JPH03190959A - Lithium ion-conductive polyelectrolyte - Google Patents

Abstract

PURPOSE:To provide the title polyelectrolyte solid at room temperature, excellent in lithium ion conductivity, suitable as e.g. an electrolyte for lithium cells, electrochromic displays etc., made up of a specific organic polymer and a lithium salt. CONSTITUTION:The objective polyelectrolyte can be obtained by incorporating (A) a crosslinked polymer produced by crosslinking a siloxane-polyether grafted product of formula I (m is 3-10; n is 1-200; x is 0.1-1; R is -OH, -OCH=CH2, etc.) with (B) 0.1-40 (pref. 3-20)wt.% of a lithium salt (e.g. LiBr, LiI). Specifically, the present polyelectrolyte can be produced through the following process: the above-mentioned crosslinked polymer is immersed in a lithium salt solution to effect the penetration of the solution into the polymer followed by evaporating and removing the organic solvent. Said lithium salt is bound, in the form of a complex, to oxygen of ether in the crosslinked polymer.

Description

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

[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. In addition, due to its flexibility, it is thought to be useful as an electrolyte for electrochromic displays and as a lithium ion concentration sensor.

Organic polymers constituting such polymer electrolytes include polyethylene oxide, polyethyleneimine,
A number of materials have been proposed, including polyethylene succinate and crosslinked triol polyethylene oxide.

[Problem to be solved by the invention]

However, the conventional polymer electrolyte described above has low lithium ion conductivity at 25°C, and its performance is not fully satisfactory when applied to lithium batteries, which are mostly used at room temperature F, and various applications such as those mentioned above. There was a problem.

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 the above-mentioned organic polymers as the organic polymer of the polymer electrolyte.

[Means to solve the problem]

As a result of extensive research in order to achieve the above object, the present inventors have developed a lithium salt obtained by crosslinking a specific cyrogisan-polyether grafted product as an organic polymer constituting a polymer electrolyte. It was discovered that by using a polymer that is sufficiently soluble, has a low glass transition temperature, and has a low degree of crystallinity, a solid polymer electrolyte that exhibits good lithium ion conductivity at room temperature can be obtained, and this led to the completion of the present invention. It's arrived.

However, the present invention provides a lithium ion conductive polymer electrolyte consisting of a composite of a lithium salt and an organic polymer, in which the organic polymer has the following formula (J); 0 ((CHzCIIzO)X(CHzCHO)+ −
X) ,,CthCt(zCHzR [where m is 3 to
10, n is 1-200. , x = 0.1~1.0, R =
OHl-0CH=CH2 or the following formula (a); CIl+ CIl:I CI+3Si
-0-3i-0-3i-CI=CHz -(a
) CH3CII3 C113 This invention relates to a lithium ion conductive polymer electrolyte characterized by being made of a crosslinked polymer obtained by crosslinking a siloxane-bolyether grafted product represented by:

[Structure and operation of the invention]

The siloxane-bolyether grafted product represented by formula (1) used in the present invention has a siloxane bond in the molecule, and therefore has high molecular mobility. When this grafted product is crosslinked by appropriate means using its terminal groups, it becomes a rubbery and solid polymer.
When a lithium salt is added to this, a crosslinked polymer exhibiting high lithium ion conductivity is produced. Here, in the above-mentioned conventional cross-linked triol polyethylene oxide, etc., coagulation due to glycerin occurred at around room temperature of about 25°C, causing a large decrease in ionic conductivity, but in the present invention, the specific structure described in Since the siloxane compound is used, there is no particular concern about this, and the high lithium ion conductivity as described above is maintained well even at room temperature.

In the siloxane-polyether grafted product represented by the above formula (1) of the present invention, n indicates the number of moles of ethylene oxide or added moles of this and propylene oxide, and n is an integer of 1 to 200. is necessary. This is because when n is O, ethylene oxide or propylene oxide is not added, so complex formation with lithium salt does not occur, 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, leaving a large amount of uncrosslinked grafted material, and in this case, the lithium ion conductivity is greatly reduced.

The siloxane-polyether graph 1 to compound represented by the above formula (1) of the present invention can be produced by, for example, reacting cyclopolymethylsiloxane with polyether glycol monoallyl ether, that is, reacting one Si group of the former with a hydroxyl group of the latter. A grafting reaction is carried out to produce a grafted product having a terminal allyl group, and then the terminal allyl group is modified by an appropriate means so that R in the formula flj is -OH2OCH=CHz or a group represented by the above formula ta+. It can be obtained by making a certain grafted product.

In the grafting reaction described in Section 2, approximately 8 mol of polyether glycol monoallyl ether is used per 1 mol of cyclopolymethylsiloxane, and a metal salt such as zinc octylate or tin octylate is used as a catalyst. What is necessary is just to make it react at the temperature of 20-100 degreeC.

In addition, for modification of the terminal allyl group, for example, in the case of hydroxyl group modification, the grafted product having the terminal allyl group may be reacted with dilute sulfuric acid and then treated with alkali, and in the case of vinyl group modification, the alkyl vinyl ether may be treated with acetic acid after the above hydroxyl group modification. The reaction can be carried out in the presence of mercury or the like. Also, the formula (a
) can be introduced by reacting the grafted product having a terminal allyl group with vinylhydro-1-helisiloxane in the presence of chloroplatinate or the like.

In the present invention, the thus obtained grafted product is crosslinked to produce a crosslinked polymer. When the end of the grafted product is a hydroxyl group, a bifunctional compound that can react with the hydroxyl group, such as hexamethylene diisocyanate I, 2,4-tolylene diisocyanate, methylene bis( Diisocyanate compounds such as 4-phenylisocyanate-1-), xylylene diisocyanate, diamine compounds such as ethylenediamine and putrescine, dicarboxylic acid compounds such as oxalic acid, malonic acid, succinic acid, isophthalic acid, and terephthalic acid, succinel chloride, etc. Cycarphonic acid chloride, methylol compounds such as dimethylurea, epichlorohydrin, dimethyldichlorosilane, etc. are used.

The above crosslinking reaction is usually carried out using a catalyst, for example an organotin compound in the case of diisocyanates, at 25 to 100°C.
This can be carried out by reacting for about minutes to 2 hours. The amount of the crosslinking agent to be used is preferably 0.1 to 2.0 moles of functional groups per mole of hydroxyl groups in the grafted product. Optimally, uncrosslinked grafted materials should be used, since they can reduce ionic conductivity or react with salts.
It is preferable to react the functional groups in equimolar amounts. In addition, it is necessary to lower the glass transition temperature of the crosslinked polymer, so
The crosslinking points are preferably amide, urethane, ester, and ethyl in that order, and it is more preferable to use aliphatic and siloxane than aromatic.

-, graph 1 ~ When the terminal of the compound is a vinyl group, this group can be ring-opening polymerized such as cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, potassium peroxide, butyl hydroperoxide, dichloride, etc. Organic peroxides such as mil peroxide and di-t-butyl peroxide, azobisisobutyronitrile, azobis-2.
Azobis compounds such as 4-dimethylvaleronitrile and azobiscyclohegysanyluponitrile are used. The amount used is usually 0 per 100 parts by weight of the grafted product.
．． 01 to 1 part by weight Approximately 25 to 100 parts for crosslinking reaction
It can be carried out in about 5 minutes to 2 hours at °C. Moreover, as a crosslinking method other than this, crosslinking treatment can also be performed by irradiating with an electron beam, ultraviolet rays, visible light, or infrared rays.

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

To give specific examples, for example, LiBr, LiI, Li5
CN, LiBF< , LiAsF, , LiC1!0
4, Li CF3303, Li C6FI2SO3
, L i Hg T z and so on. The amount of these lithium salts used is usually 0.1 to
A range of 40% by weight, especially a range of 3 to 20% by weight is preferred.

The lithium ion conductive polymer electrolyte of the present invention is composed of a composite of the above-mentioned crosslinked polymer and a lithium salt, and this composite can be prepared by, for example, immersing the above-mentioned crosslinked polymer in an organic solvent solution in which a lithium salt is dissolved. It can be obtained by infiltrating a lithium salt solution into the crosslinked polymer 0 and then evaporating off the organic solvent solution.

By immersing the crosslinked polymer in the lithium salt solution as described above, the lithium salt forms a complex and bonds to the ether oxygen in the crosslinked polymer, 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. In order to obtain this sheet-like polymer electrolyte, a cross-linked polymer may be formed into a sheet-like form, this C-shaped cross-linked polymer may be soaked in an organic solvent solution of a lithium salt, and then the organic solvent may be removed by evaporation. As the above-mentioned 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, the grafted product before crosslinking, a crosslinking agent, a positive electrode active material, etc. are added in a predetermined ratio, and the grafted product is crosslinked and then molded. The molded body thus obtained may be immersed in an organic solvent solution of lithium and salt, 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 may be a solvent that sufficiently dissolves the lithium salt and does not react with the polymer, such as acetin, tetrahydrofuran, dimethoxyethane, dioxolane, propylene carbonate, Acetonitrile, 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 the same direction as the main surface bent in the direction, 3 is a bipolar current collector 1 2 opposing peripheral parts of the plates 1 and 2 This is an adhesive layer that seals between 1a and 2a.

4, 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 are formed into a sheet shape by the method described above. 6 is 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 the polymer electrolyte of the present invention interposed between the positive electrode 4 and the negative electrode 6; This is a separate lake formed into a sheet.

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, T I
S2, M OS2,, Vr.

One or two of 013, ■205, ■5eXNIPS3, polyaniline, polypyrrole, polythiophene, etc.
``2'' is used.

The lithium battery constructed in this manner has the following features: the 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. This makes it possible to contribute to making the battery thinner, improving the workability of battery production, and improving the reliability of sealing.It also has various advantages such as essentially no worries about leakage like liquid electrolytes. In addition, the polymer electrolyte has excellent lithium ion conductivity,
- It has very excellent discharge characteristics as a secondary battery and charge/discharge cycle characteristics as a secondary battery.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to provide a lithium ion conductive polymer electrolyte that is solid at room temperature and exhibits high lithium ion conductivity.

〔Example〕

EXAMPLES Below, the present invention will be explained in more detail by describing examples.

Example 1 3 4 1,3,5,7-titramethylcyclotetrasiloxane (manufactured by 1-Resilicone, molecular weight 240°5) 2.4
1g, 30g of allylated polyethylene glycol (manufactured by NOF Corporation) with an average molecular weight of 1,000, and 10++v of zinc ocdylate, and stirred with a stirrer for 10
The reaction was carried out at 0°C for 200 hours to obtain a grafted product having terminal allyl groups.

Next, 20 g of this graph 1 compound was reacted with dilute sulfuric acid, and then treated with potassium hydroxide to modify the terminal allyl group into a hydroxyl group. A grafted product having a terminal vinyl group was obtained by reacting 20 g of this hydroxyl group-modified grafted product with 4 g of butyl vinyl ether at 60° C. for 300 hours in the presence of mercury acetate.

Next, 4 g of the graph I compound having a terminal hinyl group obtained as described above and 2 g of azobisisobutyronitrile
After stirring with a magnetic stirrer, the resulting viscous solution was dropped onto an aluminum plate, heated in argon gas, and reacted on a plate at 100°C for 1 hour for crosslinking treatment. A crosslinked polymer was obtained. The obtained crosslinked polymer was peeled off from the aluminum plate and immersed in acetone, and unreacted substances were dissolved and removed in acetone.

Subsequently, this crosslinked polymer was mixed with 2% by weight of LiBF,
The above LiB F
a After impregnating the acetone solution into the crosslinked polymer, the acetone is evaporated off to form a sheet 1 with a thickness of Q, l mm.
A polymer electrolyte was obtained.

Example 2 ■ 2.4 g of 3.5.7-te1-ramethylcyclotetrasiloxane (same as in Example 1) and 11 g of allylated polyethylene glycol (manufactured by NOF Corporation) with an average molecular weight of 550 were prepared. A grafted product having a terminal allyl group was obtained in the same manner as in Example 1, except that the grafted product was modified in the same manner as in Example 1 to obtain a grafted product having a terminal vinyl group, and this was used to carry out the experiment. A sheet-like polymer electrolyte was obtained in the same manner as in Example 1.

Example 3 2.4 g of 1,3,5,7-titramethylcyclotetraci]560kizan (same as in Example 1) and allylated polyether glycol (IEI) having an average molecular weight of 1.100.
A grafted product having a terminal allyl group was obtained in the same manner as in Example 1, except that 22 g of ethylene oxide and propylene oxide copolymerization ratio 0.7510.25) manufactured by Hon Yushi Co., Ltd. was used. This was modified in the same manner as in Example 1 to obtain a grafted product having terminal vinyl groups, and this was further used to obtain a sheet-like polymer electrolyte in the same manner as in Example 1.

Example 4 Bentamethylcyclobentasiloxane manufactured by Kutoshi Silicone Co., Ltd., molecular weight 300) 3 g, and average molecular weight 1. , OO
Allylated polyethylene glycol of O (manufactured by NOF Corporation)
A grafted product having a terminal allyl group was obtained in the same manner as in Example 1, except that 30 g was used, and this grafted product was modified in the same manner as in Example 1 to obtain a grafted product having a terminal vinyl group. A sheet-like polymer electrolyte was obtained in the same manner as in Example 1.

Example 5 Using the grafted product having a terminal allyl group obtained in Example 1, 20 g of this grafted product and vinyl hydro 1-
6 g of resiloxane and 20 mg of potassium chloroplatinate were reacted at 100°C for 3 hours, and the terminal
A modified grafted product into which the group represented by was introduced was obtained.

Next, 4 g of the modified grafted product obtained in this way,
[Azobisisobutyronitrile] and Omg were placed in an Erlenmeyer flask, stirred with a magnetic star, and the resulting viscous solution was dropped onto an Aluminum J plate, heated in argon gas, and heated at 100°C on the plate. The mixture was reacted for 1 hour for crosslinking treatment to obtain a crosslinked polymer. Thereafter, a sheet-like polymer electrolyte was obtained in the same manner as in Example 1.

Example 6 The hydroxyl-modified grafted product obtained in Example 1 was used, and 3 g of this grafted product was reacted with 168 cm of hexamethylene diisocyanate and 1-5 cm of tin butyl laureate at 100°C for 2 hours to perform a crosslinking treatment. A sheet-like polymer electrolyte was obtained in the same manner as in Example 1 except that the procedure was as follows.

Comparative Example 1 1 g of polyethylene oxide having an average molecular weight of 60.000 and 40.326 g of LiBF were dissolved in 5 mβ of acetonitrile and stirred with a magnetic cooler to dissolve uniformly. The resulting viscous solution was dropped onto a glass substrate, left in argon gas under normal pressure for 5 hours, and then vacuumed to 1×1O
The mixture was treated at −2 Torr and 100° C. for 10 hours to evaporate and remove acetonitrile, thereby obtaining a sheet-like polymer electrolyte with a thickness of 0.1 mm.

In order to investigate the performance of the polymer electrolytes of Examples 1 to 6 and Comparative Example 1, the following ionic conductivity test and battery internal resistance test were conducted.

<Ionic conductivity test> The polymer electrolytes of Examples 1 to 6 were sandwiched between Au plates, and A was placed on top of the polymer electrolyte of Comparative Example 1.
A u<L type electrode was formed by a vapor deposition method, AC impedance analysis between the electrodes was performed, and ionic conductivity at 25°C was measured. The results were as shown in Table 1 below.

Table 1 In addition, the ionic conductivity under various temperature conditions was measured in the same manner as described in Section 2, and the results were as shown in FIG. In the figure, the vertical axis represents the ionic conductivity (S/
cm ), and the horizontal axis is the reciprocal of absolute temperature 103/T (
K-').

<Battery Internal Resistance Test> Using the polymer electrolytes of Examples 1 to 6 and Comparative Example 1, a square thin lithium battery having the configuration shown in FIG. was created.

An alloy of lithium and aluminum was used as the negative electrode, and a sheet-shaped molded product containing T iS z and a polymer electrolyte having the same composition as in Examples 1 to 6 and Comparative Example 1 was used as the positive electrode. For these lithium batteries, 25°C160
The internal resistance was measured at 100°C. The results were as shown in Table 2 below.

The polymer electrolytes of Table 2 Examples 1 to 6 were 2.8X10 to 1 at 25°C (approximately 3.35 on the horizontal axis of Figure 2).
Although the polymer electrolyte of Comparative Example 1 using polyethylene oxide showed a high ionic conductivity of OX 10'''S/am, the ionic conductivity at 25°C was 1 x 10-
As low as 73/am. Therefore, the internal resistance at 25°C of the lithium batteries using the polymer electrolytes of Examples 1 to 6 of the present invention was 100Ω to 3.57 KΩ, but the lithium batteries using the polymer electrolytes of Comparative Example 1 The internal resistance at 25° C. was extremely large at 100Ω.

As shown in Figure 2, the polymer electrolyte of Comparative Example 1 using polyethylene oxide has higher ionic conductivity than the polymer electrolytes of Examples 1 to 6 in the high temperature range, but the ionic conductivity decreases at around room temperature. The polymer electrolytes of Examples 1 to 6 had a significantly lower temperature than those of the polymer electrolytes of Examples 1 to 6.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing an example of a lithium battery using the lithium ion conductive polymer electrolyte of the present invention, and Figure 2 is the ionic conductivity and temperature of the lithium ion conductive polymer electrolytes of the present invention and comparative examples. FIG.

Claims (1)

[Claims] (1) In a lithium ion conductive polymer electrolyte consisting of a composite of a lithium salt and an organic polymer, the above organic polymer has the following formula (1); ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, is 3 to 10, n is 1 to 200, x is 0.1 to
1.0, R is a group represented by -OH, -OCH=CH_2 or the following formula (a); A lithium ion conductive polymer electrolyte comprising a treated crosslinked polymer.