HK1070185B

HK1070185B - Gel-type polymer electrolyte and use thereof

Info

Publication number: HK1070185B
Application number: HK05102861.7A
Authority: HK
Inventors: 小山昇; 藤本有纪; 岩濑庆幸; 西嶋孝一
Original assignee: 杜邦-三井聚合化学品株式会社; 小山昇
Priority date: 2000-10-18
Filing date: 2001-10-18
Publication date: 2007-11-02

Description

Gel-type polymer electrolyte and application thereof

Technical Field

The present invention relates to a gel-type polymer electrolyte containing a non-halogen type polymer, and more particularly to a polymer electrolyte moldable into a self-supporting (self-standing) film and, particularly, useful for a polymer lithium battery that suppresses the formation of lithium dendrites (dendrites) on the surface of a negative electrode during charging. The electrolyte can also be used in capacitors.

Prior Art

Lithium secondary batteries which have been put on the market, as electrode materials, use a carbon-intercalated material as the negative electrode and use lithium cobaltate (LiCoO)₂) As a positive electrode to reversibly release and accept lithium ions accompanying charge/discharge. In addition, the electrolyte is dissolved in a lithium salt at the time of use. What is commonly referred to as a polymer lithium battery is a so-called polymer electrolyte battery that employs a polymer electrolyte instead of a liquid electrolyte.

The polymer electrolyte battery is entirely of a solid type and does not leak liquid, and is characterized by high safety and excellent workability, whereby the thickness of the battery can be reduced or the batteries can be laminated. The polymer electrolyte battery must use an ionic conductivity as high as 10^-3Polymeric materials of the order of s/cm. As for the polymerization of such electrolytes, development and research have been conducted mainly relating to polyethylene oxide (PEO), Polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polyvinylidene fluoride (PVDF). Specifically, several PAN and PVDF type polymer gel electrolytes have been developed because a polymer maintaining a solution containing 40 to 80%, preferably 40 to 70%, of lithium salt exhibits excellent film strength. In japan, polymer gel electrolyte lithium batteries using a fluoropolymer gel electrolyte have been mass-produced since 1999.

Due to its thin thickness and light weight, lithium polymer secondary batteries have reached a level satisfying the conditions for use in mobile devices, particularly cellular phones, notebook computers, PDAs, and are steadily expanding the range of applications. In the near future, it is no longer a dream to apply them to Electric Vehicles (EVs). This is because the energy density and the output density of the conventional liquid battery do not match each other. However, it has recently been learned that a lithium polymer secondary battery is an ideal battery providing a high energy density of not less than 165W/kg and a high output density of not less than 1200W/kg.

However, the polymer electrolyte for a lithium polymer secondary battery must satisfy requirements for further improved properties, such as (1) it must not leak liquid, (2) it is flame-resistant, (3) it advantageously has high thermal conductivity, (4) it advantageously has high ion conductivity over a wide temperature range, (5) it has high mechanical strength and (6) it is chemically inert.

As for the fluoropolymer materials that have been widely used at present, there are still problems related to handling after use of the battery, since fluorine is a constituent of the polymer matrix. Accordingly, it is desirable to provide a non-halogen type polymer electrolyte material comparable or better in electrolyte performance than a fluoropolymer gel electrolyte.

Polyacrylonitrile (PAN) type and Polymethylmethacrylate (PMMA) type polymer materials are candidates for non-halogen type polymer gel electrolytes. Unlike polyvinylidene fluoride (PVDF) type films, however, these self-supporting films are not able to absorb and hold large amounts of electrolyte solutions, nor are they able to be used as a self-supporting film electrolyte simply sandwiched between the positive and negative electrodes at the time of battery manufacture.

Lithium ion batteries currently on the market employ carbon negative electrode materials that are capable of intercalating lithium ions. However, lithium metal batteries using single metal lithium or lithium alloys and other materials as the negative electrode are also expected to provide large energy density. However, at present, they are not really commercial products due to the trouble of several problems.

Among these problems, the most important to be solved is the formation and growth involving the accompanying charge/discharge of lithium dendrites. Even a negative electrode made of a lithium-intercalated carbon material involves a problem of dendrite generation under a rapid charging condition.

If allowed to continue growing, the lithium dendrites will propagate to the point where they cause an internal short circuit in the battery. If an internal short circuit occurs, an excessive current instantaneously flows through the dendrite to generate a spark, and combustion occurs, generating high temperature and high pressure, thereby possibly causing explosion. Therefore, various methods have been studied to prevent the internal short circuit. If an internal short circuit can be prevented, the battery life can be extended and can be further increased.

Japanese unexamined patent publication (Kokai)167280/1985 discloses a rechargeable electrochemical device that suppresses the occurrence of lithium dendrites by using gold-containing of lithium and other metals as a negative electrode.

In addition, methods of suppressing the occurrence of lithium dendrites using ion-conducting inorganic solid electrolytes, polymer gel electrolytes, or solid polymer electrolytes have also been studied. For example, Oyama et al reported that Polyacrylonitrile (PAN) gel electrolyte (not less than 5 wt% relative to the content of the nonaqueous solvent) inhibited the generation of metallic lithium dendrites (report on research results, new energy/industrial technology integrated development organization (NEDO), 1996, report on 5 months 1997).

With respect to new lithium batteries, there is a demand for rapid operation of the batteries within a limited charge/discharge time while increasing the energy density of the batteries. In particular, it is desired to provide a battery capable of sufficiently operating at low temperatures. The same characteristics are also proposed for capacitors.

Due to its principle of operation, the performance of batteries and capacitors is generally limited by the speed and distance of ion migration. In the case of a battery, the migration speed of ions in the electrolyte and in the electrode active material cannot be greatly increased. To solve this problem, the migration distance of ions must then be shortened, and the cell must be constructed using a material having a wide reaction area.

In the case of a capacitor, also, if carrier ions can move rapidly, the charge/discharge time can be shortened greatly. Thus, in order to improve the performance, the distance between the electrodes must be shortened, and the reaction area must be widened, as in the case of constituting a battery. For this purpose, it is necessary to prepare a thin electrolyte membrane having a very small thickness and high mechanical strength.

Even when the electrolyte is made of a gel-like polymer, first, lithium ions migrate through the electrolyte phase in the polymer matrix. Then, as in the solution electrolyte, the reaction current concentrates on a part of the surface of the negative electrode, and the local precipitation of lithium induces the lithium to precipitate like dendrites. Secondly, the mechanical strength is lower than that of solid polymers.

In conventional all solid and gel-like polymer electrolytes, the ions are not sufficiently conductive. In the case of gel-like polymers, the addition of high temperatures is disadvantageous for the retention of the liquid.

DISCLOSURE OF THE INVENTION

It is a first object of the present invention to provide a novel polymer electrolyte having high ionic conductivity, which can be used to fabricate a battery exhibiting excellent charge/discharge characteristics not only at high temperatures but also at low temperatures.

It is a second object of the present invention to provide a polymer electrolyte capable of inhibiting lithium precipitation in the form of dendrites.

According to the present invention, there is provided a gel-type polymer electrolyte, wherein the polymer comprises (a) an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof and (B) a polyoxyalkylene having a hydroxyl group at one end thereof or a derivative thereof, which are bonded together through an ester bond.

The ester bond can be generated, for example, by esterification between a carboxylic acid group of an ethylene-unsaturated carboxylic acid copolymer and a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, or by transesterification between an alkyl ester of an ethylene-unsaturated carboxylic acid copolymer or an alkyl ester derivative thereof and a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof.

Hereinafter, the present invention will be described mainly with reference to the case where an ester bond is introduced by an esterification reaction. Whenever the preferred embodiment is different due to the esterification reaction and the transesterification reaction, the case where the ester bond is introduced by the transesterification reaction will be explained.

In the gel-type polymer electrolyte of the present invention, it is preferable that:

1. the ester bond is formed by a molar ratio (B) of an ethylene-unsaturated carboxylic acid copolymer or its derivative (A) (compound (A)) to a polyoxyalkylene having a hydroxyl group at one end thereof or its derivative (B) (compound (B)) represented by the following formula_{Hydroxy radical}/A_{Carboxyl group}) Is generated through reaction (esterification),

B_{hydroxy radical}/A_{Carboxyl group}0.3 to 2.5;

wherein B is_{Hydroxy radical}Is the hydroxyl group mole number of a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, and A_{Carboxyl group}Is the mole number of carboxylic acid groups of the ethylene-unsaturated carboxylic acid copolymer or the derivative thereof,

or

In the case of transesterification, an alkyl ester of an ethylene-unsaturated carboxylic acid copolymer or an alkyl ester derivative thereof (containing neither a carboxyl group nor an acid anhydride group) is reacted as the compound (A) with a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof (B) (compound (B)) (transesterification reaction) to satisfy the above molar ratio (B)_{Hydroxy radical}/A_{Packaging base})；

2. Residual amounts of unreacted carboxylic acid groups in the polymer of not more than 30 mol%, based on the carboxylic acid of the ethylene-unsaturated carboxylic acid copolymer or derivative thereof (A); or

In the case of the transesterification, the residual carboxylic acid groups are present in an amount of essentially 0 mol%;

3. in the case of ester bond formation by esterification reaction, the composition of the compound (A) comprises 50 to 98 wt% (weight percent) of ethylene, 2 to 50 wt% of unsaturated carboxylic acid or anhydride thereof, and 0 to 30 wt% of other monomers; or

In the case of transesterification, the composition of the compound (A) comprises 50 to 98% by weight of ethylene, 2 to 50% by weight of an alkyl ester of an unsaturated carboxylic acid or an alkyl ester derivative thereof;

4. the ethylene-unsaturated carboxylic acid copolymer or derivative thereof (A) is an ionomer in which the carboxylic acid is partially neutralized with a monovalent metal or a polyvalent metal to a degree of neutralization of 0.5 to 60 mol%;

5. the ethylene-unsaturated carboxylic acid copolymer or its derivative (A) has a melt flow rate (meltflow) of 0.1 to 500g/10min at 190 ℃ under a load of 2160 g;

6. a polyoxyalkylene having a hydroxyl group at one end thereof or a derivative thereof (B) having a number average molecular weight of 200 to 100,000 and containing 30 to 100 mol% of ethylene oxide;

7. the hydroxyl group at the other end of the polyoxyalkylene or derivative thereof (B) is blocked by etherification, esterification or by reaction with a monoisocyanate (blocked);

8. the esterification of compound (a) with compound (B) is carried out in the presence of an acid catalyst; or

The transesterification of the compound (A) with the compound (B) is carried out in the presence of an organometallic catalyst, in particular a metal alkoxide;

9. the polymer is in the form of a powder, film or sheet; and

10. the esterification reaction or transesterification reaction is carried out in the presence of a small amount of a crosslinking agent (pre-crosslinking), and thus the polymer is partially crosslinked.

According to the present invention, the gel-type polymer electrolyte is generally used in the form of an electrolyte solution impregnated with a polymer matrix.

In this case, it is preferable that:

1. the solvent is present in the electrolyte solution in a proportion of 30 to 95 wt%, preferably 30 to 90 wt%, based on the sum of the polymer and the electrolyte solution;

2. an electrolyte is present in the electrolyte solution in a proportion of 1 to 30 wt%, based on the sum of the polymer and the electrolyte solution;

3. the electrolyte species in the electrolyte solution is a lithium salt; and

4. the solvent in the electrolyte solution is a non-aqueous electrolyte solvent.

In addition, in the case of having an absorbed electrolyte solution, the polymer may be incorporated with a crosslinking agent, such as an acrylic acid derivative, so as to absorb the electrolyte solution and obtain a gel polymer in a crosslinked form (post-crosslinking).

Further, according to the present invention, there is provided a secondary battery, particularly a lithium secondary battery provided with a gel-type polymer electrolyte layer.

Further, according to the present invention, there is provided a capacitor provided with a gel type polymer electrolyte layer.

The present invention also relates to a method for producing a gel-type polymer electrolyte, wherein the polymer comprises (A) an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof and (B) a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, which are bonded together via an ester bond,

wherein the polyoxyalkylene having a hydroxyl group at one end thereof or the derivative thereof (B) has a number average molecular weight of 200 to 100,000 and contains 30 to 100 mol% of ethylene oxide,

wherein the gel-type polymer is impregnated with an electrolyte solution comprising an electrolyte salt and a nonaqueous electrolyte solution,

the ester bond is generated by esterification between a carboxylic acid group of an ethylene-unsaturated carboxylic acid copolymer and a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, or

The ester bond is generated by a transesterification reaction between an alkyl ester of an ethylene-unsaturated carboxylic acid copolymer or an alkyl ester derivative thereof and a polyoxyalkylene having a hydroxyl group at one end thereof or a derivative thereof.

In the method of the present invention, the polymer is obtained by reacting an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof (A) with a monomer having a hydroxyl group at one terminal thereofIs produced by reacting a polyoxyalkylene or a derivative thereof (B) in a molar ratio represented by the following formula_{Hydroxy radical}/A_{Carboxyl group}Between 0.3 and 2.5,

wherein B is_{Hydroxy radical}Is the hydroxyl group mole number of a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, and A_{Carboxyl group}Is the number of moles of carboxylic acid groups of the ethylene-unsaturated carboxylic acid copolymer or derivative thereof.

In the process of the present invention, the residual amount of unreacted carboxylic acid groups in the polymer is not more than 30 mol%, based on the carboxylic acid groups of the ethylene-unsaturated carboxylic acid copolymer or the derivative (A) thereof.

In the process of the present invention, the hydroxyl group at the other terminal of the polyoxyalkylene or the derivative thereof (B) has been blocked by etherification, esterification or by reaction with a monoisocyanate.

In the method of the present invention, the esterification between the ethylene-unsaturated carboxylic acid copolymer or its derivative (a) and the polyoxyalkylene having a hydroxyl group at one end thereof or its derivative (B) is carried out in the presence of an acid catalyst.

In the method of the present invention, the ester bond formation process by the transesterification reaction is carried out in the presence of an organometallic catalyst.

In the method of the present invention, the polymer is partially crosslinked in the presence of at least one crosslinking agent selected from the group consisting of polyhydric alcohols, mono (meth) acrylic acids or esters thereof, polyethylene glycol di (meth) acrylates, unsaturated higher fatty acids or esters thereof, and polyethylene glycol diglycidyl ethers. In a further embodiment, the crosslinking agent is present in the reaction system in an amount of from 0.1 to 30 wt%.

Brief Description of Drawings

FIG. 1 is a perspective view of a test cell for determining the ionic conductivity and lithium ion transport number of a polymer electrolyte;

fig. 2 is a perspective view of a test cell for testing charge/discharge characteristics;

FIG. 3 is a graph showing the results of example 1, i.e., showing the change in weight of a polymer immersed in an electrolyte solution with time (Wo is the weight of the polymer itself, and W is the weight of a polymer gel at the same time); and

FIGS. 4a and 4b are graphs showing the results of example 23 (solid line) and comparative example 5 (broken line), in which FIG. 4(a) shows charge/discharge cycle characteristics; fig. 4(b) shows a charge/discharge curve of the eighth cycle.

Best mode for carrying out the invention

In order to solve the above-mentioned problems, the present invention has been made in view of a polyolefin material as a main component of a separator material, but it has not been regarded as an electrolyte so far. However, these materials cannot absorb and retain organic solvents used for lithium secondary batteries.

The present inventors have previously found that a diacrylate compound having oligo (oxyethylene) groups at both ends thereof and grafted with PMMA exhibits lithium ion transporting properties and has significantly improved compatibility between a polymer chain thereof and an electrolyte solution (this patent application is co-pending, published patent application No. 189166/2001).

The present inventors continued to pursue along this finding, and noticed that carboxylic acid-containing polyethylene, i.e., an ethylene-unsaturated carboxylic acid (including unsaturated acid anhydride thereof) copolymer as polyolefin, successfully esterified the substance with carboxylic acid (or acid anhydride thereof) with polyethylene oxide having a hydroxyl group at one terminal thereof or a derivative thereof, thereby introducing polyethylene oxide like a comb to polyethylene side chains attached to an ester bond, i.e., successfully synthesized a polyethylene unsaturated carboxylic acid copolymer to which polyethylene oxide was grafted, and studied the electrolyte properties of the polymer. As a result, the present inventors have found that the polymer can be easily formed into a self-supporting thin film and exhibits the property of absorbing and retaining a large amount of an electrolyte solution for lithium ion batteries.

The present inventors have also found that a polymer having the same properties as those described above can be obtained even when the ester bond is introduced by a transesterification reaction between an alkyl ester of an ethylene-unsaturated carboxylic acid copolymer or an alkyl ester derivative thereof and a polyethylene oxide having a hydroxyl group at one terminal thereof or a derivative thereof, instead of relying on the esterification reaction described above.

Polymer matrix

The polymer material used for the gel-type polymer electrolyte of the present invention comprises, as essential constituents, an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof (a) and a polyoxyalkylene having a hydroxyl group at one end thereof or a derivative thereof (B), both of which are bonded (grafted) together via an ester bond.

That is, the polymer material is a polymer material in which polyoxyalkylene is introduced into an ethylene-unsaturated carboxylic acid copolymer like a comb through an ester bond. Preferably, the polymer material is obtained by esterification between an ethylene-unsaturated carboxylic acid copolymer and a polyoxyalkylene having a hydroxyl group at one terminal thereof. Of course, it is also permissible to obtain the polymer material by introducing a polyoxyalkylene (alkoxy polyoxyalkylene having one end blocked), that is, by a transesterification reaction using a derivative (alkyl ester or alkyl ester derivative) of an ethylenically unsaturated carboxylic acid ester copolymer.

(1) Ethylene-unsaturated carboxylic acid copolymer or derivative thereof (a):

preferably, the composition of the ethylene-unsaturated carboxylic acid copolymer or its derivative (A) (hereinafter often referred to as compound (A)) comprises 50 to 98% by weight, particularly 60 to 95% by weight of ethylene, 2 to 50% by weight, particularly 5 to 25% by weight of an unsaturated carboxylic acid, and 0 to 30% by weight, particularly 0 to 20% by weight of other monomers.

When the ethylene content in the copolymer is too low, the resin will show an increase in melting temperature and a decrease in melt fluidity, which is not preferable for the esterification reaction with polyoxyalkylene from the viewpoint that the temperature must be increased and the stirring efficiency must be improved.

Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, ethacrylic acid (ethacrylic acid), fumaric acid, maleic acid, itaconic acid, monomethyl maleate, monoethyl maleate, maleic anhydride, and itaconic anhydride.

Of these, acrylic acid or methacrylic acid is most preferably used.

As other monomers optionally added to constitute the ethylene-unsaturated carboxylic acid copolymer, vinyl esters such as vinyl acetate and vinyl propionate; unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, isooctyl acrylate, methyl methacrylate, isobutyl methacrylate, dimethyl maleate and diethyl maleate; or even carbon monoxide and sulphur dioxide.

In the present invention, the compound (A) used in the transesterification method is an alkyl ester of an ethylene-unsaturated carboxylic acid copolymer or an alkyl ester derivative thereof. Further, the unsaturated carboxylic acid ester or derivative constituting the compound (A) is the above-mentioned unsaturated carboxylic acid ester or derivative thereof, particularly methyl ester or ethyl ester.

In the present invention, the ethylene-unsaturated carboxylic acid copolymer itself may be used, but it is also permissible to use a derivative thereof, for example, an ionomer in which some carboxyl groups in the molecule are substituted with a metal salt.

Examples of the metal constituting the metal salt of the ionomer include monovalent metals such as lithium, sodium or potassium, or polyvalent metals such as magnesium, calcium, zinc, copper, cobalt, manganese, lead or iron.

Lithium salts are preferably used for the polymer electrolyte material of the polymer lithium battery.

When the neutralization degree of the ionomer is too large, it will be difficult to obtain a uniform composition when the polyoxyalkylene is grafted thereon. Therefore, it is preferred that the degree of neutralization of the ionomer is between 0.5 and 60 mol%, especially from as low as 1 to 30 mol%.

The ethylene-unsaturated carboxylic acid copolymer of the present invention can be obtained by radical copolymerization of ethylene with an unsaturated carboxylic acid or with other monomers under high temperature and high pressure conditions. The metal ionomers can be obtained by neutralizing the above copolymers with metal salts under conditions known per se.

Desirably, the above ethylene-unsaturated carboxylic acid copolymer or its ionomer has a melt flow rate of 0.1 to 500g/10min, particularly 0.5 to 300g/10min, at 190 ℃ under a load of 2160 g.

Desirably, the weight average molecular weight (Mw) is in the range of 2,000 to 800,000, especially 4,000 to 500,000, in terms of polystyrene molecular weight. The above weight average molecular weight (Mw) corresponds to a number average molecular weight (Mn) of 500 to 150,000, preferably 1,000 to 100,000.

Further, in the present invention, two or more ethylene-unsaturated carboxylic acid copolymers or derivatives thereof may be used in admixture.

(2) A polyoxyalkylene having a hydroxyl group at one end thereof or a derivative thereof (B):

the polyoxyalkylene having a hydroxyl group at one end thereof (often referred to as a compound (B)) has a blocked hydroxyl group at the other end thereof, preferably has a number average molecular weight of 200 to 100,000 and contains 30 to 100 mol% of ethylene oxide.

As the comonomer, propylene oxide, n-butylene oxide and/or isobutylene oxide can be used, and ethylene oxide and a random copolymer thereof, a graft copolymer thereof or a block copolymer thereof can be used as the compound (B).

The polyoxyalkylene is allowed to contain 0 to 60 mol% of a propylene oxide component and 0 to 20 mol% of a butylene oxide component.

From a structural point of view, it can be linear homopolymers in which one end is blocked, copolymers based on polyhydric alcohols (e.g.glycerol, pentaerythritol) and branched graft products.

In this case, the other hydroxyl groups should be blocked stoichiometrically to ensure one hydroxyl group per molecule. Two or more kinds of polyoxyalkylene having a hydroxyl group at one terminal thereof may also be used in combination.

The hydroxyl group at the other end can be blocked by etherification, esterification or by reaction with monoisocyanates.

In the case of etherification, an alkyl group having 1 to 22 carbon atoms (for example, an ethyl group, a hexyl group, a 2-ethylhexyl group, etc.), a phenyl group and a benzyl group may be used as the substituent.

In the case of esterification, a carboxylic acid having 1 to 22 carbon atoms (e.g., acetic acid, maleic acid, or terephthalic acid) and an acid anhydride (e.g., maleic anhydride) may be used.

In the case of blocking the terminal hydroxyl groups with monoisocyanates, methyl isocyanate or phenyl isocyanate may be used.

To obtain the polymer electrolyte comprising the partially crosslinked polymer of the present invention, a polyhydric alcohol having two or more hydroxyl groups (e.g., glycerol, pentaerythritol, etc.) may be added as a crosslinking agent (pre-crosslinking), followed by esterification or etherification. The amount of the crosslinking agent added varies depending on the molecular weight of the compounds (A) and (B), but is generally 0.1 to 30% by weight, particularly 1 to 15% by weight, based on the sum of the compounds (A) and (B).

(3) Graft and polymer:

preferably, the esterification reaction of the ethylene-unsaturated carboxylic acid copolymer to carboxylic acid using the polyoxyalkylene (B) having a hydroxyl group at one terminal thereof is carried out in bulk reaction without using a solvent but using an acid catalyst.

The basic operation of the esterification reaction will be described next.

First, an acid catalyst is added to a polyoxyalkylene having a hydroxyl group at one terminal thereof or to a derivative thereof (compound (B)) under heating and stirring conditions, followed by addition of an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof (compound (A)), and the reaction is allowed to proceed for several tens of hours.

After the reaction, the reaction product was washed with water and removed of unreacted polyoxyalkylene and catalyst by soaking in methanol or ethanol, and then dried in vacuum.

Preferably, the compounds (A) and (B) are present in a molar ratio (B) represented by the following formula_{Hydroxy radical}/A_{Carboxyl group}) Feeding the mixture into a feeding machine,

B_{hydroxy radical}/A_{Carboxyl group}

Wherein B is_{Hydroxy radical}Is the hydroxyl group mole number of a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, and A_{Carboxyl group}Is the number of moles of carboxylic acid groups of the ethylene-unsaturated carboxylic acid copolymer or derivative thereof (however, the carboxylic acid groups herein include not only carboxylic acid groups but also carboxylic acid ester groups and acid anhydride groups, the acid anhydride groups being calculated as 2 carboxylic acid groups),

B_{hydroxy radical}/A_{Carboxyl group}Between 0.3 and 2.5, in particular between 0.9 and 2.0 (even in the case of transesterification).

Preferably, the reaction temperature is between 80 and 160 ℃, especially between 100 and 140 ℃.

Preferably, the reaction time is 7 to 40 hours, especially 10 to 30 hours.

The acid catalyst for esterification is preferably sulfuric acid, phosphoric acid, polyphosphoric acid, p-toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid or dodecylbenzenesulfonic acid, and is added in an amount of 0.0001 to 0.1mol, particularly, 0.001 to 0.05mol per mol of hydroxyl group.

In the transesterification reaction, for example, a metal alkoxide (sodium methoxide, potassium ethoxide, rare earth metal triisopropoxide, potassium tert-butoxide, titanium tetrabutoxide, dibutyltin oxide, etc.), sodium hydroxide, potassium hydroxide, or a heteropoly acid (molybdenum-phosphoric acid, tungsten-phosphoric acid, etc.) can be used as a catalyst. The amount added is preferably from 0.0001 to 0.5mol, in particular from 0.001 to 0.1mol, per mole of hydroxyl groups.

The reaction system is maintained under reduced pressure (e.g., 0.067 MPa-500 mm hg) to efficiently carry out the esterification reaction.

In this esterification reaction, it is also permissible to use an organic solvent (e.g., toluene, xylene, ethylene glycol or diethyl ether thereof) and an antioxidant (e.g., hydroquinone monomethyl ether). The same applies to the transesterification reaction.

Preferably, the antioxidant is added in an amount of 100 to 10,000ppm, especially 500 to 5,000ppm, with respect to the compound (B).

The polymeric materials used in the present invention are melted at elevated temperature alone or together with a non-volatile organic solvent and then moulded into self-supporting films or sheets in a manner known per se, for example by casting, T-die or inflation.

Gel-type polymer electrolyte

The gel-type polymer electrolyte of the present invention comprises the above-mentioned polymer matrix and an electrolyte solution impregnating the matrix.

In the gel-type polymer electrolyte of the present invention, it is preferred that the solvent is present in the electrolyte solution in an amount of usually 30 to 95% by weight, particularly preferably 30 to 90% by weight, particularly preferably 60 to 90% by weight, based on the sum of the polymer and the electrolyte solution. When the content of the solvent is excessively low, ionic conductivity may be reduced. When the solvent content is too high, the strength of the electrolyte tends to decrease.

It is also desirable that the electrolyte is present in the electrolyte solution in an amount of usually 1 to 30% by weight, especially 1 to 20% by weight, based on the sum of the polymer and the electrolyte solution. When the electrolyte content is higher or lower than the above range, the ionic conductivity tends to decrease.

Any electrolyte salt commonly used for such gel-type polymer electrolytes may be used in the present invention.

When the polymer electrolyte of the present invention is used in a lithium polymer secondary battery, it is preferable to use a lithium salt as an electrolyte salt, such as CF₃SO₃Li、C₄F₆SO₃Li、(CF₃SO₂)₂NLi、(CF₃SO₂)₃CLi、LiBF₄、LiPF₆、LiCLO₄Or LiAsF₆. However, the present invention is not limited to these in any sense.

As the nonaqueous electrolyte solvent (organic solvent), any nonaqueous solvent generally used for such a gel-type polymer electrolyte can be used. For example, a solvent selected from at least any one of the following solvents may be used: cyclic carbonates such as ethylene carbonate and propylene carbonate; dipropyl carbonate such as dimethyl carbonate, methylethyl carbonate, diethyl carbonate and dipropyl carbonate; cyclic esters such as gamma-butyrolactone and propiolactone; chain ethers such as diethoxyethane and dimethoxyethane; amide compounds such as dimethylacetamide and the like; nitrile compounds such as acetonitrile, propionitrile, etc.; n-methylpyrrolidone, etc.; and mixtures thereof. Of course, however, the present invention is not limited to these examples in any sense.

In the present invention, the electrolyte and the nonaqueous solvent are not limited to the above examples in any sense.

For example, when the polymer electrolyte of the present invention is used in a capacitor, as the electrolyte, a salt in which lithium of the above lithium salt is substituted with other alkali metal ion (sodium ion, potassium ion, cesium ion or the like), ammonium salt such as tetraalkylammonium, tetraalkylfluoroborate ((C)₂H₅)₄NBF₄Etc.), tetraalkylphosphonium triflates ((C)₂H₅)₄PCF₃SO₃Etc.), alkylpyridinium salts and N-alkylimidazolium salts.

As the nonaqueous solvent in this case, it is preferable to use an organic solvent having a donor number (donor number) of not less than 0.1 and a dielectric constant of not less than 10.0. Examples of such organic solvents include, in addition to the above-mentioned solvents for secondary batteries: acid anhydrides such as acetic anhydride; amide compounds such as dimethylformamide and dimethylsulfoxide; phosphate ester compounds such as trimethyl phosphate and tributyl phosphate; and amine compounds such as hydrazine, ethylenediamine, ethylamine, and triethylamine.

In the present invention, a polymer is molded into a film or a sheet, and the polymer is impregnated with an electrolyte solution, optionally in this order.

For example, a polymer film or sheet prepared by the above measures is immersed in a solution containing the above electrolyte salt to obtain a polymer electrolyte. At this time, the temperature of the electrolyte solution was controlled to change the impregnation rate.

Preferably, the polymer electrolyte of the present invention is obtained by impregnating a previously synthesized thin polymer film with the electrolyte solution. According to another method, the above-mentioned polymer material and the above-mentioned electrolyte solution are mixed together and heated up to more than 80 ℃ to obtain a molten solution, and then the solution is cast into a sheet, which can be used as a polymer electrolyte.

For example, a solution of N-methylpyrrolidone containing 1mol/L of lithium tetrafluoroborate using a chain carbonate such as dimethyl carbonate as a solvent is mixed with the above-mentioned polymer material in a weight ratio of (1.5 to 3.5): 1 and heated to a temperature exceeding 80 ℃ at most, to obtain a transparent solution. The solution was cast onto a polyethylene terephthalate film and pressurized, and as a result, an electrolyte film having a prescribed thickness was obtained.

In the above-mentioned mixing and heating of the polymer material with the electrolyte solution to prepare the molten solution in the present invention, a crosslinking agent, as widely used even in polyethylene oxide polymers, may be additionally added to promote gelation and increase mechanical strength [ reference: industrial materials 47(2), 18(1999) and Yuasa Jiho, 87, 10 months, 4 days (1999). For example, the polymer material of the present invention may be blended with a diacrylate compound having oligo (oxyethylene) groups at both ends and dissolved together with an electrolyte solution to perform the thermal polymerization (post-crosslinking). Furthermore, the polymeric material of the present invention has polyethylene chains. Therefore, Electron Beam (EB) crosslinking and ultraviolet crosslinking, which are generally used to crosslink gel polymer electrolytes, are also suitable for the polymer electrolyte of the present invention.

Applications of

The gel-type polymer electrolyte of the present invention is useful as a solid electrolyte layer for a solid secondary battery such as a lithium secondary battery, and as a solid electrolyte layer for a capacitor.

There is no particular limitation in the structure of such secondary batteries or capacitors as long as they are provided with the layer of the gel-type polymer electrolyte of the present invention.

In the case of a lithium secondary battery, it is preferable to sandwich the gel-type polymer electrolyte thin layer of the present invention between a lithium metal negative electrode and a positive electrode active material (for example, LiCoO)₂) In the meantime.

The gel-type polymer electrolyte of the present invention has a thickness of generally 1 μm to 1mm, particularly 5 μm to 0.3mm, and can be laminated as one layer in a secondary battery or a capacitor.

The accumulator according to the invention can, of course, be modified in a variety of ways.

For example, in a liquid electrolyte type lithium ion battery, a polyolefin porous film such as polyethylene is used as a separator and is given a function of cutting off current by utilizing the property of polyethylene melting when heated.

The separator is prepared by blending polyethylene and polypropylene or is composed of a film obtained by laminating polyethylene and polypropylene to each other. Thus, the membrane is advantageously fused together with the polymer material of the invention. A film having a separator function and an electrolyte function is obtained by sticking the above-mentioned electrolyte membrane on one side or both sides of the separator or applying a molten solution of a polymer electrolyte to one side or both sides of the separator and using them as a laminated film.

In addition, in recent years, a three-layer structure film in which a polyethylene fine pore film is disposed between 2 polypropylene fine pore films has been produced as a separator. By mixing the polymer material of the present invention into a polyethylene layer or by applying the polymer material of the present invention to one or both sides of a polyethylene layer, a polymer electrolyte film having a separator function and stably holding an electrolyte solution therein can be obtained.

Again, rather than using a separator, the polymeric material may be applied directly to one electrode and subsequently post-crosslinked so that it is sandwiched between the other electrode.

Various surface modification techniques (chemical modification techniques) can be applied to the surface of the polymer material of the present invention to improve the performance of holding an electrolyte solution and to improve the adhesion to the surface of a negative electrode material, the surface of a positive electrode material, and the surface of a separator. Furthermore, chemical modification techniques may be applied to the polymer electrolyte itself. Specifically, the surface of the film or the polymer electrolyte itself may be modified by the following processes: thermal or photo-crosslinking agents are applied to the surface of the film of the present invention, or mixed in with post-crosslinking upon dissolution of the electrolyte, and then irradiated with heat and light. The surface may also be modified by Electron Beam (EB) irradiation. By virtue of the implementation of the pre-crosslinking as described above, it is also possible to omit and simplify the post-crosslinking step.

Examples

The invention will be further described by means of working examples, which, however, are not intended to limit the invention in any way.

Preparation of example 1

183g of polyethylene glycol monomethyl ether PEG-MME (number average molecular weight 550, 0.33mol of hydroxyl groups) and 1.5g (0.0079mol) of paratoluenesulfonic acid hydrate (molecular weight 190) were introduced into a 500mL four-necked flask.

The mixture was heated with stirring up to 140 ℃ and then blown through a capillary with nitrogen (0.1 m)³At the same time, 100g of ethylene-acrylic acid copolymer (0.28mol of carboxylic acid groups, molar ratio hydroxyl groups/carboxylic acid groups (B)_{Hydroxy radical}/A_{Carboxyl group}) 1.18) was added gradually (within about 30 min) while confirming the dissolved state. After the addition was complete, the mixture was reacted at the same temperature for 24 h.

After the reaction, the reaction product was transferred to another vessel, cooled, and cut into about 1cm³The size of (2). 500mL of ethanol was added thereto at room temperature. After 70h of soaking, the ethanol solution was removed by decantation.

An additional 500mL of ethanol was added and the same procedure was repeated. After washing in ethanol, the esterification product is removed and dried in a vacuum dryer.

FTIR spectrum (Fourier transform infrared spectrum) observation of the obtained esterification product revealed that there was almost no absorption peak due to carbonyl group of unreacted free carboxylic acid (vCO ═ 1700cm^-1)。

The obtained esterification product was used as a polymer electrolyte material a.

Composition of polymer electrolyte material a (wt%): E/AA/PEG-MME 31.5/0.0/68.5

(E: ethylene, AA: acrylic acid)

Preparation of example 2

154g of polyethylene glycol monomethyl ether PEG-MME (number average molecular weight 550, 0.28mol of hydroxyl groups) and 1.28g (0.0067mol) of p-toluenesulfonic acid hydrate were introduced into a 500mL four-necked flask. The mixture was heated with stirring up to 140 ℃ and 100g of ethylene-acrylic acid copolymer (0.28mol of carboxylic acid, B) were then added stepwise_{Hydroxy radical}/A_{Carboxyl group}＝1.00)。

Then, the same operation as in preparation example 1 was repeated except that the reaction time was changed from 24h to 16 h.

FTIR spectrum observation of the esterification product showed an absorption peak due to carbonyl group of a shoulder-like unreacted free carboxylic acid (vCO-1700 cm)^-1)。

According to titration with potassium hydroxide, 5 mol% of the carboxylic acid of the ethylene-acrylic acid copolymer remained (0.014mol per 0.28mol of the carboxylic acid).

Titration with potassium hydroxide was carried out by heating and dissolving 5g of the sample in a solution of 200g of toluene/ethanol-1/4 and then titrating with phenolphthalein indicator in 0.1N aqueous KOH.

The obtained product was taken as a polymer electrolyte material B.

Composition of polymer electrolyte material B (wt%): E/AA/PEG-MME ═ 32.5/0.4/67.1

Preparation of example 3

123g of polyethylene glycol monomethyl ether PEG-MME (number average molecular weight 550, 0.224mol of hydroxyl group) and 1.02g (0.0054mol) of paratoluenesulfonic acid hydrate were introduced into a 500mL four-necked flask. The mixture was heated with stirring up to 140 ℃ and 100g of ethylene-acrylic acid copolymer (0.28mol of carboxylic acid, B) were then added stepwise_{Hydroxy radical}/A_{Carboxyl group}0.8). Then, the same operation as in preparation example 1 was repeated except that the reaction time was changed from 24h to 16 h.

According to titration with potassium hydroxide, 24 mol% of the carboxylic acid of the ethylene-acrylic acid copolymer remained (0.067mol per 0.28mol of the carboxylic acid).

The obtained product was taken as a polymer electrolyte material C.

Composition of polymer electrolyte material C (wt%): E/AA/PEG-MME ═ 36.8/2.2/61.0

Preparation of example 4

248g of polyethylene glycol monomethyl ether PEG-MME (number average molecular weight 750, 0.33mol of hydroxyl groups) and 1.5g (0.0079mol) of paratoluene sulfonic acid hydrate (molecular weight 190) were introduced into a 500mL four-necked flask. The mixture was heated to 140 ℃ with stirring and then nitrogen (0.1 m) was blown through a capillary³At the same time, 100g of ethylene-acrylic acid copolymer (0.28mol of carboxylic acid groups, molar ratio hydroxyl groups/carboxylic acid groups (B)_{Hydroxy radical}/A_{Carboxyl group}) 1.18) was added gradually (within about 30 min) while confirming the dissolved state. After the addition was complete, the mixture was reacted at the same temperature for 24 h.

After the reaction, the reaction product was transferred to another vessel and, after cooling, cut into about 1cm³The size of (2). 500mL of ethanol was added thereto at room temperature. After 70h of soaking, the ethanol solution was removed by decantation. An additional 500mL of ethanol was added and the same procedure was repeated. After soaking in ethanol, the esterification product was taken out and dried in a vacuum dryer.

FTIR spectrum observation of the obtained esterification product revealed that there was almost no absorption peak due to carbonyl group of unreacted free carboxylic acid (vCO-1700 cm)^-1)。

The obtained esterification product was used as a polymer electrolyte material D.

Composition of polymer electrolyte material D (wt%): E/slave/PEG-MME 32.3/0.0/67.7

Preparation of example 5

277g of polyethylene glycol-block-polypropylene glycol mono-2-methylhexyl ether (PEG-b-PPG-MEHE) (number average molecular weight 840, 50% by weight of polyethylene glycol, 0.33mol of hydroxyl groups) and 0.63g (0.0033mol) of p-toluenesulfonic acid hydrate (molecular weight 190) were introduced into a 500mL four-necked flask. The mixture was heated with stirring up to 140 ℃ and then blown through a capillary with nitrogen (0.1 m)³While adding gradually 100g of an ethylene-acrylic acid copolymer (0.28mol of carboxylic acid groups, B)_{Hydroxy radical}/A_{Carboxyl group}1.18). After the addition was complete, the mixture was reacted at the same temperature for 30 h. After the reaction, the reactionThe reaction product was transferred to another vessel and, after cooling, cut into about 1cm³The size of (2). 500mL of ethanol was added thereto at room temperature. After 48h of soaking, the ethanol solution was removed by decantation.

An additional 500mL of ethanol was added and the same procedure was repeated. After soaking in ethanol, the esterification product was taken out and dried in a vacuum dryer.

The obtained esterification product was used as a polymer electrolyte material E.

Composition of polymer electrolyte material E (wt%): E/AA/PEG-b-PPG-MEHE ═ 23.9/0.0/76.1

Table 1 shows the composition ratios (wt%) of the polymer electrolyte materials A to E prepared in preparation examples 1 to 5.

TABLE 1

	Polymer and method of making same	Ethylene	Acrylic acid	PEG-MME	PEG-b-PPG-MEHE
	Polymer and method of making same	Ethylene	Acrylic acid	PEG-MME	PEG-b-PPG-MEHE	Preparation of example 1	A	31.5	0.0	68.5	-
Preparation of example 2	B	32.5	0.4	67.1	-	Preparation of example 1	A	31.5	0.0	68.5	-
Preparation of example 2	B	32.5	0.4	67.1	-	Preparation of example 3	C	36.8	2.2	61.0	-
Preparation of example 4	D	32.3	0.0	67.7	-	Preparation of example 3	C	36.8	2.2	61.0	-
Preparation of example 4	D	32.3	0.0	67.7	-	Preparation of example 5	E	23.9	0.0	-	76.1

Preparation example 6 (transesterification)

154g of polyethylene glycol monomethyl ether (PEG-MME) (number average molecular weight 550, 0.28mol of hydroxyl groups), 1.90g (0.28mol) of sodium ethoxide (catalyst) and 50g of xylene (solvent) were introduced into a 500mL four-necked flask. The mixture was heated to 140 ℃ with stirring and then nitrogen (0.1 m) was blown through a capillary³While adding thereto (within 15 min) 56g of an ethylene-ethyl acrylate copolymer (ethyl acrylate, 25% by weight; melt index, 250g/10 min; 0.14mol of ethyl acrylate; b is_{Hydroxy radical}/A_{Carboxyl group}＝2.0)。

After the completion of the addition, a pipe for cooling the solvent and refluxing was installed, and the reaction was carried out at the same temperature for 30 hours while blowing nitrogen gas through a capillary. After the reaction, when the temperature was lowered to not higher than 100 ℃, the reaction mixture was dropped into another vessel containing 1000mL of water while the reaction mixture was kept stirred, and as a result, a slurry was obtained. After the addition was completed, the slurry was stirred for about 1 hour and then allowed to stand. The granular solid was isolated by decantation and introduced into a vessel containing 500mL of methanol, stirred for 2h and then allowed to stand. The mixture was filtered and washed again with methanol to repeat the same operation. After soaking in methanol, the transesterified product was removed and dried in a vacuum desiccator.

According to the product obtained (grafted PEG-MME carboxylic ester (vCO ═ 1731 cm)^-1) And polyethylene (vCO ═ 720cm^-1) The ratio of FTIR spectrum absorption of the internal standard and the transesterification ratio are 89%.

The obtained esterification product was used as a polymer electrolyte material F.

Preparation of example 7 (partially crosslinked polymeric Material)

193g of polyethylene glycol monomethyl ether (PEG-MME) (number average molecular weight 550, 0.35mol of hydroxyl groups), 3.0g (0.0058mol) of polyethylene glycol diacrylate (ethylene oxide repeating unit n ═ 9, molecular weight 520), and 1.5g (0.0079mol) of p-toluenesulfonic acid hydrate (molecular weight 190) were introduced into a 500mL four-necked flask.

The mixture was heated to 140 ℃ with stirring and then nitrogen (0.1 m) was blown through a capillary³At the same time, 63g of an ethylene-acrylic acid copolymer (0.18mol of carboxylic acid groups, B)_{Hydroxy radical}/A_{Carboxyl group}2.0) was added gradually (within about 20 min) while confirming the dissolved state. After the addition was complete, the mixture was reacted at the same temperature for 24 h.

After the reaction, the reaction mixture was added dropwise to another vessel containing 1000mL of water with stirring. After cooling, the precipitate was filtered using a filter cloth, and 1000mL of ethanol was added thereto at room temperature, and then the precipitate was soaked therein for 20 hours. Subsequently, the ethanol solution was removed by means of decantation.

Another 500mL of ethanol was added thereto, and the same operation was repeated. After soaking in ethanol and washing, the partially crosslinked and esterified product is removed and dried in a vacuum dryer.

The obtained product was used as a polymer electrolyte material G.

Adding 90g of a mixed solution of Propylene Carbonate (PC) and Ethylene Carbonate (EC) to 10g of the polymer electrolyte material;

PC and EC are 1: 1 (weight ratio),

containing 1mol/L LiPF₆，

Then, the compound was heated at 80 ℃ for 3 hours to be uniformly dissolved, and cooled to room temperature, and as a result, an electrolyte-containing gel-like polymer electrolyte was obtained.

Fig. 1 shows a measurement system for determining the ionic conductivity and lithium ion transport number of a polymer electrolyte in the working example described below. Fig. 1 shows the structure of the assay battery and the connection between the battery and the measuring device.

The structure of the assay cell includes: the thickness of the two pieces is 0.2mm, and the electrode area is 2.0 multiplied by 2.0cm²The lithium metal foil of (1), with a prescribed polymer electrolyte interposed therebetween. A nickel foil was interposed between the glass plate and the lithium metal foil, thereby completing the electrical connection. The measuring device is a potentiostatic/amperometric electrolyzer (model 1287, manufactured by Solatron).

Impedance was measured by connecting a frequency response analyzer (model 1250, manufactured by Solatron corporation) to the electrolyzer.

Fig. 2 shows a measuring system for determining the charge/discharge characteristics of a lithium secondary battery using a prescribed polymer electrolyte. Figure 2 shows the structure of the assay cell and the connection between the cell and the assay device.

The structure of the assay cell includes: interposing a defined polymer gel electrolyte between a lithium metal negative electrode and a positive electrode by applying 327.0g/m on both sides of an aluminum foil²An application amount of lithium cobaltate positive electrode active material, wherein the aluminum foil has a thickness of 20 μm and an electrode area of 2.0 × 2.0cm². The electrical connection is completed by inserting a nickel foil between the glass plate and the electrode. The measuring apparatus was BS-2500, manufactured by Keishku Giken.

Examples 1 to 6

< electrolyte-Polymer absorption Property >

The polymer electrolyte material of the present invention obtained in preparation example 1 was immersed in the specified electrolyte solution at room temperature (25 ℃ C.) for 2 days. The weight of the polymer gel (polymer + electrolyte solution) before and after soaking was measured to find the absorption amount of the electrolyte solution. The results are shown in Table 2

Table 2: polymer electrolyte material a.

	Electrolyte solution	Auxiliary salt	Polymer electrolyte (weight ratio)
	Electrolyte solution	Auxiliary salt	Polymer electrolyte (weight ratio)	Examples 1 example 2 example 3 example 4 example 5 example 6	Dimethyl carbonate diethyl ester dimethoxyethane propylene carbonate + ethylene carbonate gamma-butyrolactone N-methylpyrrolidone	1M LiBF₄Same as above and same as above	37∶6358∶4224∶7630∶7032∶6846∶54

Example 7

< swelling Property of Polymer gel >

Polymer electrolyte material A of the present invention was immersed in propylene carbonate and ethylene carbonate (PC: EC ═ 1: 1, containing 1mol/L LiPF) used in preparation example 7₆) The mixed solution of (4) was heated at 80 ℃ for 3 hours and then the temperature was lowered to room temperature to measure the mass of the polymer gel with the lapse of time. After 3h of soaking, the swelling of the polymer gel was terminated. At this time, the amount of the solution contained was 83.5 wt%, and thus a polymer electrolyte maintaining a sufficiently large amount of the electrolyte was obtained. In this case, a film of 100 μm thickness, after impregnation with the polymer electrolyte, achieves a thickness of 200 to 250 μm, corresponding to a 2 to 2.5 fold increase.

Example 8

< swelling Property of Polymer gel >

The polymer electrolyte material a of the present invention was immersed in a mixed solution of propylene carbonate and ethylene carbonate (used in example 7 above) at room temperature, and then the mass of the polymer gel was measured with the passage of time. After 3h of soaking, the swelling of the polymer gel was terminated. At this time, the amount of the solution contained was 61.3 wt%.

Example 9

< swelling Property of Polymer gel >

The polymer electrolyte material A of the invention is soaked in Ethylene Carbonate (EC) and dimethyl carbonate (DMC) [ EC: DMC is 1: 2 (weight ratio), and contains 1mol/L LiPF₆]The mixed solution of (4) was heated at 80 ℃ for 3 hours, and then the temperature was lowered to room temperature to measure the mass of the polymer gel with the lapse of time. After 3h of soaking, the swelling of the polymer gel was terminated. At this time, the amount of the solution contained was 88.6 wt%. Thus, a polymer electrolyte that retains a sufficiently large amount of electrolyte is obtained.

Example 10

< swelling Property of Polymer gel >

The polymer electrolyte material a of the present invention was immersed in the mixed solution of ethylene carbonate and dimethyl carbonate used in example 9 at room temperature, and the mass of the polymer gel was measured with the passage of time. After 3h of soaking, the swelling of the polymer gel was terminated. At this time, the amount of the solution contained was 72.4 wt%. The results for examples 7, 8, 9 and 10 are shown in FIG. 3 and Table 3.

TABLE 3

Example number	Polymer and method of making same	Electrolyte solution	Time of impregnation	Electrolyte content after 3 hours of immersion	Symbol of fig. 3
Example number	Polymer and method of making same	Electrolyte solution	Time of impregnation	Electrolyte content after 3 hours of immersion	Symbol of fig. 3	78910	AAAA	1M LiPF₆ PC+EC(1∶1)1M LiPF₆ PC+EC(1∶1)1M LiPF₆ PC+DMC(1∶2)1M LiPF₆ PC+DMC(1∶2)	80℃(3hr)25℃80℃(3hr)25℃	83.5% (by weight) 61.3% (by weight) 88.6% (by weight) 72.4% (by weight)	▲▼■●

Examples 11 to 14

< ion conductivity and lithium ion transport number-different depending on the electrolyte >

The polymer electrolyte material A of the present invention and the polymer electrolytes of various electrolyte solutions were measured with respect to their respective ion conductivities and lithium ion transport numbers at room temperature (25 ℃ C.). These polymer electrolytes exhibit a value of greater than 1X 10^-3Scm^-1The ion conductivity of (3) and the lithium ion transport number of about 0.2 are favorable properties (indexes) as an electrolyte.

The results are shown in Table 4. The ion conductivity and lithium ion transport number of the polymer electrolyte were calculated as follows.

Ionic conductivity-volume resistance/inter-electrode distance (thickness of polymer electrolyte)

Transference number of lithium ion ═ I_s(dV-I₀Re⁰)/I₀(dV-I_sRe^s)

I₀＝dV/(Re⁰+Rb⁰)

I₀: current before constant voltage electrolysis

Re⁰: constant voltage interface resistance before electrolysis

Rb⁰: constant voltage electrolysis precursor resistor

I_s: constant voltage post electrolysis current

Re^s: constant voltage electrolytic interface resistance

dV: electrolytic applied voltage

TABLE 4

	Supporting salt	Solvent(s)	Ion conductivity	Transference number of lithium ion
	Supporting salt	Solvent(s)	Ion conductivity	Transference number of lithium ion	Example 11 example 12 example 13 example 14	1M LiBF₄1M LiBF₄1M LiPF₆1M LiPF₆	PC+EC(1∶1)EC+DMC(1∶2)PC+EC(1∶1)EC+DMC(1∶2)	1.7x10^-3S/cm1.4x10^-3S/cm1.5x10^-3S/cm5.2x10^-3S/cm	0.140.170.120.09

Note: 10^-3Represents the index-3.

Examples 15 to 20

< ion conductivity and lithium ion transport number-varying depending on the kind of polymer >

The polymer electrolyte materials B to G obtained in preparation examples 2 to 7 were impregnated with a mixed solution of propylene carbonate and ethylene carbonate (PC: EC: 1 weight ratio, and containing 1mol/L LiBF)₄) For the obtained polymer electrolytes, their ion conductivity and lithium ion transport number at room temperature were measured. These polymer electrolytes exhibit a value of greater than 1X 10^-3Scm^-1And a lithium ion transport number of about 0.2, are favorable properties as a polymer electrolyte. The results are shown in Table 5.

TABLE 5

	Polymer and method of making same	Electrolyte solution	Ion conductivity	Transference number of lithium ion
	Polymer and method of making same	Electrolyte solution	Ion conductivity	Transference number of lithium ion	Example 15 example 16 example 17 example 18 example 19 example 20	BCDEFG	1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)	1.5×10^-3S/cm1.4×10^-3S/cm1.5×10^-3S/cm7.8×10^-3S/cm1.2×10^-3S/cm2.9×10^-3S/cm	0.200.200.190.080.200.18

Comparative examples 1 to 4

The ionic conductivity and lithium ion transport number at room temperature of the polymer electrolytes obtained by impregnating a mixed solution of propylene carbonate and ethylene carbonate used in examples 15 to 18 with a polyvinylidene fluoride/hexafluoropropylene copolymer (abbreviated as P (VDF-HFP)) manufactured by Aldrich co are measured, the results are shown in table 6.

TABLE 6

Comparative example	Polymer and method of making same	Content of electrolyte solution	Supporting salt	Ion conductivity	Transference number of lithium ion
Comparative example	Polymer and method of making same	Content of electrolyte solution	Supporting salt	Ion conductivity	Transference number of lithium ion	1234	P(VDF-HFP)P(VDF-HFP)P(VDF-HFP)P(VDF-HFP)	70％65％60％50％	1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)1M LiBF₄ PC+EC(1∶1)	1.7x10^-3S/cm1.5x10^-3S/cmL.3x10^-3S/cm0.7x10^-3S/cm	0.200.200.210.22

As can be seen from examples 15-20 and comparative examples 1-4, the polymer material of the present invention has properties comparable to PVDF polymer electrolyte.

Examples 21 to 23

< ion conductivity-temperature dependence >

As for the polymer electrolytes obtained by impregnating the polymer electrolyte materials B to G of the present invention with the mixed solution of propylene carbonate and ethylene carbonate used in example 15, their ionic conductivities at temperatures of-20, -10, 0, 10, 25, 40, 55, 70 and 85 ℃ were measured. All of these polymer gel electrolytes exhibit temperatures above 10 ℃ of greater than 1X 10^-3Scm^-1The ionic conductivity of (1). It is thus shown that favorable ionic conductivity can be obtained even at low temperatures. The results are shown in Table 7.

TABLE 7

	Polymer and method of making same	Ion conductivity (ms/cm)
	Polymer and method of making same	Ion conductivity (ms/cm)									-20℃	-10℃	0℃	10℃	25℃	40℃	55℃	70℃	85℃
Example 21 example 22 example 23	BCD	0.400.470.36	0.490.540.43	0.700.820.66	1.031.130.93	1.531.691.38	2.092.261.93	2.792.732.69	3.363.733.73	4.345.174.29	-20℃	-10℃	0℃	10℃	25℃	40℃	55℃	70℃	85℃

Example 24

< Effect of suppressing dendrite formation >

At 3mA/cm²The electrolysis was performed for 1h at a constant current of (1), and then the interface between lithium and the polymer electrolyte was observed using a CCD camera. The lithium metal electrode had a smooth surface and the polymer electrolyte of example 15 showed a remarkable inhibitory effect on the formation of dendrites at the lithium electrode interface.

Example 25

< Charge/discharge cycle characteristics >

A test cell was made using lithium cobaltate coated on the surface of an aluminum collector as a positive electrode, lithium metal as a negative electrode and the polymer electrolyte material B of example 15, and was subjected to a charge/discharge test at 20 ℃.

The cell was operated at a current density of 1.025mA/4cm with the cut-off voltage set to 4.3V²Is charged in the CC mode of (1), and the current density is 1.025mA/4cm with the cut-off voltage set to 2.5V²Under the condition of (1) to perform discharge. The storage battery can generate output voltage as high as 3.8-4.0V and high coulomb efficiency, so that the polymer electrolyte can be used as an excellent electrolyte material for a high-efficiency lithium storage battery.

The results are shown in FIG. 4.

The battery maintains not less than 90% of the initial characteristics even after the charge/discharge operation is repeated 100 times, demonstrating that the polymer electrolyte is highly stable.

Example 26

< Charge/discharge cycle characteristics >

The experiment of example 25 was repeated, but with the polymer electrolyte material D of example 17, substantially the same charge/discharge characteristics as those of example 25 were obtained.

Comparative example

< Charge/discharge cycle characteristics >

The experiment of example 25 was repeated, but with the polymer electrolyte of example 16. The charge/discharge characteristics thereof deteriorate with the increase of the number of cycles. This is considered to be because the electrolyte is affected by the action of the residual unreacted acrylic acid in the synthesis of the polymer. Therefore, it is preferable to use a polymer material which has been completely esterified.

Example 27

< Charge/discharge cycle characteristics >

Preparation example 2 the polymer electrolyte material B prepared was impregnated with a mixed solution of propylene carbonate and ethylene carbonate (containing 1mol/L LiBF) used in example 15₄). Subsequently, the film was heated at 85 ℃ to prepare a clear solution. The solution was then applied to both surfaces of a polyolefin separator (trade name TN0028 or TN0029) manufactured by Asahi Kasei Co., Ltd., and a polymer electrolyte thin film having a thickness of about 100 to 150 μm was obtained after pressurization and cooling. A test cell as in example 23 was prepared using the film as an electrolyte. In this case as well, the charge/discharge characteristics were approximately the same as those of example 25.

Example 28

The polymer material A of example 2 was impregnated with a solution containing 1mol/L (C)₂H₅)₄NCF₃SO₃The gamma-butyrolactone is prepared into a polymer electrolyte. Two electrodes were made from a nickel substrate and coated with ruthenium oxide and polyaniline films (10 μm thick). A test cell was prepared using this electrode and the above polymer electrolyte to measure the capacitor characteristics. The quantity of electricity obtained was 0.3F/cm²。

To evaluate performance, the test capacitor was charged at a rate of 10C using a constant current method. As a result of the charge/discharge test, a discharge capacity corresponding to 99% of the charge capacity was obtained, and it was thus understood that charge/discharge could be accomplished at a high rate.

It was found that when a polymer electrolyte was used in combination with a solvent having a high dielectric constant (. epsilon.). about.39 and a high boiling point (202 ℃ C./room temperature), like gamma-butyrolactone and a salt (C)₂H₅)₄NCF₃SO₃And the like, exhibit excellent capacitor characteristics.

Effects of the invention

The present invention provides a novel olefin polymer electrolyte material which has high ionic conductivity (having a lithium ion transport number comparable to PVDF), suppresses precipitation of dendritic lithium, provides favorable electrolyte solution-absorbing quality (retention property), and makes it possible to manufacture a battery characterized by excellent charge/discharge characteristics not only at high temperatures but also at low temperatures.

Claims

1. A gel-type polymer electrolyte, wherein the polymer comprises (A) an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof and (B) a polyoxyalkylene having a hydroxyl group at one end thereof or a derivative thereof, which are bonded together via an ester bond,

wherein the gel-type polymer is impregnated with an electrolyte solution comprising an electrolyte salt and a non-aqueous electrolyte solution,

wherein the composition of the ethylene-unsaturated carboxylic acid copolymer or the derivative thereof (A) comprises 50 to 98 wt% of ethylene, 2 to 50 wt% of an unsaturated carboxylic acid or an anhydride thereof, and 0 to 30 wt% of other monomers, and,

wherein the ester bond is generated by esterification between a carboxylic acid group of the ethylene-unsaturated carboxylic acid copolymer and a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof.

2. A gel-type polymer electrolyte, wherein the polymer comprises (A) an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof and (B) a polyoxyalkylene having a hydroxyl group at one end thereof or a derivative thereof, which are bonded together via an ester bond,

wherein the ester bond is generated by an ester exchange reaction between an alkyl ester of an ethylene-unsaturated carboxylic acid copolymer or an alkyl ester derivative thereof and a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, and,

wherein the composition of the alkyl ester of the ethylene-unsaturated carboxylic acid copolymer or the alkyl ester derivative thereof (A) comprises 50 to 98 wt% of ethylene and 2 to 50 wt% of the alkyl ester of the unsaturated carboxylic acid or the alkyl ester derivative thereof.

3. The gel-type polymer electrolyte according to claim 2, wherein the alkyl ester of the ethylene-unsaturated carboxylic acid copolymer is methyl ester or ethyl ester.

4. A gel-type polymer electrolyte according to claim 1 or 2, wherein the ethylene-unsaturated carboxylic acid copolymer or the derivative (a) thereof is an ionomer whose carboxylic acid is partially neutralized with a monovalent metal or a polyvalent metal, and the degree of neutralization is 0.5 to 60 mol%.

5. The gel-type polymer electrolyte according to claim 1 or 2, wherein the ethylene-unsaturated carboxylic acid copolymer or the derivative thereof (a) has a melt flow rate of 0.1 to 500g/10min at 190 ℃ under a load of 2160 g.

6. A gel-type polymer electrolyte according to claim 1 or 2, wherein the gel-type polymer is in the form of a powder, a film or a sheet.

7. A gel-type polymer electrolyte as claimed in claim 1 or 2, wherein a solvent is present in the electrolyte solution in a proportion of 30 to 95% by weight, based on the sum of the polymer and the electrolyte solution.

8. A gel-type polymer electrolyte as claimed in claim 1 or 2, wherein the electrolyte is present in the electrolyte solution in a proportion of 1 to 30% by weight, based on the sum of said polymer and said electrolyte solution.

9. A gel-type polymer electrolyte according to claim 1 or 2, wherein the electrolyte in the electrolyte solution is a lithium salt.

10. A gel-type polymer electrolyte according to claim 1 or 2, wherein the solvent in the electrolyte solution is a non-aqueous electrolyte solvent.

11. A secondary battery provided with the gel-type polymer electrolyte layer according to claim 1 or 2.

12. The battery of claim 11, wherein the battery is a lithium battery.

13. A capacitor provided with the gel-type polymer electrolyte layer according to claim 1 or 2.

14. A method for producing a gel-type polymer electrolyte, wherein the polymer comprises (A) an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof and (B) a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, which are bonded together via an ester bond,

15. The method of claim 14, wherein the polymer is produced by reacting an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof (A) with a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof (B) in a molar ratio represented by the following formula,

the ratio of B hydroxyl group/A carboxyl group is 0.3 to 2.5,

wherein B hydroxyl is the number of moles of hydroxyl groups of a polyoxyalkylene having a hydroxyl group at one terminal thereof or a derivative thereof, and A carboxyl is the number of moles of carboxylic acid groups of an ethylene-unsaturated carboxylic acid copolymer or a derivative thereof.

16. The process of claim 14, wherein the residual amount of unreacted carboxylic acid groups in the polymer is not more than 30 mol%, based on the carboxylic acid groups of the ethylene-unsaturated carboxylic acid copolymer or derivative thereof (a).

17. The process according to claim 14, wherein the hydroxyl group at the other terminal of the polyoxyalkylene or the derivative thereof (B) has been blocked by etherification, esterification or by reaction with a monoisocyanate.

18. The method according to claim 14, wherein the esterification between the ethylene-unsaturated carboxylic acid copolymer or the derivative thereof (a) and the polyoxyalkylene having a hydroxyl group at one terminal thereof or the derivative thereof (B) is carried out in the presence of an acid catalyst.

19. The method of claim 14, wherein the ester bond formation by transesterification is carried out in the presence of an organometallic catalyst.

20. The method of claim 14, wherein the polymer is partially crosslinked in the presence of at least one crosslinking agent selected from the group consisting of a polyhydric alcohol, a mono (meth) acrylic acid or ester thereof, a polyethylene glycol di (meth) acrylate, an unsaturated higher fatty acid or ester thereof, and a polyethylene glycol diglycidyl ether.

21. The method of claim 20, wherein the crosslinking agent is present in the reaction system in an amount of 0.1 to 30 wt%.