WO2013100083A1 - レドックスフロー二次電池及びレドックスフロー二次電池用電解質膜 - Google Patents
レドックスフロー二次電池及びレドックスフロー二次電池用電解質膜 Download PDFInfo
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- WO2013100083A1 WO2013100083A1 PCT/JP2012/083953 JP2012083953W WO2013100083A1 WO 2013100083 A1 WO2013100083 A1 WO 2013100083A1 JP 2012083953 W JP2012083953 W JP 2012083953W WO 2013100083 A1 WO2013100083 A1 WO 2013100083A1
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- H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
- H01M8/1023—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having only carbon, e.g. polyarylenes, polystyrenes or polybutadiene-styrenes
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- C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
- C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
- C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
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Definitions
- the present invention relates to a redox flow secondary battery and an electrolyte membrane for a redox flow secondary battery.
- the redox flow secondary battery stores and discharges electricity, and belongs to a large stationary battery used for leveling the amount of electricity used.
- a redox flow secondary battery is formed by separating an electrolyte containing a positive electrode and a positive electrode active material (positive electrode cell) and a negative electrode electrolyte containing a negative electrode and a negative electrode active material (negative electrode cell) with a diaphragm, and oxidizing both active materials. Charging and discharging is performed using a reductive reaction, and an electrolytic solution containing both active materials is circulated from a storage tank to an electrolytic cell to be used.
- an iron-chromium system for example, an iron-chromium system, a chromium-bromine system, a zinc-bromine system, or a vanadium system utilizing a difference in charge is used.
- vanadium-based secondary batteries have the advantages of high electromotive force, fast electrode reaction of vanadium ions, small amount of hydrogen generation as a side reaction, high output, and so on. .
- the diaphragm is devised so as not to mix the electrolyte containing the active material of both electrodes.
- the conventional diaphragm has a problem that it is easily oxidized and the electric resistance must be sufficiently low.
- permeation of each active material ion contained in the cell electrolyte solution of both electrodes contamination of the electrolyte in the electrolyte solution
- An ion exchange membrane excellent in ion selective permeability that (H + ) is sufficiently permeable is required.
- the oxidation-reduction reaction of (V 5+ ) is used. Therefore, since the electrolyte solution of the positive electrode cell and the negative electrode cell has the same kind of metal ion species, even if the electrolyte solution is mixed through the diaphragm, it is normally regenerated by charging, so compared to other types of metal species Hard to be a big problem. However, since active materials that are wasted increase and current efficiency decreases, it is preferable that active material ions do not permeate the diaphragm as freely as possible.
- Patent Document 1 discloses a polytetrafluoroethylene (hereinafter also referred to as “PTFE”) porous membrane, a polyolefin (hereinafter also referred to as “PO”) porous membrane, a PO nonwoven fabric, etc. as a redox battery diaphragm. Is disclosed.
- PTFE polytetrafluoroethylene
- PO polyolefin
- Patent Document 2 discloses a composite membrane combining a porous membrane and a hydrous polymer for the purpose of improving the charge / discharge energy efficiency of a redox flow secondary battery and improving the mechanical strength of the diaphragm.
- Patent Document 3 for the purpose of improving the charge / discharge energy efficiency of a redox flow secondary battery, a nonporous hydrophilic polymer film having a hydrophilic hydroxyl group excellent in ion permeability is used as a cellulose or ethylene-vinyl alcohol copolymer. A technique using a polymer film is disclosed.
- Patent Document 4 discloses that by using a polysulfone membrane (anion exchange membrane) as a hydrocarbon ion exchange resin, the current efficiency of a vanadium redox secondary battery is 80% to 88.5%, and resistance to radical oxidation. It is also described that it is excellent.
- Patent Document 5 discloses a method of increasing the reaction efficiency by supporting expensive platinum on porous carbon of the positive electrode in order to increase the current efficiency of the redox flow secondary battery.
- Nafion manufactured by DuPont is disclosed.
- N117 and polysulfone-based ion exchange membrane are described as the diaphragm.
- Patent Document 6 discloses an iron-chromium redox flow battery in which a hydrophilic resin is applied to pores of a porous film such as polypropylene (hereinafter also referred to as “PP”).
- a hydrophilic resin is applied to pores of a porous film such as polypropylene (hereinafter also referred to as “PP”).
- PP polypropylene
- Patent Document 7 discloses a vanadium-based redox flow secondary battery in which cell electrical resistance is reduced as much as possible by improving the electrode, such as using a two-layer liquid-permeable porous carbon electrode having a specific surface lattice. An example is disclosed.
- Patent Document 8 discloses a vanadium redox using an anion exchange type diaphragm made of a crosslinked polymer having low membrane resistance, excellent proton permeability and the like, having a pyridinium group, and using N + as a cation.
- An example of a flow battery is disclosed.
- As the crosslinked polymer a polymer obtained by copolymerizing a pyridinium group-containing vinyl polymerizable monomer, a styrene monomer, and a crosslinking agent such as divinylbenzene is disclosed.
- a cation exchange membrane fluorine polymer or other hydrocarbon polymer
- an anion exchange membrane polysulfone type
- a redox flow secondary battery using a membrane having a structure in which membranes such as polymers) are alternately laminated and having a cation exchange membrane disposed on the side of the membrane in contact with the positive electrode electrolyte.
- Patent Document 10 discloses a vinyl heterocyclic ring having two or more hydrophilic groups on a porous substrate made of a porous PTFE resin as a membrane having excellent chemical resistance, low electrical resistance and excellent ion selective permeability.
- a secondary battery using an anion exchange membrane combined with a crosslinked polymer having a repeating unit of a compound (such as vinylpyrrolidone having an amino group) as a diaphragm is disclosed.
- a potential difference when a potential difference is applied, metal cations having a large ionic diameter and charge amount are electrically repelled by cations on the surface of the diaphragm and the metal cation is inhibited from passing through the membrane. It is described that proton (H + ) which is small and monovalent can easily diffuse and permeate a diaphragm having a cation, so that electric resistance is reduced.
- Cited Document 11 discloses an example using Nafion (registered trademark of DuPont) or Gore Select (Gore Select: registered trademark of Gore).
- JP 2005-158383 A Japanese Patent Publication No. 6-105615 JP-A-62-226580 JP-A-6-188005 JP-A-5-242905 JP-A-6-260183 Japanese Patent Laid-Open No. 9-92321 JP-A-10-208767 Japanese Patent Laid-Open No. 11-260390 JP 2000-235849 A Special table 2008-544444
- Patent Document 1 simply thinning the diaphragm is insufficient for improving the ion selective permeability, lowering the electrical resistance derived from the diaphragm, and improving the current efficiency.
- the composite membrane disclosed in Patent Document 2 has high electric resistance, and each ion is not as large as the porous membrane, but has a problem that it diffuses freely, and the current efficiency of the battery is not high.
- the film disclosed in Patent Document 3 also has the same problem as described above and is inferior in oxidation resistance.
- the battery disclosed in Patent Document 4 still has insufficient current efficiency, is inferior in oxidation resistance deterioration in a sulfuric acid electrolyte over a long period of time, and has insufficient durability.
- Cited Document 7 Since the battery disclosed in Cited Document 7 uses a polysulfone-based diaphragm, the ion selective permeability and oxidation resistance deterioration of the diaphragm are not sufficient, and the electric resistance, current efficiency, and durability of the battery are not sufficient.
- the battery disclosed in Patent Document 8 has problems that current efficiency is insufficient, and the characteristics deteriorate when used for a long period of time because of oxidative deterioration.
- the film disclosed in Patent Document 9 has a problem that electrical resistance increases when used for a long period of time. In the battery disclosed in Patent Document 10, it cannot be said that the internal resistance (electrical resistance) of the film is sufficiently low, and oxidation deterioration becomes a problem when used for a long period of time.
- the battery disclosed in the cited document 11 still has room for improvement in terms of reliably preventing the active material ions from permeating through the diaphragm and improving the current efficiency.
- Conventional electrolyte membranes for vanadium redox flow batteries consist of a cell (negative electrode side) containing a majority of vanadium ion ions, which are the active material of the electrolyte solution of both electrodes, and a high electric charge.
- the active material ions are prevented from diffusing, moving and transmitting to the counter electrode (cell), and the proton (H + ) Is selectively transmitted.
- the performance is not sufficient.
- a membrane substrate mainly composed of a hydrocarbon-based resin As a membrane substrate mainly composed of a hydrocarbon-based resin, a simple porous membrane that does not simply have ion-selective permeability that simply isolates the electrolyte containing the electrolyte that plays a leading role in both cells, or has no ion-selective permeability (no For example, a porous membrane substrate having pores, or a porous membrane embedded or coated with a hydrophilic membrane substrate is used.
- cation exchange membranes having various anion groups themselves, or composite membranes in which pores of a porous membrane substrate are coated or embedded with cation exchange resins, similarly, anion exchange membranes in which the membrane itself has cation groups, and the like
- composite membranes in which an anion exchange resin is coated or embedded in a porous membrane base material, a laminated type of a cation exchange membrane and an anion exchange membrane, etc. are used as a diaphragm. Yes.
- An ion-exchange resin diaphragm that sufficiently satisfies the two contradictory properties of electrical resistance (mainly dependent on proton permeability) and metal ion (polyvalent cation) permeability blocking as a main active material as a diaphragm, Furthermore, an ion exchange resin membrane that satisfies long-term acid resistance or deterioration resistance (hydroxy radical resistance) in addition to the above two properties has not been developed so far. Fluorine ion exchange resins also have excellent proton (H + ) permeability and have not been fully studied for contradictory properties of suppressing the permeation of active material ions, resulting in low electrical resistance and high current. A redox flow battery sufficiently satisfying efficiency and long-term oxidation deterioration resistance (hydroxy radical resistance) and an electrolyte membrane therefor have not been developed.
- the present invention has excellent ion selective permeability that can suppress the ion selective permeability of the active material without deteriorating proton (H + ) permeability, and has low electrical resistance.
- An object of the present invention is to provide an electrolyte membrane for a redox flow secondary battery that can realize high current efficiency and also has oxidation resistance (hydroxyl radical resistance) and a redox flow secondary battery using the same.
- the present inventors have achieved excellent ion selective permeability and low electrical resistance by using an electrolyte membrane containing a polymer electrolyte polymer and further having a predetermined reinforcing material.
- the present invention has been completed by discovering that it is possible to achieve high performance, high current efficiency, and resistance to oxidation deterioration (hydroxy radical resistance). That is, the present invention is as follows.
- a positive electrode cell chamber including a positive electrode made of a carbon electrode;
- a negative electrode cell chamber including a negative electrode made of a carbon electrode;
- An electrolyte membrane as a diaphragm for separating and separating the positive electrode cell chamber and the negative electrode cell chamber; Having an electrolytic cell containing
- the positive electrode cell chamber contains a positive electrode electrolyte containing an active material, and the negative electrode cell chamber contains a negative electrode electrolyte containing an active material,
- a redox flow secondary battery that charges and discharges based on a valence change of an active material in the electrolyte solution,
- the electrolyte membrane includes an ion exchange resin composition mainly composed of a polymer electrolyte polymer, A redox flow secondary battery in which the electrolyte membrane has a reinforcing material made of a fluorine microporous membrane.
- a positive electrode cell chamber including a positive electrode made of a carbon electrode;
- a negative electrode cell chamber including a negative electrode made of a carbon electrode;
- An electrolyte membrane as a diaphragm for separating and separating the positive electrode cell chamber and the negative electrode cell chamber; Having an electrolytic cell containing
- the positive electrode cell chamber contains a positive electrode electrolyte containing an active material, and the negative electrode cell chamber contains a negative electrode electrolyte containing an active material,
- a redox flow secondary battery that charges and discharges based on a valence change of an active material in the electrolyte solution,
- the electrolyte membrane includes an ion exchange resin composition mainly composed of a polymer electrolyte polymer, A redox flow secondary battery in which the electrolyte membrane has a reinforcing material made of a nonwoven fabric and / or a hydrocarbon-based microporous membrane.
- a positive electrode cell chamber including a positive electrode made of a carbon electrode;
- a negative electrode cell chamber including a negative electrode made of a carbon electrode;
- An electrolyte membrane as a diaphragm for separating and separating the positive electrode cell chamber and the negative electrode cell chamber; Having an electrolytic cell containing
- the positive electrode cell chamber contains a positive electrode electrolyte containing an active material, and the negative electrode cell chamber contains a negative electrode electrolyte containing an active material,
- a redox flow secondary battery that charges and discharges based on a valence change of an active material in the electrolyte solution,
- the electrolyte membrane includes an ion exchange resin composition mainly composed of a polymer electrolyte polymer, A redox flow secondary battery in which the electrolyte membrane has a reinforcing material made of woven fabric.
- the redox flow secondary battery is a redox flow secondary battery according to any one of [1] to [4], wherein the redox flow secondary battery is a vanadium redox flow secondary battery using a sulfuric acid electrolyte containing vanadium as a positive electrode and a negative electrode electrolyte.
- the electrolyte membrane includes an ion exchange resin composition mainly comprising a fluorine-based polymer electrolyte polymer having a structure represented by the following formula (1) as the polymer electrolyte polymer.
- the redox flow secondary battery according to any one of the above.
- X 1 , X 2 and X 3 each independently represents one or more selected from the group consisting of a halogen atom and a perfluoroalkyl group having 1 to 3 carbon atoms.
- X 4 Represents COOZ, SO 3 Z, PO 3 Z 2 or PO 3 HZ, where Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an amine (NH 4 , NH 3 R 1 , NH 2 R 1 R 2 , NHR 1 R 2 R 3 , NR 1 R 2 R 3 R 4 ), R 1 , R 2 , R 3 and R 4 are each independently selected from the group consisting of an alkyl group and an arene group.
- R 1 and R 2 are each independently a halogen atom, Selected from the group consisting of C 1-10 perfluoroalkyl groups and fluorochloroalkyl groups
- D, e and f each independently represent an integer of 0 to 6 (provided that d, e and f are not 0 at the same time).
- the electrolyte membrane includes an ion exchange resin composition mainly composed of perfluorocarbon sulfonic acid resin (PFSA), which is a fluorine-based polymer electrolyte polymer having a structure represented by the following formula (2) as the polymer electrolyte polymer.
- PFSA perfluorocarbon sulfonic acid resin
- the redox flow secondary battery according to any one of [1] to [6].
- the polymer electrolyte polymer has an equivalent mass EW (dry mass in grams per equivalent of ion exchange groups) of 300 to 1300 g / eq, and the equilibrium water content of the electrolyte membrane is 5 to 80% by mass.
- EW dry mass in grams per equivalent of ion exchange groups
- the redox flow secondary battery as described in any one of [7] to [7].
- the redox flow secondary battery according to 1.
- An ion exchange resin composition mainly comprising a polyelectrolyte polymer, Having a fluorine-based porous membrane as a reinforcing material, Electrolyte membrane for redox flow secondary battery.
- An ion exchange resin composition mainly comprising a polyelectrolyte polymer, Having a reinforcing material comprising a nonwoven fabric and / or a hydrocarbon-based microporous membrane, Electrolyte membrane for redox flow secondary battery.
- An ion exchange resin composition mainly comprising a polyelectrolyte polymer, Having a reinforcement made of woven fabric, Electrolyte membrane for redox flow secondary battery.
- the reinforcing material has a structure impregnated with the polymer electrolyte polymer and substantially blocks an internal volume of the reinforcing material for the redox flow secondary battery.
- the electrolyte membrane for redox flow secondary batteries as described.
- the electrolyte membrane for a redox flow secondary battery includes the ion exchange resin composition mainly comprising a fluorine-based polymer electrolyte polymer having a structure represented by the following formula (1) as the polymer electrolyte polymer.
- the electrolyte membrane for redox flow secondary batteries as described in any one of [13] to [13].
- X 1 , X 2 and X 3 each independently represents one or more selected from the group consisting of a halogen atom and a perfluoroalkyl group having 1 to 3 carbon atoms.
- X 4 Represents COOZ, SO 3 Z, PO 3 Z 2 or PO 3 HZ, where Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an amine (NH 4 , NH 3 R 1 , NH 2 R 1 R 2 , NHR 1 R 2 R 3 , NR 1 R 2 R 3 R 4 ), R 1 , R 2 , R 3 and R 4 are each independently selected from the group consisting of an alkyl group and an arene group.
- the polymer electrolyte polymer has an equivalent mass EW (dry mass in grams per equivalent of ion-exchange groups) of 300 to 1300 g / eq, and the equilibrium water content of the electrolyte membrane is 5 to 80% by mass.
- EW dry mass in grams per equivalent of ion-exchange groups
- the electrolyte membrane for redox flow secondary batteries as described in any one of [15].
- the redox flow secondary battery according to 1.
- the electrolyte membrane for a redox flow secondary battery of the present invention has excellent ion selective permeability. Therefore, it has high proton (hydrogen ion) permeability, low electrical resistance, and can suppress the permeation of active material ions in the electrolytic solution. Furthermore, when a normal hydrocarbon electrolyte is used in order to demonstrate high current efficiency and to exhibit a high oxidative degradation prevention effect for a long time against hydroxy radicals generated in the electrolyte cell in the system, It is possible to suppress the detachment of ionic groups and the collapse phenomenon of the polymer electrolyte.
- the present embodiment a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail.
- this invention is not limited to the following this embodiment.
- the redox flow secondary battery of this embodiment is A positive electrode cell chamber including a positive electrode made of a carbon electrode; A negative electrode cell chamber including a negative electrode made of a carbon electrode; An electrolyte membrane as a diaphragm for separating and separating the positive electrode cell chamber and the negative electrode cell chamber; Having an electrolytic cell containing
- the positive electrode cell chamber contains a positive electrode electrolyte containing an active material
- the negative electrode cell chamber contains a negative electrode electrolyte containing an active material
- a redox flow secondary battery that charges and discharges based on a valence change of an active material in the electrolyte solution
- the electrolyte membrane includes an ion exchange resin composition mainly composed of a polymer electrolyte polymer,
- the electrolyte membrane is a redox flow secondary battery having a predetermined reinforcing material.
- FIG. 1 shows an example of a schematic diagram of a redox flow secondary battery of the present embodiment.
- the redox flow secondary battery 10 in this embodiment includes a positive electrode cell chamber 2 including a positive electrode 1 made of a carbon electrode, a negative electrode cell chamber 4 including a negative electrode 3 made of a carbon electrode, the positive electrode cell chamber 2, and the negative electrode cell.
- An electrolytic cell 6 including an electrolyte membrane 5 as a diaphragm for separating and separating the chamber 4 is provided.
- the positive electrode cell chamber 2 contains a positive electrode electrolyte containing a positive electrode active material
- the negative electrode cell chamber 4 contains a negative electrode electrolyte containing a negative electrode active material.
- the positive electrode electrolyte and the negative electrode electrolyte containing the active material are stored, for example, by the positive electrode electrolyte tank 7 and the negative electrode electrolyte tank 8, and are supplied to each cell chamber by a pump or the like (arrows A and B).
- the current generated by the Redox flow secondary battery may be converted from direct current to alternating current via the AC / DC converter 9.
- a liquid permeable and porous current collector electrode (for negative electrode, for positive electrode) is arranged on both sides of the diaphragm, and when pressed, a negative electrode, a positive electrode,
- a structure in which one of the partitions separated by the diaphragm is a positive electrode cell chamber and the other is a negative electrode cell chamber, and the thickness of both cell chambers is secured by a spacer.
- the positive electrode cell chamber is composed of a sulfuric acid electrolyte containing vanadium tetravalent (V 4+ ) and vanadium pentavalent (V 5+ ).
- the battery is charged and discharged by allowing the cathode electrolyte to flow through the anode cell chamber through the anode electrolyte containing vanadium trivalent (V 3+ ) and vanadium divalent (V 2+ ).
- V 4+ is oxidized to V 5+ because vanadium ions emit electrons in the positive electrode cell chamber, and V 3+ is changed to V 2 by electrons returning through the outer path in the negative cell chamber. Reduced to + .
- protons (H + ) are excessive in the positive electrode cell chamber, while protons (H + ) are insufficient in the negative electrode cell chamber.
- the diaphragm selectively moves excess protons in the positive electrode cell chamber to the negative electrode chamber, thereby maintaining electrical neutrality.
- the reverse reaction proceeds during discharge.
- the battery efficiency (%) at this time is expressed as a ratio (%) obtained by dividing the discharge power amount by the charge power amount. Both power amounts depend on the internal resistance of the battery cell, the ion selectivity of the diaphragm, and other current losses. To do.
- the reduction of the internal resistance of the battery cell improves the voltage efficiency, the improvement of the ion selective permeability of the diaphragm and the reduction of the other current loss improve the current efficiency. Therefore, in the redox flow secondary battery, Become.
- an electrolyte membrane has the reinforcing material which consists of a fluorine-type microporous film.
- the electrolyte membrane has a reinforcing material made of a nonwoven fabric and / or a hydrocarbon-based microporous membrane.
- the electrolyte membrane has a reinforcing material made of a woven fabric.
- mainly means that the corresponding component in the ion exchange resin composition is preferably about 33.3 to 100% by mass, more preferably 40 to 100% by mass, and still more preferably 50 to 99.%. It means that 5 mass% is contained.
- the electrolyte membrane constituting the redox flow secondary battery of the present embodiment includes an ion exchange resin composition mainly composed of a polymer electrolyte polymer.
- Preferred examples of the polymer electrolyte polymer include a fluorine-based polymer electrolyte polymer and a hydrocarbon-based polymer electrolyte polymer described later.
- the fluorine-based polymer electrolyte polymer preferably has a structure represented by the following formula (1).
- the fluoropolymer electrolyte polymer is not particularly limited as long as it has a structure represented by the following formula (1), and may include other structures.
- X 1 , X 2 and X 3 each independently represents one or more selected from the group consisting of a halogen atom and a perfluoroalkyl group having 1 to 3 carbon atoms.
- X 4 Represents COOZ, SO 3 Z, PO 3 Z 2 or PO 3 HZ, where Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an amine (NH 4 , NH 3 R 1 , NH 2 R 1 R 2 , NHR 1 R 2 R 3 , NR 1 R 2 R 3 R 4 ), R 1 , R 2 , R 3 and R 4 are each independently selected from the group consisting of an alkyl group and an arene group.
- R 1 and R 2 are each independently a halogen atom, From the group consisting of a C 1-10 perfluoroalkyl group and a fluorochloroalkyl group Indicating one or more members-option.
- b represents an integer of 0 to 8.
- c represents 0 or 1; d, e and f each independently represent an integer of 0 to 6 (provided that d, e and f are not 0 at the same time). )
- X 1 , X 2 and X 3 are each independently one or more selected from the group consisting of a halogen atom and a perfluoroalkyl group having 1 to 3 carbon atoms.
- the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
- X 1 , X 2 and X 3 are preferably a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms from the viewpoint of chemical stability such as resistance to oxidation and deterioration of the polymer.
- X 4 represents COOZ, SO 3 Z, PO 3 Z 2 or PO 3 HZ as described above.
- X 4 is also referred to as an ion exchange group.
- Z represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or an amine (NH 4 , NH 3 R 1 , NH 2 R 1 R 2 , NHR 1 R 2 R 3 , NR 1 R 2 R 3 R 4 ).
- it does not specifically limit as an alkali metal atom, A lithium atom, a sodium atom, a potassium atom, etc. are mentioned.
- it does not specifically limit as an alkaline-earth metal atom, A calcium atom, a magnesium atom, etc.
- R 1 , R 2 , R 3 and R 4 each independently represent one or more selected from the group consisting of an alkyl group and an arene group.
- X 4 is PO 3 Z 2
- Z may be the same or different.
- X 4 is preferably SO 3 Z from the viewpoint of chemical stability of the polymer.
- R 1 and R 2 each independently represents one or more selected from the group consisting of a halogen atom, a C 1-10 perfluoroalkyl group and a fluorochloroalkyl group.
- examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
- b represents an integer of 0 to 8.
- c represents 0 or 1;
- d, e and f each independently represent an integer of 0 to 6. However, d, e, and f are not 0 at the same time.
- the fluoropolymer electrolyte polymer is preferably a perfluorocarbon sulfonic acid resin (hereinafter also referred to as “PFSA resin”).
- PFSA resin has a main chain composed of a PTFE skeleton chain, a perfluorocarbon as a side chain, and one to two or more sulfonic acid groups in each side chain (some of which may be in a salt form). ) Is a bonded resin.
- the PFSA resin is A repeating unit represented by-(CF 2 -CF 2 )-; It is preferable to contain a repeating unit derived from a compound represented by the following formula (3) or (4), and the repeating unit represented by — (CF 2 —CF 2 ) — (3) or a repeating unit derived from the compound represented by the formula (4).
- [A] represents (CF 2 ) m —SO 3 H (m represents an integer of 0 to 6.
- Formula (4) CF 2 ⁇ CF—O— (CF 2 ) P —CFX (—O— (CF 2 ) K —SO 3 H) or CF 2 ⁇ CF—O— (CF 2 ) P —CFX (— (CF 2 ) L —O— (CF 2 ) m —SO 3 H) (wherein X represents a perfluoroalkyl group having 1 to 3 carbon atoms, P represents an integer of 0 to 12, and K represents L represents an integer of 1 to 5, L represents an integer of 1 to 5, and m represents an integer of 0 to 6. However, K and L may be the same or different, and P, K, and L are simultaneously It will not be 0.)
- the PFSA resin includes a repeating unit represented by — (CF 2 —CF 2 ) — and — (CF 2 —CF (—O— (CF 2 CFXO) n — (CF 2 ) m —SO 3 H.
- n in the repeating unit represented by — (CF 2 —CF (—O— (CF 2 CFXO) n — (CF 2 ) m —SO 3 H)) — is 0, m Is an integer of 1 to 6, or —CF 2 —CF (—O— (CF 2 ) P —CFX (—O— (CF 2 ) K —SO 3 H) — represented by formula (4) And —CF 2 —CF (—O— (CF 2 ) P —CFX (— (CF 2 ) L —O— (CF 2 ) m —SO 3 H) — And the hydrophilicity of the resulting electrolyte membrane tends to increase.
- PFSA perfluorocarbon sulfonic acid resin
- the fluorinated polyelectrolyte polymer represented by the above formula (1) and the PFSA resin having the structure represented by the above formula (2) are the structures represented by the above formula (1) and the above formula (2), respectively. If it has, it will not specifically limit, Other structures may be included.
- the fluorinated polyelectrolyte polymer represented by the above formula (1) and the PFSA resin having the structure represented by the above formula (2) are partially or indirectly between some molecules of the ion exchange group. It may be cross-linked.
- the partial crosslinking is preferable from the viewpoint of controlling solubility and excessive swelling. For example, even if the EW of the fluorine-based polymer electrolyte polymer is about 280, the water solubility of the fluorine-based polymer electrolyte polymer can be reduced (water resistance is improved) by performing the partial crosslinking.
- a fluorine-type polymer electrolyte polymer is a low melt flow area
- the intermolecular entanglement can be increased by the said partial bridge
- Examples of the partial crosslinking reaction include a reaction between an ion exchange group and a functional group or main chain of another molecule, a reaction between ion exchange groups, an oxidation-resistant low molecular compound, an oligomer, or a high molecular substance. In some cases, it may be a reaction with a salt (including an ionic bond with a SO 3 H group) forming substance.
- Examples of the oxidation-resistant low molecular weight compound, oligomer or polymer substance include polyhydric alcohols and organic diamines.
- the molecular weight of the fluorine-based polymer electrolyte polymer in the present embodiment is not particularly limited, but is 0 as a melt flow index (MFI) value measured according to ASTM: D1238 (measurement conditions: temperature 270 ° C., load 2160 g). 0.05 to 50 (g / 10 minutes) is preferable, 0.1 to 30 (g / 10 minutes) is more preferable, and 0.5 to 20 (g / 10 minutes) is even more preferable. preferable.
- MFI melt flow index
- the equivalent weight EW of the fluorine-based polymer electrolyte polymer (dry mass in grams of the fluorine-based polymer electrolyte polymer per equivalent of ion-exchange group) is preferably 300 to 1300 (g / eq), more preferably 350 To 1000 (g / eq), more preferably 400 to 900 (g / eq), and particularly preferably 450 to 750 (g / eq).
- the ion exchange resin composition containing it is excellent in combination with the chemical structure.
- the electrolyte membrane obtained by using the resin composition can impart hydrophilicity, has lower electrical resistance, higher hydrophilicity, and smaller clusters (the ion exchange groups coordinate water molecules and / or Or a large number of adsorbed minute portions), and oxidation resistance (hydroxy radical resistance) and ion selective permeability tend to be further improved.
- the equivalent mass EW of the fluorine-based polymer electrolyte polymer is preferably 300 or more from the viewpoint of hydrophilicity and water resistance of the film, and is 1300 (g / eq) or less from the viewpoint of hydrophilicity and electric resistance of the film. Is preferred.
- the equivalent mass EW of the fluorine-based polymer electrolyte polymer can be measured by salt-substituting the fluorine-based polymer electrolyte polymer and back titrating the solution with an alkaline solution.
- the equivalent mass EW can be adjusted by the copolymerization ratio of the fluorine-based monomer that is a raw material of the fluorine-based polymer electrolyte polymer, the selection of the monomer type, and the like.
- the fluorine-based polymer electrolyte polymer can be obtained, for example, by producing a precursor of a polymer electrolyte polymer (hereinafter also referred to as “resin precursor”) and then hydrolyzing it.
- the fluoropolymer electrolyte polymer is a PFSA resin
- the PFSA resin is represented by, for example, a fluorinated vinyl ether compound represented by the following general formula (5) or (6) and the following general formula (7). It can be obtained by hydrolyzing a PFSA resin precursor comprising a copolymer with a fluorinated olefin monomer.
- Formula (5) CF 2 ⁇ CF—O— (CF 2 CFXO) n —A
- X represents F or a perfluoroalkyl group having 1 to 3 carbon atoms
- n represents an integer of 0 to 5
- A represents (CF 2 ) m -W
- m represents 0.
- Formula (6) CF 2 ⁇ CF—O— (CF 2 ) P —CFX (—O— (CF 2 ) K —W), or CF 2 ⁇ CF—O— (CF 2 ) P —CFX (— ( CF 2 ) L —O— (CF 2 ) m —W)
- X represents a perfluoroalkyl group having 1 to 3 carbon atoms
- P represents an integer of 0 to 12
- K represents an integer of 1 to 5
- L represents an integer of 1 to 5
- W represents a functional group that can be converted to SO 3 H by hydrolysis.
- Formula (7): CF 2 CFZ (In Formula (7), Z represents H, Cl, F, a perfluoroalkyl group having 1
- W which represents a functional group that can be converted to SO 3 H by hydrolysis
- W is not particularly limited, and examples thereof include SO 2 F, SO 2 Cl, and SO 2 Br.
- X CF 3
- W SO 2 F
- Z F.
- the polymer electrolyte polymer precursor can be synthesized by a known means.
- fluorinated olefins such as tetrafluoroethylene (TFE).
- the polymerization method is not particularly limited, and includes a method (solution polymerization) in which the vinyl fluoride compound or the like and a gas of fluorinated olefin are charged and dissolved in a polymerization solvent such as fluorine-containing hydrocarbon and reacted.
- a method of polymerizing vinyl fluoride compound itself as a polymerization solvent without using solvents such as hydrocarbons (bulk polymerization), and reacting with an aqueous solution of surfactant filled with a vinyl fluoride compound and a fluoroolefin gas
- Polymerization method emulsion polymerization
- the suspension stabilizer is charged and suspended in a solution of vinyl fluoride compound and fluorinated olefin gas. How to (suspension polymerization), and the like.
- the fluoropolymer electrolyte polymer precursor may be produced by any of the polymerization methods described above.
- the fluorine-based polymer electrolyte polymer precursor may be a block-like or tapered polymer obtained by adjusting polymerization conditions such as the amount of TFE gas supplied.
- the polymer electrolyte polymer precursor may be prepared by removing impurities generated in the resin molecular structure during the polymerization reaction, or a portion that is structurally susceptible to oxidation (CO group, H bond portion, etc.) by a known method. It may be fluorinated by treatment under.
- a part of an ion exchange group precursor group (for example, SO 2 F group) may be partially imidized (including intermolecular) (such as alkyl imidization).
- the molecular weight of the precursor is measured from the viewpoint of workability in electrolyte polymer synthesis and the strength of the electrolyte membrane according to ASTM: D1238 (measurement conditions: temperature 270 ° C., load 2160 g). ) Value of 0.05 to 50 (g / 10 min).
- a more preferable range of MFI of the fluorine-based polymer electrolyte polymer precursor is 0.1 to 30 (g / 10 minutes), and a more preferable range is 0.5 to 20 (g / 10 minutes).
- the shape of the fluorine-based polymer electrolyte polymer precursor is not particularly limited, but from the viewpoint of increasing the treatment speed in the hydrolysis treatment and acid treatment described later, it is a pellet of 0.5 cm 3 or less or dispersed It is preferably in the form of liquid or powder particles, and among them, it is preferable to use a powdered material after polymerization. From the viewpoint of cost, an extruded film-like fluorine-based polymer electrolyte polymer precursor may be used.
- the method for producing the fluorinated polymer electrolyte polymer of the present embodiment from the resin precursor is not particularly limited. For example, the resin precursor is extruded using a nozzle or a die using an extruder and then hydrolyzed. There is a method in which a hydrolysis treatment is performed after the treatment is performed or the product obtained by polymerization is used in the form of a dispersed liquid or a powder that is precipitated and filtered.
- the method for producing the fluorine-based polymer electrolyte polymer from the precursor is not particularly limited, for example, after the resin precursor is extruded with a nozzle or a die using an extruder, a hydrolysis treatment is performed, There is a method of carrying out a hydrolysis treatment after the polymerized product is produced as it is, that is, in the form of a dispersed liquid, or a powder that is precipitated and filtered. More specifically, the fluorine-based polymer electrolyte polymer precursor obtained as described above and molded as necessary is subsequently immersed in a basic reaction liquid and subjected to a hydrolysis treatment.
- the basic reaction solution used for the hydrolysis treatment is not particularly limited, but is an aqueous solution of an amine compound such as dimethylamine, diethylamine, monomethylamine and monoethylamine, or hydroxide of an alkali metal or alkaline earth metal.
- An aqueous solution of the product is preferable, and an aqueous solution of sodium hydroxide and potassium hydroxide is particularly preferable.
- an alkali metal or alkaline earth metal hydroxide is used, its content is not particularly limited, but it is preferably 10 to 30% by mass with respect to the entire reaction solution.
- the reaction solution further preferably contains a swellable organic compound such as methyl alcohol, ethyl alcohol, acetone, and dimethyl sulfoxide (DMSO). The content of the swellable organic compound is preferably 1 to 30% by mass with respect to the entire reaction solution.
- the fluoropolymer electrolyte polymer precursor is hydrolyzed in the basic reaction liquid, sufficiently washed with warm water or the like, and then acid-treated.
- the acid used for the acid treatment is not particularly limited, but preferred are mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid and trifluoroacetic acid, and a mixture of these acids and water. Is more preferable.
- the said acids may be used individually by 1 type, or may use 2 or more types together.
- the basic reaction solution used in the hydrolysis treatment may be removed in advance before the acid treatment, for example, by treatment with a cation exchange resin.
- the ion exchange group precursor group of the fluorine-based polymer electrolyte polymer precursor is protonated to produce an ion exchange group.
- W in the formula (5) is protonated by acid treatment to become SO 3 H.
- the fluorine-based polymer electrolyte polymer obtained by the hydrolysis and acid treatment can be dispersed or dissolved in a protic organic solvent, water, or a mixed solvent of both.
- the electrolyte membrane constituting the redox flow secondary battery of this embodiment includes an ion exchange resin composition mainly composed of a polymer electrolyte polymer.
- the polymer electrolyte polymer include a hydrocarbon-based polymer electrolyte polymer in addition to the above-described fluorine-based polymer electrolyte polymer.
- the hydrocarbon-based polymer electrolyte polymer include a polysulfone-based polymer and a crosslinked polymer obtained by copolymerizing an anion exchange type having a pyridinium group with a styrene-based polymer and divinylbenzene.
- the polymer electrolyte polymer in the ion exchange resin composition contained in the electrolyte membrane used in the redox flow secondary battery of the present embodiment is not limited to the fluorine polymer electrolyte polymer, but other polymer electrolyte polymers such as hydrocarbons. Also in the case of a high molecular weight polymer, the equivalent mass EW (the dry mass in grams of the polymer electrolyte polymer per equivalent of ion exchange groups) is preferably adjusted to 300 to 1300 (g / eq).
- the equivalent mass EW of the polyelectrolyte polymer is more preferably 350 to 1000 (g / eq), still more preferably 400 to 900 (g / eq), and still more preferably 450 to 750 (g / eq).
- the equivalent mass EW of the polymer electrolyte polymer is preferably 300 (g / eq) or more from the viewpoint of hydrophilicity and water resistance of the membrane, and 1300 (g / eq) from the viewpoint of hydrophilicity and low electrical resistance of the electrolyte membrane. It is preferable that Further, when the EW of the polyelectrolyte polymer is close to the lower limit value, it can be increased by directly or indirectly partially cross-linking a part of the ion exchange groups in the side chain of the polyelectrolyte polymer.
- the molecular electrolyte polymer may be modified to control solubility and excessive swelling.
- Examples of the partial crosslinking reaction include, but are not limited to, for example, a reaction between an ion exchange group and a functional group or main chain of another molecule, a reaction between ion exchange groups, or an oxidation-resistant low molecular compound.
- a crosslinking reaction (covalent bond) through an oligomer or a polymer substance, and the like, and in some cases, it may be a reaction with a salt (including an ionic bond with a SO 3 H group) forming substance.
- Examples of the oxidation-resistant low molecular weight compound, oligomer or polymer substance include polyhydric alcohols and organic diamines.
- the EW of the polymer electrolyte polymer may be about 280 (g / eq). That is, the water solubility should be reduced (water resistance improved) without sacrificing the ion exchange group (in other words, EW) much. Further, even when the polymer electrolyte polymer is in a low melt flow region (polymer region) and there are many intermolecular entanglements, the EW of the polymer electrolyte polymer may be about 280 (g / eq).
- a part of the functional group before hydrolysis of the polymer electrolyte polymer may be partially imidized (including intermolecular) (such as alkyl imidization).
- the equivalent mass EW of the polyelectrolyte polymer can be measured by subjecting the polyelectrolyte polymer to salt substitution and back titrating the solution with an alkaline solution. Specifically, it can measure by the method described in the Example mentioned later.
- the equivalent mass EW of the polymer electrolyte polymer can be adjusted by the copolymerization ratio of the monomers, the selection of the monomer type, and the like.
- the electrolyte membrane for a redox flow secondary battery of the present embodiment includes an ion exchange resin composition
- the ion exchange resin composition mainly includes a polymer electrolyte polymer.
- the content of the polyelectrolyte polymer contained in the ion exchange resin composition is preferably about 33.3 to 100% by mass, more preferably 40 to 100% by mass, and still more preferably 50 to 99.5% by mass. It is.
- the ion exchange resin composition contained in the electrolyte membrane may contain a predetermined material in addition to the polymer electrolyte polymer described above.
- the predetermined material include polyazole compounds, and instead of / in addition to basic polymers (including low molecular weight substances such as oligomers).
- the chemical stability mainly oxidation resistance etc.
- These compounds partially form an ion complex in the form of fine particles or close to molecular dispersion in the ion exchange resin composition to form an ion cross-linked structure.
- the ion exchange resin composition contains a polyazole compound, or instead of / in addition, a basic polymer (oligomer) From the viewpoint of balance of water resistance and electrical resistance.
- Examples of the predetermined material contained in the ion exchange resin composition include polyphenylene ether resin and / or polyphenylene sulfide resin.
- the content of the polyphenylene ether resin and / or polyphenylene sulfide resin in the ion exchange resin composition is preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of the polymer electrolyte polymer described above, from the viewpoint of membrane strength. 0.5 to 10 parts by mass is more preferable, and 1 to 5 parts by mass is even more preferable.
- the polyelectrolyte polymer is a partial salt (0.01 to 5 equivalent% of the total ion exchange group equivalent) with an alkali metal, alkaline earth metal or other radical-degradable transition metal (Ce compound, Mn compound, etc.). Degree) alone or in combination with a basic polymer.
- the fluorine-based polymer electrolyte polymer includes fluorine-based resins (including carboxylic acid, phosphoric acid, etc.) other than the compound represented by the formula (1). Resin or other known fluororesin). When two or more of these resins are used, they may be mixed in a solvent or dispersed in a medium, or resin precursors may be extruded and mixed.
- the fluororesin is preferably contained in an amount of 30 to 50 parts by mass, preferably 10 to 30 parts by mass with respect to 100 parts by mass of the fluoropolymer electrolyte polymer represented by the formula (1) used in the present embodiment. More preferably, it is more preferably 0 to 10 parts by mass.
- the electrolyte membrane constituting the redox flow secondary battery of the present embodiment has an equilibrium water content of preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more. Moreover, as an upper limit, Preferably it is 80 mass% or less, More preferably, it is 50 mass% or less, More preferably, it is 40 mass% or less. When the equilibrium water content of the electrolyte membrane is 5% by mass or more, the electric resistance, current efficiency, oxidation resistance, and ion selective permeability of the electrolyte membrane tend to be good.
- the equilibrium moisture content of the electrolyte membrane is related to 23 ° C. and 50% based on a membrane obtained by forming a predetermined resin composition constituting the electrolyte membrane from a dispersion of water and an alcohol solvent and drying at 160 ° C. or less. It is represented by equilibrium (24 hr left) saturated water absorption (Wc) at humidity (RH).
- the equilibrium moisture content of the electrolyte membrane can be adjusted by the same method as the above-described equivalent mass EW of the polymer electrolyte polymer. Specifically, it can be adjusted by the copolymerization ratio of the monomers of the polymer electrolyte polymer constituting the electrolyte membrane, the selection of the monomer type, and the like.
- the electrolyte membrane for redox flow secondary batteries of this embodiment has a reinforcing material as described above.
- the electrolyte membrane for a redox flow secondary battery of the present embodiment preferably has a structure in which the above-described polymer electrolyte polymer is impregnated in a reinforcing material and the internal volume of the reinforcing material is substantially closed.
- the structure in which the internal volume is substantially closed is a structure in which the polymer electrolyte polymer is impregnated in the internal volume of the reinforcing material and is substantially closed.
- the polymer electrolyte polymer is reinforced. When the material is impregnated, the internal volume of the reinforcing material is blocked by 90% or more.
- the impregnation ratio of the polyelectrolyte polymer into the reinforcing material can be determined as follows.
- the electrolyte membrane was cut along the film thickness direction, and the cross section appearing thereby was observed with a scanning electron microscope (SEM) at a magnification of 30000 to determine the cross-sectional area of the reinforcing material layer. From the obtained image, the void portion and the other portion are binarized, the total area of the void portions is calculated, and the porosity of the reinforcing material layer is obtained by the following formula.
- Polymer impregnation rate of reinforcing material layer (%) 100 ⁇ ⁇ [total void area ( ⁇ m 2 ) / cross-sectional area of reinforcing material layer ( ⁇ m 2 )] ⁇ 100 ⁇
- the polymer electrolyte polymer impregnation ratio of the reinforcing material layer is preferably 80% or more, more preferably 80% to 90%, and further preferably 90% or more.
- the impregnation rate of the polymer electrolyte polymer in the reinforcing material layer is in the above range, when the electrolyte membrane is immersed in the electrolyte solution, the electrolyte solution penetrates into the void portion, and the electrolyte membrane is excessively expanded. There is a tendency that it is possible to suppress an increase in electrical resistance or a decrease in current efficiency after the cycle test.
- a method of adjusting the polymer electrolyte polymer impregnation rate of the reinforcing material layer when preparing a dispersion of the ion exchange resin composition in water and an alcohol solvent, a method of changing the composition ratio of water and alcohol solvent, Examples thereof include a method of changing the addition amount and molecular weight of the surfactant added to the dispersion liquid in order to enhance the impregnation property to the reinforcing material.
- the electrolyte membrane for a redox flow secondary battery of this embodiment has a reinforcing material made of a fluorine microporous membrane as a first embodiment.
- the fluorine-based microporous membrane is not particularly limited as long as the affinity with the fluorine-based polymer electrolyte polymer is good, and examples thereof include a microporous membrane made of polytetrafluoroethylene (PTFE), which is stretched and porous. Polytetrafluoroethylene (PTFE) based membranes are preferred.
- a reinforcing material in which a fluorine-based polymer electrolyte polymer is embedded in the PTFE-based membrane substantially without gaps is more preferable from the viewpoint of the strength of the thin film and the suppression of dimensional changes in the plane (vertical and horizontal) directions.
- the reinforcing material impregnated with the above-mentioned fluorine-based polymer electrolyte polymer is a reinforcing material comprising an appropriate amount of a dispersion of an ion exchange resin composition having an appropriate concentration in an organic solvent or alcohol-water as a solvent, and comprising a fluorine-based microporous membrane. It can be obtained by impregnating and drying.
- the solvent used in the production of the reinforcing material impregnated with the fluorine-based polymer electrolyte polymer is not particularly limited.
- a solvent having a boiling point of 250 ° C. or lower is preferable, and a boiling point is more preferable.
- water and aliphatic alcohols are preferable, and specific examples include water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol.
- the said solvent may be used by a single solvent, or may use 2 or more types together.
- the method for producing a PTFE microporous membrane suitably used as a reinforcing material composed of a fluorine-based microporous membrane is not particularly limited, but is preferably an expanded PTFE microporous membrane from the viewpoint of suppressing dimensional change of the electrolyte membrane.
- a method for producing an expanded PTFE microporous membrane for example, known methods as disclosed in JP-A-51-30277, JP-A-1-01876, JP-A-10-30031 and the like are known. Can be mentioned.
- a liquid lubricant such as solvent naphtha and white oil is added to fine powder obtained by coagulating an aqueous PTFE emulsion polymerization dispersion, and paste extrusion is performed in a rod shape. Thereafter, this rod-like paste extrudate (cake) is rolled to obtain a PTFE green body.
- the green tape at this time is stretched at an arbitrary magnification in the longitudinal direction (MD direction) and / or the width direction (TD direction). At the time of stretching or after stretching, the liquid lubricant filled at the time of extrusion can be removed by overheating or extraction to obtain a stretched PTFE microporous membrane.
- Reinforcing materials made of a fluorine-based microporous membrane are known additives such as non-fibrinated materials (for example, low molecular weight PTFE), ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments as necessary. May be contained within a range that does not impair the achievement and effects of the present invention.
- non-fibrinated materials for example, low molecular weight PTFE
- ultraviolet absorbers for example, low molecular weight PTFE
- light stabilizers for example, antistatic agents, antifogging agents, and coloring pigments as necessary. May be contained within a range that does not impair the achievement and effects of the present invention.
- the reinforcing material composed of the fluorine-based microporous membrane preferably has a pore distribution center (peak) in the range of pore diameters of 0.08 ⁇ m to 5.0 ⁇ m, more preferably 0.1 to 4.0 ⁇ m. More preferably, it is in the range of 0.3 to 3.0 ⁇ m.
- the pore distribution of the fluorine-based microporous membrane refers to a value measured by a bubble point half dry method using a bubble point method described in JIS-K-3832.
- the distribution center of the pore diameter is 0.08 ⁇ m or more, it is easy to fill with an additive or an electrolyte solution having a hydrogen peroxide suppression effect and the like, and it is possible to suppress the generation of voids in the electrolyte membrane, and the polymer electrolyte polymer is sufficient. Therefore, the processability tends to be excellent. If the distribution center of the pore diameter is 5.0 ⁇ m or less, the dimensional change of the electrolyte membrane can be suppressed, and a sufficient membrane reinforcing effect tends to be obtained.
- the distribution center of the pore distribution of the reinforcing material composed of the fluorine-based microporous membrane is preferably 0.1 ⁇ m or more, more preferably 0.3 ⁇ m or more, and More preferably, it is 5 ⁇ m or more, and even more preferably 0.7 ⁇ m or more.
- the distribution center of the pore distribution of the fluorine-based microporous membrane is preferably 4.5 ⁇ m or less, more preferably 4.0 ⁇ m or less, and more preferably 3.5 ⁇ m. Or less, more preferably 3.0 ⁇ m or less.
- the pore distribution of the reinforcing material composed of the fluorine-based microporous membrane is such that the amount of pores having a pore diameter of 0.08 ⁇ m to 5.0 ⁇ m in the fluorine-based microporous membrane is 0.5 or more (quantity ratio). It is preferable.
- the “abundance of pores” in the microporous membrane means a pore diameter measurement range of 0.065 ⁇ m to 10.0 ⁇ m by the bubble point half dry method using the bubble point method described in JIS-K-3832. The ratio of the number of pores existing in the range of the pore diameter of 0.08 ⁇ m to 5.0 ⁇ m to the total number of pores of the microporous membrane measured.
- the amount of pores having a pore size of 0.08 ⁇ m to 5.0 ⁇ m in the fluorine-based microporous membrane is adjusted to be 0.5 or more (quantity ratio)
- the pore size of the fluorine-based microporous membrane is relatively uniform. Therefore, it becomes easy to uniformly fill the polymer electrolyte polymer in the voids of the fluorine-based microporous membrane.
- the polyelectrolyte polymer contains an additive, the additive can be uniformly dispersed in the electrolyte membrane, so voids are unlikely to occur in the electrolyte membrane, and the electrolyte membrane tends to exhibit high chemical durability. is there.
- the pores of the fluorine-based microporous membrane are not blocked by the additive by increasing the pore size of the fluorine-based microporous membrane to the same or larger than the median diameter of the additive.
- the pore diameter of the reinforcing material comprising a fluorine-based microporous membrane: 0.08 ⁇ m to 5.0 ⁇ m is more preferably 0.7 or more, and even more preferably 0.8 or more. 0.9 or more is even more preferable, and 1 is even more preferable.
- the abundance (quantity ratio) of pores having a pore diameter of 0.5 ⁇ m to 5.0 ⁇ m of the reinforcing material made of a fluorine-based microporous membrane is preferably 0.5 or more, more preferably 0.7 or more, Preferably it is 0.8 or more, still more preferably 0.9 or more, and particularly preferably 1.
- the abundance (quantity ratio) of pores having a pore diameter of 0.7 ⁇ m to 5.0 ⁇ m of the reinforcing material comprising a fluorine-based microporous membrane is preferably 0.5 or more, more preferably 0.7 or more, Preferably it is 0.8 or more, still more preferably 0.9 or more, and particularly preferably 1.
- the reinforcing material made of a fluorine-based microporous membrane preferably has at least two distribution centers in the pore distribution.
- the distribution center having a large pore diameter plays a role of promoting discharge of reaction product water and easy filling of additives (ii) ) Since the distribution center with a small pore diameter has a part that plays a role of suppressing the volume swelling of the electrolyte by the mechanical strength of the microporous membrane, the electrolyte membrane including this fluorine-based microporous membrane is chemically It tends to be easy to achieve both physical durability and physical durability.
- the pore diameter of the reinforcing material made of a fluorine-based microporous membrane is the type of lubricant, the dispersibility of the lubricant, the stretching ratio of the microporous membrane, the lubricant extraction solvent, the heat treatment temperature, the heat treatment time, the extraction time, and the extraction.
- the numerical value can be adjusted to the above range depending on the temperature.
- the reinforcing material composed of the fluorine-based microporous membrane may be a single layer or may be composed of multiple layers as necessary. From the standpoint that defects do not propagate even when defects such as voids and pinholes occur in each single layer, a multilayer is preferable. On the other hand, from the viewpoint of the filling property of the polymer electrolyte polymer and the additive, a single layer is preferable. Examples of the method for forming a fluorine-based microporous film as a multilayer include a method of bonding two or more single layers by thermal lamination, a method of rolling a plurality of cakes, and the like.
- the fluorine-based microporous membrane preferably has an elastic modulus of at least one of a machine flow direction (MD) and a direction perpendicular to the machine flow direction (MD) of 1000 MPa or less, more preferably 500 MPa or less. More preferably, it is 250 MPa or less.
- MD machine flow direction
- the elastic modulus of the fluorine-based microporous membrane refers to a value measured in accordance with JIS-K7113.
- Proton conduction in the polymer electrolyte polymer is made possible by the polymer electrolyte polymer absorbing water and hydrating the ion exchange groups. Therefore, the conductivity at the same humidity increases as the ion exchange group density increases and the ion exchange capacity increases. Also, the higher the humidity, the higher the conductivity.
- the polyelectrolyte polymer exhibits high conductivity even under low humidity, but has a problem of extremely containing water under high humidity.
- starting and stopping are usually performed once or more once a day, but the electrolyte membrane repeats swelling and shrinking due to a change in humidity at that time. It is negative in terms of both performance and durability that the electrolyte membrane repeats such wet and dry dimensional changes.
- the ion exchange capacity of the polymer electrolyte polymer is high, the polymer electrolyte is easily hydrated, and when the electrolyte membrane is formed as it is, the wet and dry dimensional change is large.
- the elastic modulus of the reinforcing material composed of the fluorine-based microporous membrane is preferably 1 to 1000 MPa, more preferably 10 to 800 MPa, and further preferably 100 to 500 MPa.
- the reinforcing material composed of the fluorine-based microporous membrane preferably has a porosity of 50% to 90%, more preferably 60% to 90%, and still more preferably 60% to 85%. Even more preferably, it is 50% to 85%.
- the porosity of the reinforcing material made of a fluorine-based microporous membrane is a value measured by a mercury porosimeter (for example, manufactured by Shimadzu Corporation, trade name: Autopore IV 9520, initial pressure of about 20 kPa) by a mercury intrusion method.
- the porosity of the reinforcing material made of a fluorine-based microporous membrane depends on the number of holes, the hole diameter, the hole shape, the draw ratio, the amount of liquid lubricant added, and the type of liquid lubricant in the reinforcing material made of a fluorine-based microporous film.
- the numerical value can be adjusted to the above range.
- a means for increasing the porosity of the reinforcing material made of a fluorine-based microporous membrane for example, a method of adjusting the amount of liquid lubricant added to 5 to 50% by mass can be mentioned.
- the moldability of the resin constituting the reinforcing material composed of the fluorine-based microporous film is maintained and the plasticizing effect is sufficient.
- the fibers of the resin constituting the reinforcing material can be highly fibrillated in the biaxial direction, and the draw ratio can be increased efficiently.
- examples of means for lowering the porosity include reducing the amount of the liquid lubricant and reducing the draw ratio.
- the reinforcing material comprising a fluorine-based microporous membrane preferably has a thickness of 0.1 ⁇ m to 50 ⁇ m, more preferably 0.5 ⁇ m to 30 ⁇ m, still more preferably 1.0 ⁇ m to 20 ⁇ m, and 2.0 ⁇ m. Even more preferably, it is ⁇ 20 ⁇ m.
- the film thickness is in the range of 0.1 ⁇ m to 50 ⁇ m, the polymer electrolyte polymer can fill the pores in the reinforcing material composed of the fluorine-based microporous film, and the dimensional change of the electrolyte film tends to be suppressed.
- the film thickness of the reinforcing material composed of the fluorine-based microporous film is determined by, after allowing the film constituting the reinforcing material to stand sufficiently in a constant temperature and humidity room of 50% RH, A value measured using a product name “B-1” manufactured by Toyo Seiki Seisakusho.
- the film thickness of the reinforcing material made of a fluorine-based microporous membrane should be adjusted to the above range according to the solid content of the cast solution, the amount of extruded resin, the extrusion rate, and the stretch ratio of the reinforcing material made of the fluorine-based microporous membrane. Can do.
- the reinforcing material composed of the fluorine-based microporous film is further subjected to heat setting treatment to reduce shrinkage.
- shrinkage of the reinforcing material composed of the fluorine-based microporous membrane in a high temperature atmosphere can be reduced, and the dimensional change of the electrolyte membrane can be reduced.
- the heat fixation can be performed on a reinforcing material composed of a fluorine-based microporous film by relaxing a stress in the TD (width direction) direction within a temperature range below the melting point of the fluorine-based microporous film raw material with a TD (width direction) tenter, for example.
- a preferable stress relaxation temperature range is 200 ° C. to 420 ° C.
- the reinforcing material composed of the fluorine-based microporous film may be subjected to surface treatment such as application of a surfactant or chemical modification, as long as the problems and effects of the present invention are not impaired.
- surface treatment such as application of a surfactant or chemical modification, as long as the problems and effects of the present invention are not impaired.
- the electrolyte membrane for a redox flow secondary battery of this embodiment has a reinforcing material made of a nonwoven fabric and / or a hydrocarbon-based microporous membrane as a second form.
- the nonwoven fabric is not particularly limited as long as the affinity with the polymer electrolyte polymer is good, and is not limited to the following.
- polyester fiber, glass fiber, aramid fiber, polyphenylene sulfide fiber, nanofiber fiber Non-woven fabric made of nylon fiber, cellulose fiber, vinylon fiber, polyolefin fiber, rayon fiber and the like.
- a polyester fiber is preferable, and in particular, a polymer composed of a structural unit represented by the following general formula (I), and an aromatic liquid crystal polyester classified as a thermotropic liquid crystal polyester Is preferred.
- the ratio of m and n is arbitrary, and either a homopolymer or a copolymer may be used. Further, it may be a random polymer or a block polymer.
- the film thickness of the nonwoven fabric is not particularly limited, but is preferably 5 to 50 ⁇ m, more preferably 10 to 50 ⁇ m. If the thickness of the non-woven fabric is 50 ⁇ m or less, the electric resistance tends to decrease and the battery performance tends to improve. If the thickness is 5 ⁇ m or more, defects such as breakage may occur during the process of impregnating the fluoropolymer electrolyte polymer. Is small and the mechanical properties tend to be sufficient.
- the porosity of the nonwoven fabric is not particularly limited, but is preferably 40 to 95%, more preferably 50 to 90%, and further preferably 60 to 80%.
- the porosity of the nonwoven fabric is 95% or less, the durability of the battery tends to improve as the dimensional stability of the electrolyte membrane improves.
- the porosity is 40% or more, the ion conductivity as the electrolyte membrane improves. Tend to.
- the raw material for the hydrocarbon-based microporous membrane is not particularly limited.
- a polyamide resin, a polyimide resin, a polyolefin resin, a polycarbonate resin or the like can be used alone or a mixture thereof. From the viewpoint, it is preferable to use a polyolefin resin as a raw material.
- polystyrene resin used as a raw material for the hydrocarbon-based microporous membrane
- a polymer containing propylene or ethylene as a main monomer component is preferable.
- This polyolefin resin may be composed of only the above main monomer components, but may further contain monomer components such as butene, pentene, hexene, 4-methylpentene.
- polyolefin resins include ultra high molecular weight polyethylene (UHMWPE), high density polyethylene (HDPE), medium density polyethylene, low density polyethylene (LDPE), and linear low density obtained using Ziegler multisite catalysts.
- Polyethylene such as polyethylene and ultra-low density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene polymer obtained using a single site catalyst, and copolymer with other monomers copolymerizable with propylene (Propylene-ethylene copolymer, propylene-ethylene- ⁇ -olefin copolymer, etc.).
- the above polyolefin resins may be used alone or in combination.
- polyethylene is preferable from the viewpoint of moldability of the hydrocarbon-based microporous membrane, more preferably ultra high molecular weight polyethylene or high density polyethylene, and still more preferably ultra high molecular weight polyethylene.
- the weight average molecular weight is preferably 1 ⁇ 10 5 or more, more preferably 3 ⁇ 10 5 or more, and still more preferably.
- Ultra high molecular weight polyethylene of 5 ⁇ 10 5 or more and 5 ⁇ 10 5 to 15 ⁇ 10 6 is particularly preferable.
- polypropylene is preferable.
- the hydrocarbon-based microporous film preferably has a multilayer structure.
- a multilayer structure means a puff pastry-like multilayer structure in which resin layers and air layers are alternately stacked in the thickness direction. That is, the hydrocarbon-based microporous membrane has a multilayer structure in which two layers, three layers, four layers,... Are laminated like a pie dough, and a conventional microporous membrane having a three-dimensional network structure; Is different.
- the hydrocarbon-based microporous membrane having a multilayer structure is used, the dimensional change stability and mechanical strength of the electrolyte membrane are further improved compared to the case of using a conventional microporous membrane having a three-dimensional network structure. be able to.
- the “air layer” is a space between resin layers adjacent to each other in the film thickness direction (between pie dough).
- the mechanism for further improving the dimensional change stability and mechanical strength of the electrolyte membrane by using a hydrocarbon-based microporous membrane having a multilayer structure is considered as follows.
- the polymer electrolyte polymer filled in the hydrocarbon-based microporous membrane can stop the propagation of deterioration of the polymer electrolyte at the interface with the hydrocarbon-based microporous membrane.
- the water content of the molecular electrolyte polymer is high, it may not be able to withstand the stress due to the volume change of the polyelectrolyte polymer that has been remarkably increased, and part of the hydrocarbon microporous film may undergo creep deformation.
- the hydrocarbon-based microporous membrane has a single-layer structure, the effect of suppressing dimensional change is reduced from the creep-deformed location, the deterioration of the electrolyte membrane is accelerated, and the mechanical strength is reduced. As a result, durability cannot be expressed. There is a case.
- the hydrocarbon-based microporous membrane has a multilayer structure, the details are not detailed, but it is possible to appropriately diffuse the stress due to the volume change of the polymer electrolyte. Due to the above estimated mechanism, even higher durability can be achieved by combining the hydrocarbon-based microporous membrane having a multilayer structure with the electrolyte polymer.
- the sol-formed composition thus obtained is formed into a tape at a temperature equal to or higher than the gelation temperature, and the tape-like product is rapidly cooled below the gelation temperature to produce a gelled sheet.
- the gelled sheet is stretched uniaxially or biaxially at a temperature equal to or higher than the glass transition temperature of the polyolefin resin, and then heat-set, whereby a polyolefin microporous film having a multilayer structure can be produced.
- the gelling solvent when the polyolefin resin is polyethylene, usually, decalin (decahydronaphthalene), xylene, hexane, paraffin and the like can be mentioned.
- the gelation solvent may be a mixture of two or more solvents.
- the layer spacing of the air layer of the hydrocarbon-based microporous membrane is preferably 0.01 ⁇ m to 20 ⁇ m from the viewpoint of layer spacing retention and moldability.
- the air layer spacing is more preferably 0.01 ⁇ m to 10 ⁇ m, still more preferably 0.05 ⁇ m to 5 ⁇ m, and even more preferably 0.1 ⁇ m to 3 ⁇ m.
- the layer interval of the air layer can be observed by a cross-sectional photograph of a scanning electron microscope (SEM).
- a reinforcing material in which an ion exchange resin composition mainly composed of a polymer electrolyte polymer is embedded in a non-woven fabric and / or a hydrocarbon-based microporous membrane with substantially no gaps is used in view of the strength of the thin film and dimensions in the plane (vertical and horizontal) directions. From the viewpoint of suppressing changes, it is more preferable.
- the reinforcing material is dried by immersing an appropriate amount of a dispersion of an ion exchange resin composition in an organic solvent or alcohol-water as a solvent in a nonwoven fabric and / or a hydrocarbon-based microporous membrane. Can be obtained.
- the solvent used for producing the reinforcing material is not particularly limited, but a solvent having a boiling point of 250 ° C. or lower is preferable, a solvent having a boiling point of 200 ° C. or lower is more preferable, and a boiling point of 120 ° C. or lower is more preferable. It is a solvent. Of these, water and aliphatic alcohols are preferable, and specific examples include water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol.
- the said solvent may be used by a single solvent, or may use 2 or more types together.
- the nonwoven fabric and / or hydrocarbon-based microporous membrane used as a reinforcing material for the electrolyte membrane may be subjected to surface treatment.
- the subsequent impregnation of the polymer electrolyte can be suitably performed.
- Examples of such surface treatment include corona discharge treatment, ultraviolet irradiation treatment, and plasma treatment.
- the surface of the substrate is wetted in advance with the solvent used in the impregnation solution, or the impregnation solution is diluted and applied, or a solution such as a basic polymer is used. May be applied to the substrate in advance.
- the electrolyte membrane has a reinforcing material made of a nonwoven fabric and / or a hydrocarbon-based microporous membrane, the strength is improved, and further, a dimensional change in the plane (vertical and horizontal) direction can be suppressed.
- the dimensional change in the surface direction of the electrolyte membrane is preferably 20% or less, and more preferably 15% or less. When the dimensional change in the surface direction of the electrolyte membrane is 20% or less, the stress on the battery cell tends to be small and the durability tends to be improved.
- the breaking strength of the electrolyte membrane is preferably 200 kgf / cm 2 or more, more preferably 300 kgf / cm 2 or more.
- the breaking strength of the electrolyte membrane is 200 kgf / cm 2 or more, the dimensional change tends to be easily suppressed.
- the electrolyte membrane for a redox flow secondary battery of the present embodiment has a reinforcing material made of a woven fabric as a third form.
- the woven fabric is not particularly limited as long as the affinity with the polymer electrolyte polymer is good.
- fluorine fiber polyester fiber, glass fiber, aramid fiber, polyphenylene sulfide fiber, nanofiber fiber, nylon fiber, cellulose fiber.
- woven fabric made of vinylon fiber, polyolefin fiber, rayon fiber and the like.
- fluorine fibers are preferable, and among them, PTFE fibers are preferable.
- the method for producing the reinforcing material made of woven fabric is not particularly limited, and examples thereof include plain weave, oblique weave, and satin weave.
- the fiber used for the woven fabric may be a filament or a multifilament. In the case of a multifilament, the cross section of the yarn can be flattened. This is preferable because the increase in resistance can be reduced.
- the thickness of the reinforcing material made of woven fabric is not particularly limited, but is preferably 5 to 50 ⁇ m, more preferably 10 to 50 ⁇ m.
- the thickness of the reinforcing material made of woven fabric is 50 ⁇ m or less, the electric resistance tends to decrease and the battery performance tends to be improved. There is little possibility that the defect will occur, and the mechanical characteristics tend to be sufficient.
- the porosity of the reinforcing material made of woven fabric is not particularly limited, but is preferably 40 to 95%, more preferably 50 to 90%, and further preferably 60 to 80%.
- the porosity of the woven fabric is 95% or less, the durability of the battery tends to improve as the dimensional stability of the electrolyte membrane improves.
- the porosity is 40% or more, the ionic conductivity as the electrolyte membrane is high. It tends to improve.
- the method for producing the electrolyte membrane is not particularly limited, and a known extrusion method or cast film formation can be used.
- the electrolyte membrane may be a single layer or a multilayer (2 to 5 layers). In the case of a multilayer, it is possible to improve the performance of the electrolyte membrane by laminating films having different properties (for example, EW and resins having different functional groups). it can. In the case of a multilayer, it may be laminated at the time of extrusion film formation or casting, or the obtained respective films may be laminated.
- the electrolyte membrane formed by the above method is thoroughly washed with water (or treated with dilute aqueous acidic liquid such as hydrochloric acid, nitric acid, sulfuric acid, etc., if necessary) to remove impurities.
- the film is preferably heat-treated in air (preferably in an inert gas) at 130 to 200 ° C., preferably 140 to 180 ° C., more preferably 150 to 170 ° C. for 1 to 30 minutes.
- the heat treatment time is more preferably 2 to 20 minutes, further preferably 3 to 15 minutes, and particularly preferably about 5 to 10 minutes.
- water resistance is particularly desirable for the purpose of entanglement between the particles and molecules. It is useful to stabilize the water absorption (particularly the ratio of hot water-soluble components), stabilize the water absorption rate of water, and generate stable clusters. It is also useful from the viewpoint of improving the film strength. This is particularly useful when a cast film forming method is used.
- Another reason is that by forming minute intermolecular cross-links between the molecules of the polymer electrolyte polymer, it contributes to water resistance and stable cluster formation, and further makes the cluster diameter uniform and small. This is because there is an effect.
- the ion exchange group of the polyelectrolyte polymer in the ion exchange resin composition reacts at least partially with the active reaction site (such as an aromatic ring) of other additive (including resin) components. Then, through this, minute cross-links are generated and stabilized (especially due to the reaction of ion-exchange groups existing in the vicinity of other resin components that are dispersed additives).
- the degree of this crosslinking is preferably 0.001 to 5%, more preferably 0.1 to 3%, and still more preferably 0.2 to 0.2% in terms of EW (degree of EW reduction before and after heat treatment). About 2%.
- the electrolyte membrane constituting the redox flow secondary battery in the present embodiment has excellent ion selective permeability, low electrical resistance, and excellent durability (mainly, hydroxyl radical oxidation resistance). Excellent performance as a diaphragm for secondary batteries.
- each physical property in this specification can be measured according to the method described in the following Examples, unless otherwise specified.
- MFI Melt flow index
- Pore distribution of reinforcing material The pore distribution of the microporous membrane constituting the reinforcing material was measured as follows. First, a microporous membrane sample was cut into a size of ⁇ 25 mm, and measurement was performed using a through pore distribution / gas, fluid permeability analyzer (manufactured by Xonics Corporation, apparatus name: Porometer 3G).
- the measurement of this apparatus complies with the bubble point method described in JIS-K-3832, and after first completely filling the pore volume of the microporous membrane with a test-dedicated liquid (porofil (registered trademark)), By gradually increasing the pressure applied to the porous membrane, the pore distribution was determined from the surface tension of the test liquid, the pressure of the applied gas, and the supply flow rate (bubble point half-dry method).
- the pore distribution of the microporous membrane was measured in a pore measurement range: 0.065 ⁇ m to 10.0 ⁇ m, flow rate gas: compressed air, and the distribution center of the pore distribution was determined. Further, the abundance ratio of the pores was calculated by the following formula.
- the wet membrane sample which absorbed water and expanded was taken out from the hot water, and each dimension in the planar direction (longitudinal (MD) direction and width (TD) direction) was measured. Taking each dimension in the planar direction in the dry state as a reference, the average of the increment of each dimension in the planar direction in the wet state from each dimension in the dry state was taken as the dimensional change (%) in the planar direction.
- a redox flow secondary battery has a liquid-permeable porous current collector electrode (for negative electrode and positive electrode) arranged on both sides of a diaphragm (electrolyte film), sandwiched by pressure, and separated by a diaphragm.
- a diaphragm electrolyte film
- the positive electrode cell chamber is composed of a sulfuric acid electrolyte containing vanadium tetravalent (V 4+ ) and pentavalent (V 5+ ), and the negative electrode cell chamber is composed of vanadium trivalent (V 3+ ) and the same.
- a negative electrode electrolyte containing divalent (V 2+ ) was circulated to charge and discharge the battery.
- An aqueous electrolyte solution having a total vanadium concentration of 2 M / L and a total sulfate radical concentration of 4 M / L is used, and the thickness of each of the installed positive and negative electrode cell chambers is 5 mm.
- Both porous electrodes and diaphragms (electrolytes)
- a porous felt made of carbon fiber having a thickness of 5 mm and a bulk density of about 0.1 g / cm 3 was sandwiched between them.
- the charge / discharge experiment was conducted at a current density of 80 mA / cm 2 .
- the current efficiency (%) was obtained by calculating a ratio (%) obtained by dividing the discharge electricity amount by the charge electricity amount.
- Both quantities of electricity depend on the ion selective permeability of the diaphragm and other current losses.
- a decrease in internal resistance, that is, cell electrical resistivity, improves voltage efficiency, and an improvement in ion selective permeability and other reductions in current loss increase current efficiency, and are therefore an important indicator in redox flow secondary batteries.
- the cell electrical resistivity was determined by measuring the DC resistance value at an AC voltage of 10 mV and a frequency of 20 kHz at the start of discharge using the AC impedance method, and multiplying this by the electrode area. About the said current efficiency and cell electrical resistivity, both the initial value and the value after implementing a charging / discharging test 200 cycles were calculated
- Polymer impregnation rate of reinforcing material layer (%) 100 ⁇ ⁇ [total void area ( ⁇ m 2 ) / cross-sectional area of reinforcing material layer ( ⁇ m 2 )] ⁇ 100 ⁇
- the case of 95% or more was evaluated as “A”
- the case of 90% or more and less than 95% was evaluated as “B”
- the case of less than 90% was evaluated as “C”.
- TFE tetrafluoroethylene
- the TFE gas is continuously supplied to keep the pressure of the autoclave at 0.7 MPa, which corresponds to 0.70 times in mass ratio with respect to the supplied TFE.
- the amount of CF 2 ⁇ CFO (CF 2 ) 2 —SO 2 F is continuously supplied for polymerization, and the polymerization conditions are adjusted to an optimum range to obtain a perfluorocarbon sulfonic acid (PFSA) resin precursor powder. It was.
- the melt flow index (MFI) of the obtained PFSA resin precursor powder (precursor of PFSA resin A1 in Table 1) was 1.5 (g / 10 min).
- the EW of the obtained PFSA resin A1 was 650 (g / eq).
- ASF1 dispersion liquid
- this unsintered PTFE film was stretched in the longitudinal direction (MD direction) at a stretching ratio of 6.6 times and wound up. Both ends of the obtained MD direction stretched PTFE film were sandwiched between clips, stretched in the width direction (TD direction) at a stretch ratio of 8 times, heat-set, and a stretched PTFE film having a thickness of 10 ⁇ m was obtained.
- the stretching temperature at this time was 290 ° C., and the heat setting temperature was 360 ° C.
- the PTFE microporous membrane produced as described above was designated as microporous membrane 1.
- the distribution center of the pore distribution of the microporous membrane 1 was 1.29 ⁇ m.
- the dispersion ASF1 was applied onto a base film using a bar coater (manufactured by Matsuo Sangyo, bar No. 200, WET film thickness 200 ⁇ m) (application area: width of about 200 mm ⁇ length of about 500 mm), the PTFE microporous membrane 1 (film thickness: 10 ⁇ m, porosity: 82%, sample size: width 200 mm ⁇ length 500 mm) is laminated on the dispersion while the dispersion is not completely dry.
- the dispersion and the microporous membrane were pressure-bonded from above the microporous membrane using a rubber roller.
- this membrane that is, a laminate of the PTFE microporous membrane and the base film is dried in an oven at 90 ° C. for 20 minutes. I let you.
- the dispersion is laminated again in the same manner from above the PTFE microporous membrane of the obtained membrane to sufficiently fill the voids of the microporous membrane with the dispersion, and this membrane is further heated in an oven at 90 ° C. for 20 minutes. Dried.
- the “PTFE microporous membrane sufficiently impregnated with the dispersion” thus obtained was heat-treated in an oven at 170 ° C.
- the evaluation results of the electrolyte membrane are shown in Table 1.
- ASF1 was 12 mass%.
- the maximum water content of the electrolyte membrane in water at 25 ° C. for 3 hours was 23% by mass for ASF1.
- the maximum moisture content indicates the maximum value observed when measuring the equilibrium moisture content.
- the dimensional change in the planar direction of the electrolyte membrane was 14%.
- a charge / discharge test was performed using the electrolyte membrane as a diaphragm of a vanadium redox flow secondary battery.
- electrolyte membrane obtained from ASF1 Using the electrolyte membrane obtained from ASF1, a charge / discharge experiment was performed after sufficiently equilibrating in the electrolytic solution, and then the initial current resistance and cell electrical resistivity were measured after a stable state was achieved.
- the (current efficiency / cell electrical resistivity) of the electrolyte membrane was (97.5 / 0.90).
- Example 2 Production of PTFE microporous membrane 2 300 kg of hydrocarbon oil as an extruded liquid lubricating oil was added at 20 ° C. and mixed with 1 kg of PTFE fine powder having a number average molecular weight of 12 million. Next, the round bar-like molded body obtained by extruding this mixture by paste extrusion was molded into a film shape by a calender roll heated to 70 ° C. to obtain a PTFE film. This film was passed through a hot air drying oven at 250 ° C. to evaporate and remove the extrusion aid, thereby obtaining an unfired film having an average thickness of 200 ⁇ m and an average width of 280 mm.
- this unsintered PTFE film was stretched in the longitudinal direction (MD direction) at a stretch ratio of 5 and wound up. Both ends of the obtained MD direction stretched PTFE film were sandwiched between clips, stretched in the width direction (TD direction) at a stretch ratio of 5 times, heat fixed, and a stretched PTFE film having a thickness of 12 ⁇ m was obtained.
- the stretching temperature at this time was 290 ° C., and the heat setting temperature was 360 ° C.
- the produced PTFE microporous membrane was designated as microporous membrane 2.
- the distribution center of the pore distribution of the PTFE microporous membrane 2 was 1.18 ⁇ m.
- the current efficiency / cell electric resistance was (97.3% / 0.90 ⁇ ⁇ cm 2 ), and the initial current efficiency (%) / The change was extremely small compared to the cell electrical resistivity ( ⁇ ⁇ cm 2 ), and the durability was excellent.
- Example 3 Production of PTFE microporous membrane 3
- MD direction stretching ratio in the longitudinal direction
- TD direction stretching ratio in the width direction
- PTFE microporous membrane 3 A microporous membrane having a thickness of 8 ⁇ m (the distribution center of the pore distribution is 0.2 ⁇ m) was produced, and this was designated as PTFE microporous membrane 3.
- Example 4 Production of PTFE microporous membrane 4 The same as PTFE microporous membrane 2 except that the stretching ratio in the longitudinal direction (MD direction) is 3 times and the stretching ratio in the width direction (TD direction) is 8.3 times. By the method, a 12 ⁇ m-thick microporous membrane (pore distribution distribution center is 0.2 ⁇ m) was produced and manufactured, and this was designated as PTFE microporous membrane 4.
- a 12 ⁇ m-thick microporous membrane pore distribution distribution center is 0.2 ⁇ m
- the thickness of the electrolyte membrane was changed from 20 ⁇ m to 25 ⁇ m by using the PTFE microporous membrane 4 and applying the dispersion using a bar coater having a different WET thickness. 2 was used to obtain an electrolyte membrane.
- the equilibrium moisture content of the obtained electrolyte membrane was 12% by mass, and the maximum moisture content of the electrolyte membrane in 25 ° C. water for 3 hours was 23% by mass.
- the dimensional change in the plane direction was measured using the obtained electrolyte membrane, it was 5%, and the dimensional change was small.
- the current efficiency (%) / cell electrical resistivity ( ⁇ ⁇ cm 2 ) was (97.5 / 0.90).
- Example 5 Manufacture of electrolyte membrane
- the dispersion ASF1 PFSA resin dispersion
- a bar coater manufactured by Matsuo Sangyo, Bar No. 200, WET film thickness 200 ⁇ m
- application area width about 200 mm ⁇ length about 500 mm.
- a liquid crystal polymer non-woven fabric of wholly aromatic polyester (Vecules MBBK14FXSP manufactured by Kuraray Co., Ltd.) (film thickness: 20 ⁇ m, porosity: 83%), sample size: width 200 mm ⁇ length 500 mm It laminated
- this film that is, a laminate of the liquid crystal polymer nonwoven fabric of the wholly aromatic polyester and the base film is placed in an oven at 90 ° C. for 20 minutes. Dried for minutes.
- the dispersion was laminated again in the same manner from above the nonwoven fabric of the membrane so that the voids of the nonwoven fabric were sufficiently filled with the dispersion, and this membrane was further dried in an oven at 90 ° C. for 20 minutes.
- the “nonwoven fabric sufficiently impregnated with the dispersion” thus obtained was heat-treated in an oven at 170 ° C. for 1 hour to obtain an electrolyte membrane having a thickness of about 40 ⁇ m.
- the evaluation results of the electrolyte membrane are shown in Table 1.
- ASF1 was 12 mass%.
- the maximum water content of the electrolyte membrane in water at 25 ° C. for 3 hours was 23% by mass for ASF1.
- the maximum moisture content indicates the maximum value observed when measuring the equilibrium moisture content.
- the dimensional change in the planar direction of the electrolyte membrane was 14%, and the breaking strength was 570 kgf / cm 2 .
- a charge / discharge test was performed using the electrolyte membrane as a diaphragm of a vanadium redox flow secondary battery.
- electrolyte membrane obtained from ASF1 Using the electrolyte membrane obtained from ASF1, a charge / discharge experiment was performed after sufficiently equilibrating in the electrolytic solution, and then the cell electrical resistivity and current efficiency were measured after a stable state was achieved.
- the cell electrical resistivity / current efficiency of the electrolyte membrane was (97.5% / 0.90 ⁇ ⁇ cm 2 ).
- Example 6 An electrolyte membrane was obtained in the same manner as in Example 5 except that an aramid nonwoven fabric (AH20CC manufactured by Poval Kogyo Co., Ltd.) (film thickness 20 ⁇ m, porosity 90%) was used.
- the equilibrium moisture content of the obtained electrolyte membrane was 12% by mass, and the maximum moisture content of the electrolyte membrane in 25 ° C. water for 3 hours was 23% by mass.
- the dimensional change in the plane direction was measured using the obtained electrolyte membrane, it was 8%, and the dimensional change was small.
- the current efficiency (%) / cell electrical resistivity ( ⁇ ⁇ cm 2 ) was (97.5 / 0.90).
- Example 7 An electrolyte membrane was obtained in the same manner as in Example 5 except that a polyolefin microporous membrane (manufactured by DSM SoItech, grade: SoIupor 3PO7A, film thickness: 8 ⁇ m, porosity: 86%) was used.
- the equilibrium moisture content of the obtained electrolyte membrane was 13% by mass, and the maximum moisture content of the electrolyte membrane in 25 ° C. water for 3 hours was 22% by mass.
- the dimensional change in the planar direction was measured and found to be 11%.
- the polyolefin microporous membrane is cut into strips of about 3 mm ⁇ 15 mm, vapor-stained with ruthenium oxide, and then frozen for cutting to observe the cross section of the polyolefin microporous membrane.
- a sample was prepared. After this split piece was fixed on the sample stage, osmium plasma coating treatment (conducting treatment) was performed to obtain a sample for observing the cross-sectional shape.
- morphology observation is performed by SEM (manufactured by Hitachi, product number: S-4700, acceleration voltage: 5 kV, detector: secondary electron detector, backscattered electron detector), and multilayered from the observed image It was observed to have a structure.
- SEM manufactured by Hitachi, product number: S-4700, acceleration voltage: 5 kV, detector: secondary electron detector, backscattered electron detector
- the stress which is impregnated with electrolyte solution and volume change is moderately disperse
- Example 8 (1) Production of PFSA resin dispersion (ASF2)
- ASF2 dispersion liquid
- the current efficiency / cell electrical resistivity was (92.1% / 1.05 ⁇ ⁇ cm 2 ) in the results of 200 cycles of charge and discharge. Compared with the initial current efficiency (%) / cell electrical resistivity ( ⁇ ⁇ cm 2 ), the change was extremely small and the durability was excellent.
- Example 9 Manufacture of electrolyte membrane
- An electrolyte membrane was obtained by the same method using the same reinforcing material as in Example 5 except that the dispersion ASF2 was used.
- the equilibrium moisture content of the obtained electrolyte membrane was 16% by mass, and the maximum moisture content of the electrolyte membrane in 25 ° C. water for 3 hours was 27% by mass.
- the dimensional change in the planar direction was measured and found to be 17%.
- the initial current efficiency (%) / cell electrical resistivity ( ⁇ ⁇ cm 2 ) was 95.0 / 0.95.
- the current efficiency / cell electrical resistivity was (91.7% / 1.05 ⁇ ⁇ cm 2 ) in the results of 200 cycles of charge and discharge. Compared with the initial current efficiency (%) / cell electrical resistivity ( ⁇ ⁇ cm 2 ), the change was extremely small and the durability was excellent.
- Example 10 An electrolyte membrane was obtained by the same method as in Example 5 except that PTFE fiber was used and a woven fabric produced by a plain weave method was used. The equilibrium moisture content of the obtained electrolyte membrane was 13% by mass, and the maximum moisture content of the electrolyte membrane in 25 ° C. water for 3 hours was 22% by mass. Using the obtained electrolyte membrane, the dimensional change in the planar direction was measured and found to be 14%. As a result of conducting a charge / discharge test in the same manner as in Example 1, the current efficiency (%) / cell electrical resistivity ( ⁇ ⁇ cm 2 ) was (97.0 / 0.95).
- Example 1 Manufacture of electrolyte membrane
- the dispersion (ASF1) prepared in Example 1 was cast on a polyimide film as a carrier sheet by a known ordinary method, and hot air at 120 ° C. (20 minutes) was applied to almost completely remove the solvent.
- the film was formed by skipping and drying. This was further heat-treated in a hot air atmosphere at 160 ° C. for 10 minutes to obtain an electrolyte membrane having a thickness of 20 ⁇ m.
- the equilibrium moisture content of the obtained electrolyte membrane was 12% by mass, and the maximum moisture content of the electrolyte membrane in 25 ° C. water for 3 hours was 23% by mass.
- the dimensional change in the planar direction was measured and found to be 24%.
- the current efficiency (%) / cell electrical resistivity ( ⁇ ⁇ cm 2 ) was 93.0 / 0.85, which was a level lower than that of the Example. there were.
- the current efficiency / cell electrical resistivity was (84.4% / 1.20 ⁇ ⁇ cm 2 ) even after 200 cycles of charge and discharge, and the initial current efficiency (%) / The change was large compared with the cell electrical resistivity ( ⁇ ⁇ cm 2 ), and the durability was inferior.
- Table 1 shows the measurement results of the physical properties of Examples 1 to 9 and Comparative Example 1.
- the electrolyte membrane of the present invention has industrial applicability as a diaphragm for a redox flow secondary battery.
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Abstract
Description
レドックスフロー二次電池は、正極と正極活物質を含む電解液(正極セル)と、負極と負極活物質を含む負極電解液(負極セル)とを、隔膜で隔離して、両活物質の酸化還元反応を利用して充放電し、該両活物質を含む電解液を、備蓄タンクから電解槽に流通させて電流を取り出し利用される。
電池の電流効率を上げるためには、両極のセル電解液に含まれるそれぞれの活物質イオンの透過(両極電解液中の電解質のコンタミ)は、できるだけ防ぐことが要求されるが、電荷を運ぶプロトン(H+)は充分透過しやすいという、イオン選択透過性に優れたイオン交換膜が要求される。
その原理については、電位差を掛けられたときに、イオン径及び電荷量の多い金属カチオンは、隔膜表層部のカチオンにより電気的反発を受けて金属カチオンの膜透過が阻害されるが、イオン径も小さく、1価であるプロトン(H+)はカチオンを有する隔膜を容易に拡散透過できるので電気抵抗が小さくなると記載されている。
特許文献2に開示された複合膜は、電気抵抗が高く、また、各イオンは多孔膜ほどではないが、自由に拡散してしまうという問題があり、電池の電流効率は高くない。特許文献3に開示された膜についても、上記と同様の問題があり、耐酸化耐久性にも劣る。
特許文献4に開示された電池は、電流効率が未だ不十分であり、長期にわたる硫酸電解液中での耐酸化劣化性にも劣り、耐久性も不十分である。また、同文献には、比較例として、PTFE系イオン交換膜を使用する電池が開示されているが、その電流効率が64.8~78.6%であり、不十分であることが記載されている。
特許文献5に開示された電池も、上記と同様の問題点を解決できておらず、また、大型設備では、価格的にも高価となってしまうという問題がある。
特許文献6に開示された膜は、塗布膜の厚みを極薄(数μm)にしないと、内部抵抗が増加するという問題を有している。また、イオン選択透過性を向上させる工夫については一切記載されていない。
引用文献7に開示された電池は、ポリスルホン系隔膜を使用するため、隔膜のイオン選択透過性や耐酸化劣化せいが十分ではなく、電池の電気抵抗、電流効率、耐久性が十分ではない。
特許文献8に開示された電池は、電流効率が不十分であり、また、酸化劣化するため長期間使用すると、特性が劣化するという問題を有している。
特許文献9に開示された膜は、長期間使用すると、電気抵抗が高くなるという問題点を有している。
特許文献10に開示されている電池においては、膜の内部抵抗(電気抵抗)が十分低いとは言えず、また、長期間使用すると、酸化劣化が問題となる。
炭化水素系樹脂を主とした膜基材としては、両セルの主役の電解質を含む電解液を単に隔離するだけの単なるイオン選択透過性のない単なる多孔膜や、イオン選択透過性のない(無孔の)親水性膜基材、多孔膜に親水性膜基材を埋め込むか又は被覆したもの等が用いられている。また、膜自身が各種アニオン基を有する所謂カチオン交換膜、又は多孔質膜基材の孔にカチオン交換性樹脂を被覆又は埋め込んだ複合膜、同様に膜自身がカチオン基を有するアニオン交換膜、同様に多孔膜基材に、アニオン交換性樹脂を被覆又は埋め込んだ複合膜、カチオン交換膜とアニオン交換膜との積層型等が隔膜として用いられており、それぞれの特徴を生かした研究が行われている。
すなわち、本発明は以下のとおりである。
炭素電極からなる正極を含む正極セル室と、
炭素電極からなる負極を含む負極セル室と、
前記正極セル室と、前記負極セル室とを隔離分離させる、隔膜としての電解質膜と、
を含む電解槽を有し、
前記正極セル室は活物質を含む正極電解液を、前記負極セル室は活物質を含む負極電解液を含み、
前記電解液中の活物質の価数変化に基づき充放電するレドックスフロー二次電池であって、
前記電解質膜が、高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
前記電解質膜がフッ素系微多孔膜からなる補強材を有するレドックスフロー二次電池。
〔2〕
炭素電極からなる正極を含む正極セル室と、
炭素電極からなる負極を含む負極セル室と、
前記正極セル室と、前記負極セル室とを隔離分離させる、隔膜としての電解質膜と、
を含む電解槽を有し、
前記正極セル室は活物質を含む正極電解液を、前記負極セル室は活物質を含む負極電解液を含み、
前記電解液中の活物質の価数変化に基づき充放電するレドックスフロー二次電池であって、
前記電解質膜が、高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
前記電解質膜が不織布及び/又は炭化水素系微多孔膜からなる補強材を有するレドックスフロー二次電池。
〔3〕
炭素電極からなる正極を含む正極セル室と、
炭素電極からなる負極を含む負極セル室と、
前記正極セル室と、前記負極セル室とを隔離分離させる、隔膜としての電解質膜と、
を含む電解槽を有し、
前記正極セル室は活物質を含む正極電解液を、前記負極セル室は活物質を含む負極電解液を含み、
前記電解液中の活物質の価数変化に基づき充放電するレドックスフロー二次電池であって、
前記電解質膜が、高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
前記電解質膜が織布からなる補強材を有するレドックスフロー二次電池。
〔4〕
前記補強材は、前記高分子電解質ポリマーが、補強材に含浸され、前記補強材の内部体積を実質的に閉塞した構造である、前記〔1〕乃至〔3〕のいずれか一に記載のレドックスフロー二次電池。
〔5〕
前記レドックスフロー二次電池は、バナジウムを含む硫酸電解液を、正極及び負極電解液として用いたバナジウム系レドックスフロー二次電池である、前記〔1〕乃至〔4〕のいずれか一に記載のレドックスフロー二次電池。
〔6〕
前記電解質膜は、前記高分子電解質ポリマーとして下記式(1)で表される構造を有するフッ素系高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含む、前記〔1〕乃至〔5〕のいずれか一に記載のレドックスフロー二次電池。
-[CF2CX1X2]a-[CF2-CF((-O-CF2-CF(CF2X3))b-Oc-(CFR1)d-(CFR2)e-(CF2)f-X4)]g- (1)
(式(1)中、X1、X2及びX3は、それぞれ独立して、ハロゲン原子及び炭素数1~3のパーフルオロアルキル基からなる群から選択される1種以上を示す。X4は、COOZ、SO3Z、PO3Z2又はPO3HZを示す。Zは、水素原子、アルカリ金属原子、アルカリ土類金属原子、又はアミン類(NH4、NH3R1、NH2R1R2、NHR1R2R3、NR1R2R3R4)を示す。R1、R2、R3及びR4は、それぞれ独立して、アルキル基及びアレーン基からなる群から選択されるいずれか1種以上を示す。ここで、X4がPO3Z2である場合、Zは同じでも異なっていてもよい。R1及びR2は、それぞれ独立して、ハロゲン原子、炭素数1~10のパーフルオロアルキル基及びフルオロクロロアルキル基からなる群から選択される1種以上を示す。a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示す。bは0~8の整数を示す。cは0又は1を示す。d、e及びfは、それぞれ独立して、0~6の整数を示す(ただし、d、e及びfは同時に0ではない。)。)
〔7〕
前記電解質膜は、前記高分子電解質ポリマーとして下記式(2)で表される構造を有するフッ素系高分子電解質ポリマーであるパーフルオロカーボンスルホン酸樹脂(PFSA)を主体とするイオン交換樹脂組成物を含む、前記〔1〕乃至〔6〕のいずれか一に記載のレドックスフロー二次電池。
-[CF2CF2]a-[CF2-CF(-O-(CF2)m-X4)]g- (2)
(式(2)中、a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示し、mは1~6の整数を示し、X4はSO3Hを示す。)
〔8〕
前記高分子電解質ポリマーの当量質量EW(イオン交換基1当量あたりの乾燥質量グラム数)が300~1300g/eqであり、前記電解質膜の平衡含水率が5~80質量%である、前記〔1〕乃至〔7〕のいずれか一に記載のレドックスフロー二次電池。
〔9〕
前記イオン交換樹脂組成物が、前記高分子電解質ポリマー100質量部に対して0.1~20質量部のポリフェニレンエーテル樹脂及び/又はポリフェニレンスルフィド樹脂を含む、前記〔1〕乃至〔8〕のいずれか一に記載のレドックスフロー二次電池。
〔10〕
高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
フッ素系多孔膜を補強材として有する、
レドックスフロー二次電池用電解質膜。
〔11〕
高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
不織布及び/又は炭化水素系微多孔膜からなる補強材を有する、
レドックスフロー二次電池用電解質膜。
〔12〕
高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
織布からなる補強材を有する、
レドックスフロー二次電池用電解質膜。
〔13〕
前記補強材は、前記高分子電解質ポリマーが含浸され、前記レドックスフロー二次電池用の補強材の内部体積を実質的に閉塞した構造である、前記〔10〕乃至〔12〕のいずれか一に記載のレドックスフロー二次電池用電解質膜。
〔14〕
前記レドックスフロー二次電池用電解質膜は、前記高分子電解質ポリマーとして下記式(1)で表される構造を有するフッ素系高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含む、前記〔10〕乃至〔13〕のいずれか一に記載のレドックスフロー二次電池用電解質膜。
-[CF2CX1X2]a-[CF2-CF((-O-CF2-CF(CF2X3))b-Oc-(CFR1)d-(CFR2)e-(CF2)f-X4)]g- (1)
(式(1)中、X1、X2及びX3は、それぞれ独立して、ハロゲン原子及び炭素数1~3のパーフルオロアルキル基からなる群から選択される1種以上を示す。X4は、COOZ、SO3Z、PO3Z2又はPO3HZを示す。Zは、水素原子、アルカリ金属原子、アルカリ土類金属原子、又はアミン類(NH4、NH3R1、NH2R1R2、NHR1R2R3、NR1R2R3R4)を示す。R1、R2、R3及びR4は、それぞれ独立して、アルキル基及びアレーン基からなる群から選択されるいずれか1種以上を示す。ここで、X4がPO3Z2である場合、Zは同じでも異なっていてもよい。R1及びR2は、それぞれ独立して、ハロゲン原子、炭素数1~10のパーフルオロアルキル基及びフルオロクロロアルキル基からなる群から選択される1種以上を示す。a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示す。bは0~8の整数を示す。cは0又は1を示す。d、e及びfは、それぞれ独立して、0~6の整数を示す(ただし、d、e及びfは同時に0ではない。)。)
〔15〕
前記高分子電解質ポリマーは、下記式(2)で表される構造を有するフッ素系高分子電解質ポリマーである、パーフルオロカーボンスルホン酸樹脂(PFSA)である、前記〔10〕乃至〔14〕のいずれか一に記載のレドックスフロー二次電池用電解質膜。
-[CF2CF2]a-[CF2-CF(-O-(CF2)m-X4)]g- (2)
(式(2)中、a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示し、mは1~6の整数を示し、X4はSO3Hを示す。)
〔16〕
前記高分子電解質ポリマーの当量質量EW(イオン交換基1当量あたりの乾燥質量グラム数)が300~1300g/eqであり、前記電解質膜の平衡含水率が5~80質量%である、前記〔10〕乃至〔15〕のいずれか一に記載のレドックスフロー二次電池用電解質膜。
〔17〕
前記イオン交換樹脂組成物が、前記高分子電解質ポリマー100質量部に対して0.1~20質量部のポリフェニレンエーテル樹脂及び/又はポリフェニレンスルフィド樹脂を含む、前記〔10〕乃至〔16〕のいずれか一に記載のレドックスフロー二次電池。
〔18〕
前記レドックスフロー二次電池用電解質膜は、130~200℃にて1~60分間加熱処理されたものである、前記〔10〕乃至〔17〕のいずれか一に記載のレドックスフロー二次電池用電解質膜。
本実施形態のレドックスフロー二次電池は、
炭素電極からなる正極を含む正極セル室と、
炭素電極からなる負極を含む負極セル室と、
前記正極セル室と、前記負極セル室とを隔離分離させる、隔膜としての電解質膜と、
を含む電解槽を有し、
前記正極セル室は活物質を含む正極電解液を、前記負極セル室は活物質を含む負極電解液を含み、
前記電解液中の活物質の価数変化に基づき充放電するレドックスフロー二次電池であって、
前記電解質膜が高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
前記電解質膜が所定の補強材を有するレドックスフロー二次電池である。
本実施形態におけるレドックスフロー二次電池10は、炭素電極からなる正極1を含む正極セル室2と、炭素電極からなる負極3を含む負極セル室4と、前記正極セル室2と、前記負極セル室4とを隔離分離させる、隔膜としての電解質膜5と、を含む電解槽6を有している。
前記正極セル室2は正極活物質を含む正極電解液を、前記負極セル室4は負極活物質を含む負極電解液を、それぞれ含む。
活物質を含む正極電解液及び負極電解液は、例えば、正極電解液タンク7及び負極電解液タンク8によって貯蔵され、ポンプ等によって各セル室に供給される(矢印A、B)。
また、レッドクスフロー二次電池によって生じた電流は、交直変換装置9を介して、直流から交流に変換されてもよい。
本実施形態のレドックスフロー二次電池がバナジウム系レドックスフロー二次電池の場合、正極セル室には、バナジウム4価(V4+)及びバナジウム5価(V5+)を含む硫酸電解液からなる正極電解液を、負極セル室には、バナジウム3価(V3+)及びバナジウム2価(V2+)を含む負極電解液を流通させることにより、電池の充電及び放電が行われる。
このとき、充電時には、正極セル室においては、バナジウムイオンが電子を放出するためV4+がV5+に酸化され、負極セル室では外路を通じて戻って来た電子によりV3+がV2+に還元される。
この酸化還元反応では、正極セル室ではプロトン(H+)が過剰になり、一方負極セル室では、プロトン(H+)が不足する。
隔膜は正極セル室の過剰なプロトンを選択的に負極室に移動させ電気的中性が保たれる。放電時には、この逆の反応が進む。
この時の電池効率(%)は、放電電力量を充電電力量で除した比率(%)で表され、両電力量は、電池セルの内部抵抗と隔膜のイオン選択性及びその他電流損失に依存する。
前記電池セルの内部抵抗の減少は電圧効率を向上させ、隔膜のイオン選択透過性の向上及びその他電流損失の低減は、電流効率を向上させるので、レドックスフロー二次電池においては、重要な指標となる。
本実施形態におけるレドックスフロー二次電池用電解質膜の第1の形態としては、電解質膜が、フッ素系微多孔膜からなる補強材を有する。
本実施形態におけるレドックスフロー二次電池用電解質膜の第2の形態としては、電解質膜が、不織布及び/又は炭化水素系微多孔膜からなる補強材を有する。
本実施形態におけるレドックスフロー二次電池用電解質膜の第3の形態としては、電解質膜が、織布からなる補強材を有する。
これらの補強材については、後述する。
本実施形態のレドックスフロー二次電池を構成する前記電解質膜は、高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含む。
当該高分子電解質ポリマーとしては、後述するフッ素系高分子電解質ポリマーや、炭化水素系高分子電解質ポリマーが好ましいものとして挙げられる。
前記フッ素系高分子電解質ポリマーは、下記式(1)で表される構造を有するものであれば、特に限定されず、他の構造を含むものであってもよい。
-[CF2-CX1X2]a-[CF2-CF((-O-CF2-CF(CF2X3))b-Oc-(CFR1)d-(CFR2)e-(CF2)f-X4)]g- (1)
(式(1)中、X1、X2及びX3は、それぞれ独立して、ハロゲン原子及び炭素数1~3のパーフルオロアルキル基からなる群から選択される1種以上を示す。X4は、COOZ、SO3Z、PO3Z2又はPO3HZを示す。Zは、水素原子、アルカリ金属原子、アルカリ土類金属原子、又はアミン類(NH4、NH3R1、NH2R1R2、NHR1R2R3、NR1R2R3R4)を示す。R1、R2、R3及びR4は、それぞれ独立して、アルキル基及びアレーン基からなる群から選択されるいずれか1種以上を示す。ここで、X4がPO3Z2である場合、Zは同じでも異なっていてもよい。R1及びR2は、それぞれ独立して、ハロゲン原子、炭素数1~10のパーフルオロアルキル基及びフルオロクロロアルキル基からなる群から選択される1種以上を示す。
a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示す。bは0~8の整数を示す。cは0又は1を示す。d、e及びfは、それぞれ独立して、0~6の整数を示す(ただし、d、e及びfは同時に0ではない。)。)
Zは、水素原子、アルカリ金属原子、アルカリ土類金属原子、又はアミン類(NH4、NH3R1、NH2R1R2、NHR1R2R3、NR1R2R3R4)を示す。ここで、アルカリ金属原子としては、特に限定されず、リチウム原子、ナトリウム原子、カリウム原子等が挙げられる。また、アルカリ土類金属原子としては、特に限定されず、カルシウム原子、マグネシウム原子等が挙げられる。
また、R1、R2、R3及びR4は、それぞれ独立して、アルキル基及びアレーン基からなる群から選択されるいずれか1種以上を示す。ここで、X4がPO3Z2である場合、Zは同じでも異なっていてもよい。X4としては、ポリマーの化学的安定性の観点から、SO3Zが好ましい。
R1及びR2は、それぞれ独立して、ハロゲン原子、炭素数1~10のパーフルオロアルキル基及びフルオロクロロアルキル基からなる群から選択される1種以上を示す。ここで、ハロゲン原子としては、フッ素原子、塩素原子、臭素原子、ヨウ素原子が挙げられる。
-(CF2-CF2)-で表される繰り返し単位と、
下記式(3)又は(4)で表される化合物から誘導される繰り返し単位と、を含有することが好ましく、さらに、-(CF2-CF2)-で表される繰り返し単位と、前記式(3)又は前記式(4)で表される化合物から誘導される繰り返し単位とからなることが好ましい。
式(3):CF2=CF(-O-(CF2CFXO)n-[A])(式中、Xは、F又は炭素数1~3のパーフルオロアルキル基を示し、nは0~5の整数を示す。[A]は(CF2)m-SO3H(mは0~6の整数を示す。ただし、nとmは同時に0にならない。)、
式(4):CF2=CF-O-(CF2)P-CFX(-O-(CF2)K-SO3H)若しくはCF2=CF-O-(CF2)P-CFX(-(CF2)L-O-(CF2)m-SO3H)(式中、Xは、炭素数1~3のパーフルオロアルキル基を示し、Pは0~12の整数を示し、Kは1~5の整数を示し、Lは1~5の整数を示し、mは0~6の整数を示す。ただし、KとLは同じでも、異なっていてもよく、P、K、Lは同時に0とはならない。)。
本発明者らが検討したところ、レドックスフロー二次電池用電解質膜として使用する場合には、前記ナフィオンに比べて、前記-(CF2-CF(-O-(CF2CFXO)n-(CF2)m-SO3H))-で表される繰り返し単位中のnが0であり、mが1~6の整数であるもの、又は式(4)で表される-CF2-CF(-O-(CF2)P-CFX(-O-(CF2)K-SO3H)-及び-CF2-CF(-O-(CF2)P-CFX(-(CF2)L-O-(CF2)m-SO3H)-の両方の繰り返し単位を含むPFSA樹脂の方が、親水性やイオン選択透過性が優れており、得られるレドックスフロー二次電池の電気抵抗が低く、電流効率も向上する傾向にあることがわかった
-[CF2CF2]a-[CF2-CF(-O-(CF2)m-X4)]g- (2)
(式(2)中、a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示し、mは1~6の整数を示し、X4はSO3Hを示す。)
例えば、フッ素系高分子電解質ポリマーのEWが280程度であっても、前記部分架橋を行うことにより、フッ素系高分子電解質ポリマーの水溶解性を低下(耐水性が向上)させることができる。
また、フッ素系高分子電解質ポリマーが低メルトフロー領域(高分子領域)である場合にも、前記部分架橋により、分子間絡みを増加し、溶解性や過剰膨潤性を低下できる。
フッ素系高分子電解質ポリマーの当量質量EW(イオン交換基1当量あたりのフッ素系高分子電解質ポリマーの乾燥質量グラム数)は、300~1300(g/eq)であることが好ましく、より好ましくは350~1000(g/eq)、更に好ましくは400~900(g/eq)、特に好ましくは450~750(g/eq)である。
前記フッ素系高分子電解質ポリマーは、例えば、高分子電解質ポリマーの前駆体(以下、「樹脂前駆体」ともいう。)を製造した後、それを加水分解処理することにより得ることができる。
前記フッ素系高分子電解質ポリマーがPFSA樹脂の場合、当該PFSA樹脂は、例えば、下記一般式(5)又は(6)で表されるフッ化ビニルエーテル化合物と、下記一般式(7)で表されるフッ化オレフィンモノマーとの共重合体からなるPFSA樹脂前駆体を加水分解することにより得られる。
(式(5)中、Xは、F又は炭素数1~3のパーフルオロアルキル基を示し、nは0~5の整数を示し、Aは(CF2)m-Wを示し、mは0~6の整数を示し、nとmは同時に0にならず、Wは加水分解によりSO3Hに転換し得る官能基を示す。)
式(6):CF2=CF-O-(CF2)P-CFX(-O-(CF2)K-W)、又はCF2=CF-O-(CF2)P-CFX(-(CF2)L-O-(CF2)m-W)
(式(6)中、Xは、炭素数1~3のパーフルオロアルキル基を示し、Pは0~12の整数を示し、Kは1~5の整数を示し、Lは1~5の整数を示し(ただし、L、K、mは同時に0とならない。)、mは0~6の整数を示し、Wは加水分解によりSO3Hに転換し得る官能基を示す。)
式(7):CF2=CFZ
(式(7)中、Zは、H、Cl、F、炭素数1~3のパーフルオロアルキル基、又は酸素を含んでいてもよい環状パーフルオロアルキル基を示す。)
例えば、過酸化物等のラジカル発生剤等の存在下、加水分解等によりイオン交換基(式(1)におけるX4)に転換し得る基(イオン交換基前駆体基)を有するフッ化ビニル化合物とテトラフルオロエチレン(TFE)などのフッ化オレフィンを重合することにより製造できる。前記重合方法は、特に限定されず、前記フッ化ビニル化合物等とフッ化オレフィンのガスを含フッ素炭化水素等の重合溶剤に充填溶解して反応させることにより重合する方法(溶液重合)含むフッ化炭化水素等の溶媒をしようせず、フッ化ビニル化合物そのものを重合溶剤として重合する方法(塊状重合)、界面活性剤の水溶液を媒体としてフッ化ビニル化合物とフッ化オレフィンのガスを充填して反応させることにより重合する方法(乳化重合)、界面活性剤及びアルコール等の助乳化剤の水溶液に、フッ化ビニル化合物とフッ化オレフィンのガスを充填、乳化して反応させることにより重合する方法(エマルジョン重合)、及び懸濁安定剤の水溶液にフッ化ビニル化合物とフッ化オレフィンのガスを充填懸濁して反応させることにより重合する方法(懸濁重合)等が挙げられる。
前記フッ素系高分子電解質ポリマー前駆体のMFIのより好ましい範囲は0.1~30(g/10分)であり、さらに好ましい範囲は0.5~20(g/10分)である。
前記樹脂前駆体から本実施形態のフッ素系高分子電解質ポリマーを製造する方法は、特に限定されず、例えば、前記樹脂前駆体を押し出し機を用いてノズル又はダイ等で押し出し成型した後、加水分解処理を行うか、重合した時の産出物のまま、即ち分散液状、又は沈殿、ろ過させた粉末状の物とした後、加水分解処理を行う方法がある。
より具体的には、上記のようにして得られ、必要に応じて成型されたフッ素系高分子電解質ポリマー前駆体は、引き続き塩基性反応液体中に浸漬し、加水分解処理される。
加水分解処理に使用する塩基性反応液としては、特に限定されるものではないが、ジメチルアミン、ジエチルアミン、モノメチルアミン及びモノエチルアミン等のアミン化合物の水溶液や、アルカリ金属又はアルカリ土類金属の水酸化物の水溶液が好ましく、水酸化ナトリウム及び水酸化カリウムの水溶液が特に好ましい。
アルカリ金属又はアルカリ土類金属の水酸化物を用いる場合、その含有量は特に限定されないが、反応液全体に対して10~30質量%であることが好ましい。
上記反応液は、さらにメチルアルコール、エチルアルコール、アセトン及びジメチルスルホキシド(DMSO)等の膨潤性有機化合物を含有することがより好ましい。膨潤性の有機化合物の含有量は、反応液全体に対して1~30質量%であることが好ましい。
酸処理に使用する酸としては、特に限定されないが、塩酸、硫酸及び硝酸等の鉱酸類や、シュウ酸、酢酸、ギ酸及びトリフルオロ酢酸等の有機酸類が好ましく、これらの酸と水との混合物がより好ましい。また、上記酸類は1種のみを単独で用いても2種以上を併用してもよい。また、加水分解処理で用いた塩基性反応液は、カチオン交換樹脂で処理すること等により、酸処理の前に予め除去してもよい。
例えば、前記式(5)を用いて製造されるPFSA樹脂前駆体の場合、式(5)のWは、酸処理によってプロトン化され、SO3Hとなる。加水分解及び酸処理することによって得られたフッ素系高分子電解質ポリマーは、プロトン性有機溶媒、水、又は両者の混合溶媒に分散又は溶解することが可能となる。
当該高分子電解質ポリマーとしては、上述したフッ素系高分子電解質ポリマーの他、炭化水素系高分子電解質ポリマーが挙げられる。
炭化水素系高分子電解質ポリマーとしては、ポリスルホン系ポリマーや、ピリジニウム基を有する陰イオン交換型とスチレン系及びジビニルベンゼンとを共重合した架橋型ポリマー等が挙げられる。
本実施形態のレドックスフロー二次電池に用いる電解質膜に含まれるイオン交換樹脂組成物中の高分子電解質ポリマーは、フッ素系高分子電解質ポリマーに限られず、その他の高分子系電解質ポリマー、例えば炭化水素系高分子ポリマーである場合も、当量質量EW(イオン交換基1当量あたりの高分子電解質ポリマーの乾燥質量グラム数)は、300~1300(g/eq)に調整することが好ましい。
当該高分子電解質ポリマーの当量質量EWは、より好ましくは350~1000(g/eq)、さらに好ましくは400~900(g/eq)、さらにより好ましくは450~750(g/eq)である。
具体的には、後述する実施例に記載する方法により測定することができる。
前記イオン交換樹脂組成物中に含まれる高分子電解質ポリマーの含有量としては、好ましくは約33.3~100質量%、より好ましくは40~100質量%、さらに好ましくは50~99.5質量%である。
前記所定の材料としては、ポリアゾール系化合物や、それに代えて/加えて、塩基性重合体(オリゴマーなどの低分子量物質を含む)が挙げられる。
上記材料を含有することにより、イオン交換樹脂組成物としての化学的安定性(主に耐酸化性等)が増加する傾向にある。
これらの化合物は、イオン交換樹脂組成物中で微細粒子状又は分子分散に近い形でイオンコンプレックスを部分的に作りイオン架橋構造を形成する。特に、高分子電解質ポリマーのEWが低い場合(例えば、300~500の場合)には、イオン交換樹脂組成物がポリアゾール系化合物を含有するか、それに代えて/加えて、塩基性重合体(オリゴマーなどの低分子量物質を含む)を含有することが、耐水性と電気抵抗等のバランス面の観点から好ましい。
当該ポリフェニレンエーテル樹脂及び/又はポリフェニレンスルフィド樹脂のイオン交換樹脂組成物中の含有量は、膜強度の観点から、上述した高分子電解質ポリマー100質量部に対して0.1~20質量部が好ましく、0.5~10質量部がより好ましく、1~5質量部がさらに好ましい。
これらの樹脂を2種以上用いる場合は、溶媒に溶解又は媒体に分散させて混合してもよく、樹脂前駆体同士を押し出し混合してもよい。
上記フッ素系樹脂としては、本実施形態で用いる式(1)で表されるフッ素系高分子電解質ポリマー100質量部に対して30~50質量部含むことが好ましく、10~30質量部含むことがより好ましく、0~10質量部含むことがさらに好ましい。
電解質膜の平衡含水率が5質量%以上であると、電解質膜の電気抵抗や電流効率、耐酸化性、イオン選択透過性が良好となる傾向にある。
一方、平衡含水率が80質量%以下であると、電解質膜の寸法安定性や強度が良好となり、また水溶解性成分の増加を抑制できる傾向にある。電解質膜の平衡含水率は、電解質膜を構成する所定の樹脂組成物を水とアルコール系溶媒での分散液から成膜し、160℃以下で乾燥した膜を基準とし、23℃、50%関係湿度(RH)での平衡(24Hr放置)飽和吸水率(Wc)で表す。
具体的には、電解質膜を構成する高分子電解質ポリマーのモノマーの共重合比、モノマー種の選定等により調整することができる。
本実施形態のレドックスフロー二次電池用電解質膜は、上述したように補強材を有している。
ここで、「内部体積を実質的に閉塞した構造」とは高分子電解質ポリマーが補強材の内部体積に含浸され、実質的に閉塞した構造であり、具体的には、高分子電解質ポリマーが補強材に含浸されることにより、補強材の内部体積が90%以上閉塞された状態である。
このように電解質膜の内部体積を実質的に閉塞した構造とすることにより、電解質膜を電解液に接触させた際に、電解液の含浸による高分子電解質ポリマーの体積変化を抑制し、その結果、電流効率や電気抵抗改良の効果が得られる。
電解質膜を膜厚方向に沿って切断加工して、それにより現れる断面を、走査型電子顕微鏡(SEM)で、30000倍で観察して、補強材層の断面積を求めた。得られた像から、空隙部分と、それ以外の部分とを二値化処理し、空隙部分の面積の総和を算出し、下記式により補強材層の空隙率を求める。
補強材層のポリマー含浸率(%)=100-{[空隙面積の総和(μm2)/補強材層の断面積(μm2)]×100}
補強材層の高分子電解質ポリマーの含浸率が上記の範囲にあることにより、電解質膜を電解液中に浸漬した際に、電解液が空隙部分に浸入し、電解質膜が過度に膨張することにより、サイクル試験後に電気抵抗が高くなったり、電流効率が低下したりするのを抑制できる傾向がある。
本実施形態のレドックスフロー二次電池用電解質膜は、第1の形態として、フッ素系微多孔膜からなる補強材を有する。
フッ素系微多孔膜としては、フッ素系高分子電解質ポリマーとの親和性が良好であれば特に限定されず、例えば、ポリテトラフルオロエチレン(PTFE)からなる微多孔膜が挙げられ、延伸されて多孔化したポリテトラフルオロエチレン(PTFE)系膜が好ましい。
このPTFE系膜にフッ素系高分子電解質ポリマーを実質的に隙間無く埋め込んだ補強材が、薄膜の強度の観点、及び面(縦横)方向の寸法変化を抑える観点から、より好ましい。上記フッ素系高分子電解質ポリマーを含浸させた補強材は、有機溶媒又はアルコール-水を溶媒とした、適度な濃度のイオン交換樹脂組成物の分散液を、適量フッ素系微多孔膜からなる補強材に含浸させて、乾燥させることにより得ることができる。
延伸PTFE微多孔膜の製造方法としては、例えば、特開昭51-30277号公報、特表平1-01876号公報および特開平10-30031号公報等に開示されているような公知の方法が挙げられる。
具体的には、まずPTFE乳化重合水性分散液を凝析して得られたファインパウダーに、ソルベントナフサ、ホワイトオイルなどの液状潤滑剤を添加し、棒状にペースト押出を行う。その後、この棒状のペースト押出物(ケーク)を圧延して、PTFE未焼成体を得る。この時の未焼成テープを長手方向(MD方向)及び/又は幅方向(TD方向)に任意倍率延伸する。延伸時もしくは、延伸後、押出時に充填した液状潤滑剤を過熱もしくは抽出により除去し、延伸PTFE微多孔膜を得ることができる。
フッ素系微多孔膜の細孔分布が2つの分布中心を有すると、(i)細孔径の大きい分布中心が、反応生成水の排出の促進及び添加剤の易充填性といった役割を担う、(ii)細孔径の小さい分布中心が、電解質の体積膨潤を微多孔膜の機械強度により抑制する役割を担う、といった別々の役割を果たす部分を有するため、このフッ素系微多孔膜を含む電解質膜は化学的耐久性と物理的耐久性を両立し易くなる傾向にある。
各単層に仮にボイドやピンホール等の欠陥が発生した場合にも欠陥が伝播しないという観点からは、複層であることが好ましい。
一方、高分子電解質ポリマー及び添加剤の充填性の観点からは、単層であることが好ましい。フッ素系微多孔膜を複層にする方法としては、2つ以上の単層を熱ラミネートで接着する方法やケークを複数重ねて圧延する方法等が挙げられる。
しかしながら、弾性率が1000MPa以下のフッ素系微多孔膜からなる補強材を用いることにより、電解質膜の体積変化による応力をフッ素系微多孔膜からなる補強材で緩和し、寸法変化を抑制することが可能となる。一方、フッ素系微多孔膜からなる補強材の弾性率が小さすぎると、電解質膜の強度が低下する傾向にある。したがって、フッ素系微多孔膜からなる補強材の弾性率は、1~1000MPaが好ましく、10~800MPaがより好ましく、100~500MPaがさらに好ましい。
空隙率が50%~90%の範囲にあることにより、電解質膜のイオン導電性の向上と電解質膜の強度の向上及び寸法変化の抑制を両立することができる傾向にある。
ここで、フッ素系微多孔膜からなる補強材の空隙率は、水銀圧入法により水銀ポロシメータ(例えば、島津製作所製、商品名:オートポアIV 9520、初期圧約20kPa)によって測定される値を言う。
フッ素系微多孔膜からなる補強材の空隙率を高くする手段としては、例えば、液状潤滑剤の添加量を5~50質量%に調整する方法が挙げられる。この範囲に液状潤滑剤の添加量を調整することで、フッ素系微多孔膜からなる補強材を構成する樹脂の成形性が維持されると共に可塑化効果が十分となるため、フッ素系微多孔膜からなる補強材を構成する樹脂の繊維を二軸方向に高度にフィブリル化させることができ効率よく延伸倍率を増加させることができる。逆に、空隙率を低くする手段としては、例えば、液状潤滑剤を減量すること、延伸倍率を減少すること等が挙げられる。
膜厚が0.1μm~50μmの範囲にあることにより、高分子電解質ポリマーがフッ素系微多孔膜からなる補強材中に孔充填できるとともに、電解質膜の寸法変化が抑制される傾向にある。ここで、フッ素系微多孔膜からなる補強材の膜厚は、当該補強材を構成する膜を50%RHの恒温恒湿の室内で十分に静置した後、公知の膜厚計(例えば、東洋精機製作所製、商品名「B-1」)を用いて測定される値を言う。
本実施形態のレドックスフロー二次電池用電解質膜は、第2の形態として、不織布及び/又は炭化水素系微多孔膜からなる補強材を有する。
不織布としては、高分子電解質ポリマーとの親和性が良好であれば特に限定されず、以下に限定されるものではないが、例えば、ポリエステル繊維、ガラス繊維、アラミド繊維、ポリフェニレンスルフィド繊維、ナノファイバー繊維、ナイロン繊維、セルロース繊維、ビニロン繊維、ポリオレフィン繊維、レーヨン繊維等からなる不織布が挙げられる。
上記の中でも、含水時の寸法変化の観点から、ポリエステル繊維が好ましく、特に下記一般式(I)で表される構造単位からなる重合体であり、サーモトロピック液晶ポリエステルに分類される芳香族液晶ポリエステルが好ましい。
不織布の空隙率が95%以下である場合、電解質膜の寸法安定性の向上に伴って電池の耐久性が向上する傾向にあり、40%以上である場合、電解質膜としてのイオン伝導性が向上する傾向にある。
上記ポリオレフィン樹脂は、単独で用いても、併用してもよい。
上記の中でも、炭化水素系微多孔膜の成形性の観点から、ポリエチレンが好ましく、より好ましくは超高分子量ポリエチレンや高密度ポリエチレン、さらに好ましくは超高分子量ポリエチレンである。
炭化水素系微多孔膜の成形性及び物性(機械強度、空隙率、膜厚)の観点からは、重量平均分子量が好ましくは1×105以上、より好ましくは3×105以上、更に好ましくは5×105以上であり、5×105~15×106の超高分子量ポリエチレンが特に好ましい。また、耐熱性の観点からは、ポリプロピレンが好ましい。
多層構造とは、樹脂層と空気層が厚み方向に交互に積み重なったパイ生地状の多層構造を意味する。すなわち、炭化水素系微多孔膜がパイ生地のように2層、3層、4層・・・と積層された多層構造を有するものであって、従来の3次元網目構造を有する微多孔膜とは異なる。このような多層構造を有する炭化水素系微多孔膜を用いると、従来の3次元網目構造を有する微多孔膜を使用したときに比べ、電解質膜の寸法変化安定性や機械強度をより一層向上させることができる。なお、「空気層」とは、膜厚方向に隣接した樹脂層の間(パイ生地間)の空間のことである。
通常、炭化水素系微多孔膜に充填された高分子電解質ポリマーは、炭化水素系微多孔膜部との界面で高分子電解質の劣化の伝播を停止することができると考えられているが、高分子電解質ポリマーの含水率が高い場合、著しく増大した高分子電解質ポリマーの体積変化による応力に耐え切れず炭化水素系微多孔膜の一部がクリープ変形を起こす場合がある。このとき炭化水素系微多孔膜が単層構造であるとクリープ変形した箇所から寸法変化抑制効果が減少し、電解質膜の劣化が加速されて機械強度が減少するため、結果として耐久性を発現できない場合がある。しかしながら炭化水素系微多孔膜が多層構造であると、その詳細は詳らかではないが、適度に高分子電解質の体積変化による応力を拡散させることが可能となる。上記推定されるメカニズムにより、多層構造を有する炭化水素系微多孔膜と、電解質ポリマーと紹み合わせることより、より一層高度な耐久性を発現し得る。
例えば、有機或いは無機の粒子を、ミリング装置等を用いて適当なゲル化溶媒中に分散させた後、結着剤としてのポリオレフィン樹脂と適当な前記ゲル化溶媒の残りを加えて、該ポリオレフィンと該溶媒を加熱溶解させることによりゾル化させる。このようにして得られたゾル化組成物をゲル化温度以上の温度にてテープ状に成形し、該テープ状物をゲル化温度以下に急冷することによりゲル化シートを製造する。このゲル化シートを、ポリオレフィン樹脂のガラス転移温度以上の温度で1軸或いは2軸に延伸し、その後熱固定することにより多層構造を有するポリオレフィン微多孔膜を製造することができる。ゲル化溶媒としては、ポリオレフィン樹脂がポリエチレンの場合、通常、デカリン(デカヒドロナフタレン)、キシレン、ヘキサン、パラフィン等が挙げられる。このゲル化溶媒は2種以上の溶媒の混合物であってもよい。
上記補強材は、有機溶媒又はアルコール-水を溶媒とした、イオン交換樹脂組成物の適度な濃度の分散液を、適量不織布及び/又は炭化水素系微多孔膜に含浸漬させて、乾燥させることにより得ることができる。
中でも、水と脂肪族アルコール類が好ましく、具体的には、水、メタノール、エタノール、1-プロパノール、2-プロパノール、1-ブタノール、2-ブタノール、イソブチルアルコール及びtert-ブチルアルコール等が挙げられる。上記溶媒は、単独の溶媒で用いても、2種以上を併用してもよい。
表面処理を行うと、その後の高分子電解質の含浸を好適に行うことができる。このような表面処理の一例としては、コロナ放電処理、紫外線照射処理、プラズマ処理が挙げられる。また、含浸性や、接着性を高める目的で、含浸液に用いている溶媒で事前に基材の表面を濡らしたり、含浸液を希釈して塗布するか、或いは、塩基性重合体等の溶液をあらかじめ基材に塗布してもよい。
電解質膜の面方向の寸法変化は、20%以下であることが好ましく、より好ましくは15%以下である。電解質膜の面方向の寸法変化が20%以下であると、電池セルへの応力が小さくなり耐久性が向上する傾向にある。
本実施形態のレドックスフロー二次電池用電解質膜は、第3の形態として、織布からなる補強材を有する。
織布としては、高分子電解質ポリマーとの親和性が良好であれば特に限定されず、例えば、フッ素繊維、ポリエステル繊維、ガラス繊維、アラミド繊維、ポリフェニレンスルフィド繊維、ナノファイバー繊維、ナイロン繊維、セルロース繊維、ビニロン繊維、ポリオレフィン繊維、レーヨン繊維等からなる織布が挙げられる。上記の中でも、高分子電解質ポリマーとの親和性の観点から、フッ素繊維が好ましく、その中でもPTFE繊維が好ましい。
また、織布に用いられる繊維は、フィラメントであってもまたマルチフィラメントであってもよいが、マルチフィラメントの場合は糸断面を偏平化できるため、織布の空隙率を小さくさせても電解質膜の抵抗の上昇を小さくできるため好ましい。
織布からなる補強材の膜厚が50μm以下である場合、電気抵抗が小さくなり電池性能が向上する傾向にあり、5μm以上である場合、フッ素系高分子電解質ポリマーを含浸する工程中等で破損等の不良が生じるおそれが小さく、機械特性が十分となる傾向にある。
電解質膜の製造方法(成膜法)としては、特に限定されず、公知の、押し出し方法、キャスト成膜を用いることができる。
電解質膜は単層でも多層(2~5層)でもよく、多層の場合は性質の異なる膜(例えば、EWや官能基の異なる樹脂)を積層することにより、電解質膜の性能を改善することができる。
多層の場合は、押出し製膜時、キャスト時に積層させるか、又は得られたそれぞれの膜を積層させればよい。
熱処理の時間は、より好ましくは2~20分であり、更に好ましくは3~15分、特に好ましくは5~10分程度である。
先ず、成膜時のままの状態では、原料由来の粒子間(一次粒子及び二次粒子間)及び分子間が充分に絡み合っていないため、その粒子間及び分子間を絡み合わす目的で、特に耐水性(特に熱水溶解成分比率を下げ)、水の飽和吸水率を安定させ、安定なクラスターを生成させるために有用である。
また、膜強度向上の観点からも有用である。
特にキャスト成膜法を用いた場合には有用である。
なお、本明細書中の各物性は、特に明記しない限り、以下の実施例に記載された方法に準じて測定することができる。
(1) 高分子電解質ポリマーであるPFSA樹脂の前駆体のメルトフローインデックス(MFI)
ASTM:D1238に準拠して、測定条件:温度270℃、荷重2160gで測定を行った。
PFSA樹脂0.3gを、25℃、飽和NaCl水溶液30mLに浸漬し、攪拌しながら30分間放置した。
次いで、飽和NaCl水溶液中の遊離プロトンを、フェノールフタレインを指示薬として0.01N水酸化ナトリウム水溶液を用いて中和滴定した。中和後に得られた、イオン交換基の対イオンがナトリウムイオンの状態となっているPFSA樹脂分を純水ですすぎ、さらに真空乾燥して秤量した。
中和に要した水酸化ナトリウムの物質量をM(mmol)、イオン交換基の対イオンがナトリウムイオンの状態となっているPFSA樹脂の質量をW(mg)とし、下記式より当量質量EW(g/eq)を求めた。
EW=(W/M)-22
電解質膜サンプルを、23℃、50%RHの恒温恒湿の室内で1時間以上静置した後、膜厚計(東洋精機製作所製、商品名「B-1」)を用いて膜厚を測定した。
補強材を構成する微多孔膜の細孔分布は、以下のようにして測定した。
まず、微多孔膜サンプルをφ25mmの大きさに切り出し、貫通細孔分布/ガス、流体透過性解析装置(Xonics Corporation製、装置名:Porometer3G)を用いて測定を行った。
本装置の測定は、JIS-K-3832に記載のバブルポイント法に準拠しており、まず微多孔膜の細孔体積を試験専用液体(porofil(登録商標))で完全に満たした後、微多孔膜にかかる圧力を徐々に増加させることで、試験専用液の表面張力と印加した気体の圧力、供給流量から細孔分布を求めた(バブルポイント・ハーフドライ法)。
微多孔膜の細孔分布は、細孔測定範囲:0.065μm~10.0μm、流量ガス:圧縮空気で測定し、細孔分布の分布中心を求めた。
また、細孔の存在比を下記式により算出した。
(細孔の存在比)=(細孔径0.3μm~5.0μmの範囲に存在する細孔数)/(細孔径0.065μm~10.0μmに存在する微多孔膜の全細孔数)
膜サンプルを70mm×10mmの矩形膜に切り出し、JIS K-7127に準拠して平面方向の各寸法(長手(MD)方向および幅(TD)方向)の弾性率を測定した。
水銀ポロシメータ(島津製作所製、商品名:オートポアIV 9520、初期圧約20kPa)を用いて、水銀圧入法により測定した。
膜サンプルを4cm×3cmの矩形膜に切り出し、恒温恒湿の室内(23℃、50%RH)に1時間以上放置した後、その乾燥状態の矩形膜サンプルの平面方向の各寸法を測定した。
次に、上記寸法を測定した矩形膜サンプルを80℃の熱水中で1時間煮沸し、電解質膜の水分による質量変化量が5%以下の湿潤状態になるよう(水分吸収による体積膨潤が飽和に達するように)充分に水を吸収させた。この際、熱水中から膜を取り出し、表面の水分を十分に除去した状態で、電子天秤で質量変化量が5%以下となったことを確認した。
この水を吸収して膨張した湿潤状態の膜サンプルを熱水中から取り出し、平面方向の各寸法(長手(MD)方向および幅(TD)方向)を測定した。
乾燥状態での平面方向における各寸法を基準として、その乾燥状態での各寸法から湿潤状態での平面方向における各寸法の増分の平均を取って、平面方向寸法変化(%)とした。
後述する実施例及び比較例における、高分子電解質ポリマーであるPFSA樹脂の分散液を、清澄なガラス板上に塗布し、150℃で約10分間乾燥し、剥離して約30μmの膜を形成させ、これを23℃の水中に約3時間放置し、その後23℃、関係湿度(RH)50%の部屋に24時間放置した時の平衡含水率を測定した。
基準の乾燥膜としては、80℃真空乾燥膜を用いた。
平衡含水率は、電解質膜の質量変化から算出した。
最大含水率として、上述した平衡含水率測定時に観測される最大値を測定した。
JIS K7113に基づき、島津製作所製精密万能試験機AGS-1KNGを用いて電解質膜の破断強度を測定した。サンプルは23℃、65%の恒温室で12時間以上放置した後に幅5mm、長さ50mmに切出し測定に供した。測定は3サンプルについて行い、その平均値を求めた。
後述する実施例及び比較例のレドックスフロー二次電池を用いて充放電試験を行った。
レドックスフロー二次電池は、液透過性で多孔質の集電体電極(負極用、正極用)を隔膜(電解質膜)の両側にそれぞれ配置し、押圧でそれらを挟み、隔膜で仕切られた一方を正極セル室、他方を負極セル室とし、スペーサーで両セル室の厚みを確保した。
正極セル室には、バナジウム4価(V4+)及び同5価(V5+)を含む硫酸電解液からなる正極電解液を、負極セル室にはバナジウム3価(V3+)及び同2価(V2+)を含む負極電解液を流通させ、電池の充電及び放電を行った。
全バナジウム濃度が2M/Lで、全硫酸根濃度が4M/Lでの水系電解液を使用し、また、設置した正極及び負極セル室の厚みがそれぞれ5mmで、両多孔質電極と隔膜(電解質膜)との間には炭素繊維からなる厚み5mmで嵩密度が約0.1g/cm3の多孔質状のフエルトを挟んで用いた。充放電実験は電流密度80mA/cm2で実施した。
電流効率(%)は、放電電気量を充電電気量で除した比率(%)を算出することにより得た。両電気量は、隔膜のイオン選択透過性及びその他電流損失に依存する。
内部抵抗すなわちセル電気抵抗率の減少は、電圧効率を向上させ、イオン選択透過性の向上及びその他電流損失の低減は、電流効率を向上させるので、レドックスフロー二次電池において、重要な指標となる。
セル電気抵抗率は、ACインピーダンス法を用いて、放電開始時においてAC電圧10mV、周波数20kHzでの直流抵抗値を測定し、それに電極面積を掛けることによって求めた。
上記電流効率及びセル電気抵抗率については、初期値と、充放電試験を200サイクル実施した後の両方の値を求めた。
実施例1~9で得られた電解質膜について、補強材層のポリマー含浸率を求めた。
高分子電解質ポリマーの補強材への含浸率は、以下のようにして求めた。
電解質膜を膜厚方向に沿って切断加工して、それにより現れる断面を、走査型電子顕微鏡(SEM)で、30000倍で観察して、補強材層の断面積を求めた。
得られた像から、空隙部分と、それ以外の部分とを二値化処理し、空隙部分の面積の総和を算出し、下記式により補強材層の空隙率を求める。
補強材層のポリマー含浸率(%)=100-{[空隙面積の総和(μm2)/補強材層の断面積(μm2)]×100}
95%以上の場合を「A」、90%以上95%未満の場合を「B」、90%未満の場合を「C」と評価した。
〔実施例1〕
(1)PFSA樹脂前駆体の製造
ステンレス製攪拌式オートクレーブに、C7F15COONH4の10%水溶液と純水とを仕込み、十分に真空、窒素置換を行った後、テトラフルオロエチレン(CF2=CF2)(以下、「TFE」とも略記する。)ガスを導入してケージ圧力で0.7MPaまで昇圧した。
引き続いて、過硫酸アンモニウム水溶液を注入して重合を開始した。
重合により消費されたTFEを補給するため、連続的にTFEガスを供給してオートクレーブの圧力を0.7MPaに保つようにして、供給したTFEに対して、質量比で0.70倍に相当する量のCF2=CFO(CF2)2-SO2Fを連続的に供給して重合を行い、重合条件を最適な範囲に調整して、パーフルオロカーボンスルホン酸(PFSA)樹脂前駆体粉末を得た。
得られたPFSA樹脂前駆体粉末(表1中のPFSA樹脂A1の前駆体)のメルトフローインデックス(MFI)は1.5(g/10分)であった。
得られたPFSA樹脂前駆体粉末を、水酸化カリウム(15質量%)とメチルアルコール(50質量%)を溶解した水溶液中に、80℃で20時間接触させて、加水分解処理を行った。その後、60℃水中に5時間浸漬した。
次に、60℃の2N塩酸水溶液に1時間浸漬させる処理を、毎回塩酸水溶液を更新して5回繰り返した後、イオン交換水で水洗、乾燥した。
これにより、スルホン酸基(SO3H)を有し、上記式(2)(m=2、X4=SO3H)で表される構造を有するPFSA樹脂を得た。
得られたPFSA樹脂A1のEWは650(g/eq)であった。
次に、この100gのPFSA樹脂分散液に純水100gを添加、攪拌した後、この液を80℃に加熱、攪拌しながら、固形分濃度が20質量%になるまで濃縮した。
得られたPFSA樹脂A1の分散液を、分散液(ASF1)とした。
数平均分子量650万のPTFEファインパウダー1kg当たり、押出液状潤滑油としての炭化水素油を20℃において463mL加えて混合した。
次に、この混合物をペースト押出しすることにより得られた丸棒状成形体を、70℃に加熱したカレンダーロールによりフィルム状に成形し、PTFEフィルムを得た。このフィルムを250℃の熱風乾燥炉に通して押出助剤を蒸発除去し、平均厚み300μm、平均幅150mmの未焼成フィルムを得た。
次に、この未焼成PTFEフィルムを長手方向(MD方向)に延伸倍率6.6倍で延伸し、巻き取った。得られたMD方向延伸PTFEフィルムの両端をクリップで挟み、幅方向(TD方向)に延伸倍率8倍で延伸し、熱固定を行い、厚み10μmの延伸PTFE膜を得た。このときの延伸温度は290℃、熱固定温度は360℃であった。
上述したようにして製造したPTFE微多孔膜を微多孔膜1とした。微多孔膜1の細孔分布の分布中心は1.29μmであった。
上記分散液ASF1をバーコーター(松尾産業製、バーNo.200、WET膜厚200μm)を用いて基材フィルム上に塗布した(塗布面積:幅約200mm×長さ約500mm)後、分散液が乾ききっていない状態で、前記PTFE微多孔膜1(膜厚:10μm、空隙率:82%、サンプルサイズ:幅200mm×長さ500mm)を分散液上に積層し、微多孔膜上からゴムローラーを用いて分散液と微多孔膜を圧着させた。
このとき微多孔膜の一部に分散液が充填していることを目視にて確認した後、この膜、すなわちPTFE微多孔膜と基材フィルムとの積層体を90℃のオーブンで20分乾燥させた。
次に、得られた膜のPTFE微多孔膜上から分散液を再度同様にして積層させることで微多孔膜の空隙を分散液で十分に充填させ、この膜を90℃のオーブンでさらに20分乾燥させた。
このようにして得られた「分散液が十分に含浸したPTFE微多孔膜」を170℃のオーブンで1時間熱処理し、膜厚約25μmの電解質膜を得た。
電解質膜の評価結果を表1に示す。
得られた電解質膜の平衡含水率は、ASF1は12質量%であった。
25℃水中3時間における電解質膜の最大含水率は、ASF1は23質量%であった。ここで、最大含水率は、平衡含水率測定時に観測される最大値を示す。
電解質膜の平面方向寸法変化は、14%であった。
ASF1から得られた電解質膜を用いて、電解液中で充分平衡にしてから充放電実験を行い、その後安定な状態にしてから、初期の電流抵抗及びセル電気抵抗率を測定した。
電解質膜の(電流効率/セル電気抵抗率)は、(97.5/0.90)であった。
その結果、電流効率(%)/セル電気抵抗率(Ω・cm2)は、(97.3/0.90)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていることが分かった。
(1)PTFE微多孔膜2の製造
数平均分子量1200万のPTFEファインパウダー1kg当たりに、押出液状潤滑油としての炭化水素油を20℃において300mL加えて混合した。
次に、この混合物をペースト押出しすることにより得られた丸棒状成形体を、70℃に加熱したカレンダーロールによりフィルム状に成形し、PTFEフィルムを得た。このフィルムを250℃の熱風乾燥炉に通して押出助剤を蒸発除去し、平均厚み200μm、平均幅280mmの未焼成フィルムを得た。
次に、この未焼成PTFEフィルムを長手方向(MD方向)に延伸倍率5倍で延伸し、巻き取った。
得られたMD方向延伸PTFEフィルムの両端をクリップで挟み、幅方向(TD方向)に延伸倍率5倍で延伸し、熱固定を行い、厚み12μmの延伸PTFE膜を得た。このときの延伸温度は290℃、熱固定温度は360℃であった。作製したPTFE微多孔膜を微多孔膜2とした。PTFE微多孔膜2の細孔分布の分布中心は1.18μmであった。
PTFE微多孔膜2を用いたこと以外は、実施例1と同様の方法により電解質膜を得た。
得られた電解質膜の平衡含水率は、12質量%であり、25℃水中3時間における電解質膜の最大含水率は、23質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ8%であり、寸法変化が小さかった。
実施例1と同様の方法により充放電試験を行った結果、初期の電流効率(%)/セル電気抵抗率(Ω・cm2)は(97.5/0.90)であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗は、(97.3%/0.90Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
(1)PTFE微多孔膜3の製造
長手方向(MD方向)の延伸倍率15倍及び幅方向(TD方向)の延伸倍率を8倍としたこと以外は、PTFE微多孔膜2と同様の方法により、厚み8μmの微多孔膜(細孔分布の分布中心は0.2μm)を製造し、これをPTFE微多孔膜3とした。
PTFE微多孔膜3を用いたこと以外は実施例1と同様の方法により電解質膜を得た。
得られた電解質膜の平衡含水率は、12質量%で、25℃水中3時間における電解質膜の最大含水率は、23質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ8%であり、寸法変化が小さかった。
実施例1と同様の方法により充放電試験を行った結果、初期の電流効率(%)/セル電気抵抗率(Ω・cm2)は、97.5/0.90であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗率は、(97.3%/0.90Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
(1)PTFE微多孔膜4の製造
長手方向(MD方向)の延伸倍率3倍及び幅方向(TD方向)の延伸倍率を8.3倍としたこと以外は、PTFE微多孔膜2と同様の方法により、厚み12μmの微多孔膜(細孔分布の分布中心は0.2μm)を作製製造し、これをPTFE微多孔膜4とした。
(2)電解質膜の製造
PTFE微多孔膜4を用い、分散液をWET膜厚の異なるバーコーターを用いて塗布することで、電解質膜の膜厚を20μmから25μmに変更したこと以外は実施例2と同様の方法により電解質膜を得た。
得られた電解質膜の平衡含水率は、12質量%で、25℃水中3時間における電解質膜の最大含水率は、23質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ5%であり、寸法変化が小さかった。
実施例1と同様の方法により充放電試験を行った結果、電流効率(%)/セル電気抵抗率(Ω・cm2)は、(97.5/0.90)であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗率は、(97.3%/0.90Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
(電解質膜の製造)
上記分散液ASF1(PFSA樹脂分散液)をバーコーター(松尾産業製、バーNo.200、WET膜厚200μm)を用いて基材フィルム上に塗布した(塗布面積:幅約200mm×長さ約500mm)後、分散液が乾ききっていない状態で、全芳香族ポリエステルの液晶ポリマー不織布(クラレ社製ベクルス MBBK14FXSP)(膜厚20μm、空隙率83%)を、サンプルサイズ:幅200mm×長さ500mmとして分散液上に積層し、不織布上からゴムローラーを用いて分散液と不織布を圧着させた。
このとき不織布の一部に分散液が充填していることを目視にて確認した後、この膜、すなわち全芳香族ポリエステルの液晶ポリマー不織布と基材フィルムとの積層体を90℃のオーブンで20分乾燥させた。
次に、得られた膜の不織布上から分散液を再度同様にして積層させることで不織布の空隙を分散液で十分に充填させ、この膜を90℃のオーブンでさらに20分乾燥させた。
このようにして得られた「分散液が十分に含浸した不織布」を170℃のオーブンで1時間熱処理し、膜厚約40μmの電解質膜を得た。
電解質膜の評価結果を表1に示す。
得られた電解質膜の平衡含水率は、ASF1は12質量%であった。
25℃水中3時間における電解質膜の最大含水率は、ASF1は23質量%であった。ここで、最大含水率は、平衡含水率測定時に観測される最大値を示す。
その結果、電流効率(%)/セル電気抵抗率(Ω・cm2)は(97.3%/0.90Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐酸化性に優れていることが分かった。
アラミドからなる不織布(ポバール興業株式会社製 AH20CC)(膜厚20μm、空隙率90%)を用いたこと以外は実施例5と同様の方法により電解質膜を得た。
得られた電解質膜の平衡含水率は、12質量%で、25℃水中3時間における電解質膜の最大含水率は、23質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ8%であり、寸法変化が小さかった。
実施例1と同様の方法により充放電試験を行った結果、電流効率(%)/セル電気抵抗率(Ω・cm2)は(97.5/0.90)であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗率は、(97.3%/0.90Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
ポリオレフィン微多孔膜(DSM SoIutech社製、グレード:SoIupor 3PO7A、膜厚:8μm、空隙率:86%)を用いたこと以外は、実施例5と同様の方法により電解質膜を得た。
得られた電解質膜の平衡含水率は、13質量%で、25℃水中3時間における電解質膜の最大含水率は、22質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ11%であった。
実施例1同様の方法により充放電試験を行った結果、電流効率(%)/セル電気抵抗率(Ω・cm2)は(98.3/0.95)であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗率は、(98.2%/0.95Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
この割断片を試料台に固定後、オスミウムプラズマコート処理(導電処理)を行って、断面形態観察用試料とした。
断面形態観察用試料を用いて、SEM(日立製作所製、品番:S-4700、加速電圧:5kV、検出器:2次電子検出器、反射電子検出器)により形態観察を行い、観察画像より多層構造を有することを観察した。多層構造を有することにより寸法変化を抑制でき、膜強度を高めることができる。また、電解液を含浸し、体積変化しようとする応力が適度に分散され、耐久性の向上効果が得られる。
(1)PFSA樹脂分散液(ASF2)の製造
実施例1で得られたPFSA樹脂を、エタノール水溶液(水:エタノール=85:15(質量比))と共に5Lオートクレーブ中に入れて密閉し、翼で攪拌しながら160℃まで昇温して5時間保持した。
その後、オートクレーブを自然冷却して、5質量%の均一なPFSA樹脂分散液を調製した。
次に、この100gのPFSA樹脂分散液に純水100gを添加、攪拌した後、この液を80℃に加熱、攪拌しながら、固形分濃度が20質量%になるまで濃縮した。
得られたPFSA樹脂A1の分散液を、分散液(ASF2)とした。
分散液ASF2を用いたこと以外は、実施例1と同様の方法により、実施例1と同じ補強材を用いて電解質膜を得た。
得られた電解質膜の平衡含水率は、14質量%で、25℃水中3時間における電解質膜の最大含水率は、26質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ16%であった。
実施例1と同様の方法により充放電試験を行った結果、初期の電流効率(%)/セル電気抵抗率(Ω・cm2)は、95.0/0.95であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗率は、(92.1%/1.05Ω・cm2)であった。上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
(電解質膜の製造)
分散液ASF2を用いたこと以外は、実施例5と同じ補強材を用い、同様の方法により電解質膜を得た。
得られた電解質膜の平衡含水率は、16質量%で、25℃水中3時間における電解質膜の最大含水率は、27質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ17%であった。
実施例1と同様の方法により充放電試験を行った結果、初期の電流効率(%)/セル電気抵抗率(Ω・cm2)は、95.0/0.95であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗率は、(91.7%/1.05Ω・cm2)であった。上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
PTFE繊維を用い、平織り方式で作製した織布を用いたこと以外は実施例5と同様の方法により電解質膜を得た。
得られた電解質膜の平衡含水率は、13質量%で、25℃水中3時間における電解質膜の最大含水率は、22質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ14%であった。
実施例1と同様の方法により充放電試験を行った結果、電流効率(%)/セル電気抵抗率(Ω・cm2)は(97.0/0.95)であった。
また、耐久試験として、充放電を200サイクル実施した結果においては、電流効率/セル電気抵抗率は、(96.8%/0.95Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が極めて小さく、耐久性に優れていた。
(電解質膜の製造)
実施例1において調製した分散液(ASF1)を、公知の通常の方法にて、担体シートであるポリイミド製フィルム上にキャストし、120℃(20分)の熱風を当てて、溶媒をほぼ完全に飛ばし、乾燥させることにより成膜した。
これを更に、160℃10分の条件下における熱風空気雰囲気下で、熱処理することにより膜厚20μmの電解質膜を得た。
得られた電解質膜の平衡含水率は、12質量%で、25℃水中3時間における電解質膜の最大含水率は、23質量%であった。
得られた電解質膜を用いて、平面方向寸法変化を測定したところ24%であった。
また、耐久試験として、充放電を200サイクル実施した結果においても、電流効率/セル電気抵抗率が、(84.4%/1.20Ω・cm2)であり、上記初期の電流効率(%)/セル電気抵抗率(Ω・cm2)と比較して変化が大きく、耐久性にも劣っていた。
2 正極セル室
3 負極
4 負極セル室
5 電解質膜
6 電解槽
7 正極電解液タンク
8 負極電解液タンク
9 交直交換装置
Claims (18)
- 炭素電極からなる正極を含む正極セル室と、
炭素電極からなる負極を含む負極セル室と、
前記正極セル室と、前記負極セル室とを隔離分離させる、隔膜としての電解質膜と、
を含む電解槽を有し、
前記正極セル室は活物質を含む正極電解液を、前記負極セル室は活物質を含む負極電解液を含み、
前記電解液中の活物質の価数変化に基づき充放電するレドックスフロー二次電池であって、
前記電解質膜が、高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
前記電解質膜がフッ素系微多孔膜からなる補強材を有するレドックスフロー二次電池。 - 炭素電極からなる正極を含む正極セル室と、
炭素電極からなる負極を含む負極セル室と、
前記正極セル室と、前記負極セル室とを隔離分離させる、隔膜としての電解質膜と、
を含む電解槽を有し、
前記正極セル室は活物質を含む正極電解液を、前記負極セル室は活物質を含む負極電解液を含み、
前記電解液中の活物質の価数変化に基づき充放電するレドックスフロー二次電池であって、
前記電解質膜が、高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
前記電解質膜が不織布及び/又は炭化水素系微多孔膜からなる補強材を有するレドックスフロー二次電池。 - 炭素電極からなる正極を含む正極セル室と、
炭素電極からなる負極を含む負極セル室と、
前記正極セル室と、前記負極セル室とを隔離分離させる、隔膜としての電解質膜と、
を含む電解槽を有し、
前記正極セル室は活物質を含む正極電解液を、前記負極セル室は活物質を含む負極電解液を含み、
前記電解液中の活物質の価数変化に基づき充放電するレドックスフロー二次電池であって、
前記電解質膜が、高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
前記電解質膜が織布からなる補強材を有するレドックスフロー二次電池。 - 前記補強材は、前記高分子電解質ポリマーが、補強材に含浸され、前記補強材の内部体積を実質的に閉塞した構造である、請求項1乃至3のいずれか一項に記載のレドックスフロー二次電池。
- 前記レドックスフロー二次電池は、バナジウムを含む硫酸電解液を、正極及び負極電解液として用いたバナジウム系レドックスフロー二次電池である、請求項1乃至4のいずれか一項に記載のレドックスフロー二次電池。
- 前記電解質膜は、前記高分子電解質ポリマーとして下記式(1)で表される構造を有するフッ素系高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含む、
請求項1乃至5のいずれか一項に記載のレドックスフロー二次電池。
-[CF2CX1X2]a-[CF2-CF((-O-CF2-CF(CF2X3))b-Oc-(CFR1)d-(CFR2)e-(CF2)f-X4)]g- (1)
(式(1)中、X1、X2及びX3は、それぞれ独立して、ハロゲン原子及び炭素数1~3のパーフルオロアルキル基からなる群から選択される1種以上を示す。X4は、COOZ、SO3Z、PO3Z2又はPO3HZを示す。Zは、水素原子、アルカリ金属原子、アルカリ土類金属原子、又はアミン類(NH4、NH3R1、NH2R1R2、NHR1R2R3、NR1R2R3R4)を示す。R1、R2、R3及びR4は、それぞれ独立して、アルキル基及びアレーン基からなる群から選択されるいずれか1種以上を示す。ここで、X4がPO3Z2である場合、Zは同じでも異なっていてもよい。R1及びR2は、それぞれ独立して、ハロゲン原子、炭素数1~10のパーフルオロアルキル基及びフルオロクロロアルキル基からなる群から選択される1種以上を示す。a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示す。bは0~8の整数を示す。cは0又は1を示す。d、e及びfは、それぞれ独立して、0~6の整数を示す(ただし、d、e及びfは同時に0ではない。)。) - 前記電解質膜は、前記高分子電解質ポリマーとして下記式(2)で表される構造を有するフッ素系高分子電解質ポリマーであるパーフルオロカーボンスルホン酸樹脂(PFSA)を主体とするイオン交換樹脂組成物を含む、請求項1乃至6のいずれか一項に記載のレドックスフロー二次電池。
-[CF2CF2]a-[CF2-CF(-O-(CF2)m-X4)]g- (2)
(式(2)中、a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示し、mは1~6の整数を示し、X4はSO3Hを示す。) - 前記高分子電解質ポリマーの当量質量EW(イオン交換基1当量あたりの乾燥質量グラム数)が300~1300g/eqであり、前記電解質膜の平衡含水率が5~80質量%である、請求項1乃至7のいずれか一項に記載のレドックスフロー二次電池。
- 前記イオン交換樹脂組成物が、前記高分子電解質ポリマー100質量部に対して0.1~20質量部のポリフェニレンエーテル樹脂及び/又はポリフェニレンスルフィド樹脂を含む、請求項1乃至8のいずれか一項に記載のレドックスフロー二次電池。
- 高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
フッ素系多孔膜を補強材として有する、
レドックスフロー二次電池用電解質膜。 - 高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
不織布及び/又は炭化水素系微多孔膜からなる補強材を有する、
レドックスフロー二次電池用電解質膜。 - 高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含み、
織布からなる補強材を有する、
レドックスフロー二次電池用電解質膜。 - 前記補強材は、前記高分子電解質ポリマーが含浸され、前記レドックスフロー二次電池用の補強材の内部体積を実質的に閉塞した構造である、請求項10乃至12のいずれか一項に記載のレドックスフロー二次電池用電解質膜。
- 前記レドックスフロー二次電池用電解質膜は、前記高分子電解質ポリマーとして下記式(1)で表される構造を有するフッ素系高分子電解質ポリマーを主体とするイオン交換樹脂組成物を含む、請求項10乃至13のいずれか一項に記載のレドックスフロー二次電池用電解質膜。
-[CF2CX1X2]a-[CF2-CF((-O-CF2-CF(CF2X3))b-Oc-(CFR1)d-(CFR2)e-(CF2)f-X4)]g- (1)
(式(1)中、X1、X2及びX3は、それぞれ独立して、ハロゲン原子及び炭素数1~3のパーフルオロアルキル基からなる群から選択される1種以上を示す。X4は、COOZ、SO3Z、PO3Z2又はPO3HZを示す。Zは、水素原子、アルカリ金属原子、アルカリ土類金属原子、又はアミン類(NH4、NH3R1、NH2R1R2、NHR1R2R3、NR1R2R3R4)を示す。R1、R2、R3及びR4は、それぞれ独立して、アルキル基及びアレーン基からなる群から選択されるいずれか1種以上を示す。ここで、X4がPO3Z2である場合、Zは同じでも異なっていてもよい。R1及びR2は、それぞれ独立して、ハロゲン原子、炭素数1~10のパーフルオロアルキル基及びフルオロクロロアルキル基からなる群から選択される1種以上を示す。a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示す。bは0~8の整数を示す。cは0又は1を示す。d、e及びfは、それぞれ独立して、0~6の整数を示す(ただし、d、e及びfは同時に0ではない。)。) - 前記高分子電解質ポリマーは、下記式(2)で表される構造を有するフッ素系高分子電解質ポリマーである、パーフルオロカーボンスルホン酸樹脂(PFSA)である、請求項10乃至14のいずれか一項に記載のレドックスフロー二次電池用電解質膜。
-[CF2CF2]a-[CF2-CF(-O-(CF2)m-X4)]g- (2)
(式(2)中、a及びgは、0≦a<1、0<g≦1、a+g=1を満たす数を示し、mは1~6の整数を示し、X4はSO3Hを示す。) - 前記高分子電解質ポリマーの当量質量EW(イオン交換基1当量あたりの乾燥質量グラム数)が300~1300g/eqであり、前記電解質膜の平衡含水率が5~80質量%である、請求項10乃至15のいずれか一項に記載のレドックスフロー二次電池用電解質膜。
- 前記イオン交換樹脂組成物が、前記高分子電解質ポリマー100質量部に対して0.1~20質量部のポリフェニレンエーテル樹脂及び/又はポリフェニレンスルフィド樹脂を含む、請求項10乃至16のいずれか一項に記載のレドックスフロー二次電池。
- 前記レドックスフロー二次電池用電解質膜は、130~200℃にて1~60分間加熱処理されたものである、請求項10乃至17のいずれか一項に記載のレドックスフロー二次電池用電解質膜。
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ES2778108T3 (es) | 2020-08-07 |
JPWO2013100083A1 (ja) | 2015-05-11 |
EP3046174B1 (en) | 2020-02-19 |
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US9905875B2 (en) | 2018-02-27 |
DK3046174T3 (da) | 2020-04-14 |
EP3046174A1 (en) | 2016-07-20 |
EP2800194A4 (en) | 2015-08-19 |
CN107254058A (zh) | 2017-10-17 |
KR101797274B1 (ko) | 2017-11-13 |
JP5797778B2 (ja) | 2015-10-21 |
DK2800194T3 (en) | 2017-10-09 |
KR20140088889A (ko) | 2014-07-11 |
EP2800194B1 (en) | 2017-06-28 |
EP2800194A1 (en) | 2014-11-05 |
ES2637430T3 (es) | 2017-10-13 |
CN104040775A (zh) | 2014-09-10 |
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