WO2016097827A1

WO2016097827A1 - Flow battery

Info

Publication number: WO2016097827A1
Application number: PCT/IB2014/067157
Authority: WO
Inventors: Angelo D'anzi
Original assignee: Proxhima SRL
Current assignee: Proxhima SRL
Priority date: 2014-12-19
Filing date: 2014-12-19
Publication date: 2016-06-23
Anticipated expiration: 2017-06-19

Abstract

A flow battery (1 ) comprising a first tank (2) for an anode electrolyte, a second tank (3) for a cathode electrolyte, and respective plumbing circuits (4, 5) that are provided with corresponding pumps (6, 6a) for supplying electrolytes to at least one pack of planar cells (7). Either or both of the first tank (2) and the second tank (3) are constituted by a plurality of vessels (8, 9) which are mutually interconnected in a cascade arrangement by way of specific plumbing ducts (10, 11). The overall volume of such plurality of vessels (8, 9) is substantially similar to that of a single traditional tank.

Description

FLOW BATTERY

The present invention relates to a flow battery or redox battery, particularly of the vanadium type.

A flow battery is a type of rechargeable battery, in which electrolytes containing one or more dissolved electrically active substances flow through an electrochemical cell that converts the chemical energy directly to electricity. The electrolytes are stored in adapted external tanks and are pumped through the cells of the reactor.

Redox flow batteries have the advantage of having a flexible layout (owing to the separation of the power components and the energy components), a long life cycle and short response times, plus they do not need load leveling and they do not produce harmful emissions.

Flow batteries are used for non-portable applications with energy needs of between 1 kWh and many MWh: they are used for grid load leveling, where the battery is used to accumulate low-cost energy at night and return it to the grid when the cost is higher, but also for accumulating energy from renewable sources such as solar energy and wind energy, in order to supply it later during peak periods of energy demand.

In particular a vanadium redox battery consists of a group of electrochemical cells where the two electrolytes are separated by a proton exchange membrane. Both electrolytes are based on vanadium: the electrolyte in the positive half-cell contains V0₂ ⁺ and V0²⁺ ions, while the electrolyte in the negative half-cell contains V³⁺ and V²⁺ ions. The electrolytes can be prepared in various ways, for example by electrolytic dissolution of vanadium pentoxide (V₂O₅) in sulfuric acid (H₂S0₄). The solution used remains highly acidic. In vanadium flow batteries, the two half-cells are furthermore connected to reserve tanks containing a very large volume of electrolyte, which is caused to circulate through the cell with adapted pumps. This circulation of liquid electrolytes requires a certain space, and limits the possibilities of using vanadium flow batteries in portable applications, essentially restricting them to large, fixed installations.

When the battery is being charged, in the positive half-cell the vanadium is oxidized, converting V0₂ ⁺ to V0²⁺. The electrons removed are moved to the negative half-cell, where they reduce the vanadium from V³⁺ to V²⁺. During use the process occurs in the opposite direction, and a potential difference is obtained of 1.41 V at 25 °C with the circuit open.

The vanadium redox battery is the only battery that accumulates electricity in the electrolyte and not on the plates or electrodes, as usually occurs in all other battery technologies.

Differently from all other batteries, in a vanadium redox battery the electrolyte contained in the tanks, once charged, is not subject to self- discharge, whereas the portion of the electrolyte that remains inside the electrochemical cell over time is subject to self-discharge.

The quantity of electric power stored in the battery is determined by the volume of electrolyte contained in the tanks.

According to a specific and particularly efficient embodiment, a vanadium redox battery consists of a set of electrochemical cells within which the two electrolytes flow, separated from each other by a polymeric membrane. Both of the electrolytes are constituted by an acid solution of dissolved vanadium. The positive electrolyte contains V⁵⁺ and V⁴⁺ ions, while the negative electrolyte contains V²⁺ and V³⁺ ions. When the battery is being charged, in the positive half-cell the vanadium is oxidized while in the negative half-cell the vanadium is reduced. During discharge, the process is reversed.

Connecting multiple cells in electrical series makes it possible to increase the voltage at the terminals of the battery, which will be equal to the number of cells multiplied by 1.41 volt.

During the charging process for storing energy, the pumps are switched on, making the electrolyte flow inside the electrochemical cell. The electric power applied to the electrochemical cell promotes the exchange of protons through the membrane, charging the battery.

During discharging, the pumps are switched on, making the electrolyte flow inside the electrochemical cell, thus delivering the accumulated energy.

The electrochemical process is based on the oxidation/reduction of the vanadium contained in the anode and cathode electrolytes, where the positive electrolyte being charged is oxidized, while the negative electrolyte is reduced. Differently from all other batteries, in a vanadium redox battery the electrolyte contained in the tanks, once charged, is not subject to self- discharge, whereas the portion of the electrolyte that remains inside the electrochemical cell over time can be subject to self-discharge.

The amount of electric power stored in the battery is determined by the volume of the electrolyte contained in the tanks.

A vanadium battery of this type consists of a set of electrochemical cells, within which the two electrolytes flow, separated from each other by a proton exchange membrane. Both of the electrolytes are constituted by an acid solution of dissolved vanadium. The positive electrolyte contains V⁵⁺ and V⁴⁺ ions, while the negative electrolyte contains V²⁺ and V³⁺ ions. When the battery is being charged, in the positive half-cell the vanadium is oxidized while in the negative half-cell the vanadium is reduced. During discharge, the process is reversed.

In flow batteries, a problem exists relating to the storage of large quantities of electrolyte in acid form in tanks that are made, generally, of plastic resins.

In the event of rupture of one or both of the tanks, the acid electrolyte will be spilled into the environment, creating grave safety problems. In addition to the tank risk, there is a risk associated with the pipes that take the electrolyte to the electrochemical cell: in the event of leakage or rupture of one of such pipes, the pumps once switched on would disperse the electrolyte into the environment. The loss of electrolyte, in addition to creating a safety and environmental problem, also results in a substantial economic loss, since the electrolyte contains the vanadium, which is a particularly costly element.

Depending on the regulations in force in various countries, this risk is managed in different ways.

Generally, a containment basin is created, within which the battery is installed. In the event of a leak, the electrolyte 2 will thus be collected in the basin. Typically the capacity of this containment basin must be equal to the quantity of electrolyte stored in the battery. Given the large quantity of electrolyte stored in the battery, the containment basin is generally bulky, leading to problems of placement in the plant in situ, as well as increasing the installation costs.

The main aim of the present invention is to solve the above- mentioned drawbacks, by providing a flow battery with which the risk of dispersion of electrolyte into the environment is minimized.

Within this aim, an object of the invention is to provide a flow battery that does not require the creation of large containment basins for any leaks of the tanks or of the associated plumbing.

Another object of the invention is to provide a flow battery that is easy to transport and install.

Another object of the present invention is to provide a flow battery that is low-cost, relatively easily and practically implemented, and safe in application.

This aim and these and other objects which will become more apparent hereinafter are achieved by a flow battery of the type comprising a first tank for an anode electrolyte, a second tank for a cathode electrolyte, and respective plumbing circuits that are provided with corresponding pumps for supplying electrolytes to at least one pack of planar cells, characterized in that either or both of said first tank and said second tank are constituted by a plurality of vessels which are mutually interconnected in a cascade arrangement by way of specific plumbing ducts, the overall volume of said plurality of vessels being substantially similar to that of a single traditional tank.

Further characteristics and advantages of the invention will become more apparent from the description of a preferred, but not exclusive, embodiment of the flow battery according to the invention, which is illustrated by way of non-limiting example in the accompanying drawing wherein:

Figure 1 is a schematic view of a flow battery according to the invention.

In this figure, a flow battery is generally designated by the reference numeral 1.

The flow battery 1 according to the invention is of the type comprising a first tank 2 for an anode electrolyte, a second tank 3 for a cathode electrolyte, and respective plumbing circuits 4 and 5 that are provided with corresponding pumps 6 and 6a for supplying electrolytes to at least one pack of planar cells 7.

With particular reference to the innovation proposed with the present invention, either or both of the first tank 2 and the second tank 3 are constituted by a plurality of vessels 8 and 9 which are mutually interconnected in a cascade arrangement by way of specific plumbing ducts 10 and 1 1.

It is important to note that the overall volume of the plurality of vessels 8 and 9 will be substantially similar to that of a single traditional tank.

In this manner the rupture of a single vessel 8 or 9 will result in the outflow of a reduced quantity of electrolyte (i.e. equal to the internal volume of the vessel 8 or 9 itself) thus minimizing the environmental impact of a similar spill and also reducing the costs of the dispersed electrolyte with respect to a flow battery of the conventional type.

If it is necessary to create a basin for containing the electrolyte that might be dispersed in the event of a malfunction, it can be dimensioned to reflect the consideration of the minimal extent of losses, since, even in the case of simultaneous ruptures involving two or more vessels rupturing at the same moment, the overall volume of electrolyte spilled will still be much less than the overall volume of all the vessels 8 or 9.

In order to ensure a high standard of safety of the battery 1 according to the invention, it should be noted that, according to a particularly advantageous embodiment in terms of application, both of the tanks 2 and 3 can be constituted by a plurality of vessels 8 and 9.

It should furthermore be noted that at least one of the plumbing circuits 4 and 5 comprises a container 12 and 13 for collecting the electrolyte that arrives from the at least one pack of planar cells 7 which is arranged upstream of the respective pump 6 and/or 6a.

The purpose of such collection container 12 and 13 is to interrupt the continuity of the respective hydraulic circuit 4 and 5 in order to prevent the triggering of capillarity phenomena or unwanted intakes of electrolyte when a malfunction and/or a rupture occurs.

In fact such phenomena could increase the amount of electrolyte that could flow out owing to the malfunction (rupture): interrupting the continuity of the circuit 4 or 5, owing to the fact that it is open to the outside environment at the container 12 or 13, prevents the occurrence of the aforementioned phenomena.

According to a specific embodiment of undoubted practical interest, the plumbing ducts 10 and 1 1 can preferably comprise at least one branch for drawing electrolyte from the vessel 8 or 9 which is arranged upstream and at least one branch for dispensing electrolyte to the vessel 8 or 9 which is arranged downstream.

According to this embodiment the vessels 8 and 9 will be closed.

The drawing branch and the dispensing branch will thus be coupled hermetically to respective holes of an upper closure wall 14 or 15 (respectively of the vessels 8 or 9 ).

It should be noted that in such case the end edge of the drawing branch will be aligned with the respective closure wall 14 or 15.

By contrast, the end edge of the dispensing branch will face and be proximate to the bottom of the respective vessel 8 or 9.

In this manner the electrolyte can be conveyed to the vessel 8 or 9 that is arranged downstream of the one in which it is located only if the quantity thereof inside the vessel in which it is located rises to the point that it exceeds the volume of the vessel, as a result overflowing through the drawing branch of the duct 10 or 1 1.

It should be noted that, in order to minimize the corresponding costs and permit an easy and smooth transport thereof, the vessels 8 and 9 will preferably be made of polymeric material.

In practice therefore the vessels 8 and 9 will be connected in series by piping and the sum of their capacity will coincide with the total capacity of electrolyte that it is intended to store.

The flow of electrolyte flows in the vessels 8 and 9 through the ducts 10 and 1 1 : the electrolyte enters from above and descends to the base of the vessel 8 or 9 through the dispensing branch.

The outflow of the electrolyte from the vessel 8 or 9 occurs through a discharge hole present in an upper wall thereof to which the drawing branch is connected that is arranged in an upper region in the vessel 8 or 9. In this manner the electrolyte flows within the vessel 8 or 9 from below and flows out from the top by overflowing. This path is necessary in order to ensure a correct mixing of electrolyte without regions of low turbulence being created where the electrolyte could settle without participating in the charging and discharging reactions.

In the event of rupture of a pipe of the system that is the subject matter of the invention, the portion of electrolyte that will be dispersed relates only to the portion in the container 12 or 13 which is pumped in circulation, and when this is exhausted the pump 6 or 6a will aspirate only air and cease to pump electrolyte, thus preventing additional dispersion thereof.

If an intermediate vessel 8 or 9 ruptures, the portion of electrolyte that is dispersed is the one that corresponds to the portion contained in the container 12 or 13 as well as the one contained in the vessel 8 or 9 in which the rupture occurred. Once the amount of electrolyte contained in the container 12 or 13 is exhausted, the pump 6, 6a will aspirate only air and will cease to pump electrolyte 7 in circulation, in effect ceasing to disperse it.

By adopting a flow battery 1 according to the invention the potential loss is limited to only a fraction of the overall quantity of electrolyte present, thus reducing the necessary dimensions of the containment basin that is required by safety regulations to a size equal to only the fraction of electrolyte that is potentially exposed to the risk of spillage.

Advantageously the present invention solves the above-mentioned problems, by providing a flow battery 1 in which the risk of dispersion of electrolyte into the environment is minimized.

Conveniently the flow battery 1 according to the invention does not require the creation of large containment basins for any leaks of the tanks (which are constituted by a plurality of vessels 8 or 9) or of the associated plumbing circuits 4 or 5.

Positively the flow battery 1 according to the invention is easy to transport and install, since the individual vessels 8 and 9 are light and not bulky and can be transported separately, and interconnected only at the installation time.

Conveniently the flow battery 1 is low-cost (in terms of both production and running costs) and is relatively easily and practically implemented and safe in application.

The invention, thus conceived, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.

In the embodiments illustrated, individual characteristics shown in relation to specific examples may in reality be interchanged with other, different characteristics, existing in other embodiments.

In practice, the materials employed, as well as the dimensions, may be any according to requirements and to the state of the art.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A flow battery of the type comprising a first tank (2) for an anode electrolyte, a second tank (3) for a cathode electrolyte, and respective plumbing circuits (4, 5) that are provided with corresponding pumps (6, 6a) for supplying electrolytes to at least one pack of planar cells (7), characterized in that either or both of said first tank (2) and said second tank (3) are constituted by a plurality of vessels (8, 9) which are mutually interconnected in a cascade arrangement by way of specific plumbing ducts (10, 1 1 ), the overall volume of said plurality of vessels (8, 9) being substantially similar to that of a single traditional tank.

2. The flow battery according to claim 1 , characterized in that both tanks (2, 3) are constituted by a plurality of vessels (8, 9).

3. The flow battery according to claim 1 , characterized in that at least one of said plumbing circuits (4, 5) comprises a container (12, 13) for collecting the electrolyte that arrives from said at least one pack of planar cells (7) which is arranged upstream of the respective pump (6, 6a).

4. The flow battery according to claim 1 , characterized in that said plumbing ducts ( 10, 1 1 ) comprise at least one branch for drawing electrolyte from the upstream vessel (8, 9) and at least one branch for dispensing electrolyte to the downstream vessel (8, 9).

5. The flow battery according to claim 4, characterized in that said vessels (8, 9) are closed, said drawing branch and said dispensing branch being coupled hermetically to respective holes of an upper closure wall (14, 15).

6. The flow battery according to claim 5, characterized in that the end edge of said drawing branch is aligned with said closure wall (14, 15).

7. The flow battery according to claim 5, characterized in that the end edge of said dispensing branch faces and is proximate to the bottom of the respective vessel (8, 9).

8. The flow battery according to one or more of the preceding claims, characterized in that said vessels (8, 9) are made of polymeric material.