Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
  • H01M8/184—Regeneration by electrochemical means
  • H01M8/188—Regeneration by electrochemical means by recharging of redox couples containing fluids; Redox flow type batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• Electrical energy can be stored by various processes.
• One possibility is the conversion of electrical energy into chemical energy by chemical reactions on electrode surfaces by electric current.
• This type of energy storage is used technically in secondary batteries (accumulators) on a large scale.
• a secondary battery is an electrochemical cell that consists of two half-cells, which in turn are separated by an ion-conducting separator.
• the separator ensures a charge balance, but prevents the mass transfer between the half-cells.
• In the negative half cell takes place during the storage process, a reduction of the active substance, in the positive half-cell oxidation.
• In the storage process electrons thus flow from the positive half-cell into the negative half-cell, in the discharge process in the opposite direction.
• electrolyte liquid substance or substance mixture
• the electrode is the phase boundary between the electrical conductor and the ionic conductor.
• the active material may be the electrode itself, a substance dissolved in the electrolyte or substances stored in the electrode material. If the active material consists of negative electrolyte (anolyte) and positive electrolyte (catholyte) of substances dissolved in the electrolyte, the result is that in this type of battery the amount of energy and power can be scaled independently, since the electrolyte from reservoirs at the electrodes can be passed. This type of electrochemical energy storage is called the redox flow battery.
• the electrolyte of redox flow batteries typically consists of mineral acids or organic acids dissolved in water.
• Water as a component of the electrolyte is a potential window of about -0.5 V to 1.2 V with graphite electrodes over a standard hydrogen electrode possible. Beyond these limits, which are referred to as potential windows, a decomposition of water, and thus the destruction of the water-based electrolyte, gas evolution and loss of efficiency begins.
• the total voltage of a water-based redox flow battery with graphite electrodes is thus limited to max. Limited to 1.7V.
• the energy density of redox flow batteries depends on the solubility of the redox couples. For the highest possible energy density, the redox pairs are at the limit of solubility in the electrolyte.
• One type of redox flow battery is the vanadium redox flow battery. The reaction equation of such a vanadium redox flow battery is as follows:
• vanadium In this electrochemical energy storage vanadium is used in different oxidation states in the positive (catholyte) and in the negative (anolyte) electrolyte.
• concentration of vanadium When using aqueous sulfuric acid as solvent, the concentration of vanadium is limited to about 1.6 mol / L. The reason for this is the limited solubility of divanadyl cations (VO 2 + ) in aqueous sulfuric acid.
• the electrochemical potential window i. the voltage range between formation of oxygen and hydrogen, i. the decomposition (electrolysis) of water relative to the standard hydrogen electrode is dependent on the material of the electrode.
• Metallic electrodes usually have a much lower potential window than carbon-based electrodes made of graphite or form passivating, i. performance-reducing layers.
• the widest possible electrochemical potential window is needed to use the redox pairs, as already explained above, one resorts to carbon in its modifications diamond, graphite and glassy carbon. Pure graphite electrodes have much lower strength and electrical conductivity than metals.
• composite materials of graphite / polymer mixtures are used. The use of polymers, however, in turn leads to a reduction of the electrical conductivity and thus to performance losses due to resistance losses.
• acids or bases are used as constituents of the electrolyte in higher concentrations or stabilizers added.
• the precipitation of vanadium pentoxide is a problem with vanadium redox flow batteries.
• four measures are commonly employed in the art.
• the operating temperature of the battery system is set between 0 0 C ⁇ T ⁇ 40 0 C.
• T ⁇ 0 0 C the aqueous electrolyte begins to go into the solid state, wherein the viscosity of the electrolyte from the work area increases with decreasing temperature.
• a freezing of the electrolyte causes a destruction of the battery.
• irreversible precipitations of solid vanadium pentoxide are formed.
• a limitation of the temperature in this work area means a temperature monitoring and control of the system. On the one hand, it must be ensured, eg by heating, that the electrolyte does not freeze and thus the system is destroyed and, on the other hand, the temperature in the reaction space must not rise above 40 ° C. If necessary, this must be ensured by cooling.
• the precipitation of solid vanadium pentoxide is dependent on the ratio of vanadyl / divanadyl cations.
• concentration of divanadyl cations which increases during the charging process, the higher the probability of precipitation of solid vanadium pentoxide even within the temperature limits of 0 0 C ⁇ T ⁇ 40 0 C.
• vanadium concentration> 1 6 mol / L only up to 80% of the vanadyl cations converted to divanadyl cations during charging, corresponding to a charge state of 80%.
• the standard concentration of vanadium electrolyte is 1.6 mol / L in 3 M sulfuric acid (H 2 SO 4 ). This forms a compromise between increased viscosity at higher sulfuric acid concentrations (increased energy expenditure for pumps, hence loss of efficiency) and energy density. In the temperature limits the precipitation of vanadium pentoxide is prevented by about 0.05 mol / L phosphoric acid.
• the working temperature is far below the boiling point of the
• Electrolyte limited since due to the rapidly increasing partial pressure of the electrolyte, a pressure build-up in the entire system begins, which can lead to leaks and the electrolyte can not participate in the reaction. Therefore, the currently used redox flow batteries can only be operated in a very limited temperature range.
• An object of the present invention is to provide a redox flow battery in which the disadvantages described above are avoided as far as possible and an improved variability in the selection of operating parameters such as operating temperature or choice of electrode material is made possible.
• This object is achieved according to the present invention by providing a redox flow battery comprising an electrolyte containing at least one ionic liquid.
• redox flow battery In the context of the present invention, the term "redox flow battery” is used in its usual meaning The basic structure of a redox flow battery is known to the person skilled in the art.
• the redox flow battery stores electrical energy in chemical compounds and is therefore related to the accumulators.
• the two energy-storing electrolytes circulate in two separate circuits, between which a charge exchange is possible in the battery by means of a membrane or a separator.
• the electrolytes are stored outside the battery in separate tanks, which means that the stored energy no longer depends on the size of the cell, so energy and power can be scaled separately.
• the redox flow battery according to the invention therefore has a positive half cell, a negative half cell, a separator separating the two half cells, two electrodes, and two electrolyte containers located outside the cells.
• the separator provides charge balance, but prevents mass transfer between the half cells. In the negative
• FIG. 1 shows the basic structure of a redox flow battery with (a) an ion-conducting separator, (b) electrodes, (c) electrolyte containers, (d) electrolyte pumps, (e) electrical source / sink and (f) positive or positive negative half cell.
• ionic liquid is used in its usual meaning, ie ionic liquids are understood as meaning organic, ionic compounds which are composed of an organic or inorganic anion and a voluminous organic cation 0 C is molten, it is called RTILs (Room Temperature Ionic Liquids).
• Typical properties of ionic liquids are high chemical stability, - wide potential window (high electrochemical stability), high ionic conductivity, - low vapor pressure, non-combustible, high thermal stability.
• both (ie, the positive and negative) half cells of the redox flow battery contain an ionic liquid, wherein the ionic liquids may be the same or different.
• the electrolyte contains less than 0.05% by weight of water, more preferably less than 0.02% by weight, even more preferably less than 0.01% by weight of water.
• the electrolyte is anhydrous.
• anhydrous electrolytes By using anhydrous electrolytes, a larger electrochemical potential window can be realized than with water-based redox flow batteries. Increasing the voltage increases the performance and energy density of the system.
• the content of ionic liquid in the electrolyte can be varied over a wide range and is preferably in the range of 0.1 to 100 wt .-%.
• the electrolyte of the inventive redox flow battery is at least 80 wt .-%, more preferably at least 90 wt .-%, more preferably at least 100 wt .-% of the / the ionic liquid / s.
• the anion of the ionic liquid (s) is halide, phosphate, e.g. Hexafluorophosphate, arsenate, antimonate, nitrite, nitrate, sulfate, e.g. Alkyl sulfate, hydrogen sulfate, carbonate, bicarbonate, phosphonate, phosphinate, borate, e.g. Tetrafluoroborate, sulfonate, e.g. Tosylate or methanesulfonate, carboxylate, e.g. Formate, imide, e.g. bis (trifluoromethylsulfonyl) imide, methide, or mixtures thereof.
• phosphate e.g. Hexafluorophosphate
• arsenate antimonate
• nitrite nitrate
• sulfate e.g. Alkyl sulfate
• hydrogen sulfate carbonate,
• Preferred anions may be mentioned by way of example: fluoride,
• Ra to Rd independently of one another are fluorine or a carbon-containing organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical having 1 to 30 carbon atoms and containing one or more heteroatoms and / or may be substituted by one or more functional groups or halogen,
• organic sulfonate of the general formula wherein R e is a carbon-containing organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical having 1 to 30 carbon atoms, which contain one or more heteroatoms and / or may be substituted by one or more functional groups or halogen, stands,
• Carboxylate of the general formula [R f -COO] " wherein R f is hydrogen or a carbon-containing organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical having 1 to 30 carbon atoms which contain one or more heteroatoms and or may be substituted by one or more functional groups or halogen,
• R m to R 0 are independently hydrogen or a carbon-containing organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical having 1 to 30 carbon atoms containing one or more heteroatoms and / or by one or more functional Groups or halogen may be substituted;
• organic sulfate of the general formula [RPO SOs] "where Rp is a carbon-comprising organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical having 1 to 30 carbon atoms, which contain one or more hetero atoms and / or by one or more functional groups or halogen may be substituted is.
• the cation of the ionic liquid (s) of imidazolium, pyridinium, pyrazolium, quinolinium, thiazolium, triazinium, pyrrolidinium, phosphonium, ammonium, sulfonium, or mixtures thereof is selected.
• n is O, 1, 2, 3 or 4;
• R is hydrogen, C 1-12 alkyl or phenylC 1-4 alkyl
• R x is d- 6 alkyl, halogen, amino, cyano, CI_ 4 alkoxy, carboxylate or sulfonate.
• Ionic liquids offer the possibility to dissolve redox couples and to use them as an electrolyte in redox flow batteries.
• the redox flow battery is a vanadium redox flow battery, ie, for the positive half cell, V 4+ AV 5+ becomes the redox pair and the negative half cell V 3+ AV 2 + used as a redox couple.
• the following redox flow batteries can be mentioned by way of example:
• Positive half-cell Fe 2+ ZFe 3+ ; negative half-cell: Cr 2+ / Cr 3+
• the vanadium redox flow battery has an operating temperature in the range of -30 0 C to 400 0 C, more preferably in the range of -20 0 C to 200 0 C. In a preferred embodiment, the operating temperature of the vanadium redox flow battery is above 40 ° C., more preferably above 50 ° C.
• the concentration of vanadium ions in the electrolyte is in the range of 0.1 mol / L to 10 mol / L, more preferably in the range of 0.1 mol / L to 5 mol / L , In a preferred In the embodiment, the concentration of vanadium ions in the electrolyte is above 2 mol / L, more preferably above 3 mol / L.
• solid vanadium pentoxide is formed at temperatures above 40 ° C. and vanadium concentrations above 1.6 mol / l.
• ionic liquids preferably anhydrous ionic liquids
• the formation of solid vanadium pentoxide does not take place.
• higher concentrations of vanadium in the electrolyte can be achieved.
• the operating range of the battery can be extended beyond 40 0 C, resulting in a higher power density.
• Ionic liquids have melting and boiling points other than water and acids and bases dissolved in water. This results in other work areas that can not be achieved with aqueous electrolytes. Thus, operating temperatures well above the boiling point of water (100 0 C), concomitantly higher power densities can be achieved. Any cooling and monitoring devices can be omitted. Similarly, with ionic liquids operating temperatures below the freezing point of water (0 0 C) can be achieved. This can be omitted any heating of the system.
• the redox couple is formed by the ionic liquid.
• Ionic liquids can themselves form the redox pairs. As a result, it is no longer necessary to dissolve substances as redox couples to the limit of their solubility in a liquid, but to use the solvent itself as the electrolyte and redox couple. This has the advantage that the energy density of the system no longer depends on the solubility of the redox pairs in the electrolyte and the voltage, but on the molar mass of the ionic liquids and the resulting voltage. Thus, much higher energy densities can be achieved than in current systems with aqueous electrolytes.
• the redox flow battery according to the invention has metallic electrodes.
• the metal is selected from iron, iron alloys, copper, copper alloys, nickel, nickel alloys, zinc, zinc alloys, silver, silver alloys, aluminum, aluminum alloys.
• ionic liquids with very low water content or anhydrous ionic liquids the decomposition of water can be completely or at least largely avoided.
• the potential window is within the decomposition of the ionic liquids.
• metallic electrodes can thus be used.
• the electrode is diamond or indium tin oxide (ITO). These electrode materials are chemically inert to a variety of materials, mechanically stable.
• the electrodes are either deposited on a suitable substrate by known coating techniques (e.g., CVD, PVD) or separately prepared and pressed with the substrate.
• CVD chemical vapor deposition
• PVD physical vapor deposition
• the last-mentioned variant is used when no coating processes are available for the desired substrate.
• Diamond electrodes are preferably doped with boron, nitrogen and / or phosphorus to set the desired electrical conductivity. By the Choice of dopant and the degree of doping, the electrical conductivity can be adjusted.
• the electrolyte of the redox flow battery according to the invention has no addition of stabilizers and / or acids or bases.
• Redox couples have different solubilities in ionic liquids than in aqueous systems. In addition, the solubilities are also very different from the ionic liquids. Redox couples can have a higher solubility in ionic liquids than would be possible in aqueous systems. Stabilizing agents or the addition of acids or bases can be omitted.
• the separator between the two half-cells is selected from
• NAFION Fumasep FAP, FAD, FAB, FKE, FCS, FKB, FTCM-A, FTCM-E, FKL, FAA, FTAM-E, FTAM-A, FAS, FBM; microporous separators.
• the present invention relates to the use of an electrolyte containing an ionic liquid in a redox flow battery.
• VCI3 vanadium (III) chloride
• the V solution served as the anolyte and was pumped into the negative half cell of an electrochemical flow cell.
• the V 4+ solution served as the catholyte and was filled in the positive half cell of the flow cell.
• FIG. 2 plots the voltage curve of the first 10 charging and discharging cycles.
• FIG. 3 shows the course of the discharge capacity, based on the first discharge capacity, of the first 5000 charging and discharging cycles.
• FIG. 2 shows the first ten charging and discharging curves of a stationary vanadium redox flow battery with 2-hydroxyethylammonium formate as solvent.
• the cell was charged galvanostatically with a constant current of 0.25 A up to a voltage of 1.65 V. Thereafter, the switching to the potentiostatic charging was carried out at a voltage of 1.65 V up to a current of 0.15 A. Subsequently, the discharge took place immediately. At a current strength 0.25 A, the battery was galvanostatically discharged to a voltage of 0.5 V. Thereafter, the potentiostatic discharge was carried out at a voltage of 0.5 V until a lower current limit of 0.15 A was reached.
• FIG. 3 shows the capacitance calculated from the current, voltage, and time measurements in relation to the first discharge capacity.
• the discharge capacity of the first discharge in ampere-hours (Ah) was set to 1 and the discharge capacity of the following cycles related to the first value. During the first 1000 cycles, a large drop in the capacity can be seen, which subsequently recovers shortly after the initial value. Even after 5000 cycles, a capacity of approx. 20% of the output capacity can still be measured.

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• 2009
  • 2009-02-18 DE DE102009009357A patent/DE102009009357B4/de not_active Expired - Fee Related
• 2010
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  • 2010-02-15 CA CA2751982A patent/CA2751982C/en not_active Expired - Fee Related
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