JPH02235956A - Lithium-ion conductive polymer electrolyte - Google Patents

Abstract

PURPOSE:To prepare a polymer electrolyte exhibiting an excellent lithium-ion conductivity at a temp. lower than room temp. by using, as an org. polymer to constitute said polymer electrolyte, a cross-linked polymer which has a crystallinity lower than a specified value and is obtd. by cross-linking a glycerin ether of polyethylene oxide. CONSTITUTION:A cross-linked polymer having a crystallinity of 20% or lower and obtd. by cross-linking a glycerin ether of polyethylene oxide of the formula (wherein n is 10 to 50) is used as an org. polymer to constitute an ionically conductive polymer electrolyte comprising a lithium salt and said org. polymer. The lithium ion conductive polymer electrolyte thus obtd. is solid at room temp. and excellent in the ionic conductivity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to electrolytes for lithium batteries, electrochromic displays, etc., 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.

[Prior Art] 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 applied to lithium batteries, which require the following, it would be advantageous in terms of workability and sealing for battery production, and would also have the advantage of being useful for cost reduction. Furthermore, due to its flexibility, it can be used as a lithium ion separation membrane, and it is also thought to be useful as an electrolyte for electrochromic displays and as a lithium ion concentration sensor.

As organic polymers for the above-mentioned lithium ion conductive polymer electrolyte, polyethylene oxide I1 polyethyleneimine, polyethylene oxypropylene, etc. have been proposed so far [for example, FasL Jo
n Transport in Solid P. 13
1 (1979)).

[Problem to be solved by the invention]

However, in polymer electrolytes made of composites of these organic polymers and lithium salts, the polymer component loses crystallinity at high temperatures and exhibits good lithium ion conductivity, but it becomes crystalline at room temperature of about 25°C. Due to its high ion conductivity, 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 the above organic polymer as the organic polymer of the polymer electrolyte. .

[Means for Solving the Problems] As a result of extensive research to achieve the above object, the present inventors have discovered that polyethylene oxide → NeuI glycerin ether is used as an organic polymer constituting the polymer electrolyte. It was discovered that when a crosslinked polymer with a crosslinked crystallinity of 20% or less is used, a solid polymer electrolyte exhibiting good lithium ion conductivity at room temperature can be obtained, and the present invention was completed.

That is, the wood invention provides a lithium ion conductive polymer electrolyte consisting of a complex of a lithium salt and an organic bo-17mer, in which the organic polymer of (CHzCHz○)nH1{ C
O(CHzCHzO)nr-T (
I) + { − C−0 ( C H 2 C H z
Lithium characterized by being a cross-linked polymer with a crystallinity of 20% or less obtained by cross-linking glycerin ether of polyethylene oxide represented by O) n t{H (in the formula, n is 10 to 50) Relating to ionically conductive polymer electrolytes.

If the above-mentioned crosslinked polymer has a crystallinity of 20% or less, the formula [1]
A glycerin ether of volutelene oxai 1 shown by is added with a cross-linking agent in an equimolar molar ratio or more to the glycerin ether, and a catalyst is used to increase the reactivity of the ○I group, Obtained by crosslinking.

In the present invention, the reason for using the crosslinked polymer described in "2" and the reason why the polymer electrolyte exhibits high lithium ion conductivity when the above crosslinked polymer is used are as follows.

First, the crystallinity of uncrosslinked glycerin ether, that is, polyethylene oxide represented by formula (1), is about 40 to 60%. This polyethylene okizui 1
The glycerin ether has a large amount of ether oxygen based on polyethylene oxyl, and this ether oxygen forms a complex with lithium ions and exhibits lithium ion conductivity.

However, since the glycerin ether of polyethylene autozyme L represented by the formula CI+ has a high degree of crystallinity and therefore a high melting point, the movement of the polymer molecular chains is restricted at room temperature, making it difficult to conduct lithium ions. sex becomes lower. In addition, in terms of the number of ether oxygens per molecule, polyethylene oxy-I which has not been converted into a glycerin ether has more ether oxygen than the glycerin ether of the polyethylene oxy-noid represented by the formula [1, but polyethylene oxy Cy-F has higher crystallinity, and therefore has a higher melting point and lower lithium ion conductivity at room temperature. Therefore, by etherifying it with glycerin, the degree of crystallinity is lowered, the melting point is lowered, and the film-forming ability is increased.

However, as described above, even the glycerin ether of polyethylene oxide represented by formula (11) has a high degree of crystallinity and low lithium ion conductivity at room temperature.

Then, when the glycerin ether of polyethylene oxite represented by 2fI is crosslinked with a crosslinking agent, the crystallinity is reduced to 30%. This increases the movement of the polymer's molecular chains and improves lithium ion conductivity at room temperature, but this is still not sufficient.

Therefore, in the present invention, a crosslinking agent is added in a molar ratio of at least the same mole to the glycerin ether of polyethylene oxide represented by the above formula (Il), and O H
Crosslinking with increased reactivity of the groups increases crystallinity by 20%
Hereinafter, it is desirably lowered to 15% or less to activate the movement of the polymer molecular chains at room temperature and improve lithium ion conductivity. In other words, lithium ion conductivity at room temperature is improved by reducing the number of unreacted polyethylene oxide chains that have high crystallinity and impede the movement of polymeric molecular chains.

In the present invention, the crystallinity of the crosslinked polymer is set to 20
% or less, but this is because when the crystallinity of the cross-linked polymer is 20% or less, the molecular chains of the polymer move more easily, and compared to the case of normal cross-linking, the This is because the lithium ion conductivity becomes even higher.

And when the crystallinity of the crosslinked polymer becomes even lower,
The lithium ion conductivity at room temperature is even higher, and when the crystallinity of the crosslinked polymer is below 15%, more desirable results are obtained, and when the crystallinity is reduced to 0%,
More desirable results are obtained.

In the formula (I) representing glycerin ether of polyethylene oxide, n indicates the number of monomers of polyethylene oxide, and in the present invention, n is set to 10 to 50; If it is small, the distance between the crosslinking points will be short and it will be difficult for the polymer chain to move when crosslinked.On the other hand, if n is more than 50, the O
This is because the reactivity of the H group becomes low and unreacted polyethylene oxide chains remain, making it difficult for the polymer chains to move.

As the crosslinking agent for crosslinking the glycerin ether of polyethylene ogizide represented by the formula fT), for example, diisocyanates, dicarboxylic acids, dicarboxylic acid chlorides, methylol compounds, shrimp chlorohydrin, etc. are used.

Examples of the diisocyanate used as the crosslinking agent include hexamethylene diisocyanate, 2,4-
Examples include tolylene diisocyanate, medilene bis(4-phenyl isocyanate), and xylylene diisocyanate.

Examples of carboxylic acids used as the crosslinking agent include oxalic acid, malonic acid, succinic acid, phthalic acid, isophthalic acid, and terephthalic acid. Examples of the dicarboxylic acid chloride used as the crosslinking agent include succinel chloride, and examples of the methylol compound include dimethylurea.

These crosslinking agents are used in an equimolar or more molar ratio to the glycerin ether of polyethylene oxide represented by formula fl. This is because if the amount of the crosslinking agent used is less than equimolar, even if partial crosslinking can be achieved, the degree of crystallinity will not be reduced.

When crosslinking the glycerin ether of polyethylene oxite represented by 2m, a catalyst is used to increase the reactivity of the ○l1 group, allow the crosslinking reaction to proceed sufficiently, and reduce the crystallinity of the crosslinked polymer. It will be done. This catalyst varies depending on the type of crosslinking agent.

For example, when a diisocyanate is used as a crosslinking agent, a urethanization catalyst is used as a catalyst. When a dicarboxylic acid is used as a crosslinking agent, Ti. ．． GeXSn. ．． When oxides of metals such as Pb and Mn are used and dicarboxylic acid chlorides are used as crosslinking agents, sodium hydroxide, sodium lauryl sulfate, etc. are used as catalysts, and when methylol compounds are used as crosslinking agents, Iodine as a catalyst, A1■0,
, TiO2, dimethyl sulfoxide, etc., and when shrimp chlorohydrin is used as a crosslinking agent, triethylaluminum is used as a catalyst.

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, LiSCN. LiBF4, LiA
sF. , , LiC1 04, Li CF:lSOZ
, L i C6F+zSOz, L i H g 1
There are 2 etc. The amount of these lithium L salts used is usually in the range of 1 to 30% by weight, especially 3% by weight, based on the crosslinked polymer described in L.
ItTrE is weak in the range of ~20%.

The lithium ion conductive polymer electrolytic negative of the present invention is composed of a composite of the above-mentioned crosslinked polymer and a lithium salt. It can be obtained by immersing the crosslinked polymer in an organic solvent solution, allowing the lithium salt i8 solution to permeate into the crosslinked polymer, and then removing the organic solvent solution from the stem.

By immersing the crosslinked polymer in the lithium salt solution as described above, the lithium salt forms a complex and bonds with the ether oxygen in the crosslinked polymer, and the above bond is maintained even after the solvent is removed. A complex of lithium salt and lithium salt 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 seal shape. To obtain this C-shaped polymer electrolyte, a cross-linked polymer is formed into a C-1 shape, and this C-shaped cross-linked polymer is injected with a lidium salt.
After the lithium salt solution is permeated into the crosslinked polymer by immersing it in an organic solvent solution, the organic solvent may be removed by evaporation. ”
As the polymer electrolyte sheet 1, an extremely thin sheet on the order of microns, which is generally called a film 1, can also be produced.

In addition, when the polymer electrolyte of the present invention is applied to a positive electrode of a battery, glycerin ether of 2 (represented by Il), a crosslinking agent,
Add the catalyst, cathode active material, etc. in a predetermined ratio, = 1 - Note 2 (
After cross-linking glycerin ether of polyethylene oxide represented by Il, it is molded, and the obtained I-shaped body is immersed in an organic solvent containing lithium oxide and salt. The organic solvent may be removed by bluing and then removing the organic solvent. By doing so, a mixture of the polymer electrolyte and the positive electrode active material can be obtained.

To obtain the polymer electrolyte, an organic solvent for dissolving the lithium salt is used, which dissolves the salt sufficiently, and
And organic that does not react with cross-linked polymers? Any container may be used, such as ace1・n, te1・rahitrofuran, jime1
・Xyethane, dioxolane, polypylene/carbonate, acetonate, dimethylformamide, etc. are used.

Figure 1 shows an example of a lithium battery using the polymer electrolyte of the present invention described above. In the figure, (1) is a rectangular positive electrode construction plate made of stainless steel, and (2) is a surrounding [bent in steps toward the negative side]: 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 surface, (3) is a bipolar collector plate. Electric board (1), (
2) is an adhesive layer that seals between the opposing peripheral parts (1a) and (2a).

(4) has already included the polymer electrolyte of the present invention and the positive electrode active material 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). 1 using the method described above.
・The positive electrode formed into a shape, (6) is the Lichiu J loaded on the negative electrode current collector plate (2) side in the space (5), and εJ
Negative electrode made of lithium alloy (the force is between the positive electrode (4) and the negative electrode (
6) This is a separator formed by molding the polymer electrolyte of the present invention interposed between the separator and the polymer electrolyte of the present invention into a seal shape.

Note that the positive electrode (4) may be formed into a sheet by mixing a positive electrode active material with a binder such as Bolite 1/Lafluoroethylene powder or an electron conduction aid, as the case may be. Examples of positive electrode active materials used in the positive electrode (4) include T i Sz , tvio S2 , VbO+3,
V 2 0 5, V S e - N r P S 3
, polyaniline, polypyrrole, polythiophene, etc., or two or more thereof may be used.

The lithium battery configured in this way has a separator (7
) is a sheet-like material made of the lithium ion-conductive polymer electrolyte, and the positive electrode (4) is a similar sheet-like material containing the lithium-ion conductive polymer electrolyte. Contributes to improving workability for manufacturing and reliability of sealing! j, In addition to having various advantages such as being able to slide and not having to worry about leakage like liquid electrolytes, polymer electrolytes have excellent lithium ion conductivity. This results in extremely excellent discharge characteristics as a primary battery and excellent charge/discharge cycle characteristics as a secondary battery.

〔Example〕

Examples of the present invention will be described below.

Example 1 4 g of glycerin ether of polyethylene oxide represented by formula fl (average molecular weight of about 3,000, n in formula (■) is about 22, manufactured by Daiichi Kogyo Seiyaku) and 336 mg of hexamethylene diisocyanate ( CNCO!) One (
OH group], this formula (indicates that the NGO group is equimolar to the OH group of the glycerin ether of polyethylene oxide represented by I+) is placed in a flask, stirred with a magnetic stirrer, and then converted into urethane. After adding a catalyst (tin butyl laurate), the mixture was dropped onto an aluminum plate and reacted on a pot plate in argon gas at 100°C for 1 hour to obtain a crosslinked polymer.

The obtained crosslinked polymer was peeled off from the aluminum plate and immersed in acetone, and unreacted substances were dissolved and removed in acetone. The degree of crystallinity of the obtained crosslinked polymer was measured by thermal analysis, and the degree of crystallinity was 0%.

Subsequently, the above crosslinked polymer was immersed in a 2% by weight LiBF4 acetone solution for 8 hours, and after the above LiBFn acetone solution was permeated into the crosslinked polymer, the acetone was removed by evaporation to form a sheet with a thickness of 0.1 mm. A polymer electrolyte was obtained.

Example 2 A glycerin ether of polyethylene oxide of the formula (Il) with an average molecular weight of about 5,000 and a formula fIl
n is about 37, 4 g of Daiichi Kogyo Seiyaku) and 202 mg of hexamethylene diisocyanate ((NCO group) -
A crosslinked polymer was obtained in the same manner as in Example 1 except that OH group]) was used. The degree of crystallinity of the obtained crosslinked polymer was measured by thermal analysis and was found to be 10%.

Subsequently, the above crosslinked polymer was treated with LiB as in Example 1.
It was immersed in an acetone solution of F4 and subjected to the same operations as in Example 1 to obtain a sheet-like polymer electrolyte with a thickness of 0.1 mm.

Example 3 4 g of glycerin ether of polyethylene oxide represented by formula (■) (average molecular weight about 2,000, n in formula (I+ is about 14, manufactured by Daiichi Kogyo Seiyaku) and 504 mg of hexamethylene diisocyanate ((NC○ group) one (OH group)
) A crosslinked polymer was obtained in the same manner as in Example 1 except that the following was used. The degree of crystallinity of the obtained crosslinked polymer was measured by thermal analysis, and the degree of crystallinity was 0%.

Subsequently, the above crosslinked polymer was treated with the same Li as in Example 1.
A sheet-like polymer electrolyte having a thickness of 0.1 mm was obtained by immersing it in an acetone solution of BFa and performing the same operations as in Example 1.

Comparative Example 1 4 g of glycerin ether of polyethylene oxide (average molecular weight of about 3,000, formula (n in Il is about 22, manufactured by Daiichi Kogyo Seiyaku) represented by formula (Il) and 224 mg of hexamethylene diisocyanate ( (NCO group)/(OH
group) = 2/3, which indicates that the molar ratio of the NGO group to the OH group of the glycerin ether of the polyethylene oxide represented by the formula fIl is 273,
A crosslinked polymer was obtained in the same manner as in Example 1 except that no urethanization catalyst was added.

The degree of crystallinity of the obtained crosslinked polymer was measured by thermal analysis and was found to be 30%.

Subsequently, the above crosslinked polymer was treated with LiB as in Example 1.
A sheet-like polymer electrolyte having a thickness of 0.1 mm was obtained by immersing it in an acetone solution of Fa and performing the same operations as in Example 1.

Comparative Example 2 4 g of glycerin ether of polyethylene oxide represented by formula (Il, average molecular weight of about 5,000, formula (n in 11 is about 37, manufactured by Daiichi Kogyo Seiyaku) and 202 mg of hexamethylene diisocyanate ( (NCO group) -[OH
A crosslinked polymer was obtained in the same manner as in Example 1 except that the urethanization catalyst was not added.

The degree of crystallinity of the obtained crosslinked polymer was measured by thermal analysis and was found to be 40%.

Subsequently, the above crosslinked polymer was treated with the same Li as in Example 1.
It was immersed in an acetylene solution of B F 4 and subjected to the same operation as in Example 1 to a thickness of O. I. A polymer electrolyte in the form of C.I.mm was obtained.

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

<Ionic conductivity test> The polymer electrolytes of Examples 1 to 3 and Comparative Examples 1 to 2 were sandwiched between lithium boilers in a switch shape, and the AC impedance between the lithium electrodes was measured. The ionic conductivity at °C) was measured. The results were as shown in Table 1 below.

Table 2 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 Figure 2, the vertical axis is 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 3 and Comparative Examples 1 to 2, a square-shaped thin film with a total thickness of 0.5 mm and a side length of 1 cm as shown in FIG. A type lithium battery was fabricated. The negative electrode was made of an alloy of TiS. A sheet-like molded product containing the following was used. For these lithium batteries, 25°C, 60°C
The internal resistance was measured at 100'C. The results were as shown in Table 2 below.

As is clear from the results of the ionic conductivity test shown in Table 1, the polymer electrolytes of Examples 1 to 3 of the present invention had a conductivity of 1.5X10-5S/cm to 4XIO at 25°C. ”
Although it showed high ionic conductivity of 'S/cm, Comparative Examples 1~
Polymer electrolyte 2 has an ionic conductivity of 1× at 25°C.
It was as low as 10-6S/mark-IX 10-'S/cm. Therefore, as shown in Table 2, Example 1 of the present invention
The internal resistance at 25°C of the lithium battery using the polymer electrolyte of Comparative Example 1 was 670 to 2500 Ω.
~25°C for lithium batteries using polymer electrolytes of ~2
The internal resistance was as large as 10 kΩ to 100 kΩ. Moreover, as shown in FIG.
In Figure 2, high ionic conductivity was shown in the region on the left side of the horizontal axis, but the temperature was around 25°C (3.35°C on the horizontal axis).
), the ionic conductivity was lower than in Examples 1 to 3,
As the temperature further decreases (that is, moving to the right on the horizontal axis), the ionic conductivity decreases further, and Examples 1 to
The difference in ionic conductivity with No. 3 becomes large.

〔Effect of the invention〕

As explained below, in the present invention, a crosslinked polymer having a crystallinity of 20% or less obtained by crosslinking glycerin ether of polyethylene oxide represented by the formula fIl is used as the organic polymer constituting the complex with the lithium salt. By using this method, it was possible to provide a lithium ion-conducting polymer electrolyte that was solid at room temperature and had near ion-conductivity.

[Brief explanation of the drawing]

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 as a separator, and Figure 2 is the ionic conductivity and temperature of the lithium ion conductive polymer electrolytes of Examples and Comparative Examples. FIG. (7)...Severator (polymer electrolyte)7...
Cenomareta (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 (I)▲Mathematical formula, chemical formula, table, etc.▼(I) (in the formula , n is 10 to 50.) A lithium ion conductive polymer electrolyte characterized by being a crosslinked polymer having a crystallinity of 20% or less, which is obtained by crosslinking glycerin ether of polyethylene oxide.