JP2012018909A - Electrolyte and electrolyte film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte film exhibiting ionic conductivity equivalent to that of a gel electrolyte and having high transport number of a lithium ion, and also to provide an electrolyte suitable for manufacturing the electrolyte film.SOLUTION: An electrolyte is characterized by being formed by blending (A) a polyanion type lithium salt, (C) a boron compound and (D) an organic solvent, and an electrolyte film is characterized by being obtained by using such blended electrolyte.

Description

  The present invention relates to an electrolyte suitable for application to a lithium ion secondary battery and an electrolyte membrane obtained using the electrolyte.

  Lithium ion secondary batteries are characterized by high energy density and electromotive force compared to lead-acid batteries and nickel metal hydride batteries, so they are widely used as power sources for mobile phones and laptop computers that require small size and light weight. ing. Currently, in many of the lithium ion secondary batteries used in these devices, a nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent is used as the electrolytic solution.

However, secondary batteries using non-aqueous electrolytes have the potential of reducing charge / discharge cycle life characteristics due to leakage of organic solvents and the risk of internal short circuits due to the deposition of dendrites growing from the negative electrode to the positive electrode. In the worst case, it may cause a fire accident. In recent years, lithium-ion secondary batteries are expected to be applied as large-scale stationary power sources for power storage and power sources for electric vehicles, and further higher energy density and improved safety are strongly desired.
Therefore, a system utilizing a solid or gel electrolyte is devised, and research is being conducted rapidly. By using these electrolytes, the volatile diffusion and leakage of the electrolyte can be prevented, so that the reliability and safety of the battery can be improved. Furthermore, since it is easy to thin and laminate the electrolyte itself, it is expected to improve processability and simplify the package.

A solid electrolyte is an ionic conductor in which various polymer compounds are used as a matrix polymer and a lithium salt is uniformly dissolved therein, and includes, for example, alkylene ethers such as polyethylene oxide and polypropylene oxide, polyesters, and polyamines. , Polyphosphazene and polysiloxane materials are being actively studied.
However, the electrolyte membranes using these solid electrolytes have an ionic conductivity as small as about 10 ⁻⁵ S / cm near room temperature, and electrolyte membranes using a non-aqueous electrolyte (the ionic conductivity at room temperature is 10 ⁻³ S / cm). There is a difference of two orders of magnitude compared to (cm).

Therefore, in recent years, in order to improve the ionic conductivity of an electrolyte membrane using a solid electrolyte, practical studies of gel electrolytes in which a non-aqueous electrolyte is held in a matrix polymer have been promoted.
For example, it is disclosed that an electrolyte membrane using an electrolyte in which polyvinylidene fluoride is used as a matrix polymer and a nonaqueous electrolytic solution is held therein exhibits an ionic conductivity of 1 × 10 ⁻³ S / cm or more even near room temperature. (See Patent Document 1).
In addition, an electrolyte using an alkylene ether polymer compound having a high affinity for a non-aqueous electrolyte as a matrix polymer has been proposed, and its practical application has been studied (see Patent Document 2).
Furthermore, an electrolyte using a polymer compound obtained by three-dimensionally crosslinking a polyfunctional acrylate as a matrix polymer has been proposed, and an electrolyte membrane using the electrolyte exhibits an ionic conductivity of 10 ⁻³ S / cm or more even near room temperature. Is disclosed (see Patent Documents 3 and 4).

However, electrolyte membranes using gel electrolytes holding these non-aqueous electrolytes exhibit ionic conductivity of 10 ⁻³ S / cm or more near room temperature, but low molecular lithium salts such as LiClO ₄ and LiPF ₆ are used. Therefore, the dissociated lithium ions are strongly solvated, and as a result, the transport number of lithium ions (ratio of ionic conductivity by lithium ions in the entire ionic conductivity) is 0.3 for non-aqueous electrolytes. In the case of a solid electrolyte, there is a problem that it becomes 0.1 or less. When an electrolyte membrane using such an electrolyte is applied to a lithium ion secondary battery, not only lithium ions but also their counter anions move during charging and discharging. Therefore, particularly in an environment where charging and discharging with a large current such as an electric vehicle is required, there is a problem that the concentration polarization of anions is caused on the electrode, and the battery performance deteriorates due to the increase in resistance. .
Under such circumstances, in order to improve the transport number of lithium ions, a polymer composite in which only cations move in the electrolyte, that is, a method of applying a single ion conductor to the electrolyte membrane of a lithium ion secondary battery has been proposed. (See Non-Patent Documents 1 to 4).

JP-T-08-507407 JP-A-8-298126 US Pat. No. 5,603,982 Japanese Patent No. 4156495

M.M. Watanabe, Y. et al. Suzuki, A .; Nishimoto, Electrochimica Acta, vol. 45, p. 1187 (2000). M.M. Watanabe, H.M. Tokuda, Electrochimica Acta, vol. 46, p. 1487 (2001). Y. Tominaga, H .; Ohno, Electrochimica Acta, vol. 45, p. 3081 (2000). D. Benrabah, S.M. Sylla, F.M. Allion, JY. Sanchez, M.M. Armand, Electrochimica Acta, vol. 40, p. 2259 (1995).

However, the electrolyte membrane to which the above single ion conductor is applied has a problem that it is impossible to achieve both high ionic conductivity equivalent to the gel electrolyte and high lithium ion transport number.
The present invention has been made in view of the above circumstances, and provides an electrolyte membrane exhibiting an ionic conductivity equivalent to that of a gel electrolyte and excellent in lithium ion transport number, and an electrolyte suitable for the production of the electrolyte membrane. This is the issue.

To solve the above problem,
The present invention provides an electrolyte comprising (A) a polyanionic lithium salt, (C) a boron compound, and (D) an organic solvent.
The electrolyte of the present invention preferably further comprises (B) a matrix polymer.
In the electrolyte of the present invention, the (C) boron compound is selected from the group consisting of a boron halide, a boron halide alkyl ether complex, a boron halide alcohol complex, and a boron halide salt. It is preferable that it is 1 or more types.
In the electrolyte of the present invention, the boron compound (C) is boron trifluoride, boron trifluoride dimethyl ether complex, boron trifluoride diethyl ether complex, boron trifluoride di n-butyl ether complex, boron trifluoride di tert. -Butyl ether complex, boron trifluoride tert-butyl methyl ether complex, boron trifluoride tetrahydrofuran complex, boron trifluoride methanol complex, boron trifluoride propanol complex, and boron trifluoride phenol complex, and boron trifluoride piperidinium It is preferable that it is 1 or more types selected from the group which consists of.
In the electrolyte of the present invention, the (A) polyanion type lithium salt is preferably at least one selected from the group consisting of a polycarboxylic acid lithium salt and a polysulfonic acid lithium salt.
In the electrolyte of the present invention, the polyanionic lithium salt (A) is poly (2-acrylamido-2-methyl-1-propanesulfonic acid lithium), poly (lithium styrenesulfonic acid), poly (lithium vinylsulfonic acid), Poly (lithium perfluorosulfonate), poly (lithium (meth) acrylate), lithium polymaleate, lithium polyfumarate, lithium polymuconate, lithium polysorbate, poly (acrylonitrile-butadiene-lithium acrylate) copolymer, poly One or more selected from the group consisting of (tert-butyl acrylate-ethyl acrylate-lithium methacrylate) copolymer, poly (ethylene-lithium acrylate) copolymer and poly (methyl methacrylate-lithium methacrylate) copolymer. Is It is preferred.
In the electrolyte of the present invention, the (B) matrix polymer is preferably at least one selected from the group consisting of polyether polymers and fluorine polymers.
In the electrolyte of the present invention, the (B) matrix polymer is polyethylene oxide, polypropylene oxide, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-hexafluoroacetone copolymer One or more selected from the group consisting of a coalescence and polytetrafluoroethylene is preferred.
In the electrolyte of the present invention, the (D) organic solvent is preferably one or more selected from the group consisting of a carbonate compound, a lactone compound, and a sulfone compound.
In the electrolyte of the present invention, the (D) organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, and sulfolane. Is preferred.
The electrolyte of the present invention preferably further comprises (E) a lithium salt not corresponding to the (A) polyanionic lithium salt.
The present invention also provides an electrolyte membrane obtained by using the electrolyte of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the electrolyte membrane which shows the ion conductivity equivalent to a gel electrolyte, and is excellent also in the transport number of lithium ion, and the electrolyte suitable for manufacture of this electrolyte membrane can be provided.

It is the graph which plotted the ionic conductivity ((sigma)) of the electrolyte membrane in Examples 1-2 and Comparative Examples 1-3. It is the graph which plotted the ionic conductivity ((sigma)) of the electrolyte membrane in Examples 3-4. It is a graph which shows SN ratio ((eta)) and sensitivity (S) of the electrolyte membrane in Experimental examples 1-18. It is a factor effect figure regarding the SN ratio ((eta)) of the electrolyte membrane in Experimental examples 1-18. It is a factor effect figure regarding the SN ratio ((eta)) of the electrolyte membrane in Experimental examples 1-18. It is a factor effect figure regarding the sensitivity (S) of the electrolyte membrane in Experimental Examples 1-18. It is a factor effect figure regarding the sensitivity (S) of the electrolyte membrane in Experimental Examples 1-18.

<Electrolyte>
The electrolyte of the present invention comprises (A) a polyanionic lithium salt, (C) a boron compound, and (D) an organic solvent.
The electrolyte of the present invention realizes excellent ionic conductivity and lithium ion transport number by using (C) a boron compound in combination. In the present invention, “transport number of lithium ions” refers to “ratio of ion conductivity due to lithium ions in the entire ion conductivity”. For example, in an electrolyte membrane in a lithium ion secondary battery, the closer to 1 preferable.

[(A) Polyanionic lithium salt]
(A) The polyanion-type lithium salt is not particularly limited, and any poly-anion-type lithium salt is suitable as long as it includes a plurality of anion parts and a lithium cation (lithium ion, Li ⁺ ) that forms a salt with the anion part. Can be used for Preferred examples include those containing a plurality of sites that are lithium salts of acids, and examples of the acids include carboxylic acids and sulfonic acids.
That is, (A) As a preferable thing of polyanion type lithium salt, polycarboxylic acid lithium salt and polysulfonic acid lithium salt can be illustrated.

  Preferred examples of the lithium polycarboxylic acid salt include poly ((meth) lithium acrylate), lithium polymaleate, lithium polyfumarate, lithium polymuconate, lithium polysorbate, and poly (acrylonitrile-butadiene-lithium acrylate) copolymer. Examples thereof include a polymer, a poly (tert-butyl acrylate-ethyl acrylate-lithium methacrylate) copolymer, a poly (ethylene-lithium acrylate) copolymer, and a poly (methyl methacrylate-lithium methacrylate) copolymer. In the present specification, “(meth) acrylic acid” refers to both “acrylic acid” and “methacrylic acid”.

  Preferred examples of the lithium polysulfonate include poly (2-acrylamido-2-methyl-1-propanesulfonate), poly (lithium styrenesulfonate), poly (lithium vinylsulfonate), and poly (perfluorosulfone). Lithium acid) can be exemplified. Examples of poly (lithium perfluorosulfonate) include poly (lithium perfluoroalkene sulfonate) and those represented by the following general formula (1).

（式中、ｍ及びｎはそれぞれ独立して１以上の整数である。）

(In the formula, m and n are each independently an integer of 1 or more.)

(A) A polyanion type lithium salt may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
In the present invention, (A) the polyanionic lithium salt is preferably at least one selected from the group consisting of a lithium polycarboxylic acid salt and a lithium polysulfonic acid salt, and poly (2-acrylamido-2-methyl-1- It may be at least one selected from the group consisting of lithium propane sulfonate), poly (lithium styrene sulfonate), poly (lithium vinyl sulfonate), poly (lithium perfluorosulfonate) and poly (lithium acrylate). More preferred.

  The blending amount of the (A) polyanion type lithium salt is not particularly limited, and may be appropriately adjusted according to the type. Usually, the molar concentration of lithium atoms in the (A) polyanion type lithium salt ([(A) The blending amount so that the number of moles of lithium atoms in the polyanionic lithium salt] / [(D) volume of organic solvent] is preferably 0.1 to 10 mol / L, more preferably 0.2 to 5 mol / L. By setting the amount within such a range, the electrolyte membrane exhibits better ionic conductivity regardless of temperature.

[(C) Boron compound]
(C) a boron compound is not particularly limited, specifically as preferred, boron halide boron trifluoride; boron trifluoride dimethyl ether complex _{(BF 3 O (CH 3)} 2), boron trifluoride Diethyl ether complex (BF ₃ O (C ₂ H ₅ ) ₂ ), boron trifluoride di n-butyl ether complex (BF ₃ O (C ₄ H ₉ ) ₂ ), boron trifluoride di tert-butyl ether complex (BF ₃ O ((CH ₃ ) ₃ C) ₂ ), boron trifluoride tert-butyl methyl ether complex (BF ₃ O ((CH ₃ ) ₃ C) (CH ₃ )), boron trifluoride tetrahydrofuran complex (BF ₃ OC ₄ boron halide alkyl ether complex of H ₈₎ or the like; boron trifluoride methanol complex _{(BF 3} HOCH 3), boron trifluoride propanol Complex _{(BF 3 HOC 3 H 7)} , boron halide alcohol complexes such as boron trifluoride phenol complex _{(BF 3 HOC 6 H 5)} ; boron halide salts trifluoride piperidinium like; 2,4,6 2,4,6-trialkoxyboroxine such as trimethoxyboroxine; trimethyl borate, triethyl borate, tri-n-propyl borate, tri-n-butyl borate, tri-n-pentyl borate, boron Trialkyl borate such as tri-n-hexyl acid, tri-n-heptyl borate, tri-n-octyl borate, triisopropyl borate, trioctadecyl borate; triaryl borate such as triphenyl borate; Examples thereof include tris (trialkylsilyl) borate such as tris (trimethylsilyl) borate.
(C) The boron compound has a function of accelerating dissociation of lithium ions from the anion portion in the polyanion type lithium salt (A) in the electrolyte membrane and improving the ionic conductivity of the electrolyte membrane and the transport number of lithium ions. Presumed to be.

(C) A boron compound may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
In the present invention, the boron compound (C) is preferably at least one selected from the group consisting of boron halides, boron halide alkyl ether complexes, boron halide alcohol complexes, and boron halide salts. More preferably, it is at least one selected from the group consisting of boron fluoride, boron trifluoride alkyl ether complex, boron trifluoride alcohol complex, and boron trifluoride salt, boron trifluoride dimethyl ether complex, trifluoride Boron diethyl ether complex, boron trifluoride di n-butyl ether complex, boron trifluoride di tert-butyl ether complex, boron trifluoride tert-butyl methyl ether complex, boron trifluoride tetrahydrofuran complex, boron trifluoride methanol complex, Boron trifluoride propanol complex It is particularly preferable boron trifluoride phenol complex, and at least one selected from the group consisting of boron trifluoride piperidinium.

  (C) The compounding quantity of a boron compound is not specifically limited, What is necessary is just to adjust suitably according to the kind of (C) boron compound and (A) polyanion type lithium salt. Usually, it is preferable that the molar ratio of [(C) Boron compound content (number of moles)] / [(A) Number of moles of lithium atoms in polyanionic lithium salt] is 0.05 or more. More preferably, it is 08 or more. By setting it as such a range, an electrolyte membrane will show the more excellent ionic conductivity irrespective of temperature. The upper limit of the molar ratio is not particularly limited as long as the effect of the present invention is not hindered, but is preferably 3, and more preferably 2.5. (C) Although the compounding quantity of a boron compound may be larger than the said upper limit, sufficient effect is acquired even if it is a small quantity like the said range.

[(D) Organic solvent]
(D) Although the organic solvent is not particularly limited, specific examples of preferable organic solvents include carbonate compounds such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; lactone compounds such as γ-butyrolactone. A sulfone compound such as sulfolane.
(D) An organic solvent may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
In the present invention, (D) the organic solvent is preferably at least one selected from the group consisting of a carbonate ester compound, a lactone compound and a sulfone compound.

  (D) Although the compounding quantity of an organic solvent is not specifically limited, What is necessary is just to adjust suitably in the range which does not impair the retainability of the electrolyte solution in an electrolyte membrane, or film | membrane intensity | strength. Usually, it is preferable that the mass ratio of [(D) organic solvent blending amount (mass)] / [total amount of blending components (mass)]) is 0.25 to 0.9. By setting it as the lower limit value or more, the electrolyte membrane exhibits better ionic conductivity regardless of the temperature. Moreover, the film | membrane intensity | strength of an electrolyte membrane improves further by setting it as below an upper limit.

[(B) Matrix polymer]
The electrolyte of the present invention preferably comprises (B) a matrix polymer in addition to (A) polyanionic lithium salt, (C) boron compound and (D) organic solvent.
(B) A matrix polymer is not specifically limited, A well-known thing can be used suitably in the solid electrolyte field.
(B) Specific examples of preferred matrix polymers include polyether polymers such as polyethylene oxide and polypropylene oxide; polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polyvinylidene fluoride. Fluoropolymers such as hexafluoroacetone copolymer and polytetrafluoroethylene; polyacrylic polymers such as poly (meth) acrylate methyl, poly (meth) ethyl acrylate, polyacrylamide, and polyacrylate containing ethylene oxide units; Examples include polyacrylonitrile; polyphosphazene; polysiloxane.

(B) A matrix polymer may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
In the present invention, the (B) matrix polymer is preferably at least one selected from the group consisting of polyether polymers, fluorine polymers, polyacrylic polymers, polyacrylonitrile, polyphosphazenes, and polysiloxanes. , Polypropylene oxide, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-6-propylene fluoride copolymer, polyvinylidene fluoride-hexafluoroacetone copolymer, polytetrafluoroethylene, polyacrylonitrile, polyphosphazene and polysiloxane More preferably, it is one or more selected from the group consisting of:

  The blending amount of the (B) matrix polymer is not particularly limited, and may be appropriately adjusted according to the type, but the blending amount of the (B) matrix polymer in the total amount of the blending components is 2 to 50% by mass. Is preferred. By setting the lower limit value or more, the film strength can be further improved.

  The ratio of the total blending amount of (A) polyanion type lithium salt and (B) matrix polymer to the blending amount of (D) organic solvent ([(A) blending amount of polyanion type lithium salt + (B) matrix polymer Compounding amount]: [(D) Compounding amount of organic solvent] (mass ratio)) is preferably 70:30 to 8:92, and more preferably 60:40 to 10:90. By setting it as such a range, an electrolyte membrane shows the more outstanding ion conductivity irrespective of temperature, and the film | membrane intensity | strength of an electrolyte membrane improves further.

[(E) lithium salt]
The electrolyte of the present invention preferably further comprises (A) a lithium salt that does not fall under the polyanion type lithium salt. By doing in this way, ion conductivity can be further improved in the electrolyte membrane without reducing the transport number of lithium ions.

(E) Lithium salt will not be specifically limited if it does not correspond to (A) polyanion type lithium salt, Any of organic lithium salt and inorganic lithium salt may be sufficient. Specifically, preferable examples include bis (trifluoromethylsulfonyl) imido lithium (LiN (SO ₂ CF ₃ ) ₂ ), lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), tetrafluoro lithium borohydride (LiBF _4), trifluoromethane sulfonic lithium _(LiCF 3 _SO 3), lithium hexafluoro antimonate (LiSbF _6), hexafluoroarsenate arsenate periodate lithium (LiAsF _6), lithium tetraphenylborate ( LiB (C ₆ H ₅ ) ₄ ) can be exemplified.
(E) A lithium salt may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  (E) The compounding quantity of lithium salt is not specifically limited, What is necessary is just to adjust suitably according to the kind etc. Usually, the molar ratio of [(E) mol number of lithium atoms in lithium salt] / [(A) mol number of lithium atoms in polyanion type lithium salt] is preferably 1/20 to 1/1. The blending amount is preferably adjusted to be 1/10 to 1/2. By setting it as the lower limit value or more, the electrolyte membrane exhibits better ionic conductivity regardless of the temperature. Moreover, by setting it as an upper limit or less, an electrolyte membrane will show the more outstanding ionic conductivity, without causing the fall of the transport number of lithium ion.

[Other ingredients]
In addition to (A) polyanionic lithium salt, (B) matrix polymer, (C) boron compound, (D) organic solvent, and (E) lithium salt, the electrolyte of the present invention further includes other components not corresponding to these. A blended product may be used. Examples of the other components include (F) inorganic filler and (G) plasticizer.

((F) inorganic filler)
(F) The inorganic filler is not particularly limited, but specific examples of preferable aluminum filler include aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), silicon dioxide (SiO ₂ ), barium titanate, and mesoporous silica. it can.
(F) An inorganic filler may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  (F) The compounding quantity of an inorganic filler is not specifically limited, What is necessary is just to adjust suitably according to the kind etc. Usually, it is preferable that the mass ratio of [(F) blending amount of inorganic filler (mass)] / [total amount of blending components (mass)] is 0.02 to 0.3. By setting it as such a range, an electrolyte membrane will show the more excellent ionic conductivity irrespective of temperature. (F) Although the compounding quantity of an inorganic filler may be larger than the said upper limit, sufficient effect is acquired even if it is a small quantity like the said range.

((G) Plasticizer)
(G) Although the plasticizer is not particularly limited, specific examples of preferable plasticizers include oligoethylene oxides such as diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and polyethylene glycol dimethyl ether.
(G) A plasticizer may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
(G) The compounding quantity of a plasticizer is not specifically limited, What is necessary is just to adjust suitably according to the kind etc. For example, it can be set as the compounding quantity of about 1-20 mass% with respect to the total amount of a compounding component.

[Method for producing electrolyte]
The electrolyte of the present invention can be produced by blending (A) a polyanionic lithium salt, (C) a boron compound and (D) an organic solvent, and if necessary, other components.
At the time of blending each component, it is preferable to add these components and thoroughly mix them by various means. Moreover, when manufacturing the electrolyte membrane of this invention mentioned later later, the organic solvent used at this time may further be added, and you may make it mix the obtained composition collectively.
Each component may be mixed while sequentially adding them, or may be mixed after all the components have been added, as long as the blended components can be uniformly dissolved or dispersed.
The mixing method of each component is the same as the mixing method at the time of manufacturing the electrolyte membrane described later.

  In the case of a solid electrolyte using a conventional polyanion type lithium salt or the like, the obtained electrolyte membrane has insufficient ion conductivity even though the transport number of lithium ions is good. In the case of a gel electrolyte in which a non-aqueous electrolyte solution is held in a matrix polymer, the obtained electrolyte membrane has an insufficient lithium ion transport number even though the ion conductivity is good. On the other hand, the electrolyte of the present invention is suitable for producing an electrolyte membrane excellent in both ionic conductivity and lithium ion transport number, particularly by blending the (C) boron compound. .

<Electrolyte membrane and manufacturing method thereof>
The electrolyte membrane of the present invention is obtained by using the electrolyte of the present invention.
The electrolyte membrane of the present invention can be produced, for example, by adding and mixing an organic solvent to the electrolyte of the present invention, pouring the resulting composition into a mold or container, drying it, and molding it into a desired shape.

  The organic solvent to be added to the electrolyte is not particularly limited. For example, those capable of sufficiently dissolving or dispersing any of the blending components are preferable. Specifically, a nitrile solvent such as acetonitrile; an ether system such as tetrahydrofuran A solvent can be illustrated. These organic solvents are suitable for, for example, (B) dissolving the matrix polymer or (A) dispersing the polyanionic lithium salt.

  The mixing method after the addition of the organic solvent is not particularly limited, and for example, a known method using a stirrer, a stirring blade, a ball mill, a stirrer, an ultrasonic disperser, an ultrasonic homogenizer, a self-revolving mixer, etc. may be applied. . What is necessary is just to set mixing conditions suitably according to various methods, and what is necessary is just to mix for a predetermined time under room temperature or heating conditions, For example, the method of mixing for about 1 to 72 hours at 15-70 degreeC is mentioned. At the time of mixing, it is preferable to sufficiently disperse (A) the polyanionic lithium salt, and when (B) the matrix polymer is blended, it is preferable to completely dissolve it.

  As the mold or the container, any mold that can mold the electrolyte membrane into a desired shape can be used, and for example, a polytetrafluoroethylene is preferable.

  The method for drying the composition is not particularly limited, and for example, a known method using a dry box, a vacuum desiccator, a vacuum dryer or the like may be applied.

The electrolyte membrane of the present invention exhibits a high ion conductivity of 1.5 × 10 ⁻⁴ S / cm or more at room temperature, which is required when applied to, for example, a lithium ion secondary battery. Further, by adjusting the composition, a high ionic conductivity of 1.0 × 10 ⁻³ S / cm or more is exhibited.
Furthermore, the electrolyte membrane of the present invention exhibits an extremely excellent lithium ion transport number, for example, preferably at 25 ° C. of preferably 0.3 or more, more preferably 0.5 or more.

  As described above, the electrolyte membrane of the present invention exhibits an equivalent ionic conductivity with respect to the gel electrolyte, and is excellent in the transport number of lithium ions. Therefore, for example, when applied to a lithium ion secondary battery, the movement of lithium ions during charge / discharge is promoted, while the movement of the counter anion is suppressed, so even if charging / discharging with a large current is performed, Concentration polarization of anions on the electrode is suppressed, and a decrease in battery performance due to an increase in resistance is suppressed. In addition, the electrolyte membrane of the present invention is generally in a gel form, and the deterioration of charge / discharge cycle life characteristics and internal short circuit due to volatile diffusion and leakage of the electrolyte are suppressed, so that high energy density is possible and safety is ensured. High nature. Further, since the electrolyte membrane can be easily made thin and laminated, processability can be improved and the package can be simplified.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples.

(1) Chemical substances used The chemical substances used in this example are shown below.
(A) Raw material of polyanion type lithium salt Poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (hereinafter abbreviated as PAMPS) (15% by mass aqueous solution, mass average molecular weight 2000000, manufactured by Aldrich)
Polyacrylic acid (hereinafter abbreviated as PAc) (mass average molecular weight 25000, manufactured by Wako Pure Chemical Industries, Ltd.)
Lithium hydroxide monohydrate (LiOH.H ₂ O) (Aldrich)
(B) Matrix polymer Polyethylene oxide (hereinafter abbreviated as PEO) (mass average molecular weight 6000000, manufactured by Aldrich)
Polyvinylidene fluoride-6-fluoropropylene copolymer (hereinafter abbreviated as PVdF-HFP, manufactured by Aldrich)
-(C) Boron compound Boron trifluoride diethyl ether complex (BF ₃ O (C ₂ H ₅ ) ₂ ) (manufactured by Aldrich)
Boron trifluoride di tert-butyl ether complex (BF ₃ O ((CH ₃ ) ₃ C) ₂ ) (Aldrich)
Boron trifluoride piperidinium (BF ₃ C ₅ H ₁₀ NH) (Aldrich)
(D) Organic solvent Ethylene carbonate (hereinafter abbreviated as EC) (Aldrich)
Propylene carbonate (hereinafter abbreviated as PC) (Aldrich)
γ-butyrolactone (hereinafter abbreviated as GBL) (manufactured by Aldrich)
Sulfolane (hereinafter abbreviated as SL) (manufactured by Aldrich)
(E) lithium salt bis (trifluoromethylsulfonyl) imido lithium (LiN (SO ₂ CF ₃ ) ₂ ) (manufactured by Kishida Chemical Co., Ltd.)
(F) Inorganic filler Aluminum oxide (Al ₂ O ₃ ) (particle diameter: 40-47 nm, manufactured by Aldrich)
・ (G) Plasticizer Tetraethylene glycol dimethyl ether (hereinafter abbreviated as TEGME) (manufactured by Aldrich)
Polyethylene glycol dimethyl ether (mass average molecular weight 2000, hereinafter abbreviated as PEG) (manufactured by Aldrich)
・ Other organic solvents acetonitrile (dehydrated, manufactured by Aldrich)
Tetrahydrofuran (dehydrated, manufactured by Aldrich)

(2) (A) Preparation of polyanionic lithium salt (2-1) Preparation of poly (lithium acrylate) (hereinafter abbreviated as PAc-Li) PAc (10.0 g, 138.8 mmol) was added to a round bottom flask. Weighed and dissolved in 100 mL of distilled water. A solution obtained by dissolving LiOH.H ₂ O (5.99 g, 139.5 mmol) in 60 ml of distilled water was slowly added dropwise thereto. After stirring for 24 hours at room temperature, the solution was concentrated using a rotary evaporator. The concentrated solution was slowly added dropwise to 500 mL of methanol, and the precipitated solid was washed again with methanol to obtain white PAc-Li.

(2-2) Preparation of poly (2-acrylamido-2-methyl-1-propanesulfonic acid lithium) (PAMPS-Li) A 15% by mass aqueous solution of PAMPS (33.3 g, 24.1 mmol) was weighed into a round bottom flask. A solution of LiOH.H ₂ O (1.05 g, 24.6 mmol) dissolved in 60 ml of distilled water was slowly added dropwise thereto. After stirring for 24 hours at room temperature, the solution was concentrated using a rotary evaporator. The concentrated solution was slowly added dropwise to 400 mL of 2-propanol, and the precipitated solid was washed again with 2-propanol to obtain pale yellow PAMPS-Li.

(3) Production of electrolyte membrane Production of electrolyte membranes in the following examples and comparative examples was all performed in a dry box or a vacuum desiccator.

[Example 1]
_<PEO, Preparation of _{PAc-Li, BF 3 O (} C 2 H 5) 2, LiN (SO 2 CF 3) gel electrolyte film containing _2>
PEO (0.50 g), PAc-Li (0.018 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.032 g), LiN (SO ₂ CF ₃ ) ₂ (0.036 g), a mixed solvent of EC and GBL as an organic solvent (EC: GBL = 30: 70 (volume ratio)) (0.52 g) was weighed into a sample bottle, acetonitrile (12 mL) was added, and at room temperature Stir for 24 hours. After confirming that PEO was completely dissolved in acetonitrile and PAc-Li was sufficiently dispersed in the solution, the obtained dispersion was cast into a petri dish (diameter: 5.0 cm) made of polytetrafluoroethylene. . Next, the petri dish was transferred into a vacuum desiccator, and dried for 24 hours or more while flowing dry nitrogen at a flow rate of 2 L / min to obtain an electrolyte membrane. (A) Ratio of total blending amount of polyanionic lithium salt and (B) matrix polymer to blending amount of (D) organic solvent ([(A) + (B)] :( D) (mass ratio)), and Table 1 shows the molar ratio ((C) / Li (molar ratio)) of [(C) boron compound content (molar number)] / [(A) molar number of lithium atoms in polyanionic lithium salt]. . The same applies to the following examples and comparative examples.

[Example 2]
<PEO, Preparation of _{PAc-Li, BF 3 O (} C 2 H 5) gel electrolyte film containing _2>
PEO (0.50 g), PAc-Li (0.018 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.032 g), EC and GBL as organic solvents A mixed solvent (EC: GBL = 30: 70 (volume ratio)) (0.52 g) was weighed into a sample bottle, acetonitrile (12 mL) was added, and then an electrolyte membrane was produced in the same manner as in Example 1.

[Comparative Example 1]
<PEO, Preparation of _{PAc-Li, LiN (SO 2} CF 3) gel electrolyte film containing _2>
PEO (0.50 g), PAc-Li (0.018 g) obtained in (2-1) above, LiN (SO ₂ CF ₃ ) ₂ (0.036 g), EC and GBL mixed solvent as organic solvents (EC: GBL = 30: 70 (volume ratio)) (0.52 g) was weighed into a sample bottle, acetonitrile (12 mL) was added, and then an electrolyte membrane was produced in the same manner as in Example 1.

[Comparative Example 2]
<Preparation of Gel Electrolyte Membrane Containing PEO, LiN (SO ₂ CF ₃ ) ₂ >
PEO (0.50 g), LiN (SO ₂ CF ₃ ) ₂ (0.036 g), EC and GBL mixed solvent (EC: GBL = 30: 70 (volume ratio)) (0.50 g) as an organic solvent sample After weighing into a bottle and adding acetonitrile (12 mL), an electrolyte membrane was prepared in the same manner as in Example 1.

[Comparative Example 3]
<Preparation of gel electrolyte membrane containing PEO and PAc-Li>
PEO (0.50 g), PAc-Li (0.018 g) obtained in (2-1) above, a mixed solvent of EC and GBL as an organic solvent (EC: GBL = 30: 70 (volume ratio)) ( 0.52 g) was weighed into a sample bottle, acetonitrile (12 mL) was added, and an electrolyte membrane was prepared in the same manner as in Example 1.

[Example 3]
<Preparation of _{PVdF-HFP, PEO, PAc-} Li, BF 3 O (C 2 H 5) 2, LiN (SO 2 CF 3) gel electrolyte film containing ₂ (1)>
PVdF-HFP (0.4 g), PEO (0.10 g), PAc-Li (0.035 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.032 g ), LiN (SO ₂ CF ₃ ) ₂ (0.036 g), a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (0.55 g) as an organic solvent was weighed into a sample bottle, Tetrahydrofuran (4 mL) and acetonitrile (2 mL) were added and stirred for 48 hours. At this time, in order to completely dissolve PVdF-HFP, heating at 60 ° C. for about 1 hour was performed three times. After confirming that PVdF-HFP and PEO were completely dissolved in the solvent and PAc-Li was sufficiently dispersed in the solution, the obtained dispersion was treated with a petri dish made of polytetrafluoroethylene (diameter: 5. 0 cm). Next, the petri dish was transferred into a vacuum desiccator, and dried for 24 hours or more while flowing dry nitrogen at a flow rate of 2 L / min to obtain an electrolyte membrane.

[Example 4]
<Preparation of _{PVdF-HFP, PEO, PAc-} Li, BF 3 O (C 2 H 5) 2, LiN (SO 2 CF 3) gel electrolyte film containing ₂ (2)>
PVdF-HFP (0.4 g), PEO (0.10 g), PAc-Li (0.053 g) obtained in the above (2-1), BF ₃ O (C ₂ H ₅ ) ₂ (0.032 g ), LiN (SO ₂ CF ₃ ) ₂ (0.072 g), a mixed solvent of EC and GBL as an organic solvent (EC: GBL = 30: 70 (volume ratio)) (1.11 g) was weighed into a sample bottle, Tetrahydrofuran (4 mL) and acetonitrile (2 mL) were added, and then an electrolyte membrane was produced in the same manner as in Example 3.

[Example 5]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ (1)>
10 mass% THF solution (2.0 g) of PVdF-HFP, PAc-Li (0.079 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.072 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (1.12 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and the mixture was stirred at room temperature for 48 hours. The obtained solution was cast in a petri dish (diameter 7.5 cm) made of polytetrafluoroethylene in which a predetermined amount of a polyolefin nonwoven fabric (porosity 76%) was set. Next, the petri dish was transferred into a vacuum desiccator, and dried for 24 hours or more while flowing dry nitrogen at a flow rate of 2 L / min to obtain an electrolyte membrane.

[Example 6]
<Preparation of _{PVdF-HFP, PAMPS-Li,} BF 3 O (C 2 H 5) gel electrolyte film containing _2>
10 mass% THF solution (2.0 g) of PVdF-HFP, PAMPS-Li (0.322 g) obtained in (2-2) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.11 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (2.09 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and then the same as in Example 5 An electrolyte membrane was prepared by this method.

[Comparative Example 4]
<Production of gel electrolyte membrane containing PVdF-HFP and PAc-Li>
PVdF-HFP in 10 mass% tetrahydrofuran solution (2.5 g), PAc-Li (0.067 g) obtained in (2-1) above, a mixed solvent of EC and GBL as an organic solvent (EC: GBL = 30 : 70 (volume ratio)) (1.26 g) was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and an electrolyte membrane was prepared in the same manner as in Example 5.

[Example 7]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ (2)>
10 mass% tetrahydrofuran solution (2.5 g) of PVdF-HFP, PAc-Li (0.086 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.016 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (1.0 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and then the same as in Example 5 An electrolyte membrane was prepared by this method.

[Example 8]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ (3)>
10 mass% tetrahydrofuran solution (2.5 g) of PVdF-HFP, PAc-Li (0.089 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.048 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (1.0 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and then the same as in Example 5 An electrolyte membrane was prepared by this method.

[Example 9]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ (4)>
10 mass% tetrahydrofuran solution (2.5 g) of PVdF-HFP, PAc-Li (0.092 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.10 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (1.0 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and then the same as in Example 5 An electrolyte membrane was prepared by this method.

[Example 10]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ (5)>
PVdF-HFP in 10 mass% tetrahydrofuran solution (2.5 g), PAc-Li (0.10 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.18 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (1.0 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and then the same as in Example 5 An electrolyte membrane was prepared by this method.

[Example 11]
<Production of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ (6)>
10 mass% tetrahydrofuran solution (2.0 g) of PVdF-HFP, PAc-Li (0.088 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.24 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (0.8 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and then the same as in Example 5 An electrolyte membrane was prepared by this method.

[Example 12]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ (7)>
PVdF-HFP in 10 mass% tetrahydrofuran solution (2.0 g), PAc-Li (0.098 g) obtained in (2-1) above, BF ₃ O (C ₂ H ₅ ) ₂ (0.36 g) Then, a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (0.8 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and then the same as in Example 5 An electrolyte membrane was prepared by this method.

[Example 13]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ C ₅ H ₁₀ NH>
10 mass% tetrahydrofuran solution (2.0 g) of PVdF-HFP, PAc-Li (0.088 g) obtained in (2-1) above, BF ₃ C ₅ H ₁₀ NH (0.17 g), organic solvent As a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (1.15 g) was weighed into a sample bottle and tetrahydrofuran (2 mL) was added. A membrane was prepared.

[Example 14]
<Preparation of Gel Electrolyte Membrane Containing PVdF-HFP, PAc-Li, BF ₃ O ((CH ₃ ) ₃ C) ₂ >
PVdF-HFP in 10 mass% tetrahydrofuran solution (2.0 g), PAc-Li (0.094 g) obtained in (2-1) above, BF ₃ O ((CH ₃ ) ₃ C) ₂ (0. 24 g), a mixed solvent of EC and GBL (EC: GBL = 30: 70 (volume ratio)) (1.18 g) as an organic solvent was weighed into a sample bottle, tetrahydrofuran (2 mL) was added, and Example 5 and An electrolyte membrane was produced in the same manner.

(4) Measurement of the ionic conductivity of the electrolyte membrane The electrolyte membrane obtained above is cut into a predetermined size so as to enter a spacer having a hole with an inner diameter of 5 mm, and sandwiched between stainless steel plates in a cell. Incorporated. And the cell was connected to the complex alternating current impedance measuring apparatus, and resistance value was measured from the Nyquist plot. At this time, the cell was put in a thermostat set at 80 ° C., and after the electrolyte and the stainless steel plate were blended, the temperature was lowered and the resistance value at a predetermined temperature was measured. The resistance value at each temperature was measured after holding the cell for 30 minutes at each temperature. And from the obtained resistance value, the ionic conductivity (σ) (S / cm) of the electrolyte membrane was calculated according to the following formula (I). Table 2 shows the ionic conductivity of the electrolyte membranes in Examples 1 to 14 and Comparative Examples 1 to 4. Moreover, the graph which plotted the ionic conductivity ((sigma)) of the electrolyte membrane in Examples 1-2 and Comparative Examples 1-3 logarithmically in FIG. 1, and the ionic conductivity ((sigma)) of the electrolyte membrane in Examples 3-4 is logarithmically. The plotted graphs are shown in FIG.
σ = l / s · R (I)
(Wherein l represents the thickness (cm) of the sample (electrolyte membrane); s represents the area (cm ² ) of the sample (electrolyte membrane); R represents the resistance value (Ω).)

(5) Measurement of lithium ion transport number (t +) of electrolyte membrane The lithium ion transport number of the electrolyte membrane obtained above was determined by the combined use of DC polarization measurement and complex impedance measurement.
That is, the electrolyte membrane was cut into a predetermined size so as to enter a spacer having a hole with an inner diameter of 16 mm, and was sandwiched between Li plates and incorporated into a cell. And after connecting the cell to the complex alternating current impedance measuring apparatus and putting the cell in a thermostat set to 60 ° C. for 1 hour, the temperature was changed to 25 ° C. and the measurement was started after being placed for 1 hour or more. The measuring method is as follows. First, complex impedance measurement was performed, and a resistance value (hereinafter abbreviated as R0) was estimated. Then, DC polarization measurement was performed to confirm that the current value became constant (hereinafter, the initial current value was abbreviated as I0, and the current value when it became constant was abbreviated as Is, respectively), and then the complex impedance measurement was performed again. The resistance value (hereinafter abbreviated as Rs) was estimated. And the transport number of lithium ion was computed from the Evans formula represented by following formula (II). Table 2 shows the lithium ion transport number (t +) of the electrolyte membranes in Examples 1 to 14 and Comparative Examples 1 to 4.
t + = Is (ΔV−I0 · R0) / I0 (ΔV−Is · Rs) (II)
(In the formula, ΔV represents an applied voltage; R0, Rs, I0, Is are the same as described above.)

From Example 2, it can be confirmed that, if PAc-Li, BF ₃ O (C ₂ H ₅ ) ₂ and an organic solvent are blended in the matrix polymer, high ionic conductivity and lithium ion transport number can be realized in the electrolyte membrane. It was. From Example 1, it was confirmed that the presence of a small amount of LiN (SO ₂ CF ₃ ) ₂ further improved the ion conductivity without lowering the lithium ion transport number.
Further, from Example 3, it was confirmed that even when the matrix polymer was changed, the ionic conductivity of the electrolyte membrane was hardly affected.
And from Example 4, it has confirmed that the ionic conductivity of an electrolyte membrane further improved by increasing the compounding quantity of an organic solvent.
And from Examples 5-14, it has confirmed that a high ion conductivity and the transport number of lithium ion were realizable similarly to Examples 1-4 with the combination and the mixture ratio of various compounding components.
On the other hand, it was confirmed from Comparative Example 1 that BF ₃ O (C ₂ H ₅ ) ₂ is an essential component for improving the ionic conductivity and the lithium ion transport number near the room temperature of the electrolyte membrane.
Further, from Comparative Example 2, BF ₃ O (C ₂ H ₅ ) ₂ and PAc-Li are not blended, so that LiN (SO ₂ CF ₃ ) ₂ becomes the only ionic conductor, It was confirmed that the ionic conductivity was greatly reduced and the transport number of lithium ions was also reduced.
Further, from Comparative Example _3, by _{BF 3 O (C 2 H 5} ) 2 and _LiN (SO 2 _{CF 3) 2} is absent, it was confirmed that the ionic conductivity is lowered even greater. This is presumed to be because PAc-Li cannot be sufficiently dissociated. Similarly to Comparative Example 3, the ionic conductivity of Comparative Example 4 was greatly reduced.

(6) Confirmation of the relationship between the amount of raw material used and the ionic conductivity of the electrolyte membrane Applying quality engineering techniques, the amount of each raw material used during the production of the electrolyte membrane and its effect on the ionic conductivity of the electrolyte membrane It was confirmed. More specifically, it is as follows.

(6-1) Assignment of control factors In the quality engineering, what changes the characteristics by changing the amount and type of raw materials used is called a control factor. In this experiment, 2 levels are 1 factor and 3 levels are 7 A total of 8 factors were assigned. As shown in Table 3, the control factors are
(A) The type of polyanion type lithium (Li) salt is changed to PAMPS-Li, PAc-Li,
(B) The blending amount of the polyanion type lithium salt is 1/48, 1/24, 1/12 (Li / PEO (molar ratio)),
(C) LiN (SO ₂ CF ₃ ) ₂ is blended in amounts of 0, 1/100, 1/50 (Li / PEO (molar ratio)),
(D) The blending amount of the organic solvent is 10, 40, 100 (organic solvent / PEO (mass ratio)),
(E) The type of the organic solvent is EC + PC, EC + PC + GBL, EC + PC + SL (1: 1 or 1: 1: 1 (volume ratio)),
_{(F) BF 3 O (C} 2 H 5) 2 of the amount _{0,1,2 (BF 3 O (C 2} H 5) 2 / polyanion lithium salt (molar ratio)),
(G) the amount of _{Al 2 O 3 0,2,10 (Al 2} O 3 / PEO ( mass ratio)),
(H) Made of plasticizer, TEGME, PEG (10% by mass based on PEO)
It was.

(6-2) Assignment to L18 orthogonal table and production of electrolyte membrane Based on the assignment of control factors, the L18 orthogonal table shown in Tables 4 and 5 was created, and an electrolyte membrane was produced according to this orthogonal table (Experimental Example 1). To 18). Tables 6 and 7 show the blending amount of each raw material at this time.
For example, in Experimental Example 3, PEO (1.0 g), PAMPS-Li (0.101 g), LiN (SO ₂ CF ₃ ) ₂ (0.13 g), BF ₃ O (C ₂ H ₅ ) ₂ (0. 013 g), Al ₂ O ₃ (0.1 g), PEG (0.1 g) as a plasticizer, EC, PC and SL mixed solvent (1: 1: 1, volume ratio) (1 g) as an organic solvent After adding acetonitrile (20 mL), an electrolyte membrane was prepared in the same manner as in Example 1.
Similarly for the other experimental trains, the raw materials were blended as shown in Tables 6 and 7 (both the PEO blending amount was 1.0 g and the acetonitrile blending amount was 20 mL). An electrolyte membrane was prepared by this method.

(6-3) Data analysis of electrolyte membrane The ion conductivity at each temperature of the electrolyte membrane in Experimental Examples 1 to 18 was measured by the same method as described above. Table 8 shows the measurement results. Further, the SN ratio (η) and sensitivity (S) were calculated based on the evaluation characteristic called the desired characteristic. Here, when the ion conductivity measured at a certain temperature Tn is yn (where n represents an integer of 2 or more), the SN ratio (η) and sensitivity (S) are expressed by the following formula (III). Using (VI), it can be calculated by the following formulas (VII) and (VIII), respectively. The SN ratio (η) and sensitivity (S) of the electrolyte membrane in Experimental Examples 1 to 18 are shown in FIG.
Here, the SN ratio (η) indicates the degree of variation of the ionic conductivity due to temperature, and the larger the numerical value, the smaller the variation and the better. Moreover, sensitivity (S) shows the height of ionic conductivity, and it shows that ionic conductivity is high and it is excellent, so that a numerical value is large.
Sum of all squares: ST = y1 ² + y2 ² + y3 ² +... + Yn ² ... (III)
Average fluctuation: SM = (y1 + y2 + y3 +... + Yn) ² / n (IV)
Noise fluctuation: SN = ST-SM (V)
Total error variance: VN = SN / (n-1) (VI)
Signal to noise ratio: η = (1 / n) SM / VN (VII)
Sensitivity: S = (1 / n) SM (... VIII)

  In Experimental Examples 1 to 18, factor effect diagrams were created from the calculated SN ratio (η) and sensitivity (S) according to a well-known and commonly used method. Factor effect diagrams at this time are shown in FIGS. Here, the factor effect diagram is a graph of the magnitude of the main effect. FIGS. 4 and 5 are factor effect diagrams relating to the SN ratio (η), and FIGS. 6 and 7 are factor effects relating to the sensitivity (S). Each figure is shown.

Next, in order to test the reliability of this factor effect, the following confirmation experiment was performed.
That is, for each factor in the obtained factor-effect diagram, a level having a high SN ratio (η) and sensitivity (S) was selected and optimum conditions were determined (conditions of Experimental Examples 19 and 20). For example, the S / N ratio expected under the optimum condition can be estimated to be η1 from the factor effect diagram (estimated value). And the electrolyte membrane of this invention was again produced on the optimal conditions, the ion conductivity was measured by the method similar to the above, and SN ratio was further calculated (Experimental Examples 19 and 20). The SN ratio at this time is η2 (experimental value). Similarly, as comparison conditions, the SN ratio estimated from the factor-effect diagram of Experimental Example 1 was η3 (estimated value), and the SN ratio calculated from actual ionic conductivity was η4 (experimental value) (Experimental Example 1). Results). The difference between the optimum condition (the conditions of Experimental Examples 19 and 20) and the comparison condition is referred to as a gain. It can be said that the reliability of the effect chart is high. The same applies to the sensitivity (S).
Table 9 shows the measurement results of the ionic conductivity of the electrolyte membranes in Experimental Examples 19 and 20.

The range of the desirable blending form of each raw material can be specified from the factor effect diagrams shown in FIGS. For example, it is as follows.
In the electrolyte membrane, as the polyanion type lithium salt, there was no significant difference between the sulfonic acid lithium salt and the carboxylic acid lithium salt, and it was confirmed that the polyanion type lithium salt can be used regardless of the type of acid.
It was confirmed that the blending amount of the polyanion type lithium salt was not a problem within the range of 1/48 to 1/12.
It was confirmed that the amounts of LiN (SO ₂ CF ₃ ) ₂ and Al ₂ O ₃ were small.
It was confirmed that a larger amount of the organic solvent was better as long as the retention of the electrolytic solution and the film strength were not impaired.
It was confirmed that the type of the organic solvent is not particularly limited.
It was confirmed that the blending amount of BF ₃ O (CH ₂ CH ₃ ) ₂ was preferably 1 mol or more with respect to 1 mol of the polyanion type lithium salt.
It was confirmed that the plasticizer is not an essential component in the gel electrolyte.

According to the above method, the gain of the estimated value and the gain of the experimental value were calculated for the SN ratio (η) and the sensitivity (S). The results are shown in Table 10.
As is apparent from Table 10, since the gains were relatively close in Experimental Examples 19 and 20, it was confirmed that the factor effect obtained in this Experimental Example was highly reliable.

  The present invention can be used in the field of lithium ion secondary batteries.

Claims (12)

  An electrolyte comprising (A) a polyanionic lithium salt, (C) a boron compound, and (D) an organic solvent.   Furthermore, (B) matrix polymer is mix | blended, The electrolyte of Claim 1 characterized by the above-mentioned.   The (C) boron compound is at least one selected from the group consisting of boron halides, boron halide alkyl ether complexes, boron halide alcohol complexes, and boron halide salts. 2. The electrolyte according to 2.   The boron compound (C) is boron trifluoride, boron trifluoride dimethyl ether complex, boron trifluoride diethyl ether complex, boron trifluoride di n-butyl ether complex, boron trifluoride di tert-butyl ether complex, trifluoride. Selected from the group consisting of boron tert-butyl methyl ether complex, boron trifluoride tetrahydrofuran complex, boron trifluoride methanol complex, boron trifluoride propanol complex, and boron trifluoride phenol complex, and piperidinium boron trifluoride The electrolyte according to any one of claims 1 to 3, wherein the electrolyte is one or more types.   The electrolyte according to any one of claims 1 to 4, wherein the (A) polyanionic lithium salt is at least one selected from the group consisting of a lithium polycarboxylic acid salt and a lithium polysulfonic acid salt. .   The (A) polyanionic lithium salt is poly (2-acrylamido-2-methyl-1-propanesulfonate lithium), poly (lithium styrenesulfonate), poly (lithium vinylsulfonate), poly (perfluorosulfonic acid). Lithium), poly (lithium (meth) acrylate), lithium polymaleate, lithium polyfumarate, lithium polymuconate, lithium polysorbate, poly (acrylonitrile-butadiene-lithium acrylate) copolymer, poly (tert-butyl acrylate) It is at least one selected from the group consisting of an ethyl acrylate-lithium methacrylate copolymer, a poly (ethylene-lithium acrylate) copolymer, and a poly (methyl methacrylate-lithium methacrylate) copolymer. Request The electrolyte according to any one of 1 to 5.   The (B) matrix polymer is at least one selected from the group consisting of polyether polymers, fluorine polymers, polyacrylic polymers, polyacrylonitrile, polyphosphazenes, and polysiloxanes. The electrolyte according to any one of 6.   The (B) matrix polymer is polyethylene oxide, polypropylene oxide, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-hexafluoroacetone copolymer, polytetrafluoroethylene. The electrolyte according to claim 2, wherein the electrolyte is at least one selected from the group consisting of polyacrylonitrile, polyphosphazene, and polysiloxane.   The electrolyte according to any one of claims 1 to 8, wherein the organic solvent (D) is at least one selected from the group consisting of a carbonate compound, a lactone compound, and a sulfone compound.   The organic solvent (D) is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, and sulfolane. The electrolyte according to any one of 1 to 9.   Furthermore, (E) lithium salt which does not correspond to said (A) polyanion type lithium salt is mix | blended, The electrolyte as described in any one of Claims 1-10 characterized by the above-mentioned.   An electrolyte membrane obtained by using the electrolyte according to any one of claims 1 to 11.

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