JPH03190960A - Lithium low-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) an organic polymer consisting of a crosslinked polymer produced by crosslinking a siloxane-polyether grafted product of formula I [m is 1-3; Z is of formula II (n is 1-200; x is 0.1-1); R is -OH, -OCH=CH2 or of formula III] 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 solution. 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 is directed to a lithium ion conductive material used in electrolytes, lithium ion concentration sensors, lithium ion separation membranes, etc. in lithium batteries, electrocomic displays, etc. Concerning polymer 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 in reducing costs. Furthermore, due to its flexibility, it is thought to be useful as an electrolyte in electrochromic displays, a lithium ion concentration sensor, etc.

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

[Problem to be solved by the invention]

However, the above-mentioned conventional polymer electrolytes have low lithium ion conductivity at 25°C (which means that they are not fully satisfactory in terms of performance when applied to lithium batteries, which are mostly used at room temperature, and the various applications 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 organic polymers as the organic polymer of the polymer electrolyte.

[Means to solve the problem]

As a result of intensive research to achieve the above object, the present inventors have discovered that a lithium salt obtained by crosslinking a specific siloxane-bolyether graph 1 compound as an organic polymer constituting a polymer electrolyte. The present invention was completed based on the knowledge that a solid polymer electrolyte that exhibits good lithium ion conductivity at room temperature can be obtained by sufficiently dissolving lithium ions, having a low glass transition temperature, and using a polymer with a low degree of crystallinity. reached.

That is, the present invention provides a lithium ion conductive polymer electrolyte comprising a composite of a lithium salt and an organic polymer, in which the f-bomber has the following structure (1): [where m is 1 to 3] , Z is the following formula; CI+3 0 ((C11□C+120)-(CH2CHO)I
-8: A group represented by l,, CHzCHzCHzR, where n is 1 to 200, X is 0.1 to 1.0, and R is 10]
, -〇CH-CH2 Split formula (a); CH3C1h Cth Si OSt O5i--CI=C1lz ・-
The present invention relates to a lithium ion conductive polymer electrolyte comprising a crosslinked polymer obtained by crosslinking a siloxane-polyether grafted product represented by (a group represented by alCH3CtlaCH3).

[Structure and operation of the invention]

The siloxane-polyether grafted product represented by formula (1) used in the present invention has a siloxane bond in its molecule, and therefore has high molecular mobility. When this grafted product is cross-linked by appropriate means using its terminal groups, it becomes a rubber-like and solid polymer with a low glass transition temperature and low crystallinity, and when a lithium salt is added to this polymer, This produces crosslinked polymers that exhibit high lithium ion conductivity. Here, in the conventional cross-linked triol polyethylene oxide mentioned above, 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 siloxane compound with the above-mentioned specific structure was used. Since it 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. When n is 0, ethylene oxide or ethylene oxide and propylene oxide are not added, so no complex formation with 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, leaving a large amount of uncrosslinked grafted material, and in this case, the lithium ion conductivity is greatly reduced.

The siloxane-bolyether grafted product represented by the above formula ('') of the present invention can be obtained by, for example, reacting methyltris(dimethylsiloxyl)silane with polyether glycol monoallyl ether, that is, by reacting the former's S i -H group with the latter's The hydroxyl group is subjected to a grafting reaction to produce a grafted product having a terminal allyl group 7, and then the terminal allyl group is modified by an appropriate means so that the terminal group R is -○H, -OC
It can be obtained by forming a grafted product of H=CHz or a group represented by the above formula (al).

In the above grafting reaction, approximately 1 to 6 moles of polyether glycol monoallyl ether are used per mole of methyltris(dimethylsiloxyl)silane, 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. Depending on the above reaction mole number, m in formula (1) is 1.
A graph I compound corresponding to 2 or 3 is produced.

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 may be carried out in the presence of mercury or the like. Also, 2(a)
) can be introduced by reacting the grafted product having a terminal allyl group with vinylhydrotrisiloxane 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 capable of reacting with the hydroxyl group may be used as a crosslinking agent to crosslink this, such as hexamethylene diisocyanate, 2,4-tolylene diisocyanate, methylene bis(4-phenylisocyanate). ), diisocyanate compounds such as xylylene diisocyanate, diamine compounds such as ethylene diamine and putrescine, dicarboxylic acid compounds such as oxalic acid, malonic acid, succinic acid, isophthalic acid, and terephthalic acid, dicarboxylic acid compounds such as succinel chloride, dimethyl urea, etc. Methylol compounds, epichlorohydrin, dimethyldichlorosilane, etc. are used.

The above crosslinking reaction is usually carried out using a catalyst such as diisocyanate.
In the case of
This can be carried out by reacting for about minutes to 2 hours. The amount of crosslinking agent used is 2. Hydroxyl group 1 of the above grafted product
The amount of functional groups is usually 0.1 to 2.0 moles per mole. Optimally, if the uncrosslinked graft remains,
Since the functional groups may reduce ionic conductivity or react with salts, it is preferable to use equimolar amounts of the functional groups. In addition, since it is necessary to lower the glass transition temperature of the crosslinked polymer, if the crosslinking point is amide 1. Urethane, ester and ethyl are preferred in this order, and aliphatic and siloxane are more preferred than aromatic.

On the other hand, when the end of the grafted product is a vinyl group, this group can undergo ring-opening polymerization such as cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, potassium peroxide, butyl hydroperoxide, dicumyl peroxide, di -Organic peroxides such as t-butyl peroxide, abbisisobutyronitrile, azobis-2,4-
Azobis compounds such as dimethylvaleronitrile and abiscyclohegysanyluponitrile are used. The amount used is usually 0.0 parts by weight per 100 parts by weight of the grafted product.
1 to 1 part by weight, crosslinking reaction at 25 to 100°C
This can be done in about 5 minutes to 2 hours. 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 this case as well, it is necessary to carry out the reaction so that no uncrosslinked grafted product remains.

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 a specific example, for example, LiBr, Lil, Li5
CNs LiBFa, LiAsF+, , T-1c0 p○4, LiCF35○3, L I Cb
Examples include F +2s O:l and L i Hg I 2 . The amount of these lithium salts used is usually in the range of 0.1 to 40% by weight, especially 3% by weight based on the above crosslinked polymer.
A range of 20% by weight is preferred.

The lithium ion conductive polymer electrolyte of the present invention consists of a composite of the above-mentioned crosslinked polymer and a lithium salt, which is prepared by, for example, dissolving the above-mentioned crosslinked polymer in an organic solvent solution in which the lithium salt is dissolved. It can be obtained by soaking, infiltrating a salt solution into a crosslinked polymer, 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 is formed into a shape of 1~, this cross-linked polymer of 1- shape is immersed in an organic solvent solution of a lithium salt, and then the organic solvent is removed by evaporation. As for the above-mentioned sheets, extremely thin ones on the order of microns, which are generally called films, 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 grafted product, a crosslinking agent, a positive electrode active material, etc. are added in a predetermined ratio, the grafted product is crosslinked, and then molded. The molded article 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, organic solvents for dissolving the lithium salt include organic solvents that sufficiently dissolve the lithium salt and do not react with the polymer, such as acetone, tetrahydrofuran, dimethoxyethane, dioxolane, propylene carbonate, etc. 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 in the same direction as the bent main surface; This is an adhesive layer that seals the gap.

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 a polymer electrolyte of the present invention interposed between the positive electrode 4 and the negative electrode 6; This is a separator formed into a sheet shape.

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, Ti
32, MO32, Vr+0□3, V2O5, VSe1
One or more of NiPS3, polyaniline, polypyrrole, polythiophene, etc. are used.

In the lithium battery constructed in this way, 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 contributes to making the battery thinner, improving the workability of battery manufacturing, and improving the reliability of sealing.Also, it is possible to improve the reliability of sealing by making the battery thinner.In addition, it is possible to improve the reliability of sealing by making the battery thinner. In addition to the advantages, the polymer electrolyte has low lithium ion conductivity, -
The discharge characteristics as a secondary battery and the charge/discharge cycle characteristics as a secondary battery are extremely poor.

〔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 2.69 g of methyltris(dimethylsiloxyl)silane (manufactured by Toshi Silicone Co., Ltd., molecule i1269) and allylated polyethylene glycol (with an average molecular weight of 000) were prepared.
Mix 30 g of zinc octylate (manufactured by NOF Corporation) and 10 g of zinc octylate, and heat at 100°C for 200 ml while stirring with a cooler.
The reaction was carried out for a period of time to obtain a grafted product having a terminal allyl group.

Next, 20 g of this grafted product was reacted with dilute sulfuric acid, and then treated with potassium hydroxide to modify the terminal allyl group into a hydroxyl group. 20 g of this hydroxyl-modified grafted product was reacted with 4 g of butyl vinyl ether at 60° C. in the presence of mercury acetate for 3 hours to obtain a grafted product having a terminal vinyl group [m-3 in 2 (1)].

Next, 4 g of the grafted product having a terminal vinyl group obtained as described above and 20 r of azohisisobutyronitrile were added.
rg in an Erlenmeyer flask and stirred with a magnetic stirrer, the resulting viscous solution was dropped onto an aluminum plate and reacted at 100°C for 1 hour on a pot play 1 in argon gas 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 added to 2% by weight of L 1BF4
The polymer electrolyte was immersed in an acetone solution for 8 hours to impregnate the crosslinked polymer with the 1BF4 acetone solution described above, and then the acetone was removed by evaporation to obtain a sheet-like polymer electrolyte with a thickness of 0.1 mm.

Example 2 2.69 g of methyl I-lis(dimethylsiloxyl)silane (5 6 same as in Example I) and an average molecular weight of 550
Allylated polyethylene glycol (manufactured by NOF Corporation) 1
A grafted product having a terminal allyl group was obtained in the same manner as in Example 1, except that 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 [formula (1 m-2] in ), and further using this, a sheet-like polymer electrolyte was obtained in the same manner as in Example 1.

Example 3 Methyltris(dimethylsiloxyl)silane (Example 1
), 2.69 g of allylated polyether glycol with an average molecular weight of 1°100 (manufactured by NOF Corporation, copolymerization ratio of ethylene oxide and propylene oxide 0.75)
10.25) Example except that 22 g was used]
In the same manner as above, a grafted product having a terminal allyl group was obtained,
This graph 1~ compound was modified in the same manner as in Example 1 to obtain a grafted product having a terminal vinyl group [m-2 in formula (1)], and this was further used in the same manner as in Example 1 to produce a sheet-like polymer. Obtained electrolytes.

Example 4 Using the grafted product having a terminal allyl group obtained in Example 1, 22.4 g of this grafted product, 6 g of vinyl hydrotrisiloxane, and 20 μ of potassium chloroplatinate were heated at 100°C for 3 hours. The above formula (a
Modified grafted product C formula (1
) was obtained.

Next, 4 g of the modified grafted product obtained in this way,
Place 10 μm of azobisisobutyronitrile in an Erlenmeyer flask, stir with a magnetic stirrer, drop the resulting viscous solution onto an aluminum plate, and react at 100°C for 1 hour on a hot plate in argon gas. This was followed by crosslinking treatment to obtain a crosslinked polymer. Thereafter, a sheet-like polymer electrolyte was obtained in the same manner as in Example 1.

Example 5 The hydroxyl-modified Graph I compound [m-3 in formula (1)] obtained in Example 1 was used, and 3 g of the Graph 1 compound, 168 cm of hexamethylene diisocyanate, and 5 mg of tin butyl lauret) were added. A C1-like polymer electrolyte was obtained in the same manner as in Example 1, except that the crosslinking treatment was carried out by reacting 8 at 100'C for 2 hours.

Comparative Example 1 1 g of polyethylene oxide with an average molecular weight of 60.000 and 40.326 g of LiBF were mixed in 5 m of acetonitrile.
A and stirred with a magnetic cooler to uniformly dissolve. Drop the obtained viscous solution onto a glass substrate,
After being left in argon gas under normal pressure for 5 hours, the degree of vacuum]
, X1O-2 Torr, and a temperature of 100° C. for 10 hours to evaporate and remove acetonitrile, thereby obtaining a polymer electrolyte in the form of a 0.1-tuna-thick sheet.

In order to examine the performance of the polymer electrolytes of Examples 1 to 5 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 5 were sandwiched between Au plates, and the polymer electrolyte of Comparative Example 1 was sandwiched between Au plates.
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 Also, the ionic conductivity under various temperature conditions was measured in the same manner as above, and the results were as shown in FIG.

In addition, in the same figure, the vertical axis represents the ionic conductivity (S/c
m), and the horizontal axis is the reciprocal of absolute temperature] 0'/T
(K-').

<Battery Internal Resistance Test> Using the polymer electrolytes of Examples 1 to 5 and Comparative Example 1, a square thin lithium battery having a total thickness IB and a side length 1 cm as shown in FIG. 1 was produced.

90 Note that an alloy of lithium and aluminum was used as the negative electrode, and a sheet-shaped molded product containing a polymer electrolyte and T i S z having the same composition as in Examples 1 to 5 and Comparative Example 1 was used as the positive electrode. For these lithium batteries, 25℃, 60℃
The internal resistance at 100° C. was measured. The results were as shown in Table 2 below.

As is clear from the test results in Table 2 and above, Example 1 of the present invention
~5 polymer electrolyte at 25°C (approximately 3.35 on the horizontal axis of Figure 2). X
However, the ionic conductivity of Comparative Example 1 using polyethylene oxide was 1 x 10-'S/cm at 25°C. and low. Therefore, the internal resistance at 25°C of the lithium batteries using the polymer electrolytes of Examples 1 to 5 of the present invention was approximately 71Ω to 3.33 KΩ, but the internal resistance of the lithium batteries using the polymer electrolytes of Comparative Example 1 was approximately 71Ω to 3.33KΩ. The internal resistance of the lithium battery at 25°C was extremely large, at 100Ω.

As shown in Figure 2, the ionic conductivity of the polymer electrolyte of Comparative Example 1 using polyethylene oxide is rather higher than that of the polymer electrolytes of Examples 1 to 5 in the high temperature range, but the ionic conductivity is higher at around room temperature. The conductivity was significantly reduced and was much lower than the polymer electrolytes of Examples 1-5.

[Brief explanation of drawings]

Figure 1 is a longitudinal 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. 4... Positive electrode (polymer electrolyte and positive electrode active material) 7... Separator (polymer electrolyte)

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.▼ ...(1 ) [In the formula, m is 1 to 3, Z is the following formula; ▲ There are mathematical formulas, chemical formulas, tables, etc.
, R is -OH, -OCH=CH_2 or the following formula (a
); ▲There are mathematical formulas, chemical formulas, tables, etc.▼... (a) A lithium ion characterized by being made of a crosslinked polymer obtained by crosslinking a siloxane-polyether grafted product represented by Conductive polymer electrolyte.