mixed solution was good, and the gel electrolyte sheet having good ion conductivity was obtained. This is probably because sufficient gel electrolyte was not generated in the voids of the core polyolefin nonwoven fabric.

Further, in Comparative Example 3, the 80 mA discharge capacity was the same as in Example 1, and it can be seen that almost no bubbles were generated in the gel electrolyte sheet immediately after the production. However, Comparative Example 3 had a shorter cycle life than Example 1. This is considered to be because in the case of Comparative Example 3, the internal resistance increased significantly during the cycle test. That is, in the case of Comparative Example 3, it is considered that the polyethylene terephthalate fiber was decomposed during the charge / discharge cycle, and the decomposition product increased the internal resistance and shortened the cycle life.

As shown in Example 1 above, according to the present invention, a gel electrolyte sheet having good ionic conductivity can be obtained by immersion in a short time in the normal state, and the productivity is excellent. The cycle life was long and the cycle characteristics were excellent.

[0037]

As described above, according to the present invention, a polymer battery having high productivity and excellent cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an example of a polymer battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Gel electrolyte sheet 4 Package

Claims (1)

[Claims] 1. A polymer battery comprising a sheet-shaped positive electrode, a sheet-shaped negative electrode and a gel electrolyte sheet, wherein a porous polyolefin sheet subjected to a gas phase surface treatment is used as a core material of the gel electrolyte sheet. Characteristic polymer battery.