JP5140822B2 - Cation conductive medium using ionic liquid and method for improving cation conductivity in ionic liquid - Google Patents

Description

The present invention, cation-conductive medium containing an ionic liquid and an inorganic oxide powder, and about the upper cation conductivity direction of ionic liquid.

An ionic liquid that is an ionic substance and a liquid at room temperature is non-volatile, non-flammable, and has a relatively high ionic conductivity, so a new electrolyte for electrochemical devices such as secondary batteries and fuel cells. It is attracting attention as a material.
In electrochemical devices, only specific ion conduction is required for the intended reaction, and the ion mobility needs to be increased.

For example, a lithium ion battery is one in which lithium ion conduction is caused to react in an electrolyte solution in which a lithium salt is dissolved, and the ionic liquid is expected as a nonvolatile and nonflammable electrolyte.
However, when lithium ions are added to the ionic liquid, lithium has a small ionic radius, so that lithium ions and anions exhibit a strong electrostatic interaction. As a result, the viscosity of the system increases, the ionic conduction decreases due to viscous resistance, and the electrical conductivity decreases. Because of this phenomenon, the lithium ion conductivity of ionic liquids is insufficient for electrolyte applications of lithium ion batteries, and in lithium ion batteries, methods for improving the conductivity of lithium ions in ionic liquids have not been developed. It is desired.

In addition, the fuel cell conducts and reacts protons through the electrolyte from the fuel electrode to the air electrode, and the ionic liquid is expected to be non-volatile, has high thermal stability, and does not need to be humidified. ing.
However, the proton conductivity of ordinary ionic liquids does not reach the level required for fuel cell applications, and therefore, development of ionic liquids with high proton conductivity is desired in fuel cells.

Patent Document 1 discloses a cation conductive or proton conductive membrane made of a substance-permeable carrier and having an ionic liquid in a void. It is said that an organic ion conductive material or an inorganic ion conductive material may be present in the voids of the film, and examples of the inorganic ion conductive material include inorganic oxides. However, as the inorganic ion conductive material, sulfonic acid or the like is oriented, and the inorganic oxide is merely an example, and there is no description about the specific mode and specific action of the inorganic ion conductive material. In addition, the examples are only membrane production examples, and the effect on cation conductivity or proton conductivity is unknown.
JP-T-2004-515351

In view of the above circumstances, the problem to be solved by the present invention is to provide a cation conductive medium having improved cation conductivity in an ionic liquid.

  As a result of intensive studies by the present inventors, an inorganic oxide powder having a specific specific surface area, the surface of which has a specific charge in terms of zero charge, is added to the ionic liquid. Thus, it has been found that the cation conductivity in the ionic liquid can be remarkably improved.

That is, the present invention contains an ionic liquid and an inorganic oxide powder, the surface charge of the inorganic oxide powder is pH ^{5 to} 13 in terms of zero charge, and the specific surface area is 0.3 to 50 m ² / g. The cation conductive medium is characterized in that the content of the ionic liquid is 10 to 30% by volume .
The present invention, the content of the ionic liquid is, in the cationic conductive medium, preferably from 1 to 70% by volume, the inorganic oxide powder is selected from aluminum oxide, titanium oxide and zirconium bromide or Ranaru group At least one kind is preferable, and the ionic liquid is preferably a combination of a cation represented by the formula (I) described later and a fluorine-based organic anion. These preferred embodiments exhibit very good cation conduction.
In addition, when the cation conductive medium of the present invention is a proton ion conductive medium or a lithium ion conductive medium, it can be applied to a fuel cell, a lithium ion secondary battery, and the like, and is particularly useful.

In addition, the present invention provides an inorganic cation liquid having 10 to 30% by volume of an ionic liquid , a surface charge of pH 5 to 13 in terms of zero charge, and a specific surface area of 0.3 to 50 m ² / g. and characterized by the inclusion of oxide powder, the concentration of ionic liquid cation conducting ionic liquid, a molar fraction be 0.01 to 0.6, very excellent cation This is preferable because the effect of improving the conductivity is exhibited.

According to the onset bright, it is possible to improve the cation conductivity of the ionic liquid. Therefore, the electrical conductivity of the ionic liquid can be improved. In addition, the cation conductive medium of the present invention has characteristics unique to ionic liquids such as non-volatility and non-flammability, and is excellent in cation conductivity, and therefore useful as an electrolyte material for electrochemical devices such as secondary batteries and fuel cells. It is.

The cation conducting medium of the present invention contains an ionic liquid and an inorganic oxide powder, the surface charge of the inorganic oxide powder is pH ^{5 to} 13 in terms of zero charge, and the specific surface area is 0.3 to 50 m ^2. / G and a ionic liquid content of 10 to 30% by volume .

  Although the ionic liquid is said to have high ionic conductivity, especially when a cation with a small ionic radius is added to the ionic liquid, the viscosity of the system increases to show strong electrostatic interaction with the anion, Since viscous resistance hinders the conduction of ions, its cation conductivity was not at a level applicable to electrochemical device applications.

The present inventors have found that when a specific inorganic oxide powder is added to an ionic liquid to which a cation has been added, the cation conductivity is improved. The reason why the cation conductivity is improved may be that an ion conductive layer is formed at the solid-liquid interface between the ionic liquid and the inorganic oxide powder. In fact, when the present inventors performed FT-IR measurement on a composite made of proton, ionic liquid and aluminum oxide powder (see FIG. 1), the ionic liquid only system, inorganic oxide powder was added to the ionic liquid. Absorption due to stretching vibration of OH bond, which was not seen in the added system, appeared in the vicinity of 3600 cm ⁻¹ . From this, if the surface charge of the inorganic oxide powder is within a specific range in terms of zero charge, the added cation is dissociated from the anion as a pair by interaction with the surface. Therefore, it is considered that it exists on the surface. The cations present on the surface of the inorganic oxide powder move smoothly on the surface of the powder only when the inorganic oxide powder has a specific specific surface area. As a result, it is considered that the conductivity of the cation is improved.

  In the present invention, the ionic liquid means a liquid that is in a liquid state at room temperature among melts composed only of ions. Examples of the cation species of the ionic liquid include a cation (aliphatic quaternary ammonium ion) represented by the following formula (I), a cation (phosphonium ion) represented by the formula (II), and a formula (III). Cations (imidazolium ions), cations represented by formula (IV) (pyridinium ions), and the like.

Wherein R ^{1 to} R ¹¹ are the same or different and each represents a saturated aliphatic group, or R ³ and R ⁴ together with the nitrogen atom to which they are bonded form an aliphatic heterocyclic ring However, the sum of the carbon numbers of R ^{1 to} R ⁴ and R ^{5 to} R ⁸ is 6 or more, the sum of the carbon numbers of R ⁹ and R ¹⁰ is 3 or more, and the carbon number of R ¹¹ is 2 or more.)

The saturated aliphatic group represented by R ^{1 to} R ¹¹ may be linear or branched, and examples thereof include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec- Examples include a butyl group, a tert-butyl group, a hexyl group, an octyl group, a decyl group, and the like, and further, a heteroatom such as S or O is bonded to the exemplified group by a bond represented by -S- or -O-. Examples thereof include groups and the like (provided that R ¹¹ has 2 or more carbon atoms). The saturated aliphatic group is preferably an alkyl group having 1 to 8 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms.

Examples of the aliphatic hetero ring formed by R ³ and R ⁴ together with the nitrogen atom to which they are bonded include a pyrrolidine ring, a piperidine ring, a diazepine ring, a piperazine ring, a morpholine ring, and the like. A membered aliphatic heterocycle is preferred.

  Of the cations represented by the above formulas (I) to (IV), the cation represented by the formula (I) is preferable.

As the cation represented by the formula (I), R ¹ and R ² are preferably a methyl group or an ethyl group, R ³ is an alkyl group having 1 to 4 carbon atoms, and R ⁴ is an alkyl group having 1 to 8 carbon atoms. It is a cation which is an alkyl group. The cation represented by formula (I) is particularly preferably a cation (TMPA) in which R ^{1 to} R ³ are methyl groups and R ⁴ is a propyl group; R ¹ and R ² are methyl groups, and R ³ is isopropyl. A cation in which R ⁴ is a hexyl group; R ¹ is a methyl group, R ² and R ³ are ethyl groups, and R ⁴ is a 2-methoxyethyl group.
Further, when R ³ and R ^{4 of the} cation represented by the formula (I) form an aliphatic heterocyclic ring together with the nitrogen atom to which the cation is bonded, the cation represented by the formula (I) Preferably, a cation in which R ¹ is a methyl group, R ² is an ethyl group, and a nitrogen atom to which R ³ and R ⁴ are bonded together forms a pyrrolidine ring; R ¹ is a methyl group, R ² is a butyl group, R A cation (BMP) that forms a pyrrolidine ring together with the nitrogen atom to which ³ and R ⁴ are bonded.

Preferably, as the cation represented by the formula (II), R ⁵ and R ⁶ are each independently a methyl group or an ethyl group, R ⁷ is an alkyl group having 1 to 4 carbon atoms, and R ⁸ is carbon. It is a cation which is an alkyl group of formula 1-8.
The cation represented by the formula (III) is preferably a cation in which R ^{9 to} R ¹⁰ are each independently a C 1-4 alkyl group, particularly preferably R ⁹ is a methyl group, A cation (EMI) in which R ¹⁰ is an ethyl group; a cation (BMI) in which R ⁹ is a methyl group and R ¹⁰ is a butyl group.
The cation represented by the formula (IV) is preferably a cation in which R ¹¹ is an alkyl group having 2 to 8 carbon atoms, and particularly preferably a cation (BP) in which R ¹¹ is a butyl group.

Examples of the anionic species of the ionic liquid include chloroaluminate anions such as AlCl ₄ ⁻ and Al ₂ Cl ₇ ^— ; fluorine inorganic anions such as BF ₄ ⁻ , PF ₆ ⁻ and F (HF) _n ⁻ ; CF _{3 ^{COO -, CF 3 SO 3 -}} (TfO), (CF 3 SO 2) 2 N - (TFSI), (CF 3 SO 2) 3 C - (TFSM) fluorinated organic anions such _as; ^NO _{3 -;} CH 3 COO ^-, and the like. Of these, fluorine-based organic anions are preferred.

  The ionic liquid may be one or a combination of two or more of the above cation species and one or more of the above anion species, but preferably a cation represented by the formula (I) A combination with a fluorine-based organic anion, most preferably a combination of TMPA and TFSI.

  The ionic liquid can be obtained by a known method (for example, see Chem. Lett., 2000, page 922, J. Phys. Chem. B, 103, page 4164 (1999), etc.). May be used.

In the present invention, the inorganic oxide powder needs to have a surface charge on the surface of the particle of pH 5 to 13 in terms of zero charge, and a specific surface area of 0.3 to 50 m ² / g.
Although it has been conventionally known that an ion conductive layer can be formed at the interface of a foreign substance (see, for example, Adv. Matter. 2004, 16, No. 9-10, May 17), in the present invention, inorganic oxidation is performed. The substance powder has a specific surface charge, so that it is possible to dissociate the cation from the anion which is a counter ion in the ionic liquid. By doing so, the ion conductive layer can be formed.

In the present invention, the zero charge point (pzc) is the pH (hydrogen) when the surface of the inorganic oxide powder particles is not charged positively or negatively when the inorganic oxide powder particles are in water. Ion index).
The zero charge point is obtained, for example, as a pH value at the intersection of two titration curves obtained by creating a titration curve using acid and alkali for water and water added with inorganic oxide powder, respectively. Can do.

Examples of inorganic oxide inorganic oxide is pH5~13 in surface charge zero charge point in terms of the powder particles, the aluminum oxide (conventional commercial product, zero charge point corresponding value of surface charge of about 7 to 11 at a), the titanium oxide (usually commercially available, zero charge point corresponding value of the surface charge is about 5-7), the oxide zirconium bromide (conventional commercial product, zero charge point of the surface charge The conversion value is about 5 to 7). Aluminum oxide is particularly preferred from the viewpoint of higher cation conductivity improving effect.
Moreover, it is preferable from the point of the higher cation conductivity improvement effect that the surface charge of the powder particle | grains of an inorganic oxide is pH 7-10 in conversion of a charge zero point.

The zero-point converted value of the surface charge can also be adjusted by treating the inorganic oxide powder with acid, alkali or the like. For example, when the inorganic oxide is immersed in an alkali, the zero-point converted value of the surface charge of the inorganic oxide powder increases to the alkali side. Therefore, titanium oxide commercial products, some of such oxide zirconium chloride, although zero charge point corresponding value of the surface charge is there also of about pH 4, an inorganic oxide such less than zero charge point conversion value pH5 Even when powder is used, the charge to zero point converted value of the surface charge can be adjusted to an appropriate range by the alkali treatment.

In the present invention, the inorganic oxide takes the shape of a powder, but the powder needs to have a specific surface area of 0.3 to 50 m ² / g as a particle size standard, and higher cation conductivity is improved. inorganic oxide powders are preferred specific surface area from the viewpoint of effect is 1.1~32.8m ² / g, the inorganic oxide powder is 2 to 5 m ² / g is more preferable.
In the present invention, the specific surface area means a value determined by the BET method.

  In the cation conductive medium of the present invention, it is preferable that the inorganic oxide powder is impregnated with an ionic liquid. When an inorganic oxide powder material impregnated with an ionic liquid is used, the molding process by compression molding or the like is easy and the convenience is high. The degree of impregnation is preferably impregnated until the surface of the inorganic oxide powder is just covered with the ionic liquid (the inorganic oxide powder appears to be wet with the ionic liquid). This is because the state is suitable for forming the ion conductive layer.

  As a standard of the usage amount of the ionic liquid for obtaining such a state, it is 1 to 70% by volume, preferably 10 to 30% by volume of the ion conductive medium. In addition, when the ionic liquid contains a cation or a salt containing a cation, the volume of the cation or the salt containing the cation is also included in the volume of the ionic liquid.

  Impregnation can be performed by a conventional method, for example, by a method of mixing inorganic oxide powder and ionic liquid using a stirrer or the like.

  In the present invention, the cation of the cation conductive medium means not a cation of the ionic liquid itself constituting the cation conductive medium but a cation added separately to the conductive medium. That is, the present invention is a medium that conducts separately added cations.

The type of cation added and conducted separately is not particularly limited as long as it is a monoatomic cation. If it is a monoatomic cation, the conductivity improvement effect in an ionic liquid will be acquired.
In particular, when a salt composed of a cation with a small ionic radius is added to the ionic liquid, the cation with a small ionic radius has a high charge density, so that it is difficult to ionize in the ionic liquid. Does not occur, and the electrical conductivity of the ionic liquid decreases. Therefore, a cation with a smaller ionic radius is more significant for the effect of the present invention. As the cation conducted by the cation conducting medium of the present invention, alkali metal ions, alkaline earth metal ions, silver ions, transition metal ions and the like are preferable because they can exhibit a particularly high conductivity improving effect. From the viewpoint of application to batteries and secondary batteries, protons and lithium ions are particularly preferable.

In the present invention, the effect of improving cation conductivity can be evaluated by measuring the electric conductivity of a cation conductive medium to which a cation is added. When evaluated by electrical conductivity, the electrical conductivity of the ionic liquid itself is usually the same as when the ionic liquid is added only with a cation such as lithium or when only an inorganic oxide is added. Decrease than degree. Nevertheless, the present invention in which both a cation such as lithium and an inorganic oxide are added to the ionic liquid has the effect of increasing the electrical conductivity.
The electrical conductivity can be measured using, for example, an LCR meter.

Since the cation conductive medium of the present invention exhibits excellent cation conductivity, it can be applied to a battery or the like as a powder electrolyte material according to a known method.
Moreover, since the composite which added said cation to the cation conduction medium of this invention shows the outstanding electrical conductivity, it is useful as an electroconductive material.

In the present invention , in the cation conducting medium, 10 to 30% by volume of an ionic liquid, an inorganic oxidation having a surface charge of pH 5 to 13 in terms of zero charge and a specific surface area of 0.3 to 50 m ² / g by containing Monokotai can increase the cation conductivity of the ionic liquid.

Ionic liquids used in the present onset bright, inorganic oxide anhydride powder, for cation is the same as defined above.
As this onset Ming embodiment, for example, the addition of the cationic to the ionic liquid, manner thereto adding the inorganic oxide powder, blended the inorganic oxide powder in the ionic liquid thereto The aspect etc. which add the said cation are mentioned.

  The cation may be added as it is in the form of ions or may be added in the form of a salt. When added in the form of a salt, there is no particular limitation on the type of anion serving as a counter ion of the cation, and it is preferably the same as the anion species of the ionic liquid, more preferably the anion of the ionic liquid to be used Select the same type of anion as the species.

  The concentration of the cation to be added in the ionic liquid may be appropriately selected according to the kind of the cation to be added, and is preferably 0.01 to 0.6 mol / mol. , A system containing HTFSI and the like) is 0.2 to 0.4 mol / mol, and in the case of a system containing lithium ions (eg, a system containing LiTFSI and the like), 0.03 to 0.06 mol / mol. Mole is most preferred. When the cation concentration is within the above range, the effect of improving the cation conductivity can be obtained particularly well.

According to the onset bright, it is possible to effectively improve the cation conductivity of the ionic liquid, for example, for improving the proton conductivity in the case of using an ionic liquid electrolyte of the fuel cell, also ionic liquids Can be applied to improve the lithium ion conductivity when used as an electrolyte of a lithium ion battery. Further, according to this onset bright, it is possible to improve the electrical conductivity of the ionic liquid containing a cation.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not restrict | limited to these Examples at all.

Examples Preparation of ionic liquid Preparation of trimethylpropylammonium bistrifluorosulfimide (TMPATFSI) was carried out using known literature (eg, Chem. Lett., 2000, page 922, J. Phys. Chem. B, 103, page 4164 ( First, trimethyl n-propylammonium iodide (TMPAI) was obtained by reacting n-propyl iodide with trimethylamine, and an aqueous solution of TMPAI and an aqueous solution of LiTFSI were mixed and washed with water. This was performed until a precipitate derived from by-products such as lithium iodide was not observed even when an aqueous silver nitrate solution was added to the aqueous layer, and the layer separated from the aqueous layer was purified by concentration and heat treatment to obtain TMPATFSI. The water content of TMPATFSI determined by Karl Fischer titration was 0. 08 was less than% by weight.

Preparation of cation-containing ionic liquid HTFSI was added to TMPATFSI in a molar fraction range of 0.1 to 0.6 and dissolved by mixing and heat treatment. Although the water content of HTFSI is less than 1% by weight, it was reduced to about 0.25% by weight under vacuum for several days. The water content of TMPATFSI (HTTFSI / TMPATFSI) containing protons after the heat treatment was 0.2% by weight. The prepared HTFSI / TMPATFSI was stored in a glove box with an air dry purifier filled with dry nitrogen dried with diphosphorus pentoxide.
Moreover, LiTFSI was added to TMPATFSI in the range of 0.02 to 0.15 in terms of molar fraction, and mixed and heated to dissolve. The water content of LiTFSI was less than 1% by weight, but it was reduced to about 0.25% by weight by placing it under vacuum for several days. The water content of TMPATFSI (LiTFSI / TMPATFSI) containing lithium ions after the heat treatment was 0.2% by weight. The prepared LiTFSI / TMPATFSI was stored in a glove box with an air dry purifier filled with dry nitrogen dried with diphosphorus pentoxide.

The specific surface area was determined by preparing the BET method of the inorganic oxide powder, respectively ^{1.18m 2 /g,3.00m 2 / g, 10m} 2 /g,32.8m is _{^{2 / g α-Al 2 O}} 3 The powder was heat treated at a temperature above 400 ° C. for 6 hours.
The α-Al ₂ O ₃ powder was subjected to acid-base titration using 0.1 mol / L hydrochloric acid and a sodium hydroxide aqueous solution, respectively. As a result, the surface charge was 9.1 in terms of zero charge. Met.

Preparation of cation-containing cation-conducting medium sample The cation-containing ionic liquid prepared above and the inorganic oxide powder prepared above were vigorously used in a glove box filled with dry nitrogen at a volume ratio of 30:70 using a mixer. Stir and mix. The obtained mixture was compression-molded using an alumina press under a vacuum at a pressure of 53 MPa for 30 minutes to prepare a tablet-shaped sample having a diameter of 20 mm.

Measurement of electric conductivity The electric conductivity of the tablet-type sample of the cation conductive medium prepared above was measured in a frequency range of 20 to 30 Hz using 4286A and 4285A manufactured by Hured Packard. The electric conductivity was tried by a method of measuring a potential difference between Pt electrodes inserted in the middle chamber of the Hittorf cell, and an IE plot was obtained at 25 ° C. to 50 ° C. and calculated from the slope. The cell constant was calculated at 25 ° C. using a KCl solution.
The obtained results are shown in FIGS.

Comparative Example An SiO ₂ powder having a specific surface area of 7.83 m ² / g determined by the BET method and a surface charge of 3.1 (evaluated by the same method as the α-Al ₂ O ₃ powder) in terms of zero charge, Heat treatment was performed at 800 ° C. for 4 hours. Using the LiTFSI / TMPATFSI prepared in the same manner as in the example and this SiO ₂ powder, a tablet-shaped sample having a diameter of 20 mm was prepared in the same manner as in the above example. About the obtained sample, it carried out similarly to the above, and measured the electrical conductivity.
The obtained results are shown in FIG.

As is clear from FIGS. 2 and 3, it can be seen that the cation conductivity in the ionic liquid is dramatically improved by adding α-Al ₂ O ₃ to the ionic liquid. Moreover, the effect of improving the cation conductivity of ionic liquids, it can be seen that there is a difference by the specific surface area of α-Al ₂ O ₃ powder.
On the other hand, as apparent from the results of FIG. 4, when SiO ₂ powder was used, the cation conductivity in the ionic liquid did not show a cation conductivity higher than that of the ionic liquid. Therefore, it can be seen that in order to improve the cation conductivity in the ionic liquid, the inorganic oxide powder having a surface charge within a specific range must be used.

The cation conductive medium of the present invention can be used as an electrochemical reaction medium in the electrochemical device field, and can be used for sensors, such as batteries, fuel cells, and electrolytic cells .

It is a DR-FTIR spectrum of α-Al ₂ O ₃ / HTFSI / TMPATFSI system measured using an FT-IR measurement apparatus FT-IR 615 (manufactured by JASCO) connecting a diffuse reflection FT-IR measurement cell DR 600B. (A) is HTFSI, (b) is TMPATFSI / α-Al ₂ O ₃ , (c) is TMPATFSI / HTFSI = 6: 4 + α-Al ₂ O ₃ , and (d) is TMPATFSI / HTFSI = 8: 2 + α-Al ₂ O ₃ and (e) show DR-FTIR spectra of composites composed of TMPATFSI / HTFSI = 9: 1 + α-Al ₂ O ₃ , respectively. It is a graph which shows the electrical conductivity of the cation conductive medium of an Example (invention). The horizontal axis represents the concentration of protons in the molar fraction, and the vertical axis represents the electric conductivity. Further, Bulk in the figure means a system to which no inorganic oxide powder is added. It is a graph which shows the electrical conductivity of the cation conductive medium of an Example (invention). The horizontal axis represents the concentration of lithium ions in the molar fraction, and the vertical axis represents the electric conductivity. Further, Bulk in the figure means a system to which no inorganic oxide powder is added. It is a graph which shows the electrical conductivity of the cation conductive medium of a comparative example. The horizontal axis represents the concentration of lithium ions in the molar fraction, and the vertical axis represents the electric conductivity.

Claims (4)

Containing ionic liquid and inorganic oxide powder,
The surface charge of the inorganic oxide powder is pH 5 to 13 in terms of zero charge , the specific surface area is 0.3 to 50 m ² / g ,
And the content of an ionic liquid is 10-30 volume% , The cation conductive medium characterized by the above-mentioned. Inorganic oxide powder, aluminum oxide is at least one selected from titanium oxide and zirconium bromide or Ranaru group, cation-conductive medium according to claim 1. The cation conducting medium according to claim 1 or 2 , wherein the ionic liquid is a combination of a cation represented by formula (I) and a fluorine-based organic anion.
(Wherein R ^{1 to} R ⁴ are the same or different and each represents a saturated aliphatic group, or R ³ and R ⁴ together with the nitrogen atom to which they are bonded form an aliphatic heterocyclic ring) (However, the sum of the carbon numbers of R ^{1 to} R ⁴ is 6 or more.) It is proton ion conductivity or lithium ion conductivity, The cation conductive medium in any one of Claims 1-3 .