JP2001093575A - Gel electrolyte for use in polymer battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel polymer electrolyte suitable for use in a non-aqueous battery, particularly a lithium ion battery. SOLUTION: The gel electrolyte consists of a matrix polymer, a non-aqueous solvent, and an inorganic lithium salt. The matrix polymer contains a chemically cross-linked body, which consists of acrylic oil-containing compound represented by the formula (1), and a cross-linking compound containing vinyl ether at both ends as represented by the formula (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a gelled solid electrolyte suitable for use in non-aqueous batteries, particularly lithium ion batteries. In particular, the present invention relates to a gel electrolyte for polymer batteries containing a chemically cross-linked product of an acryloyl group-containing compound and a cross-linking compound having a vinyl ether group at both terminals as a matrix polymer and further containing a lithium inorganic salt and a non-aqueous solvent.

[0002]

2. Description of the Related Art In recent years, with the rapid development of electronics, electronic devices, especially portable electronic devices such as mobile phones and notebook computers, have been reduced in weight, size and performance.
The development of thin-film secondary batteries with high energy density is urgent. In particular, lithium secondary batteries are becoming the mainstream of secondary batteries because they have a discharge voltage and energy density far exceeding those of lead-acid batteries, Ni-Cd batteries, and nickel-metal hydride batteries. As described above, a lithium secondary battery having a high energy density, a large battery capacity, and good repetitive charge / discharge properties includes a positive electrode made of a lithium composite oxide such as lithium cobalt oxide and lithium manganate, and lithium and lithium. A porous membrane separator is immersed in a non-aqueous electrolyte solution containing a lithium salt between negative electrodes made of a material capable of doping and undoping lithium ions such as an alloy or a carbon material and sealed in a conductive closed container. Are known. In the case of such a lithium secondary battery, the outer container is made of a metal container, that is, a metal can, in order to prevent the non-aqueous electrolyte present inside the battery from leaking to the outside. There are processing limitations. Further, the container structure becomes complicated, and there is a problem that leakage of the electrolyte is likely to occur due to impact such as dropping.

In order to solve such a liquid leakage problem of a lithium secondary battery using a non-aqueous electrolyte, and to further improve the performance of the battery, polymerization of each component of the battery has been studied in recent years. In particular, electrolyte polymerization has been developed mainly for polyoxyethylene oxide, polyacrylonitrile, polymethyl methacrylate, and polyvinylidene fluoride materials. Polymerization of the electrolyte was initially studied as a completely solid electrolyte containing no non-aqueous electrolyte solution, but the ionic conductivity was low and it was far from practical use. However, when a polymer is impregnated with a non-aqueous electrolyte to form a gel electrolyte, the ionic conductivity is higher than that of a completely solid electrolyte, and the electrolyte is gelled and a liquid non-aqueous electrolyte is directly used. Therefore, the risk of leakage is reduced, and a polymer film can be used in place of metal, so that the thickness can be further reduced.

As a lithium secondary battery using such a polymer electrolyte, a gel electrolyte formed by impregnating an electrolyte solution comprising a non-aqueous solvent and a lithium inorganic salt electrolyte into a polymer matrix is disposed between a positive electrode and a negative electrode. Lithium ion batteries having the following structure have been proposed (JP-A-9-22)
727, etc.). As described above, as the polymer matrix used for the gel electrolyte of the lithium ion battery having such a structure, a fluororesin or the like is used, and in particular, a copolymer of vinylidene fluoride and hexafluoropropylene is used. Although practicality is expected, the ionic conductivity of the gelled polymer solid electrolyte still used is smaller than that of the conventional non-aqueous electrolyte, and the polymerization of the electrolyte is under development.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a gel-like solid polymer electrolyte having better ionic conductivity than conventional polymer electrolytes. Still another object of the present invention is to provide a polymer solid matrix suitable for use in a gel solid electrolyte for a lithium ion battery.

[0006]

The present invention for solving the above-mentioned problems includes the following inventions. (1) A gel solid electrolyte comprising a matrix polymer, a non-aqueous solvent, and a lithium inorganic salt, wherein the matrix polymer has a general formula (1):

Embedded image (Wherein R ¹ is a hydrogen atom, an alkyl group, an aryl group, an acyl group, an alkenyl group, a cycloalkyl group or an aralkyl group, and these groups may be alkylene oxide-modified). Containing compound and general formula (2)

Embedded image (Wherein R ² and R ³ may be the same or different from each other;
A hydrogen atom or an alkyl group having 1 to 5 carbon atoms;
Is an integer of 1 to 50. A gelled solid electrolyte for a secondary battery, comprising a chemically crosslinked product formed from a crosslinked compound having a vinyl ether group at both ends represented by the formula (1).

(2) The matrix polymer comprises a compound having an acryloyl group represented by the general formula (1) and a cross-linking compound having a vinyl ether group at both terminals represented by the general formula (2) in a molar ratio of (1) / ( 2) = 100/1 to 10
The gelled solid electrolyte for a secondary battery according to item (1), comprising a chemically crosslinked product containing 0/10. (3) The chemically crosslinked product is used as a matrix polymer in the form of 5-
Item (1) or (2), characterized by containing 50% by weight.
10. The gelled solid electrolyte for a secondary battery according to item 8.

(4) General formula (1),

Embedded image (In the formula, R ¹ is a hydrogen atom, an alkyl group, an aryl group, an acyl group, an alkenyl group, a cycloalkyl group or an aralkyl group, and these groups may be alkylene oxide-modified.) Containing compound and general formula (2)

Embedded image (Wherein R ² and R ³ may be the same or different from each other;
A hydrogen atom or an alkyl group having 1 to 5 carbon atoms;
Is an integer of 1 to 50. A) a chemically crosslinked substance formed from a crosslinked compound having a vinyl ether group at both ends represented by the formula

(5) The acryloyl group-containing compound represented by the general formula (1) and the vinyl ether group-containing cross-linked compound at both ends represented by the general formula (2) are represented by a molar ratio of (1) /
(2) = A chemically crosslinked substance contained at 100/1 to 100/10.

(6) The gel solid electrolyte for a secondary battery according to any one of the above items (1) to (3) is formed by mixing a positive electrode active material made of a lithium composite oxide material and a negative electrode made of a conductive carbonaceous material. A lithium-ion battery having a structure arranged between them.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A gel polymer solid electrolyte for a secondary battery according to the present invention comprises an acryloyl group-containing compound represented by the general formula (1) and a vinyl ether group-containing compound having both ends represented by the general formula (2). It is constituted by using a chemically crosslinked body formed from a crosslinked compound as a matrix polymer, and further containing a non-aqueous solvent and a lithium inorganic salt.

The acryloyl group-containing compound represented by the general formula (1), which is one of the components forming the matrix polymer used in the gelled solid electrolyte of the present invention, includes methyl acrylate, ethyl acrylate, propyl acrylate, and propylene. Acrylate, isopropyl acrylate, butyl acrylate, sce-butyl acrylate, tert-butyl acrylate, pentyl acrylate, isopentyl acrylate, neopentyl acrylate, tert-pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, Lauryl acrylate, methoxyethylene oxide acrylate, methoxypolyethylene oxide acrylate,
Methoxy propylene oxide acrylate, methoxy polypropylene oxide acrylate, phenoxyethyl acrylate, phenoxy polyethylene oxide acrylate, phenoxypropylene oxide acrylate,
Phenoxy polypropylene oxide acrylate, acrylic acid dimer and the like can be mentioned.

As the other component forming the matrix polymer used in the gelled solid electrolyte of the present invention, the cross-linking compound having a vinyl ether group at both ends represented by the general formula (2) includes diethylene glycol divinyl ether and triethylene Examples thereof include glycol divinyl ether, polyethylene glycol divinyl ether, dipropylene glycol divinyl ether, tripropylene glycol divinyl ether, and polypropylene oxide divinyl ether.

The crosslinking reaction between the acryloyl group-containing compound of the general formula (1) and the cross-linking compound having a vinyl ether group at both ends of the general formula (2) is carried out in a molar ratio of the compound (1) / compound (2) = 100/1 to 100/1. It is carried out by causing a crosslinking reaction at a ratio of 100/10. The crosslinking reaction is usually performed using a suitable polymerization initiator. As the polymerization initiator, a radical initiator selected from an organic peroxide, an azo compound and the like is used. For example, azobisisobutyronitrile,
Examples include azobisisovaleronitrile, benzoyl peroxide, lauroyl peroxide, methyl ethyl ketone peroxide, bis- (4-t-butylcyclohexyl) peroxydicarbonate, diisopropyl peroxycarbonate, and the like.

[0015] The amount used is 0.005 to 1% by weight, preferably 0.01 to 1% by weight, based on the total amount of the gel solid electrolyte constituents.
0.8% by weight. The cross-linking reaction can be carried out by maintaining a mixture of both compounds at a heating temperature of 30 ° C to 90 ° C, preferably 35 ° C to 65 ° C for 0.5 hours to 8 hours, preferably 2 hours to 6 hours. it can.

As the non-aqueous solvent used for the gel solid electrolyte of the present invention, an organic solvent used for an electrolyte for a lithium ion battery or a gel electrolyte is usually used.
For example, ethylene carbonate, propylene carbonate, γ-butyrolactone, butylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-dimethoxypropane, 3-methyl-2-oxazolidone, tetrahydrofuran, 2-hydrofuran
Methyltetrahydrofuran, 1,3-dioxolane,
4,4-dimethyl-1,3-dioxolan, tert-
Butyl ether, isobutyl ether, 1,2-ethoxymethoxyethane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, ethylene glyme, ethylene diglyme , Methyldiglyme, methyltriglyme, methyltetraglyme, methyl formate, methyl acetate, methyl propionate, dimethyl sulfoxide, N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N
-Methylacetamide, N-ethylacetamide, N-
Methylpyrrolidone, N-vinylpyrrolidone, sulfolane and the like can be mentioned. A mixture of two or more of these may be used.

As the lithium inorganic salt used in the gelled solid electrolyte of the present invention, lithium inorganic salts which are generally known to be usable as an electrolyte for a gelled lithium ion battery can be used. For example, lithium tetrafluoroborate (LiBF ₄ ), LiPF ₆ , L
iAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN
(CF ₃ OSO ₂ ) ₂ , LiCH ₃ SO ₃ , LiC (C
F ₃ OSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN
(CF ₃ SO ₂ ) ₂ , LiCl, LiBr, etc. can be used. These lithium inorganic salts are mixed with the matrix polymer while being dissolved in an organic solvent that is not reactive with them. The mixing amount is 1 liter of non-aqueous solvent,
It is 0.5 to 2 mol%, preferably 0.8 to 1.5 mol%.

The lithium ion battery containing the gelled solid electrolyte according to the present invention is constituted by arranging ordinary positive and negative electrode materials with the gelled solid electrolyte interposed therebetween. As the positive electrode material and the negative electrode material, those known as materials used for lithium ion batteries can be used as they are.

[0019]

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

Example 1 (Preparation of gel electrolyte) A mixture of ethylene carbonate and propylene carbonate at a weight ratio of 1: 1 as a non-aqueous solvent, and lithium tetrafluoroborate (LiBF ₄ ) as a lithium inorganic salt To 1 liter of non-aqueous solvent
Mole dissolved [Sollite manufactured by Mitsubishi Chemical Corporation]
And methyl acrylate [manufactured by Tokyo Chemical Industry Co., Ltd.] as an acryloyl group-containing compound, and triethylene glycol divinyl ether [Rap-CureD manufactured by ASP Japan Co., Ltd.] as a compound containing a vinyl ether group at both ends.
VE-3] was mixed at a molar ratio of 100/3. Furthermore, azobisisobutyronitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) was added as a thermal polymerization initiator in an amount of 0.03% based on the total weight. This mixture was reacted at 65 ° C. for 6 hours to prepare a gel electrolyte. Preparation of the sample and preparation of the gel were all performed in a dry box under an argon gas atmosphere.

(Evaluation of Gel State) After completion of the reaction, the gel state was visually evaluated. The sample was in the form of a gel and maintained the shape, was rated as ○, the sample in the form of a gel but could not maintain the shape (flowable) was rated △, and the sample that remained in the liquid was rated as ×. ○ can be used as a gel electrolyte. Table 1 shows the results.

(Measurement of Ion Conductivity) The prepared gel electrolyte was cut into 20 × 20 mm, and both sides were sandwiched between electrodes of a lithium metal foil having a thickness of 200 μm, which was also cut into 20 × 20 mm. The electric conductor and the outermost layer were sandwiched between glass plates to prepare a cell for measuring ion conductivity. The measurement of ionic conductivity uses an alternating current impedance measurement method, and the measuring instrument is potentiostat SI 1287
[Toyo-Technica Co., Ltd.] and Frequency Response Analyzer 1250 [Toyo-Technica Co., Ltd.] were used.
The ionic conductivity was determined by the le-Plot method. Table 1 shows the results. In addition, the work of cell production and the measurement of ion conductivity were all performed in a dry box under an argon gas atmosphere.

Example 2 In Example 1, tripropylene glycol divinyl ether [Rapi-Cure D manufactured by ASP Japan Co., Ltd.] was used as the compound containing a vinyl ether group at both ends.
A gel electrolyte was prepared in the same manner as in Example 1 except that PE-3] was used. With respect to the obtained electrolyte, the operation of preparing the cell and the measurement of the ionic conductivity were performed in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1 A gel electrolyte was prepared in the same manner as in Example 1 except that methyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of methyl acrylate.
In the same manner as in Example 1, the operation of preparing the cell and the measurement of the ionic conductivity were performed. The results are shown in Table 1.

Comparative Example 2 A gel electrolyte was prepared in the same manner as in Example 1 except that triethylene glycol diacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of triethylene glycol divinyl ether. went. In the same manner as in Example 1, the operation of preparing the cell and the measurement of the ionic conductivity were performed. The results are shown in Table 1.

[0026]

[Table 1]

[0027]

As is clear from Table 1, the gelled solid electrolyte containing the matrix polymer of the present invention has a sufficient ionic conductivity and excellent gel properties, and has a gel-like shape for lithium ion batteries. It has characteristics that can be sufficiently used as a solid electrolyte, and greatly contributes to practical use of a polymer battery.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J011 PA06 PA14 PA26 PA29 PA30 PA35 PA37 PA45 QA03 QA13 WA10 4J100 AG68Q AL03P AL04P AL05P AL08P AL74P BA02Q BA04P BA05P BA08P BA08Q BC43P CA04 JA45 5H029 AJ00 AM04 AM05 BJ04 HJ01 HJ02 HJ07

Claims (3)

[Claims] 1. A gel electrolyte comprising a matrix polymer, a non-aqueous solvent and a lithium inorganic salt, wherein the matrix polymer has a general formula (1): (In the formula, R ¹ is a hydrogen atom, an alkyl group, an aryl group, an acyl group, an alkenyl group, a cycloalkyl group or an aralkyl group, and these groups may be alkylene oxide-modified.) Containing compound and a compound represented by the general formula (2): (Wherein R ² and R ³ may be the same or different from each other;
A hydrogen atom or an alkyl group having 1 to 5 carbon atoms;
Is an integer of 1 to 50. A gel electrolyte for a polymer battery, characterized by containing a chemically crosslinked product composed of a crosslinked compound having a vinyl ether group at both ends represented by the formula (1). 2. The matrix polymer according to claim 1, wherein the acryloyl group-containing compound represented by the general formula (1) and the vinyl ether group-containing cross-linked compound at both ends represented by the general formula (2) are in a molar ratio of (1) / (2). ) = 100/1 to 100
The gel electrolyte for a polymer battery according to claim 1, comprising a chemically crosslinked product containing / 10. 3. The gel electrolyte for a polymer battery according to claim 1, wherein the chemically crosslinked body is contained as a matrix polymer in an amount of 5 to 50% by weight.