JPH0869816A - Manufacture of polymer solid electrolyte - Google Patents

Abstract

PURPOSE: To provide a manufacturing method of a polymer solid electrolyte having high ion conductivity and mechanical strength. CONSTITUTION: A dispersing medium is removed from mixed dispersing liquid of high polarity polymer particulates and low polarity polymer particulates having crosslinking reactivity, and after a polymer matrix composed of a high polarity high polymer phase and a low polariry polymer phase is formed by coagulating and fusing the mutual polymer particulates, the high polarity high polymer phase is impregnated with an electrolyte. In a polymer matrix forming process, a polymer matrix precursor is soaked in a good solvent of the low polarity polymer phase, and the low polariry polymer phase is heated and crosslinked. Or in a heat treatment process in the high polymer matrix forming process, heat treatment is performed at a temperature less than and not less than a crosslinking reaction temperature of a low polariry polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polymer solid electrolyte which can be used in high energy density batteries such as lithium secondary batteries.

[0002]

2. Description of the Related Art With the development of portable electronic devices, batteries for supplying electric power to these devices have attracted great interest. Among them, the lithium secondary battery has the highest energy density and is being actively developed. For such a lithium secondary battery, a polymer solid electrolyte that has no liquid leakage and is provided with workability such that it can be mounted in a gap between devices is attracting interest. Polymer solid electrolytes are required to have high ionic conductivity and mechanical strength. In order to satisfy such requirements, the present inventors have proposed a polymer solid electrolyte in which a high polarity polymer phase of a polymer matrix composed of a low polarity polymer phase and a high polarity polymer phase is impregnated with an electrolytic solution. (See Japanese Patent Application No. 5-22014). With this electrolyte,
The low-polarity polymer phase maintains the mechanical strength, and the high-polarity polymer phase impregnated with the electrolyte is the ionic conduction path phase. Such a polymer solid electrolyte is prepared by removing a dispersion medium from a mixed dispersion liquid of high-polarity polymer particles and low-polarity polymer particles by heat treatment, aggregating and fusing the polymer particles together to form a high-polarity polymer phase. It can be produced by forming a polymer matrix composed of a low-polarity polymer phase and then immersing the polymer matrix in an electrolytic solution to impregnate the high-polarity polymer phase with the electrolytic solution. In the process of forming the polymer matrix, the polymer particles are gradually aggregated as the dispersion medium is removed, and the polymers near the surface of the polymer particles are fused to each other (this phenomenon is called mutual diffusion). And a continuous low polarity polymer phase and a high polarity polymer phase are formed. Further, in the process of impregnating with the electrolytic solution, the electrolytic solution selectively permeates the highly polar polymer phase and becomes the ionic conduction path phase.

[0003]

In the process of producing such a polymer solid electrolyte, the low-polarity polymer phase is slightly invaded by the electrolytic solution, and the low-polarity polymer phase is plasticized,
There is a problem that the strength of the polymer solid electrolyte is lowered. It was previously proposed that such a decrease in strength can be suppressed by introducing a crosslinked structure into the low polar polymer phase. However, since the introduction of this crosslinked structure was performed by performing a heat treatment under a certain condition when the polymer matrix was formed, the crosslinking reaction proceeds before the low-polarity polymer fine particles are fused and the low-polarity polymer particles are low in polarity. There was a new problem that the fusion between the fine particles was obstructed and the strength was not sufficiently increased. The present invention has been made in view of such a current situation,
The object is to provide a method for producing a polymer solid electrolyte having high ionic conductivity and mechanical strength.

[0004]

The present invention will be summarized. The first invention of the present invention relates to a method for producing a polymer solid electrolyte, which has low cross-linking reactivity with highly polar polymer fine particles. The dispersion medium is removed from the mixed dispersion liquid of polar polymer particles, and the polymer particles are aggregated and fused to form a polymer matrix composed of a high polarity polymer phase and a low polarity polymer phase. In the method for producing a polymer solid electrolyte, which comprises immersing a matrix in an electrolyte solution and impregnating the high polarity polymer phase with the electrolyte solution, the polymer matrix forming step comprises: Agglomeration
A first step of immersing the polymer matrix precursor in a good solvent for the low polarity polymer phase before fusion is completed, and a crosslinking reaction temperature of the low polarity polymer or higher for crosslinking the low polarity polymer phase. It is characterized by including a second step of heating to.
A second invention of the present invention is an invention relating to another method for producing a polymer solid electrolyte, which comprises heat-treating a mixed dispersion liquid of high-polarity polymer particles and low-polarity polymer particles having a crosslinkable reactivity. The dispersion medium is removed by, and the polymer particles are aggregated and fused to form a polymer matrix composed of a high polarity polymer phase and a low polarity polymer phase, and then the polymer matrix is immersed in an electrolytic solution. In the method for producing a polymer solid electrolyte, which comprises impregnating an electrolyte solution in the high polarity polymer phase, a heat treatment step in a polymer matrix forming step is performed so that the low polarity polymer particles are aggregated and fused together. A first heat treatment step of maintaining the cross-linking reaction temperature of the low-polar polymer phase below completion until the low-polar polymer phase is formed;
After that, in order to cross-link the low-polarity polymer phase, it is characterized by comprising a second heat treatment step of raising and maintaining the temperature above the crosslinking reaction temperature of the low-polarity polymer.

In order to achieve the above-mentioned object, the inventors of the present invention have made diligent efforts as to the processing conditions at the time of forming the polymer matrix, and as a result, agglomerated the low-polarity polymer fine particles and fused them by mutual diffusion. In order for the cross-linking reaction of the low-polarity polymer phase to proceed sufficiently, the formation of the polymer matrix must be completed (the polymer fine particle aggregate / fusion material in this state is referred to as the polymer matrix precursor). It was clarified that it is effective to swell and plasticize the polymer phase with a solvent. In addition, the inventors of the present invention have made diligent research efforts on heat treatment conditions at the time of forming a polymer matrix to achieve the above-mentioned object, and as a result, low-polarity polymer fine particles are aggregated and fused by mutual diffusion, and further, It was clarified that it is effective to control the heating conditions during the formation of the polymer matrix in order to promote the crosslinking reaction of the low-polar polymer phase sufficiently.

Hereinafter, the present invention will be described in detail. First, in the process of forming the polymer matrix in the first invention of the present invention, 1) evaporation of the dispersion medium, 2) aggregation of the polymer particles, 3) mutual diffusion of the polymer between the polymer particles and the accompanying polymer It consists of fusion of fine particles. Therefore, in the above step 3), it is most effective to increase the strength of the polymer solid electrolyte by fusing the low-polarity polymer fine particles and cross-linking them after the mutual diffusion of the polymer is sufficiently advanced. Therefore, in order to promote the fusion of the low-polarity polymer fine particles and the mutual diffusion of the polymers in the process of 3), it is effective to swell and plasticize the low-polarity polymer with a good solvent of the low-polarity polymer. Target. Then, after that, it is necessary to heat the cross-linking reaction temperature of the low-polar polymer or higher to allow the cross-linking reaction to proceed.

On the other hand, the process of forming the polymer matrix in the second invention of the present invention is as follows: 1) evaporation of the dispersion medium, 2) aggregation of the polymer particles, 3) fusion between the polymer particles and the accompanying polymer. Consists of mutual diffusion between. In this process,
If the ambient temperature is higher than the crosslinking reaction temperature of the low polarity polymer, the crosslinking reaction proceeds. Therefore, in the process of 3) above, the strength of the polymer solid electrolyte can be most effectively increased by performing the fusion of the low-polarity polymer fine particles and the mutual diffusion of the polymer sufficiently and then performing the crosslinking. Therefore, 1) and 2)
In the step (3), and further in the step (3), until the fusion of the low-polarity polymer fine particles and the mutual diffusion of the polymer are sufficiently advanced, the film forming atmosphere temperature needs to be lower than the temperature at which the crosslinking reaction of the low-polarity polymer occurs. . Then, after that, it is necessary to heat the cross-linking reaction temperature or higher to proceed the cross-linking reaction.

As a concrete method for producing a polymer solid electrolyte, for example, the following method can be mentioned. After mixing the latex containing the high polarity polymer particles and the latex containing the low polarity polymer particles and removing the dispersion medium, the polymer particles will agglomerate and fuse together, resulting in a high polarity polymer phase and a low polarity polymer phase. A polymer matrix sheet having is formed. This polymer matrix sheet is immersed in an electrolytic solution to produce a polymer solid electrolyte. At this time, the electrolytic solution selectively permeates and is absorbed in the highly polar polymer phase. In such a production method, as a component of the low-polarity polymer fine particles, butadiene,
A polymer obtained by polymerizing a diene-based monomer such as isoprene or a polymer obtained by copolymerizing these diene-based monomers with another low-polarity monomer can be preferably used. Such a polymer has a double bond in the molecular chain and is reactive. When this double bond is cleaved by heat or the like, a crosslinked structure can be formed intramolecularly or intermolecularly by an addition reaction, a cyclization reaction or the like. Then, by introducing this cross-linked structure, it is possible to effectively suppress a decrease in mechanical strength due to the electrolytic solution penetrating into the low-polarity polymer phase.

The above-mentioned diene-based copolymer is synthesized from a diene-based monomer such as butadiene and isoprene and a low-polarity monomer. A typical example thereof is a styrene-butadiene copolymer synthesized from butadiene and styrene. Rubber (SBR) is preferably used. Examples of other low-polarity monomers to be copolymerized with are propylene, isobutene, and ethylene. Further, a derivative of styrene such as divinylbenzene or α-methylstyrene can be used. These monomers may be used alone or in combination of two or more.

Examples of other cross-linking bonds connecting between polymer chains or within polymer chains include ester bond, amide bond, urethane bond, ether bond, and ketone bond. For example, in the case of an ester bond, these bonds can be formed by condensing the carboxyl group of the polymer chain and the alcoholic or phenolic hydroxyl group of the polymer chain.
In the case of an amide bond, it can be formed, for example, by reacting a carboxyl group with an amino group. In the case of a urethane bond, it can be formed, for example, by reacting an alcoholic or phenolic hydroxyl group with an isocyanate group. In addition, also in the case of a polymer containing a reactive double bond such as an acrylic group or a methacrylic group, a cross-linking bond can be generated between the molecules or in the molecule by heating. Also, a cross-linking bond can be formed by reacting an epoxy group.

In the second aspect of the present invention, in the process of forming the polymer matrix, the crosslinking reaction proceeds at ambient temperature until fusion of the low-polarity polymer fine particles and mutual diffusion of the polymer sufficiently proceed. Must be maintained below the temperature

As the component of the highly polar polymer phase of the polymer solid electrolyte of the present invention, it is sufficient that it has a polarity capable of impregnating an electrolytic solution. Examples of the monomer that forms the highly polar polymer include acrylonitrile, vinylidene fluoride, vinyl chloride, methyl methacrylate, methyl acrylate, methacrylic acid (and metal salts), acrylic acid (and metal salts), vinyl alcohol, vinylidene chloride, and ethyleneimine. , Methacrylonitrile, vinyl acetate, vinylpyrrolidone or derivatives thereof. Highly polar polymers are synthesized by polymerizing these monomers individually or by copolymerizing a plurality of them. Further, these monomers can be used by being copolymerized with other monomers. For example, butadiene,
Copolymerization with a conjugated diene-based monomer such as isoprene is preferable because the polymer is flexible and has rubber elasticity, and when a polymer electrolyte is prepared, it has good adhesion to an electrode. As a typical one, acrylonitrile-butadiene copolymer rubber (NBR) synthesized from butadiene and acrylonitrile is preferably used.

The electrolytic solution used for the solid polymer electrolyte of the present invention varies depending on its application and is not particularly limited. For example, considering the application to a lithium battery, the metal salts of the components of the electrolytic solution include LiClO ₄ , LiBF ₄ , and LiP.
F ₆ , LiNbF ₆ , LiSCN, Li (CF ₃ S
O ₃ ), Li (C ₆ H ₅ SO ₃ ), LiAsF _{6 and} other lithium salts are used alone or in combination.

The solvent of the electrolyte is propylene carbonate, ethylene carbonate, γ-butyrolactone,
Dimethyl carbonate, dimethyl sulfoxide, acetonitrile, sulfolane, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, diethyl carbonate, methylethyl carbonate, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, methyl acetate, etc. The aprotic solvent and the mixture containing these are preferably used. Incidentally, the concentration of this electrolytic solution is a molar concentration,
It is preferably 0.01 to 5 mol / kg.

The solid polymer electrolyte of the present invention is prepared from a dispersion of fine polymer particles, but a stabilizer may be used for stabilizing the dispersion of fine polymer particles, and a surfactant is preferred for this purpose. Used, for example, include the following: fatty acid metal salt, polyoxyethylene, polyethylene glycol, polyoxypropylene, alkylbenzene sulfonic acid metal salt, alkyl sulfate metal salt, dioctyl sulfosuccinic acid metal salt, polyoxyethylene nonyl. Phenyl ether, polyoxyethylene stearic acid ester, polyoxyethylene sorbitan monolauric acid ester, polyoxyethylene-polyoxypropylene block copolymer, polyether modified silicone oil, etc., alone or in a mixture. Water is preferably used as the dispersion medium of the polymer particle dispersion, but an organic solvent such as alcohols or a mixture with water can also be used.

The method of removing the dispersion liquid of polymer fine particles may be an ordinary method, and may be dried under normal pressure or reduced pressure.

In the first aspect of the present invention, in the process of forming the polymer matrix, the polymer matrix precursor is in the state of the polymer matrix precursor in which the low-polarity polymer fine particles are agglomerated and fusion is progressing. The body is immersed in a good solvent for the low polarity polymer to swell the low polarity polymer phase of the polymer matrix precursor. This can promote mutual diffusion of polymers between the low-polarity polymer particles. At this time, it is preferable to select a solvent that absorbs 10% by weight or more of the low polar polymer weight. The choice of such a solvent depends on the low polarity polymeric component of the polymeric matrix. For example, when the low-polarity polymer component of the polymer matrix is a hydrocarbon-based polymer such as SBR, hydrocarbons such as benzene, toluene, xylene, hexane, heptane, or tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxane. Low polar solvents such as ether are preferable, and they can be used alone or mixed with each other, or mixed with other solvents. The method of swelling the polymer matrix may be an ordinary method, for example,
The polymer matrix precursor may be dipped in a solvent. The soaking temperature must be above the freezing point of the solvent. Further, from the viewpoint of workability, it is desirable that it is lower than the boiling point of the solvent. The immersion time is preferably until the absorption of the solvent reaches 10% by weight or more of the weight of the low polar polymer. After that, the fusion of the low-polarity polymer fine particles may be allowed to proceed while being immersed in the solvent, or may be discharged out of the solvent. The process of fusion progress proceeds by leaving it under such a condition. The temperature of this process is also preferably higher than the freezing point of the solvent and lower than the boiling point. Further, it is desirable to set the temperature above the glass transition temperature of the polymer matrix. After the fusion of the low-polarity polymer fine particles is sufficiently advanced, the cross-linking reaction is allowed to proceed by heating the cross-linking reaction temperature of the low-polarity polymer or higher. The heating temperature varies depending on the crosslinking reaction, but in the case of the reaction of a carboxyl group and an alcoholic hydroxyl group, for example, it is 90
C. or higher is preferable, and 110.degree. C. or higher is more preferable. Regarding the heating time, it is preferable to heat until the elastic modulus of the rubber elastic region increases by 10% or more. The heating method may be an ordinary method, or may be heating or a combination of heating and depressurization. However, in order to produce a uniform polymer matrix film, it is preferable to heat the glass transition temperature of the component of the polymer particles or higher. If necessary, the polymer matrix can be molded into an arbitrary shape by pressing under pressure. When the dispersion medium of the polymer fine particles or the solvent that plasticizes the low-polarity polymer adversely affects the battery to which the solid electrolyte is applied, heat the dispersion medium or the solvent to the boiling point or higher, or combine the heating and the decompression treatment. , The dispersion medium must be removed.

In the second aspect of the present invention, in the process of forming the polymer matrix, the ambient temperature is set to a temperature at which the crosslinking reaction proceeds until fusion of the low-polarity polymer fine particles and mutual diffusion of the polymer sufficiently proceed. However, it is preferable to heat the mixture to proceed the crosslinking reaction. The method of removing the dispersion liquid of polymer fine particles may be an ordinary method, and the atmospheric temperature may be controlled under normal pressure or reduced pressure. The heating method may be an ordinary method, or may be heating or a combination of heating and depressurization. However, in order to produce a uniform polymer matrix film, it is preferable to heat the glass transition temperature of the component of the polymer particles or higher. If necessary, the polymer matrix can be molded into an arbitrary shape by pressing under pressure. When the dispersion medium has an adverse effect on the battery or the like to which the solid electrolyte is applied, it must be heated to a temperature higher than the boiling point of the dispersion medium or combined with heating and decompression treatment to remove the dispersion medium.

The impregnation with the electrolytic solution may be carried out by a usual method, for example, by immersing the polymer matrix film in the electrolytic solution. The amount of electrolyte impregnation can be controlled by the length of immersion time,
It is preferable to impregnate the polymer electrolyte with 10% by weight or more.

[0020]

EXAMPLES The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Example 1 As a polymer fine particle dispersion liquid, a self-crosslinking styrene-butadiene copolymer latex (low polar polymer component) manufactured by Zeon Corporation (SBR latex; trade name: Nipol2570)
X5) and acrylonitrile-butadiene copolymer (high-polarity polymer component) latex (NBR latex; brand name: Nipol 1571) manufactured by Nippon Zeon Co., Ltd. in a solid content weight ratio of 5:
After mixing in 5, the mixture was cast on a glass substrate and then vacuum dried at room temperature for 8 hours to obtain a polymer matrix precursor film. Next, this polymer matrix precursor film was immersed in a mixed solvent of equal volume of benzene / hexane for 2 hours. Next, in order to cause the crosslinking reaction of the SBR molecule, 13
Heated at 0 ° C. for 5 hours in a vacuum atmosphere. At this time, the degree of vacuum was 0.1 Torr. The polymer matrix film electrolyte prepared by dissolving LiClO ₄ in propylene carbonate and 2-methyltetrahydrofuran equal volume mixed solvent (LiClO ₄ concentration: 0.1 mol / liter) and soaked for 1 hour, the resulting solid polymer electrolyte It was This polymer electrolyte was punched into a dumbbell-shaped test piece [JIS2 (1/3)], and the tensile strength was measured with a tensile tester manufactured by Instron (pulling speed = 20 mm / min). Tensile strength is 19kg
f / cm ² . Moreover, the ionic conductivity is 1 × 10 ^−3.
It was S / cm.

Comparative Example 1 A polymer matrix film was obtained by a method except that the step of immersing the polymer matrix precursor film in the solvent was omitted in the process of forming the polymer matrix in the process of preparing the polymer solid electrolyte of Example 1. Thus prepared polymeric matrix film was dissolved LiClO ₄ in propylene carbonate and 2-methyltetrahydrofuran equal volume mixed solvent electrolyte (LiClO ₄ concentration: 0.1 mol / liter)
It was immersed in the solution for 1 hour to obtain a polymer solid electrolyte. Example 1
When the tensile strength was measured in the same manner as, it was 11 kgf / cm.
^{Was 2} .

Example 2 As a polymer fine particle dispersion liquid, a self-crosslinking styrene-butadiene copolymer (low polarity polymer component) latex (SBR latex; trade name: Nipol2570) manufactured by Nippon Zeon Co., Ltd.
X5) and acrylonitrile-butadiene copolymer (high-polarity polymer component) latex (NBR latex; brand name: Nipol 1571) manufactured by Nippon Zeon Co., Ltd. in a solid content weight ratio of 5:
After mixing in 5, after casting on a glass substrate and drying at atmospheric pressure and 20 ° C. for 5 hours, the crosslinking reaction does not proceed 2
It was vacuum dried at 0 ° C. for 8 hours. Then, in order to cause a crosslinking reaction of the SBR molecule, it was heated in a vacuum atmosphere at 130 ° C. for 5 hours. At this time, the degree of vacuum was 0.1 Torr. The polymer matrix film electrolyte prepared by dissolving LiClO ₄ in propylene carbonate and 2-methyltetrahydrofuran equal volume mixed solvent (LiClO ₄ concentration: 0.1 m
(ol / liter) for 1 hour to obtain a polymer solid electrolyte. A dumbbell-shaped test piece [JIS2
(1/3)], and the tensile strength was measured by a tensile tester manufactured by Instron (tensile speed = 20 mm / mi
n). The tensile strength was 13 kgf / cm ² . The ionic conductivity of this film was also on the order of 1 × 10 ⁻³ S / cm.

Comparative Example 2 In the process of forming the polymer matrix in the process of producing the polymer solid electrolyte of Example 2, the product was dried at atmospheric pressure and 100 ° C. for 5 hours and then vacuum dried at 130 ° C. for 5 hours to obtain a film having a thickness of 200 μm. A polymer matrix film was obtained. Thus prepared polymeric matrix film electrolyte prepared by dissolving LiClO ₄ in propylene carbonate and 2-methyltetrahydrofuran equal volume mixed solvent (LiClO ₄ concentration: 0.1 m
(ol / liter) for 1 hour to obtain a polymer solid electrolyte. When the tensile strength was measured in the same manner as in Example 2, it was 7
It was kgf / cm ² .

[0025]

As is apparent from the above description, the present invention has an advantage that a polymer solid electrolyte having high ionic conductivity and mechanical strength can be provided.

Claims (2)

[Claims] 1. A dispersion medium is removed from a mixed dispersion liquid of high-polarity polymer particles and low-polarity polymer particles having a cross-linking reactivity, and the polymer particles are aggregated and fused to form a high-polarity polymer phase. A method for producing a polymer solid electrolyte, comprising forming a polymer matrix composed of a low-polarity polymer phase, and immersing the polymer matrix in an electrolyte solution to impregnate the high-polarity polymer phase with the electrolyte solution. In the step of forming the polymer matrix, a step of immersing the polymer matrix precursor in a good solvent for the low polarity polymer phase before the aggregation and fusion of the low polarity polymer particles are completed. A method for producing a polymer solid electrolyte, comprising a second step of heating the low-polar polymer phase to a temperature equal to or higher than a crosslinking reaction temperature of the low-polar polymer in order to cross-link the low-polar polymer phase. 2. A dispersion medium is removed from a mixed dispersion liquid of high-polarity polymer particles and low-polarity polymer particles having a cross-linking reactivity by heat treatment, and the polymer particles are agglomerated and fused to form a high-polarity polymer. A polymer solid electrolyte comprising: forming a polymer matrix composed of a molecular phase and a low-polarity polymer phase, and then immersing the polymer matrix in an electrolyte solution to impregnate the high-polarity polymer phase with the electrolyte solution. In the manufacturing method of step 1, the heat treatment step in the polymer matrix formation process is performed until the low-polarity polymer phase is cross-linked at a crosslinking reaction temperature until the aggregation and fusion of the low-polarity polymer particles are completed and the low-polarity polymer phase is formed. And a second heat treatment step of keeping the temperature higher than the cross-linking reaction temperature of the low-polar polymer to cross-link the low-polar polymer phase. And high Method for producing child solid electrolyte.