JPH02295005A - Lithium ion conductive polymer electrolyte - Google Patents

Abstract

PURPOSE:To obtain a solid-state polymer electrolyte exhibiting excellent lithium ion conductivity at room temperature by using a polymer prepared through the process of reacting specified polymethyl hydrosiloxane with an unsaturated radical at the end of a graft polymerized material of polyether glycol for being subjected to cross- linking treatment. CONSTITUTION:There is used a polymer prepared through the process of reacting polyethyl hydrosiloxane represented by a formula 1 with the unsaturated radical of a polymerized material formed by graftpolymerizing polyether glycol which is represented by a formula II or III and has an unsaturated radical at the end of the formula for being subjected to cross-linking treatment. In the formulas of I, II and III, m is equal to or larger than a number of 1, R represents -H or -CO3, n equals a number of 1 to 200 and x equals a number of 0.1 to 1.0 respectively. The polymethyl hydrosiloxane represented by the formula 1 exhibits high conductivity because of high mobility of its molecular chain. Meanwhile, the polyether glycol represented by the formula II or III has a lot of ether oxygen which may combine lithium ions into a complex to exhibit conductivity, so that it may cause the exhibition of high conductivity. Also this polymer is softened at room temperature and easy to form a conductive film. Thus, a polymer electrolyte can be obtained with its excellent ion conductivity as well as maintaining its solid state under room temperature.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to electrolytes such as lithium batteries and electrochromic displays, lithium ion concentration sensors,
This invention relates to a lithium ion conductive polymer electrolyte that is used for applications such as lithium ion separation membranes.

[Conventional technology]

Attempts have been made to use polymer electrolytes, which are flexible and can be easily formed into a film, as lithium ion conductive solid electrolytes for lithium batteries and the like.

This polymer electrolyte is made of a composite of lithium salt and an organic polymer that dissolves lithium salt. Taking advantage of its flexibility and ease of forming into a film, it can be made thinner and more compact. If it is applied to lithium batteries, which are required to be improved, it will be advantageous in terms of workability and sealing for battery production, and it will also have the advantage of being useful for cost reduction. Furthermore, due to its flexibility, it is thought to be useful as an electrolyte in ``ζelectrochromic displays'' or as a lithium ion concentration sensor.

As organic polymers constituting such polymer electrolytes, polyethylene oxide, polyethyleneimine, polyethylene succinate, etc. have been proposed so far [for example, Fast 1 on Transp.
ort jn Solid P. 131 (197
9) ).

[Problem to be solved by the invention]

However, in the conventional polymer electrolyte made of a composite of an organic polymer and a lithium salt, the polymer component loses crystallinity at high temperatures and exhibits lithium ion conductivity, but at room temperature of about 25"C, the polymer electrolyte loses crystallinity. Due to the high lithium ion conductivity, the lithium ion conductivity is low, and when applied to lithium batteries, which are mostly used at room temperature, and the various applications mentioned above, there is a problem that the performance cannot be fully satisfied.

Therefore, an object of the present invention is to provide a polymer electrolyte that is solid at room temperature and exhibits good lithium ion conductivity by using a polymer different from conventionally used organic polymers as the organic polymer of the polymer electrolyte. shall be.

[Failure to solve the problem]

As a result of intensive research to achieve the above object, the present inventors have found that polymethylsiloxane, which has a low glass transition point, has been selected as an organic polymer constituting the polymer electrolyte.
A crosslinked polymer with a soft crosslinking point obtained by graft polymerizing a polyether glycol having an unsaturated group such as a vinyl group at the end, and then crosslinking the unsaturated group at the end of the resulting graft polymer by reacting the unsaturated group at the end. It was discovered that a solid polymer electrolyte exhibiting good lithium ion conductivity at room temperature can be obtained by using the above method, and the present invention was completed based on this finding.

That is, the present invention provides a lithium ion conductive polymer electrolyte consisting of a composite of a lithium salt and an organic borimer, in which the organic polymer of "2" is a polymethylhydrosiloxane represented by the following formula (1). , consisting of a crosslinked polymer obtained by graft-polymerizing polyether glycol having an unsaturated group at the end represented by formula (IT) or formula (1), and crosslinking the unsaturated groups of the graft polymer by reacting -U. The present invention relates to a lithium ion conductive polymer electrolyte characterized by:

In the present invention, the crosslinked polymer used to constitute the polymer electrolyte is a polymethylhydrosiloquinone represented by the formula (1), a polymethylhydrosiloquinone represented by the formula (1), and a formula (II) or a formula (Ill) as described in "2". Polyether glycol having unsaturated groups at the terminals as shown is graft-polymerized, and the resulting graft polymer is cross-linked by reacting the terminal unsaturated groups. The polymethylhydrosiloxane of formula (1) is
The low glass transition temperature and high molecular chain mobility result in polymer electrolytes exhibiting high lithium ion conductivity.

In addition, polyether glycol having an unsaturated group at the terminal represented by formula (IT) or formula (Ill) has a large amount of ether oxygen based on ethylene oxide or propylene oxide, and this ether oxygen forms a complex with lithium ion. Since it forms and exhibits lithium ion conductivity, it becomes a factor in exhibiting high lithium ion conductivity. Moreover, this formula (I
Since polyether glycol having an unsaturated terminal represented by I) or formula (III) is graft-polymerized to polymethylhy-1-rosiloxane represented by formula (1), it is polymerized in a linear chain. In comparison, even if the molecular weight is increased, the melting point does not increase, and therefore, it is soft and has the characteristic that it is easy to form a film having high lithium ion conductivity at room temperature.

Graph I is obtained by graft polymerizing polyether glycol having an unsaturated group at the end represented by the formula (formerly or formula (III)) to polymethylhydrosiloxane represented by the binary formula (I). Since the unsaturated groups of the polymer are crosslinked by reacting them with gamma rays, electron beams, ultraviolet rays, visible light, radical initiators, etc., the resulting crosslinked polymer is urethane-treated with the diisocyanate that has been studied so far. The crosslinking point is softer than that of a crosslinked material, and therefore, when complexed with a lithium salt, it exhibits high lithium ion conductivity.

In the polymethylhydrosiloxane represented by the formula (1), m in the formula is m≧1, but this means that when m is 0, the number of S i H groups is 2 or less, and when polyether glycol is added to this, the number of S i H groups is 2 or less. This is because a soft polymer cannot be obtained even if the grafted polymer is crosslinked. As m becomes larger, the glass transition temperature increases accordingly, so m is desirably 200 or less. Especially desirable
L;i:, m-1 to 50.

Formula (II) and formula (T[l) having an unsaturated group at the terminal
In the formula, the number of n indicates the number of monomer units of polyether glycol, but n is 1 to 2.
Must be 00. When the dirt G'n is 0, no ether glycol is added, so no complex formation with the lithium salt occurs, and as a result, lithium ion conductivity cannot be obtained, and when n is larger than 200, This is because the crosslinking reaction becomes difficult to occur and a large amount of uncrosslinked graft polymer remains, resulting in a large decrease in ion conductivity. Desirably, n=2 to 100. In addition, in the formula (rib and formula (III)), χ represents the EO/(EO+PO) ratio of EO (ethylene oxide) and PO (propylene oxide) in the polymer;
．． It needs to be between 1 and 1.0. This means that χ is 0.
If it is smaller than 1, the amount of ethylene oxide is small, making it difficult to form a complex with a lithium salt, resulting in low lithium ion conductivity.

To react the terminal unsaturated groups of the graft polymer, T
Radiation, electron beam, ultraviolet light, visible light or radical initiators are used, such as cumene hydroperoxide, henzoyl peroxide, lauroyl peroxide, potassium peroxide, petit hydroperoxide, Organic peroxides such as dicumyl peroxide and di-butyl peroxide, azobis compounds such as azobisisobutyronitrile, azobis-2,4-dimethylbatonitrile, and azobiscyclohexatonitrile are used, and the amount used is is usually 0.01 to 1 part by weight per 100 parts by weight of the graft polymer, and the reaction is 2 parts by weight.
The reaction is carried out at 5 to 100°C for a reaction time of about 5 minutes to 2 hours, and the desired crosslinked polymer is obtained.

In the present invention, any of the lithium salts used in conventional polymer electrolytes can be used together with the above-mentioned crosslinked polymer to form the lithium ion conductive polymer electrolyte.

Specific examples include LiBr, Li1. ．．
L i SCNXL i BF,, L iΔsF+. ,
LIC104, L ] CF 3 SO. , l-
i C+, F 13s Oa, L i H z I. and so on. The amount of these lithium salts used is usually in the range of 1 to 30% by weight, especially 3 to 30%, based on the crosslinked polymer.
A range of 20% focus is desirable.

The lithium ion conductive polymer electrolyte of the present invention is composed of a composite of the above-mentioned cross-linked polymer and a lithium salt. The lithium salt solution can be impregnated into the crosslinked polymer by immersion in the crosslinked polymer, and then the organic solvent solution is evaporated off.

By immersing the crosslinked polymer in the lithium salt solution as described above, the lithium salt forms a complex with the ether oxygen in the crosslinked polymer and bonds, and even after the solvent is removed, the above bond is maintained, and the crosslinked polymer and lithium salt A complex with is obtained.

The form of the polymer electrolyte is appropriately determined depending on its intended use. For example, when a polymer electrolyte is used as an electrolyte for a lithium battery and also functions as a separator between positive and negative electrodes, the polymer electrolyte may be formed into a sheet shape. To obtain this sheet-shaped polymer electrolyte, a cross-linked polymer is formed into a sheet-like shape, and this sheet-shaped cross-linked polymer is immersed in an organic solvent solution of lithium salt, and the lithium salt solution is applied to the cross-linked polymer. After letting it penetrate, is it okay? The TJ medium may be removed by evaporation. As the above-mentioned polymer electrolyte sheet, an extremely thin sheet on the order of microns, which is generally called a film, can also be produced.

In addition, when applying the polymer electrolyte of the present invention to a positive electrode of a lithium battery, a pre-crosslinked graft polymer, a radical initiator, a positive electrode active material, etc. are added in a predetermined ratio, and the unsaturated groups of the graft polymer are reacted. The resulting molded product may be immersed in a solution of a lithium salt in an organic solvent, and then the organic solvent may be removed by evaporation. By doing so, a mixture of the polymer electrolyte and the positive electrode active material can be obtained.

In obtaining the polymer electrolyte, the organic solvent for dissolving the lithium salt is Lithium J, which sufficiently dissolves the salt,
Any organic solvent may be used as long as it does not react with the crosslinked polymer.
For example, acetate, dihydrofuran, dimethoxyethane, dioxolane, polypylenecarbofluoride,
, ace1,21-lyl, dimethylformamide, etc. are used.

Figure 1 shows an example of a lithium battery using the polymer electrolyte of the present invention described above. A shallow rectangular dish-shaped negative electrode current collector plate made of stainless steel with a flat peripheral part (2a) facing in the same direction as the main surface bent stepwise to the side, (3) is a bipolar current collector plate (1 ), (2) is an adhesive layer that seals between the opposing peripheral parts (li) and (2a).

(4) refers to the polymer electrolyte of the present invention, the positive electrode active material, etc. arranged on the positive electrode current collector plate (1) side in the space (5) formed between the two electrode current collector plates (1) and (2). A positive electrode formed into a sheet shape by the method described above, (6) a negative electrode made of lithium or a lithium alloy loaded on the negative electrode current collector plate (2) side in the space (5), (7) is a separator formed by molding the polymer electrolyte of the present invention into a sheet shape, which is interposed between a positive electrode (4) and a negative electrode (6).

The positive electrode (4) may be formed into a sheet by mixing a positive electrode active material with a binder such as polytetrafluoroethylene powder or an electron conduction aid, as the case may be. As the positive electrode active material used for the positive electrode (4), for example, Tie. , MoS2, V b 01 :l, ■205
, VSe, NiPS:+, polyaniline, polypyrrole, polythiophene, or two or more of them are used.

A lithium battery configured in this way has a separator (7
) is a sheet material made of the lithium ion conductive polymer electrolyte, and the positive electrode (4) is a similar sheet material containing the lithium ion conductive polymer electrolyte, thereby making it possible to make the battery thinner and It has various advantages such as contributing to improvements in manufacturing workability and reliability of sealing, and there is essentially no fear of leakage unlike liquid electrolytes. Since the polymer electrolyte described above has excellent lithium ion conductivity, it has excellent discharge performance as a primary battery and extremely excellent charge/discharge cycle characteristics as a secondary battery.

〔Example〕

EXAMPLES The present invention will be described in more detail with reference to Examples below.

Example 1 Polyether glycol [manufactured by NOF, average molecular weight 1,
000) and 26 g of acetylene were reacted in an O-1 grape at 50° C. for 6 hours with the addition of potassium hydroxide to convert the terminal end into vinyl ether.

The polyether glycol whose terminal end is modified to vinyl ether in this way has a vinyl group at the end represented by formula (III) (the unsaturated group is a vinyl group, so in order to clarify this fact, the unsaturated group is a vinyl group). These are polyether glycols having a vinyl group (not expressed as an unsaturated group), and have n, χ, R, n-22, Z-1.0 in formula (III). , R is -H.

[
Graft polymerization was carried out by reacting 20.8 g (manufactured by Toshiba Silicone, average molecular weight 208, according to formula (1), m = 1, R is H) at 100 ° C for 3 hours using zinc octylate as a catalyst. I got something. That is, a graft polymer was obtained by graft polymerizing polyether glycol having a vinyl group at the end to pentamethyltrisiloxane.

Next, 5 g of the graft polymer obtained as described above and 2 mg of azobisisobutyronitrile were placed in a sample bottle, stirred with a magnetic stirrer, and the resulting viscous solution was dropped onto an aluminum plate, and argon gas was added. A crosslinking treatment was carried out by reacting at 100'C for 1 hour on a hot plate in a gas atmosphere to obtain a crosslinked polymer.

I7 The obtained crosslinked polymer was peeled off from the aluminum plate and immersed in acetone to remove unreacted materials.

Subsequently, this cross-linked polymer was immersed in a solution of LiBF4 in acetone for 8 hours to impregnate the cross-linked polymer with the LiBF4 acetone solution, and the acetone was removed by evaporation to reduce the thickness to O. ．． ] mm of C-shaped polymer electrolyte was obtained.

Example 2 Polyether glycol [manufactured by Hiki Yushi Co., Ltd., average molecular weight 40
A sheet-shaped polymer electrolyte having a thickness of 0.1 mm was obtained in the same manner as in Example 1, except that 40 g of polyether glycol whose terminal end was modified to vinyl ether was used.

That is, the terminal end of 40 g of the above polyether glycol was modified to vinyl ether in the same manner as in Example 1 to obtain a polyether glycol having a vinyl group at the end represented by formula (1). When this polyether glycol having a vinyl group at the end is shown according to the formula (■), n=
9, χ-1.0, and R is -H.

Next, 40 g of the above-mentioned polyether glycol having a vinyl group at the end was graft-polymerized to pentamethyltrisiloxane in the same manner as in Example 1, and the obtained graft polymer was cross-linked in the same manner as in Example 1, The obtained crosslinked polymer was immersed in a lithium salt solution in the same manner as in Example 1 to obtain a sheet-like polymer electrolyte with a thickness of 0.1 mm.

Example 3 Polyether glycol [manufactured by NOF, average molecular weight 3,
A sheet-like polymer electrolyte having a thickness of 01 mm was obtained in the same manner as in Example 1, except that 300 g of polyether glycol whose terminal end was converted into vinyl ether was used.

That is, the terminal end of 40 g of the polyether glycol was modified to vinyl ether in the same manner as in Example 1 to obtain a polyether glycol having a vinyl group at the end represented by 2N). When this polyether glycol having a vinyl group at the end is shown according to the formula (■), n-6
8, χ-1.0, R is -I].

Next, 40 g of the above-mentioned polyether glycol having a vinyl group at the end was graft-polymerized to pentamethyltrisiloxane in the same manner as in Example 1, and the obtained graft polymer was cross-linked in the same manner as in Example 1. The obtained crosslinked polymer was immersed in a lithium salt solution in the same manner as in Example 1 to obtain a sheet-like polymer electrolyte having a thickness of 0.1 mm.

Example 4 A sheet with a thickness of 0.1 mm was prepared in the same manner as in Example 1, except that 35 g of polymethylhydrosiloxane (manufactured by Toray Silicone, m = 5 in 2 (1)) was used instead of pentamethylsiloxane. {·-shaped polymer electrolyte was obtained.

Example 5 Polymethylhydrosiloxane [Nitrogen Q!] was used instead of pentamethylsiloxane. In formula (1), m =
20) A sheet-like polymer electrolyte with a thickness of 0.1 mm was obtained in the same manner as in Example 1 except that 137 g was used.

Example 6 A C1-like polymer electrolyte was obtained in the same manner as in Example 1, except that 100 g of polyether glycol having a vinyl group at the end of Example 1 was used.

Example 7 Instead of polyether glycol having a vinyl group at the end of Example 1, polyether glycol having a vinyl group at the end represented by the formula (formerly) in which the end of polyether glycol was modified to acrylate [NOF] product, average molecular weight 1,000, in formula (II), n-22, χ=1
．． A C1-shaped polymer electrolyte having a thickness of 0.1 mm was obtained in the same manner as in Example 1, except that 100 g of the polymer electrolyte was used.

Comparative Example 1 4 g of glycerin ether of polyethylene oxide (manufactured by Daiichi Kogyo Seiyaku, average molecular weight 3,000) and 232 mg of tolylene 2,4-diisocyanate were placed in a flask, stirred with a magnetic stirrer, and then placed on an aluminum plate. 100% on a Bottle plate in argon gas.
A crosslinked polymer was obtained by reacting at °C for 8 hours. Thereafter, in the same manner as in Example 1, a sheet-like polymer electrolyte having a thickness of 0.1 mm was obtained.

In order to investigate the performance of the polymer electrolyte obtained as described above, the following ionic conductivity test and internal resistance test were conducted.

Ionic conductivity test> The polymer electrolytes of Examples 1 to 7 and Comparative Example 1 were sandwiched between lithium foils in a Nantesian shape, and the alternating current impedance between the lithium electrodes was measured. ) was measured. The results are shown in Table 1 below.

Table 1 In addition, the ionic conductivity under various temperature conditions was measured in the same manner as in Section 2, and the results are shown in FIG.

In Figure 2, the vertical axis represents the ionic conductivity (S/cm
), and the horizontal axis is the reciprocal of absolute temperature 10'/T (K-'
).

Internal resistance test of a battery> Using the polymer electrolytes of Examples 1 to 7 and Comparative Example 1, a total thickness of 0.5 mm and a side length of 1 with a total thickness of 0.5 mm and a configuration shown in FIG.
A square-shaped thin lithium battery of cII1 was manufactured. The negative electrode was made of an alloy of lithium and aluminum, and the positive electrode was a sheet-like molded product containing the same polymer electrolyte and TiSz as used in Examples 1 to 7 and Comparative Example 1.

For these lithium batteries, 25°C, 60°C,
The internal resistance at ioo'c was measured. The results are shown in Table 2 below.

Table 2 As is clear from the ionic conductivity results shown in Table 1 above, the polymer electrolytes of Examples 1 to 7 of the present invention had an IX 10-5S/cm - ] ×IO-' at 25°C. S
/cm, but the polymer electrolyte of Comparative Example 1 had an ionic conductivity of IXIO− at 25°C.
It was as low as 6S/cm. Therefore, as shown in Table 2, the internal resistance of the lithium batteries using the polymer electrolytes of Examples 1 to 7 of the present invention at 25°C is 100Ω to 1000Ω.
Ω, but the internal resistance of the lithium battery using Comparative Example 1 at 25°C was as large as 10,000 Ω.

〔Effect of the invention〕

As explained above, in the present invention, polymethylhy-1-rosiloxane having a low glass transition point represented by formula (I) is used as an organic polymer constituting a composite with a lithium salt.
By graft polymerizing a polyether glycol having a vinyl group at the terminal represented by formula (II) or formula (Ill), and using a crosslinked polymer obtained by crosslinking by reacting the vinyl Go of the obtained graft polymer. We were able to provide a lithium ion conductive polymer electrolyte that is solid at room temperature and has excellent ion conductivity.

[Brief explanation of the drawing]

2. The image is a longitudinal cross-sectional view showing an example of a lithium battery using the lithium ion conductive polymer electrolyte of the present invention as a separate layer, and the second image is a longitudinal sectional view showing an example of a lithium battery using the lithium ion conductive polymer electrolyte of the present invention. FIG. 3 is a characteristic diagram showing the relationship between ionic conductivity and temperature. (7) Separate leaves made of polymer electrolyte...
-, Shock 7... Procedural amendment for separator made of polymer electrolyte (spontaneous) August 11, 1999 Patent Application No. 116737 2. Name of the invention Lithium ion conductive polymer electrolyte 3. Relationship with the case of those who cheated on amendments Address of the applicant for permission 1-1-88 Ushitora, Ibaraki City, Osaka Name (58
1) Hitachi Maxell, Ltd. Representative Sumihiro Watari 4. Agent 〒550 Phone 06 (531) 8
277 Address 1-23 Kitahorie 1-chome, Nishi-ku, Osaka 7. List of attached documents (1) Drawings (2nd session)

Claims (1)

[Claims] (1) In a lithium ion conductive polymer electrolyte consisting of a composite of a lithium salt and an organic polymer, the organic polymer described above is combined with polymethylhydrosiloxane represented by the following formula (I) and the formula (II) or the formula A lithium ion conductive material characterized by being made of a crosslinked polymer obtained by graft polymerization of polyether glycol having an unsaturated group at the end represented by (III) and crosslinking by reacting the unsaturated groups of the graft polymer. Polymer electrolyte. Formula (I): ▲There are mathematical formulas, chemical formulas, tables, etc.▼・ [In the formula, m≧1, R is -H or -CO_3 Formula (II): ▲There are mathematical formulas, chemical formulas, tables, etc.▼・・・( II) [In the formula, n = 1 to 200, χ = 0.1 to 1.0 is the formula (1
) has the same meaning as in formula (II)] Formula (III): ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(III) [In the formula, n, χ and R have the same meaning as in formula (II) have]