JP2013137957A - Redox flow secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance redox flow secondary battery in which the activity of oxidation-reduction reaction is remarkably enhanced.SOLUTION: A redox flow secondary battery comprises an electrolytic bath comprising: a positive electrode cell room including a positive electrode made of a carbon electrode; a negative electrode cell room including a negative electrode made of a carbon electrode; and an electrolyte membrane operative as a barrier membrane to seclude and separate the positive electrode cell room from the negative electrode cell room, the positive electrode cell room containing positive electrode electrolyte that contains an active material, the negative electrode cell room containing negative electrode electrolyte that contains an active material. The redox flow secondary battery charges/discharges in accordance with the change in valence of the active material in the electrolyte. The carbon electrodes comprises carbon particles and a binding agent.

Description

  The present invention relates to a redox flow secondary battery.

  The redox flow secondary battery belongs to a large stationary battery used for leveling the amount of electricity used for storage and discharge of electricity, and the structure of the battery includes an anode and the anode active material. The electrolyte solution (anode cell) containing, the cathode and the cathode electrolyte solution (cathode cell) containing the cathode active material are separated by a diaphragm, and charged and discharged using the oxidation-reduction reaction of both active materials. The active material contained in the electrolytic solution, which is used by flowing the electrolytic solution containing the active material from the storage tank to the electrolytic layer and taking out the current, is iron-chromium, chromium-bromine, zinc- There are bromine and vanadium.

For example, in the case of a vanadium system, liquid collector and porous electrodes are arranged on both sides of a diaphragm with two current collector plates (for cathode and anode) on both sides of the diaphragm, and sandwiched by pressing, One of the cells 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 stores is secured by a spacer. The positive electrode cell chamber has vanadium tetravalent (V ⁴⁺ ) and pentavalent (V ⁵⁺ ), a positive electrode electrolyte made of a sulfuric acid electrolyte, and a negative electrode cell made of trivalent vanadium (V ³⁺ ) and divalent (V ²⁺ ) in the negative electrode cell chamber was circulated and charged and discharged. The At the time of charging, in the positive electrode cell chamber, vanadium ions emit electrons and V ⁴⁺ is oxidized to V ⁵⁺ . In the negative electrode cell chamber, V ³⁺ is reduced to V ²⁺ by the electrons returning through the outer path. This oxidation-reduction reaction is carried out with a porous electrode disposed on the diaphragm.

  The porous electrode has a structure and a form that are excellent in the ability to pass through the electrolytic solution, providing only a place for generating a redox reaction when vanadium ions in the electrolytic solution pass through the cell. Therefore, it is important that the surface area is as large as possible and the electrical resistance is low. In general, as the porous electrode, a woven fabric, a non-woven fabric, or the like made of carbon fibers usually called carbon felt is used. In addition, carbon materials usually exhibit water repellency, but from the viewpoint of redox reaction activation, it is important to have good affinity with the electrolyte solution (aqueous solution), and water decomposition as a side reaction is also important. From the standpoint of not generating it, characteristics with high hydrogen overvoltage and oxygen overvoltage are required.

Large-scale power storage battery Nikkan Kogyo Shimbun, Chapter 3 p. 63-72

However, when carbon felt is used, there is a limit to increasing the surface area, and at the same time, there is a limit to improving the affinity with the electrolytic solution (aqueous solution). In order to reduce the cost of the redox flow secondary battery, it was necessary to solve the above problems and increase the activity of the electrode to increase the reaction rate of the oxidation-reduction reaction. Another problem is that the carbon felt itself is expensive.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-performance redox flow secondary battery in which the activity of the oxidation-reduction reaction is remarkably improved.

  As a result of intensive investigations to achieve the above object, the present inventors have found that a carbon electrode containing carbon particles and a binder, and further, by joining the carbon electrode to an electrolyte membrane, the activity of the oxidation-reduction reaction can be improved. Remarkably improved and succeeded in obtaining a high-performance redox flow secondary battery, leading to the present invention.

That is, the present invention is as follows.
[1]
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 redox flow secondary battery in which the carbon electrode includes carbon particles and a binder.
[2]
The redox flow secondary battery according to [1], wherein the carbon electrode is joined to the electrolyte membrane.

  According to the present invention, the activity of the redox reaction can be remarkably improved, and a high-performance redox flow secondary battery can be provided.

  The best mode for carrying out the present invention (hereinafter abbreviated as “embodiment”) will be described in detail below. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

The redox flow secondary battery of the present invention 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 electrolytic cell including an electrolyte membrane as a diaphragm for separating and separating the positive electrode cell chamber and the negative electrode cell chamber;
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 carbon electrode includes carbon particles and a binder.

A redox flow secondary battery is usually used in the form of a flow-type electrolytic cell, and generally has a cell stack structure in which a plurality of cells are stacked. The main members constituting the cell include an electrode, a diaphragm, a bipolar plate, and a frame.
The electrode includes carbon particles and a binder.

The carbon particles are not particularly limited, but coke such as pitch coke and needle coke, non-graphitizable carbon obtained by firing and carbonizing an organic material at a temperature of about 700 to 1500 ° C., and mesocarbon microbeads. Representative spherical graphite, fibrous graphite, carbon fiber, graphite, carbon black, acetylene black, furnace black, channel black, thermal black, acetylene black, graphitized carbon black, and the like can be used.
The shape of the carbon particles is not particularly limited, and may be spherical, crushed, scaly, or fibrous. A plurality of types of carbonaceous materials may be mixed and used.

  Examples of the binder include polytetrafluoroethylene, polytrifluoroethylene, polyethylene, nitrile rubber, polybutadiene rubber, butyl rubber, polystyrene, styrene butadiene rubber, styrene butadiene latex, polysulfide rubber, nitrocellulose, acrylonitrile butadiene rubber, Copolymerization of one or more selected from the group consisting of polyvinyl fluoride, fluororubber, polyvinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, trifluoromonochloroethylene, and maleic anhydride and vinylidene fluoride Coalescence is mentioned. In addition, the said copolymer may be used individually by 1 type, or may use 2 or more types together.

As a blending ratio of the carbon particles and the binder, the amount of the binder is desirably 0.1 to 50 parts by mass, more desirably 0.2 to 20 parts by mass with respect to 100 parts by mass of the carbon particles. More desirably, it is 0.5 to 10 parts by mass, and most desirably 1 to 5 parts by mass.
In addition, the proportion of the total amount of carbon particles and binder in the entire carbon electrode is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and 100% by mass. %.

  Examples of the method for forming the carbon electrode include a method in which carbon particles and a binder are mixed and compression-molded, and the carbon particles are dispersed in a solution containing the binder and then applied, dried, and added as necessary. A method of pressing, a method of coating, drying, pressurizing as necessary after dispersing carbon particles in an aqueous or oily binder dispersion are preferably applied.

Here, when wet-mixing, a thickening stabilizer is preferably blended in order to improve viscosity stability.
The thickening stabilizer is not particularly limited. For example, inorganic particles such as alumina and boron nitride, sodium alginate, propylene glycol alginate, sodium carboxymethylcellulose, calcium carboxymethylcellulose, sodium starch glycolate, sodium starch phosphate, poly Synthetic additives such as sodium acrylate and methylcellulose, polysaccharides based on seeds (guar gum, kazib bean gum, tara gum, tamarind seed gum, etc.), resins, polysaccharides based on sap (arabic gum, tragacanth gum, karaya gum, etc.), Polysaccharides made from seaweed (alginic acid, carrageenan, etc.), fermentation product polysaccharides (xanthan gum, dielan gum, curdlan, etc.), plant extracts (peritin), crustaceans Distillate (chitin, chitosan, chitosamine, etc.), and the polysaccharide and / or a derivative of a natural product like. Moreover, a polyether-type viscoelasticity adjusting agent, an acrylic copolymer alkali thickening emulsion, a polyacrylic acid-based polymer-type viscoelasticity adjusting agent, a condensation reaction derivative of D-sorbinol and benzaldehyde, and the like are also included.

  The carbon electrode is preferably joined to the diaphragm. As a method of joining the carbon electrode to the diaphragm, a method of transferring the carbon electrode comprising the carbon particles and the binder produced as described above to the diaphragm, a solution or dispersion containing the carbon particles and the binder is used as the diaphragm. The method of apply | coating directly etc. are mentioned.

  Although it does not specifically limit as said diaphragm, The thing of porous membranes, such as PTFE porous film described in Unexamined-Japanese-Patent No. 2005-158383, a polyolefin-type porous film, and a polyolefin-type nonwoven fabric, The porous_hole | pipe of Japanese Patent Publication No. 6-105615 Composite membrane combining membrane and water-containing polymer, cellulose or ethylene-vinyl alcohol copolymer membrane described in JP-B-62-226580, polysulfone-based membrane anion exchange described in JP-A-6-188005 A membrane having a hydrophilic resin in the pores of a porous membrane formed of a fluorine-based or polysulfone-based ion exchange membrane described in JP-A-5-242905, a polypropylene described in JP-A-6-260183, Fluorine ion exchange resin (made by DuPont) that is thin and several μm on both surfaces of a polypropylene porous membrane A membrane coated with a standard Nafion (“b = 1, d = 2” type in PFSA described later), an anion exchange type having a pyridium group described in JP-A No. 10-208767, and styrene and divinylbenzene. A membrane comprising a polymerized crosslinked polymer, a cation ion exchange membrane (fluorine polymer or hydrocarbon polymer) and an anion ion exchange membrane (polysulfone polymer, etc.) described in JP-A No. 11-260390 A repeating unit of a vinyl heterocyclic compound (having an amine group, vinylpyrrolidone, etc.) having two or more hydrophilic groups on a porous substrate described in JP-A-2000-235849 An anion exchange membrane formed by combining a cross-linked polymer having

Among these, the diaphragm which consists of a fluorine-type polymer electrolyte polymer (PFSA) represented by following formula (1) is preferable.
_{^{- [CF 2 CX 1 X 2}} ] a - [CF 2 -CF ((- O-CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( CF) _f -X ⁴ )] _g- (1)
In the formula (1), X ¹ , X ² and X ³ are each independently selected from the group consisting of a halogen atom and a C 1 to C 3 perfluoroalkyl group, and the halogen atom includes a fluorine atom, a chlorine atom, Bromine atom and iodine atom. X ⁴ is COOZ, SO ₃ Z, PO ₃ Z ₂ or PO ₃ HZ. Z is a hydrogen atom, lithium atom, alkali metal atom such as sodium atom or potassium atom, alkaline earth metal atom such as calcium atom or magnesium atom, or amines (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 alkyl groups and arene groups. When X ⁴ is PO ₃ Z ₂ , Z may be the same or different. R ¹ and R ² are each independently selected from the group consisting of a halogen atom, a C 1-10 perfluoroalkyl group and a fluorochloroalkyl group, and the halogen atom includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. Is an atom. a and g are numbers satisfying 0 ≦ a <1, 0 <g ≦ 1, and a + g = 1.
Moreover, b is an integer of 0-8. c is 0 or 1; d, e and f are each independently an integer of 0 to 6 (provided that d, e and f are not 0 at the same time).

Furthermore, PFSA represented by the following formula (2) is more desirable.
_{- [CF 2 CF 2] a} - [CF 2 -CF ((- O- (CF 2) m -X 4)] g - ··· (2)
Here, in formula (2), m represents an integer of 1 to 6, and X ⁴ represents SO ₃ H.

  The equivalent mass EW of the PFSA resin (the dry mass in grams of PFSA resin per equivalent of proton exchange groups) is preferably adjusted to 300 to 1300. The equivalent mass EW of the PFSA resin in the present embodiment is more preferably 350 to 1000, still more preferably 400 to 900, and most preferably 450 to 750.

Bipolar plates used in redox flow secondary batteries are required to electrically connect adjacent positive and negative electrodes, and not to mix adjacent positive and negative electrode electrolytes. Any material that has corrosion resistance and oxidation resistance to an applied voltage may be used. A typical example is a mixture of carbon and resin called conductive plastic.
As a frame used for redox flow secondary batteries, the above materials are housed, the electrolyte is sent to and discharged from each cell, and the cell is formed as a structure that carries the electrolyte sealing function between the external and positive and negative electrodes Typical examples include general-purpose plastic materials such as vinyl chloride and polyethylene in consideration of acid resistance, processability during production, and the like.

  When the carbon electrode formed from the carbon particles and the binder thus obtained and the electrolyte membrane to which the carbon electrode is joined are used in a redox flow secondary battery, the activity of the redox reaction is remarkably improved. A high-performance redox flow secondary battery can be obtained, and the cost of the battery can be reduced.

Next, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist. In addition, the physical property in an Example was measured with the following method.
(1) Battery efficiency (%)
Battery efficiency (energy efficiency) (%) is expressed as a ratio (%) obtained by dividing discharge energy by charge energy. Both energy values are the internal resistance of the battery cell, the ion selective permeability of the diaphragm, and other current losses. Depends on. The current efficiency (%) is expressed as a ratio (%) obtained by dividing the amount of discharged electricity by the amount of charged electricity, and both the amounts of electricity depend on the ion selective permeability of the diaphragm and other current losses. Battery efficiency is expressed as the product of current efficiency and voltage efficiency. A decrease in internal resistance, ie, cell electrical resistivity, improves voltage efficiency, and an improvement in ion selective permeability and other reductions in current loss improve current efficiency, and thus are important indicators in redox flow secondary batteries.

[Example 1]
Ketjen Black EC600JD manufactured by Lion Co., Ltd. as the carbon particles, styrene / butadiene latex L-7063 manufactured by Asahi Kasei Chemicals Co., Ltd., and electrolyte membrane Nafion ^™ NRE-212CS manufactured by DuPont Co., Ltd. as the diaphragm are used. An example of producing a redox flow battery will be described.
100 parts by mass of Ketjen Black EC600JD, 4 parts by mass of styrene / butadiene latex L-7063 (solid content 48% by mass), and sodium carboxymethylcellulose as a thickener (Serogen ^™ BSH-12 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) An aqueous solution (solid content: 1% by mass) containing 85 parts by mass was added and mixed to obtain a coating solution. This coating solution was applied to both sides of the diaphragm and dried to form an electrode having a thickness of about 1 mm.

One of the cells separated by the joined body having electrodes formed on both surfaces of the diaphragm was defined as a positive electrode cell chamber (thickness 5 mm), the other as a negative electrode cell chamber (thickness 5 mm), and the thicknesses of both cell stores with a spacer. In the positive electrode cell chamber, a sulfuric acid electrolyte solution (vanadium concentration 2M, sulfate radical concentration 4M) composed of tetravalent vanadium (V ⁴⁺ ) and pentavalent (V ⁵⁺ ) is used in the negative electrode cell chamber. A sulfuric acid electrolyte solution (vanadium concentration 2M, sulfate radical concentration 4M) composed of vanadium trivalent (V ³⁺ ) and divalent (V ²⁺ ) was circulated and charged and discharged.

At the time of charging, in the positive electrode cell chamber, vanadium ions release electrons and V ⁴⁺ is oxidized to V ⁵⁺ , and in the negative electrode cell chamber, V ³⁺ is reduced to V ²⁺ by electrons returning through the outer path. Is done. 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.
In this example, when charging / discharging was performed at a current density of 80 mA / cm ² , a high battery efficiency of 81% was obtained.

[Example 2]
Denka Black ^TM powder manufactured by Denki Kagaku Kogyo Co., Ltd. as carbon particles, Kureha KF polymer (polyvinylidene fluoride resin, hereinafter referred to as PVdF) manufactured by Kureha Co., Ltd., and electrolyte manufactured by DuPont Co., Ltd. as a diaphragm. An example of producing a redox flow battery using the membrane Nafion ^™ NRE-212CS will be described below.

  A solution obtained by dissolving PVdF in N-methyl-2-pyrrolidone (13% by mass, hereinafter referred to as a PVdF solution) is added to 100 parts by mass of the carbon particles so that PVdF becomes 5 parts by mass, and N-methyl-2- Pyrrolidone is added so that the solid content ratio ((mass of carbon material + mass of PVdF) / total mass × 100) is 52 wt%, mixed and stirred to obtain a slurry, and this slurry is applied to both sides of the diaphragm. Then, an electrode having a thickness of about 1 mm was formed by drying. Production and evaluation of the redox flow battery were performed in the same manner as in Example 1. As a result, a high battery efficiency of 79% was obtained.

[Comparative Example 1]
A felt made of carbon fiber with a thickness of 5 mm and a bulk density of about 0.1 g / cm ³ as an electrode and an electrolyte membrane Nafion ^™ NRE-212CS manufactured by DuPont as a diaphragm, felt on both sides of the diaphragm. The redox flow battery was manufactured and evaluated in the same manner as in Example 1 except that the battery efficiency was not included. As a result, only a low battery efficiency of 68% was obtained.

  As described above, the redox flow secondary battery obtained in this embodiment is a high-performance redox flow secondary battery in which the activity of the oxidation-reduction reaction is remarkably improved.

Claims (2)

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 redox flow secondary battery in which the carbon electrode includes carbon particles and a binder.   The redox flow secondary battery according to claim 1, wherein the carbon electrode is bonded to the electrolyte membrane.