JP2005093376A - Solid polyelectrolyte film and battery made by using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polyelectrolyte film of a superior quality in both of ion conductivity and cation mobility, and provide a battery made by using it. <P>SOLUTION: This is a solid polyelectrolyte film containing electrolyte salt, an ion conductive polymer, and a compound having anion capturing ability. In a preferable embodiment, this solid electrolyte film has a layer composed of the electrolyte salt and the compound having anion capturing ability, preferably a polymer having boroxine ring on the surface of the film composed of a composition of the electrolyte salt and the ion conductive polymer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer solid electrolyte film and a battery using the same.

  A solid electrolyte is a substance having high ion conductivity in a solid state. Among them, a polymer solid electrolyte using a polymer substance as a solid is derived from flexibility and flexibility, which are unique properties of organic polymers. In recent years, it has attracted much attention as an electrolyte for next-generation lithium secondary batteries because it has excellent flexibility in processing and adhesion to the electrode interface, and research is being promoted worldwide. .

Such a polymer solid electrolyte has a high degree of freedom in its shape, such as no risk of liquid leakage and can be made into a thin film, as compared with a conventional electrolyte solution. However, conventionally known non-aqueous polymer solid electrolytes have a problem that their electrical conductivity is remarkably lower than that of an electrolyte solution. For example, a non-aqueous polymer solid electrolyte obtained by combining a polymer substance such as polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyphosphazene, and polysiloxane with an electrolyte salt is conventionally known. Nothing exceeding 10 ⁻³ S / cm at room temperature has been found (for example, see Patent Document 1).

  Conventionally, these polymer solid electrolytes often have a branched structure in which a polymer main chain has a side chain, and further, a multi-branched structure in which the side chain also has a branch. Thus, the conventional polymer solid electrolyte has a branched structure because fast molecular motion of a side chain such as multi-branched polyethylene oxide remarkably improves the ion transport ability as the polymer solid electrolyte.

  Generally, a polymer solid electrolyte is prepared by uniformly mixing a lithium salt with a polymer material. Therefore, in such a polymer solid electrolyte, both a cation and an anion move in the electrolytic solution when charging and discharging a battery incorporating the polymer solid electrolyte. Anion migration does not participate in battery reactions.

  In particular, in a lithium battery, only the movement of a lithium ion, which is a cation, is necessary to perform a required battery reaction. However, at the same time, an anion also moves, and the concentration of the anion in the electrolyte is moved by the movement of the anion. Polarization occurs. As a result, the electrolyte resistance gradually increases at the time of charging, and immediately reaches a predetermined charging voltage, causing a problem that a predetermined amount of lithium ions cannot be introduced into the negative electrode. On the other hand, at the time of discharging, there is a drawback that the voltage drop due to the electrolyte resistance gradually increases and the voltage drop to a predetermined voltage occurs quickly, making it difficult to take out the charged lithium ions. This is particularly noticeable when performing rapid charge / discharge.

As a method of preventing concentration polarization due to anions of these polymer solid electrolytes, conventionally, a solid electrolyte film in which an anion species is fixed in a polymer to form an ion exchange membrane (for example, see Patent Document 2), only cations are used. A method of adding a conducting inorganic electrolyte to a polymer solid electrolyte (see, for example, Patent Document 3), adding an electrolyte salt to an ion conductive polymer, and adding an additive having the ability to trap anions of the electrolyte salt, Or the method (for example, refer patent document 4) etc. which incorporate in an ion conductive polymer is known. Such a method is an attempt to make only the contribution of the cation the conductivity of the solid electrolyte, and is evaluated by an index called a cation transport number.
JP-A-10-204172 Japanese Patent Laid-Open No. 08-259698 JP 2001-316583 A JP 2000-080265 A

  According to such a polymer solid electrolyte, all have an improvement in cation transport number, but all have low conductivity, and thus a high conductivity having a high conductivity while maintaining a high cation transport number. A molecular solid electrolyte has not been obtained conventionally.

  The present invention has been made to solve the above-mentioned problems in conventional polymer solid electrolytes, and uses a polymer solid electrolyte film excellent in both ionic conductivity and cation transport number, and the same. It aims at providing the battery which becomes.

  The polymer solid electrolyte film according to the present invention provides a polymer solid electrolyte film comprising an electrolyte salt, an ion conductive polymer, and a compound having an anion scavenging ability.

  According to a preferred aspect of the present invention, a layer made of a composition of an electrolyte salt and a compound having an anion scavenging ability is provided on the surface of a film made of the composition of an electrolyte salt and an ion conductive polymer. A solid polymer electrolyte film is provided.

  According to another preferred embodiment of the present invention, a polymer solid electrolyte characterized in that a compound having an anion scavenging ability is dispersed in the form of particles in a film comprising a composition of an electrolyte salt and an ion conductive polymer. A film is provided.

  The solid polymer electrolyte film according to the present invention contains an electrolyte salt, an ion conductive polymer and a compound having an anion scavenging ability, has a high cation transport number without lowering the conductivity, and has an interface resistance. Thus, the polymer solid electrolyte film according to the present invention can be suitably used as a solid electrolyte in, for example, a lithium secondary battery.

  In the polymer solid electrolyte film according to the present invention, any conventionally known ion conductive polymer can be used without limitation. Examples of such ion conductive polymers include polyethylene oxide, polypropylene oxide, and polyethylene oxide. -A linear or branched polymer such as a propylene oxide copolymer, polyacrylonitrile, polysiloxane, polyphosphazene, or a cross-linked product thereof.

Further, in the polymer solid electrolyte film according to the present invention, an alkali metal salt is preferably used as the electrolyte salt. Among them, for example, LiPF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAsF ₆ , LiSbF ₆ , LiAlF ₄ , LiGaF ₄ , LiInF ₄ , LiClO ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiSiF ₆ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) and other lithium A salt is preferably used.

  According to the present invention, at least one selected from a boron compound, an aluminum compound, and a gallium compound is used as the compound having anion scavenging ability. Examples of the boron compound include boron oxide, boron nitride, boron fluoride, tri (s-butyl) borane, 9- (isopropyl) -9-borabicyclo [3.3.1] nonane, diisopropyl chloromethylboronate, [ (3,3,4,4-tetramethyl-2,5,1-dioxaboryl) methyl] diethyl malonate, 2- (cyclopentyl) -1,3,2-benzodioxaborole, 2- (2,2 -Dimethylcyclopropyl) -1,3,2-benzodioxaborol, dimethyl (S) -2-butylboronate, triphenylborane, 3-pyridyldiethylborane, dimesitylfluoroborane, dimesitylethylborane, Tris (dimethoxyboryl) methane, tris (ethylenedioxyboryl) methane, 9-trifluoromethanesulfonyloxy-9 Borabicyclo [3.3.1] nonane, dibutylboryltriflate, 9-bromoborabicyclo [3.3.1] nonane, 9-methoxy-9-borabicyclo [3.3.1] nonane and the like are listed as preferred specific examples. be able to.

  A polymer having a boroxine ring (boroxine ring) (hereinafter simply referred to as a boroxine polymer) can also be mentioned as a preferred specific example. In particular, according to the present invention, the boroxine polymer preferably has a boroxine ring having a trialkoxyboroxine structure as already known. Thus, a boroxin polymer having a trialkoxyboroxine structure in a boroxine ring (hereinafter simply referred to as trialkoxyboroxin polymer) is described in, for example, literature (Chemistry Letters, The Chemical Society of Japan (Chemistry).・ Letters, The Chemical Society of Japan (1997, page 915) and Japanese Patent Application Laid-Open No. 11-54151, etc., synthesized from tetraethylene glycol, polyethylene glycol monomethyl ether, and boron oxide. can do.

  Aluminum compounds include tri-n-propylaluminum, tricyclopropylaluminum, tri-t-butylaluminum, tribenzylaluminum, cyclopentadienylethylaluminum, triphenylaluminum, dimethylphenylaluminum, diethylaluminum hydride, hydrogenated Boron dimethylaluminum, bromodiethylaluminum, diiodomethylaluminum, azidodiethylaluminum, methoxydimethylaluminum, dimethyl (phenoxy) aluminum, diethyl (propanoate) aluminum, dimethyl (1,3-diphenyl-1,3-propanedionate) aluminum Tetraethyl-μ-oxodialuminum, ethanethiolate diethylaluminum, (ethylamino) dimethyl Le aluminum, diethyl (dimethylamino) aluminum, may be mentioned as preferred examples of (diethylamino) diphenyl aluminum. Moreover, the polymer which contains these in a structure can also be mentioned as a preferable specific example.

  Further, preferred examples of the gallium compound include triethyl gallium, triphenyl gallium, chlorodiethyl gallium, chlorodiphenyl gallium, ethoxydiethyl gallium, acetylidinomethyl gallium, dimethyl (tetrahydroborate) gallium, and the like. Moreover, the polymer which contains these in a structure can also be mentioned as a preferable specific example.

  Among the various compounds described above, in the present invention, a boroxin polymer or boron oxide is particularly preferably used as the compound having an anion scavenging ability.

  The solid electrolyte film according to the present invention may contain a non-aqueous organic solvent as necessary in order to further improve the ion conduction performance. The non-aqueous organic solvent is not particularly limited as long as it is compatible with the above-described ion conductive polymer and electrolyte salt. For example, ethylene carbonate, propylene carbonate, butylene carbonate, γ -Cyclic esters such as butyrolactone, ethers such as tetrahydrofuran and dimethoxyethane, and chain esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. These can be used alone or as a mixture of two or more.

  In the solid polymer electrolyte film according to the present invention, the amount of the electrolyte salt is appropriately determined according to the ion conductive polymer to be used, but is usually in the range of 10 to 40% by weight of the obtained polymer electrolyte. .

  The polymer solid electrolyte film according to the present invention comprises the above-described electrolyte salt, an ion conductive polymer, and a compound having an anion scavenging ability, where the compound having an anion scavenging ability is, for example, on the surface of the film. It may be localized in a layered manner, or may be uniformly dispersed in the film in the form of particles.

  A solid polymer electrolyte film as a preferred embodiment according to the present invention has a layer comprising a composition of an electrolyte salt and a compound having an anion scavenging ability on the surface of a film comprising a composition of an electrolyte salt and an ion conductive polymer. Preferably, the electrolyte salt is a lithium salt, and the compound having an anion scavenging ability is a boroxine polymer.

  In particular, according to the present invention, the boroxin polymer is preferably a trialkoxy boroxine polymer as described above. Here, the composition comprising such a lithium salt and a trialkoxyboroxin polymer is itself a solid electrolyte.

  That is, the polymer solid electrolyte film as a preferred embodiment according to the present invention is formed from a lithium salt and a boroxine polymer, preferably a trialkoxyboroxine polymer on the surface of a film comprising a composition of an electrolyte salt and an ion conductive polymer. A solid electrolyte layer. In such a polymer solid electrolyte film, according to the present invention, the ratio of the number of lithium salts and the number of boroxine rings having a solid electrolyte layer composed of a lithium salt and a trialkoxyboroxine polymer is In general, the number of boroxine rings is preferably in the range of 1-20.

  Thus, a solid polymer electrolyte having a solid electrolyte layer comprising a lithium salt and a boroxine polymer, preferably a trialkoxyboroxine polymer, on the surface of a film comprising a composition of an electrolyte salt and an ion conductive polymer The film can be obtained, for example, as follows. That is, an electrolyte salt and an ion conductive polymer are dissolved in an appropriate volatile organic solvent to form a solution, and this solution is spread on an appropriate substrate and heated to volatilize the solvent. A film comprising a composition of a salt and an ion conductive polymer is prepared. Separately, a lithium salt and trialkoxyboroxine polymer are dissolved in an appropriate volatile organic solvent to form a solution, and this solution is applied to the surface of the film, and then heated to volatilize the solvent, To form a solid electrolyte layer composed of the lithium salt and trialkoxyboroxine polymer.

  A polymer solid electrolyte film having a solid electrolyte layer composed of a lithium salt and a trialkoxyboroxine polymer on the surface of a film composed of a composition of an electrolyte salt and an ion conductive polymer, in particular, has a conductivity and a cation transport number. Both of them are high and the interface resistance is low. Therefore, they can be advantageously used as a solid electrolyte in a battery.

  The polymer solid electrolyte film according to another preferred embodiment of the present invention is obtained by dispersing a compound having an anion scavenging ability in a particulate form in a film comprising a composition of an electrolyte salt and an ion conductive polymer. Such a polymer solid electrolyte film is prepared by adding, for example, an electrolyte salt, an ion conductive polymer, and particles of a compound having an anion capturing ability such as boron oxide to an appropriate volatile organic solvent, and mixing and stirring. Then, the particles of a compound having an anion scavenging ability are dispersed in a solution of an electrolyte salt and an ion conductive polymer, and this is spread on an appropriate substrate, heated, and then volatilized out of the solvent. . Thus, in the polymer solid electrolyte film in which boron oxide is dispersed in a film made of a lithium salt and an ion conductive polymer, the ratio of the lithium salt to the boron atom is the number of boron atoms relative to the lithium salt 1. Is usually in the range of 1-4.

  The polymer solid electrolyte film according to the present invention can have a core material such as a nonwoven fabric, a porous membrane, a split fabric, and a mesh. For example, as described above, such a polymer solid electrolyte film is obtained by dissolving an ion conductive polymer and an electrolyte salt in an appropriate volatile organic solvent to form a solution, and impregnating the core material with the solution. After heating, volatilizing the solvent to prepare a film made of an ion conductive polymer and an electrolyte salt, the surface of the film is made of a composition of a lithium salt and a boroxine polymer as described above. A layer may be formed.

  As another method, an electrolyte salt, an ion conductive polymer, and particles of a compound having an anion capturing ability such as boron oxide are added to an appropriate volatile organic solvent, mixed and stirred, and then the electrolyte salt and the ion conductive polymer are mixed. In this solution, particles of a compound having an anion scavenging ability are dispersed, and the core material is impregnated with the solution, followed by heating to volatilize the solvent.

  Such a polymer solid electrolyte film according to the present invention can be advantageously used, for example, in the production of batteries and capacitors. FIG. 1 is a longitudinal sectional view of a coin-type lithium secondary battery using such a polymer solid electrolyte film. In this lithium secondary battery, the positive electrode can 1 also serving as a positive electrode terminal is made of, for example, a nickel-plated stainless steel plate, and the negative electrode can 3 also serving as a negative electrode terminal insulated from the positive electrode can via an insulator 2. In combination with a battery can (container). The negative electrode can is also made of, for example, a stainless steel plate plated with nickel.

  Inside the battery can thus formed, the positive electrode 4 is disposed in contact with the positive electrode can via the positive electrode current collector 5. For example, the positive electrode 4 is prepared by mixing a positive electrode active material such as lithium manganese composite oxide and a conductive material such as graphite with a binder resin such as polyethylene, polypropylene, and polytetrafluoroethylene, and then pressing the mixture. Can be obtained. Similarly, the negative electrode 6 is disposed in contact with the negative electrode can via the negative electrode current collector 7. The negative electrode is made of, for example, a lithium plate. A polymer solid electrolyte film 8 according to the present invention is disposed between the positive electrode and the negative electrode to constitute a battery. Thus, according to such a battery, electric energy can be taken out using the positive electrode can and the negative electrode can as terminals.

  The present invention will be described below with reference examples and examples, but the present invention is not limited to these examples. In the following, the thickness, conductivity, cation transport number and interface resistance of the polymer solid electrolyte film were measured as follows.

(Thickness of polymer solid electrolyte film)
Measurement was performed using a 1/10000 mm dial gauge.
(Conductivity)
The obtained polymer solid electrolyte film was sandwiched between platinum plates having a diameter of 10 mm in an argon glove box, and an impedance measuring device (263A potentiostat and 5210 lock-in amplifier manufactured by Princeton Applied Research) was used at room temperature (23 (° C.), the real component impedance at the intersection of the arc on the high frequency side and the straight line on the low frequency side was determined by the complex impedance method, and the conductivity σ (S / cm) was calculated by the following equation.

                              σ = d / (R · A)

Here, d is the thickness (cm) of the sample, R is the impedance (Ω), and A is the area (cm ² ) of the platinum plate.

(Cation transport number)
A lithium metal plate having a diameter of 15 mm and a thickness of 1 mm was used as an electrode, and the polymer solid electrolyte film obtained in each example was sandwiched between the electrodes. A 2016-type coin battery was manufactured by using a current collector (aluminum net) on the electrode side. Thereafter, an AC voltage of ± 10 mV was applied, and the electrolyte bulk resistance Rb and the interface resistance Re were separated by a complex impedance method. Thereafter, a DC voltage of 10 mV is applied, the change with time of the current flowing through the battery is measured, the initial current value I (0) and the steady state current value I (∞) are obtained, and the cation transport number t ₊ Asked. The measurement was performed at 23 ° C. in an argon glove box.

t ₊ = [I (∞) {ΔV−I (0) Re}] / [I (0) {ΔV−I (∞) Re}]

(Interface resistance)
The interface resistance at the time of measuring the cation transport number was used as it was.

Reference example 1
(Synthesis of trialkoxyboroxin polymer)
Trialkoxyboroxine polymers were synthesized according to the method described in the literature (Chemistry Letters, The Chemical Society of Japan, 1997, page 915). That is, 10 g of polyethylene glycol monomethyl ether (manufactured by Aldrich) and 7.63 g of tetraethylene glycol (manufactured by Aldrich) were dissolved in 75 g of tetrahydrofuran to obtain a solution. After adding 373 g of boron oxide (manufactured by Aldrich), It heated at 120 degreeC under airflow for 6 hours, and obtained the transparent and viscous liquid as a reaction product. Subsequently, this liquid was stirred at 120 ° C. under reduced pressure for 4 hours to remove tetrahydrofuran and generated water to obtain a trialkoxyboroxine polymer as a very viscous liquid. The trialkoxyboroxine polymer thus obtained was measured for an infrared absorption spectrum and subjected to elemental analysis to confirm the structure. That is, a boroxine ring was formed, and it was confirmed that polyethylene gericol monomethyl ether and tetraethylene glycol were almost quantitatively bound to this boroxine ring.

(Preparation of solid electrolyte comprising trialkoxyboroxin polymer and lithium salt (hereinafter referred to as trialkoxyboroxin polymer electrolyte))
1 g of the above trialkoxyboroxine polymer and 0.15 g of the lithium salt LiN (CF ₃ SO ₂ ) ₂ were dissolved in 9 g of tetrahydrofuran at room temperature, and then the tetrahydrofuran was distilled off under reduced pressure, followed by vacuum drying at 40 ° C. for 12 hours. Thus, a trialkoxyboroxin polymer electrolyte was obtained as a soft solid. This was stored in an argon glove box.

Example 1
5 parts by weight of a lithium salt LiN (CF ₃ SO ₂ ) _{2, 20} parts by weight of polyethylene oxide (manufactured by Aldrich, molecular weight 100,000, linear structure) and 75 parts by weight of acetonitrile are mixed, and the solution is stirred at 60 ° C. Obtained. This solution was spread on a petri dish, and then heat-dried at 80 ° C. for 3 hours and vacuum-dried at 60 ° C. for 12 hours to obtain a film having a thickness of about 80 μm.

  The trialkoxyboroxine polymer electrolyte obtained in Reference Example 1 was dissolved in tetrahydrofuran, applied to both sides of the film with a wire bar, and vacuum-dried at 40 ° C. for 12 hours to obtain a polymer solid electrolyte according to the present invention. A film was obtained. This was stored in an argon glove box. When the surface of the polymer solid electrolyte film was observed with a transmission electron microscope, a layer made of the trialkoxyboroxine polymer electrolyte was formed to a thickness of about 1 μm on any surface of the film. About this polymer solid electrolyte film, the conductivity and the cation transport number were measured. The results are shown in Table 1.

Example 2
In the same manner as in Example 1, a film composed of a lithium salt and polyethylene oxide was prepared. The trialkoxyboroxine polymer electrolyte obtained in Reference Example 1 was dissolved in tetrahydrofuran, applied to both sides of the film with a wire bar, and vacuum-dried at 40 ° C. for 12 hours to obtain a polymer solid electrolyte according to the present invention. A film was obtained. This was stored in an argon glove box. When the surface of the polymer solid electrolyte film was observed with a transmission electron microscope, a layer made of the trialkoxyboroxine polymer electrolyte was formed to a thickness of about 5 μm on any surface of the film. About this polymer solid electrolyte film, the conductivity and the cation transport number were measured. The results are shown in Table 1.

Example 3
Lithium salt LiN (CF ₃ SO ₂ ) ₂ 5 parts by weight, polyethylene oxide (Aldrich, molecular weight 100,000, linear structure) 20 parts by weight and granular borane oxide (Aldrich) 2 parts by weight acetonitrile 75 parts by weight In addition, the solution was stirred at 60 ° C. to obtain a solution in which borane oxide particles were dispersed. This solution was spread on a petri dish, then heated and dried at 80 ° C. for 3 hours, and vacuum dried at 60 ° C. for 12 hours to obtain a polymer solid electrolyte film having a thickness of about 100 μm. About this polymer solid electrolyte film, the conductivity and the cation transport number were measured. The results are shown in Table 1.

Comparative Example 1
While adding 5 parts by weight of a lithium salt LiN (CF ₃ SO ₂ ) ₂ and 20 parts by weight of polyethylene oxide (manufactured by Aldrich, viscosity average molecular weight 100,000, linear structure) to 75 parts by weight of acetonitrile, heating at 80 ° C. Stir to obtain a solution. This solution was spread on a petri dish, then dried by heating at 80 ° C. for 3 hours, and then vacuum dried at 60 ° C. for 12 hours to obtain a polymer solid electrolyte film having a thickness of about 20 μm. Then, it preserve | saved at room temperature in the argon glove box. About this polymer solid electrolyte film, the conductivity and the cation transport number were measured. The results are shown in Table 1.

Comparative Example 2
The trialkoxyboroxine polymer electrolyte obtained in Reference Example 1 is dissolved in tetrahydrofuran to form a solution. This solution is developed in a petri dish, then heated and dried at 80 ° C. for 3 hours, and then vacuum dried at 60 ° C. for 12 hours. Thus, a trialkoxyboroxine polymer electrolyte film having a thickness of about 100 μm was obtained. Then, it preserve | saved at room temperature in the argon glove box. The trialkoxyboroxine polymer electrolyte film was measured for conductivity and cation transport number. The results are shown in Table 1.

It is sectional drawing which shows an example of a coin type solid electrolyte secondary battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positive electrode can 2 ... Insulator 3 ... Negative electrode can 4 ... Positive electrode 5 ... Positive electrode collector 6 ... Negative electrode 7 ... Negative electrode collector 8 ... Polymer solid electrolyte film

Claims (10)

  A solid polymer electrolyte film comprising an electrolyte salt, an ion conductive polymer, and a compound having an anion scavenging ability.   A polymer solid electrolyte film comprising a layer made of a composition of an electrolyte salt and a compound having an anion scavenging ability on the surface of the film made of a composition of an electrolyte salt and an ion conductive polymer.   A polymer solid electrolyte film, wherein a compound having an anion scavenging ability is dispersed in the form of particles in a film comprising a composition of an electrolyte salt and an ion conductive polymer.   The polymer solid electrolyte film according to claim 1, wherein the compound having an anion scavenging ability is at least one selected from a boron compound, an aluminum compound, and a gallium compound.   The polymer solid electrolyte film according to claim 1 or 2, wherein the compound having an anion scavenging ability is a polymer having a boroxine ring.   The polymer solid electrolyte film according to claim 5, wherein the polymer having a boroxine ring has a trialkoxyboroxine structure.   The polymer solid electrolyte film according to claim 1 or 3, wherein the compound having an anion scavenging ability is boron oxide.   The polymer solid electrolyte film according to any one of claims 1 to 3, wherein the electrolyte salt is an alkali metal salt.   The polymer solid electrolyte film according to claim 8, wherein the electrolyte salt is a lithium salt. A battery comprising the polymer electrolyte film according to claim 1.

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