NL2031840B1

NL2031840B1 - Prolinol bromide as bromine complexing agent in battery applications

Info

Publication number: NL2031840B1
Application number: NL2031840A
Authority: NL
Inventors: Arie Vermaas David; Verena Holland-Cunz Matthäa
Original assignee: Univ Delft Tech
Priority date: 2022-05-12
Filing date: 2022-05-12
Publication date: 2023-11-20
Also published as: WO2023219492A1

Abstract

The present invention is in the field of a battery, that is for direct conversion of chem— ical energy into electrical energy, and vice versa, in particular a redox battery, more in par— ticular a redox ﬂow battery. Said batteries comprise electrolytes, typically a solvent, elec— 5 trodes, and typically a pump. Such batteries may contribute to reduction of greenhouse gas and may mitigate climate change to some extent.

Description

Prolinol bromide as bromine complexing agent in battery applications

FIELD OF THE INVENTION

The present invention is in the field of a battery, that is for direct conversion of chem- ical energy into electrical energy, and vice versa, in particular a redox battery, more in par- ticular a redox flow battery. Said batteries comprise electrolytes, typically a solvent, elec- trodes, and typically a pump. Such batteries may contribute to reduction of greenhouse gas and may mitigate climate change to some extent.

BACKGROUND OF THE INVENTION

A redox flow battery is a type of a battery for providing electrical energy typically in the form of a current. Energy is stored therein in the form of chemicals, hence the term electrochemical. In an electrochemical cell chemical energy is typically provided by two chemical components which may be dissolved in liquids, such as water, contained within a system. The electrochemical cell reversibly converts chemical energy directly to electricity, using e.g. electroactive elements in solution that can take part in an electrode reaction or that can be adsorbed on an electrode. Additional electrolyte is typically stored externally from the cell itself, such as in (small) tanks. The electrolyte is then usually pumped through the cell’s reactor compartment. Flow batteries can be rapidly recharged, such as by replac- ing the electrolyte liquid whereas converted redox species may be recovered. The two chemical components are separated such as by a membrane. The electrochemical cell typi- cally involves ion transport. Ion transport occurs through the membrane, such as an ion ex- change membrane. Both liquids can circulate (hence flow) in their own respective flow path. Over the ion exchange part also a tlow of electric current is established, when in use.

An electrochemical cell voltage is determined by the chemicals used and is considered to follow the Nernst equation and ranges. In practical applications the (absolute) cell voltages may vary from 0.2 to 2.5 volts.

A flow battery may be used as a fuel cell and as a rechargeable battery. Some tech- nical advantages over prior art rechargeable batteries are separable liquid tanks and ex- tended use, present implementations are comparatively less powerful and require more so- phisticated electronics.

Various types of flow cells exist, such as redox, hybrid, organic, metal hydride, nano- network, semi-solid, and without membrane. As mentioned above, a fundamental differ- ence between conventional batteries and flow cells is that energy is stored not as the elec- trode material in conventional batteries but as the electrolyte in flow cells.

Clearly the energy capacity is a function of electrolyte volume, solvent, and type of electrolyte, whereas power is a function of surface area of the electrodes. Typical power densities are from about 1000-20000 W/m, a fluid energy density is from about 10-1500

Wh/kg, and a number of recharging cycles is from about 10-2000.

Redox flow batteries have certain advantages, such as a flexible layout, a long cycle life, quick response times, no harmful emissions, easy state-of-charge determination, low maintenance costs, good tolerance to overcharge and to over discharge, high current and 1 power densities, which are suited for large-scale energy storage. However energy densities and efficiency are in general lower, compared to solid battery alternatives.

Flow batteries can be applied in relatively large (1 kWh —10 MWh) stationary appli- cations. They may be applied for load balancing. Therein the flow battery is connected to an electrical grid to store excess electrical power during off-peak hours and release electri- cal power during peak demand periods. They may be applied for storing energy, such as from renewable sources as wind or solar, and for discharging during periods of peak de- mand. The may be used for providing an uninterrupted supply and for peak shaving. They may be used in combination, such as in power conversion. The electrolyte may be charged using a given number of cells and discharged with a different number of cells, or likewise cycles. The battery can be used in combination with a DC-DC converter. Power conversion can also be AC/DC, AC/AC, or DC-AC. Flow batteries can be used in vehicles. And they can be used as a stand-alone power system.

In particular a bromine battery with a Bromine Complexing Agent (BCA) is consid- ered. Applying BCAs to batteries is generally focused on zinc-bromine batteries. Bromine (Br2) dissolves in aqueous ZnBr: solutions by complexing with bromide (Br) into monoan- ions (Brz to Brit”) or dianions (Brs>-, Brio’). Aqueous-phase Bra concentration in such elec- trolytes must be reduced from 2 M to < 0.1 M (in separator-batteries) and even lower in membrane-less batteries in order to mitigate Zn corrosion at the anode, and increase battery coulombic efficiency. A BCA typically is a quaternary ammonium bromide salt (ionic lig- uid, QBr) which combines during charging with the generated Br2 into a separate polybro- mide phase. The polybromide phase is also known as a fused salt, and can be described as a non-stochiometric mix of QBrn, where n = 1, 3,5, 7 — i.e. a maximum of 3 Br: per 1 QBr.

As a result, the equilibrium aqueous Br2 concentration is low. During battery operation, the aqueous and polybromide phases can be kept separated, or can be mixed together to form an emulsion. After complexation with BCA, the aqueous-phase Br2 concentration, [Br2}aq, increases with temperature and Br concentration. [Br2}aq also decreases with increasing

BCA strength or concentration of non-complexing anions, e.g. SO4* or CI.

The present invention relates to an improved redox flow battery for heat to power conversion which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a battery, comprising a single phase fluid, in particular a liquid, in contact with at least one first negative electrode and at least one first positive electrode, the fluid comprising an electrolyte, wherein the electrolyte is a halogen, and in the single phase fluid, a halogen complexing agent, in particular a positively charged halogen complexing agent, more in particular a complexing agent comprising at least one amine, in particular 2-6 amines, in partic- ular an amine with a positively charged N. It is found that adding halogen complex- ing agents (BromineCAs) to the battery electrolyte allows for displacing halogen, in 2 particular bromine (Brz), from the aqueous phase to a separate polybromide phase.

Advantages are an improved energy density, a reduced halogen crossover in mem- brane-less systems, and a reduced halogen vapour pressure. However, some prior art

BCAs demonstrate incompatibility with use in porous flow through cathodes em- ployed by the membrane-less H2-Br:2 cell, which was attributed to clogging of cath- ode pores. This was largely due to the multiphase nature of electrolytes, as the vis- cous polybromide phase would settle and clog pores, preventing significant battery performance. In order to overcome this issue novel complexing agents are provided which maintain a single phase during operation. An exemplary embodiment thereof is the L-prolinol (bromide). Prolinol is a chiral amino-alcohol that is used as a chiral building block in organic synthesis. It exists as two enantiomers: the D and L forms.

This BCA has a high potential for further use, as it hardly compromises the rate ki- netics (something that many other BCA’s do), it remains in the same phase through- out the full state of charge (SoC) range, and is inexpensive to synthesize. The cell op- eration demonstrates that charging and discharging are possible over a wide range of

SoC’s. The energy density of an exemplary developed solution with L-prolinol bro- mide has an energy density of 209 Wh/L. Energy densities above 300 Wh/L are to be obtained. Furthermore, a solid-phase BCA (sBCA), is used in particular for complex- ing Br: inside the storage tank. The advantage of this solid BCA is that the cell de- sign is more versatile, as this solid BCA does not share the problem regarding clog- ging pores and phase-separation inside the cell. This BCA has been tested in cell tests, and the current, voltaic and energy efficiency were similar to the cell cycling data without use of sBCA, showing that actually there is no detrimental effect of sBCA on the cell performance at the applied current density other that functioning as capturing material for the excessively formed Br2. At the same time, the energy den- sity of the electrolyte was increased by 58%, and reaches a maximum of 205 Wh/L.

Exemplary solid BCA may be composed of solid porous beads of 0.1-3mm diameter, in particular 0.5-1 mm, embedded with functional groups that bind Br2 to the surface through complexation. The porosity of sBCAs may be 10-50%, in particular 30-40%.

Advantages of SBCA are that they allow the cell to charge up higher [Br2}r at which normally liquid Br: will separate from the catholyte due to inability to form Bra, Brs and Br7 etc., and further that aqueous complexation of Bra(aq) to sBCA minimizes the deterioration of cell components, i.e. deterioration of bipolar plates can takes place upon intercalation of Br2. The adsorption capacity of the SBCA was determined by adding sBCA to a 100 ml catholyte comprising 2.8M [HBr] and 3.0M [Bra] (based on 48% HBr) and study the amount of Br2 that is captured by the added sBCA. The results clearly indicate that sBCA is capable of adsorbing Br2 in a linear fashion with the added amount of sBCA, e.g. 0.00933 mol Br: per g of sBCA. This linear relations means that the amount of the required sBCA to capture of Br2 can well be tuned in the catholyte of the present cell. 3

The present invention in particular relates to a battery comprising at least one fluid flow controller 14 for providing a continuous circulation of at least one fluid electro- lyte, wherein the fluid flow controller is selected from a pump, a mass flow controller, and a pressure controller, an typically adapted to provide circulation in both directions depend- ing on the state of charge, at least one first fluid electrolyte flowing from a catholyte con- tainer 11 to the battery cell and at least one second fluid electrolyte flowing from an anolyte container 12 to the battery cell, respectively, and vice versa, wherein the at least one first electrolyte each individually is dissolved in a solvent, wherein a first flow 31 comprises a first set of redox species and wherein a second flow 32 comprises a second set of redox spe- cies, wherein both flows are separated from one and another, wherein, under discharging conditions, the battery is adapted to subject the first redox species to an oxidation reaction and adapted to subject the second redox species to a reduction reaction, and at least one separator 10, wherein the at least one first fluid, in particular a liquid, is adapted to be in contact with at least one first electrode 13, in particular a positive electrode, such as a cur- rent collector depending on the state of charge, wherein the at least one a second fluid, in particular a liquid, is adapted to be in contact with the at least one second electrode 13, in particular a negative electrode, such as a current collector, depending on the state of charge, wherein the at least one first set of redox species comprises Halogenide /Halogenidez, and wherein the second set of redox species comprises H*/H>, wherein the at least one first set of redox species and the at least one first fluid electrolyte form a single phase fluid, in par- ticular a liquid, wherein the single phase fluid comprises a halogen complexing agent, in particular a positively charged halogen complexing agent, more in particular a complexing agent comprising at least one amine, in particular 2-6 amines, in particular an amine with a positively charged N. It is noted that typically the electrode in contact with the second set of redox species is given a potential of OV (RHE), and thus the other set of redox secies is in this case a positive electrode (about 1V (RHE)).

In a second aspect the present invention relates to an array comprising two or more redox flow battery system according to the invention in series and/or in parallel, such as 3-200 systems in series and/or 2-100 systems in parallel.

In a third aspect the present invention relates to redox flow battery system accord- ing to the invention or an array according to the invention, for generating electricity.

Thereby the present invention provides a solution to one or more of the above men- tioned problems.

Advantages of the present battery are detailed throughout the description. References to the figures are not limiting, and are only intended to guide the person skilled in the art through details of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a redox flow battery.

In an exemplary embodiment of the present redox flow battery the complexing agent comprises at least one saturated, partly saturated, or unsaturated secondary amine or a 4 tertiary amine, in particular a cyclic secondary amine or cyclic tertiary amine, such as a pyr- rolidinium comprising compound, an imidazolium comprising compound, a pyridinium comprising compound, a quinolinium comprising compound, more in particular an amino alcohol.

In an exemplary embodiment of the present redox flow battery the complexing agent is selected from five or six atoms comprising ring comprising amines, in particular from chiral amino alcohols, such as prolinol [CAS 68832-13-3], from 1-Ethyl-1-methylpyr- rolidinium bromide, 1-Butyl-1-methylpyrrolidinium bromide, 1-Ethyl-3-methylimidazo- lium bromide, 1-Buty1-3-methylimidazolium bromide, Tetra-N-butylammonium bromide,

N-pentylpyridinium bromide, N-octylquinolinium bromide, L-prolinol bromide, D-prolinol bromide, Pyridine hydrobromide perbromide, Phenyltrimethylammonium tribromide, 4- (Dimethylamino)pyridine tribromide, 1-n-Butylpyridinium bromide, and 1,1'-Bis[3-(trime- thylamonium) propyl]-4,4'-bipyridinium Tetrabromide.

In an exemplary embodiment of the present redox flow battery the halogen is se- lected from fluor, chlorine, iodine, and bromine, in particular bromine.

In an exemplary embodiment of the present redox flow battery the battery is a re- dox flow battery, the redox flow battery comprising at least one first chamber comprising electrolyte, at least one second chamber comprising oxidant and halogen complexing agent, and at least one separator separating the at least one first chamber and the at least one sec- ond chamber, wherein the separator is substantially permeable for H” and is substantially impermeable for Ha.

In an exemplary embodiment of the present redox flow battery the battery is void of a membrane.

In an exemplary embodiment of the present redox flow battery the battery com- prises a single liquid solvent, wherein the solvent is selected from water, polar organic sol- vents, and mixtures thereof. It is an advantage that no co-solvent may be used.

In an exemplary embodiment the present redox flow battery comprises a voltage supply.

In an exemplary embodiment of the present redox flow battery the at least one first negative electrode and at least one first positive electrode are each independently se- lected from carbon, and carbon comprising materials, such as graphite, in particular iso- molded graphite, porous graphite, carbon-comprising films, carbon-comprising layers, in particular wherein the first negative electrode comprises a catalyst, such as Pt, and Ir, in particular wherein the second positive electrode comprises a catalyst.

In an exemplary embodiment of the present redox flow battery the halogen com- plexing agent is provided in an amount of 0.1-10 vol.%, in particular 1-5 vol. %, based on the total volume of the single phase fluid.

In an exemplary embodiment of the present redox flow battery the halogen com- plexing agent is provided in an amount of 100-100 g/1, in particular 500-700 g/l based on the total volume of the single phase fluid. 5

In an exemplary embodiment of the present redox flow battery the halogen com- plexing agent is provided as a solid and is adapted to remain in said solid phase.

In an exemplary embodiment of the present redox flow battery the complexing agent is adapted to complex at least one Hal entity, in particular wherein x is an odd num- ber, more in particular wherein x is selected from 1, 3,5, 7 and 9.

In an exemplary embodiment the present redox flow battery comprises at least one operation device selected from a mass flow controller, a peristaltic pump, wherein the pump (14) is adapted for providing a continuous circulation of a fluid electrolyte, in partic- ular of a catholyte, more in particular at a flow rate of 1-20% of the battery volume per mi- nute, such as 5-12%.

In an exemplary embodiment of the present redox flow battery the battery has en- ergy density of >200 WA, in particular > 250 W/1, such as > 300 W/1, and a voltage of 1.5- 12 V. wherein a current density magnitude is 0.1-1000 mA/cm?, in particular 1-500 mA/cm?, more in particular 5-50 mA/cm?, and/or wherein an output voltage is 0.1-1.1 V, such as 0.6-1 V.

In an exemplary embodiment of the present redox flow battery the solvent with the electrolyte has a conductivity of > 50 mS/cm, such as 100-400 mS/cm.

In an exemplary embodiment of the present redox flow battery the redox poten- tials of both first and second sets of redox species are in a range of -4V-+4 V with respect to a reversible hydrogen electrode (RHE).

In an exemplary embodiment of the present redox flow battery the first redox species are present in a concentration of 0.1-18M, in particular 1-10 M, such as HBr, and

MEP (N-ethyl-N-methyl pyrrolidinium bromide).

In an exemplary embodiment of the present redox flow battery the second redox species are present in a concentration of 0.1-13M, in particular 0.2-10 M, such as Bra.

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

SUMMARY OF FIGURES

Figure 1 shows principles of a redox flow battery.

Fig. 2 shows schematics of a present exemplary cell.

Figures 3a,b show a schematic representation of an example of the present battery.

Figs. 4a,b show prolinol, and fig. 5 a synthesizing route.

Figs. 6-7 show experimental results. 6

DETAILED DESCRIPTION OF FIGURES

100 redox flow battery 10 membrane ll catholyte tank 12 anolyte tank 13 contact (current collector) 14 pump 15 current flow 16 first chamber 17 second chamber 31 first electrolyte flow 32 second electrolyte flow 51 PVDF endplate 52 PTFE/PCGEF gasket (e.g. 1 mm, 0.5 mm, 0.2 mm) 53 CC isomolded/impervious graphite (1.5 mm/3 mm) 54 carbon paper with Pt catalyst 55 Ti-sheet 56 Viton gasket (0.5 mm) 57 Cellgard sheet 58 carbon paper (e.g. 0.28 mm)

Figure 1 shows principles of a redox flow battery. Therein a single cell is shown. The cell comprises a membrane 10, and contacts 13 (current collector). Also a catholyte tank 11 and an anolyte tank 12 is shown. Two pumps 14 are provided for driving a flow. As a result an electrical current 15 flows.

Figure 2: Exploded view schematic of the prototype membraneless H2-Br2 cell used for testing the effect of BCAs on cell performance.

Figure 3b shows a cell wherein the membrane 10 is a cation (+) exchange membrane and wherein the redox species are all negatively (-) charged.

Figure 3c shows a cell wherein the membrane 10 is an anion (-) exchange membrane and wherein the redox species are all positively (+) charged.

Figs. 4a,b show prolinol.

Fig. 5 shows a synthesis route of BCA 14.

Fig. 6. Cycling data of exemplary cell build at Elestor without BCAS (first 8 cycles) and with BCA8 (cycles #9-#20).

Fig. 7. The maximum energy density of the catholyte in Wh/L upon charging 13.6M and 17.6M HBr to various [Brz}r.

The figures are further detailed in the description of the experiments below.

EXAMPLES/EXPERIMENTS

An exemplary flow cell was designed. To test the use of MEP in battery catho- lytes, we developed a separate cell with 1.5 cm2 active area, shown schematically in 7

Figure 2. The components used in our prototype cell were two PVDF porting plates, a graphite cathode current collector, a composite anode current collector to prevent hy- drogen gas leaks (http://GraphiteStore.com, IL), both viton and PTFE coated glass fi- ber gaskets (American Durfilm, MA) and a fuel cell anode with 0.5 mg cm2 platinum loading in the catalyst layer supported by a carbon cloth substrate (http://FuelCell-

Store.com). The cathode assembly consisted of six layers of SGL 29AA porous carbon paper as cathode material (SGL Group, Germany), and a layer of porous polyethylene with 80 nm diameter pores as dispersion blocker (K1650, Celgard, NC). The carbon paper was pre-treated using a 3 h soak at 500C in a 3:1 volume ratio of 98% H2S04 to 70% HNO:3. The electrolyte and oxidant channels were cut into the gaskets, and these determined the active area of our cell of 1.5 cm?

The performance of the cell was tested mainly via polarization curve experiments performed at room temperature using fresh electrolyte, oxidant, and hydrogen gas. Gas flow was controlled via a mass flow controller (Cole Parmer, H) set to 200 sccm, and liquid flowrates were controlled via peristaltic pump (Harvard Apparatus, MA) at around 2 mL/min through the electrolyte channel and 1 mL/min through the cathode.

The electrolyte was 3 M HBr, and the oxidant was a mixture of 0.5 M Br2 in 3 M HBr and 1 M MEP for cases where BCA was added (we identify oxidant solutions via their initial, pre-complexation, concentration of Br2). For cases where BCA was added, we allowed the oxidant solution to come to equilibrium by placing the solution in a glass container and in a shaker for at least 12 h. We then used either the aqueous phase of the resulting separated solution, or a mixture of the aqueous phase with some polybro- mide phase (between 1 and 5 % polybromide by volume). A potentiostat (Reference 3000, Gamry, PA) was used to set the discharge and charge currents and measure the cell voltage. The cell was run at a specified current for at least 30 s, and then all voltage measurements for a given current were averaged to obtain the polarization curve volt- age (the voltage typically took < 5 s to reach steady state). The polarization curves for the case with BCA and without BCA in the oxidant are nearly identical at low currents, where the cell with BCA then reached a limiting current, unlike the cell without BCA.

To investigate the (electro-)chemical properties and impacts of the BCAs on the

Br2/Br- redox kinetics, different structures based on pyrrolidine-, imidazole-, pyridine- , quinoline- and alkyl-backbones were selected to cover many different chemical prop- erties and complexing strengths.

Table 1 List of tested BCAs. # BCA formula M / g/mol 1 1-Ethyl-1-methylpyrrolidinium bromide C7H16BrN 194.11 2 1-Butyl-1-methylpyrrolidiniam bromide C9H20BrN 222.17 3 1-Ethyl-3-methylimidazolium bromide CO6HI1BrN2 191.07 4 1-Butyl-3-methylimidazolium bromide C8HISBrN2 219.12 5 Tetra-N-butylammonium bromide CI6H36BrN 322.38 8

6 N-pentylpyridinium bromide CIOH16BrN 230.14 7 N-octylquinolinium bromide C9H8BrN 322.29 8 L-prolinol bromide CSHI2NOBr 182.06 9 Pyridine hydrobromide perbromide C5H6NBr3 319.82

Phenyltrimethylammonium tribromide C9H14NBr3 375.93 11 4-(Dimethylamino)pyridine tribromide C7H11N2Br3362.89 12 1-n-Butylpyridinium bromide CO9H14NBr 216.12 13 (3-Carboxypropyhtriphenyl phosphonium Br C22H2202PBr 429.29 14 1,1'-Bis{3-(trimethylamonium) propyl]-4,4'-bipyridinium 10 Tetrabromide C22H38N4Br4 678.17

BCAs 1 -5 and BCAs 9 — 13 are commercially available (not in use as BCA) and

BCAs 6 — 8 and 14 were synthesized. For instance, BCA6 was synthesized by using 6.0 ml (47.78 mmol) 1-bromopentane which was added to a 100 ml three-necked round- bottom flask containing 20 ml of pyridine. The mixture was heated to reflux with con- stant stirring for 5 h. After cooling to room temperature, the volatile components were removed under reduced pressure to give the crude product. After recrystallization from pyridine—ether (1 : 3), 10 g (91% yield) of purified BCA6 were obtained. BCA7 was synthesized by using 162.23 g 1-octylbromide (0.84 mol, 1.11 eq) which was added to a solution of 97.86 g quinoline (0.76 mol, 1 eq) in 200 ml acetonitrile. The mixture was stirred under reflux for 48 h. Afterwards the volatile components were removed under reduced pressure. The remaining dark red oil was diluted with 100 ml of water and extracted with diethyl ether ten times at 70 ml each. After evaporation of the water, the product was crystallized from ethanol and dried under vacuum to obtain BCA7 with a yield of 95%. BCAS (prolinol, see. Fig. 4a,b) was synthesized by using a solution of (S)-(+)-2-Pyrrolidinemethanol (1 eq) in water, HBr 48% (1 eq) was added dropwise under stirring. The reaction mixture was kept at RT under mechanical stirring for ap- proximately 1 h and the water was removed under reduced at 60°C. Without any further purification, prolinol bromide was obtained as straw yellow viscous liquid (99% yield).

BCA14 was synthesized by using a 250 ml N2 purged Schlenk flask, 4,4’ -bipyridine (2.0 g, 12.8 mmol) was combined with (3-bromopropyl)trimethylammonium bromide (10 g, 38.3 mmol) in 15 ml of DMSO and stirred at 100C for 3 h. The resulting light- yellow precipitate was filtered and washed with 10 ml of cold DMSO, three times with 20 ml acetonitrile and then dried under vacuum [see fig. 5].

Br2/HBr/BCA were mixed in equimolar ratio and the formation of a polybromide phase and aqueous phase was observed {except in the casing using BCA8). Propylene carbonate and acetonitrile were added dropwise, respectively, to form single phase.

The bromine complexing strength of BCA8 was tested. Therefore, BCA8 and Br: were combined in equimolar ratio (1:1) in a round bottom flask, attached to a rotary vacuum evaporator and kept for 1 h at 200 mbar at 60C. The experiment was repeated with BCA8/Br: in 1:2 molar ratio. Before and after the experiments, the weight of the 9 round bottom flask containing the mixture under investigation was checked. In both cases no weight-loss was observed, hence, BCA8 is able to complex bromine and to reduce bromine’s vapour pressure drastically under aforementioned conditions, even when forming Brs’ species. From the temperature dependence an activation energy of 25.98 kJ/mol for BCAR was determined. With the BCA8 300 Wh/I cells were obtained, e.g. at about 12.2 mol Br’ concentrations.

The following section includes the cycling data gathered for catholyte containing 0.4M

BCAS and staring [HBr]rT of 6.6M.

Table 2 Operating conditions for the first test with L-Prolinol.

Operating parameter Test value

Current density 0.3 Am?

Potential window 0.6-0.98 V

Dispersion blocker PVDF

Geometric electrode surface 64 cm?

Start composition catholyte First 8 cycles: 6.6M [HBr]T

Following 12 cycles: 0.4 M [BCA8]}, 6.6M [HBr]T

Electrolyte volume 0.3L

The following procedure was used to perform the first test with BCA8: 1) First, a 300 ml of a 6.6M [HBr]T is charged up to 1.5M [Br2]T (3.6M [HBr]T remaining). This limit of 1.5M [Br2]T is set by Elestor as the limit at which cell cycling is feasible without initiating material degradation such as the bipolar plates and elec- trode swelling. 2) After the first charging period the catholyte, 8 cycles were run to obtain the cur- rent, voltaic and energy efficiency, in addition to the energy density of the catholyte. 3) After these 12 cycles, BCA8 was added to the 300 ml to reach 0.4M BCA8. 4) After addition of BCA 8, the catholyte was charged this time up to 2.3M [Br2]T (2.0M [HBr]T remaining). The idea is that the BCAS 5) After this first charging moment, the cycling procedure was continued for another 10 cycles, thereby obtaining the current, voltaic and energy efficiency, in addition to the energy density of the catholyte when BCAR is added to the electrolyte.

Exemplary solid BCA (referred to as SBCA) are composed of solid porous beads of 0.1-3mm diameter, in particular 0.5-1 mm, embedded with functional groups that bind Br: to the surface through complexation. The porosity of 10-50%, in particular 30-40%, and the high surface area enables for high complexation kinetics with the functional groups of the sBCA.

Cell cycling study using 6.6M HBr in a membrane cell are perormed. The cell was cycled up to 2.3M [Brz2]r, where 2.0M HBr remains to maintain high electrolyte conductivity. Note that the cell can safely be charged up to 1.5M Br: (3.6M HBr re- maining) without the need of sBCA; above this 1.5M [Bra]r, cell degradation and cell component deterioration takes place. In this experiment, the amount of sBCA is added 10 to complex the [Bra2]rT difference of 0.8M. This amounts 8.6 g of sBCA. Without SBCA, the energy density of the electrolyte was 33 Wh/L. After adding sBCA, the use of SBCA enabled to increase the Wh/L from 33 to 52 Wh/L, which is a 58% increase in energy density of the electrolyte. The current, voltaic and energy efficiency were similar to the cell cycling data without use of SBCA, showing that actually there is no effect of sBCA on the cell performance at the applied current density other that functioning as capturing material for the excessively formed Bra.

In case no sBCA is used. as shown in Fig. 7, the max achievable energy density is 146 Wh/L. Higher Wh/L is not feasible due to phase separation of Br2 and increased material degradation. When 118 g/L of sBCA is added to complex 1.1M of [Brz}r and prevent liquid separation of Brz, the max. achievable energy density is 152 Wh/L.

When 484 g/L of sBCA is used to complex 4.5M of [Br2]7, and prevent cell deteriora- tion, the maximum energy density is 169 Wh/L. The highest energy density of 205

Wh/L is feasible when all Br2 is complexed to sBCA. In that case, around 667 g/L of sBCA is required per L of catholyte.

Polarization curves for a 0.75 cm2 H2-Br2 flow battery (with and without

BCA8) at 50 °C

Several experiments (Exp 19, 21-24) using a 0.75 cm? Ho-Br2 flow battery at 50 °C were performed (anolyte channel thickness 480 pm, catholyte channel thickness 650 um, 3M HBr + 2M Br2, cathode Sigracet 29AA thermally treated for 1 h at 500 °C in air, H2 flowrate 200 mL/min, separator Celgard 3501). A fresh anode, cathode and Celgard were used in each experiment. The varying parameters were: anolyte and catholyte flowrates, H2 backpressure, experimental technique (either CC steps or I-V characterization), usage of BCAS. The polarization curve was always the same with very little variations: OCV 905-915 mV, a nearly perfect linear I-V relationship (slope 198-205 mOhm*cm?) was found, and the cut-off current of 2000 mA/cm?, with no apparent dependance on the H? backpressure and catholyte flowrate.

The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures.

It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention.

In view of searching the next section is added, of which the subsequent section repre- sents a translation into Dutch. 1. Battery, comprising at least one fluid flow controller (14) for providing a continuous circulation of at least one fluid electrolyte, wherein the fluid flow controller is selected from a pump, a mass flow controller, and a pressure controller, at least one first fluid electrolyte adapted to flow from a catholyte container (11) to the battery cell and at least one second fluid electrolyte adapted to flow from an anolyte container (12) to the battery cell, respectively, and vice 11 versa, wherein the at least one first electrolyte each individually is dissolved in a solvent, wherein a first flow (31) comprises a first set of redox species and wherein a second flow (32) comprises a second set of redox species, wherein both flows are separated from one and another, wherein, under discharging conditions, the battery is adapted to subject the first redox species to an oxidation reaction and adapted to subject the second redox species to a reduction reaction, and at least one separator (10), wherein the at least one first fluid, in particular a liquid, is in contact with at least one first positive electrode (13), in particular a positive current collector, wherein the at least one a second fluid, in particular a liquid, is in contact with the at least one first negative electrode (13), in particular a negative current collector, wherein the at least one first set of redox species comprises Halogenide"/Halogenide2, and wherein the second set of redox species comprises H/Ha, wherein the at least one first set of redox species and the at least one first fluid elec- trolyte form a single phase fluid, in particular a liquid, wherein the single phase fluid com- prises a halogen complexing agent, in particular a positively charged halogen complexing agent, more in particular a complexing agent comprising at least one amine, in particular 2- 6 amines, in particular an amine with a positively charged N. 2. Battery according to embodiment I, wherein the complexing agent comprises at least one saturated, partly saturated, or unsaturated secondary amine or a tertiary amine, in particular a cyclic secondary amine or cyclic tertiary amine, such as a pyrrolidinium comprising com- pound, an imidazolium comprising compound, a pyridinium comprising compound, a quin- olinium comprising compound, more in particular an amino alcohol. 3. Battery according to embodiment 2, wherein the complexing agent is selected from five or six atoms comprising ring comprising an amine, in particular from chiral amino alcohols, such as prolinol [CAS 68832-13-3], from 1-Ethyl-1-methylpyrrolidinium bromide, 1-Butyl- 1-methylpyrrolidinium bromide, 1-Ethy1-3-methylimidazolium bromide, 1-Butyl-3-me- thylimidazolium bromide, Tetra-N-butylammonium bromide, N-pentylpyridinium bromide,

N-octylquinolinium bromide, L-prolinol bromide, D-prolinol bromide, Pyridine hydrobro- mide perbromide, Phenyltrimethylammonium tribromide, 4-(Dimethylamino)pyridine tri- bromide, 1-n-Butylpyridinium bromide, and 1,1'-Bis[3-(trimethylamonium) propyl}-4,4'- bipyridinium Tetrabromide. 4. Battery according to any of embodiments 1-3, wherein the halogen is selected from fluor, chlorine, iodine, and bromine, in particular bromine. 5. Battery according to any of embodiments 1-4, wherein the battery is a redox flow bat- tery, the redox flow battery comprising at least one first chamber comprising electrolyte, at least one second chamber comprising oxidant and halogen complexing agent, and at least one separator separating the at least one first chamber and the at least one second chamber, 12 wherein the separator is substantially permeable for H* and is substantially impermeable for

Ha», wherein the battery is void of a membrane. 6. Battery according to any of embodiments 1-5, wherein the battery comprises a single lig- uid solvent, wherein the solvent is selected from water, polar organic solvents, and mixtures thereof. 7. Battery according to any of embodiments 1-6, comprising a voltage supply. 8. Battery according to any of embodiments 1-7, wherein the at least one first negative elec- trode and at least one first positive electrode are each independently selected from carbon, and carbon comprising materials, such as graphite, in particular isomolded graphite, porous graphite, carbon-comprising films, carbon-comprising layers, in particular wherein the first negative electrode comprises a catalyst, such as Pt, and Ir, in particular wherein the second positive electrode comprises a catalyst. 9. Battery according to any of embodiments 1-8, wherein the halogen complexing agent is provided in an amount of 0.1-10 vol.%, in particular 1-5 vol. %, based on the total volume of the single phase fluid, and/or wherein the halogen complexing agent is provided in an amount of 100-100 g/l, in particu- lar 500-700 g/l based on the total volume of the single phase fluid, and/or wherein the halogen complexing agent is provided as a solid and is adapted to remain in said solid phase, and/or wherein said complexing agent is adapted to complex at least one

Hal entity, in particular wherein x is an odd number, more in particular wherein x is se- lected from 1, 3,5, 7 and 9. 10. Battery according to any of embodiments 1-9, comprising at least one operation device selected from a mass flow controller, a peristaltic pump, wherein the pump (14) is adapted for providing a continuous circulation of a fluid electrolyte, in particular of a catholyte, more in particular at a flow rate of 1-20% of the battery volume per minute, such as 5-12%. 11. Battery according to any of embodiments 1-10, wherein the battery has energy density of >200 W/1, in particular > 250 W/L, such as > 300 W/1, and a voltage of 1.5-12 V, wherein a current density magnitude is 0.1-1000 mA/cm?, in particular 1-500 mA/cm?, more in particular 5-50 mA/cm?, and/or wherein an output voltage is 0.1-1.1 V, such as 0.6- 1V. 12. Battery according to any of embodiments 1-11, wherein the solvent with the electrolyte has a conductivity of > 50 mS/cm. such as 100-400 mS/cm, and/or wherein the redox potentials of both first and second sets of redox species are in a range of -4V-+4 V with respect to a reversible hydrogen electrode (RHE). 13. Battery according to any of embodiments 1-12, wherein the first redox species are pre- sent in a concentration of 0.1-18M, in particular 1-10 M, such as HBr, and MEP (N-ethyl-

N-methyl pyrrolidinium bromide), and/or wherein the second redox species are present in a concentration of 0.1-13M, in particular 0.2-10 M, such as Br. 13

14. Array comprising two or more redox flow battery system according to any of embodi- ments 1-10 in series and/or in parallel, such as 3-200 systems in series and/or 2-100 sys- tems in parallel. 15. Redox flow battery system according to any of embodiments 1-10 or an array accord- ing to embodiment 14, for generating electricity. 14

Claims

Conclusions

A battery comprising at least one fluid flow controller (14) for providing continuous circulation of at least one fluid electrolyte, the fluid flow controller being selected from a pump, a mass flow controller, and a pressure regulator, wherein at least one first fluid electrolyte is adapted to flow from a catholyte container (11) to the battery cell and at least one second fluid electrolyte adapted to flow from an anolyte container (12) to the battery cell, respectively, vice versa, where the at least one first fluid electrolyte is each separately contained in a solvent is dissolved, wherein a first stream (31) comprises a first set of redox species and wherein a second stream (32) comprises a second set of redox species, where both streams are separated from each other, wherein, under discharge conditions, the battery is adapted to expose the first redox species to an oxidation reaction and adapted to expose the second redox species to a reduction reaction, and at least one separator (10), in which the at least one first fluid, in particular a liquid, adapted to be in contact with at least one first positive electrode (13), in particular a positive current collector, where the at least one second fluid, in particular a liquid, adapted to be in contact with the at least one first negative electrode (13), in the in particular, a negative current collector in which the at least one first series of redox substances comprises halide-/Halogenide2, and wherein the second series comprises redox species H*/H2, wherein the at least one first series of redox substances and the at least one first fluid electrolyte forms a single phase fluid, in particular a liquid, wherein the single phase fluid comprises a halogen complexing agent, in particular a positively charged halogen complexing agent, more in particular a complexing agent comprising at least one amine, in particular 2-6 amines, in particular an amine with a positively charged N.

2. Battery according to claim 1, wherein the complexing agent comprises at least a saturated, partially saturated or unsaturated secondary amine or a tertiary amine, in particular a cyclic secondary amine or cyclic tertiary amine, such as a pyrrolidinium comprising compound, an imidazolium-containing compound, a pyridinium-containing compound, a quinolinium-containing compound, more particularly an amino alcohol.

3. Battery according to claim 2, wherein the complexing agent is selected from rings comprising five or six atoms comprising an amine, in particular from chiral amino alcohols, such as prolinol [CAS 68832-13-3}, from 1-Ethyl-1-methylpyrrolidinium bromide, 1-Butyl-1-methylpyrrolidinium bromide, 1-Ethyl-3-methylimidazolium bromide, 1-Butyl-3-methylimidazolium bromide, Tetra-N-butylammonium bromide, N-pentylpyridinium bromide, N-octylquinolinium bromide, L-prolinol bromide, D -prolinol bromide, Pyridine hydrobromide perbromide, phenyltrimethylammonium tribromide, 4-(dimethylamino)pyridine tribromide, 1-n-butylpyridinium bromide, and 1, 1'-bis[3-(trimethylamonium)propyl]-4,4'-bipyridinium tetrabromide.

4. Battery according to any one of claims 1-3, wherein the halogen is selected from fluorine, chlorine, iodine, and bromine, in particular bromine.

5. Battery according to any one of claims 1-4, wherein the battery is a redox flow battery, wherein the redox flow battery comprises at least one first chamber comprising electrolyte, at least one second chamber comprising oxidant and halogen complexing agent, and at least one separator separating the at least one first chamber and the at least one second chamber, the separator being substantially permeable to H” and substantially impermeable to Hz, and wherein the battery does not contain a membrane.

The battery of any one of claims 1 to 5, wherein the battery comprises a single liquid solvent, the solvent being selected from water, polar organic solvents, and mixtures thereof.

7. Battery according to any one of claims 1-6, comprising a voltage source.

8. Battery according to any one of claims 1-7, wherein the at least one first negative electrode and at least one first positive electrode are each independently selected from carbon and carbon-comprising materials, such as graphite, in particular isomolded graphite, porous graphite , carbon-comprising films, carbon-comprising layers, in particular wherein the first negative electrode comprises a catalyst, such as Pt, and Ir, in particular wherein the second positive electrode comprises a catalyst.

Battery according to any one of claims 1 to 8, wherein the halogen complexing agent is provided in an amount of 0.1-10 vol.%, in particular 1-5 vol.%. based on the total volume of the single-phase liquid, and/or in which the halogen complexing agent is provided in an amount of 100-100 g/l, in particular 500-700 g/l, based on the total volume of the single-phase liquid, and/or the halogen complexing agent is provided as a solid and is adapted to remain in the solid phase, and/or the halogen complexing agent is adapted to complex at least one Halx entity, in particular where x is an odd number, more in particular where x is selected from 1, 3.5, 7, and 9.

Battery according to any one of claims 1 to 9, comprising at least one operating device selected from a mass flow controller, a peristaltic pump, wherein the pump (14) is adapted to provide a continuous circulation of a liquid electrolyte, in particular of a catholyte, more particularly with a flow rate of 1-20% of the battery volume per minute, such as 5-12%.

11. Battery according to any one of claims 1-10, wherein the battery has an energy density of > 200 W/l, in particular > 250 W/l, such as > 300 W/l, and a voltage of 1.5-12 V, where a current density of 0.1-1000 mA/cm? is, in particular 1-500 16 mA/cm?, more in particular 5-50 mA/cm?, and/or where an output voltage is 0.1-1.1 V, such as 0.6-1 V.

12. Battery according to any one of claims 1-11, wherein the solvent with the electrolyte has a conductivity of > 50 mS/cm, such as 100-400 mS/cm, and/or wherein the redox potentials of both the first and second series redox species are in a range of -4V-+4 V compared to a reversible hydrogen electrode (RHE).

13. Battery according to any one of claims 1-12, wherein the first redox species are present in a concentration of 0.1-18M, in particular 1-10M, such as HBr, and MEP (N-ethyl-N- methylpyrrolidinium bromide), and/or in which the second redox species are present in a concentration of 0.1-13M, in particular 0.2-10M, such as Br.

An array comprising two or more redox flow battery systems according to any one of claims 1-10 in series and/or parallel, such as 3-200 systems in series and/or 2-100 systems in parallel.

15. Redox flow battery system according to any one of claims 1-10 or an array according to claim 14, for generating electricity. 17